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Food Grade Welding
Welding food grade stainless steel is delicate work that requires a deft touch. It can be all too easy to make some severe welding mistakes if the designer or welder aren’t aware of the specific requirements of the specific food application the steel wire basket or tray is going to be used for.
So, what are some of the worst food grade welding mistakes and how can they be avoided?
The Case for Sanitary Welding
Stainless steel has become a standard material used for construction of product-contact equipment in the produce industry. As operators have
adopted routine use of this material, I have noticed one issue that causes occasional concern. Quite often, stainless steel
parts assembled into produce handling structures are welded together. While visiting produce packing and processing operations I have noticed wide variation sin the quality of welds on production
equipment. Welding is an art that involves a great deal of science. It is a skill requiring considerable knowledge anda great deal of judgment acquired only
through practice. My observations lead me to believe that there is considerable variation in the welding skills of those constructing and repairing produce handling equipment.
What grade of stainless steel is food grade?
When looking for the most common type of food grade welding material you have to consider this ” The most common food grade stainless steel is Type 304. But 304 grade stainless steel also goes by another name or code, 18/8 and 18/10 stainless steel. These numbers refer to the composition of the stainless steel; the amount of chromium and nickel in the product. Both 18/8 and 18/10 contain 18% chromium, and 8% or 10% of nickel respectively.
304 grade stainless steel is so popular in the food industry because of its resistance to oxidization and corrosion. The chromium protects the product from oxidization or rust, whereas the nickel content rescues the food grade drum from corrosion. The higher the nickel content, the more resistant the stainless steel is to corrosion.
Here are tip to help you weld food grade material
The key to any good weld is clean metal, but what is the best way to clean metal before you start welding? Depending on the tools you have and the overall goal of the project there are a few ways to prep your metal to get a nice clean weld every time.
The best welds come from pure clean metal to metal contact, any foreign materials in the welding area can cause welding imperfections. Even brand new metal must be prepped before it can be welded because there is usually a coating put on new metal so it does not rust or oxidize during the shipping process. This is a factor that is often overlooked and will always result in a weak and ugly weld. Be mindful, once you remove this coating the metal is exposed to the elements, if left out unprotected steel will begin to rust, even indoors.
To start, the type of welding you are doing will determine how you prep the metal. Inherently MIG welding steel does not need the metal to be perfectly clean. On the other extreme, TIG welding aluminum requires contaminant free metal to create a strong clean weld. In all of the examples below you can see the difference the dull color of the “new metal” (left) compared to how it looks after it is properly prepped (right).
No. 1: Blending Welded Connections on Railings
Blending welded surfaces on corners, squares, and rounds is the key to producing attractive welded connections on railings (see Figure 1). Use 40-, 60-, or 80-grain belts in a belt grinder to grind down the weld. Then use a coarse, medium, fine, or ultrafine conditioning belt to blend the surface. For flat surfaces, use an elastic drum and nonwoven nylon flat brush. Use a tube polishing wrap for pipes and tubes. Grain sizes up to 320 will produce the desired results even on extremely small radii.
Using a grinder with a speed regulator will help you achieve the optimal finish. An adjustable belt grinder arm on the tool makes it easier to use, decreases the fatigue you’ll experience, and yields better results.
No. 2: Prep and Finishing Work on Pressure Vessels
For a typical No. 4 finish with RA 15-25 on a pressure vessel, use a 40- to 320-grain belt grind and finish with a flap brush. You can create a satin finish by using a nylon flap brush followed by polishing with a buffing wheel and a cutting/polishing compound (see Figure 2).
Many finishing tools offer quick-change tooling systems to reduce downtime, and many are portable. Keep in mind that portable tools with detachable handpieces reduce fatigue because they don’t have to carry the weight of the entire drive unit (see Figure 3). Some models are available for working in very confined and hard-to-reach places.
Look for dust-sealed units with low noise levels and vibration-free operation. Air-cooled induction motors can provide long service life and minimum wear.
No. 3: Grinding on Commercial Food Service Grills
Reducing the size of surface weld beads is a key challenge when working on commercial-grade food service grills (see Figure 4). Start by using a pneumatic grinder with 36- to 80-grit discs to rough-grind the surface. Finish with a pneumatic drum with a 40- to 220-grit abrasive belt, and then work all surfaces with an extended pneumatic straight grinder and 60- to 240-grit fiber brushes. Finishing discs made of synthetic fiber, grit, and resin will eliminate welding discoloration.
No. 4: Polishing Stainless Steel Tubes to a Mirror Finish
To polish a stainless steel tube to a mirror finish, begin by preparing the surface with a belt grinder using an 80- to 120-grit zirconia belt. Then switch to a surface conditioning belt for medium to ultrafine finishes. Use a prepolish wheel and polishing compound.
Polish with a polishing wheel and polishing compound, and then complete the mirror finish using a buffing wheel and a polishing paste (see lead photo).
No. 5: Grinding Weld and Miter Joints on Structural Steels
Remove the weld beads from structural steel miter joints using 60- to 150-grit zirconium-fiber discs. Then use a drum sander with a 40- to 220-grit zirconium-blend belt. Cover with a template. A surface conditioning belt will give you a fine finish, while a 100- to 200-grit fine flap brush will result in a satin finish.
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