Process and technical requirements of cast iron tee

Cast iron tees are made from materials such as cast iron, stainless steel, alloy steel, malleable iron, and carbon steel. They can be connected to pipes using methods such as direct welding (the most common method), flange connections, threaded connections, and socket joints. Cast iron tees are commonly used in pipeline installations, especially for connections outside of pipe bends.

1. Classification of Cast Iron Tees

Cast iron tees are classified into: reducing tees, Y-type tees, high-pressure tees, and others.
Classification by material: carbon steel, cast steel, alloy steel, stainless steel, copper, and aluminum alloy.
Classification by manufacturing method: pushing, pressing, forging, and casting.


2. Cast Iron Tee Manufacturing Process
Cast iron tees are used at pipe branches. For seamless pipes, the commonly used processes for manufacturing cast iron tees are hydraulic bulging and hot pressing.

a. Hydraulic Bulging
Hydraulic bulging of cast iron tees involves axially compensating the metal material to expand the branch tube. A dedicated hydraulic press is used to inject liquid into a tube of the same diameter as the cast iron tee. The press's two horizontal side cylinders move synchronously and align to squeeze the tube. This compression reduces the tube's volume, and the pressure of the liquid within it increases as the tube's volume decreases. When the required pressure for expanding the branch tube of the cast iron tee is reached, the metal material, under the combined action of the side cylinders and the pressure of the liquid within the tube, flows along the mold cavity, expanding the branch tube.

The hydraulic bulging process for cast iron tees allows for a single-step process, resulting in high production efficiency. The wall thickness of the main tube and shoulder sections of the cast iron tee is increased.

Because the hydraulic bulging process for seamless cast iron tees requires relatively large equipment, it is currently primarily used in China to manufacture standard-walled cast iron tees with a wall thickness less than DN400. Suitable forming materials include low-carbon steel, low-alloy steel, and stainless steel, which have relatively low cold workhardening tendencies, as well as some non-ferrous metals such as copper, aluminum, and titanium.

b. Hot Pressing
Hot press forming of cast iron tees involves flattening a tube billet, larger than the diameter of the cast iron tee, to approximately the same diameter. A hole is then opened where the branch pipe will be drawn. The tube billet is heated and placed in a forming die, where a punch for drawing the branch pipe is installed. Pressure compresses the tube billet radially, causing the metal to flow toward the branch pipe and form under the tension of the punch. The entire forming process is a combination of radial compression of the tube billet and drawing of the branch pipe. Unlike hydraulically expanded cast iron tees, the metal in the branch pipe of hot press cast iron tees is compensated for by the radial movement of the tube billet, hence the name "radial compensation process."

Because the cast iron tee is pressed after heating, the equipment required for forming the material is reduced. Hot-pressed cast iron tees are widely adaptable to various materials, including low-carbon steel, alloy steel, and stainless steel. This forming process is particularly common for large diameter and thick-walled cast iron tees.

3.Technical Requirements for Cast Iron Tees
Cast iron tees are manufactured according to specific processes and principles to ensure high quality and reliability during production. Geometric dimensions include outer diameter, inner diameter, and wall thickness. Packaging requirements also apply. Small pipes, such as those destined for export, require wooden crates of approximately one cubic meter. The number of elbows in such a crate cannot exceed one ton. The standard allows for sets (large within a small), but the total weight generally cannot exceed one ton. Larger pieces, such as 24-inch pipes, must be individually packaged. Furthermore, packaging markings must be specified, including the size, steel grade, batch number, and manufacturer's trademark. Cast iron tees must be stamped and accompanied by documentation such as a packing list and warranty. Controlled curvature radius is also required. For example, if the radius is 1.5D, the radius of curvature must be within the required tolerance. Since most of these pipe fittings are used for welding, to improve weld quality, the ends are beveled, leaving a certain angle and edge. This requirement is quite strict, with regulations on edge thickness, angle, and tolerance. The geometric dimensions include many more items than pipe fittings. The surface quality and mechanical properties are essentially the same as those of pipes. To facilitate welding, the steel grade used is the same as the pipe being connected. All tee fittings undergo surface treatment, shot blasting to remove scale from the inner and outer surfaces, followed by a coating of anti-corrosion paint. This is done both for export and to facilitate domestic transportation to prevent rust and oxidation.

For elbow fittings, for example, when making long-radius elbows, the specifications must be selected and the pipe material must be sourced. This can be calculated through theoretical calculations, and then cut to the desired length. Finally, the material is hot-pressed. You've probably seen press-press machines; they're actually quite simple. The elbow is a horn-shaped core or mandrel that gradually thickens. The elbow is expanded and bent during the pushing process. A support is placed at the back to thread the cut pipe section through the mandrel, and a frame at the back secures the mandrel. A trolley, sometimes driven hydraulically or mechanically (via a lead screw), pushes the trolley forward. The trolley pushes the pipe along the mandrel. An induction coil on the outside of the mandrel heats the pipe. Once heated, the trolley pushes the pipe down, completing the elbow. After pushing, the elbow is shaped while still hot. Theoretically, the expansion ratio is generally between 33% and 35%, and this is calculated backwards. For a short radius of 219mm, the typical expansion ratio is 50%. After selecting the raw material, the material is cut according to the elbow specifications, taking the curvature radius into consideration. For example, for a 90° elbow, the curvature can be used to calculate the required length of material to produce the desired 90° elbow.

The process for making cast iron tees is basically the same. Cutting is done according to the different specifications of cast iron tee fittings. After cutting, the fittings must first be sandblasted to remove the surface iron oxide scale before forming. Forming is done using the hydraulic expansion method. A mold is used with a flat bottom and a flange hole on the top. After the pipe is placed in, it is fixed with a hydraulic cylinder. Liquid is filled on both sides to bulge inward, squeezing the pipe into a "convex" shape. The bulge is then cut off at the appropriate position and grooved. It undergoes two shot peening treatments. Since work hardening occurs during the processing, heat treatment is also required. This is the production process flow of cast iron tee fittings.