| |
Slide bearing plates are a very cost-effective way of
providing for movement of mechanical systems. Piping Technology
& Products, Inc. supplies slide bearing plates for a variety
of applications including support of piping, heavy equipment such
as pressure vessels, and structural steel members. The plates
provide a surface with a low coefficient of friction which can be
attached to a supporting structure. This combination provides
support while simultaneously allowing an object to move (slide)
freely along the supporting surface. Most designers use the
"sandwich" concept when applying slide plates to their
systems. Diagram A shows a "sandwich" composed of two
identical slide plates, one on top and another on the bottom.
Each slide plate is composed of two components: a metal backing
plate (which is like the bun of the 'sandwich") and a low
coefficient of friction material which is bonded to the metal
backing plate. In a typical application, a slide bearing plate is
welded to a structural steel member which is strong enough to
provide the required support, but whose coefficient of friction
is too high. When the pipe supported by the member moves (due to
thermal expansion, for example) it slides across the surface of
the bearing plate without contacting the steel beam. To return to
our "sandwich" metaphor, the top half of the
"sandwich' is bonded to the pipe, and the bottom half to the
steel beam. One combination of materials that we recommend is
that of PTFE, 25% Glass Filled, bonded to stainless steel. Both materials resist
oxidation and have long lives even in stressful environments. For
large slide plates, galvanized steel can be used in place of
stainless to reduce the cost.

TEMPERATURE CONSIDERATIONS PTFE, 25% Glass Filled, provides a
low coefficient of friction for most combinations of temperature
and load. Diagram B (see PTFE, 25% Glass Filled, Slide Plate link) shows the
recommended conditions for N32inch PTFE, 25% Glass Filled. For most
applications, PTFE, 25% Glass Filled, is adequate when the temperature is less
than 4OO degrees F. When the slide bearing plate must function at
higher temperatures, graphite can be used instead of PTFE, 25% Glass Filled.
The load-bearing capacity of graphite is not sensitive to
increases in temperature, but the adhesive used to bond the
graphite to its metal backing is. It is good practice to use
additional mechanical fasteners such as counter-sunk screws to
help hold the graphite in place when the temperatures are above
500 degrees F. For combinations of temperature and load beyond
the capabilities of graphite, special designs must be considered.
ATTACHMENT CONSIDERATIONS Welding is the most
common method of attaching the slide bearing plate to supporting
metal structures. When this approach is used a "lip"
must be built since the welding's extreme temperature may break
the bond between the low-friction material and the metal plate. A
0.25 inch "lip" is adequate for most welded
installations. When welding cannot be used (for safety or other
reasons) to attach the slide plates, bolting is the most common
substitute.
Before we can begin constructing your slide bearing plates, we
need to know the following:
- The material you desire for the low-friction surface,
based on the highest combinations of temperature and load
the component will experience.
PTFE, 25% Glass Filled, and
graphite are
the most common choices.
- The desired size and shape for the low-friction surface.
- The type of metal you desire for the plate backing. Most
designers choose galvanized or stainless steel.
- The size and shape for the metal plate backing of the
low-friction surface.
Slide bearing plates are components of many products Piping
Technology & Products, Inc. supplies such as guided pipe
shoes and upthrust constants. As a result, we have extensive
experience in bonding PTFE, 25% Glass Filled, and graphite to metal plates.
Modern adhesives are adequate for most applications. However,
mechanical fasteners such as counter-sunk screws can be added
when needed. If you have unique problems, we will be happy to
custom-design a practical solution to your problem.
|