Troubleshooting Two-part Epoxy Adhesive Dispensing Issues
Manual Dispensing from Cartridge
Remove cap from cartridge – you can normally see on the stoppers a coating of adhesive – keep in mind which prong goes into which side if you want to put the cap back on (otherwise it will become bonded on if you cross-contaminate).
Affix the recommended nozzle onto the cartridge. Some customers are tempted to use shorter nozzles to minimise wastage but epoxy adhesives are very sensitive to proper mixing so this is not recommended. Make sure to purge the nozzle as it is likely the new cartridge will have slightly unbalanced pistons, resulting in the first squeeze of adhesive being resin or hardener rich (this affects curing and strength properties).
Pay attention to the “Pot Life” (found on the two-part epoxy adhesive product technical datasheet) and also the ambient temperature you are working in, this will give you an indication of nozzle life for your two-part epoxy adhesive. For example, a product with a 10 minute pot life at 23°C, if you have put your dispensing gun down with material in the nozzle whilst you are busy assembling and clamping parts, you would need to return to using the adhesive (or purge the nozzle) within 10 minutes to continue using it. If you are working in a very hot environment, the cure time would be a lot faster – e.g. at 31°C the nozzle may only have 5 minutes life before the adhesive gels inside. Keeping the adhesive cool is one way of extending the nozzle life – but this brings other problems…
Cold Dispensing Conditions
Adhesive thickens when cold so if you store epoxy in refrigerated conditions or are working in a cold environment, it will become a lot more difficult to dispense. Some high viscosity grades may become virtually impossible to dispense from a cartridge. In this case you can warm the adhesive to reduce the viscosity to something more workable. However, don’t forget warmer adhesive will cure faster in the nozzle – but hey, at least you got it in there!
Common Two-part Epoxy Adhesive Dispensing Problems
Adhesive not coming out of cartridge:
- Check – has the cap been removed? Is there any sort of seal which requires piercing? (This is more likely to be seen with certain methyl methacrylate based adhesives on the market rather than epoxy).
- Back of cartridge is still sealed – sometimes cartridges have a foil seal you can pull off. Beneath this are pistons, these should be fairly level and not leaking. They should not be interfered with.
- Without putting the nozzle on, try to dispense some adhesive directly from the mouth of the cartridge.
- If nothing is coming out, unfurl a paper clip and poke it into the mouth of the cartridge (use a separate one for resin and hardener so you do not cross-contaminate). It will be apparent if the adhesive has gone hard or has become really thick when you prod it.
- If it has gone thick, you can warm it and then see if you can dispense. If not it could be time to get some fresh stock.
- If the epoxy adhesive is still liquid and doesn’t come out, check you are using the right gun with plungers that fit the back piston of the cartridges correctly. If the adhesive does come out without the nozzle but won’t go through the nozzle, it could be either a blocked nozzle or too high a viscosity for the nozzle creating too much back-pressure.
- Sometimes cartridges are just really hard to dispense by hand unless you’re Popeye or Arnold Schwarzenegger, in which case one that is fed by pressurised air would solve the problem.
Automatic Dispensing Equipment
If set-up and used correctly, there shouldn’t be any problems with using two part epoxy adhesives through dispensing equipment. Normally the dispensing equipment provider will assess the viscosity and thixotropy measurements, as well as mix ratio information from the adhesive datasheet, before designing and installing a system.
However, it is not unknown for production line operatives to “fiddle” with settings (such as the air pressure gauge, mix ratio settings etc.). This can result in dispensed material of incorrect mix ratio.
If material is not dispensing at all then check:
- Machine is fully switched on, timer / foot pedal is plugged in etc.
- The compressed airline is properly attached (and the compressor the other end is working!)
- There are no blockages in the nozzles, valves and other components of the dispensing equipment
- Dip tubes are properly inserted and the adhesive level is high enough
- There is adhesive in the machine
- Any pressure pots have no leaks under vacuum or extraneous objects caught in the seal (such as the unfurled paperclip – they do get about!).
Top Two-part Epoxy Adhesive Dispensing Tips
- Don’t muddle up resin and hardener, keep them separate and make sure operators are aware it is a two component adhesive. Never let the resin and hardener come into contact unless you are mixing / applying – do not muddle up tubing, dip tubes, reservoirs, spatulas or palette knives.
- After use, remove parts from dispensing equipment for cleaning – e.g. the mixing head, anywhere the two-part epoxy adhesive will have mixed. Often mixing components are made of stainless steel so they can be soaked overnight in solvent.
- Disposable mixing nozzles can be left to cure on the machine and then replaced when ready to be used the next day.
- Most two-part epoxies have different coloured resin and hardener so it is possible to see the cross-pigmentation and level of mixing. Successful mixing will result in a homogenous product with no streaking and no air bubbles.
For further help, please contact the Permabond technical team here.