Society of Plastics Engineers
Society of Plastics Engineers Product Design & Development Division Newsletter
Spring, 2010 Edition Special Message from the Board
The Board of Directors and committee members of the Product Design and Development Division would like to extend our condolences to Jay Doyle, on the loss of his wife in late 2009. Jay has served on our board for several years in the TPC committee and, most recently, as our President for the 2009-2010 term. Our thoughts and prayers go out to Jay and his family, and we wish for them peaceful quiet and healing.
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Society of Plastics Engineers Product Design & Development Division Newsletter
President’s Message Hello to all in the Product Design and Development Division of SPE. Writing this message is yours truly, Mark MacLean-Blevins, Secretary of PD3, filling in for Division Chair, Jay Doyle. Those of us who have volunteered and been involved with the PD3 division over the past few years are sort of scratching our heads and wondering – what happened? We are the division that brings it all together – no other division touches every other SPE division, or can be touched by every other SPE division quite like the Product Design and Development Division. Yet, we seem to be drifting apart. Drifting away from what we have in common and what we can gain from the interaction with each other. Are we compartmentalized as a result of societal changes? Or, are we just complacent and content to let it fade? We need to address this issue and soon. You, the PD3 members, are invited to take part in this discussion. Write to the editor of the newsletter – tell us what you want to hear and see; better yet, submit an article or a case study. Become involved, volunteer your time and expertise – help on a committee, attend ANTEC, be a part of the division, help us to make it a valuable resource to every member. The past year has been a challenge for our division, not unlike the challenges faced every day on many different levels throughout our great nation. Our goal for the coming year is to re-set, get back to where we belong and chart a sustainable course for the future. Your help and enthusiasm are needed and requested in this effort. Join us – make new contacts – learn from others – teach others – enhance your career - enhance your life - bring value to your customers – bring value to our shared humanity. Respectfully, Mark MacLean-Blevins Interim Division Chair
In This Issue President’s Message Editor’s Message Councilor’s Message Recent Past BOD Meeting Minutes SPE Hotline Number
2 3 4 5 8
Feature Articles (2) SPE ANTEC—Coming Soon! SPE News—From the Home Office PD3 Board of Directors
9 17 17 18
Disclaimer: The editorial content published in this newsletter is the sole responsibility of the authors. The Product Development & Design Division publishes this content for the use and benefit of its members, and is not responsible for the accuracy or validity of editorial content contributed by various sources.
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Editor’s Message Spring has finally arrived, and so has the Spring, 2010 Edition of the Product Design and Development Division (PD3) Newsletter. For the first time in several issues, this one contains not one but two articles that contain a wealth of useful information related to plastic part design. One is by Glenn Beall, and is the fifth installment of his series on rotational molding. If you missed any of the first four, they are here. The other is by Rick Fischer, and gives you everything you ever wanted to know about Heat Distortion Temperature (HDT) but were afraid to ask. Both Glenn and Rick are members of the PD3 Board of Directors, and they’d love to hear from you about their articles. Rick responded to my request in the last newsletter for suggestions on topics to address in this publication. He not only provided a suggestion, but went the extra mile and included the content as well. Another suggestion came from Niels van der Stappen in the Netherlands, who wrote: “After giving it some thought my ideas would be to present some cases in the newsletter that show developments on the field of the interaction between technical or material innovations and design. Two examples:
How do OEMs respond to the trend for biobased materials in their products, e.g. housings of consumer products or packaging?
How are cradle-2-cradle principles applied in design and development?
GOT AN ARTICLE? GOT A TIP? GOT A QUESTION? CONTACT PD3 TO PUBLISH.
Personally I would be pleased to read these kinds of stories. I would imagine there are people around who would like to tell them. I hope this has been of any help!” Thanks Niels! Hopefully one of our readers will offer an answer that can be converted to an article in this newsletter. Please forward it to me at [email protected]. If we get a sustained response, I’ll add a “Letters to the Editor” section to this newsletter. As in the last newsletter, look for the embedded hyperlinks throughout this one, as they are intended to make it a bit easier for you to get more information about a story, an article, or a person mentioned in this newsletter. As always, thank you for reading this newsletter, and happy designing! Al McGovern Editor
Spring, 2010
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Society of Plastics Engineers Product Design & Development Division Newsletter
Councilor’s Message Editor’s Note: The Councilor for the PD3 is Lance Neward. His role is to represent the interests of our division on the SPE International Council, the ultimate authority for SPE business; it is the only required role for each Section and Division. Contact Lance to learn more about the role or duties of the Councilor (there is one for each SPE Section and Division).
SPE Product Design and Development Division (PD3) Councilor’s Report from Council Meeting held February 19, 2010 Council Enters a New Era On February 19 of this year, the SPE Council entered a new era. In view of the internationally expanding presence of the Society, and the enormous advances in technology, Dr. Paul Andersen, the current SPE President, convened the first “Virtual Council Meeting,” with both face-to-face and electronic participants. While the Society has for a number of years used teleconferences for smaller meetings and allowed remote participation at Council for a limited number of people, this was the first attempt at an entire Council meeting in which the majority of Councilors were not face-to-face. While not without a few glitches, most who attended the meeting were generally pleased with the way it went. The participants were required to be both online with a computer hookup to see the presentations and vote, and on the telephone, to actively engage in the discussions. The resultant view seemed to be that the remote meeting technique worked relatively well, and we can anticipate that we will have more such meetings. The remote meetings will not replace all the Council’s face-to-face meetings but, particularly for meetings which deal with relatively simple or routine matters, virtual Council meetings will add a new dimension to governance. This will be of particular advantage to the international participants. Even though they may be joining the meeting at odd hours, it would seem to be less onerous and/or expensive than a trip to a physical Council meeting. As in most matters, a multiplicity of approaches (both face-to-face and virtual) will be most effective. One of the reasons this particular meeting was called as a virtual meeting was the fact that the subjects tackled were relatively routine and lent themselves to this type of meeting: Six bylaw actions, the selection of the location for the 2013 Annual Business Meeting (at which the ANTEC is held), and the Officer Report Summary. Since it was our first meeting in which we attempted to engage all the participants remotely and electronically, and we wanted to keep the meeting relatively short, it was felt that it was appropriate to deal with only such routine items. The 2013 Annual Business Meeting will be held in Cincinnati, OH. Since the bylaws require that a technical conference is held in conjunction with the ABM, this will be the location of the 2013 ANTEC.
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The bylaw actions were these: o Changes regarding the Nominating Committee and eligibility for nomination (7.3.1.1 and 7.3.3.3) o Recommendation of changes regarding special meetings of Council (6.2.2) o Recommendation of changes regarding the deactivation of Student Chapters (12.3) o First reading of a bylaw change to require at least two nominations by the Nominating Committee for Society officer candidates o First reading of a bylaw change establishing the SPE Europe Board as a standing committee of the Society President-elect Braney outlined the details of the full officer reports, filed on the extranet at: http://extranet.4spe.org/council/index.php?dir=200910%20Term/2010.02%20Council%20%28Remote%29/Council/ President Andersen thanked the Color and Appearance Division for its return of its rebate to the Society. A moment of silence was observed in honor of Dr. Charles Beatty, the Councilor from Central Florida Section, and longtime SPE participant and supporter. Respectfully submitted, Lance Neward Councilor, PD3 Division
Minutes from Recent PD3 BOD Meetings The Board of Directors held a meeting via conference call on September 23, 2009 to discuss various PD3 business matters. A summary of that meeting, compiled by Mark MacLean-Blevins, follows: PD3 Board Meeting – Teleconference September 23rd, 2009 1. Members in Attendance – Roll-Call: o Jay Doyle – Chair o Barbara Arnold-Feret o Glenn Beall o Al McGovern o James McDowell o Mike Lacey o Anthony Onochie
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o o o o
Dejin Li Jordan Rotheiser Lance Neward Mark MacLean-Blevins
2. Meeting opened by Jay Doyle – introductions and welcome. 3. Minutes from last meeting were distributed via e-mail prior to the meeting – motion was made to accept of the minutes as distributed – seconded and motion carried. 4. Financial Report forwarded via e-mail from Mark Wolverton to Jay Doyle – Jay reviewed the report with the board – no actions required at this time. 5. Technical Program Committee – Barbara Arnold-Feret reporting: a. Seven papers have been submitted thus far. One paper is returned to the Polyolefin Division for review. b. All papers submitted were academic papers – no abstracts for hands-on or how-to were submitted. c. The keynote paper will be from Michael Paloian – PD3 Board Member. d. Tentatively looking at a joint session – possibly with the mold making division or the rotational molding division. e. All papers will be handed out and marked-up as electronic documents – no hard copy mark-ups. f. 4SPE website has a “write-it-now” format for use in preparing and submitting papers. 6. Possibility of a TOPCON 2010 – TPC committee will “think-on-it” and notify the board via e-mail of any bright ideas or topics for consideration. 7. Newsletter – Al McGovern with help from Mike Lacey – discussion regarding the final edit before publishing. 8. Councilor’s Report a. Society is looking at electronic meeting participation – computer/teleconference. b. One meeting schedule for the coming year at SPE HQ on October 22nd – topics are elections and budget approvals. Possibility of an all electronic meeting in January of 2010. c. Society is in hard financial times – HQ building was sold and HQ has now moved to a new location with a staff of 15 – as compared to last year’s staff of 28. d. ANTEC at Chicago – attendance was lower as was NPE attendance. 9. Request for all new board members to send their contact information over to Mark MacLeanBlevins to be incorporated into the board roster. 10. ANTEC 2010 a. Discussion regarding a meet and greet at ANTEC Orlando – possibly jointly with other divisions – spread the cost. b. Motion by Barbara Arnold-Feret to ask Lance Neward to present to the divisions committee that we have a divisions reception – and to have Lance report back to the board after the Councilor’s meeting with the results/decision and possible costs to the
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division. Seconded by Jay Doyle. Discussion followed – ANTEC used to have a divisions and a sections reception – perhaps funded by participating divisions – specifically for board members and committee members. 11. Next Board Meeting – to be scheduled by Jay in one month’s time or so. 12. Motion to adjourn was made and carried at 7 PM Eastern.
The Board of Directors held a meeting via conference call on January 13, 2010 to discuss various PD3 business matters. A summary of that meeting, compiled by Mark MacLean-Blevins, follows: PD3 Board Meeting – Teleconference Meeting January 13, 2010 1. Members in Attendance – Roll-Call: o Glenn Beall o Al McGovern o James McDowell o Anne Bernhardt o Anthony Onochie o Paul Rothweiler o Jordan Rotheiser o Lance Neward o Dennis Malpass o Jack Elder o Michael Paloian o Karen Hately – SPE Europe o Mark MacLean-Blevins - acting Chair 2. Meeting opened by Mark MacLean-Blevins – introductions and welcome. 3. Minutes from last meeting were distributed via e-mail prior to the meeting – motion was made by Jim McDowell to accept of the minutes as distributed – seconded by Jack Elder - motion carried. 4. Glenn Beall requested that we discuss the Board for next year and nominations early in the meeting – discussed possible candidates for the Secretary position for next year. Glenn and Mark Wolverton will discuss off-line and prepare an e-mail ballot to distribute. 5. Financial Report forwarded via e-mail from Mark Wolverton prior to the meeting - – no actions required at this time – report accepted as submitted. 6. Newsletter – Al McGovern reporting limited feedback from the newsletter – asking for more technical information articles. Discussion followed regarding types of articles that might be appropriate for our members. Al McGovern will work off-line with those wishing to submit articles – please contact Al directly. Next newsletter to be out in late April – in time to generate some interest for ANTEC. 7. Councilors Report – Lance Neward reported on the SPE elections and officers for the next year; several by-laws (mostly housekeeping) were passed; five sections are now abandoned; SPE right
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now is at 14,500 members; new incentives for divisions to recruit members are being discussed; and, the councilor’s meeting is going to attempt an all electronic meeting to see how it goes. 8. Nominations - Mark Wolverton is looking to hear from anyone wishing to contribute and fill a board or committee position for the coming year – please e-mail Mark if you are interested. 9. Technical Program Committee – No report at this time a. Barbara has been discussing things with the committee and has potentially set-up a combined session with Mold Making for ANTEC. OLD BUSINESS 10. Strategic Planning – joint activities with other SPE groups - Nothing to discuss at this time. NEW BUSINESS 11. European Design SIG – Karen Hately from SPE Europe described for us the events unfolding in Europe as they are beginning to enter the formation stages for a design SIG there. It seems as though there is much interest in Europe for a group focusing on design related issues. a. A motion was made by Lance Neward that “The PD3 Division of SPE formally endorses the formation of a European Design SIG and will provide whatever assistance possible in the endevour” – the motion was seconded by Jim McDowell and discussion followed – motion carried. b. Al McGovern will place some announcement in the next newsletter to the effect that PD3 is supporting the formation of this group in Europe. c. Karen Hately will be publishing some information in the European newsletter as well and would like to include some background on PD3 to help promote the group within the European membership. 12. ANTEC 2010 a. Discussion regarding attendance of board members at ANTEC – roll-call inquiry shows 8 members indicating attendance at ANTEC, 3 members questionable and 2 members definitely not attending. 13. Motion to adjourn was made and carried at 7:08 PM Eastern.
SPE Phone Numbers U.S.: +1 203-775-0471 Europe: +44 1962 736495 or +44 7500 829007
SPE E-Mail Addresses U.S.: [email protected] Europe: [email protected]
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Feature Articles Editor’s Note: This is the fifth in a series of articles on Rotational Molding by Glenn Beall. The previous articles, which dealt with rotational molding product design, the important differences between product design and part design and wall thickness considerations can be found in the Spring 2007, January 2008 and Fall 2009 PD3 newsletters.
WARPAGE CONSIDERATIONS Rotationally molded parts are produced in hollow molds without cores. The inside surfaces of the parts are free-formed in this open molding process. During the cooling portion of the molding process, the plastic material contracts or shrinks. Shrinkage of these hollow parts allows them to pull away from the cavity before the material has cooled enough to be strong enough to retain its shape. This condition encourages large, flat surfaces to warp, as shown in Figure 5.
Figure 5 This type of warpage comes as a surprise to engineers who are accustomed to designing parts for closed-molding processes such as injection molding, structural foam, and reaction injection molding. Engineers who are not familiar with rotational molding can be guided by following the industry recommended flat panel warpage standards listed in Table 2. TABLE 2: Flat-Panel Warpage Standards for Commonly Molded Materials (All units are ±cm / cm and in. / in.) Plastic Material Ideal Commercial Precision PE PP PVC Nylon PC
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0.050 0.050 0.050 0.010 0.010
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0.020 0.020 0.020 0.005 0.005
0.010 0.010 0.010 0.003 0.003
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The “ideal” warpage standard can normally be achieved with no additional cost. The “commercial” standard requires special care and may or may not result in a longer molding cycle and added cost. The “precision” standard will almost always be the most costly of the three ranges. The best design is, therefore, the one that can accommodate the “ideal” warpage standard. Shrinkage-related warpage can be significantly reduced, or eliminated, by pressurizing a hollow part during the cooling part of the molding cycle. This internal pressure forces the part to cool while being held in contact with the cavity. Forcing the part into contact with the cool cavity has the added benefit of reducing the time required to cool the part. Cooling with internal pressure also reduces part-to-part dimensional variations. The use of pressurized air or inert gas has many benefits, but not all molding machines are equipped for this type of molding.
Figure 6 A simpler approach to discouraging the warpage of large, flat surfaces is to avoid designs of that type. If flat surfaces cannot be eliminated, they can be strengthened to resist warpage with the use of stiffening ribs, steps, crowns, and domes, as illustrated in Figure 6. In this case, a
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large, round, flat-topped tank has been redesigned to resist warpage. A dome as small as 0.015 cm/cm (0.015 in./in.) is enough to discourage warpage, but the larger the doming or crowning, the less warpage there will be. Glossy surfaces that reflect light exaggerate the appearance of a warped surface. Deeply textured surfaces do not reflect light and this makes warpage less noticeable. Incorporating a graphic or engraving on a flat surface has the same effect. This article is a condensed extract from Glenn L. Beall’s book entitled “Rotational Molding Design, Materials, Tooling, & Processing” published by Hanser Publishers and available from the SPE Bookstore.
Editor’s Note: This is the first article by Rick Fischer in the PD3 Newsletter. Rick has 35 years of engineering experience, including plastic part design, mold design, structural and process simulation FEA and, failure analysis. He got his BSME from IIT in Chicago and recently acquired a Certificate in Polymer Engineering Fundamentals from UMass Lowell. Eleven patents have been granted in his name.
THE HEAT DEFLECTION TEMPERATURE: Exactly What Is It, and How Do I Use It? The heat deflection temperature (HDT) is a common data value used in the design of plastic parts, but I've seen some real confusion on the part of some of the designers I've worked with as to what it means and how to use it. So let’s start with three definitions and see if we can take some of the mystery out of it. Definition #1: The HDT is the temperature at which a half inch deep by five inch long specimen, configured as a simple beam with supports four inches apart and center loaded so as to produce a 264 psi (or 66 psi) maximum fiber stress, deflects an additional 0.010” as the specimen is slowly heated. Now, that’s something of a mouthful, but it happens to be correct, and it comes from ASTM D-648, the test specification used in the United States to define HDT. But what does it mean in a practical sense? Why the 264 psi load? The basic setup used in ASTM D-648 is shown schematically in Figure 1. A load is applied to the beam to produce the desired stress, the dial indicator is set to zero, and then the temperature is slowly raised. When the deflection gets to 0.010", the temperature is recorded. That's the heat deflection temperature. The temperature is slowly raised because plastics are poor conductors of heat. Slow heating is used to try and achieve a uniform temperature in the specimen.
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Figure 1
Elastic Modulus, ksi.
In practical terms, the HDT is a measure of softening of a plastic as it is heated. Figure 2 shows plots of the elastic modulus as a function of temperature for three plastics. Curve A is typical of an unfilled, pure (no additives) amorphous plastic. It starts with a slightly negative slope as the temperature is increased from room temperature, but then suddenly drops off a cliff. That cliff occurs at the glass transition temperature, and the HDT occurs in the steep portion of the curve after the
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350
curve A 300 250
curve B 200
curve C
150 100 50 0 50
100
150
200
250
Temperature F
Figure 2 cliff. From this we might conclude that if the temperature stays
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somewhat below the HDT, say 10°C below, the material is still useable. Curve B is typical of an amorphous material that is not so pure. It might have plasticizers, impact modifiers, etc. or it might be blended or alloyed with another resin. Anyway, the cliff isn’t as distinct as the one in Curve A, and it may not be clear where the HDT is located. Curve C is a typical semi-crystalline material. It has no cliff, and at this point, there is no clue as to where the HDT is located. So, where does this leave us? The HDT is a data sheet value, and data sheets usually don’t have curves. All a data sheet provides is a number. What does it really mean and how do we use it? Definition #2: The HDT is the temperature at which the elastic modulus of a plastic resin reaches 100 ksi (264 psi test stress) or 30 ksi (66 psi test stress). Now this definition looks a little more useful. The HDT is the temperature at which the stiffness falls to a certain level. Design to that stiffness, stay below the HDT, and you’ll be OK (maybe). But where do those stiffness values come from? The familiar equation for the deflection of a simple beam is:
δ=
PL3 48EI
(1)
The maximum fiber stress is given by:
σ=
Mc PL 4 ⋅ h 2 8σI = ⇒P= I I Lh
(2)
When the beam is initially loaded before the temperature is increased, the initial deflection is:
δ0 =
PL3 8σI L3 σL2 = ⋅ = 48E 0 I Lh 48E 0 I 6 E 0 h
(3)
where E0 is the elastic modulus at room temperature. Now, at the HDT, the deflection is:
δ HDT =
PL3 σL2 σL2 = = δ 0 + .010 = + .010 48E HDT I 6 E HDT h 6E0 h
(4)
Solving for EHDT gives: E HDT =
βE0 0.10 ⋅ E 0 + β
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, where β =
σL2
(5)
6h
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What we now have is an expression for the elastic modulus at the HDT as a function of the room temperature modulus and test stress. This yields Error! Reference source not found.Error! Reference source not found.. 160,000
140,000
120,000 D648 264 psi 100,000
Ehdt, psi
What we see is that the elastic modulus at the HDT is approaching 35 ksi for the 66 psi test condition, and 137 ksi at the 264 psi test condition. But, that's at really high initial modulus values, much higher than typical neat polymers. If we look at Error! Reference source not found., which goes only to 500 ksi, the plots approach about 30 ksi at the 66 psi test condition and 100 ksi at 264 psi test condition. These values are, of course, just a rule of thumb, and equation 5 could be used to get an exact number, but this is close enough for government work.
D648 66 psi
80,000
60,000
40,000
20,000
0
160,000
140,000
0.0E+00
1.0E+06
2.0E+06
3.0E+06
4.0E+06
5.0E+06
6.0E+06
Ert, psi
D648 264 psi D648 66 psi
Figure 3
120,000
OK, so why two test conditions? HDT values taken at 66 psi are supposed to be used for low modulus materials like 80,000 polyethylene, and values taken at 264 psi are used for higher modulus plastics. My 60,000 guess is they started with a convenient test 40,000 specimen, chose the 0.01" deflection as a good compromise between ease of 20,000 measurement and a desire to keep the beam deflection response close to linear, picked a 0 0.0E+00 1.0E+05 2.0E+05 3.0E+05 4.0E+05 5.0E+05 couple of target modulus values, and Ert, psi worked the math backwards to get 66 psi Figure 4 and 264 psi. Now, what you will sometimes see on some data sheets, leading to nothing but confusion and grief, is high modulus materials rated at both stress levels. Why? Because the 66 psi test produces higher numbers for some materials and makes the material look better. Ehdt, psi
100,000
It's time to think about what these numbers mean. If we have a material with an elastic modulus of 350 ksi and we use it near its 264 psi HDT, the material will have softened to about 100 ksi. That's a lot of softening. Have we designed the part based on an elastic modulus of 350 ksi or 100 ksi? And, if the material is evaluated at 66 psi and we use that number, my elastic modulus is down to 30 ksi. That's a 91% drop in stiffness. Yikes! Really, you never want to use 66 psi data with anything but the most flexible polymers. Similarly, consider what happens with
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fiber reinforced resin. DuPont Zytel 70G33L, a typical 33% glass filled nylon resin, has an elastic modulus of 1160 ksi when conditioned at 50% relative humidity. So, at a 264 psi HDT, its elastic modulus is down to 100 ksi, which is a 91% drop. (The scary part is that this material has a 66 psi HDT value listed, which represents a 97% drop in elastic modulus. Double yikes!) ISO 75 addresses this with its Method C which uses a flexural stress of 8 MPa (1160 psi), but I’ve not yet seen any materials rated per Method C. Definition #3: The HDT is the safe maximum use temperature.
This is absolutely not true! I've included this definition because I've heard this often enough to know that a lot of engineers and designers believe this and use the HDT this way. The HDT does not represent a maximum use temperature because it does not take into account the effects of time. For instance, when plastics are held at elevated temperatures for extended periods of time, various degradation mechanisms are initiated and / or accelerated. Two obvious degradation mechanisms are oxidation and hydrolysis. These are chemical reactions that result in chain scission, which reduces molecular weight. Mechanical properties are hugely dependent on molecular weight, and when you start chopping up your polymer chains, heartbreak and anguish are sure to follow. Another form of degradation is plasticizer loss. While some materials may loose plasticizers at room temperature (flexible PVC, for instance), this is accelerated at elevated temperatures. There is another obvious time-related long term effect, and that is creep. All plastics creep, and the creep rate is increased by higher temperatures. The standard method for dealing with creep is to treat it as a loss of stiffness over time, and this is done by manipulating your creep data to derive an apparent modulus. But the HDT quantifies a loss of stiffness due to increased temperature. So, I have a loss of stiffness from elevated temperature, and a loss of stiffness from creep, and more stiffness loss because the creep rate increases with elevated temperature... Is this messy enough?
OK, so the proper way to use the HDT is to treat it as the short term temperature where the elastic modulus hits 100 ksi (or 30 ksi). But really, this is pretty limited. What if
350
curve A 300 Elastic Modulus, ksi.
Anyway, you get the idea. The HDT is not suited, nor intended, to be used as a maximum use temperature. It may be useful when used with other data, like the UL Relative Thermal Indexes, for instance, but should never be used alone as a maximum use temperature.
250
curve B 200
curve C 150 100 50 0 50
100
150
200
Temperature F
Figure 5 Spring, 2010
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I need at least 200 ksi at 175 ˚F? What's my maximum temperature then? The HDT can't tell me that, because it is a single data point. In Error! Reference source not found., which is a repeat of Error! Reference source not found. with some more lines, we see first that all three materials have the same HDT, which is 215 ˚F. We also see that their stiffness at 175 ˚F varies from about 175 ksi to 280 ksi. Thus, curves A and B work for us, but Curve C would not. Again, we can’t get this from the HDT on a datasheet. We need the complete curve. This is a serious limitation of using the HDT in plastic part design. Is there a way to get the full curve? Well, of course there is. Dynamic Mechanical Analysis (DMA) is a method that can be used to generate a plot of elastic modulus as a function of temperature. Figure 6, taken from reference 2, shows just such a plot. This is obviously much more useful than a single data point. There is ASTM D5026, Dynamic Mechanical Properties in Tension, but ASTM D5279, Dynamic Mechanical Properties in Torsion, is preferred by the Figure 6 labs I talked to because thermal strains are parallel to the tensile strains in the tensile test, causing some accuracy issues. The torsion test avoids this. DMA testing is relatively cheap at just a few hundred bucks a run, and takes a lot of the guess work out of part design and material selection. References
1. Takemori, Michael T., “Towards an Understanding of the Heat Distortion Temperature of Thermoplastics”, Polymer Engineering and Science, Vol.19, No. 15, Nov., 1979 2. Sepe, Michael P., “The Usefulness of HDT and a Better Alternative to Describe the Temperature Dependence of Modulus,” Limitations of Test Methods for Plastics, ASTM STP 1369, American Society for Testing and Materials, West Conshohocken, PA, 2000. 3. Sepe, Michael P, “The Materials Analyst, Parts 36,37 and 38, Myths of the Heat Deflection Temperature”, Injection Molding Magazine, Oct., Nov., and Dec., 2000. 4. Standard Test Method for Deflection Temperature of Plastic Under flexural Load, ASTM D 648 07, American Society for Testing and Materials, West Conshohocken, PA 2007.
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SPE ANTEC Coming Soon! Don’t Forget—SPE-ANTEC® 2010 will take place in Orlando, Florida, at the Orlando World Center Marriott Resort and Convention Center from May 16 to 20. To learn more about the ANTEC Technical Program, click here. Editor’s Note: According to Lesley Kyle (+1 203-740-5452), the Senior Event Planner at SPE handling ANTEC 2010, SPE members can attend the entire ANTEC 2010 program – more than 600 technical presentations, 115+ technical sesssions, 3 plenary sessions and the exhibit hall – for $550, the lowest price for this event since 1999! Register for ANTEC 2010 at their website. SPE Student Activities Committee Seeks Your Support for ANTEC There are plenty of activities for students at this year’s ANTEC, including a mixer at Mickey & Minnie’s house!. Go here for details. SPE PD3 BOD and General Membership to Meet at ANTEC The PD3 Board meeting will be held on Monday, May 17th at 8:00AM Eastern Time at ANTEC. The meeting will be held at the Orlando World Center Marriott Resort and Conference Center, in the Chicago Room. A General PD3 Division Membership meeting will follow the Board Meeting in the same Room at 9:00 AM Eastern Time. If you are attending ANTEC please join us for the membership meeting. We hope to see you there!
SPE: News: From the Home Office The folks back at the SPE home office have been very busy these past months, as evidenced by these stories of interest:
SPE’s Subscription Plan Gives Unlimited Access to Technical Training SPE is excited to continue its subscription plan for the e-Learning Center that makes it even more affordable for you to learn and stay competitive in your field! This plan will continue to offer unlimited, affordable access to live technical presentations over the Web! The subscription program will grant you VIP access to as many e-Live® Webinars as you would like during a 3-month* period. What types of webinars are offered? To view our current calendar, please click here: www.4spe.org/elearning How much does it cost? You will be able to attend as many webinars as you want for $199 (SPE member pricing). Where do I register? Register here: http://www.4spe.org/e-learning-subscriptions Once you are registered, you will receive further instructions about how to access any webinar you would like!
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Society of Plastics Engineers Product Design & Development Division Newsletter
The Society of Plastics Engineers (SPE) Introduces Email-Based News Briefs With new technologies, new procedures, and new operational strategies, the plastics industry is continually evolving. To that end, the Society of Plastics Engineers (SPE) has launched the new SPE Industry Update, an opt-in email resource providing comprehensive news briefs of the industry’s top stories. Each edition of the SPE Industry Update contains articles gathered from an extensive list of sources, such as The Associated Press, The New York Times, Plastics News, and other more industry-specific publications. Professionals from the field will also contribute timely news and information "just in time" so leaders can keep on the cutting edge of industry developments. Beginning immediately, the SPE Industry Update will be delivered to the inboxes of SPE members and nonmembers alike, keeping plastics leaders abreast of topics that impact the daily operations of their businesses. The SPE Industry Update is a great way to keep informed. The electronic publication can be easily read on your office or home computer, or via your mobile phone or PDA. The SPE Industry Update is powered by MultiBriefs, a division of MultiView. “We understand that as the plastics industry evolves, it’s becoming increasingly important for SPE to keep its members informed. The SPE Industry Update has been designed with the needs of SPE members in mind,” says Dan Maitland, president of MultiView. “We look forward to delivering the news and information that SPE members have asked for.” In case you missed the e-mail, the latest two industry updates can be found here and here.
SPE Product Development and Design Division Board of Directors Roster Chair John J. Doyle R&D Manager, Bioscience Div Millipore Corp [email protected] (978) 762-5173 office (603) 770-2036 cell Secretary Mark MacLean-Blevins MacLean-Blevins & Associates, Inc. [email protected] (410) 848-6232 office (410) 346-7274 fax
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Chair-elect Mark MacLean-Blevins MacLean-Blevins & Associates, Inc. [email protected] (410) 848-6232 office (410) 346-7274 fax Councilor Lance Neward Turner Group, Intermountain Area [email protected] (801) 568-6771 office (801) 541-9414 cell
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Treasurer Mark Wolverton Senior Technical Service Engineer FHR Polymers [email protected] (630) 240-5110 office TPC Team Barbara Arnold-Feret (Chair) Development Manager Enviro Plastics Inc [email protected] (817) 271-3574 home Mike Paloian Mark Wolverton
SPE PD3 Newsletter
Society of Plastics Engineers Product Design & Development Division Newsletter Historian Glenn Beall Glenn Beall Plastics [email protected] (847) 549-9970 office
Past Chair Ronald Minke Aptimise, LLC. [email protected] (260) 407-0382 office
Anne Bernhardt Plastics Instructor Skyline HS - Dallas ISD [email protected] (972) 502-3565 office (972) 385-8483 home Paul Rothweiler Aspen Research Paul.Rothweiler@aspenmaterials .com (651) 341-5427 office
Jordan Rotheiser President Rotheiser Design Inc [email protected] (847) 433-4288 office
Dejin (Derek) Li Process Chemist Sabic Innovative Plastics [email protected] (304) 863-7148 office Jack Elder Multiject [email protected] (248) 608-0005 office (248) 563-3179 cell
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Mark Matsco Director Bayer Material Science LLC [email protected] (412) 777-4194 office (724) 244-7764 cell Rick Fischer Sr. Project Engineer IMPACT Engineering Solutions [email protected] (630) 487-6250 cell James K. McDowell, PhD Engineering Manager Newpark Mats & Integrated Svcs [email protected] (337) 896-8976 office (337) 565-2133 direct (337) 288-7272 mobile Todd Cook Staff Engineer, Plastics Remington Arms Company, Inc. [email protected] (270) 769-7604 office (270) 766-7656 cell
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Newsletter Al McGovern (Editor), Director of Mechanical Engineering Shure, Inc. [email protected] (847) 600-8451 office (630) 660-6217 cell Mike Lacey Micheal Paloian President Integrated Design Systems [email protected] (516) 482-2181 x101 office Mike Lacey Phoenix Contact [email protected] (717) 944-1300, x3679 office (717) 877-8492 cell D Malpass Consultant (Polyolefins) [email protected] (281) 770-5411 cell Anthony N. Onochie Vice President Onosta Global Engineering Ltd. [email protected] m (713) 205-3885 office
SPE PD3 Newsletter
Spring, 2010 Edition Special Message from the Board
The Board of Directors and committee members of the Product Design and Development Division would like to extend our condolences to Jay Doyle, on the loss of his wife in late 2009. Jay has served on our board for several years in the TPC committee and, most recently, as our President for the 2009-2010 term. Our thoughts and prayers go out to Jay and his family, and we wish for them peaceful quiet and healing.
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President’s Message Hello to all in the Product Design and Development Division of SPE. Writing this message is yours truly, Mark MacLean-Blevins, Secretary of PD3, filling in for Division Chair, Jay Doyle. Those of us who have volunteered and been involved with the PD3 division over the past few years are sort of scratching our heads and wondering – what happened? We are the division that brings it all together – no other division touches every other SPE division, or can be touched by every other SPE division quite like the Product Design and Development Division. Yet, we seem to be drifting apart. Drifting away from what we have in common and what we can gain from the interaction with each other. Are we compartmentalized as a result of societal changes? Or, are we just complacent and content to let it fade? We need to address this issue and soon. You, the PD3 members, are invited to take part in this discussion. Write to the editor of the newsletter – tell us what you want to hear and see; better yet, submit an article or a case study. Become involved, volunteer your time and expertise – help on a committee, attend ANTEC, be a part of the division, help us to make it a valuable resource to every member. The past year has been a challenge for our division, not unlike the challenges faced every day on many different levels throughout our great nation. Our goal for the coming year is to re-set, get back to where we belong and chart a sustainable course for the future. Your help and enthusiasm are needed and requested in this effort. Join us – make new contacts – learn from others – teach others – enhance your career - enhance your life - bring value to your customers – bring value to our shared humanity. Respectfully, Mark MacLean-Blevins Interim Division Chair
In This Issue President’s Message Editor’s Message Councilor’s Message Recent Past BOD Meeting Minutes SPE Hotline Number
2 3 4 5 8
Feature Articles (2) SPE ANTEC—Coming Soon! SPE News—From the Home Office PD3 Board of Directors
9 17 17 18
Disclaimer: The editorial content published in this newsletter is the sole responsibility of the authors. The Product Development & Design Division publishes this content for the use and benefit of its members, and is not responsible for the accuracy or validity of editorial content contributed by various sources.
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Editor’s Message Spring has finally arrived, and so has the Spring, 2010 Edition of the Product Design and Development Division (PD3) Newsletter. For the first time in several issues, this one contains not one but two articles that contain a wealth of useful information related to plastic part design. One is by Glenn Beall, and is the fifth installment of his series on rotational molding. If you missed any of the first four, they are here. The other is by Rick Fischer, and gives you everything you ever wanted to know about Heat Distortion Temperature (HDT) but were afraid to ask. Both Glenn and Rick are members of the PD3 Board of Directors, and they’d love to hear from you about their articles. Rick responded to my request in the last newsletter for suggestions on topics to address in this publication. He not only provided a suggestion, but went the extra mile and included the content as well. Another suggestion came from Niels van der Stappen in the Netherlands, who wrote: “After giving it some thought my ideas would be to present some cases in the newsletter that show developments on the field of the interaction between technical or material innovations and design. Two examples:
How do OEMs respond to the trend for biobased materials in their products, e.g. housings of consumer products or packaging?
How are cradle-2-cradle principles applied in design and development?
GOT AN ARTICLE? GOT A TIP? GOT A QUESTION? CONTACT PD3 TO PUBLISH.
Personally I would be pleased to read these kinds of stories. I would imagine there are people around who would like to tell them. I hope this has been of any help!” Thanks Niels! Hopefully one of our readers will offer an answer that can be converted to an article in this newsletter. Please forward it to me at [email protected]. If we get a sustained response, I’ll add a “Letters to the Editor” section to this newsletter. As in the last newsletter, look for the embedded hyperlinks throughout this one, as they are intended to make it a bit easier for you to get more information about a story, an article, or a person mentioned in this newsletter. As always, thank you for reading this newsletter, and happy designing! Al McGovern Editor
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Councilor’s Message Editor’s Note: The Councilor for the PD3 is Lance Neward. His role is to represent the interests of our division on the SPE International Council, the ultimate authority for SPE business; it is the only required role for each Section and Division. Contact Lance to learn more about the role or duties of the Councilor (there is one for each SPE Section and Division).
SPE Product Design and Development Division (PD3) Councilor’s Report from Council Meeting held February 19, 2010 Council Enters a New Era On February 19 of this year, the SPE Council entered a new era. In view of the internationally expanding presence of the Society, and the enormous advances in technology, Dr. Paul Andersen, the current SPE President, convened the first “Virtual Council Meeting,” with both face-to-face and electronic participants. While the Society has for a number of years used teleconferences for smaller meetings and allowed remote participation at Council for a limited number of people, this was the first attempt at an entire Council meeting in which the majority of Councilors were not face-to-face. While not without a few glitches, most who attended the meeting were generally pleased with the way it went. The participants were required to be both online with a computer hookup to see the presentations and vote, and on the telephone, to actively engage in the discussions. The resultant view seemed to be that the remote meeting technique worked relatively well, and we can anticipate that we will have more such meetings. The remote meetings will not replace all the Council’s face-to-face meetings but, particularly for meetings which deal with relatively simple or routine matters, virtual Council meetings will add a new dimension to governance. This will be of particular advantage to the international participants. Even though they may be joining the meeting at odd hours, it would seem to be less onerous and/or expensive than a trip to a physical Council meeting. As in most matters, a multiplicity of approaches (both face-to-face and virtual) will be most effective. One of the reasons this particular meeting was called as a virtual meeting was the fact that the subjects tackled were relatively routine and lent themselves to this type of meeting: Six bylaw actions, the selection of the location for the 2013 Annual Business Meeting (at which the ANTEC is held), and the Officer Report Summary. Since it was our first meeting in which we attempted to engage all the participants remotely and electronically, and we wanted to keep the meeting relatively short, it was felt that it was appropriate to deal with only such routine items. The 2013 Annual Business Meeting will be held in Cincinnati, OH. Since the bylaws require that a technical conference is held in conjunction with the ABM, this will be the location of the 2013 ANTEC.
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The bylaw actions were these: o Changes regarding the Nominating Committee and eligibility for nomination (7.3.1.1 and 7.3.3.3) o Recommendation of changes regarding special meetings of Council (6.2.2) o Recommendation of changes regarding the deactivation of Student Chapters (12.3) o First reading of a bylaw change to require at least two nominations by the Nominating Committee for Society officer candidates o First reading of a bylaw change establishing the SPE Europe Board as a standing committee of the Society President-elect Braney outlined the details of the full officer reports, filed on the extranet at: http://extranet.4spe.org/council/index.php?dir=200910%20Term/2010.02%20Council%20%28Remote%29/Council/ President Andersen thanked the Color and Appearance Division for its return of its rebate to the Society. A moment of silence was observed in honor of Dr. Charles Beatty, the Councilor from Central Florida Section, and longtime SPE participant and supporter. Respectfully submitted, Lance Neward Councilor, PD3 Division
Minutes from Recent PD3 BOD Meetings The Board of Directors held a meeting via conference call on September 23, 2009 to discuss various PD3 business matters. A summary of that meeting, compiled by Mark MacLean-Blevins, follows: PD3 Board Meeting – Teleconference September 23rd, 2009 1. Members in Attendance – Roll-Call: o Jay Doyle – Chair o Barbara Arnold-Feret o Glenn Beall o Al McGovern o James McDowell o Mike Lacey o Anthony Onochie
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o o o o
Dejin Li Jordan Rotheiser Lance Neward Mark MacLean-Blevins
2. Meeting opened by Jay Doyle – introductions and welcome. 3. Minutes from last meeting were distributed via e-mail prior to the meeting – motion was made to accept of the minutes as distributed – seconded and motion carried. 4. Financial Report forwarded via e-mail from Mark Wolverton to Jay Doyle – Jay reviewed the report with the board – no actions required at this time. 5. Technical Program Committee – Barbara Arnold-Feret reporting: a. Seven papers have been submitted thus far. One paper is returned to the Polyolefin Division for review. b. All papers submitted were academic papers – no abstracts for hands-on or how-to were submitted. c. The keynote paper will be from Michael Paloian – PD3 Board Member. d. Tentatively looking at a joint session – possibly with the mold making division or the rotational molding division. e. All papers will be handed out and marked-up as electronic documents – no hard copy mark-ups. f. 4SPE website has a “write-it-now” format for use in preparing and submitting papers. 6. Possibility of a TOPCON 2010 – TPC committee will “think-on-it” and notify the board via e-mail of any bright ideas or topics for consideration. 7. Newsletter – Al McGovern with help from Mike Lacey – discussion regarding the final edit before publishing. 8. Councilor’s Report a. Society is looking at electronic meeting participation – computer/teleconference. b. One meeting schedule for the coming year at SPE HQ on October 22nd – topics are elections and budget approvals. Possibility of an all electronic meeting in January of 2010. c. Society is in hard financial times – HQ building was sold and HQ has now moved to a new location with a staff of 15 – as compared to last year’s staff of 28. d. ANTEC at Chicago – attendance was lower as was NPE attendance. 9. Request for all new board members to send their contact information over to Mark MacLeanBlevins to be incorporated into the board roster. 10. ANTEC 2010 a. Discussion regarding a meet and greet at ANTEC Orlando – possibly jointly with other divisions – spread the cost. b. Motion by Barbara Arnold-Feret to ask Lance Neward to present to the divisions committee that we have a divisions reception – and to have Lance report back to the board after the Councilor’s meeting with the results/decision and possible costs to the
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division. Seconded by Jay Doyle. Discussion followed – ANTEC used to have a divisions and a sections reception – perhaps funded by participating divisions – specifically for board members and committee members. 11. Next Board Meeting – to be scheduled by Jay in one month’s time or so. 12. Motion to adjourn was made and carried at 7 PM Eastern.
The Board of Directors held a meeting via conference call on January 13, 2010 to discuss various PD3 business matters. A summary of that meeting, compiled by Mark MacLean-Blevins, follows: PD3 Board Meeting – Teleconference Meeting January 13, 2010 1. Members in Attendance – Roll-Call: o Glenn Beall o Al McGovern o James McDowell o Anne Bernhardt o Anthony Onochie o Paul Rothweiler o Jordan Rotheiser o Lance Neward o Dennis Malpass o Jack Elder o Michael Paloian o Karen Hately – SPE Europe o Mark MacLean-Blevins - acting Chair 2. Meeting opened by Mark MacLean-Blevins – introductions and welcome. 3. Minutes from last meeting were distributed via e-mail prior to the meeting – motion was made by Jim McDowell to accept of the minutes as distributed – seconded by Jack Elder - motion carried. 4. Glenn Beall requested that we discuss the Board for next year and nominations early in the meeting – discussed possible candidates for the Secretary position for next year. Glenn and Mark Wolverton will discuss off-line and prepare an e-mail ballot to distribute. 5. Financial Report forwarded via e-mail from Mark Wolverton prior to the meeting - – no actions required at this time – report accepted as submitted. 6. Newsletter – Al McGovern reporting limited feedback from the newsletter – asking for more technical information articles. Discussion followed regarding types of articles that might be appropriate for our members. Al McGovern will work off-line with those wishing to submit articles – please contact Al directly. Next newsletter to be out in late April – in time to generate some interest for ANTEC. 7. Councilors Report – Lance Neward reported on the SPE elections and officers for the next year; several by-laws (mostly housekeeping) were passed; five sections are now abandoned; SPE right
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now is at 14,500 members; new incentives for divisions to recruit members are being discussed; and, the councilor’s meeting is going to attempt an all electronic meeting to see how it goes. 8. Nominations - Mark Wolverton is looking to hear from anyone wishing to contribute and fill a board or committee position for the coming year – please e-mail Mark if you are interested. 9. Technical Program Committee – No report at this time a. Barbara has been discussing things with the committee and has potentially set-up a combined session with Mold Making for ANTEC. OLD BUSINESS 10. Strategic Planning – joint activities with other SPE groups - Nothing to discuss at this time. NEW BUSINESS 11. European Design SIG – Karen Hately from SPE Europe described for us the events unfolding in Europe as they are beginning to enter the formation stages for a design SIG there. It seems as though there is much interest in Europe for a group focusing on design related issues. a. A motion was made by Lance Neward that “The PD3 Division of SPE formally endorses the formation of a European Design SIG and will provide whatever assistance possible in the endevour” – the motion was seconded by Jim McDowell and discussion followed – motion carried. b. Al McGovern will place some announcement in the next newsletter to the effect that PD3 is supporting the formation of this group in Europe. c. Karen Hately will be publishing some information in the European newsletter as well and would like to include some background on PD3 to help promote the group within the European membership. 12. ANTEC 2010 a. Discussion regarding attendance of board members at ANTEC – roll-call inquiry shows 8 members indicating attendance at ANTEC, 3 members questionable and 2 members definitely not attending. 13. Motion to adjourn was made and carried at 7:08 PM Eastern.
SPE Phone Numbers U.S.: +1 203-775-0471 Europe: +44 1962 736495 or +44 7500 829007
SPE E-Mail Addresses U.S.: [email protected] Europe: [email protected]
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Feature Articles Editor’s Note: This is the fifth in a series of articles on Rotational Molding by Glenn Beall. The previous articles, which dealt with rotational molding product design, the important differences between product design and part design and wall thickness considerations can be found in the Spring 2007, January 2008 and Fall 2009 PD3 newsletters.
WARPAGE CONSIDERATIONS Rotationally molded parts are produced in hollow molds without cores. The inside surfaces of the parts are free-formed in this open molding process. During the cooling portion of the molding process, the plastic material contracts or shrinks. Shrinkage of these hollow parts allows them to pull away from the cavity before the material has cooled enough to be strong enough to retain its shape. This condition encourages large, flat surfaces to warp, as shown in Figure 5.
Figure 5 This type of warpage comes as a surprise to engineers who are accustomed to designing parts for closed-molding processes such as injection molding, structural foam, and reaction injection molding. Engineers who are not familiar with rotational molding can be guided by following the industry recommended flat panel warpage standards listed in Table 2. TABLE 2: Flat-Panel Warpage Standards for Commonly Molded Materials (All units are ±cm / cm and in. / in.) Plastic Material Ideal Commercial Precision PE PP PVC Nylon PC
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0.050 0.050 0.050 0.010 0.010
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0.020 0.020 0.020 0.005 0.005
0.010 0.010 0.010 0.003 0.003
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The “ideal” warpage standard can normally be achieved with no additional cost. The “commercial” standard requires special care and may or may not result in a longer molding cycle and added cost. The “precision” standard will almost always be the most costly of the three ranges. The best design is, therefore, the one that can accommodate the “ideal” warpage standard. Shrinkage-related warpage can be significantly reduced, or eliminated, by pressurizing a hollow part during the cooling part of the molding cycle. This internal pressure forces the part to cool while being held in contact with the cavity. Forcing the part into contact with the cool cavity has the added benefit of reducing the time required to cool the part. Cooling with internal pressure also reduces part-to-part dimensional variations. The use of pressurized air or inert gas has many benefits, but not all molding machines are equipped for this type of molding.
Figure 6 A simpler approach to discouraging the warpage of large, flat surfaces is to avoid designs of that type. If flat surfaces cannot be eliminated, they can be strengthened to resist warpage with the use of stiffening ribs, steps, crowns, and domes, as illustrated in Figure 6. In this case, a
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large, round, flat-topped tank has been redesigned to resist warpage. A dome as small as 0.015 cm/cm (0.015 in./in.) is enough to discourage warpage, but the larger the doming or crowning, the less warpage there will be. Glossy surfaces that reflect light exaggerate the appearance of a warped surface. Deeply textured surfaces do not reflect light and this makes warpage less noticeable. Incorporating a graphic or engraving on a flat surface has the same effect. This article is a condensed extract from Glenn L. Beall’s book entitled “Rotational Molding Design, Materials, Tooling, & Processing” published by Hanser Publishers and available from the SPE Bookstore.
Editor’s Note: This is the first article by Rick Fischer in the PD3 Newsletter. Rick has 35 years of engineering experience, including plastic part design, mold design, structural and process simulation FEA and, failure analysis. He got his BSME from IIT in Chicago and recently acquired a Certificate in Polymer Engineering Fundamentals from UMass Lowell. Eleven patents have been granted in his name.
THE HEAT DEFLECTION TEMPERATURE: Exactly What Is It, and How Do I Use It? The heat deflection temperature (HDT) is a common data value used in the design of plastic parts, but I've seen some real confusion on the part of some of the designers I've worked with as to what it means and how to use it. So let’s start with three definitions and see if we can take some of the mystery out of it. Definition #1: The HDT is the temperature at which a half inch deep by five inch long specimen, configured as a simple beam with supports four inches apart and center loaded so as to produce a 264 psi (or 66 psi) maximum fiber stress, deflects an additional 0.010” as the specimen is slowly heated. Now, that’s something of a mouthful, but it happens to be correct, and it comes from ASTM D-648, the test specification used in the United States to define HDT. But what does it mean in a practical sense? Why the 264 psi load? The basic setup used in ASTM D-648 is shown schematically in Figure 1. A load is applied to the beam to produce the desired stress, the dial indicator is set to zero, and then the temperature is slowly raised. When the deflection gets to 0.010", the temperature is recorded. That's the heat deflection temperature. The temperature is slowly raised because plastics are poor conductors of heat. Slow heating is used to try and achieve a uniform temperature in the specimen.
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Figure 1
Elastic Modulus, ksi.
In practical terms, the HDT is a measure of softening of a plastic as it is heated. Figure 2 shows plots of the elastic modulus as a function of temperature for three plastics. Curve A is typical of an unfilled, pure (no additives) amorphous plastic. It starts with a slightly negative slope as the temperature is increased from room temperature, but then suddenly drops off a cliff. That cliff occurs at the glass transition temperature, and the HDT occurs in the steep portion of the curve after the
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350
curve A 300 250
curve B 200
curve C
150 100 50 0 50
100
150
200
250
Temperature F
Figure 2 cliff. From this we might conclude that if the temperature stays
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somewhat below the HDT, say 10°C below, the material is still useable. Curve B is typical of an amorphous material that is not so pure. It might have plasticizers, impact modifiers, etc. or it might be blended or alloyed with another resin. Anyway, the cliff isn’t as distinct as the one in Curve A, and it may not be clear where the HDT is located. Curve C is a typical semi-crystalline material. It has no cliff, and at this point, there is no clue as to where the HDT is located. So, where does this leave us? The HDT is a data sheet value, and data sheets usually don’t have curves. All a data sheet provides is a number. What does it really mean and how do we use it? Definition #2: The HDT is the temperature at which the elastic modulus of a plastic resin reaches 100 ksi (264 psi test stress) or 30 ksi (66 psi test stress). Now this definition looks a little more useful. The HDT is the temperature at which the stiffness falls to a certain level. Design to that stiffness, stay below the HDT, and you’ll be OK (maybe). But where do those stiffness values come from? The familiar equation for the deflection of a simple beam is:
δ=
PL3 48EI
(1)
The maximum fiber stress is given by:
σ=
Mc PL 4 ⋅ h 2 8σI = ⇒P= I I Lh
(2)
When the beam is initially loaded before the temperature is increased, the initial deflection is:
δ0 =
PL3 8σI L3 σL2 = ⋅ = 48E 0 I Lh 48E 0 I 6 E 0 h
(3)
where E0 is the elastic modulus at room temperature. Now, at the HDT, the deflection is:
δ HDT =
PL3 σL2 σL2 = = δ 0 + .010 = + .010 48E HDT I 6 E HDT h 6E0 h
(4)
Solving for EHDT gives: E HDT =
βE0 0.10 ⋅ E 0 + β
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, where β =
σL2
(5)
6h
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What we now have is an expression for the elastic modulus at the HDT as a function of the room temperature modulus and test stress. This yields Error! Reference source not found.Error! Reference source not found.. 160,000
140,000
120,000 D648 264 psi 100,000
Ehdt, psi
What we see is that the elastic modulus at the HDT is approaching 35 ksi for the 66 psi test condition, and 137 ksi at the 264 psi test condition. But, that's at really high initial modulus values, much higher than typical neat polymers. If we look at Error! Reference source not found., which goes only to 500 ksi, the plots approach about 30 ksi at the 66 psi test condition and 100 ksi at 264 psi test condition. These values are, of course, just a rule of thumb, and equation 5 could be used to get an exact number, but this is close enough for government work.
D648 66 psi
80,000
60,000
40,000
20,000
0
160,000
140,000
0.0E+00
1.0E+06
2.0E+06
3.0E+06
4.0E+06
5.0E+06
6.0E+06
Ert, psi
D648 264 psi D648 66 psi
Figure 3
120,000
OK, so why two test conditions? HDT values taken at 66 psi are supposed to be used for low modulus materials like 80,000 polyethylene, and values taken at 264 psi are used for higher modulus plastics. My 60,000 guess is they started with a convenient test 40,000 specimen, chose the 0.01" deflection as a good compromise between ease of 20,000 measurement and a desire to keep the beam deflection response close to linear, picked a 0 0.0E+00 1.0E+05 2.0E+05 3.0E+05 4.0E+05 5.0E+05 couple of target modulus values, and Ert, psi worked the math backwards to get 66 psi Figure 4 and 264 psi. Now, what you will sometimes see on some data sheets, leading to nothing but confusion and grief, is high modulus materials rated at both stress levels. Why? Because the 66 psi test produces higher numbers for some materials and makes the material look better. Ehdt, psi
100,000
It's time to think about what these numbers mean. If we have a material with an elastic modulus of 350 ksi and we use it near its 264 psi HDT, the material will have softened to about 100 ksi. That's a lot of softening. Have we designed the part based on an elastic modulus of 350 ksi or 100 ksi? And, if the material is evaluated at 66 psi and we use that number, my elastic modulus is down to 30 ksi. That's a 91% drop in stiffness. Yikes! Really, you never want to use 66 psi data with anything but the most flexible polymers. Similarly, consider what happens with
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SPE PD3 Newsletter
Society of Plastics Engineers Product Design & Development Division Newsletter
fiber reinforced resin. DuPont Zytel 70G33L, a typical 33% glass filled nylon resin, has an elastic modulus of 1160 ksi when conditioned at 50% relative humidity. So, at a 264 psi HDT, its elastic modulus is down to 100 ksi, which is a 91% drop. (The scary part is that this material has a 66 psi HDT value listed, which represents a 97% drop in elastic modulus. Double yikes!) ISO 75 addresses this with its Method C which uses a flexural stress of 8 MPa (1160 psi), but I’ve not yet seen any materials rated per Method C. Definition #3: The HDT is the safe maximum use temperature.
This is absolutely not true! I've included this definition because I've heard this often enough to know that a lot of engineers and designers believe this and use the HDT this way. The HDT does not represent a maximum use temperature because it does not take into account the effects of time. For instance, when plastics are held at elevated temperatures for extended periods of time, various degradation mechanisms are initiated and / or accelerated. Two obvious degradation mechanisms are oxidation and hydrolysis. These are chemical reactions that result in chain scission, which reduces molecular weight. Mechanical properties are hugely dependent on molecular weight, and when you start chopping up your polymer chains, heartbreak and anguish are sure to follow. Another form of degradation is plasticizer loss. While some materials may loose plasticizers at room temperature (flexible PVC, for instance), this is accelerated at elevated temperatures. There is another obvious time-related long term effect, and that is creep. All plastics creep, and the creep rate is increased by higher temperatures. The standard method for dealing with creep is to treat it as a loss of stiffness over time, and this is done by manipulating your creep data to derive an apparent modulus. But the HDT quantifies a loss of stiffness due to increased temperature. So, I have a loss of stiffness from elevated temperature, and a loss of stiffness from creep, and more stiffness loss because the creep rate increases with elevated temperature... Is this messy enough?
OK, so the proper way to use the HDT is to treat it as the short term temperature where the elastic modulus hits 100 ksi (or 30 ksi). But really, this is pretty limited. What if
350
curve A 300 Elastic Modulus, ksi.
Anyway, you get the idea. The HDT is not suited, nor intended, to be used as a maximum use temperature. It may be useful when used with other data, like the UL Relative Thermal Indexes, for instance, but should never be used alone as a maximum use temperature.
250
curve B 200
curve C 150 100 50 0 50
100
150
200
Temperature F
Figure 5 Spring, 2010
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SPE PD3 Newsletter
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Society of Plastics Engineers Product Design & Development Division Newsletter
I need at least 200 ksi at 175 ˚F? What's my maximum temperature then? The HDT can't tell me that, because it is a single data point. In Error! Reference source not found., which is a repeat of Error! Reference source not found. with some more lines, we see first that all three materials have the same HDT, which is 215 ˚F. We also see that their stiffness at 175 ˚F varies from about 175 ksi to 280 ksi. Thus, curves A and B work for us, but Curve C would not. Again, we can’t get this from the HDT on a datasheet. We need the complete curve. This is a serious limitation of using the HDT in plastic part design. Is there a way to get the full curve? Well, of course there is. Dynamic Mechanical Analysis (DMA) is a method that can be used to generate a plot of elastic modulus as a function of temperature. Figure 6, taken from reference 2, shows just such a plot. This is obviously much more useful than a single data point. There is ASTM D5026, Dynamic Mechanical Properties in Tension, but ASTM D5279, Dynamic Mechanical Properties in Torsion, is preferred by the Figure 6 labs I talked to because thermal strains are parallel to the tensile strains in the tensile test, causing some accuracy issues. The torsion test avoids this. DMA testing is relatively cheap at just a few hundred bucks a run, and takes a lot of the guess work out of part design and material selection. References
1. Takemori, Michael T., “Towards an Understanding of the Heat Distortion Temperature of Thermoplastics”, Polymer Engineering and Science, Vol.19, No. 15, Nov., 1979 2. Sepe, Michael P., “The Usefulness of HDT and a Better Alternative to Describe the Temperature Dependence of Modulus,” Limitations of Test Methods for Plastics, ASTM STP 1369, American Society for Testing and Materials, West Conshohocken, PA, 2000. 3. Sepe, Michael P, “The Materials Analyst, Parts 36,37 and 38, Myths of the Heat Deflection Temperature”, Injection Molding Magazine, Oct., Nov., and Dec., 2000. 4. Standard Test Method for Deflection Temperature of Plastic Under flexural Load, ASTM D 648 07, American Society for Testing and Materials, West Conshohocken, PA 2007.
Spring, 2010
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SPE PD3 Newsletter
Society of Plastics Engineers Product Design & Development Division Newsletter
SPE ANTEC Coming Soon! Don’t Forget—SPE-ANTEC® 2010 will take place in Orlando, Florida, at the Orlando World Center Marriott Resort and Convention Center from May 16 to 20. To learn more about the ANTEC Technical Program, click here. Editor’s Note: According to Lesley Kyle (+1 203-740-5452), the Senior Event Planner at SPE handling ANTEC 2010, SPE members can attend the entire ANTEC 2010 program – more than 600 technical presentations, 115+ technical sesssions, 3 plenary sessions and the exhibit hall – for $550, the lowest price for this event since 1999! Register for ANTEC 2010 at their website. SPE Student Activities Committee Seeks Your Support for ANTEC There are plenty of activities for students at this year’s ANTEC, including a mixer at Mickey & Minnie’s house!. Go here for details. SPE PD3 BOD and General Membership to Meet at ANTEC The PD3 Board meeting will be held on Monday, May 17th at 8:00AM Eastern Time at ANTEC. The meeting will be held at the Orlando World Center Marriott Resort and Conference Center, in the Chicago Room. A General PD3 Division Membership meeting will follow the Board Meeting in the same Room at 9:00 AM Eastern Time. If you are attending ANTEC please join us for the membership meeting. We hope to see you there!
SPE: News: From the Home Office The folks back at the SPE home office have been very busy these past months, as evidenced by these stories of interest:
SPE’s Subscription Plan Gives Unlimited Access to Technical Training SPE is excited to continue its subscription plan for the e-Learning Center that makes it even more affordable for you to learn and stay competitive in your field! This plan will continue to offer unlimited, affordable access to live technical presentations over the Web! The subscription program will grant you VIP access to as many e-Live® Webinars as you would like during a 3-month* period. What types of webinars are offered? To view our current calendar, please click here: www.4spe.org/elearning How much does it cost? You will be able to attend as many webinars as you want for $199 (SPE member pricing). Where do I register? Register here: http://www.4spe.org/e-learning-subscriptions Once you are registered, you will receive further instructions about how to access any webinar you would like!
Spring, 2010
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SPE PD3 Newsletter
Society of Plastics Engineers Product Design & Development Division Newsletter
The Society of Plastics Engineers (SPE) Introduces Email-Based News Briefs With new technologies, new procedures, and new operational strategies, the plastics industry is continually evolving. To that end, the Society of Plastics Engineers (SPE) has launched the new SPE Industry Update, an opt-in email resource providing comprehensive news briefs of the industry’s top stories. Each edition of the SPE Industry Update contains articles gathered from an extensive list of sources, such as The Associated Press, The New York Times, Plastics News, and other more industry-specific publications. Professionals from the field will also contribute timely news and information "just in time" so leaders can keep on the cutting edge of industry developments. Beginning immediately, the SPE Industry Update will be delivered to the inboxes of SPE members and nonmembers alike, keeping plastics leaders abreast of topics that impact the daily operations of their businesses. The SPE Industry Update is a great way to keep informed. The electronic publication can be easily read on your office or home computer, or via your mobile phone or PDA. The SPE Industry Update is powered by MultiBriefs, a division of MultiView. “We understand that as the plastics industry evolves, it’s becoming increasingly important for SPE to keep its members informed. The SPE Industry Update has been designed with the needs of SPE members in mind,” says Dan Maitland, president of MultiView. “We look forward to delivering the news and information that SPE members have asked for.” In case you missed the e-mail, the latest two industry updates can be found here and here.
SPE Product Development and Design Division Board of Directors Roster Chair John J. Doyle R&D Manager, Bioscience Div Millipore Corp [email protected] (978) 762-5173 office (603) 770-2036 cell Secretary Mark MacLean-Blevins MacLean-Blevins & Associates, Inc. [email protected] (410) 848-6232 office (410) 346-7274 fax
Spring, 2010
Chair-elect Mark MacLean-Blevins MacLean-Blevins & Associates, Inc. [email protected] (410) 848-6232 office (410) 346-7274 fax Councilor Lance Neward Turner Group, Intermountain Area [email protected] (801) 568-6771 office (801) 541-9414 cell
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Treasurer Mark Wolverton Senior Technical Service Engineer FHR Polymers [email protected] (630) 240-5110 office TPC Team Barbara Arnold-Feret (Chair) Development Manager Enviro Plastics Inc [email protected] (817) 271-3574 home Mike Paloian Mark Wolverton
SPE PD3 Newsletter
Society of Plastics Engineers Product Design & Development Division Newsletter Historian Glenn Beall Glenn Beall Plastics [email protected] (847) 549-9970 office
Past Chair Ronald Minke Aptimise, LLC. [email protected] (260) 407-0382 office
Anne Bernhardt Plastics Instructor Skyline HS - Dallas ISD [email protected] (972) 502-3565 office (972) 385-8483 home Paul Rothweiler Aspen Research Paul.Rothweiler@aspenmaterials .com (651) 341-5427 office
Jordan Rotheiser President Rotheiser Design Inc [email protected] (847) 433-4288 office
Dejin (Derek) Li Process Chemist Sabic Innovative Plastics [email protected] (304) 863-7148 office Jack Elder Multiject [email protected] (248) 608-0005 office (248) 563-3179 cell
Spring, 2010
Mark Matsco Director Bayer Material Science LLC [email protected] (412) 777-4194 office (724) 244-7764 cell Rick Fischer Sr. Project Engineer IMPACT Engineering Solutions [email protected] (630) 487-6250 cell James K. McDowell, PhD Engineering Manager Newpark Mats & Integrated Svcs [email protected] (337) 896-8976 office (337) 565-2133 direct (337) 288-7272 mobile Todd Cook Staff Engineer, Plastics Remington Arms Company, Inc. [email protected] (270) 769-7604 office (270) 766-7656 cell
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Newsletter Al McGovern (Editor), Director of Mechanical Engineering Shure, Inc. [email protected] (847) 600-8451 office (630) 660-6217 cell Mike Lacey Micheal Paloian President Integrated Design Systems [email protected] (516) 482-2181 x101 office Mike Lacey Phoenix Contact [email protected] (717) 944-1300, x3679 office (717) 877-8492 cell D Malpass Consultant (Polyolefins) [email protected] (281) 770-5411 cell Anthony N. Onochie Vice President Onosta Global Engineering Ltd. [email protected] m (713) 205-3885 office
SPE PD3 Newsletter
