10 BRAMMER Handle with care


Best practice in the mounting, handling and checking the operational functionality of newly mounted rolling bearings are discussed by Malcolm Watson of Brammer and Tony Synnott of NSK


W


hen handling, checking and mounting a bearing,


it is important to take care and consideration to ensure the product’s longevity and effectiveness. If bearings are not handled correctly, they can be prone to failing quickly and unexpectedly, but some basic checks will help avoid some of the common problems associated with their handling and usage.


General tips on handling Since rolling bearings are high- precision machine parts, they must be handled carefully. Even high-quality bearings will not deliver the desired service life and performance quality if they are not handled used and maintained correctly. The observation of a few basic


precautions will help prevent the possibility of premature failure. Firstly, the bearing and its surroundings must be kept clean. The presence of any dust and dirt – even particles not visible to the human eye – is one of the key causes of bearing failure. Bearings must also be protected


from corrosion. Perspiration on an operator’s hands and a variety of other contaminants may cause corrosion, so hands should be clean and dry before handling bearings, with gloves worn if possible. Care should also be taken when handling the bearing itself. Heavy shocks may scratch or cause other damage to the bearing, while physical impact may result in


November 2013


brinelling, breaking or cracking. Proper tools should always be used for any work involving bearings – general purpose tools should be avoided. The manufacturer’s instructions are generally the best place to start for a guide on this.


Mounting The mounting process is absolutely key to the bearing’s running accuracy, life and performance, therefore the manufacturer’s mounting instructions should be followed precisely. Failure to do so could result not just in premature failure but in damage to other components, unscheduled downtime and invalidation of the product warranty. In the first instance, the bearing and any surrounding components should be thoroughly cleaned and dried, with the dimensions and finish conditions of related parts then checked. The mounting procedure should


then be followed. Since most bearings rotate with the shaft, the bearing mounting method is generally an interference (tight) fit for the inner ring and shaft, with a clearance (loose) fit for the outer ring and housing. The correct type and quantity of lubricant should be applied. After mounting the bearing, an


operating test should be undertaken to verify that the mounting has been carried out correctly.


Checks and common faults On small machines operated manually, the bearing should be


turned by hand. Checks should be made for stick-slip – these will be manifested in the form of debris, cracks and dents; uneven rotating torque, which generally indicates faulty mounting; and excessive torque, which again shows either a mounting error or insufficient radial internal clearance. Once these checks are complete,


the machine should be turned on and operated at a low speed without a load, gradually increasing the speed and load till the typical rating is reached. Checks should be made at this


stage for irregular noise, bearing temperature rise, lubricant leakage and lubricant discoloration. Several types of noise may be


heard. A loud metallic sound can be caused by an abnormal load, incorrect mounting, insufficient or incorrect lubricant, or contact with rotating parts. A loud regular sound can be the result brinelling or flaws, corrosion, scratches or flaking on the raceways. Meanwhile, an irregular sound will be heard in the event of excessive clearance, penetration of foreign particles, or flaws or flaking on balls. An abnormal temperature rise is


frequently the result of lubrication issues – either too much or too little, or the wrong type. However, it can also be caused


by an abnormal load, incorrect mounting, ‘creep’ on the fitted surface, or excessive seal friction. Brinelling, flaking, incorrect mounting and foreign particle penetration can all contribute to excessive vibration or axial runout. Lubricant leakage or discoloration


is usually the result of overzealous application, or the ingress of foreign matter or abrasion chips. In the event of any of these occurring, the appropriate remedial action should be taken immediately. Failure to do so will almost inevitably result in failure of the bearing, with the likelihood of associated damage to other components. Once the bearing has passed all these checks and is fully operational, it is good practice to check the bearings on a regular basis with the aim of identifying any damaged or failing components as early as possible. More information from Brammer


UK Ltd, Claverton Court, Claverton Road, Wythenshawe, Manchester M23 9NE, United Kingdom. Tel: 44 844 736 3665. www.brammer.co.uk


Brammer at a glance Brammer UK is part of Europe’s leading distributor of industrial, maintenance, repair and overhaul products and services, with an extensive product range covering bearings, mechanical power transmission products (including gearboxes and motors), pneumatics, hydraulics, seals and industrial automation. The company is an authorised distributor for brands including SKF, NSK, Renold, Parker, Siemens, Flender, SMC, Norgren, Festo, Rocol, 3M, Loctite and Schaeffler UK.


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