Artem Komarov clarified that to get the most common stainless-steel finish, you often must follow many steps in a specific order. Because of this process, and because stainless steel is more susceptible to heat and contamination, you may find that the material is more time consuming and more expensive to work with than carbon steel.
It is important to understand how stainless steel reacts to finishing and why it is important to use products specifically designed for this material. This can save you time and money by allowing you to achieve the results you want.
Problems associated with finishing stainless steel.
Stainless steel is used in many industries where high purity or special aesthetic requirements are important, including food service, medical, aerospace, energy, and architectural metalworking. Although the material has strength, long life, and corrosion resistance, it presents some problems in welding and finishing. Here are a few factors to consider:
— Stainless steel is susceptible to contamination. In fact, it may be more prone to contamination than carbon steel. In applications where high cleanliness is important and most welds are X-ray inspected, such as medical equipment and power generation, it is important to maintain uniformity throughout the weld and avoid inclusions to avoid contamination. This also applies to the finishing process. You don’t want the finishing process to introduce contaminants that can later corrode the weld or weaken the joint.
— Stainless steel is soft. Because it is softer than higher carbon steel, it is easier to damage or gouge the workpiece. Take extra precautions to avoid removing too much material which could subsequently weaken the weld. Stainless steel also discolours when heated, so excessive pressure during grinding or finishing can turn the metal purple or brown, requiring secondary treatment to remove the stains, costing you time and money.
— Stainless steel finishing is a multi-step process. To properly sand stainless steel, you must follow certain steps and be guided by the grit level of the abrasives you are using. No single product can do it all when it comes to finishing stainless steel. Usually start with a bonding abrasive to remove heavy residues, move on to a flap disc for mixing, then use a polymer fiber disc to mix the starting material into the weld, and finally finish with a polishing or grinding disc. While it can be tempting to skip steps to save time, it can lead to costly rework if the results aren’t what you want.
— Mistakes that lead to rework and abandonment are costly. Reworking stainless steel can cost twice as much as reworking carbon steel. To begin with, stainless steel is a more expensive material than carbon steel and usually requires more labor. Stainless steel is less forgiving, and you must watch the finishing process carefully to avoid damaging the material. Abrasives used on stainless steel can also be more expensive because they require contaminant-free products.
Do’s and Don’ts When Finishing Stainless Steel
Because stainless steel can be a difficult and costly material to work with, it is important to get proper preparation before you start grinding and finishing it.
- Choose products based on your finishing requirements. Common types of stainless-steel finishes are non-directional polished, No. 4 finish, or mirror polished. The choice of abrasive depends on the requirements for visual finish or medium roughness (Ra). For coarse sanding, a 36 or 40 grit disc works well. But if you want a mirror finish, you need to increase the grit and add some polishing compounds or fiber wheels to polish the material to the desired appearance. A product specifically designed for stainless steel will work more efficiently with this material because it will cut faster, last longer, and dissipate heat better than a product designed for carbon steel.
- Avoid cross contamination. Just because a product is labeled for use with carbon or stainless steel does not mean it is free of contaminants. The contaminant-free product contains less than 0.1% iron, sulfur and chlorine—elements that cause oxidation.
- Start with the desired finish of the base material. A common practice to save time and money in many operations is to have the base material pre-processed to the required specifications. For example, a base sheet metal part can be machined in the process of welding with directional machining No. 4 or mirror polished on a machine. This minimizes the amount of finishing you must do by hand after the parts are welded together.
- Don’t apply too much pressure. With abrasives, pressure equals heat, and heat can damage stainless steel more easily than carbon steel. You can control the temperature when sanding or finishing by applying less pressure and letting the abrasive brush or disc do the job as intended.
- Continue moving the product. When grinding or finishing stainless steel, use a uniform and consistent pattern. Staying in the same room for too long can lead to heat build-up that can damage the base metal and lead to more time and rework.
- Do not neglect safety precautions. The use of appropriate personal protective equipment (PPE) is important in all welding and finishing work on metal, but especially on stainless steel. When finishing any steel, it is recommended to use a respirator due to the dust generated from the abrasives as well as the base material. Stainless steel poses an additional hazard due to the large amount of nickel that can be released into the air along with other particles during grinding, which can cause lung damage.
- Document the process. A detailed description of the step-by-step process for finishing stainless steel is important to get consistent results every time. This helps avoid guesswork and reduces the likelihood of rework. This is especially important for applications that require a very specific finish that will be measured every time, such as in the medical or food industries. Your documentation should list the processes you use and the specific type and grit of abrasives for each step.
In addition to choosing the right product for your application and the finish you require, it’s also important to follow the steps in the finishing process and understand how stainless steel reacts. This will help you reduce rework, save time and money, and achieve the best results when working with stainless steel, emphasized Komarov Artem.
