Steps to Designing a Hot Air System – Part One of Four

On the surface, designing an effective hot air system can seem like a simple exercise. However there is an underlying complexity which, when ignored, can result in wasted time and money. At STANMECH we have been approached by customers who believe they know exactly what they need.

Customers go to the website and pick out a tool without going through the full design process. The best case scenario is that the customer wastes a small amount of money and time selecting and buying the wrong equipment. The worst case scenario is that the customer designs, builds, commissions a complete processing line, spends a great deal of money and time and end up in a situation where it doesn’t work, they’re in a corner, and much more money and time must be spent to correct the problem.

The purpose of this series of articles is to keep the reader from going down the wrong path when in most cases it can be avoided by more thinking more carefully about the hot air system they are designing.
​
In this article we are discussing the first step in designing a hot air system (or any system) – carefully defining the problem. It is tempting to skip right to a solution or jump into analysis without defining the problem you are trying to solve. Properly defining your problem will help to get to the appropriate solution and helps you work with third parties, such as equipment suppliers, more effectively.

Step 1 - Define the problem

​One of the most frustrating things we encounter is a poorly defined problem. Finding out there was some critical piece missing from the problem definition after we’ve gone down a solution path wastes time and effort solving the wrong problem and can even mean money spent on the wrong solution. Unfortunately, in many cases designers go straight to a solution without properly defining the problem. Specifically for a potential hot air system, the designer should consider the following:

1. What is the problem we are trying to solve?

Avoid being vague or general when defining your problem. The more detail that is put into this step the better. Include information such as material type and size, specific temperature goals, potential unwanted results, next process steps, etc. 

For example:

• General: We are heating the end of a plastic pipe.
  
• Detailed: We are heating the end of a HDPE pipe to a temperature of 200 degrees so that it can be flared over a mandrel.
  

 

• General: We need to dry a metal part.
  
• Detailed: We need to cure the paint on a stamped steel sheet measuring 10cmx10cm without causing any ripples in the painted surface.
  

• General: We need to dry a metal part.
  
• Detailed: We need to remove cooling liquid off a meter wide steel sheet before it enters a welding process.
  

Defining the problem with enough detail is important; these details inform the direction of the solution. Details such as “without causing rippling” are important because they tell the designer how the hot air needs to be applied.
​
The second and third examples together show the danger of generalizing. The word “dry” can be used for both curing and for removing liquid. The solution for each of these is vastly different; without enough details the designer or their suppliers could easily recommend the wrong one.

2. Is hot air the right technology?

Now that the problem has been defined the designer can look at the technology choice to judge its effectiveness. Hot air has a wide range of applications but there are times when it may not be the right choice. In the examples above, hot air would be the right choice for curing the paint on a steel part but would not be a good choice for removing cooling liquid from the wide steel sheet. Rather than hot air, an air knife would likely be used to strip the liquid off the surface. Using hot air would be far too slow and energy intensive to be practical.

The designer may have to consider this point several times in the design process. It is possible that after the thermal calculations have been completed that they may have to revisit the technology choice. There are occasions when the energy required (kW) or some other variable for the process, makes the choice of hot air unfeasible.

​
This step is easy to write about but sometimes difficult to put into practice if you don’t have the experience to know what is important and what isn’t. Call STANMECH and let us use our expertise to keep you from making mistakes early in a project that can cost a lot of money in the long run.