Accurate dispensing

A patented two-component reactive adhesive dispensing system has been developed that, through an entirely new principle of electro-mechanical liquid metering, is capable of dispensing to an accuracy of two decimal places.

A patented two-component reactive adhesive dispensing system has been developed that, through an entirely new principle of electro-mechanical liquid metering, is capable of dispensing to an accuracy of two decimal places.

This technology, the subject of a UK Government Smart Award, has been developed by Kettering-based Failsafe Metering International.

In operation, it makes use of an important fundamental property of liquids under pressure, in this case, the reactive liquids in a two-part adhesive system. When subjected to high pressure, both liquids become hydraulic and exhibit a maximum density per unit volume. While in this compressed state, each liquid stream is divided uniformly into precise volumetric shots or dots at a pre-specified relative ratio (usually from 1:1 to 10:1). Each one is then electronically checked for accuracy and, if okay, fired forward at high rates to form mixed liquid shots or flow.

This is where the biggest distinction lies between this and a conventional two-part metering and mixing system. In most processes, an occasional manual weight check of the two outputs, prior to the mixer, is the only way to check for the required ratio. For example, with conventional machines, if a two-part resin system is used in the manufacture of a car, the current way to check for the correct ratio content of the two-part adhesive is by taking representative unmixed samples, at intervals, from that specific application.

However, any ratio test results generated would only be relevant to that specific ‘off line’ adhesive ratio check and would not be representative of the production output.

By using the Failsafe Metering system, all the adhesive is checked, dot by dot, for ratio just before it is mixed and applied. For these reasons, this process is already being successfully applied to vehicle component bonding and in several different kinds of automotive sealing systems.

The qualification of this new metering process is based on the receipt of an individual electronic signal that is generated when each metered dot is verified for its correct volume. The dots are produced at high speeds and the signals generated are sent to a PLC which will shut down the system immediately should one single dot metering not occur, preventing any errors from reaching the point of adhesive application.

For example, if you require a ratio of 10:1 and the metered output is at 9.99:1, the dispensing process is halted.

Once checked as okay, the correct adhesive liquid components are pumped through to a ‘static’ mixer, which dispenses the adhesive smoothly and uniformly onto the product. There is no possibility for a ratio error whatsoever because it is checked before it leaves the metering system. In a conventional meter-mix-dispense system, the final adhesive quality remains unknown. This new principle of guaranteed metering is also being applied to the robotic application of single-component adhesives because it is equally important that their presence and volume per product is guaranteed.

Laurence Penn, managing director of Failsafe Metering, had the idea for this new system while toying with a replica revolver. One evening, as he spun the barrel of the gun, it occurred to him that, instead of sending a constant flow of liquid through the ‘barrel’ of a mixing system, he could ‘machine gun’ the liquid through. The result would be the joining together of a series of discrete high accuracy ‘dots’, each of which could be independently measured and verified with regard to their volumetric accuracy.

‘Using conventional metering methods it is perfectly possible for a product to make it all the way down the production line with no adhesive on it at all. It could be, literally, only held together by its component parts,’ explained Penn.

‘This would not be possible with our system. When companies come to us, talking about quality assurance standards such as ‘Six Sigma’ and asking for failure rates of no more than 3.4 defect parts per million, I ask ‘why such a high failure rate?’ With Failsafe Metering there need not be any failures.’