Here at Hix Industrial Ovens we often times get questions regarding the processes many of our Industrial Ovens are used for. This is especially true from people who are new to Industrial Ovens in general. In this blog we will be covering the process that materials go through while in an Industrial Annealing Oven. To begin, we have to cover some of the basics.
What is Annealing?
Annealing is one of the most critical manufacturing steps. By heating and slowly cooling a material, annealing ovens are able to greatly increase the strength of that material. This prevents unexpected cracks and breaks in critical products in a number of industries, from high end ceramics and glass windows, to safety cages on automobiles, and a wide range of composites and plastics. The annealing process works slightly differently from product to product, but the general idea is the same.
How Does Annealing Work?
Let’s look at a quick example. This is one of our Industrial Plastic Annealing Ovens:
This particular model is a cabinet style batch oven that is used for plastics, but we have Industrial Ovens that come in a variety of sizes and configurations, from Infra-Air (Infrared w/ recirculating air) and Electric Hot Air Convection conveyor ovens to large gas fired convection walk-in ovens. Plastic is a substance that everyone knows well so we’re using this for an example. This particular annealing oven is used for polypropylene, but there is a wide variety of plastics that it will work with. More types than we can list in this post.
When you are going to anneal any substance, you have to raise its temperature to the “glass transition” temperature point. In substances that are not amorphous, different names apply. Regardless, for most substances the annealing point is just over half of the melting point. From polypropylene oven handles or pipe fittings to numerous parts in automobile manufacturing. To achieve the highest strength, it is heated to about 185°F. This Industrial Oven is heated using Infra-Air (Infrared w/ recirculating air).
Depending on the thickness and material type, the oven needs to heat at various rates. The thicker the material, the slower the heating and cooling rates are to ensure that the heating occurs evenly. In our plastics annealing ovens we use ramping heat controllers so that it heats at about 50°F per hour per 0.25in of thickness. Once it reaches the preset temperature in about 2 hours, the controller holds the oven temperature at a precise 185°F for 30 minutes.
That is is a little more than halfway to the melting point of the plastic molecule chains (polymers). That leaves enough energy in the material so the molecules can move around a bit and they will naturally spread out, thus removing the imperfections in the plastic. All crystalline or amorphous materials need to be arranged in relative harmony. They have an order in them that is preferred. Stress points are areas in the material where there are is a large amount of disorder in the layout. The annealing process gives the molecules enough energy to move and rearrange themselves into order. Even controlled heating in the Industrial Oven is critical. That’s why we have custom built Infrared heaters inside of our ovens. Our Infrared heaters are excellent at holding precise temperatures in the oven chamber and the added airflow system is designed to recirculate the air and increase the process and energy efficiency.
After the preset holding time has finished, the material has to cool, but just like before, it’s very important to cool the material at a steady rate so that the temperatures within the material stay uniform throughout. If the temperatures cool too quickly or unevenly, a completely new set of stress points will occur that will weaken the plastic and threaten it’s stability.
Once the material has cooled all the way, the newly strengthened part can be moved on to the next stage of production. Oftentimes, this means that it will next be milled, coated, or fit into an assembly. Back at the annealing oven, operators or robotic assemblies reload the oven with a new batch of parts and begin the critical heating and cooling process all over again. Depending on the demand, many of these ovens run day and night, driving our American industry and the products we produce.
If you are needing more information on our Industrial Annealing Ovens, our sales team and engineers are here to help. Contact us today with your questions, or for a free quote.