Sheet metal surface polishing process

In the field of sheet metal processing, surface polishing is a crucial process. It can not only make sheet metal products show a smooth and bright appearance, but also improve its corrosion resistance and wear resistance to a certain extent. The following is a detailed introduction to the sheet metal surface polishing technology process and related precautions.

 

Sheet metal surface polishing process is mainly divided into 3 aspects

 

Rough polishing: This is the initial stage of mechanical polishing. Tools such as a grinder or an Angle grinder with coarse sandpaper (e.g. 80-120 mesh) are usually used. The operator holds a tool to make the sandpaper or grinding wheel contact the surface of the sheet metal and polish it in a certain direction and force. This process is mainly to remove the obvious defects of the sheet metal surface, such as welding marks, stamping burrs, rough processing lines and other large uneven places. The speed of rough polishing is relatively fast, but the control accuracy of surface roughness is relatively low.

 

Medium toss: After completing the rough toss, the medium toss process is carried out. At this time, a finer grit sandpaper will be used, generally around 240-400 mesh. Equipment such as a belt sander or electric polisher can be used. The purpose of medium casting is to further refine the surface, reduce the scratches left by rough casting, and make the surface more flat and smooth. In the operation process, it is necessary to pay attention to the uniformity of the polishing strength and speed, to avoid local excessive polishing or insufficient polishing.

 

Finishing: This is the last key step in mechanical polishing. The grit of the sandpaper used is usually more than 600 mesh, and even sandpaper up to about 2000 mesh can be used. Finishing usually uses a specialized polishing machine, which can provide a more stable and uniform polishing effect. In the finishing process, the polishing wheel is in contact with the sheet metal surface, and through high-speed rotation, the sandpaper makes a fine grinding of the surface. At this stage, special attention should be paid to the polishing skills to ensure that the surface reaches a mirror-like smoothness.

Degreasing treatment: Before chemical polishing, ensure that the sheet metal surface is clean and free of oil. Usually, organic solvents (such as acetone, alcohol, etc.) are used to wipe or soak in alkaline degreaser solution to remove the oil on the surface. This step is a key prerequisite for the success of chemical polishing, because the presence of oil can seriously affect the reaction effect of the chemical polishing liquid with the sheet metal surface.

 

Configuration of chemical polishing fluid: The composition of chemical polishing fluid varies with different sheet metal materials. In general, chemical polishing liquid contains oxidants (such as nitric acid, sulfuric acid, etc.), corrosion inhibitors, additives and other ingredients. The proportions of these components need to be precisely configured according to the actual situation. For example, for stainless steel sheet metal, the ratio of sulfuric acid and phosphoric acid in the commonly used chemical polishing liquid is about 3:1, while adding an appropriate amount of chromic acid as an oxidizing agent.

 

Chemical polishing process: the degreased sheet metal is soaked in the configured chemical polishing liquid, and the reaction is carried out under certain temperature and time conditions. In the reaction process, the chemical polishing liquid will chemically react with the sheet metal surface to remove the microscopic roughness of the surface and make the surface smooth. The temperature and time of the reaction need to be determined according to the type of sheet metal material, thickness, and the formula of the chemical polishing liquid. Generally speaking, the temperature is between 50-100 ° C, and the reaction time varies from 5-30 minutes.

 

Cleaning and neutralization: After chemical polishing is complete, remove the sheet metal from the polishing liquid immediately and rinse with water to remove the residual polishing liquid on the surface. Then, in order to prevent the residual chemical substances from causing corrosion to the sheet metal surface, neutralization is required. A weakly alkaline solution, such as sodium bicarbonate solution, is usually used for neutralization.

 

Preparation: First of all, it is also necessary to thoroughly degreasing and cleaning the sheet metal. Then, the sheet metal is used as the anode, a suitable cathode (usually an inert electrode such as a stainless steel plate) is selected, and they are placed in the electrolytic polishing tank.

 

Configuration of electrolytic polishing liquid: the composition of electrolytic polishing liquid mainly includes phosphoric acid, sulfuric acid, chromic acid and other strong electrolytes. Different sheet metal materials require different electrolytic polish formulations. For example, for aluminum and aluminum alloy sheet metal, the electrolytic polishing liquid may be mainly phosphoric acid, and add an appropriate amount of sulfuric acid and additives.

 

Electrolytic polishing process: In the electrolytic polishing tank, direct current is passed. Under the action of an electric field, the metal atoms on the surface of the anode (sheet metal) will dissolve, and a passivation film will be formed on the surface. This layer of passivation film is continuously removed and re-formed under the action of electrolyte flow and electric field, so that the micro-convex part of the sheet metal surface is preferently dissolved to achieve the effect of smooth surface. The process parameters of electrolytic polishing (such as current density, voltage, polishing time, etc.) need to be optimized and adjusted according to the nature and thickness of the sheet metal material.

 

Post-treatment: After the electrolytic polishing, the sheet metal needs to be removed from the electrolytic cell, washed with water first, and then dried.

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