Features of work with hot glue equipment
Specific of working with hot melt dispensing equipment
If the tank temperature is too high, hot melt adhesive will get oxidized and will burn which will worsen its adhesive properties.
At low temperature hot melt viscosity will be too high which may result in stringing, poor flow properties and mechanical failure of the pump.
Hose and nozzle
The temperature being too high may result in excessive amount of adhesive applied which will increase open time and lead to low bond quality.
Low temperature causes difficult flow of adhesive through the nozzle and insufficient amount of applied adhesive.
During operation of the gluing station, deposits of carbonized adhesive (char) are built up on the tank and hose walls and may come off in course of further operation causing filter clogging and nozzle blockage. In this case tank, hose and nozzle should be cleaned thoroughly with a special cleaning agent.
Normally the best results are achieved at the temperature of materials to be bonded over 15°C.
When hot melt contacts cold surface its temperature goes down quickly resulting in sudden change of viscosity and further insufficient wetting of the surface, and therefore poor bond.
If the pressure is too low, the adhesive flow will be significantly weaker which may cause insufficient application of adhesive.
High pressure may result in increase of the hot melt adhesive consumption rate, increased wear of operating units of the pump.
If pressing is insufficient, quality bond is not possible to achieve. This may lead to joint failure or failure of joint integrity over time.
Excessive pressing strength may result in package deformation, adhesive-surface contact will become unreliable and the joint may fail during hardening. This may be especially problematic in cases when the package contents are irregular in shape or box/carton is not completely filled.
Many of modern packaging materials have coating exhibiting barrier properties that allow protecting the contents from moist and drying out.
Such coatings have low surface energy and may cause problems for wetting of the surface by the adhesive.
This may result in weakening of the joint and may influence its integrity over time.
It’s very important to make sure that the hot melt adhesive corresponds to the open time of the assembly procedure.
If open time is too short the surface will not get impregnated and bond will not be achieved, or it will fail soon after.
If open time is too long, the adhesive will lose its heat and will not gain enough strength.
Open time may change to some extent with adjustment of temperature and pressure.
Amount of adhesive
For quality bond performance it’s important to apply optimal amount of hot melt adhesive. Excessive amount of adhesive applied may cause problems with open time and increase in consumption rate. Adhesive may also be squeezed out in the pressing section. This may also cause poor cut-off at the nozzle resulting in stringing and contamination of the equipment: excess adhesive may fly off and affect further operation on the line (for instance, staining the rollers).
Too little adhesive will harden quickly not allowing for proper wetting and joint formation.