Process flow of industrial steel elbows

Seamless steel elbows: steel elbows are a type of pipe fittings used at the bends of pipes. Among all the pipe fittings used in the pipeline system, the proportion is about 80%. Usually, different forming processes are selected for steel elbows of different materials or wall thicknesses. Common seamless steel elbow-forming processes used by manufacturers include hot pushing, stamping, extrusion, etc. The hot pushing steel elbow forming process is a process in which a special steel elbow pushing machine, a core mold, and a heating device are used to make the blank on the mold move forward under the push of the pushing machine, and the blank is heated, expanded and bent during the movement. The deformation characteristics of the hot-pushing steel elbow are to determine the diameter of the tube blank according to the law that the volume of the metal material remains unchanged before and after plastic deformation. The diameter of the tube blank used is smaller than the diameter of the steel elbow. The deformation process of the blank is controlled by the core mold, so that the compressed metal at the inner arc flows and compensates for other parts that are thinned due to the expansion of the diameter, thereby obtaining a steel elbow with uniform wall thickness.

Hot push steel elbow: The forming process has the characteristics of a beautiful appearance, uniform wall thickness, and continuous operation, which is suitable for mass production. Therefore, it has become the main forming method for carbon steel and alloy steel elbows and is also used in the forming of stainless steel elbows of certain specifications. The heating methods of the forming process include medium-frequency or high-frequency induction heating (the heating coil can be multiple coils or a single coil), flame heating, and reverberatory furnace heating. The heating method used depends on the requirements of the formed product and the energy situation. Stamping steel elbows is the earliest forming process used in the mass production of seamless steel elbows. In the production of steel elbows of common specifications, it has been replaced by hot push or other forming processes, but in some specifications of steel elbows, the production quantity is small, and the wall thickness is too thick or too thin.

It is still used when there are special requirements for the product. The stamping forming of the steel elbow uses a tube blank with the same outer diameter as the steel elbow, and a press is used to directly press it in the mold.

Before stamping, the tube blank is placed on the lower die, the inner core and the end die are loaded into the tube blank, and the upper die moves downward to start pressing. The steel elbow is formed by the constraint of the outer die and the support of the inner die.

Compared with the hot push process, the appearance quality of stamping is not as good as the former; the outer arc of the stamped steel elbow is in a stretched state during forming, and there is no excess metal in other parts to compensate, so the wall thickness at the outer arc is thinned by about 10%. However, due to its suitability for single-piece production and low cost, the stamping elbow process is mostly used for the manufacture of small batches and thick-walled elbows.

Stamping steel elbows: divided into cold stamping and hot stamping. Cold stamping or hot stamping is usually selected according to the material properties and equipment capacity.

The forming process of the cold extrusion steel elbow is to use a special steel elbow-forming machine to put the tube blank into the outer mold. After the upper and lower molds are closed, the tube blank moves along the gap reserved by the inner and outer molds under the push of the push rod to complete the forming process.

The steel elbows manufactured by the cold extrusion process of the inner and outer molds have a beautiful appearance, uniform wall thickness, and small dimensional deviation. Therefore, this process is often used for the forming of stainless steel elbows, especially thin-walled stainless steel elbows. The inner and outer molds used in this process have high precision requirements; the wall thickness deviation requirements of the tube blank are also relatively stringent.

Middle plate welding: Use the middle plate to press to make half of the steel elbow section, and then weld the two sections together. This process is generally used to make steel elbows above DN700. In addition to the above three commonly used forming processes, seamless steel elbow forming also uses a forming process that squeezes the tube billet into the outer mold and then passes the ball through the tube billet to shape it. However, this process is relatively complex, and cumbersome to operate, and the forming quality is not as good as the above process, so it is rarely used.