GETTING THE RIGHT FINISH FOR STAINLESS STEEL FOOD GRADE APPLICATIONS AND USAGES
The processes of designing, assembling, finishing, and cleaning equipment for food-grade applications has a number of applications, regardless of the alloy used, and the requirements in every step have to be met. Food grade surfaces need to have a sanitary finish that is safe for processing food products and easy to clean.
To prevent growth of bacteria, the surfaces should be devoid of lines, grooves, pits, or divots. Plus, they should be able to withstand corrosion from food and chemicals.
In most of the applications, a finish at the high end of No. 4 is appropriate for food grade. This finish is done by using a high-grit abrasive in the range of 150-220 and is identified by short, parallel lines that run the length of the material. To determine the finish’s surface roughness average (Ra), a diamond stylus is moved across the workpiece’s surface for a particular distance and using a specified contact force. In most food-grade applications, 60-36 Ra is achieved with 150-220 grit. Dairy products spoil quicker and carry more bacteria, and therefore require a finer finish, No. 4A (40-24 Ra achieved with a 220-grit abrasive or finer).
Areas that do not come in direct contact with food don’t need to adhere to the sanitary finish guidelines, but should be able to withstand the harsh treatment of cleaning and sanitizing.
Finishing the inside of a pipe or tube is challenging. After flushing out welding slag, long arms and elbow grease are the best tools to use. For small diameters, one can mount a flap wheel to a flexible shaft. For the length of the pipe, simple tools like an abrasive mounted on a long broomstick can be used.
Choosing abrasives and tools
The abrasive and the tool should be picked together, not separately, in order to know the right combination for the job.
For each project, several products with various grits are needed to achieve the final finish. Conventional abrasives composed of aluminum oxide or zirconium are recommended, although ceramic materials are also used these days. Fleece is a non-woven abrasive that provides an even finish without shadows, reducing surface chattering with its softness. Unitized abrasives are also another useful class of abrasives.
Due to the unique design of most fabricated pieces, only very few make mass production of a finish possible. As a result, most finishing is done by hands or using hand tools.
Choosing the right tool and abrasive are only a part of the job. We still need to make sure the geometry of every component meets the requirements. Round pipes are better suited for circumferential finishing while square pieces are best finished lengthwise on all the four sides in the same direction. Going around all for sides at once will lead to an uneven finish with poor grain quality. Flat expanses of material should be taken a section at a time for best results, and always working in the same direction. The areas where the sections join need to be carefully paid attention to and blended until the transitions become nonexistent.
The customer’s expectations are of utmost importance. Simple finishes have a lower time-cost factor than a more difficult one.
Before assembling them, one should ensure that all the pre-ingrained pieces have a consistent pattern. While welding together two or more pieces, the grain patterns have to be aligned as closely as possible, as any mistake in this will be impossible to correct later.
To increase productivity and reduce total expenses, always select the right application-specific tool required for the project. Making the finished spot as a starting mark, work towards the unfinished parts. Do not go in the other direction as it may lead to mismatches.
Do not hurry. To achieve the best possible finish, you need time and patience. Hurrying may result in you choosing an unsuitable material, which might be aggressive and need too much pressure. Or do not use your tools at such a high speed that it becomes incapable of application. You might leave the surface rough, with scratches and it might need rework.
Finishing a food-grade project successfully requires immense technical knowledge and adherence to established guidelines. At Diamond Brite Metals, we are consistently trying to enhance metal processes and provide you extensive knowledge on metal industry. Visit our website to know more.