Plastics Technology

SEP 2018

Plastics Technology - Dedicated to improving Plastics Processing.

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29 C (84 F) the energy required to break the test specimens was only 1.5 N-m (1.1 ft-lb), a value associated with a very brittle material. Altering the melt temperature across a fairly wide range from 218 C (425 F) to 274 C (525 F) did not appreciably change this result. However, when the mold temperature was increased, the impact resistance improved dramatically. With the mold temperature set at 85 C (185 F), the impact resistance improved to 30 N-m (22 ft-lb) with the melt temperature set at the upper end of the experimental range. This improvement is attributable to the smaller difference in until the part is in the field and experiences an environmental condition such as elevated temperature, contact with a certain chemical, or an impact event. Elevated levels of stress will result in a less-than-optimal response to these application influences. Warpage is one of the mechanisms by which stress is relieved. When molders fail to deal with root causes and elect to either fixture a part to prevent movement while it cools, or alter the processing conditions to reduce warpage, they are often building in even higher levels of stress. Most processors know that reducing the temperature of the mold is a very effective way of reducing warpage. We have discussed the temporary nature of this improvement when talking about semi-crystalline polymers. But what about materials that do not crystallize? How do amorphous polymers like polycar- bonate, ABS, and polysulfone react to the faster cooling rate associated with a lower mold temperature? A study performed on ABS some years ago offers some insights into this question. The accompanying graph shows the results of this study; an evaluation of the effect of mold and melt temperatures on the impact resistance of test specimens molded from a particular grade of the polymer. ABS is generally considered to be a reasonably tough material, and materials in this class will typically produce falling dart energies-to break in the range of 30-40 N-m (22-30 ft-lb) and exhibit a ductile failure mode. However, note that when specimens were prepared in a mold set at a relatively low temperature of C-20 DeDuster® – removes dust and streamers Better systems for brilliant products and higher margins. Learn more: www.pelletroncorp.com streamers Better systems for brilliant products and higher margins. streamers streamers Better systems for brilliant products and higher margins. No dust + No streamers = Reduced scrap rate and production costs www.pelletroncorp.com www.pelletroncorp.com and production costs Get more insights on Materials from our expert author: short.ptonline.com/materialsKH Learn more at PTonline.com KNOW HOW MATERIALS When molders fail to deal with root causes and elect to either fixture a part to prevent movement while it cools, or alter the processing condi- tions to reduce warpage, they are often building in even higher levels of stress. @plastechmag 31 Plastics Technology M AT E R I A L S

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