See below for disclaimer on the trademarks regarding Teflon® and FLUOROGOLD®.
For this discussion Teflon® shall be referred to by its industrial name PTFE.
Most frequently our Steel Fabricating customers are called on to use PTFE (Teflon®) in the basic Slide Bearing configuration. The actual product in a Slide Bearing should be a glass fiber reinforced PTFE known as FLUOROGOLD®.
As engineering and environmental standards have evolved there is also an increasing demand for PTFE in other uses in steel construction.
- Gaskets - Typically on carbon steel to carbon steel connections gaskets are not required. When connecting dis-similar metals a gasket will often be used to eliminate galvanic corrosion. In the photo to the right PTFE inserts were used to separate carbon steel from aluminum. (Note white pad beneath the clip angle)
- Electrical Insulation - PTFE is an excellent electrical insulator. Standard measurements indicate PTFE can insulate 500 volts per thousandth of an inch. Note again the drawing to the right. We were unable to verify with the engineer why Teflon® was required in this application, but these beams are supporting the ground floor of a laboratory that uses a lot of radiology and medical imaging equipment. Excluding any considerations for insulation against electrical current, more common insulations would be a high durometer commercial grade neoprene or Korolath HDPE plastic, both of which are supplied by The Steel Supply Company.
Bearing Pads - For light loads standard white (virgin) PTFE can be used as a bearing pad. For heavier loads the design usually calls for a Teflon® Bearing made with FLUOROGOLD® which provides much greater dimension strength.
Thermal Break - PTFE is also an excellent insulator to prevent thermal bridging. Thermal bridging is the path energy would follow to move from a heated environment into a colder environment. Uses such as these are becoming increasing more common as designers and engineers adapt to LEEDS standards and other environmentally conservative practices.
PTFE has a number of characteristics that are very attractive to engineers;
- Very low co-efficient of friction
- Corrosion Resistance
- Chemically Inert ( i.e. PTFE is unaffected by almost all acids, caustics and solvents)
- Excellent machine-ability
- Temperature feasibility ; PTFE can have operating temperatures from - 100° F to 500° F
- Good abrasion resistance
At times a drawing will call for the Fluorogold® or Teflon® to have a dimpled surface. This would be a case where an addition lubricant will be applied. The dimples serve to collect the lubricant and distribute it sparingly as the surfaces move. Otherwise two perfectly flat surfaces would very quickly squeeze the lubricant out. Situations like this are usually applications subject to "Stick-Slip" conditions that are produced by sudden movement. An example would be a Slide Bearing being utilized on the mounting of an electrical generator. In building construction the anticipated movements are not sudden enough that Stick-Slip will be a factor.
To maximize the value of a Slide Bearing it is important the surfaces of the upper and lower member be as parallel as possible. The drawing to the right shows in exaggerated form what occurs when the bearing surfaces are not parallel. The red arrows indicate where stress is created. The Teflon® or FLUOROGOLD® can absorb some of the deflection. As well, in steel construction there is more than enough strength to offset and overcome the stress. At the least, this condition will cause accelerated wear and most likely premature failure.
Of course Steel Fabricating, and especially Erecting are subject to field conditions and physical limitations. While it may be theoretically impossible to align the bearing surfaces perfectly, care should be taken to see they are as straight as possible.
Note: Teflon® is a registered trademark of the DuPont Corporation. In general industrial terms this product is known as PTFE. (Polytetrafluoroethylene)
FLUOROGOLD® is the industry designation for the type of PTFE used in our slide bearings. It is a special formulation PTFE, reinforced with a glass fiber aggregate. This reinforcement is what allows for its exceptional compressive strength. Fluorogold® is a registered trademark of Saint Gobain and is used with permission through exclusive license.