Bushings, together with pins, form the joints of construction machines. The function of the bushings is to prevent the pins from damaging the arm during movement. They act as bearings between the arm and the pin. That’s why bushing manufacturing and production is of great importance. Bushings reduce the cost and processing time of arm damage.
We classify bushings according to the type of raw material and their shape.
Depending on the type of raw material, bronze and steel bushings are available. According to their shapes, they are classified as flat bushings, grooved and perforated bushings, helical grooved bushings and capped bushings. Of course, they can also contain more than one type. Like bushing with cap and helical groove.
Raw Material Selection in Bushing Production
We produce bronze bushings in exact dimensions. We do not harden or grind bronze bushings. Since the bronze bushing is not hard, it does not damage the bushing slot in the arm. However, the raw material of bronze material is more expensive than steel pipe. Additionally, it is difficult to find pipes like steel pipes in the market. It is necessary to produce the raw materials of these bushings specially. It will be necessary to produce it from stick material. This will increase the cost even more.
Steel bushings are produced as seamless tubes from ST52 or 42CrMo4 steel. The raw material cost is cheaper than bronze bushings. We use it in construction machines after it is completely hardened. It may cause damage during installation and removal of the bushings on the arm.
Lathe Process in Bushing Production
We produce bronze bushings in exact dimensions. Steel bushings that need to be hardened are processed by leaving allowances inside and outside, as precision will be impaired during heat treatment. We open the grooves on lathes. An important process in bushing production is to chamfer the inside and outside of the bushing, as it will enter a slot tightly and a pin will pass through them, and it is important that these chamfers are sufficient. Bushings without chamfers cause great difficulties during assembly.
Heat Treatment
Bushings made of 42CrMo4 steel pipe can be hardened only by tempering process, since there is enough carbon in the raw material. ST44 and ST52 steel pipes are carbon-poor pipes. ST 44 and ST52 steels are cannot be reach to the hardness value by temperation process. We apply a cementation process to harden this material. In the cementation process, the material is heated to 850-950 degrees Celsius and carbon gas is sent onto it, enriching the material content with carbon. It can reach hardness levels of 55-60 HRc.
Grinding
After the heat treatment of the steel pipes, the part left on the lathe grinds and brings to precise dimensions. This grinding process is important for bushings both in terms of dimension and surface quality. In order for the bushings to fit tightly into their slots, we make the outer diameters 0.10-0.15 mm larger than the slot size. Since the pin will pass through the inside, the inner diameter must be at least 0.10 mm larger than the pin size.
Grinding dimensions are important in the bushing manufacturing and production because the bushings will enter their slots on the arm and the pin will enter through them.