Sticking with adhesives
May 1st 2006

Engineering adhesives are gaining more converts among maintenance people. Colin Chapman of Henkel, makers of Loctite brand adhesives, explains why - and gives some impressive examples

Every maintenance engineer knows that if something is going to go wrong, it will happen at the most inconvenient moment. Even in the bestrun plant, problems do occur from time to time. Something breaks, a part begins to slip or perhaps a pipe joint starts leaking.

Under those circumstances, maintenance engineers are increasingly turning to their tool kits and reaching for adhesives to get them out of trouble - not just temporarily, but on a permanent basis.

But engineering adhesives are not just viewed as items to be used in an emergency. Increasingly, they are being used as part of regular maintenance programmes to ensure parts work properly - and continuously, even under the most demanding of conditions.

Take, for example, an application where a cylindrical component is being worn away by continual fretting. With purely mechanical methods, remachining would be necessary to restore the part to a useable condition. However, by using adhesives to hold the parts together, the task of remachining is no longer necessary.

Furthermore, because they create a total seal between mating surfaces, they provide an automatic protection against corrosion caused by environmental considerations.

Wrapping up a problem quickly

A company that makes transparent wrapping film has good reason to be grateful to see its engineers using an engineering adhesive. In order to meet its commitments, this manufacturer operates a non-stop process with production lines running for 24 hours a day, seven days a week. And that means any problems that crop up have to be fixed quickly.

One such difficulty involved core rollers on the huge manufacturing line. These rollers are hollow aluminium tubes around which is wound a clear polypropylene packaging film. A steel sleeve is held in the 250mm diameter tube by means of locking screws - and it was this interface between the two metal surfaces that was causing the problems.

The rotational loads of the rollers caused the softer aluminium component to stretch.

Consequently, the holes for the locking screws were gradually being elongated. The result of this elongation process was that the steel sleeves became loose. Not only that, a backlash of 25mm occurred when the roller took up the drive on the reel machine.

At first sight, it looked like the damaged core rollers would have to be removed from the machine and sent away as scrap.

Installing new rollers would solve the problem in the short term, but then the same difficulty was likely to reoccur at some time in the future. Clearly, another solution had to be found.

Maintenance engineers at the plant decided to experiment with an anaerobic retaining adhesive. An anaerobic adhesive is one that is applied as a liquid, but then hardens when the two mating surfaces are brought together. Being in a liquid state initially means that all the minute spaces between the surfaces can be filled, ensuring 100% contact and, therefore, increased strength. Within a short time, the assembly is unitised and becomes shock, vibration, corrosion and leak-proof.

Before trying the retainer - in this case Loctite 638 - on a live application, the company asked a nearby technical college to carry out some strength tests on the adhesive.

Those tests revealed that a maximum press load of 50 tonnes couldn't overcome the strength of the adhesive on a 120mm diameter mild steel trunnion with a 0.075mm diametrical clearance. Having seen those results, the engineers felt confident enough to try the adhesive on a core roller.

The adhesive was more than a match for the forces at work on the rollers and no further slippage occurred. The backlash and looseness of the rollers became things of the past. But there were other benefits, too. For instance, the fitters had no need to drill and tap the assembled rollers in order to accommodate the locking screws.

Not only was the problem solved, but there were time and cost savings, too. From that application, the company has moved on to using engineering adhesives in many other areas of its plant.

A choice of adhesives

Those applications involve retaining adhesives. But the same anaerobic principle is used for threadlocking, threadsealing and gasketing applications.

In many cases, using an adhesive has proved quicker and easier than other methods. In addition, one tube or bottle of adhesive can replace a whole range of different sized nuts, gaskets and seals - so there is cost saving, too.

But now, alongside those tubes and bottles, there is another adhesive 'solution' in the maintenance engineer's armoury.

Based on the glue stick principle that has long been available for domestic applications, these semi-solid adhesives have the same high qualities as their traditional counterparts. It is simply a case of twisting the base of the container - and the adhesive appears at the other end ready for applying.

They are small enough to carry in the pocket - or take up very little room in a tool box. The semi-solid formula means that, for example, adhesive can be applied before a maintenance engineer climbs a ladder to carry out a repair job. The adhesive will not drip before the joint is mated - and it means a high level of safety for the engineer who does not have to carry a tube or a bottle to the application.

Sticks are available as threadlockers, retainers, threadsealers and for gasketing and anti-seize applications - and they can be used in just about every situation in which traditional adhesives are already a tried and tested maintenance solution.

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