1. Dust on the surface of ductile castings

The production of steel castings is often carried out in dusty places, and there is often a lot of dust in the air, which constantly falls on the surface of the equipment. They can be removed with water or alkaline solutions. However, sticky soils require high pressure water or steam to clean.


2. Floating iron powder or embedded iron on the surface of ductile iron castings

On any surface, free iron will rust and corrode stainless steel. Therefore, the floating powder will generally fall off with the dust. It has a certain adhesion and is regarded as embedded iron. In addition to dust, there are many sources of surface iron, including plain carbon steel wire brushing and shot peening with sand, glass beads, or other abrasives previously used on plain carbon steel, low alloy steel, or cast iron, or the aforementioned non-stainless steels Stainless steel products near parts and equipment are ground. If stainless steel is not protected during cutting or lifting, wire ropes, spreaders and irons on the work surface can easily embed or stain the surface.


Order requirements and post-factory inspections can prevent and detect the presence of free iron. ASTM Standard A380 specifies a rust test method for examining iron or steel particles on stainless steel surfaces. This test method should be used when iron-free is required. If the results are satisfactory, wash the surface with clean purified water or nitric acid until the dark blue color disappears.


As stated in Standard A380, this test method is not recommended for use on technical surfaces of equipment, i.e. direct contact surfaces used in the production of human consumer products, if the rust prevention test solution is not completely clean.


An easier way to test is to expose it to water for 12 to 24 hours to check for rust spots. The test is less sensitive and time-consuming. These are test tests, not clean methods. If iron is found, use the chemistry described later. and electrochemical cleaning.


3. Nodular casting scratches

Mechanically clean scratches and other rough surfaces to prevent accumulation of process lubricants or product and/or dirt.


4. Rust spots on ductile castings

Stainless steel products or equipment sometimes rust before or during production, indicating a heavily contaminated surface. The rust should be removed before the equipment is put into use, and the cleaned surface should be checked by iron test and/or water test.


5. Rough grinding and machining

Both grinding and machining result in rough surfaces with defects such as grooves, overlaps and burrs. Each defect also damages the metal surface so badly that the damaged metal surface cannot be cleaned by pickling, electropolishing or shot peening. clean up. Rough surfaces can be a source of corrosion and deposition products. Before re-welding, clean up weld defects or excess weld stiffeners and do not use rough grinding. In the latter case, fine abrasives should be used for grinding.