Cold Drawn Seamless Hydraulic Tube

Cold drawn seamless hydraulic tubes are the key components used in high-pressure hydraulic systems in the industrial field. It is widely used due to its high strength, pressure resistance and precision dimensions. Cold drawn seamless hydraulic tube refers to a seamless steel pipe made by cold drawing process. It has high-precision dimensions, smooth inner wall and high strength. It is suitable for high-pressure hydraulic systems (such as engineering machinery, injection molding machines) and fluid transmission.

Process manufacture

The manufacturing process of cold drawn seamless hydraulic tube combines cold deformation technology and precision machining. The core steps are as follows:

1. Raw material preparation

Hot-rolled seamless steel tube is selected as the initial billet (such as 20#, 45# steel). It is necessary to ensure that the surface is free of cracks and the oxide scale is uniform. Cut the long tube billet into a length suitable for cold drawing (usually 3-6 meters).

2. Pretreatment process

Use hydrochloric acid or sulfuric acid solution to remove the iron oxide scale on the surface of the tube billet to improve the subsequent lubrication effect. Form a phosphate coating (such as phosphating film) on the surface of the tube billet to reduce friction during cold drawing and prevent strain.

3. Cold drawing

The tube billet is passed through the carbide die (or diamond die) on the cold drawing machine, and axial tension is applied at room temperature to reduce the outer diameter and wall thickness of the tube and extend the length. High-precision tubes need to be drawn multiple times, and the deformation amount is controlled at 10%-30% each time to avoid cracking. During the drawing process, the metal grains are refined, the strength is significantly improved, but the plasticity decreases.

4. Heat treatment

Eliminate the internal stress caused by cold drawing and restore the toughness of the material (such as 45# steel needs 500-650℃ annealing). Alloy steel pipes (such as 30CrMo) are quenched + high-temperature tempered to balance strength and toughness.

5. Finishing and testing

The bends caused by cold drawing are eliminated by roller straightening machine. Cut into standard lengths (such as 6 meters or customized sizes) as required. Ultrasonic flaw detection (UT) or eddy current testing (ET) to check internal cracks and inclusions. Finally, polish, apply anti-rust oil or coating (such as galvanizing).

Common materials and characteristics

The material selection of cold-drawn seamless hydraulic tubes directly affects the performance. Common materials are as follows:

1. Carbon steel

Common models are 20# and 45#. The characteristics of carbon steel are low cost, moderate strength, and easy processing; poor corrosion resistance, surface treatment is required, and it is more suitable for ordinary hydraulic systems and agricultural machinery equipment.

2. Low alloy steel

Common models are 27SiMn and 30CrMo. The characteristics of low alloy steel are high strength (tensile strength ≥800MPa), high temperature resistance (≤400℃), good fatigue resistance, and suitable for engineering machinery and heavy-duty hydraulic cylinders.

3. Stainless steel

Common models are 304 and 316L. The characteristics of stainless steel are strong corrosion resistance and beautiful appearance; high cost, difficult cold processing (easy to harden), suitable for chemical, marine, and food-grade hydraulic systems.

4. High-strength special steel

Common models are ST52 and E355. High-strength special steel generally meets European standards, has high pressure bearing capacity, and excellent welding performance. Most of them are used in shipbuilding and aerospace hydraulic pipelines.

Advantages

1. High strength and pressure resistance

Cold working hardening increases the tensile strength by 20%-50% (for example, the strength of 45# steel after cold drawing can reach more than 600MPa). The seamless structure has no weld weak points and the pressure bearing capacity is better than welded pipes.

2. High dimensional accuracy and surface quality

The outer diameter tolerance can reach ±0.1mm, and the inner wall roughness Ra≤0.8μm, which reduces the energy loss of the hydraulic system. Suitable for precision hydraulic cylinders and servo control systems.

3. Lightweight design

Thin-walled tubes (such as wall thickness 1.5mm) can achieve lighter weight under the same pressure, which is suitable for mobile equipment (such as forklifts and excavators).

4. High material utilization rate

The cold drawing process has almost no cutting waste, which is environmentally friendly and cost-controllable.

Disadvantages

1. High process complexity

Multiple drawing + heat treatment is required, and the production cycle is long (such as 5-7 days to produce a batch of precision tube). Large mold loss (carbide mold life is about 5000-10000 times).

2. Decreased material plasticity

After cold processing, the material ductility decreases, and subsequent bending or flaring processing is prone to cracking, requiring annealing to restore plasticity.

3. Wall thickness uniformity challenge

Ultra-thin wall tubes (wall thickness <2mm) are prone to eccentricity or ovality problems, requiring precision mold control.

Summary

Cold-drawn seamless hydraulic tubes achieve high strength, high precision and light weight through precision cold deformation process, and are ideal for high-pressure hydraulic systems, but the complexity of the process and the challenge of wall thickness uniformity need to be weighed. When selecting, the working pressure, medium properties and budget should be considered, and if necessary, professional suppliers should be consulted for customized design.