Manual dispensing guns vary in mechanical advantage.
High mechanical advantage dispensers can produce excessive internal pressure. The higher the pressure the higher the chances for off ratio dispensing. To minimize off ratio dispensing, use the recommended static mixer and as little pressure as possible to dispense the adhesive at a reasonable rate.
Ask your GranQuartz technical sales representative for dispensers approved for use with Nitro ONE adhesives. Use of non-approved dispensers can cause off ratio mixing and voids the manufacturer warranty.
Damaged, worn or malfunctioning dispensing guns
Malfunctioning dispensers can cause uneven or incomplete adhesive cure. Damage to the ratchet or brake mechanism and cracks or missing teeth on the plunger of a dispensing gun can cause uneven feeding of the pistons.
- Check the condition of the dispenser paying particular attention to the ratchet mechanism.
- Look for broken teeth, build up of adhesive or play in the dispensing mechanism.
- Also look for loose, bent, misaligned or missing piston rod end discs.
- Check to see if the two push rods are of equal length.
- Check to see if the dispenser body is bent, twisted or has adhesive build up that prevents the cartridge from accurately aligning to the piston rod travel.
- Purge adhesive (approximately 1 tablespoon)
- Check to see if the adhesive continues to drool out of the outlet. If drooling continues for more than a few seconds, the adhesive dispenser is not functioning properly. Check to see if the non drip feature is retracting between strokes
Leaking Cartridge Pistons
- Check the condition of the dispenser.
- Look for excessive play in the piston rods or loose piston rod ends.
- Check cartridge position in the dispenser and ensure that it sits parallel to the piston rods.
- For pneumatic systems, ensure there is a regulator on the dispenser providing controlled pressure of less than 60 PSI (5 bar).
- Adjust pressure to provide adequate flow without overpowering the system.
- If leaking occurs, your supplier may wish to inspect the molded part for defects, damage or missing o-rings as part of their quality control program.
Operator Tigger Action
Some shops find that off ratio dispensing appears to be a random event and may occur more often with some individual operators.
The triggering action used with manual dispensers is an important technique to ensure an even cure.
- Purge adhesive (approximately 1 tablespoon)
- Check to see if the adhesive continues to drool out of the outlet. If drooling continues for more than a few seconds, the adhesive dispenser is not functioning properly.
- Check to see if the non drip feature is retracting between strokes.
- Apply smooth even strokes; maintain constant feed and pressure using the full stroke of the trigger.
- Do not stop and let adhesive drool out of the tip between strokes, quickly re-trigger the gun and continue until dispensing is completed.
- To minimize off ratio dispensing, use as little pressure as possible to dispense the adhesive and maintain a constant forward motion of the cartridge pistons.
- Adhesive stored in the fridge or a cold shop, should be allowed to return to room temperature before use.
- Some adhesive components become thicker at low temperatures and may not mix as well.
- Thickened material creates higher pressure in the cartridge and tip.
- Higher pressure will flex the cartridge wall and can throw off mix ratio.
- If you re-warm adhesive, make sure the cartridge outlet plug is in place.
- A mixing tip left on the cartridge can allow expanding adhesive to back flow into the activator chamber and result in a plugged cartridge.
- Never warm adhesive above 110 degrees f. The activator may be damaged.
Cold sheet material
Bonding sheet goods that have been stored below normal room temperature will cause the adhesive to cure slowly in the joint. Fabricating with cold sheet goods may prevent a full cure from developing in areas with lower than optimum activator levels.
Fabricating cold sheets in a warm room
Warm room air temperature will cause the adhesive on the surface to cure much faster than the adhesive in the joint where the cold substrate will absorb much of the energy from the chemical reaction. This can cause joints to have low strength. For best results, allow product being joined to reach a room temperature of 60 f (18 c) before assembly.
For optimum shelf life and performance, store adhesive upright away from direct sunlight. To further extend the shelf life, the adhesive may be stored in an air conditioned room or a fridge designed for the storage of flammable products.
It is possible for an air bubble to be trapped in the activator or adhesive. Gases can also form in the activator if it is subjected to high temperatures during storage or shipping.
In the event that a gas or an air bubble was trapped in the cartridge, upright storage will allow it to reach the top (outlet) of cartridge to be eliminated during the initial purge. (remember to purge with the cartridge pointing up)
Activator exposed to high temperatures during transport or storage will break down and loose strength, this will generally show up as a slow, uneven or incomplete cure.
Activator stored correctly will last for a year or more but will slowly over time loose reactivity.
High temperature decomposition of the activator can also release gasses into the activator component.
Bubbles may appear in the dispensed product and the compressibility of the gases may act like a spring compressing with each pull of the trigger, producing fluctuations in the dispensing rate, off ratio (uneven cure) and drooling at the tip.
With some manufacturer’s activator, we have seen separation of the ingredients over time or after freezing; this can cause the proportions of active ingredients (therefore the cure) to vary.
If you suspect damaged activator, contact your supplier.
With all of the variables involved in manual and pneumatic dispensing of dual component adhesives, it is impossible to completely eliminate the possibility of any variation in mix ratio. However, if you purchase quality adhesives, store them correctly and follow these few simple procedures you can expect a near perfect seam every time. If you are having problems with uneven cure that is not corrected by the recommended procedures, contact your supplier and request assistance or replacement material.
Although it should not be necessary, it is cheap insurance to run two small beads (one over the other) instead of a larger single bead. The overlapping of adhesive streams will greatly reduce the possibility of under cured areas in any joint.