Dispensing adhesives can be a challenging application. Choosing the right type of dispensing adhesives equipment is essential for success.
The choice of dispensing adhesives equipment is largely dependent on the behavior of the adhesive material. The two most important material attributes are viscosity and cure. Viscosity refers to adhesive thickness while cure refers to the method an adhesive hardens.
When dispensing adhesives materials, fluids should be classified into the following viscosity groups.
|Low||Up to 30K Cps|
|Medium||30K to 100K Cps|
|High||100K Cps and greater|
Adhesive cure methods include:
For many low and medium-viscosity dispensing adhesives applications, a time/pressure syringe system is perfectly adequate. During operation, the dispensing adhesives system delivers a measured amount of air pressure for a preset dispensing time to a syringe. The controlled shot of air forces the adhesive out of the syringe, through the needle and onto the work surface.
The disadvantage of the syringe type system is that it depends on too many variables to maintain good repeatability rate for the entire dispensing process. One of the variables is the internal diameter of the syringe. If the internal diameter of the syringe is tapered too much then the shot size will decrease as the adhesive travels down toward the bottom. To address this problem, Techcon Systems offers various TPD valve systems for dispensing adhesives materials.
When dispensing adhesives applications require more control and durability, a diaphragm valve system may be used. This pneumatic valve uses a diaphragm to open and close the fluid path. During the adhesive dispensing cycle, the air pressure signal forces the diaphragm to pull back creating an opening for the fluid to flow through. When the air signal stops, the internal spring pushes the diaphragm down to the closed position. Virtually any low to medium viscosity fluid can be dispensed using one of Techcon diaphragm valve variations.
For dispensing adhesives with low and medium viscosity that required micro dot size, (less than 0.002CC), the micro-shot needle valve is an ideal choice. Higher viscosity dispensing adhesives, up to 100,000 cps, can be dispensed accurately with this valve. However, dispensing adhesives that are moisture sensitive and quick curing require a different valve.
When dispensing adhesives with high viscosity, a spool valve is a better choice. This valve uses an air-actuated piston to opens and closes the adhesive’s path. However, contrary to the needle valve, the air pressure signal drives the piston down to open the path. When the dispensing cycle is done, the internal compression spring lift the piston up to keep the valve in the closed position.
When viscosity fluctuation is present as is typical with epoxies, a rotary auger valve is a better adhesive dispensing solution. As the dispensing adhesives become thicker or thinner, the fluid pressure needs to be adjusted accordingly to keep the dispense repeatability rate stable. This method uses a rotary feed screw (auger) coupled with a precision DC motor for dispensing adhesive material with a rotary displacement action. A disposable material path version, TS5000DMP series, is available for dispensing adhesives applications that use two-component adhesives, quick curing adhesives or highly abrasive fluid. Wetted parts are fully disposable, eliminating the need for cleaning and repair.
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