1, dust

 

Production is often done on dusty sites, often with lots of dust in the air that constantly land on the surface of the equipment. They can be removed with water or an alkaline solution. However, adhering dust requires high pressure water or steam for cleaning.

 

2, floating iron powder or embedded iron

 

On any surface, free iron can rust and corrode stainless steel doors. Therefore, it must be cleared. Floating powder can generally be removed with dust. Some adhesion is very strong and must be treated as embedded iron. In addition to dust, there are many sources of surface iron, including cleaning with ordinary carbon steel wire brushes and shot blasting with sand, glass beads or other abrasives previously used on plain carbon steel, low alloy steel or cast iron parts, or The aforementioned non-stainless steel door products are ground near stainless steel door parts and equipment. Wire ropes, spreaders and iron on the work surface can easily embed or smear the surface if the stainless steel door is not protected during cutting or hoisting.

 

Ordering requirements and post-production inspections prevent and detect the presence of free iron. ASTM Standard A380 specifies a rust test for inspection of iron or steel particles on stainless steel door surfaces. This test should be used when there is absolutely no iron available. If the results are satisfactory, wash the surface with clean pure water or nitric acid until the dark blue color completely disappears.

 

As indicated in Standard A380, if the rust test solution cannot be completely removed, it is not recommended to use this test method on the process surface of the equipment, ie the direct contact surface used to produce human consumables. A relatively simple test method is to expose the water for 12 to 24 hours to check for rust spots. This test is poorly sensitive and time consuming. These are test tests, not cleanup methods. If iron is found to exist, it must be cleaned by chemical and electrochemical methods described later.

 

3, scratches

 

In order to prevent the accumulation of process lubricants or products and/or dirt, it is necessary to mechanically clean the scratches and other rough surfaces.

 

4. Thermal tempering and other oxide layers

 

If the building door is heated to a certain high temperature in the air during welding or grinding, the chrome oxide thermal tempering color will appear on both sides of the weld, the lower surface of the weld and the bottom. The thermal tempering color is thinner than the oxidized protective film and is clearly visible. The color depends on the thickness and can be seen in iridescence, blue, purple to pale yellow and brown. Thicker oxides are generally black. It is due to staying at a high temperature or for a long time at a higher degree. When any such oxide layer is present, the chromium content of the metal surface is reduced, resulting in reduced corrosion resistance in these areas. In this case, not only the thermal tempering color and other oxide layers are eliminated, but also the chromium-depleted metal layer underneath them should be cleaned.

 

5, rust spots

 

Stainless steel door products or equipment are sometimes rusted before or during production, which indicates that the surface is heavily contaminated. The rust must be removed before the equipment is put into use. The thoroughly cleaned surface should be inspected by iron test and/or water test.

 

6, rough grinding and machining

 

Both grinding and machining can result in rough surfaces with defects such as grooves, overlaps and burrs. Each defect can also damage the metal surface to a depth such that the damaged metal surface cannot be cleaned by pickling, electropolishing or shot peening. Rough surfaces can be the source of corrosion and deposition products. Cleaning weld defects before re-welding or removing excess welds can not be ground with coarse grinding. In the latter case, it should be ground with a fine abrasive.