Surface Treatment And Polishing Process of Stainless Steel Welded Pipe

  • By:Iris Liang
  • Date:2021/10/14

The surface polishing process of stainless steel welded pipes commonly includes stainless steel anodizing, stainless steel galvanizing, stainless steel chromium plating, stainless steel electroless nickel plating, but because stainless steel is in the production process, it is inevitably required to undergo annealing, normalizing, quenching, welding and other processes.  The surface often produces black oxide scale. Oxide scale not only affects the appearance quality of stainless steel, but also adversely affects the subsequent processing of the product. Therefore, surface treatment methods such as pickling, passivation, and polishing must be used to remove them in the subsequent pretreatment of electroplating. As a professional manufacturer of pipe making machine, Hangao Tech (SEKO Machinery) devotes ourselves to solve client's problem. Let's have a look
the problems about steel pipe polishing.

   

Common polishing includes mechanical polishing, chemical polishing, and electrochemical polishing. Batch finishing is to use the abrasive in the polishing agent to polish the surface of the part to smooth the surface and achieve the polishing effect. After polishing, a mirror surface with a surface roughness of 0.4um or less can be obtained. Parts with simple shapes can be polished with hard polishing wheels or belts, and parts with complex shapes can be polished with soft polishing wheels. Large batches of small parts are decorated in batches. There are methods such as roller rolling, vibrating machine vibrating light, centrifuge centrifugal light, and rotating light. Mechanical polishing has a small amount of surface grinding, and it is difficult to polish rough surfaces.

At this time, it needs to be polished in advance, with a polishing wheel and a polishing belt moistened with a polishing paste for grinding, which is divided into rough grinding, middle grinding and fine grinding. After fine grinding, the surface roughness can reach 0.4um. In order to meet some other requirements, such as descaling, deburring, welding slag, matting, etc., surface treatments such as sandblasting, shot blasting, and brushing with steel wire wheels are sometimes used. The surface polished with stainless steel wire wheels can be better avoid iron pollution. Considering different demand on polishing degree, we have many choice of different model, like 8 head polishing head grinding machine, 10 heads, 16 heads and 32 heads, for round tubes and squire tubes. Chemical polishing is to immerse the parts in a proper solution, because the solution dissolves the convex parts of the surface faster than the concave parts, so that the surface is leveled and the polishing purpose is achieved. Generally speaking, chemical polishing has poor polishing ability and can only improve the brightness by a small amount. But it is labor-saving and time-saving than mechanical polishing, and it can polish the inner surface of small parts.

   

Recently, it has also been reported that the surface of 18-8 type austenitic stainless steel can be polished to a mirror brightness by adding a brightener. But pay attention to the following points.


(1) The active surface is generated after chemical polishing, and the workpiece must be passivated to ensure corrosion resistance.


(2) For large quantities of small parts such as brackets and screws, mechanical stirring should be used to make the polishing uniform.


(3) When polishing large-area surfaces of stainless steel composite plates and other products, pay special attention to keeping the polished surface moist, and should be fully washed after polishing to prevent uneven surface brightness. Electrochemical polishing can improve the reflective performance of parts; improve corrosion resistance; reduce the surface hardness of processed parts; and reduce the friction coefficient due to the reduction of surface roughness. Electrochemical polishing can also be used to remove burrs and so on.

   

Compared with mechanical polishing, electrochemical polishing has the following characteristics.

  

(1) Mechanical polishing will produce surface hardened layer and abrasive inclusions, which will reduce the corrosion resistance of stainless steel, while electrochemical polishing will produce a passivated surface and increase the corrosion resistance of stainless steel.
  

(2) Electrochemical polishing has certain requirements for the substrate. For example, when the metallographic structure is not uniform, it will produce an uneven polished surface, and deep scratches cannot be polished. The mechanical polishing has much lower requirements on the substrate.
  

(3) For parts with complex shapes, wires, thin plates and small parts, electrochemical polishing is much easier than mechanical polishing.
  

(4) The production efficiency of electrochemical polishing is higher than that of mechanical polishing, but large workpieces cannot be put in the polishing tank and require a particularly large current, which makes it difficult to perform electrochemical polishing.
  

(5) The surface current density of the electrochemically polished workpiece must be uniform, and if necessary, a pictograph cathode is needed, otherwise the surface brightness will be uneven.
  

(6) The current is relatively large during electrochemical polishing, and the fixture and the workpiece must have a large enough contact area and good contact, otherwise local overheating will burn the workpiece.
  

(7) Some polishing processes used for austenitic stainless steel cannot be used for polishing martensitic stainless steel, which are prone to corrosion.

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