So you’ve spent tens or even hundreds of thousands of dollars on your dispensing system, and still you experience quality holds and rejects from your customer – all related to your fluid dispensing operation. Your best and brightest have analyzed your system and everything is working exactly as designed, yet you are still plagued with these seemingly random episodes.
Perhaps the problem is so common and so obvious that it is easily dismissed as “natural”…
In our first segment in this series, we discussed the importance of controlling your fluid dispensing process at the point of application (click here if you missed it or would like to review). In this segment, we’ll dive into more detail on point-of-application temperature control and why it is so important to stabilizing a fluid dispensing operation.
It’s All About Viscosity
We say it all the time – “It’s all about viscosity!”
Manufacturers that work with fluids understand that every fluid changes viscosity as a function of temperature (see Figure 1). As the temperature increases, the viscosity decreases, and vice-versa. Therefore, as the temperature of the fluid changes, the viscosity changes – and changes in viscosity affect the way that the fluid performs in the dispensing process.
This really shows the importance of control at the point of application. If the temperature at the point of dispense can be held constant, independent of ambient and other factors, the viscosity will be constant and the system will be stable and repeatable – two traits every manufacturer wants in their process.
The Temperature Control Envelope
The area that is contained within the temperature control system is called the “temperature control envelope.” Properly executed, this “envelope” isolates the fluid carrying components from the ambient environment, and uses them to counteract both ambient and process-generated thermal variations – just before the fluid is placed on the part.
So why is this “thermal envelope” so important?
The answer becomes obvious when we examine what happens when a gap is left in the envelope. Say, for instance, that the dispense valve is left exposed to ambient. As shown in Figure 2, during a break in production (coffee, maintenance, lunch, whatever), the temperature of the valve falls from the 90°F setpoint toward ambient, dropping a full 10°F during a short 10 minutes. Remember Figure 1? This represents a significant change in viscosity. When this cooler, more viscous material is sent to the nozzle, we see that there is a significant change in dispense pattern in the form of a narrow, heavy fan. Once the warmer fluid reaches the gun, the fan pattern instantly widens and the distribution spreads accordingly.
In short, everything else can be working perfectly in the dispense system – gun timing, pressure control, robot path – yet, this simple change in temperature at the point of application counteracts all of these systems and severely compromises the quality of the dispense. This shows how often overlooked variables can wreak havoc on our otherwise carefully constructed system.
In our next segment, we’ll examine how conditions upstream from our dispensing system can impact its performance, and how we can both recognize and rectify these situations. We hope you’ll join us…