Sealer and Adhesive Dispensing | Fluid Process Control

One Variable Left

You have controlled the robot path, the material pressure, the flow rate, the substrate and everything else you could to ensure that variability is minimized in your process. Failing to control the temperature variable can diminish those efforts and generate frustrating outcomes.  We understand that the challenges involved in this application are quite different from those of paint.  Materials are typically applied at 70°F to 90°F and commonly require both heating and cooling.  Fluids are dispensed in lower volumes using non-circulating systems and pumped at high pressures. Saint Clair Systems has made itself the industry benchmark for the design of systems within these exacting parameters.

The Effects of Variability

The picture to the right shows the effects of temperature on a bead of hem flange epoxy used in the automotive industry. Holding all other variables constant, and adjusting only temperature, the width of the bead changes dramatically. It increases by over 50% from 60°F to 80°F and by nearly 80% when the temperature goes to 100°F.

The Saint Clair Systems Temperature Control Unit monitors and maintains material temperature by heating or cooling during adhesive and sealant operations. The TCU circulates the closed-loop conditioning water through heat exchangers and ancillary components to ensure proper temperature of the material.

Another Example of the Effects of Variability

Temperature of the material in the process is the issue and just controlling ambient will not address it.  Viscous materials require a great deal of energy to pump from one place to another. Some of this energy ends up in the material as increased temperature. Moreover, when viscous, thixotropic materials shear, the temperatures at the shear interface increase and the viscosity decreases. Standard process control components such as pumps, regulators, meters, filters, etc. all contribute to this phenomenon by adding shear and friction to the material path.  The effect of temperature on the robotic dispensing process can be readily demonstrated. When all other factors (pressure, flow, path, speed, distance, angle, etc.) are held constant and temperature is varied, the pattern dispensed changes dramatically.

For this example, orifice, pressure, distance, and angle to the surface were held constant while a PVC body side material was sprayed.  Due to the direct relationship between viscosity and temperature, we used temperature to control the viscosity. Coupons were sprayed and the spray pattern measured. The picture above shows the resulting effect on spray pattern across a 40 °F change in temperature. Notice the thin coverage on the 100°F and 105°F coupons; how it smooths out between 80°F and 95°F; and how it grows uneven below 80°F.  For more detail on this test and others, see one of the following articles:

Not Too Hot, Not Too Cold: Importance of Temperature Control in Robotic Dispensing Application Robotics World (May/Jun 2000)	Using Temperature Control to Stabilize Dispensing Processes White Paper