Technical Minutes

James L. Throne Sherwood Technologies, Inc. Dunedin FL 34698-3347 Introduction This work focuses on the interface between a semi-solid polymer and a non-polymeric surface. More to the point, it focuses on the interface between polymer and non-polymer when one or both are in motion. And to a further point, it focuses on the interfacial resistance […]

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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 May 4th, 1999

Background Rotational molding focuses on the sinter-melting, densification and cooling of polymer, beginning with powder. Typically, polymer powder has a particle size range of -35 mesh to + 200 mesh. The powder is usually manually charged to the mold while the mold is in the open configuration in the servicing stage of the process cycle. […]

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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 November 4th, 1998

Power Point: Frictional Coefficients Between Plug and Sheet

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Jim Throne on September 9th, 1998

A Brief Review Rotational molding begins with -35 mesh polymer powder tumbling in a metal mold. It ends with a monolithic layer of solid polymer against the metal mold. In between, the powder tumbles against the mold until the mold temperature reaches the tack temperature of the powder, whereupon the powder begins to stick to […]

Continue reading about So… Where Does All the Air Go?

Jim Throne on September 1st, 1998

Thermoplastic structural foams have been around for several decades now. We all know that, at the same part weight, the stiffness of the structure increases in proportion to the reduction in plastic density. And that at the same part thickness, the weight decreases in proportion to that same reduction in plastic density. Injection molders and […]

Continue reading about Foaming in Rotational Molding I

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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