Before I get into how much your material may change during your dispense process, let me provide a quick summary of why it matters. As your plant temperature changes, your material temperature often changes. When material temperature changes, the viscosity changes. When viscosity changes, the end result of your dispense changes – and nothing good happens when your finished product varies. It causes rework, scrap, customer rejects and in some cases, early product failure. In this blog, we’re going to address the effects of material temperature only. There may be other factors affecting your material but they’re not going to be addressed here.
In general, nobody questions the link between temperature changes and quality output. The questions we do get, however, are more like:
• How much does the temperature have to change before I really see an impact on my process?
• How much does the temperature really change during the dispense process?
If the answers to those questions were “a lot” and “not much,” respectively, we wouldn’t have a thriving business. The real answers to those questions are more like, “not that much” and “likely more than you think.” And that’s what makes this blog relevant.
How much does the temperature have to change before I really see an impact on my process?
Materials and processes vary somewhat so there is not a definitive answer to this question. However, our experience indicates that changes at the point of dispense begin to show unacceptable variations in as little as a three-degree Fahrenheit window, (i.e. +/- 1½° F). Some materials are more forgiving, but each has a window where it will consistently produce acceptable results.
Spray applications, like this anti-chip sealer are common. Here we can see the impact of temperature on dispense – and ultimately on performance. The most obvious change is in the width of the fan pattern, but perhaps even more important is the impact of viscosity on spray consistency. Above 95°F, the coating is thin and uneven. You can see the substrate peeking through. Even if it adheres well, it can’t do its job. In the 90°F to 95°F range the coating is smooth from edge to edge. This is the optimal operating temperature for this process. Below 90°F we see heavy edges beginning to appear, which are often associated with “striping” on the finished part. As we move into the 75°F range and below, we see the combination of very uneven coating surrounded by heavy edges making it difficult to get a smooth, even coating on the finished part. Without a smooth, even coating, both performance and appearance will be compromised. And when robots are used, the problem will be repeated over and over again.
How much does the temperature really change during the dispense process?
1. How much the material temperature changes is primarily dependent on four things:1. The difference in temperature between the material and, in most cases, the plant ambient temperature – often referred to as delta (ΔT).
2. The material surface area exposed to that plant temperature. Think material in a pipe. The more pipe, the more surface area exposed to plant ambient temperatures.
3. The length of time the material is exposed to the plant ambient temperatures. Determined by material flow rate, production rate, and the size of the delivery pipe.
4. Any heat generated by the process, (i.e. pump, friction, shear, etc.).
On a day when your plant temperature is close to your ideal dispense temperature, you may see very little change. However, when the plant is either very warm or very cold and the material run is greater than say 20 feet, you can see temperature move as much as 20°F from the source to the dispense point.
So, how much does the temperature have to change before you really see an impact on your process? Not that much.
How much does the temperature really change during the dispense process? Likely more than you think.
Each dispensing operation has its own characteristics, so if you’re willing to share some details with us, we would be happy to give you our assessment of how big your problem could be.