Gearing up to prevent costly failures
November 1st 2007

Colin Chapman of Henkel, maker of Loctite brand products, provides helpful assistance to the professionals who service industrial gearboxes and who look for reliability, longevity and cost reduction

For those involved in running plant, the ultimate goal is to maximise machinery output, reliability and efficiency. And for that reason, a gearbox failure can be a costly setback to overall plant operations.

To prevent problems, a programme of proactive maintenance can minimise expensive downtime, enhance reliability and, in the log run, dramatically cut costs.

However, problems may still occur, and when they do, there is a requirement for speedy remedial action. But spare parts may not always be readily available. There is, though, a speedy and reliable method of repair using adhesive based products.

Retaining the best performance

Wear on gearbox parts can be reduced by the use of a number of readily available products. Take bearing spin, for example.

For gaps up to 0.05 mm, an oil tolerant, high strength retaining compound is the best. After using a cleaner and degreaser, a bead of the adhesive should be applied to the circumference of the shaft. The bearing is then mounted on to the shaft using normal techniques. Excess adhesive can then be wiped off (it will not have hardened while exposed to air) and the joint left to cure for about six hours.

The use of retainers during routine servicing also means that keyways can be prevented from experiencing undue wear.

Sorting the seals

As with any press fit, there are small air spaces between the housing and the oil seal – and these gaps have the potential to create a leak path.

For oil seals with elastomer press fit a toughened instant adhesive should be used during assembly. This is applied to the outside diameter of the oil seal. In the case of a cassette seal, the inside diameter to the shaft should also be bonded – using the same instant adhesive.

Where the oil seal includes a metallic clamping part, applying a medium strength threadlocker to the outside diameter of the seal can fill those potential leak paths.

Even with those benefits, the oil seal can still be easily removed with a screwdriver during the next overhaul.

Combating corrosion

Threadlockers can also be used to prevent loosening and corrosion of split gearbox housing fasteners and alignment dowels.

These fasteners can work loose when subjected to torque, vibration, thermal expansion and shock loads. And once the fasteners become loose, the preload for the gasket will be lost and it will fail. In addition, dowel pins can rust and seize into component, making disassembly very difficult.

The steps are simple: After cleaning and degreasing the threads and dowels, a heavy duty anti-seize product can be applied to the dowel. Then a medium strength threadlocking adhesive can be introduced into the lower third of the blind hole. (Where stainless steel fasteners are in use, a high strength adhesive is recommended.) The parts are then assembled and tightened. It really is that easy. And with these problems overcome, the reliability of the gasket between the upper housing and the base is ensured.

Losing the leaks

Traditional thread sealants, such as tape and pastes, are a susceptible to weeping – and the constant pressure and temperature changes that occur within a gearbox system can result in leakage.

Further, vibration between the gearbox and lubrication/cooling system leads to stress on the pipe work – another cause of leaks.

Again, though, anaerobic adhesives, this time in the form of threadsealants, will come to the rescue. When cured, Loctite Threadsealants are resistant to oil and water/glycol and ensure zero leakage.

Furthermore, threadsealants prevent fittings from loosening, yet allow easy disassembly with normal hand tools.

Leaks can also occur where flange surfaces are damaged or where there is improper sealing of T-joints where the upper and lower housings and the cover meet.

In these circumstances, an anaerobic flange sealant provides the solution. First, the old sealing material can be removed by a proprietary gasket remover. Then, after cleaning the surfaces, the adhesive is applied and the parts reassembled. Being anaerobic, the product will not start to cure until the air has been removed from the joint through the action of bringing together the mating parts.

Not only is the joint successfully sealed against leaks, but also the adhesive creates high shear strength that transmits forces from one part to the other.

Adhesive has the answers

As has been shown, the use of engineering adhesives helps prevent those expensive breakdowns and ensures that machinery keeps going and keeps going with the maximum effectiveness. At Henkel we've identified dozens of applications where adhesives provide the answers to gearbox problems.

Like other adhesive suppliers, we have a help desk that is manned by experts who can talk through your gearbox difficulties and offer solutions that will enable the maximum use of industrial plant through the reduction in downtime. All engineers have to do is ask.

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