Annealing Plastics Ensures Plastic Part Quality

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Plastics provide numerous manufacturing benefits. They’re lightweight, low cost, and corrosion-resistant. They’re also easily moldable, highly versatile, and low in density. As a result, they’re ideal for numerous applications, including roads, utensils, wire, pipes, bicycle helmets, child safety seats, automobile airbags, and buildings. What’s more, plastic use has tripled since COVID 19 started. Plastics, it seems, are ubiquitous.

But they’re not metals. So, when it comes to manufacturing products from them, they have their own set of unique challenges—challenges you must overcome to produce high-quality products. Manufacturers can eliminate some of plastics’ unique challenges by annealing them with help from Despatch industrial ovens. Subjecting plastics to this special heat-treating process helps manufacturers create top-quality products.

Annealing Plastics Reduces Internal Stress?

Plastics are poor conductors of heat. As a result, they build up stresses in the material during manufacturing when the material is heated and then cooled. Molding, cutting, casting, and extrusion can also build up internal stresses in the material. Stress makes the plastic more susceptible to the following:

  • Cracking
  • Excessive wear
  • Poor chemical resistance
  • Diminished performance

Drilling deep holes, reducing uneven thicknesses, and screw thread cutting, for example, create internal stresses in the plastic parts. Machining molded parts also creates stresses if a poorly designed tool is used and the material is locally overheated because of excessive cutting and feed speeds. Some plastics, like polycarbonate and polysolfone, are more susceptible to internal stress formation than others. That’s where annealing comes in.

Types of Annealing Methods 

Two types of heat-treating methods for plastics exist. Normalizing increases the plastic’s resistance to stresses and creates a uniform structure. With this type of heat treatment, you heat the material to a specific temperature, then let it cool down at a controlled rate. That changes its properties. Manufacturers use normalizing to get a calculable microstructure, enhancing a plastic’s mechanical features and enabling the plastic to resist more substantial impacts. Normalizing shrinks the plastic you’re heating by about 4%.

Annealing is the second type of heat-treating method. It’s ideal for many metals but also works well for plastics. This heat-treating method improves a plastic’s physical and chemical properties. It also improves the material’s ductility and wear resistance. Plus, it makes the material more malleable and produces a predictable microstructure, just like normalizing. Annealing is well-suited for plastics that require stress relief, need to remove stress after machining, or in situations where the material would crack after the post-polishing operations.

Key Features of Annealing Plastics Ovens

Manufacturers need to do their homework before buying an oven for annealing plastic. To get the most out of annealing plastics, you’ll need a high-performance industrial oven. It needs to be designed specifically for the process, be high-performing, offer a variety of chamber sizes and temperature capabilities, and feature consistent temperature uniformity flexibility. These ovens are ideal for a broad range of industries, including technology, transportation, healthcare, and manufacturing.

Specialized annealing ovens give manufacturers the ability to tightly control and monitor the heating and cooling process. That allows for proper recrystallization to occur within the materials. These materials are annealed at the eutectic point and then allowed to cool. Annealing softens the materials so they can be shaped or cut more easily, increasing their strength and ductility. Annealing, however, isn’t needed in all plastic molding. Some stresses can be eliminated without the annealing process, depending on the design and materials.

Benefits of Annealing Plastic Parts

Annealing plastics is worth the effort if you’re a manufacturer, especially in custom fabrication applications. Plastic parts and components can contract and expand over time when used. Annealing exposes the part to this process in the extreme, making the material more resistant to cracking and boosting part quality. Additional quality-supporting benefits of annealing are

  • Tighter tolerances
  • Increased dimensional stability over time
  • Better material rigidity and wear resistance
  • Increased flatness control   
  • Better chemical resistance
  • Increased ability to handle machined stresses

Annealing Differs for Different Plastics

The annealing process, however, isn’t the same for all plastics, especially when machining is involved. Engineered plastics like Ultem and Torlon, for example, benefit greatly from post-machining processes. Annealing Torlon can take as much as seven days using special industrial ovens. Other plastics, like PEEK, need more immediate annealing steps to ensure they maintain tight tolerances and flatness.

Plastics require different annealing temperatures and conditions:

  • Polycarbonate: 250°F(121°C) for as short a time as possible determined through experimenting with test data
  • Ultem: slowly brought up to 400°F(204°C) and then held for two hours
  • ABS materials: heat deflection temperature at 264 psi (170°F to 240°F) and held for 1-2 hours.
  • Supec resins: Annealed at 400°F(204°C) for 4 hours

The environment and temperature maintained, both during and after the annealing process, and cooling rate are critical. Despatch manufactures plastic tempering and plastic annealing ovens in both batch and conveyor styles. If you need more information about any of our ovens, from design to installation and maintenance services, please call us at 952-900-6635.

Image by feiern1 from Pixabay