WORKING PRESSURE OF ST 37.4 NBK HYDRAULIC TUBE

  ST37.4 NBK Hydraulic tubes are made in accordance to DIN 2391 or DIN 2445. It also called as cold drawn precision tube. ST37.4 NBK hydraulic tubes have a NBK finishing, where tubes are normalized, phospated, and oiled inside and outside. ST37.4 Hydraulic tubes  are measured by Outer Diameter (OD) and varies tube thickness (THK). Difference of OD and tube thickness will lead to different working pressure. 

There are two type of material grade for hydraulic steel tubes, ST52.4 and ST37.4. ST52.4 is high tensile strength tube means it has higher permissible working pressures by reduced tube wall thickness, and leading to reduced system overall weight. Please refer to chemical composition for ST52.4 and ST37.4 tube material:

CHEMICAL COMPOSITIONS OF HYDRAULIC STEEL TUBE MATERIALS

Chemical Composition (%)

Carbon (C)

Silicon (Si)

Manganese (Mn)

Phosphorus (P)

Sulfur (S)

E355 (ST52.4)

⩽0.22

⩽0.55

⩽1.6

⩽0.045

⩽0.045 

E235 (ST37.4)

⩽0.17

⩽0.35

⩽1.2 

⩽0.045 

⩽0.045

Steel grade

Yield strength

Tensile strength

Elongation

Name

Number

RH

Rm

A

 

 

min.

min.

min.

 

 

MPa

MPa

%

E235

1.0308

235

340 to 480

25

E355

1.0580

355

490 to 630

22

The production Process Of ST37.4 NBK Hydraulic Tubes

  1. Tube Formation
    The process begins with the selection of high-quality steel, which is then cut into the desired lengths. These steel pieces are then heated and pierced to create hollow tube shells.
  2. Cold Drawing​
    The raw steel is then subjected to a cold-drawing process. This involves pulling the steel through a series of dies to reduce its diameter and achieve the desired dimensions. This process not only ensures precise sizing but also enhances the mechanical properties of the tubes for tight tolerances and a smooth surface finish.
  3. Heat Treatment
    To further improve the strength and hardness of the tubes, they undergo a heat treatment process. This involves heating the tubes to a specific temperature and then cooling them rapidly. The controlled cooling process, known as quenching, imparts the desired mechanical properties to the tubes.
  4. Surface Finish
    Both ST37.4 hydraulic tube and St52.4 hydraulic tubes is their exceptional surface finish. This is achieved through various processes like pickling, phosphating, or passivation, depending on the application requirements in order to remove impurities and to ensure a smooth, corrosion-resistant surface.

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