Is nozzle orifice size the primary factor in determining adhesive flow rate of an application?
No. In gear pump systems with dedicated output, the nozzle does not determine the flow rate. Positive-displacement gear pumps meter a precise amount of adhesive per revolution regardless of nozzle size. Nozzle size does affect the hydraulic pressure in the system.
Does staged heating (the method of operating the melter at lower temperature than the hoses and heads) effectively reduce the amount of char in a hot melt system?
No. Polymer adhesives are poor conductors of heat. Because of their laminar flow tendencies, little mixing occurs during the transfer through hoses and applicators. Staged heating cannot significantly raise the adhesive temperature in the hoses and applicators, and generally results in the application of adhesive at lower-than-desired temperatures.
What is the most effective way to reduce char in a hot melt system?
Keep the tank full, operate the system at the recommended application temperature of the adhesive, and reduce the system temperature during long periods of inactivity.
How often should hot melt system filters be changed?
Hot melt filters should be changed on a regularly scheduled basis at a frequency sufficient to keep the filter from ever being completely blocked by contaminants.
Do melters using cast-in heaters require more time to service than similar components using cartridge heaters?
No. Properly designed cast-in heaters will far outlive the useful life of an adhesive melter. With more than 30 years of experience using cast-in heaters in tanks, grids and other components, the use of Nordson cast-in heaters virtually eliminates the need for heater maintenance.
As a filter screen becomes partially covered with contaminants, will adhesive output decrease?
Not if the system is using high-efficiency positive-displacement gear pumps, such as those used in Nordson hot melt systems.
I am spiraling adhesive onto a heat-sensitive substrate. How can I reduce the heat content of the sprayed adhesive?
As unusual as it may seem, the best way to reduce the heat content of the adhesive may be to increase the application temperature. Increasing the temperature will generally permit the Controlled Fiberization™ process to increase the frequency of the adhesive spiral. By putting the adhesive through more turns on the way to the substrate, the fiber diameter is reduced and more temperature is lost to the air.
Is there a "rule of thumb" for optimizing creep resistance on threaded elastics?
You might try a spiral nozzle with a larger orifice size. You will still use the same amount of adhesive per product, but a larger nozzle will increase the size of the adhesive fiber and reduce the number of spirals per second. This action increases the residual heat content of the adhesive and produces a stronger bond, especially when the elastic is coated with talcum powder.
Is there a quick check that will tell me if an adhesive is sprayable? Is sprayability determined by viscosity?
Adhesive sprayability is not directly linked to adhesive viscosity. Instead, it is a function of how well an adhesive will stretch without breaking (the modulus of elasticity at application temperature). To do a quick (and very rough) test of sprayability, take a piece of pressure-sensitive adhesive at room temperature and see if it will stretch. If it immediately breaks, or stretches for less than 50 millimeters, then it probably will not spray well. If it stretches well, it will most likely spray well.