Generally, the production of sanitary seamless stainless steel pipes starts with cold drawing. This article will talk about several important equipment during production.

The first is the cold drawn tube machine, which pierces the stainless steel round bar and calls it a rough tube. Usually the rough tube is Ф655mm or Ф1007mm. Generally, the sanitary stainless steel pipes used in industry range from Ф141mm to Ф2003mm. In this case, it is necessary to expand and draw small pipes, which is done by using a cold drawing machine. And sometimes it is necessary to expand the pipe or pull the small pipe several times, in which heat treatment and pickling need to be carried out in cycles.

There are many advantages to cold drawn tube machining, including high production efficiency, convenience in changing product specifications during production, greater flexibility, and easier tool equipment manufacturing and maintenance.

However, cold drawing processing also has disadvantages. For example, small deformation in each pass leads to many processing passes and a long production cycle; high metal consumption. The surface finish of the inner and outer surfaces of the tube is relatively poor.

Let’s talk about the multi-roller cold-rolled pipe machine, which is the key equipment used in China to manufacture sanitary seamless stainless steel pipes. Cold-drawn stainless steel pipes are used as blanks. After cold-rolling, the inner and outer diameter and wall thickness dimensions of the cold-rolled pipes are less than 0.02-0.05mm. The inner and outer surface roughness of the pipes is Ra≤0.8μm, and the wall thickness can also be made to 0.5mm. The internal and external surface smoothness of the tube is then polished to Ra≤0.2-0.4μm.

However, the biggest disadvantage of multi-roller cold-rolled pipes after cold rolling is the hardness, that is, the yield coefficient is large, and it is not easy to expand and bend. Strictly speaking, it does not meet the national standards, so it needs to be heat-set. Melting treatment (annealing).

Usually, after stainless steel pipes are treated in ordinary hot solution treatment furnaces, the inner and outer surfaces of the stainless steel pipes will produce oxide scale and need to be pickled. However, this will destroy the original inner and outer surface smoothness of the cold-rolled pipes and produce minor unevenness. , which does not meet the surface finish standards of sanitary pipes. Therefore, it is necessary to choose a gas-protected bright annealing furnace.

The third one is the gas shielded bright annealing furnace, which is composed of two parts, including the bright annealing furnace body and the ammonia decomposition complete device.

The main structure of the bright annealing furnace body is a muffle tank with a circular cross-section. It uses a heating method with high-temperature heating wires arranged on both sides and the bottom. Ammonia decomposition gas is used as a protective gas and circulating cooling gas. The structure is compact, the operation is safe, the control is very reliable and the maintenance is easy. The furnace temperature is uniform, and the temperature can be as high as 1150°C. The source loss is low, the protective gas can be fully utilized, and the cooling speed is fast to ensure that the reprecipitation of chromium carbide is avoided. Let all chromium carbide be completely dissolved into the austenite matrix, changing the hard state and metallographic structure of the original cold-rolled pipe, and truly achieving the purpose of solid solution treatment.

In addition, the ammonia decomposition complete set uses pure liquid chlorine to decompose into 70% hydrogen and 30% ammonia, which is filled into the furnace body to drive away air (oxygen) and reduce the air content as much as possible.