The piston of the hydraulic cylinder is a kind of support for the pressure from the working fluid in the drive. The end surface of the piston perceives the load, the cylindrical one serves to accommodate seals and guide elements.
Design
The piston can be either a single piece or an assembly unit. This directly depends on the method of installing the seals. Oversized, complex seals that hold high pressures and sliding speeds cannot be placed in the groove by manual or tool stretching. It is necessary to divide the piston into its component parts, connecting them with screws, by thread, by press fit or tightened together with the installation of the rod.
Blanks and materials
For the manufacture of pistons, steels of grades 45 and 40X are used with volumetric quenching to a hardness of 320..360 HB. If the outer cylindrical surface is in direct contact with the cylinder liner, then the piston weld with bronze (BrOF7-02, BrAZh9-4) or brass, and are also made entirely of antifriction cast iron. Some foreign manufacturers have announced the manufacture of pistons from 9SMn28 steel, which approximately corresponds to the domestic 15G.
Round bars, stamping or casting are used as blanks. The latter option is relevant only for cast iron and in cases where it is required to significantly save material consumption, since often steel casting hides a lot of defects, and already during operation, under the influence of pressure, shells can open and cracks.
Requirements
GOST 6540-68 defines a number of normal values for piston diameters - from 10 to 800 mm (in exceptional cases up to 900 mm). In practice, cylinders with a cavity over 300 mm are extremely rare.
The working contact surface of the piston is made with a tolerance field of f7, and in the case of installing guide rings - 0.5 mm less than the cavity diameter. The runout of the cylinder relative to the stem installation hole should be no more than 0.03 mm, while the accuracy of the hole itself is limited by the H8 tolerance field. The grooves for the installation of seals and guide rings are made according to h9.
The roughness of the contact surface is not higher than Ra 0.8 μm, which requires the use of polishing or other finishing operations. The ends of the piston are machined up to Ra 2.5 µm, grooves - Ra 1.25 µm.
Processing process
During the production process, the piston is turned, the hole for the rod installation is drilled and deployed. After hardening, the part is ground to the required precision and polished. Sharp edges should be rounded or chamfered - scuffs and burrs on the elements of hydraulic equipment are not allowed, as they can damage the seals during assembly.