Above: A nylon flap brush followed by polishing with a buffing wheel and cutting/polishing compound can create a satin finish on a pressure vessel.
February 2018 - Fine grinding, by definition, is the blending of the weldment to the surface of the metal for a smooth, consistent and attractive appearance. When working on stainless steel grades, choosing the right equipment and consumables for each step of the process will help you produce the desired result. This applies to the finishes for appliances, structural parts, visible sheet metal housings that are not painted or coated, and architectural adornments.
Here are some typical applications and tips on how handheld grinding equipment and consumables can affect a better outcome in your shop or production department.
1. Blending welded connections on railings
Blending welded surfaces on corners, squares, and rounds is the key to producing attractive welded connections on railings. We recommend using 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. For pipes and tubes, use a tube polishing wrap. Grain sizes to 320 will produce the desired results even on extremely small radii.
The proper use of the regulated speed on the grinder will help you achieve the optimal finish, so it is best to choose tools with speed regulators. An adjustable belt grinder arm on the tool will make the tool easier to use, lessen operator fatigue, and yield better results.
2. Prepping and finishing on pressure vessels
For a typical No. 4 finish with RA 15-25 on a pressure vessel, we recommend shops employ a 40- to 320-grain belt grind and finish with a flap brush. A satin finish can be achieved by using a nylon flap brush followed by polishing with a buffing wheel and a cutting/polishing compound.
Many popular tools offer quick-change tooling systems to reduce downtime and many are portable. Operator fatigue is reduced when the portable tools have detachable hand pieces so the weight of the entire drive unit doesn’t need to be carried from work cell to work cell. 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 provide long service life and minimum wear.
3. Grinding work on commercial foodservice grills
Many shops around North America are assembling commercial cooking appliances, especially as sales for outdoor and food truck applications increase. Reducing surface weld beads is a key challenge when working on commercial foodservice grills. We recommend that shops start by rough grinding with a pneumatic grinder with 36- to 80-grit discs. Finish grind with a pneumatic drum with a 40- to 220-grit abrasive belt.
Then work all surfaces with an extended pneumatic straight grinder and 60- to 240-grit fiber brushes. Finishing discs of synthetic fiber, grit and resin will eliminate welding discoloration.
4. Polishing 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 pre-polish wheel and polishing compound. Polish the surfaces with a polishing wheel and polishing compound, then complete the mirror finish using a buffing wheel and a polishing paste.
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, we recommend the use of a drum sander with a 40- to 220-grit zirconium blend belt. Cover with a template. Use a surface conditioning belt for a fine finish. For a satin finish, use a 100- to 200-grit fine flap brush.
6. Graining process for welds on stainless steel
We suggest operators begin the graining process on a stainless steel weld with a pre-grind. The best tool would be a pneumatic right-angle grinder with a plastic support plate with a cooling effect and an 80-grit fiber disc. Finish with a pneumatic drum using a straight grinder.
Grain the surface using a right-angle grinder with nonwoven, medium or high hardness finishing discs. Grind the weld bead with a 120-grit grinding belt and a 40- to 320-grit finishing belt.
7. Eliminating the orange peel effect
To smooth the orange peel effect that is sometimes seen on surfaces after treatments, we suggest beginning with a rough prep using a 40-grain belt. Then fine grind with a soft contact roller and Suhner A160 Trizact belt. Satin finish with a soft contact roller and medium surface conditioning belt. One can achieve an industrial-grade finish by using a flap brush and 220-grain abrasive pad.
8. Grinding inside corners
To finish the inside corners of a stainless steel component, it is best to begin by smoothing the weld with an electric angle grinder with an 80-grain mini-flap wheel. Then fine surface grind using an electric angle grinder and soft disc (between an A160 and A16 grain) with a Trizact grinding wheel. Then, we suggest the use of an electric file and nonwoven pads between a 60- and 400 grain to define the surface grain.
9. Grinding and polishing extruder feeds
We recommend starting with a preliminary grind on an extruder feed shaft using a belt grinder and zirconium corundum belt (40- to 80-grain) to grind and polish extruder feeds. Work the flanks with 80- to 120- grain Velcro fiber wheels. Fine grind the shaft and flanks with a roll attachment. Polish with twisted polishing rings and polishing paste, especially when working with stainless.
The guidelines here provide a starting point to plan your finishing jobs but most tool and abrasive suppliers are ready to offer suggestions for everyday or particularly challenging applications. If you have questions, take advantage of their experience.
Aaron Beck is national sales manager, abrasives and power tools, at Suhner Industrial Products.
Suhner Industrial Products
706/235-8046
www.suhner.com
