PTFE composite bushings are the maintenance-free solution for heavy load/medium speed applications. VIIPLUS offers a wide range of both straight and flanged PTFE composite bushings.
Straight bushings are manufactured to dimensions in accordance with ISO 3547-1.
PTFE composite plain bearings combine the mechanical strength of steel with the low friction of a PTFE-based self-lubricating lead-free sliding layer. The intermediate layer of porous tin bronze creates a strong bond between the backing and sliding surfaces and also improves the dissipation of heat generated during operation. To protect the bearings from corrosion, the steel backing is tin-plated. With the exception of the sliding surface, PTFE composite dry sliding bearings can be machined. Calibration is possible within certain limits.
Bushing material selection,3 layer bearing with PTFE-surface
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Sliding material and bushing type selection guides.
Machining the bore of PTFE composite bushings
PTFE composite bushings conform to ISO 3547:2006 and are ready for installation.
Any re-sizing of the bore, i.e. the sliding surface, will reduce the service life of the bushings and should only be done in exceptional cases. If re-sizing is necessary, the bore should be calibrated, using a mandrel/resizing tool . Because various criteria, like material and wall thickness of the housing as well as the deviation of cylindrical form, have to be taken into consideration, Viiplus recommends using a calibrated mandrel to re-size the bore. After resizing, bushing bore expansion tests and application field tests should be undertaken prior to the release of a final product.
Guideline values for the requisite interference of the calibrating mandrel as a function of the desired widening of the bushing bore for various bushing bore diameters can be obtained from diagram 1. The diagram is based on tests with bushings of different sizes and valid for bushings mounted in a housing.
with an outside diameter DG = 2* bushing outside diameter D . If mandrel expansion tests show that the bore is too wide, the calibrating mandrel should be reground and the tests repeated on new bushings.
PTFE composite bushings’ Chemical properties
The steel backing and the sintered tin/bronze layer are the primary factors in determining
the chemical resistance of Viiplus composite plain bearings, as the sliding (covering) layers
are resistant to most chemicals. The covering layer is virtually inert because of its PTFE
content, although at elevated temperatures molten alkali metals and free fluorine will attack it. The acetal resin-covering layer of the POM composite bearing is largely resistant to organic substances. At room temperature the sintered tin/bronze structure has good resistance to sea water, steam, atmospheric influences, salt solutions and sulphuric acid, but not to oxidizing acids or media containing ammonia.
All exposed surfaces of the steel backing are electrolytically tin-plated but this provides only limited protection against corrosion in most applications. In cases where the bearings are to be exposed to corrosive media, or where there is a danger of corrosion in the contact between the steel backing and the housing material, the backing can be protected by a nickel, chromium or zinc coating applied electrolytically. Further details can be supplied on request.
Where to use PTFE composite bearing?
· Because of their good sliding properties and compact design, these plain bearings are particularly suitable for bearing arrangements where:
· Maintenance-free operation is a prerequisite
· There is a risk of lubricant starvation
· Lubricants cannot be used or are forbidden
· Space is limited.
Machinability of composite materials
With the exception of the sliding layer, Viiplus composite bushings can be machined using conventional methods. If bushings are required to have a smaller width than the standard size, this can easily be achieved by turning. It is also possible to drill lubrication holes. However, any burrs must be removed, particularly from the sliding surface. Strips can be bent, pressed, cut, or drilled to fit the individual application. When cutting or drilling, it is advisable to work from the sliding surface side to avoid creating burrs in the sliding layer. Any metal surfaces that are exposed as a result of machining should be protected against corrosion.
PTFE composite bushings lubrication
The PTFE-based sliding surface permits smooth, low-friction operation without lubrication. During a short running-in phase, there will be some transfer of PTFE material from the sliding contact surface to the counterface. After this transfer, the characteristic low friction and wear properties of these bearings will be achieved.
The presence, or continuous supply of oil or other non-corrosive fluids may be advantageous and improve the performance of these bearings.
- Maintenance free
- Low friction coefficient
- Multiple areas of use
- Long lifetime
Type of applications
- Person lifts
- Packaging machines
- Pneumatic cylinders
- Cylindrical bearings
- Flanged bearings
- Thrust washers
- Slide plates
- Drawing details
Technical information and standard dimensions,contact with us today!
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