ST52 Chrome-Plated DIN 2391 Hollow Piston Rod for Hydraulic Cylinders with Reduced Weight

The ST52 chrome-plated hollow piston rod is manufactured from cold-drawn seamless precision steel tube and designed for hydraulic cylinders requiring reduced component weight, high bending resistance, accurate outside diameter, and a wear-resistant working surface. The hollow structure lowers moving mass while maintaining the mechanical strength required for reciprocating hydraulic service.

ST52 is the former DIN designation commonly associated with E355 under EN 10305-1. For normalized material, typical specified properties include a tensile strength of 490-630 MPa, minimum yield strength of 355 MPa, and minimum elongation of 22%. Hard chrome plating provides a low-friction surface with controlled roughness, dimensional accuracy, and resistance to scoring and corrosion.

The hollow cross-section reduces rod weight compared with a solid piston rod of the same outside diameter. This can decrease reciprocating inertia, improve cylinder response, and reduce the load applied to guide elements and cylinder mounting points.

The actual weight reduction depends on the relationship between the outside diameter and inside diameter. For example, a hollow rod with an outside diameter of 80 mm and an inside diameter of 50 mm has approximately 39% less steel cross-sectional area than a solid 80 mm rod.

Normalized ST52 material provides a minimum yield strength of approximately 355 MPa, tensile strength of 490-630 MPa, and minimum elongation of 22%. These properties provide a practical balance between load-bearing capacity, machinability, weldability, and dimensional stability.

The working surface can be finished to Ra ≤0.20 µm with an outside-diameter tolerance selected from ISO f7, h7, h8, or g6. This controlled surface reduces seal abrasion and supports stable oil-film formation during reciprocating movement.

A hard chrome layer of 20-100 µm can be applied according to the operating environment. General hydraulic cylinders commonly use 20-30 µm, while thicker deposits may be selected where additional grinding allowance or corrosion resistance is required.

Typical finished chrome hardness is 850-1,100 HV0.1, providing substantially higher surface hardness than the ST52 steel substrate.

Final straightening after heat treatment, grinding, and plating controls straightness to a typical maximum of 0.20 mm per 1,000 mm. This reduces eccentric loading on rod seals, bearings, guide rings, and cylinder heads.

A common purchasing concern is whether the stated diameter tolerance applies before or after plating. Chrome deposition changes the finished diameter, and uneven plating can produce local oversize areas.

The outside diameter is therefore measured after final plating, grinding, and polishing. Inspection can include multiple measuring positions along the rod and readings in two perpendicular directions. ISO f7, h7, h8, or g6 tolerance should be selected according to the mating seal and guide arrangement rather than applied as a general tolerance without engineering review.

Chrome thickness that is too low can shorten corrosion and wear life, while excessive or irregular plating may cause grinding cracks, flaking, or dimensional variation.

Chrome thickness can be verified using calibrated non-destructive measurement equipment. Surface roughness, visible pits, grinding marks, peeling, burns, and unplated areas are inspected after polishing. Hardness and adhesion testing can be added when specified in the purchase order.

Hollow piston rods depend on both the mechanical properties of the base tube and the quality of the final surface. A dimensional certificate alone does not confirm material grade, heat-treatment condition, or plating quality.

Each production batch can be linked to the raw-material heat number, chemical composition, mechanical test results, tube dimensions, heat-treatment condition, chrome-plating record, and final inspection report. EN 10204 3.1 documentation is available when specified at the quotation stage.

The product can be used as the chrome-plated piston rod in the clamping hydraulic cylinder of an injection-molding machine. The hollow construction reduces reciprocating weight, while the ST52 steel body carries the axial working load.

The polished hard chrome surface passes through the rod seal and guide system during every operating cycle. For this application, outside-diameter tolerance, straightness, surface roughness, chrome thickness, and edge condition at machined transitions must be controlled to reduce seal wear and prevent leakage.