Dispensing solutions
May 1st 2009

When it comes to dispensing adhesives or sealants in high volume situations, automated application units can boost efficiency and cut costs. Steve Ginger of Henkel,maker of Loctite brand equipment, comments

Cost savings of up to 50% – compared to manual application methods – can be achieved through reductions in product use.Moreover, automated equipment permits an adhesive or sealant to be dispensed at speeds and with precision that is impossible with manual methods. Even when a complex dispense pattern is involved, the operation takes just seconds.Application equipment gives a safer and cleaner working environment and, as operator contact with the product is eliminated, there is less chance of accidental misuse.

Important questions The choice of equipment will depend on answers to some specific questions:What type of adhesive will be used? What is the size and shape of the component(s)? How do parts travel along the assembly line? What is the production rate? At what point is the product applied? What is the time period between adhesive application and the handling of bonded components?

Equipment range The most basic dispensing equipment is a simple hand operated gun attached to standard product packs. At the other end of the scale are automated machines – for which two options exist, line-side machines and in-line systems. Lineside machines are standalone units positioned next to production lines. An operator loads components into the machine that will apply the adhesive or sealant. The component is then manually assembled to the mating part.

Where components are too heavy or cumbersome to be loaded easily on to a lineside machine, a dispensing unit may be mounted over the production line – in effect becoming part of the assembly process. The component stops at the robot station to allow adhesive or sealant to be applied directly to the part's surface. Components can then be assembled at the next available workstation.

There are pros and cons to both versions.

Line-Side – Pros: Lower cost, machine can be built remotely then installed during a planned shut-down. Cons: Operator must load component, potential for damaging bead during manual handling.

In-Line – Pros:Minimal operator involvement, beneficial where component requires subsequent manipulation. Cons: higher cost, increased guarding needs, installation not possible during production.

Clogging question A question often asked is 'will the adhesive clog up the nozzle during stops in the production run?' The answer depends on the adhesive technology. Cyanoacrylates (instant adhesives) require moisture to be present to initiate a cure.

During a prolonged stop, the adhesive could solidify at the dispensing end. However, the quick and inexpensive solution is to change the nozzle.An anaerobic will cure only in contact with a metal and when air is excluded from the area. Therefore, unless nozzle or connecting tubing has been contaminated with metal (unlikely), the adhesive will remain in liquid form. Two-part adhesives will not cure until they are mixed together. An automatic purge cycle incorporated into the system will clear the nozzle of curing material.

A visual inspection can check whether the adhesive has been dispensed, but can be time consuming and labour intensive. An easier way is to use a monitoring system that checks the dispensing process and provides an output that verifies the product has been applied correctly. The system measures the pressure of the adhesive as it passes through a dispense nozzle. Pressure values are electronically compared to a pre-determined, reference application. If a discrepancy is detected, an output is provided that can be interfaced with peripheral equipment to alert the operator and/or control system.

Automated dispensing/robotic application units are a cost effective, safe, clean and accurate way of dispensing adhesives and sealants and a manufacturer's technical specialists can help in the selection process.

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