INSOCOAT - Bartlett Bearing

1 INSOCOAT electricallyinsulatedrollingbearings2 INSOCOAT the SKF solution to prolong Bearing life in electricmachineryWhat are INSOCOAT bearings?SKF provides electrically insulatedbearings, called INSOCOAT , to protectagainst damages caused by electriccurrents. These bearings have anelectrically insulating coating on theouter ring or on the inner ring. On theouter ring (VL0241 execution) the coating can be applied to diametersabove and including 80 mm. Inner ringcoatings (VL2071 execution) can beapplied to bore diameters above andincluding 70 mm. For smaller bearingdimensions we recommend SKFhybrid bearings. The coating consists of a nominal 100 m thick aluminium oxide layerand is applied by a unique coatingprocess using plasma-spraying bearings with outer ring coating VL0241 executionIndustrial motors3 Traction motorsGeneratorsCustomer value INSOCOAT bearings provide two features in one solution: a Bearing function; electrical insulation. reduce the number of failures andimprove the machine uptime.

2 Reduce maintenance costs. are the most economical solution incomparison with other insulatingsolutions. have global availability thanks toSKF presence in more than 130countries and at 7 000 distributionlocations bearings provide the most economical solution in comparison withother insulating methodsINSOCOAT HousingShaftbearinginsulationinsulationI NSOCOAT bearingHousing insulationincluding Bearing Shaft insulationincluding Bearing Total cost4 Technical benefits The standard 100 m layer thick-ness prevents most current passageproblems. SKF performs 100 % testing up to1 000 V DC. Lab tests show that electrical breakdown occurs above 3 000 V DC. INSOCOAT bearings provide a minimum ohmic resistance of 50 M at 1 000 V DC. The application process using plasma spraying technique in com-bination with sophisticated pre- andafter preparation of the Bearing ringsgives an outstanding coating quality. INSOCOAT bearings are treated witha unique sealant ensuring insulationin humid environments.

3 It is alsoinsensitive to heat and chemicals. INSOCOAT bearings provide a betterelectrical and mechanical perform-ance than other insulation methods. SKF can supply values for relevantelectric parameters for the Bearing (capacitance, impedance). Additional benefits Simple mounting and bearings should behandled with the same care asstandard bearings. Fits up to and including p6 and P6respectively can be applied for bothcoating variants (VL2071 andVL0241). INSOCOAT Bearing with inner ring coating VL2071 executionPlasma spraying process and equipmentThe inner ring coating provides anenhanced protection of the bearingagainst electric current damages. The most important feature is theimproved insulation properties thanksto a smaller coated surface. Standard boundary dimensionsaccording to ISO 15:1998. Environmentally friendly INSOCOAT bearings are suitable forall types of housings. SKF has experience with ceramiccoatings since more than 20 years. 510-100,0050,010,0150,020,0250,0310-100, 0050,010,0150,020,0250,0310-100,0050,010 ,0150,020,0250,0310-100,0050,010,0150,02 0,0250,03Vu (Udc)Vcommon (Udc)Vv (Udc)Vw (Udc)time (s)1 FigThe three phases and their sum common mode voltageThe coating process plasma spraying technologyThis unique technology has the follow-ing benefits: Plasma spraying is the most versatilethermal coating process it pro-duces high-performance coatingsthat deliver durability and reliability.

4 The process applies coatings by injecting aluminum oxide powder intoa high temperature gas stream. Theplasma gas heats the powderedcoat-ing material to a molten state andsprays it onto substrates at highspeeds. Plasma spraying is extremely flexibleand is ideal for producing a widevariety of functional can find the living assortment forelectrical machinery applications in theenclosed assortment you cannot find the item that youneed in the standard range, pleasecontact your local SKF and sealsShields and seals are available onrequest for some bearings is important to ensure proper lubrica-tion by frequent regreasing. Sources of electric currentThe problem of electric current pass-ing through rolling bearings and caus-ing damage in the contact area ofballs or rollers and raceways of innerand outer rings has been known foralmost 70 years. In addition to thedamage to Bearing elements, it wasalso supposed that the structure of thelubricant itself might change under theinfluence of a current passage.

5 Allrotating machines, both AC and DCmotors as well as generators, poten-tially suffer from this failuresWith sinusoidal line voltages, the bear-ing current is generated due to asym-metries in the motor s magnetic asymmetric flux distribution insidethe motor induces an axial shaft volt-age, which further leads to a low-frequency circulating current flowingthrough the bearings. Bearing currentis also generated by asymmetric, non-shielded motor cabling. These clas-sical Bearing currents are a problemespecially for large motors with lownumbers of pole pairs ( 2-polemotors). They have larger flux asym-metries than small motors or motorswith many frequency currentsApart from the classic voltages andcurrents generated by the motor itself,new effects have been observed whenthe motor is supplied from a pulsewidth modulation (PWM) converter(frequencies of 3 to 16 kHz). It hasbeen discovered that the bearingdamages are caused by a high fre-quency (several kHz MHz range)current flow.

6 The current originatesfrom the so-called common mode voltage of the frequency origin of current is the highswitching speed of the integrated gatebipolar transistors (IGBTs) used insidethe arise because of threetypes of currents: High frequency shaft grounding currents High frequency circulating currents Capacitive discharge currentsThe reason for the first two types ofcurrents is the common mode voltageat the converter output. The commonmode voltage is produced due to thefact that the sum of the three phasevoltages is not equal to zero ( fig ).Furthermore, the frequency convertertries to simulate a sine wave supply byPWM signals, which have a high switch-ing frequency and very steepedgedpulses, which cause capacitive dis-charge of electric current going throughthe bearingDue to the passage of electric currentin the contact zone of rolling elementsand raceways heat is generated caus-ing local melting of the Bearing metalsurface. Craters are formed in thecontact area and particles of moltenmaterial are transferred and partlybreak loose.

7 The crater material is re-hardened and much more brittlethan the original Bearing the re-hardened layer there is a layer of annealed material, which issofter than the surrounding frequency converters aremore and more used micro-crateringis by far the most common effect ofelectric current passage. The damagedsurface appears dull, characterised bymolten pit marks ( fig ). Multiplemicro-craters cover the rolling elementand raceway surfaces. Crater sizesare small, mostly from 5 to 8 m indiameter, disregarding whether it is onthe inner ring, outer ring or a rollingelement. The real shape of these craters can only be seen under amicroscope in very high or washboardThey are patterns of multiple greylines across the raceways ( fig ).They appear shiny and molten. Thereason for this fluting is a mechanicalresonance vibration caused by thedynamic effect of the rolling elementswhen they are over-rolling smaller craters. This means that fluting is not aprimary failure mode produced by thecurrent flow through the Bearing is a secondary Bearing damage thatbecomes visible only after time andhas its initial point from discharges also cause thelubricant in the Bearing to change itscomposition and degrade local high temperature causesadditives and the base oil to react, andit can cause burning or charring of thebase oil.

8 Additives will be used upmore quickly. Thus the lubricant getsBlack discolouredgrease affected by currentdischargesFluting or wash-board in racewayThe dull surfaceof the ball is asign of micro-crateringalmost hard and blackened ( fig ).A rapid breakdown of the grease is atypical failure mode that results fromcurrent behaviour ofINSOCOAT bearingsOne has to distinguish between DCcurrent and AC current DC applications the insulating coat-ing acts as a pure resistor where theohmic resistance R of the aluminiumoxide layer is the important breakdown voltage of the stand-ard layer is larger than 1 000 V DCand the resistance is larger than 50 M , which provides efficient insulation of the AC applications, especially invariable speed drives (VSDs) one hasto consider the impedance of the cer-amiccoating. The impedance describesthe voltage-current relationship in ACcircuits. The value of the impedancedepends mainly on two electrical char-acteristics of the coating: the ohmicresistance and the capacitance.

9 Thecapacitance should be as small aspossible to counteract the effects ofhigh frequency electric impedance of the aluminiumoxide coating can be modelled as aparallel connection of a resistor and a and capacitanceFig shows a typical graph of theimpedance of a coated deep groove ballbearing (outer ring coating). Fig shows a typical graph of the capaci-tance of a coated deep groove ballbearing (outer ring coating).76 DCACD escription of voltage-Resistance RImpedance Zcurrent relationshipElectrical behaviourResistorResistor and capacitor in parallelUnitOhm [ ]Ohm [ ], Farad [F]DC ResistanceGuaranteed more than 50 M AC Impedance The value depends on the bearingsize and the frequencyAC CapacitanceConstant over the frequency range; the absolute value isdepending on the Bearing sizeElectrical behaviour of INSOCOAT bearings in DC and AC applications100 1000 10000 100000 1000000 0,01 0,1 1 10 100 1000 6316 VL0241 100 1000 10000 100000 1000000 6,6 6,8 7 7,2 7,4 6316 VL0241 Measured impedance as a function of frequencyMeasured capacitance asa function offrequency6 Fig7 FigFrequency [Hz]Frequency [Hz]Impedance [k ]Capacitance [nF]

10 5 Fig8 SKF has a range of specific bearinggreases to meet allapplication needsFor this reason SKF, the leader notonly in Bearing design and manufactur-ing but in global service, and the SKFdistributors offer customers the mostcomprehensive range of tools to ensure optimal Bearing heaters and mountingtools to preserve the quality, pullers for easy removal, equipment and soft-ware for the condition monitoring ofbearings and addition, a wide range of greasesof the highest quality for Bearing lubri-cation, consistent in quality, for gen-eral and specific requirements, avail-able worldwide through the SKF distri-bution bearings add value to yourmachine, our tools make your lifeeasy, our distribution network, provid-ing replacement Bearing , tools andgreases ensures the commitment ofSKF to your products should run faultlessly. At least foras long as planned preferably even longer. Toensure this, there are three basic requirements: Use the right bearings. Preferably from SKF.