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.

Did you realize there are probably over 300 types of Rulon? Rulon is a self-lubricating material that can almost be considered “generic” in some ways.  It is a PTFE material with various fillers; it is the type and amount of filler that makes each variation of Rulon unique.

When choosing Rulon, we ask:

1) What is the application function – bearing? Seal? Gasket? Some materials can be used for all applications.

2)  What is the temperature? -400 to +550 is the general range Rulon can accept. For design purposes, we need to know how much press fit and close in to account for in the gradient.

3)  What is the environment? Some types are made for FDA or USDA environments or for resisting abrasion. Most PTFE materials don’t do well in water, but a few do.

4)  What is the speed? All types of Rulon can take 400/500 feet per minute without lubrication; but we need the load to be a bit more accurate. Rotating? Oscillating? Linear?

5)  What are the loads on that bearing? Most can handle 1000 psi, but others can withstand higher levels.

6)  What type of hardware (consider temperature)? Only a few types of Rulon can work with stainless steel.

7)  What is the surface finish? 8-16 rms on the shaft is recommended, but for holding purposes, we would suggest 32 rms.

We can help you choose the right Rulon for your application.

We see this question often.  Plane bearings offer many advantages; a simple design, self-lubrication, a wide range of operating parameters, and lower cost.

When selecting a plane bearing, consider:

Load – this can be the most difficult attribute to define. What is the pressure? Multiply the ID times the length, and then divide the load by that number. Pressure (P) is expressed in PSI.

Speed – you may know what your shaft speed is, but you need to find the velocity (v). Take the diameter multiplied by pi, then multiply by the RPM. Divide this number by 12, because V is measured in surface feet per minute (SFPM). Every material is rated for a maximum velocity.

P and V – these must always be considered in tandem. The combination of load and speed generates frictional heat. Always review P x V or PV. Every material has a maximum PV rating.

Material Rating – look at all the values for each individual project. Plastics are insulated in nature, and heat will kill a plastic bearing faster than anything else.  Be sure to stay within the known limits to understand what materials are capable of taking.

Temperature – this is critical to getting the proper “press fit”.  Be certain there is no loss of tolerance or close-ins.

You can also visit our Plane Bearing Design Worksheet for guidance, or contact us directly.

Plane bearings are straightforward; two surfaces moving against each other without the aid of a rolling element. A shaft turning in a bushing, a slide pad damping vibration, a bridge joint expanding, and a chain running through a channel are all examples of plane bearings. Sleeve or flange bushings, thrust washers, linear-slide plates, friction bearings, and wear pads all fall into the plane-bearing category. If there are no balls, needles, retainers, or races, it’s a plane bearing.

Plane bearings stand up to most industrial and outdoor applications. They are self-lubricating and offer superior resistance to fresh water, saltwater, deionized water, slurries, acids, or bases. And because they have few moving parts, most plane bearings are not adversely affected by particulates like coal dust, quartz debris, sand, and road ballast. Plane bearings are safe for clean rooms, too, because they produce minimal debris and won’t attract dirt. Many materials also meet FDA, USDA, 3A, or NSF standards.

Our team can walk you through our complete selection to make sure you get the right fit for your application.