Dross are iron oxides that form on the surface of hot rolled steel. The scale is bluish-black. Before painting steel products, the scale must be removed, because the application of paint to the scale is difficult due to the minimal adhesion and high brittleness of the scale. In other words, the paint will not adhere well, and the dross will fall off over time, and staining defects will occur. Dross can be removed by flame blasting, pickling or sandblasting.
Instructions
Step 1
For flame treatment of steel surfaces in order to remove scale, a gas welding machine is suitable. To do this, quickly heat the surface layer of the metal with an oxygen-acetylene flame. In this case, the scale will begin to flake off and should be removed with a metal brush after the metal has cooled. If necessary, the operation can be repeated several times. Be sure to cool the metal and clean it with a brush between each repetition of the procedure.
Step 2
Etching of the surface of metals to remove oxides and scale is carried out using sulfuric or hydrochloric acid. To perform this procedure, immerse the part in a 16-20% solution of one of these acids for 40 minutes. Then neutralize the acid with lime, rinse and dry the part. The result is descaling from even the most difficult-to-reach places. Metal pickling can be combined with mild sandblasting on non-defect-free surfaces.
Step 3
Sandblasting the surface to remove scale requires the use of a sandblaster. This is the only way to remove the scale that forms from the new steel. This method differs from etching and flame treatment in high productivity and lower cost.
Step 4
Degree of descaling. According to GOST, there are four degrees of descaling of a metal surface. The roughest is simple removal of the flaking scale. With the second degree of cleaning, scale is allowed on an area of up to 5%, visible to the naked eye. The third degree prevents the presence of dross visible to the naked eye. The fourth prevents the detection of dross when viewed with 6x magnification.
Step 5
Descaling up to the third can be done manually. To do this, use a stainless steel brush or power tool (grinder or grinder).
