For the control of the reducing range, under normal circumstances, the processing range of the large and small heads is within the first grade. For example, the large and small heads of 325-159 basically need to undergo several heating treatments. The diameter of the tube is pressed to 273. This pressing also needs to be heated. The second diameter reduction is the process of 273 to 219. This time, the tube needs to be heated to the specified temperature and then pressed. Then there is the process of reducing the diameter of 219 to 159. Each time the diameter is reduced, heat treatment is required.

Various materials have their own characteristics such as hardness and tensile strength, so it is determined that the pressing force of each material is also different. The same type of head, different materials, different processing methods and procedures will also be very different, such as It is said that the head of ordinary carbon steel will be formed after 3 times of heat treatment. However, the greater the hardness of the head of the alloy material, the more times of pressing and heating, and the more complicated the forming process.