Jim Throne on February 16th, 2001

Recently, Profile Plastics has been winning major thermoforming awards on their thin-gauge twin-sheet thermoformed surgeon’s helmet. Although this is certainly not the first thin-gauge twin-sheet thermoformed part, it certainly has raised the bar in this area. This technical note discusses the nature of the process and some of the reasons why this technology has not […]

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Jim Throne on January 1st, 1999

It has always been my philosophy to obtain as much information as possible about the polymer with which I’m working. As techniques for predicting polymer performance during processing become more sophisticated and computer models for predicting polymer product response to applied temperature and force conditions become more exacting, our thirst for data seems to grow […]

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Jim Throne on August 16th, 1998

Isotactic polypropylene (iPP or usually just PP) is considered a crystalline commodity polymer of the polyolefin family. It has the following basic molecular structure: (CH2 – CHCH2). Even though the molecule appears to have a bulky pendant group, there is substantial backbone mobility, allowing the molecule to twist in such a manner as to present […]

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Jim Throne on July 1st, 1998

Background Part I detailed the arithmetic used to predict energy transfer to plastic sheet during the heating portion of the thermoforming cycle. In this part, we’ll take a look at heating of thin-gage sheet. In Part I, we considered the importance of the three modes of heat transfer – conduction, convection and radiation – on […]

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Jim Throne on June 2nd, 1998

Background In this technical note, we examine the arithmetic used to predict energy transfer to plastic sheet during the heating portion of the thermoforming cycle. Our discussion is restricted to radiantly opaque sheet. There are three modes of heat transfer: Conduction, where energy is moved through a solid or non-flowing substance. The key to conduction […]

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Jim Throne on March 27th, 1997

On 22-25 March 1997, Manfred Jacob Kunststofftechnik, together with the SPE Thermoforming Division, hosted a three-day conference on thermoforming at the new technology center in Wilhelmsdorf Germany. The conference was patterned after the highly successful SPE Thermoforming Division conference held each September in the U.S.. Management and technical papers were presented the first day. The […]

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Jim Throne on March 14th, 1997

Technically, sag is the bowing of a plastic sheet during the heating phase of thermoforming. Practically, it is a major bugbear. Many processing problems, including the following are directly attributed to sag: Nonuniform sheet thickness, even before the sheet contacts the mold. Nonuniform sheet temperature, since the top-center of the sheet moves away from the […]

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