Tech Talk Blog

Here’s a quick review of the different categories of plastics:

Plastics are classified into two categories:

1)      Thermoset – is any material that, once heated, cannot be reheated or reformed (Examples: Bakelite, Melamine, Teflon, Torlon, Celazole, glass epoxy systems, phenolic, Micarta

2)   Thermoplastic – any material that can be heated and reheated to make a finished part or stock shape (Examples: PVC, PEEK, polyethylene, nylon, acetal, acrylic)

Plastics also break down into two subcategories:

1)      Amorphous – Which is see-through or

2)      Crystalline – Not see-through.

The molecular structure is very important to the performance properties of any plastic material.

In processing, thermoset materials can only be compression or transfer molded. The process usually requires extremely high pressures and elevated temperatures. Thermoset materials usually require some form of reinforcement for stability and strength.

Thermoplastics can be extruded, injection molded, compression molded, blow molded, thermo formed, bonded to substrates, stamped and machined. And with thermoplastics, we have the ability to include additives to enhance properties like wear, fire resistance, electrical properties, and improvements in impact strength.  We can also reinforce with additives like glass fibers, carbon fibers, Kevlar, graphite, calcium carbonate.

We also classify by temperature:

1)      Commodity Plastics – lower cost and performance, typically doesn’t work above 200° F, good chemical resistance

2)      Engineering Plastics – 300° F limit, generally more versatile, used in structural and wear applications, available with enhancements

3)      High Performance Plastics -  most expensive, handle high temperatures over 300° F, associated with the most extreme operating conditions – thermally stable, excellent inherent wear properties, broad chemical resistance.

Our team is always looking at new alloys, new fillers, and extending chemistries to make new polymers.

Polymer gears are common place in many industries and applications. The advantages of a polymer gear include noise reduction, self lubricating features, dramatic weight reduction and cost savings. From paper mill gears to drive gears in copiers, polymer gears have been successfully used for years. But, everything you know about metal gear design gets thrown out the door with polymers. There are many different factors that have to be considered when designing gears out of plastics including thermal expansion and contraction, physical strength, moisture absorption and possible chemical exposure.

Typical polymers for gears are cast nylons, injection molded nylons, polyester and acetal. Various fillers help to strengthen the base polymers such as glass and carbon fiber, aramid fibers and other additives are used to improve lubricity. More recently high end polymers like PEEK and Torlon have been used to make high temperature gears or gears where exceptional strength is required. No matter what the material, designing polymer gears will require some extra thought and a change from the norm. Tooth profiles and overall height may need to be changed to accomodate bending forces. Contact conditions at the root of the tooth may need modifications from the norm. Flex strength of the polymer will definitely come into play so input and output torque requirements will need to be reviewed closely.

While there are a lot of advantages to polymer gears you can’t overlook the basic differences of steel gears and polymer gears. Material choice and adherence to design changes required to address the physical, thermal and wear requirements of the gear must all be looked at closely. Tri Star has several thermoplastic and thermoset materials used frequently for gears and our engineering department can help you in this process. Have more questions? Ask The Experts – they are bound to know something. Or check out our Video Learning Center for a deeper look.