Guides / Design

Acetal Parts for Food Processing Machines: Guides, Scrapers and Change Parts

October 5, 2026

Food processing lines use plastic for the parts that touch product or sit close to it: guides, scrapers, star wheels, rollers, wear strips, bushings and format change parts. They need to run quietly, resist wash-down, avoid trapping product and survive a cleaning regime that would corrode many metals. Acetal is a common choice, and the grade, the paperwork and the shape of the part all matter.

Typical food line parts in acetal

Part	Role	Notes
Guide rails and side guides	Position product on a conveyor	Smooth faces, see the wear strips guide
Scraper blades	Clear product from belts and drums	Edge condition affects wear on the belt
Star wheels and screws	Separate and meter containers	Tight tolerance on pockets
Change parts	Adapt a line to a new product size	Made in sets, labelled and colour coded
Rollers and idlers	Support belts and webs	See the rollers guide
Bushings and gears	Run drives in the splash zone	Low friction without grease
Cutting boards and blocks	Backing for knives	Replaceable wear surfaces

Compliance paperwork to ask for

A part that touches food needs materials that are allowed for food contact. The paperwork belongs to the grade and to the finished part:

Item	Typical request
United States	A statement from the resin or stock maker that the grade meets 21 CFR 177.2470 (polyoxymethylene copolymer) or 21 CFR 177.2480 (polyoxymethylene homopolymer), with conditions of use
European Union	A declaration of compliance for plastic food contact materials under Regulation (EU) 10/2011, with migration limits and conditions
General framework in the EU	Regulation (EC) 1935/2004, which sets the base rules and traceability
Metal detection	A detectable grade, usually blue, if the line has metal detectors or X-ray
Traceability	Lot number from stock to part, kept for recall needs
Colourants and additives	Listed and compliant

This is a pointer, not legal advice. Rules differ by country and by type of food and temperature of contact. The food grade guide covers detectable grades in detail. A shop that machines the part should use stock with the declaration and avoid cross-contamination with other materials, such as metal chips, coolant with non-food additives and release agents.

Cleaning chemicals and temperature

Food plants clean with a mix of alkaline foam, acid descaler, sanitiser and hot water. Acetal’s tolerance varies:

Agent	Typical behaviour
Alkaline cleaners	Generally good, copolymer is better
Neutral detergents	Good
Strong mineral acids	Attacks acetal
Chlorine-based sanitisers	Can degrade the surface, check concentration
Peracetic acid	Check concentration and exposure time
Hot water and steam	Limited, particularly for homopolymer
Quaternary ammonium sanitisers	Usually acceptable

Check the exact cleaning chemicals and the temperature, and compare them with the grade data. The chemical resistance guide lists general behaviour. Copolymer is often the better pick for repeated wash-down, as explained in the copolymer versus homopolymer guide.

Hygienic design of the part

A food part has to be cleaned easily, and design affects that:

• Smooth surfaces. Product contact surfaces are often specified with a roughness of Ra 0.8 micrometres or finer in hygienic design guidance, though the right value depends on the application. Agree a value with the shop, as in the surface finish guide.
• Generous inside radii. Sharp internal corners trap product and are hard to clean. Radii of 3 mm or more are a common recommendation.
• No dead pockets. Avoid blind holes and crevices where product can sit.
• Avoid threads in the product zone. Threads trap residue. Use through-bolts with sealed caps or fasteners outside the product zone. See the threads guide if threads are unavoidable.
• Drainage. Slope surfaces so liquid runs off.
• Clean edges. Burrs and fuzz release fragments. See the deburring guide.
• No cracks. Stress cracks are hiding places for bacteria, so avoid sharp notches and heavy interference fits.

Colour, marking and identification

Colour coding of change parts is common, with each product size having its own colour. Natural acetal shows contamination well, while blue acetal serves detection. The black versus natural guide discusses how colour affects inspection. Marking of part numbers should use a method that does not leave loose ink or flakes in the product zone. Laser marking is covered in the laser marking guide, and note that marking depth can create a cleaning trap.

Wear and replacement

Plastic parts in contact with product wear and shed fine particles. A worn scraper or guide should be replaced on a schedule before fragments appear. A spare set of change parts and a wear log reduce risk. Choose a grade that wears slowly against the belt or chain, and make the part so that wear is visible, for example with a thickness gauge groove.

Machining and handling at the shop

• Use stock with the compliance declaration and keep the lot number on the paperwork.
• Use a coolant that is compatible, or machine dry, and wash the finished part.
• Keep acetal separate from metal chips and from other plastics that might contaminate.
• Pack parts in clean, sealed bags with the lot code.

For the questions to ask a shop, see the supplier selection guide.

Inspection and audit trail

Food plants audit their suppliers, and the part’s paperwork matters as much as the part. A short file per order covers most questions:

Document	Purpose
Stock certificate and food contact declaration	Shows the grade and compliance basis
Lot trace from stock to part	Supports recall and complaint handling
Inspection report	Shows dimensions and surface finish checked
Cleaning and packing record	Shows how the part left the shop
Drawing revision	Ties the part to the approved design

Keep these records for the period your quality system requires. When a part changes, for example a new stock source or a new cleaning method, update the file and tell the buyer. A part that passes a visual check but lacks its declaration can still fail an audit. Asking for the file with the first order and again whenever stock changes avoids surprises later.

Checklist before you request a quote

• State the food type, temperature and the cleaning chemicals and their concentrations.
• List the compliance documents required and whether detectable grade is needed.
• Specify the surface finish and radii for product contact faces.
• Mark threads and blind holes, or avoid them.
• Ask for lot traceability and clean packaging.
• Give the quantity and the number of change parts in a set.

Send the drawing and we match it with up to three shops that machine acetal and reply within 24 business hours.

Frequently asked questions

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