Annealing (Stress-Relief) for
Full Annealing Services
Molded spacer blank from CD-ROM packaging. Heat-formed acrylic picture frame.
When any material is heated, it expands; when cooled, it will contract. Since most plastics are poor conductors of heat, any uneven or rapid heating and cooling can introduce "stress" into the material. Examples of these stress-inducing processes include molding, casting, extrusion, heat- or cold-forming, cutting, drilling and machining.
Machined stress is often created when drilling deep holes, machining inside corners without proper radius (threaded holes!), removing large amounts of material at high speeds, or when material is removed unevenly when reducing finished part thickness, such as in a hollow cup- or box-shaped part. Stress may also be caused by using improper (oil-based) or insufficient coolant.
Injection-molded acrylic drinking glass with chemical attack from dishwasher detergent and stress-induced cracks and crazing. Injection-molded polycarbonate safety glasses with as-molded stress.
Stress in a plastic material or part can result in poor performance in an application , including warping, twisting, or other dimensional changes. It may also cause cracking or "crazing" (a large network of tiny cracks), poor chemical resistance, and reduced wear resistance. In addition, some plastics are more susceptible to stress than others, especially when temperature cycling (sterilization) or chemicals are used.
Contact us to determine if your material selection or part design may cause or increase stress in your finished machined parts. Frequently, subjecting the parts to a properly specified annealing cycle can reduce or eliminate "stress" in the material which has been caused by the molding, forming, or machining process.
Example time and temperature heat cycle for stress-relieving a plastic machined part. Temperature-controlled ovens for stress-relieving of plastic materials.
Annealing for plastic materials or parts is the process of heating and cooling them slowly to relieve the stress and prevent it from recurring. The cycle of temperature and time is different for each type of plastic and part cross-section. Generally, the annealing process includes heating a plastic to a temperature just below its softening point, keeping it at the high temperature for a period of time, then cooling it very slowly until it returns to room temperature.
Boedeker Plastics has several temperature-controlled ovens that are used to anneal plastic materials (sheet, rod and tube) and machined parts. The annealing may be performed before, during and after machining to reduce or eliminate stress.
Contact us to determine oven availability or to discuss your application. Our full CNC machine shop is also an available option for those customers without machining capacity, or who may have experienced difficulty with stress in plastic machined parts.
(NOTE: click on any photo to enlarge, use arrow keys or mouse to advance to next photo)
Molded polycarbonate tube in relaxed state, under compression, and animated movie.
Machined Ultem 1000 bracket in relaxed state, under compression, and animated movie.