Seals, O-Rings, and Food-Grade Plastic Parts

Where These Parts Are

Besides stainless steel, an encrusting or forming machine contains quite a bit of rubber and plastic:

• O-rings and seal rings: At the joints between the hopper and the feeding mechanism and at pipe fittings, preventing filling or dough from leaking out.
• Scrapers and scraper blades: Scrape material off the hopper or rollers.
• Bushings and guides: Reduce friction between metal parts.
• Forming molds and cutting parts: Some are made of food-grade resin.
• Conveyor belts: See Conveyor Belt Maintenance, Adjustment, and Replacement.

Most of them contact food directly, and they wear and age more easily than metal.

Do Rubber Parts Need to Be Food Grade?

Yes. Machine parts that contact food directly are food utensils as defined in Article 3 of the Act Governing Food Safety and Sanitation (食品安全衛生管理法), and their materials must meet the Sanitation Standard for Food Utensils, Containers and Packaging (食品器具容器包裝衛生標準):

• Article 3: Food utensils must not show undesirable discoloration, off-odors, off-flavors, contamination, mold, foreign matter, or shedding fibers.
• Article 6 and Table 2: Besides the general provisions, plastic materials must also meet the requirements for the corresponding material in Table 2. Table 2 lists material tests and migration tests for "rubber (excluding infant feeding utensils)," such as limits on lead and cadmium content, and migration limits for phenol, formaldehyde, evaporation residue, zinc, heavy metals, and so on, using solvents such as water, 4% acetic acid, and 20% ethanol under specified conditions. It also covers many plastics, including polyethylene, polypropylene, polycarbonate, and polyamide (nylon).

In the EU, Regulation (EC) No 1935/2004 is the framework regulation for food contact materials. Article 3 requires that, under normal or foreseeable conditions of use, materials must not transfer their constituents to food in quantities that could endanger human health, bring about an unacceptable change in the composition of the food, or deteriorate its organoleptic characteristics. Annex I lists rubbers, silicones, plastics, metals and alloys, and others as material groups for which specific measures may be adopted. Equipment or products exported to Europe may need a relevant declaration of compliance.

When purchasing seals, ask the supplier for test reports showing compliance with the Sanitation Standard for Food Utensils, Containers and Packaging, or other food contact compliance documents required by the destination country. Don't substitute ordinary industrial O-rings from a hardware store for the manufacturer's food-grade parts.

Do Plastic Parts Leach Into Food?

Any material can transfer trace amounts of its constituents to food; the regulations require that these not exceed the limits under specified conditions. Factors that affect migration:

• Temperature: High temperatures increase migration. A part's temperature range must suit the conditions of use and cleaning.
• Fats and acids: Fatty and acidic foods have a greater effect on some plastics, which is why migration tests use different solvents such as n-heptane, acetic acid, and ethanol.
• Aging: Old parts that are cracked, discolored, or rough may shed fragments and are harder to clean.
• Chemicals: Strong alkalis, chlorine-based sanitizers, and solvents can cause some rubbers and plastics to swell or harden.

General characteristics of common materials (actual properties follow the supplier's data):

• NBR (nitrile rubber): Good oil resistance; often used for seals that contact fats.
• EPDM: Resists hot water, steam, and alkaline cleaners, but not oil.
• Silicone: Wide high- and low-temperature range, but poorer abrasion and tear resistance.
• Fluoroelastomer (FKM): Resistant to heat and chemicals, but more expensive.
• POM (polyacetal), nylon, UHMW-PE: Common for wear-resistant parts such as guides, scrapers, and gears.

How Often to Replace

Follow the manufacturer's recommendation and actual conditions. Check during daily disassembly and washing, and replace when you see:

• Cracks, chips, or deformation (flattened and not springing back).
• Hardening or tackiness, or discoloration.
• Rough surfaces, or stains or odors that won't wash out.
• The start of product or oil leaks.

Seals are inexpensive, but a failed one can cause leaks, contamination, or inaccurate weights across a whole batch, so keep them in stock.

Use and Storage

• Don't pry with sharp tools during installation, to avoid cutting the seal.
• If a seal needs lubricating for installation, use a food-grade lubricant.
• Store spares in a cool, dark, dry place. Rubber ages over time, so use first-in, first-out.

FAQ

Q: Do O-rings have to be food grade?
A: O-rings that contact food are food utensils, and their materials must meet the Sanitation Standard for Food Utensils, Containers and Packaging. Ordinary industrial parts should not be used as substitutes.

Q: Does Taiwan have test standards for rubber parts?
A: Yes. Table 2 of the Sanitation Standard for Food Utensils, Containers and Packaging sets material tests and migration tests for rubber (excluding infant feeding utensils).

Q: How often should seal rings be replaced?
A: Follow the manufacturer's recommendation and check them during daily washing; replace them when they crack, deform, harden, or start leaking.

Q: A seal ring won't go in. Can I coat it with cooking oil?
A: Use a food-grade lubricant instead; cooking oil goes rancid easily.