Slide bearings - Wolf Kunststoff-Gleitlager GmbH

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CC CC CCCorrelations on slide bearing operation11. Correlations on slide bearing operationPrefaceThe following illustration shows the courses and the direct and indirect correlations (influences) on slidebearing operation represented by arrows.chemicals * 8radial forceexerted onthe slidebearingcontact zone betweenscrew and slide bearing * 1screwspeedambienttemperatureContentsMaterialoverviewsurfacepressureslidingspeedµ* 2elastic modulus of theslide bearing materialinducted* 3 amount ofheat* 4change in screwtemperaturechange in outside screwdiameterchange in operationbearing clearance * 7wear factor * 6Ill. 19 : Correlations on slide bearing operationAbbreviations:change in slidebearingtemperaturechange incasingtemperature * 5stressdurationroughnessof the screwchange in inside slidebearing diameterchange in inside casingdiameterslidingdistancemedium betweenscrew and slidebearing*1: contact zone between screw and slide bearingdependent on the radial force, the operation bearing clearance and the elastic modulusof the slide bearing material, because e.g. a low elastic modulus causes a deeper subsidingof the screw into the slide bearing and therefore an increase of the contact zone.*2: coefficient of friction of the system screw- intermedium-slide bearing dependent on:- the surface pressure:the coefficient of friction of most polymers decreases with increasing surface pressure (see ill. 41)- the sliding speed:the coefficient of friction µ statof most polymers is bigger than the coefficient of friction µ dyn.The dynamic coefficient of friction of anti-adhesive polymers (PTFE) is directly in proportion to thesliding speed. This influence of the sliding speed on the dynamic coefficient of friction can beignored with most polymers.Wolf Kunststoff-Gleitlager GmbH • Heisenbergstr. 63 - 65 • 50169 Kerpen-Türnich • Tel. 02237/9749-0 • Fax. 02237/9749-20Index Slide bearings Slide bearings Conditions ofTribologyMathematical Design(with collar) (cylindrical) installationexample guidelines26
CCCCCC- the temperature of the sliding surface:the coefficient of friction of most polymers increases with increasing temperature.the coefficient of friction of some materials e.g. ZX-324VMT decreases with increasing temperature(see ill. 64).- the roughness of the screw:for some polymers correlations with the roughness have been ascertained, so that those polymersshow an optimum roughness zone.- the intermedium:depending on the intermedium the sliding partners become more or less separated.in case of hydrodynamics (e.g. due to highly viscous chemicals) the sliding partners becomecompletely separated and there is pure liquid friction. Whereas lower viscous chemicals (e.g. water)often cause mixing friction, so that hydrodynamic conditions can hardly be achieved.- the sliding distance:the dynamic coefficient of friction of almost every polymer decreases with increasing sliding distancewhich is due to the smoothing (see chapter 6.2).Whereas the static coefficient of friction increases with increasing sliding distance, because theadhesive friction is also increased due to the steadily increasing contact zone.*3: Elastic modulus of the slide bearing material:is for all polymers dependent on the temperature.Owing to the fact that polymers have viscoelastic properties, the elastic modulus depends also on thetime which is called creep behaviour (see ill. 33-35).Moreover, chemicals affecting the polymer also have on influence on the elastic modulus.*4: Inducted amount of heat to the systemis composed of the friction heat (drive energy converted due to internal and external friction of the slidebearing), the surrounding heat and eventually further side sources of heat (gear wheels, motors, ...)*5:Change in slide bearing temperaturethe temperature changes of the screw, the slide bearing and the slide bearing casing are dependent onthe friction power Q introduced and the amount of heat which is carried off over the screw and the casing.Initially the heat is carried off only over the screw for the plastic slide bearing works as insulator.This process creates the so-called flash temperature (see ill.114, page 73). With increasing time ofoperation this temperature decreases to the operating temperature (caused by the temporally belatedadditional heat flow running over the slide bearing and the casing). The bigger the sliding speed the biggerthe difference between flash temperature and operating temperature; therefore fast-running slidebearings quickly achieve dangerously high flash temperatures. Which contents of thermal energy arecarried off over the screw or the casing on steady operation (when achieving the operating temperature)depend on the construction of the screw, the casing and the slide bearing (e.g. screw length, screwdiameter, bushing width, wall thickness of the bushing, outside diameter of the slide bearing casing) andon the fact that the slide bearing casing is standing and the screw is rotating or vice versa (see chapter5.1.1.3).*6: The wear factor of the slide bearing material is dependent on:- the sliding distance- the surface pressure (see ill. 32)- the temperature (see ill. 31)- the roughness (see ill. 30)- the intermedium (dry run, solid friction, mixing friction, hydrodynamic lubrication)*7: The change in operation bearing clearance depends on:dimensional changes (thermal expansions), caused by changes in temperature of the screw, the casingand the slide bearing. Furthermore, the change in operating bearing clearance of hygroscopic polymersdepends on the moisture content of the polymer (e.g. polyamide). This influence can be ignored with allZEDEX-materials owing to their low water absorption (see table 2, page 10 “water absorption”)*8: Influence of eventually extant chemicals:(or hot water) which can be affect the polmersCorrelations on slide bearing operationPrefaceContentsMaterialoverviewIndex Slide bearings Slide bearings Conditions ofTribologyMathematical Design(with collar) (cylindrical) installationexample guidelinesWolf Kunststoff-Gleitlager GmbH • Heisenbergstr. 63 - 65 • 50169 Kerpen-Türnich • Tel. 02237/9749-0 • Fax. 02237/9749-2027
Page 3 and 4: CCCCCCContents9.Damping ...........
Page 5 and 6: CC CC CCZX-100Astandard material2.
Page 7 and 8: CC CC CCZX-530bearing materialZX-55
Page 9 and 10: CC CC CC2. Material overviewstrengt
Page 11 and 12: CC CC CC3.Slide bearingsSlide beari
Page 13 and 14: CCCCCCAttachment when operating on
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Page 25: CCCCCC9.DampingThe ZEDEX-materials
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Page 33 and 34: CCCCCCpv-value pv [N/mm2nom• m/mi
Page 35 and 36: CCCCCC12.2.1.2.3.Correction factor
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Page 51 and 52: CC CC CC13.5.14. Data for the order
Page 53 and 54: CCCCcoefficient or fr ictioncoeffic
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Page 65 and 66: CCcoefficient of fric tionCCcoeffic
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Page 70 and 71: CCdeformation [%]CCCC10,02m m plast
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CCCC20.Dimension list of bushings f
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CCCCCC21. Dimension list of bushing
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CCCCCCCCCC22. Indexcorrection facto
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CCCCSCCCCCC22. Indexscrew .........
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Slide bearings - Wolf Kunststoff-Gleitlager GmbH

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