Michael Sepe Independent Consultant

Materials Know How 29 Apr 2013

Dimensional Stability after Molding—Part 5

All materials possess a property called the coefficient of thermal expansion (CTE). The vast majority of materials increase in size as their temperature increases and decrease in size as their temperature declines.

Materials Know How 25 Mar 2013

Dimensional Stability After Molding: Part 4

In the first three parts of this series we focused on those influences that cause molded parts to get smaller. But there are environmental factors that also cause parts to increase in size over time.

Engineering Resins 26 Feb 2013

Dimensional Stability after Molding—Part 3

Any process that involves melting and re-solidifying a polymer involves a compromise between achieving the perfect structure and producing a part that can be sold at a price that the market is willing to pay.

Materials Know How 28 Jan 2013

Dimensional Stability After Molding—Part 2

After molding, acetal parts can continue to shrink at room temperature and even in the cold.

Injection Molding 28 Dec 2012

Dimensional Stability After Molding: Part 1

The degree to which molded parts shrink as they cool is largely dependent upon the composition of the material being processed.

Materials 2 Mar 2020

Is It Glass Filled or Glass Reinforced?

Here is how to tell the difference.

PET Processing - Extrusion 26 Oct 2012

PBT & PET Polyester: Part 2 The Performance Factor

All things being equal, PET will outperform PBT mechanically and thermally. But the processor must dry the material properly and must understand the importance of mold temperature in achieving a degree of crystallinity that allows the natural advantages of the polymer to be realized.

Materials Know How 29 Oct 2022

PBT and PET Polyester: The Difference Crystallinity Makes

To properly understand the differences in performance between PET and PBT we need to compare apples to apples—the semi-crystalline forms of each polymer.

Engineering Resins 4 Nov 2022

How Do You Like Your Acetal: Homopolymer or Copolymer?

Acetal materials have been a commercial option for more than 50 years.

Materials Know How 30 Jul 2012

Use MFR Cautiously with Filled Materials

If melt flow rate tests are used to evaluate the effect of processing on the average molecular weight of the polymer, the applicable rules must consider the contribution of the filler to the test result.