Feature Seals & bearings Ensuring you don’t lose your bearings
Bob Orme of Henkel, manufacturer of Loctite brand products, reveals the benefits of retaining adhesives when it comes to securing bearings
joint. Small micro-movements at the joint interface can produce abrasive particles which increase the wear on the surface that, in turn reduces fur- ther the metal to metal contact. Such wear creates even additional micro- movement. The outcome is fretting corrosion, resulting in the strong like- lihood of failure.
expense of quality. When it comes to the use of bearings, one option that often results in reduced costs, while maintaining (or improving) quality, involves the incorporation of engineer- ing adhesives for both original design and maintenance applications. When engineering adhesives are employed in cylindrical assemblies to bond one part that is inserted into another, for example, bearings mounted in electric motor housings, they are referred to as ‘retaining adhesives’ or ‘retainers’. First used in the early 1960s, these adhesives have successfully pro- vided manufacturing solutions and assisted in the salvage (rather than the scrapping) of worn housings.
R Anaerobic advantage
The technology behind these is known as anaerobic. That means they cure in the absence of air when in contact with metal surfaces. These adhesives are applied as a liquid that covers the area of the components and fills all the surface irregularities, however minute they might be. As the surfaces are brought together and the air is excluded, the adhesive begins to harden to form a tough plastic. This action both securely bonds the parts and, because the adhesive provides 100 per cent contact over the entire surface, prevents any moisture from entering the joint.
Preventing fretting and wear Retaining bearings through the use of anaerobic adhesives means the elimi- nation of fretting, an increase in joint strength and a reduction of worn parts. It may come as a surprise to some, that where a bearing is secured by a press fit, the actual metal to metal con- tact area accounts for only around 30 to 40 per cent of the total surface of the
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educing costs is essential to every company. But just as important is the reality that making such economies cannot be at the
No matter what size the bearing,
retaining adhesives provide a secure joint that is sealed against the ingress of moisture
Bearings are likely to spin either on their shafts or within housings, action that inevitably results in damage, regardless of the type of fit that is being employed. Adhesives can help to eliminate bearing spinout, thus pre- venting component damage, by filling all surface irregularities. In this way, movement is prevented, thus com- pletely eliminating fretting, while cre- ating a fully sealed joint.
Beyond that, tests have shown that the axial strength of an interference fit
A retaining adhesive is applied to the outside of a bearing
The utilisation of a retaining com- pound often avoids unnecessary machining and allows the parts to get back into service very quickly. In another instance, a manufacturer of motorised pedestrian operated tugs, employs a retaining adhesive to secure
‘Adhesives can help to eliminate bearing spinout, thus preventing component damage, by filling all surface irregularities’
component can be increased by a factor of up to three by introducing an adhesive to the joint.
Practical examples
A retaining grade adhesive is
employed to secure bearings into the housing holding the handle of a motorised
pedestrian operated forklift truck
Of course, the proof of the value of retaining adhesives is in their use and success. Newark Electric Motors has been supplying, maintaining and repair- ing various kinds of electric motors, gearboxes and pumps for nearly 20 years. Its engineers use Loctite 641 Retaining Compound for bearing reten- tion and for securing sleeves to end caps. In many cases, without the use of a retaining adhesive, repairs would require machining and sleeving with a heavy interference fit, even when there was just a small amount of wear.
bearings into the housing holding the unit’s handle. This housing is welded to the tug’s frame, an operation that inevitably produces some distortion to the metal. Consequently, the inside of the housing needs to be die-ground out in order to accept the bearing. During this die-grinding procedure, just enough metal is removed to enable the bearing to be inserted, even if this results in a varying gap size between the surfaces. The retaining adhesive is applied to the outside of the bearing, which is then inserted into the hous- ing. Any gaps between the bearing and the housing wall are immediately filled by the adhesive, which readily cures between the metal-to-metal surfaces.
Helpful advice
For specific advice about retaining adhesives and how they can benefit particular applications, the first action is a call to the helpdesk of a reputable adhesives manufacturer. By providing the helpdesk with the known factors of a specific bearing application, the rec- ommended adhesive and assembly method can be readily determined. The advice is there, just for the asking. Henkel T: 01442 278100
www.loctite.co.uk
Enter 330 MARCH 2011 Factory Equipment
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