Tube drawing is a cold metalworking process used to create tubes with smaller diameters. There are five methods: fixed cap, floating cap, bonded cap, rod, and tube sinking. The process produces precise measurements and greater strength. The fixed cap method produces the best internal surface finish, while the floating cap method is capable of producing very thin diameter tubing with high-quality finishes. The bonded cap method combines features of fixed and floating cap designs, while the rod method uses a mandrel to ensure constant internal diameter. Tube sinking is a cost-effective method with lower surface finish quality.
Tube drawing is a metalworking process used to create tube with a smaller diameter by pulling, or drawing, larger diameter tube through a die. There are five commonly used tube drawing methods. These methods are fixed cap drawing, floating cap drawing, bonded cap drawing, rod drawing, and tube sinking.
This process is a cold working process which means that the metal tube is not heated before being shaped in the tube drawing process. This gives the finished product greater strength because the metal pipe is unaffected by thermal expansion in the process. Additionally, this process produces tubes with more precise measurements than other manufacturing methods.
The fixed plug design is the oldest form of pipe design. Using a mandrel locked in a fixed position near the die, the fixed drawing process produces the best internal surface finish of any tube drawing method. Stationary drawing is also the slowest method in use and is extremely limited in the amount of diameter reduction possible.
Floating mandrel, or floating plug, the design incorporates a floating mandrel positioned within the tube. The cap is forced to the die throat by friction and pressure, called axial force. The floating cap method is capable of producing very thin diameter tubing. This method of drawing tubes is known for producing tubes with high quality internal and external surface finishes.
The bonded plug design, or semi-floating mandrel design, combines the features of the fixed plug design and the floating plug design. Although the mandrel floats inside the tube, it is tethered to an anchor point. Used in the straight pipe manufacturing process, this drawing method provides a better finish on the inside surface of the pipe.
The rod design, also known as the mandrel design, uses a mandrel to ensure that the internal diameter of the drawn tube remains constant. The mandrel is a 100-foot (about 30 m) long solid rod that is inserted into the pipe and pulled together with the pipe through the die. The inside surface of the finished tube takes on the characteristics of the outside of the rods as the metal tube is compressed around the rod as it passes through the die. The barrel is then pulled from the finished tube in a process called reeling.
Pipe sinking is one of the primary methods of pipe drawing for products that require quick and cost-effective installation without a great deal of concern for the internal surface finish of the pipe, such as pipe used to build patio furniture. It differs from other forms of tube drawing because there is no mandrel used inside the tube. While this is the simplest form of tube drawing, it results in a lower surface finish quality than the other four methods.
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