Transcription
SLIDE BEARINGS
slide bearingsGeneral informationSlide bearings are used in a wide range of applications, petrochemical plant, heavy machinery, pipelines,buildings and bridge girders; they accommodateexpansion, contraction and other reciprocatingmotions of any structure that moves as a result ofthermal, seismic or differential forces. The use of lowfriction materials means that supporting structures canbe designed more economically, and where used withpipework, pipe stresses and equipment loadingsresulting from high frictional loadings are reduced.Carpenter and Paterson (Asia) Limited producestandard slide plates using PTFE with stainless steeland also graphite with stainless steel. The standarddesigns are suitable for loadings up to 1000kN and arecompatible with CPAs range of pipe bases and clampbases. Slide plates for attachment by welding and alsousing countersunk head bolts are provided. In additionto the standard designs, we offer a design service forslide plates to cover any situation where sliding needsto occur.MATERIALS Virgin PTFE sliding on stainless steel. This configuration gives the lowest possible coefficient of frictionfor unlubricated materials. PTFE is suitable for useat temperatures up to 200 C. 25% glass-filled PTFE on stainless steel. The useof glass-filled PTFE allows higher bearing pressure,so that more compact designs can be used. Thecoefficient of friction is slightly higher than withvirgin PTFE. Graphite sliding on stainless steel. Graphite isnormally used where the sliding surface is at hightemperature. It can be used at up to 500 C.FRICTIONFor PTFE on stainless steel, coefficient of frictionreduces with increasing bearing pressure. The graph inFigure 1 gives an indication of how the applied loadingaffects the coefficient of friction.For graphite on stainless steel, coefficient of frictionwill be approximately 0.15.Figure 1 COEFFICIENT OF FRICTION:EFFECT OF LOADINGCoefficient of Friction0.2 The simplicity of the bearing design and its ease offabrication and installation make the unit costefficient. The costs of a construction can be reduced bydesigning for expansion rather than strain. Coefficient of friction over the bearing surfaceremains constant, even under worst caseconditions. The bearings are maintenance free – both PTFEand graphite are inherently self-lubricating, whilePTFE will absorb small dirt or grit particles. Onlysimple protection is required against the significantingress of dirt.DESIGN / SELECTIONCarpenter & Paterson (Asia) Limited offers a specialistservice, based on many years’ experience of thedesign and application of slide bearings. Low frictionslide plates with a coefficient of friction less than 0.1 areavailable. They are designed specifically for the loadsand movements required. The standard slide plateassemblies SLB01 to SLB10 (pages 4-6) are designedto operate efficiently at the loadings shown.STANDARD BEARING ASSEMBLIES SLB01 to SLB04 (page 4) use 3mm thick PTFEbonded to an 8mm thick backing plate. BondedPTFE bearings are the least expensive type of slidebearing. They can be used up to a maximumtemperature at the sliding face of 130 C. SLB05 to SLB08 (page 5) use 5mm thick PTFEbonded to a recessed backing plate. The recesseddesign allows use up to 200 C at the sliding faceand increased bearing pressure. The thicker PTFEallows greater absorption of dirt/grit into the PTFE. SLB09 and SLB10 (page 6) use 5mm thick graphitecontained in a recessed backing plate. These itemscan be used at temperatures up to 400 C at thesliding face and up to 500 C if an alloy steel orstainless steel backing plate is specified. For all slide bearing assemblies, it is essential thatthe correct movement range is selected to ensurethat the PTFE or graphite is in full contact with thestainless steel sliding plate. It is possible to choosea smaller movement range if the direction ofmovement is known and the upper plate is offsetrelative to the lower plate when installed.NON-STANDARD OPTIONS Alternative PTFE grades. Alternative backing plate material e.g. stainlesssteel. Other shapes. Higher loading. Greater movements. Different backing plate thickness. Different bolting configurations.0.1FI106B PTFE(25% glass-filled)Virgin PTFE02ADVANTAGES OF CPA SLIDE BEARINGS20406080100120140160180200Bearing Pressure (kg/cm2)Do not exceed maximum loading
SLIDING FACE TEMPERATURE AND THERMAL INSULATIONIt is important to note that the maximum servicetemperature relates to the sliding face. As a rule ofthumb, under normal conditions the temperature fallsby 200 C for every 100mm from the heat source (inambient air) - for example, a typical horizontal vesseloperating at 500 C will have a bottom-of-saddletemperature of about 150 C.Where PTFE is used and the temperature of thebearing face is likely to exceed 200 C by conductionthrough the bearing components, a thermal barrier canbe interposed between the heat source and the slidingunit. Carpenter & Paterson (Asia) Limited recommendthe use of Monolux 500. Thermal barriers are notusually needed on conventional high-pressure pipework supports.BONDING OF PTFEChemical bonding is the recommended method forlocating the bearing material on its support, because theshear value of the epoxy adhesive is greater than that ofthe PTFE. All bonded PTFE elements are not adverselyaffected by exposure to ultraviolet light, providing theminimum thickness requirement of 1.5mm is met. Sitebonding of PTFE is not recommended - strictly controlledconditions of cleanliness, pressure and temperatureare required to obtain a satisfactory bond between thePTFE and the substrate.INSTALLATIONThe bearing components can be located to the installation by bolting, tack-welding, full welding or mortarembedment, and the appropriate type of bearingshould be chosen according to the installation method.The PTFE should be adequately protected againstweld spatter, paint spray, metal swarf etc., during installation.VIBRATION/ACCOUSTIC DAMPING PADSSlide bearing units can be built with a variety of elastomer composite interlayers or backings to suit customers design parameters when acoustic or vibrationdamping is necessary. Elastomers may be used whensimple angular or rotational movements are required.DESIGN STEPSThe following steps will provide an indication of the slidebearing requirements for a particular application:1. Determine the load of the structure - this willindicate the total bearing area required at a suitablebearing pressure.2. Decide the number and positions of the bearingsaccording to the rigidity and function of the structure.3. Take account of operating temperature limits, andspecify any necessary thermal insulation.4. Consider any unusual conditions affecting the bearings, such as the need for additional thermal insulation, damping pads, etc.5. Decide the most appropriate method of mountingthe bearings.6. Select the types of bearings required and specifytheir dimensions.TECHNICAL ADVANTAGES OF PTFE SLIDE BEARINGS PTFE has the lowest coefficient of friction of anyknown solid engineering material, includinglubricated metal. There is no stick-slip action. They have indefinite life, since chemicals andweather have no effect on PTFE - moistureabsorption is less than 0.01% even under icingconditions or immersion, and the material ischemically inert. No maintenance is required, PTFE will never coldweld to itself and therefore requires no lubrication. The bearings are easily installed, either pre-assembled or on site. PTFE bearings are far less bulky than alternativeassemblies. There is no possibility of fatigue failure. Electrical and thermal insulation minimise galvaniccorrosion and heat loss. Vibrations are damped. Small particles which may become embedded donot cause binding of the surfaces. The slide bearing can accommodate somemisalignment in construction without setting upstress corrosion along a leading edge, as canoccur in conventional bearings.3
slide bearingsslb 01 & 02 - bonded virgin/glass-filled ptfe slide bearing - for weldingTop plate (Dimension L)can be square or rectangulardepending on movementsin co-ordinate directions.Ordering Example: Eslb 03 & 04 - bonded virgin/glass-filled ptfe slide bearing - for boltingTop plate (Dimension L)can be square or rectangulardepending on movementsin co-ordinate directions.Ordering Example: E4
slb 05 & 06 - recessed virgin/glass-filled ptfe slide bearing - for weldingTop plate (Dimension L)can be square or rectangulardepending on movementsin co-ordinate directions.Ordering Example: Eslb 07 & 08 - recessed virgin/glass-filled ptfe slide bearing - for boltingTop plate (Dimension L)can be square or rectangulardepending on movementsin co-ordinate directions.Ordering Example: E5
slide bearingsslb 09 - recessed graphite slide bearing - for weldingTop plate (Dimension L)can be square or rectangulardepending on movementsin co-ordinate directions.Ordering Example: SLB09-4(AxC)*500 C when using alloy orstainless steel backing plate.slb 10 - recessed graphite slide bearing - for boltingTop plate (Dimension L)can be square or rectangulardepending on movementsin co-ordinate directions.Ordering Example: SLB10-4(AxC)*500 C when using alloy orstainless steel backing plate.6
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Carpenter & Paterson (Asia) LtdBangkok Free Trade Zone88/91 Moo 15Tambol Bangsaothong,Amphoe Bangsaothong,Samuthprakarn Province, 10570ThailandTel: 66 (0)21825204-5Fax: 66 (0)21825206Email: [email protected] Manufacturing Locations:· Thailand - Carpenter & Paterson (Asia) Ltd· UK- Carpenter & Paterson Limited· India- Carpenter & Paterson India PVT Ltd
PTFE bearings are the least expensive type of slide bearing. They can be used up to a maximum temperature at the sliding face of 130 C. SLB05 to SLB08 (page 5) use 5mm thick PTFE bonded to a recessed backing plate. The recessed design allows use up to 200 C at the sliding face and increased bearing pressure. The thicker PTFE
