Typical Teflon® Slide Bearing Assemblies are made with 3/32” thick Fluorogold® bonded to a 1/8” thick backing plate. (Note: These dimensions can be changed to any size and thickness required.)
For interior applications the backing plate is plain low carbon steel in most cases. Examples would be Slide Bearings used under steel joist flanges or in a building addition between two interior steel members. These examples will not be exposed to the elements and as a rule the steel backing plate will outlive the Teflon® or Fluorogold® surface.
As the application comes in contact with weather the oxidation of the backing plate becomes a factor. One solution is to Hot Dip Galvanize the backing plate. To accomplish this the backing plate is galvanized first. Then the zinc is removed from only the surface that the Teflon® will be bonded to. The zinc removal is a time consuming and tricky process. It is done by grinding or milling the surface without going too far into the steel. It is important to keep the steel surface flat and uniform. After that the normal bonding process is employed.
Properly done Hot Dip Galvanizing to ASTM Specifications A-123 is designed to protect the underlying steel for approximately 25 years. This estimate will vary widely based on how strong the exposure to the elements is.
Recently there has been an increase in the demand for Teflon® Slide Bearings with Stainless Steel backing plates. These are almost always made with Fluorogold® Teflon as it is more durable and able to withstand more abuse than pure PTFE (Teflon®). Some of the projects requiring Stainless Steel are Oil Pipelines, exterior HVAC ducts and Bridges.
From a function standpoint a Slide Bearing Assembly made with a stainless steel backing plate will only outperform plain or HDG carbon steel in terms of length of service. The sliding action and coefficient of friction will be the same. Keeping in mind the sacrificial surface is the Fluorogold®, with each expansion and contraction the Fluorogold is wearing down. However slight the wear is sooner or later the Slide Bearing Assembly will need to be replaced. The use of Stainless Steel backing plates simply assures the plate will not be the cause of the failure. The assembly will function until the Fluorogold has worn away.
This extra level of protection is significant when the cost of replacing one, or many Slide Bearing Assemblies is considered. The photo to the above right shows one support of the Trans-Alaska Pipeline, which is 800 miles long and has approximately 30 supports per mile. In cases like this the engineers may determine the extra cost for stainless steel is justified in relation to the risk of premature failure.
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