Slide Bearing and Pipe Supports Design & Installation
The slide bearing components can be fixed to the installation by bolting, tack-welding, full welding or mortar embedment, and the appropriate type of bearing should be chosen according to the installation method. During slide bearing installation the PTFE surface should be adequately protected against weld spatter, paint spray, etc.
PTFE Slide Bearing Considerations
The following steps will provide an indication of the slide bearing requirements for a particular application:
- Determine the total load of structure - this will indicate the total slide bearing area required at a suitable bearing pressure and temperature.
- Decide the number and positions of the slide bearings according to the rigidity and function of the structure.
- Take account of operating environment and specify grades of steel for backing plates.
- Consider any unusual conditions affecting the slide bearings, such as the need for additional thermal insulation, vibration pads and deflection of slide bearing surface.
- Decide the most appropriate method of mounting the slide bearings.
- Select the types of slide bearings required from the recommended design chart and specify their dimensions.
Bonding of PTFE
We recommend chemical bonding for locating the slide bearing material on its support. The shear value of the epoxy adhesive is greater than that of the PTFE.
Our bonded FluorinoidŽ PTFE elements supplied meet the requirements of BS5400 and we recommend the use of black, glass filled FluorinoidŽ PTFE to ensure the slide bearing bond is not affected by exposure to ultra violet light.
Site bonding of PTFE is not recommended - strictly controlled conditions of cleanliness, pressure and temperature are required to obtain a satisfactory bond between the PTFE and substrate. If site slide bearing bonding is unavoidable, we recommend that Fluorocarbon engineers are consulted.
Material Thickness
From basic Fluorocarbon tests coupled with independent and empirical testing, the ideal thickness has been found to be 2.5mm, although this can be reduced to 1.5mm as an absolute minimum. This is thin enough to achieve the maximum reduction in cold flow and creep, yet thick enough to allow for some constructional misalignment and to allow for dirt and grit embedment.
Pad Dimensions
The top slide bearing pad should be larger than the bottom slide bearing pad by an amount in excess of the expected movement, in order to maintain a constant contact area and prevent ingress of dirt on to the bearing surfaces.
Bearing Temperature
The temperature at the surface of the PTFE should generally be less than 120°C and should never exceed 200°C. Typical data suggests that under normal conditions the temperature falls by 200°C for every 100mm from the heat source (in ambient air).
However, if the slide bearing temperature is likely to exceed 120°C a thermal insulator should be fitted between the structure and the slide bearing back plate.
Vibration / Acoustic Damping Pads
Slide bearing units can be built with a variety of elastomeric composite interlayer’s or backings to suit customer's design parameters when acoustic or vibration damping is necessary. Elastomers may be used when simple angular or rotational movements are required. |
