The food industry has stringent standards for many aspects of food safety, including all the contact surfaces used in the packaging and manufacturing of food products. Here are just a few examples of some of the standards that exist for metal fabrication in Umatilla County, OR for the food industry, as written in USDA guidelines.
Surfaces and finishes
“All product contact surfaces shall have a finish at least as smooth as a number 4 ground finish on stainless steel sheets, free of pits, cracks, folds, and other imperfections in the final fabricated form. The surface finish obtained by 150 grit silicon carbide properly applied to stainless steel sheets is considered as equivalent to the number 4 finish. A maximum Ra of 32 microinch (0.8 micron) is considered to be equivalent to a No. 4 finish.
The 2B mill finish on stainless steel sheets is also considered as smooth or smoother than a polished number 4 finish. No further finishing is required if the 2B finish is free of defects, such as pits, scratches, chips, or flakes, in the final fabricated form. (Use of adhesive protective paper is recommended during equipment fabrication to prevent or minimize damage to stainless steel finishes.)
Note: The 2B finish on stainless steel plate and bars is usually not as smooth as the number 4 finish on sheets due to less cold rolling and therefore unacceptable for product contact surfaces without additional surface preparation.
Mechanical surface treatment by shot peening or glass beading of product contact surfaces is acceptable provided the treatment serves a specific functional purpose, i.e., in order to prevent product sticking on butter and mozzarella cheese equipment. The surface which is to be treated must be either a 2B mill finish or have been prepared to the equivalent of the number 4 finish.
Electropolishing, glass beading or shot peening surface treatments are not acceptable alternatives to the required grinding and polishing of welded junctures to a number 4 finish. Surfaces are to be properly prepared prior to the application of these treatments.”
“Permanent joints for product contact surfaces (not intended for disassembly for cleaning) shall be designed so they are fully cleanable when assembled… The following are acceptable methods of fabrication:
- Continuously welded, ground, and polished to a number 4 finish which is free of pits, folds, crevices or projections, except that; Welds in aluminum product contact surfaces shall be free of pits, folds and crevices using the Gas Metal-Arc Welding (GMAW) process with backing bar, the Gas Tungsten-Arc Welding (GTAW) process, the combination of GMAW and GTAW, or equivalent process. The completed weld shall be lightly finished with a stainless steel wire brush, resulting in maximum weld surface irregularity of twelve thousandth of an inch (0.03mm) differential within 1/8 in. (3mm) increments. The maximum weld height shall be 1/8 in. (3mm). b. Properly constructed gasketed junctures. Flanged junctures shall be mated accurately and be constructed so the sealing edges of the flanges are not chamfered or radiused. The juncture shall create a tight pinch seal with the gasket. Interior surfaces shall be substantially flush, with no recesses or protruding unsupported gasket material.
- Silver soldered, brazed, or vacuum brazed.
- Press fits or shrink fits may be used to produce crevice free permanent joint in product contact surfaces when welding is not practical. Joints of these types may only be used to assemble parts having circular cross sections free of shoulders, chamfers, or relieved areas, or knurled surfaces. For example: they may be used to assemble round pins or round bushings into round holes. In both types of fit, the outside diameter of the part being inserted is greater than the inside diameter of the hole.”
There are many more regulations listed in the USDA guidelines, so be sure to read those thoroughly so you know all of the metal fabrication standards for the food industry. For more information or with questions about metal fabrication in Umatilla County, OR, reach out to NW Metal Fabricators Inc. today.
Categorised in: Metal Fabrication
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