Vespel®Bearings Vs. Other Materials

June 07, 2024

This brief overview shows that vespel®parts can perform well in different radioactive environments, even at relatively high dosage rates. The small losses in weight, tensile strength and elongation properties, at doses up to 1 x 108 rads, suggest that the superior properties of Vespel®

parts may be used even in environments containing gamma or electron beam radiation.

Working with radiation

Radiation from various sources may be present in the environments of a number of technical and industrial applications. At high radiation levels, it is often necessary to use remote handling or automatic equipment to avoid injury to personnel. Materials used in the construction of such equipment must be able to withstand exposure to radiation.

While metals perform well in static structures, the necessity for lubrication, with the consequent possibility of contamination from the lubricant, reduces their usefulness in bearings, bushings and sliding surfaces. For applications requiring moving parts, as in the handling systems for the production of radio chemicals, or the handling of nuclear fuel rods, self-lubricating high performance polymers such as Vespel® SP Polyimide parts can overcome some of the limitations of metals.

The performance of Vespel®SP polyimide parts when subjected to different kinds and levels of radiation is described below.

Testing To determine how well direct-formed Vespel®bars (SP-1, SP-21 and SP-22) performed after radiation exposure, three parameters

were evaluated:

1. Weight loss;

2. Change in tensile strength; and

3. Change in elongation, compared to randomly selected control bars which received no radiation exposure.

Gamma radiation was provided at a dosage of 3.8 x 106 rads/hour from a cobalt 60 source. Exposure times of 16 minutes, 2.6 hours and 26.3 hours resulted in total dosages of 106, 107 and 108 rads.

Weight Loss Tensile Strength Tensile Elongation

Less than 1.0% Less than 6.5% 19.2% loss loss loss at the maximum

Electron beam radiation from a 2,0 MV Van de Graaf generator provided a dosage rate of 4.0 x 106

rads/hour. Exposure times of 1.6 minutes, 80 minutes and 2.7 hours resulted in total dosages of 106, 5 x 107 and 108 rads.

Weight Loss Tensile Strength Tensile Elongation Less than 2.0% Less than 4.5% Less than 15.0% loss loss

Vespel® parts and neutron beam radiation Neutron beam radiation was provided by a neutron flux of 5 x 1013/cm2 /second. Tensile bars were subjected to this exposure level for 100 and 150 hours respectively. Co-incident gamma

radiation, at an average dosage rate of 1.2 x 108 rads/hour, accompanied the neutron beam exposures. Although none of the test bars swelled or were noticeably distorted, tensile strength was substantially reduced after the exposure to high levels of neutron beam irradiation. Therefore,

we suggest that you discuss applications involving neutron radiation with a Vespel®

Technical Service Engineer and that you perform specific exposure tests.

Bushings and Bearings

The earlier you think Vespel®,the more cost-effective your total design can be

The engineers and sales staff at the Division of DuPont™

Vespel®are ready to help you make the best use of the superior performance of Vespel® parts. Visit www.Vespel.com to view

Putting Vespel®to work in your system

DuPont™ Vespel®SP polyimide bearings have been hard at work for more than fifty years, keeping equipment running longer and

with less maintenance than conventional bearing materials.

Vespel®bearings are the cost-effective choice in thousands of applications, because they are tough, lightweight and resist wear and creep - even at extremes of temperature. They can outperform metals and other engineering plastics under a wide range of conditions.

This design chapter is provided to help you choose the Vespel®bearing that is best suited to your application.

Inside you will find:

• General information about bearing design;

• A method for determining pressure-velocity (PV) loading in your application;

• Guidelines for selecting the correct SP polyimide for PV loadings found in practice;

• considerations for use in the design of Vespel®bearings, and

• A sample bearing design problem.

Vespel®Bearings vs. Other Materials

The ability of a bearing to perform in a given application depends, in general, on:

• The operating environment, including temperature and lubrication;

• Load or pressure on the bearing surface;

• Sliding velocity of the mating surfaces relative to the bearing;

• Hardness and finish of the mating surface;

• Friction behavior of the bearing material;

• Thickness of the bearing material combined with the material`s ability to dissipate heat of friction.

Vespel®parts, made from DuPont polyimide resins, perform well with or without lubrication under conditions that destroy most

other plastics and cause severe wear in most metals. Vespel®bearings reduce or eliminate problems with abrasion, corrosion, adhesion, fatigue and wear that plague conventional bearing materials, especially when used without lubricants.

Vespel®bearings can accommodate higher pressure-velocity (PV) loading than most high-performance engineering plastics.

In addition, Vespel® bearings excel over a wide range of temperatures and stresses because they retain their outstanding creep resistance, abrasion resistance and strength. They have performed successfully in the following adverse environments:

• Air and inert gases at 370 °C (698 °F);

• Gamma and electron beam radiation;

• High vacuum (10–10 torr);

• Hydraulic fluids and jet fuels;

• Liquid hydrogen.

Unlike ordinary ball, needle and roller bearings, Vespel®bearings:

• Need no external lubrication;

• Perform at temperatures where lubricants break down;

• Perfom well in dirty environments;

• Can reduce noise, weight and costs.

Compared with bronze, brass and porous metal bearings,

Vespel®bearings: