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  • Writer's picturePedro Henriques

Engineering Notebook: Acetal

In this Insight Blog we are transcribing handwritten notes taken over the years working with plastics, the notebook did not site all references so we cannot give credit to where it is due. Machinists took the time to write down knowledge gained and learned, we feel it should be put to use and hopefully help someone reading this to learn from it. All materials have inherent limitations that must be considered when designing parts. To make limitations clear, each material profiled in these engineering notes are dedicated to identifying these attributes. We hope these insights about material strengths and weakness simplifies your selection process.

Engineering Notes: Acetal

When considering Acetal material in your design or application, it is important to understand the different properties of each grade. There are two (2) standard grades of Acetal that are available for machining applications. Homopolymer Acetal, known as Delrin® (Only by Dupont) and Copolymer Acetal. What's the difference: Homopolymers are plastics with molecular chains containing identical DNA repeating its sequence, Copolymers contain two different DNA sequences that repeat. These two grades of Acetal look the same, there chemistry is similar enough to be called Acetal; however, their properties are very different and if overlooked can cause costly part failures. Copolymer Acetal has a lower water absorption rate, performs better than Homopolymers in thermal, wear and chemical resistance. Homopolymers have a higher crystalline structure which gives the material a higher fatigue performance. Acetal performs well in wet environments and can be formulated to various grades like Teflon Filled, internally lubricated/enhanced wear grades. In high moisture or submerged applications, acetal bearings have outperformed standard nylon 4 to 1 due nylon's related growth when exposed to moisture.

Additional Note: Centerline Porosity

Homopolymers are also known to be susceptible to develop centerline porosity when they begin to cool during the manufacturing process (Extruded) because the exterior portions solidify first, creating loss of volume in the interior. Centerline can typically be found as a small circle in the center of a part, as for sheets and rods, it will appear as a white stripe or band in the center or middle of the material.

What Causes Centerline Porosity

The root cause of centerline porosity in Acetal is due to gasses trying to escape the strict extruded “shell” that restrains volume change, causing voids or pockets to form.

Why Be Concerned

Centerline porosity can cause many undesirable effects in applications such as, weakens the part, provide a route for leakages of liquids and gasses, and permit bacterial growth in food processing and/or medical applications.

Copolymer is not as susceptible to develop center-line porosity; however, it is indeed important to keep it in mind that it does happen, and it is in your best interest to choose a different material if you have the option.

Material Notes: Acetron GP is Quadrant EPP's general purpose acetal and is the only porosity-free acetal product available today. Investments in process technology by Quadrant EPP now provide the performance and machinability of acetal without center core porosity. Their in-line photometric quality procedure assures every plate and rod is porosity-free as measured by Quadrant EPP's quick check dye penetrant test. For details of test methods, contact Quadrant EPP. Acetron GP natural is FDA, USDA, NSF, Canada AG and 3A-Dairy compliant.

Known applications:

  • Bearings, bushings, cams, pulleys

  • Pump and valve parts (Impellers, submersible, centrifugal, proportioning, reinforced diaphragms, jet wells, beverage valves

  • Manifolds

  • Gears, spur, cluster, helical, bevel, worm

  • Jigs and fixtures

  • Food process and other packaging machinery parts

  • Wear pads

  • Electrical components

  • Hand mixers

  • Bread slicer motors

  • Door lock housings

  • Fuel system components (gas caps, floats, senders)

  • Heavy load bearing gears (window lifts, windshield wipers)

  • Fasteners

  • Window/door hardware

  • Safety system components (buckles, seatbelt hardware, spools, guide tracks, clock springs)

  • Loudspeaker grilles

  • Control switches

  • Interior trim

  • Steering components

  • Pillar loops

  • Gas and Water meter components

  • Fan and blower blades

  • Farm machinery

  • Irrigation sprinkler components

  • Shower heads

  • Hose couplings

  • Shoe base and pushing caps (Package equipment)

  • Lighter bodies

  • Pen components

  • Zippers

  • Clips, fasteners, buckles

  • Window and drapery hardware

  • Chair coasters, rollers

  • Appliance components (gears, knobs)

  • Garden chemical sprayers

  • Household water softeners

  • Soap dispensers

  • Paint mixing paddles, canisters

  • Scrubbing discs on power rug cleaners

  • Hot air: heater blowers, clothes dryers, automotive light sockets

  • 35 mm slide projector parts

  • Garage door opener components

  • Ski bindings and straps

  • Knife handles

  • Gears (toys)

  • Roller-skate brake supports

  • Salt water: marine fittings, fishing reels

  • Faucet aerators

  • Lawn sprinklers

  • Garden hose nozzles

  • Ballcocks

  • Toilet flush valves

  • Faucet valve cartridges

  • CNC Tool changers

  • Laser printer gear trains

  • Video tape drives

  • Switches

  • Coil forms

  • Telephone terminal strips

  • Relay components, buttons, and knobs

  • Audio and video tape cartridge platforms and wear parts

  • Electromechanical counter frames

Can Acetal Be Used in Abrasive Applications?

In general, acetyls do not perform as well in dry abrasive wear applications as Nylons. Compensation for moisture related growth generally allows Nylatron® nylons to be used for wet, abrasive applications. If your application requires dimensional consistency in an abrasive, high humidity or submerged environment, Ertalyte® PET–P will often offer improved performance.

All trademarks and service marks are property of their respective manufactures. All statements, technical information and recommendations contained in this publication are presented in good faith and are, as a rule, based upon tests and such tests are believed to be reliable and practical field experience. The reader, however, is cautioned that Diversified Designs does not guarantee the accuracy or completeness of this information and it is the customer’s responsibility to determine the suitability of any information provided by Diversified Designs in any given application.

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