news
news
2021.12.10
Cast iron pipe and pipe may be connected via welding, flange connection, threaded connection, socket connection, etc., depending on the application. Outside of the end of the pipeline, a pipe fitting known as a connecting pipe fitting is usually utilized. Alloy steel, stainless steel, cast iron, malleable cast iron, carbon steel, etc. are all examples of cast iron pipes. Cast iron pipe classifications, technology, and process requirements will be discussed in detail today.
Classification of cast iron pipes
Classification of cast iron pipe: reducing tee, Y-type tee, high-pressure tee, etc
1. The materials are divided into carbon steel, cast steel, alloy steel, stainless steel, copper, aluminum alloy, etc.
2. According to the manufacturing method, it can be divided into pushing, pressing, forging, casting, etc.
Technology of cast iron pipe
cast iron pipe is a kind of pipe fitting used at the branch of the pipeline. For the manufacture of cast iron pipe with seamless pipe, there are two commonly used processes: hydraulic bulging and hot pressing.
Hydraulic bulging
Hydraulic bulging of cast iron pipe is a forming process of expanding branch pipe through axial compensation of metal material. The process is to use a special hydraulic press to inject liquid into the pipe blank with the same diameter as the cast iron pipe, and squeeze the pipe blank through the synchronous centering movement of the two horizontal side cylinders of the hydraulic press. The volume of the pipe blank becomes smaller after extrusion, and the liquid in the pipe blank increases with the volume of the pipe blank. When the pressure required for the expansion of the cast iron pipe branch pipe is reached, The metal material flows along the inner cavity of the die casting and expands out of the branch pipe under the dual action of the liquid pressure in the side cylinder and the tube blank.
The hydraulic bulging process of cast iron pipe can be formed at one time with high production efficiency; The wall thickness of the main pipe and shoulder of cast iron pipe increased. Due to the large equipment tonnage required for the hydraulic bulging process of seamless cast iron pipe, it is mainly used in the manufacture of cast iron pipe with standard wall thickness less than dn400 in China. The applicable forming materials are low carbon steel, low alloy steel, and stainless steel with relatively low cold work hardening tendency, including some non-ferrous metal materials, such as copper, aluminum, titanium, etc.
Hot pressing
The hot pressing forming of cast iron pipe is to flatten the pipe blank larger than the diameter of cast iron pipe to the size of the diameter of cast iron pipe, and open a hole at the part of stretching branch pipe; The tube blank is heated and put into the forming die, and the die for drawing the branch pipe is installed in the tube blank; Under the action of pressure, the tube blank is compressed radially. In the process of radial compression, the metal flows to the branch pipe and forms a branch pipe under the tension of the die. The whole process is formed through the radial compression of pipe blank and the stretching process of the branch pipe. Different from hydraulic bulging cast iron pipe, the metal of hot-pressed cast iron pipe branch is compensated by the radial movement of pipe blank, so it is also called radial compensation process.
As the cast iron pipe is pressed after heating, the equipment tonnage required for material forming is reduced. Hot pressed cast iron pipe has wide adaptability to materials and is suitable for materials of low carbon steel, alloy steel, and stainless steel; This forming process is usually used for cast iron pipes with large diameters and thick pipe walls.
Process requirements for cast iron pipe
cast iron pipe fittings are produced according to certain process methods and principles to ensure good product quality and guarantee in the actual production and processing. The geometric dimensions include outer diameter, inner diameter, and wall thickness. It is the requirement for packaging. For small pipe fittings, such as export, wooden boxes need to be made, about 1 cubic meter. It is stipulated that the number of elbows in such boxes can not exceed 1 ton. The standard allows suits, that is, large sets and small sets, but the total weight can not exceed 1 ton. For large pieces, a single package is required. For 24 “, a single package is required.
Another is the packaging mark, which should indicate the size, steel number, batch number, and manufacturer’s trademark. The cast iron pipe fittings shall be stamped with a steel seal and attached with a packing list, warranty, and other documents. It is also required to control the radius of curvature. For example, if the radius length is 1.5D, the radius of curvature must be within the required tolerance. Since most of these pipe fittings are used for welding, in order to improve the welding quality, the ends are turned into grooves, with a certain angle and a certain edge. This requirement is also strict.
There are provisions on the thickness of the edge, the angle, and the deviation range, and there are many more geometric dimensions than the pipe fittings. The surface quality and mechanical properties are basically the same as those of pipes. For the convenience of welding, the steel grade is the same as that of the connected pipe. All three-way pipe fittings shall be subject to surface treatment, and the iron oxide scale on the internal and external surfaces shall be sprayed off by shot peening, and then coated with anti-corrosion paint. This is not only for export needs, but also to facilitate transportation and prevent corrosion and oxidation at home.
Take the elbow fitting as the reverse. If making a long radius elbow, first, select the specification and put forward the pipe material. It can be calculated through theoretical calculation, and then cut off with this length as the fixed length. Later, the material is hot pushed. Everyone may have seen the pusher. It’s actually very simple. It is an ox horn-shaped core head or core rod. The core rod changes from thin to thick. The pushing process is a process of expanding belt bending.
There is a support at the back to thread the blanking pipe section into the mandrel, and there is an archway at the back to fix the mandrel. There is a small car in the middle. Some of the cars are driven by hydraulic transmission, and some are driven by mechanical transmission, that is, lead screw transmission, and then push the car forward. The trolley pushes the pipe forward along the mandrel. There is an induction ring outside the mandrel to heat the pipe. Then the trolley pushes the pipe down and processes one.
After pushing, the elbow shall be shaped in this hot state. Through theoretical calculation, the diameter expansion rate is generally between 33% – 35%, which is pushed back. The general diameter expansion rate of 219mm short radius is 50%. After selecting the raw materials, blanking shall be carried out according to the elbow specification, and then the radius of curvature shall be considered. For example, for a 90 ° elbow, the blanking length can be calculated through its curvature, and a 90 ° elbow can be processed.
The process of cast iron pipe is basically the same. Blanking shall be carried out according to different specifications of cast iron pipe fittings. Sandblasting shall be carried out after blanking, and the iron oxide scale on the surface shall be removed before forming. The hydraulic bulging method is used for forming. There is a mold, the bottom of the mold is straight, and there is a flange hole on the top. After the pipe is put in, the pipe is fixed with a hydraulic cylinder, both sides are filled with liquid, bulge inward, squeeze the pipe into a “convex” shape, and then cut the bulge from an appropriate position to form a groove. It has to be shot-peened twice. As there is work hardening in the machining process, heat treatment is also required. The production process of cast iron pipe fittings is such a situation.