Frequently Asked Questions Regarding Dispensing of Adhesives
The following are some of the more common questions when it comes to the dispensing of adhesives, as well as a few tips for preventing adhesive dispenser tips from clogging.
When dispensing adhesive around the opening of a large plastic container, it was found that adhesive had somehow splattered on the inside of the bottle in some of the assemblies. What could be causing this?
There are two main possible causes for this situation, the first of which is due to static electricity. Static electricity is caused by dry conditions, and could cause the line of adhesive to briefly jump to the other side of the bottle rather than continue to drop directly below the dispensing needle. The second possible cause is due to stringing, which is where the adhesive doesn’t stop coming out when the pressure from the dispensing needle stops, and this last little string of adhesive may then be free-falling into the wrong side of the container.
After changing raw materials used in a particular product, a business was required to also change its adhesive so that it would bond to the new raw material. However, despite both adhesives being of the same viscosity, the new adhesive ran all over the various parts of the machinery. How is it that two materials with the same viscosity can act so differently?
Materials can have the same viscosity but differ greatly in their rheology, which is effectively their rate of flow. There are two main types of materials when it comes to flow rate: Newtonian fluids, which flow the same when the shear is fast or slow, and thixotropic materials, which will have a high viscosity when stirred slowly and a low viscosity when stirred quickly.
It depends on what your dispenser is made of, but chances are good that you will be able to reuse your dispense for this new application. To be sure, it is wise to check with the manufacturer of the dispenser.
What is the best type of dispenser tip to use to prevent clogging when dispensing adhesive through an automatic pressure pot system?
Generally speaking, you are best to use plastic tips to avoid clogging. These will normally be made from polypropylene or polyethylene, but it all depends on the type of adhesive you are using.
The following tips will help to prevent the dispenser tips for your adhesives from becoming clogged.
- If you are using a UV curable adhesive, make sure your dispenser tip is able to block the light. Whether it is metal or plastic makes little difference.
- When using instant adhesives, if you leave them idle to go on a break or end work for the day, always remove the tips and place them in an appropriate solvent.
- Avoid using metal tips when dispensing an anaerobic adhesive.
- Single part epoxies will only cure with heat, so slowly heat tips to just above room temperature to remove clogging.
- Epoxies involving two components will often start setting as soon as they are mixed, so you will likely need to replace the dispensing tip after even a brief idle period. Refer to the adhesive’s pot life to know exactly how long you have.