Stainless steel has many properties that make it attractive for a variety of applications, but these same properties can make it difficult to work with. During use, it is easily scratched and soiled, making it prone to corrosion. Last but not least, it is more expensive than carbon steel, so the material cost issue is exacerbated when stainless steel parts are produced.
Customers also have high expectations for the quality of the finish, demanding an almost mirror-like finish for a material that by its very nature will be presented as a finished product. There is very little chance of hiding the error with coating or paint.
When working with stainless steel pipes, these problems are exacerbated to a certain extent, since the choice of optimal and effective tools for easy material processing to finishing is limited.
Due to its corrosion resistance, stainless steel is ideal for applications that require the natural sheen of the metal, such as steering wheels and armrests. This also means that the outside diameter of the tube can vary from frosted to a smooth, flawless appearance.
This requires the right tool combined with the right abrasive. Often the first question we ask our customers is what investment they are willing to make to ensure that they get the desired pipe finish quickly and consistently. For those who want to keep a steady flow of pipe finishing orders, automating the process with a centerless grinder, cylindrical grinder, or other type of belt machine can certainly make it easier to sort parts to achieve the desired result. Finished product stability can also be achieved from part to part.
However, there are also options for hand tools. Depending on the size of the pipe, a belt grinder can be an effective way to ensure that the part geometry does not change during the finishing process. The use of belt slack allows the tubular profile to work without flattening it. Some belts have three contact pulleys, allowing for more flexibility around the tube. Belts are available in various sizes. File bands range from 18″ to 24″, while King-Boa requires 60″ to 90″ bands. Centerless and cylindrical belts can be 132 inches long or longer and up to 6 inches wide.
The problem with hand tools is that getting the right finish over and over again is more of an art than a science. Experienced operators can achieve excellent finishes with this technique, but it takes practice. In general, higher speeds result in finer scratches, while lower speeds result in deeper scratches. Finding a balance for a particular job depends on the operator. The recommended tape start speed depends on the desired end point.
However, it is important to avoid the use of disc or hand grinders of any type for processing pipes. It’s hard to get the pattern you want with these tools, and if you push the dial too hard, it can affect the geometry and create a flat spot on the pipe. In the right hand, if the goal is to polish a mirror surface rather than a scratch pattern, many sanding steps will be used and the last step will be a polishing compound or polishing stick.
The choice of abrasive requires a clear understanding of the final finish. Of course, this is easier said than done. Visual inspection is typically used to match parts with existing products. However, the shop abrasive supplier can help determine how best to gradually reduce the amount of abrasive to achieve the desired result.
When grinding stainless steel to the final surface, it is important to use a stepwise abrasive process. Initially, you want to make sure that all stains and dents are removed. We want to start with the best product to address these shortcomings; the deeper the scratch, the more work is required to fix it. At each subsequent step, care must be taken to remove scratches from the previous abrasive. Thus, a uniform scratch pattern is achieved on the finished product.
With traditional coated abrasives, it can be difficult to skip grades of abrasive to get the right matte finish on stainless steel due to the way the abrasive breaks down. However, some technologies allow you to skip steps, such as 3M’s Trizact abrasives, which wear in such a way that the abrasive is “refreshed” with new exposed grain as it is used. 3M
Of course, determining the degree of roughness of an abrasive depends on the material. If you need to remove defects such as scale, dents or deep scratches, you will need to use a coarse abrasive. For example, we usually start with a 3M 984F or 947A conveyor belt. Once we moved to 80 grit belts, we switched to more specialized belts.
When using traditional coated abrasives, be sure to reduce the gradation of each abrasive without missing it due to how the abrasive breaks down to get the correct matte finish on the stainless steel. Once the abrasive breaks down, more pressure is required to achieve the same result as the minerals darken or are removed from the abrasive. Matte minerals or higher forces generate heat. Because heat is a problem when finishing stainless steel, it can affect the finish and “blue” the surface.
Another issue that can arise with some cheap abrasives is the consistency of their finishing minerals. It will be difficult for an inexperienced operator to ensure that the abrasive obtains the desired surface at each step. If there are any inconsistencies, wild scratches may appear that may not be noticed until the polishing stage.
However, some methods allow you to skip steps. For example, 3M’s Trizact Abrasive uses a mixture of resin and abrasive to create a pyramidal structure that renews the abrasive surface with newly exposed particles even as the abrasive wears. This technology ensures a consistent finish throughout the life of the belt. Because each grade of Trizact tape provides a predictable finish, we were able to skip the abrasive grades in the final finish. This saves time by reducing sanding steps and reducing rework due to incomplete sanding.
The key to choosing an abrasive is determining how to get the right finish in the most time and cost efficient manner.
Since stainless steel is a hard material, the choice of abrasive and minerals is very important. When using the wrong abrasive, the longer the material is processed, the more heat is generated. It is important to use the correct type of mineral and to use an abrasive with a heat dissipative coating to remove heat from the contact zone when sanding.
If you’re using a machine, you can also use part coolant, which also helps remove debris, ensuring debris scratches don’t damage the surface. Be sure to use the correct filter so that debris does not re-enter when the coolant is recirculated in the machine.
Most people think that all stainless steel looks the same, but when it comes to the finished surface of a part, two different types of minerals can affect the look of that part. This view is user dependent.
For example, traditional silicon carbide tends to leave deeper scratches that reflect light differently and make it blue.
At the same time, traditional aluminum oxide leaves a more rounded shape that reflects light differently and makes the material yellow.
Depending on the size of the pipe, a belt grinder can be an effective way to ensure that the part geometry does not change during the finishing process. The use of belt slack allows the tubular profile to work without flattening it. 3M
Knowing the required finish of a part is important because applications often require new parts to match existing ones.
Stainless steel is an expensive material, so careful selection of finishing tools is important. Proper support from suppliers can help stores find ways to save time and money.
Gabi Miholix is ​​an Application Development Specialist in the Abrasive Systems Division of 3M Canada, 300 Tartan Dr., London, Ontario. N5V 4M9, gabimiholics@mmm.com, www.3mcanada.ca.
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