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Annealing (Stress-Relief) for Plastics Stock Shapes Annealing Icon

Annealing Guidelines

The following guidelines are presented for those machinists not familiar with post-machining annealing (stress-relief) for high-performance plastics. They are intended as guidelines only, and may not represent the most optimum conditions for all parts.

Most quality stock shape materials are stress-relieved by the manufacturer after molding to ensure the highest degree of machinability and dimensional stability. However, some components may benefit from post-machining annealing or stress-relieving using the instructions below.

When should parts be post Annealed (Stress Relief) after machining?

Experience has shown us that very few machined plastic parts require annealing after machining to meet dimensional or performance requirements.

Generally speaking, most stock shapes are annealed after molding using a proprietary stress relieving cycle to minimize any internal stresses that may result from the manufacturing process. This assures you that the material will remain dimensionally stable during and after machining.

Machined-in stress can reduce part performance and lead to premature part failure. To prevent machined-in stress, it is important to identify the causes. Machined-in stress is created by:

  • Using dull or improperly designed tooling
  • Excessive heat –– generated from inappropriate speeds and feed rates
  • Machining away large volumes of material –– usually from one side of the stock shape

To reduce the potential for machined-in stress, review the fabrication guidelines for the specific material. Recognize that guidelines change as the material type changes.

BENEFITS OF POST-MACHINING ANNEALING

  • Improved Chemical Resistance

    Polycarbonate, polysulfone, and Ultem® PEI, like many amorphous (transparent) plastics, may be annealed to minimize stress crazing. Torlon® PAI also benefits from post-machining annealing. Annealing finished parts becomes more important as machining volume increases. Annealing after machining reduces "machined-in" stresses that can contribute to premature failure.

  • Better Flatness & Tighter Tolerance Capability

    Extremely close-tolerance parts requiring precision flatness and non-symmetrical contour sometimes require intermediate annealing between machining operations. Improved flatness can be attained by rough machining, annealing, and finish machining with a very light cut. Balanced machining on both sides of the shape centerline can also help prevent warpage.

  • Improved Wear Resistance

    Extruded or injection-molded Torlon® PAI parts that require high PV's or the lowest possible wear factor benefit from an additional cure after machining. This curing process optimizes the wear properties. Only PAI benefits from such a cycle.

Post-Machining Air Annealing Guidelines

Material Heat Up Hold Cool Down Environment
ABS 50°F per hour to 200°F 30 min per 1/4" thickness 50°F per hour Nitrogen
Acrylic 2 hours to 180°F 30 min per 1/4" thickness 50°F per hour Nitrogen
Acetal copolymer 4 hours to 310°F 30 min per 1/4" thickness 50°F per hour Nitrogen or Air
Delrin® acetal homopolymer 4 hours to 320°F 30 min per 1/4" thickness 50°F per hour Nitrogen or Air
Ardel® polyarylate 50°F per hour to 330°F 30 min per 1/4" thickness 50°F per hour Nitrogen
Ertalyte® PET-P 4 hours to 350°F 30 min per 1/4" thickness 50°F per hour Nitrogen
Halar® ECTFE 50°F per hour to 225°F 30 min per 1/4" thickness 50°F per hour Nitrogen
HDPE (Polyethylene) 2 hours to 200°F 60 min per 0.4" thickness 10°F per hour Nitrogen
Hydex® 4101 PBT-P 4 hours to 300°F 60 min per 1/4" thickness 50°F per hour Nitrogen or Air
Kynar® PVDF 2 hours to 275°F 30 min per 1/4" thickness 50°F per hour Nitrogen
LDPE (Polyethylene) 2 hours to 175°F 30 min per 1/4" thickness 10°F per hour Nitrogen
Noryl® PPO 50°F per hour to 250°F 30 min per 1/4" thickness 50°F per hour Nitrogen
Noryl® PPO (30% glass filled) 50°F per hour to 260°F 30 min per 1/4" thickness 50°F per hour Nitrogen
Nylon - type 6 4 hours to 300°F 30 min per 1/4" thickness 50°F per hour Nitrogen
Nylon - type 6/6 4 hours to 350°F 30 min per 1/4" thickness 50°F per hour Nitrogen
Nylon - glass-filled 4 hours to 375°F 30 min per 1/4" thickness 50°F per hour Nitrogen
PCTFE (formerly Kel-F®) 3 hours to 225°F 60 min per 1/4" thickness 50°F per hour Air
PEEK polyetheretherketone 2 hours to 300°F, then 2 hours to 375°F 60 min per 1/4" thickness, 60 min per 1/4" thickness 50°F per hour Air
Polycarbonate (unfilled) 4 hours to 275°F 30 min per 1/4" thickness 50°F per hour Air
Polycarbonate (glass-filled) 4 hours to 290°F 30 min per 1/4" thickness 50°F per hour Air
Polyethylene (LDPE) 2 hours to 175°F 30 min per 1/4" thickness 10°F per hour Nitrogen
Polyethylene (HDPE) 2 hours to 200°F 30 min per 1/4" thickness 10°F per hour Nitrogen
Polyethylene (UHMW) 2 hours to 220°F 30 min per 1/4" thickness 10°F per hour Nitrogen
Polypropylene 2 hours to 185°F 30 min per 1/4" thickness 50°F per hour Air
Polystyrene 50°F per hour to 170°F 30 min per 1/4" thickness 50°F per hour Nitrogen
PTFE (Teflon®) 3 hours to 525°F 60 min per 1/4" thickness 50°F per hour Air
Radel® R polyethersulfone 4 hours to 390°F 30 min per 1/4" thickness 50°F per hour Nitrogen or Air
Ryton® PPS 4 hours to 350°F 30 min per 1/4" thickness 50°F per hour Air
Techtron® PPS 4 hours to 350°F 30 min per 1/4" thickness 50°F per hour Air
Torlon® PAI 4 hours to 300°F, then 4 hours to 420°F, then 4 hours to 470°F, then 4 hours to 500°F 1 day, 1 day, 1 day, 3 to 10 days 50°F per hour Air
TPX® polymethylpentene 50°F per hour to 200°F 30 min per 1/4" thickness 50°F per hour Nitrogen
Udel® polysulfone 4 hours to 330°F 30 min per 1/4" thickness 50°F per hour Air
UHMW (Polyethylene) 2 hours to 220°F 30 min per 1/4" thickness 10°F per hour Nitrogen
Ultem® PEI (unfilled) 4 hours to 390°F 30 min per 1/4" thickness 50°F per hour Air
Ultem® PEI (20%, 30% glass filled) 4 hours to 400°F 30 min per 1/4" thickness 50°F per hour Air

Finish machining of critical dimensions should be performed after annealing.

Important: Annealing cycles are generalized. Heat-up and hold times may be adjusted for thin sections. Parts should be fixtured to prevent distortion.

Contact us for additional information or materials not listed.
Trademark Acknowledgments:

RADEL and TORLON are registered trademarks of Solvay Engineering Polymers. RYTON is a registered trademark of Chevron Phillips Chemical Company. DELRIN is a registered trademark of DuPont. ULTEM is a registered trademark of SABIC IP. HYDEX is a registered trademark of Ensinger. ERTALYTE and TECHTRON are registered trademarks of Quadrant Engineering Plastic Products. PEEK is a trademark of Victrex plc.

The information on this page was originally provided by Quadrant Engineering Plastics & Westlake Plastics Company.

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