Production problems with polytetrafluoroethylene sheet
Q: The use of polytetrafluoroethylene plate is to reduce the friction between the tube holder and the axial fixing bracket. Is to reduce the friction, my first question is to ask is a piece of PTFE and tube care of the steel part of the friction or two polytetrafluoroethylene plate friction?
A: There are two pieces of PTFE sheet between the slide, but also useful a piece of PTFE board, a piece of stainless steel.
PTFE slide assemblies are used in piping systems to reduce the coefficient of friction at support locations. Where large displacements are anticipated, it is preferable to use PTFE slides to allow thermal growth of piping system and reduce frictional forces on the anchors or supporting structure.
A typical PTFE slide assembly comprises of teflon pad at the bottom and mating stainless steel plate on the top. The PTFE pad is normally supplied bonded to a carbon steel backing plate. Bonding to steel plate is done by countersunk bolts or by glue. Some manufacturers embed the PTFE pad in a recess to prevent the PTFE pad from getting sheared off from the carbon steel backing plate.
The stainless steel backing plate is supplied with mirror finish and is either supplied loose or tack welded to a carbon steel backing plate. The stainless steel plate is larger than the PTFE pad and is sized to allow the anticipated thermal movements.
In determining the size of the PTFE slide bearing pad the applied loading and the operating temperature has to be taken into consideration. At ambient temperatures a maximum bearing pressure of 60 kgf/cm2 is generally recommended. If loads are high or bearing area is small due to space constraints, glass filled PTFE pads can be used to provide higher bearing pressure."
Glass filled PTFE pads at ambient temperature can provide a load bearing capacity of about 140 kgf/cm2
Virgin PTFE can provide 0.1 coefficient of friction. For glass filled PTFE the friction coefficient is marginally higher at about 0.12.
PTFE is suitable for continuous operation at temperatures up to 150°C. Where the PTFE temperature is likely to exceed 150°C, thermal insulation is provided between the source of heat and PTFE pad.