The Difference between Polishing and Pickling & Passivating
As we all know, for beer brewing tanks, the interior shell comes into direct contact with brewing water, mash, wort, or beer. Therefore, most brewers pay great attention to the precision of polishing the inside surface. Improving the polishing precision becomes extremely important.
In general, we use “RA” to measure the polishing precision. The lower the RA value, the higher the polishing precision and sanitary class. For example, RA 0.2 is better than RA 0.4.
Now, let’s compare two different manufacturing technologies regarding the polishing precision: polishing and pickling & passivating.
The Manufacturing Process of Polishing Tank Inside
1. Roll and weld the stainless steel plate into a cylinder with a conical bottom.
2. Surround and weld the dimple plate onto the cylinder and conical bottom.
3. Polish the inside of the cylinder. First, the workers manually polish to remove obvious welding slag. Then, a professional machine with different abrasive belts is used for further polishing: 80 mesh belt (RA = 0.2mm) → 120 mesh belt (RA = 0.12mm) → 240 mesh belt (RA = 0.6um) → 400 mesh belt (RA = 0.2um). When using a 240 mesh belt, the RA value inside the tank will be 0.4-0.6um, making it sanitary enough for beer brewing. For stricter brewers, they may require an RA value lower than 0.4um, so we use a 400 mesh belt for higher polishing precision. The same polishing process is applied to the conical bottom and dished top of the tank.
4. Fabricate and weld the top, cylinder, and bottom together.
The Manufacturing Process of Pickling & Passivating
1. Roll and weld the cylinder with a conical bottom.
2. Fabricate and weld the top, cylinder, and bottom together.
3. Surround the dimple plate onto the cylinder and conical bottom.
4. Fill the tank inside with water.
5. Weld the dimple plate.
6. Perform pickling & passivating on the tank inside for 2 days. If it is winter, the time needs to be extended to 3 days for optimal reaction.
7. After 2-3 days, clean the acid, and the RA value will be 0.2-0.3um.
Comparison between Polishing and Pickling & Passivating
Regarding polishing, when welding the dimple plate onto the cylinder, the cylinder is not very strong without the top and bottom. Therefore, workers need to put a supporting ring in the cylinder to prevent the shape of the cylinder from easily changing.
However, for pickling & passivating, the dimple plate of the cylinder is welded after assembling and welding the top and bottom. At this point, the cylinder is very stable and strong, so there is no need to worry too much about the welding altering the shape. Moreover, the workers fill the tank with water before welding the dimple plate. This speeds up heat dissipation and better avoids carbonization.