Analysis of the Production Process, Characteristics, and Application Fields of Cold-drawn Tubes

 

Cold-drawn tubes are precision steel tubes manufactured through cold processing technology, and their production process differs significantly from that of hot-rolled tubes. This process involves multiple passes of drawing deformation at room temperature to make the steel tubes meet specific size and performance requirements. Cold-drawn tubes are renowned for their high surface smoothness, excellent dimensional accuracy, and stable mechanical properties, and they are widely used in fields such as petrochemical, machinery manufacturing, automotive industry, and aerospace.

 

I. Production Process Flow

1. Raw Material Selection

Hot-rolled seamless steel tubes are used as the base material. It is necessary to ensure that the material conforms to the GB/T3639 standard, with a uniform chemical composition and no surface defects. The raw materials need to undergo flaw detection, and unqualified products with cracks or inclusions are removed.

2. Pretreatment Process

- Pickling Treatment: The oxide scale and impurities on the surface of the steel tubes are removed by hydrochloric acid or sulfuric acid solution. The acid concentration is controlled at 10%-20%, and the treatment time is adjusted according to the tube thickness.

- Phosphating and Saponification: A phosphate layer is formed on the surface of the steel tubes to enhance lubricity, and then a saponifying agent such as sodium stearate is applied to reduce the friction coefficient during cold drawing.

3. Cold Drawing Processing

Single-chain or double-chain cold drawing machines (with a tonnage range of 0.5 - 100T) are used to draw the pre-treated steel tubes through cemented carbide dies. The deformation amount per pass needs to be controlled within 15%-30% to avoid excessive hardening of the material. The typical specifications cover an outer diameter of 16 - 219mm and a wall thickness of 2.5 - 40mm, and the accuracy after processing can reach ±0.05mm.

4. Post-treatment and Inspection

- Annealing Treatment: A continuous annealing furnace is used to eliminate processing stress, with the temperature set at 600 - 750°C to restore the ductility of the material.

- Straightening and Hydrostatic Test: The straightness error is adjusted by a roller straightening machine, and then a hydrostatic test at 1.5 times the working pressure is carried out to ensure no leakage.

- Non-destructive Testing: Eddy current flaw detection or ultrasonic testing technology is used to screen for internal defects. Qualified products are coated with anti-rust oil and packaged for storage.

 

II. Core Production Characteristics

1. Work Hardening Effect: Cold deformation causes lattice distortion, increasing the strength of the steel tubes (the tensile strength can be increased by 20% - 50%), but intermediate annealing is required to balance the plasticity.

2. Multi-process Collaboration: It includes at least 6 main processes and more than 10 auxiliary processes. The production cycle is usually 40% - 60% longer than that of the hot-rolling process.

3. Material Utilization Rate: The yield rate is about 75% - 85%, and the losses mainly come from pickling waste liquid, cutting of tube ends, and unqualified products.

 

III. Typical Application Scenarios

1. Hydraulic Systems: Used for manufacturing hydraulic cylinder barrels, replacing the traditional boring process, reducing metal cutting losses by 90%, and significantly reducing energy consumption.

2. Precision Machinery: Used as guide rails for automated equipment and bearing sleeves, with tolerances controllable at the H9 level and a surface roughness Ra ≤ 0.8μm.

3. Energy Equipment: Suitable for high-pressure boiler tubes and LNG cryogenic transport tubes, with a pressure resistance rating of over 45MPa.

4. Automobile Manufacturing: Used for gearbox shafts and shock absorber tubes, with a fatigue life 2 - 3 times longer than that of hot-rolled tubes.

 

IV. Quality Control Points

During the production process, it is necessary to focus on monitoring the wear degree of the dies (the dies need to be repaired every 500 draws), the uniformity of the annealing temperature (the temperature difference ≤ 15°C), and the fluctuation of the pickling solution concentration (the pH value deviation is ±0.5). The finished products need to conform to the ISO/DIS3305 standard, and the sampling inspection ratio should be no less than 10%.

 

Cold-drawn tube technology provides a cost - effective material solution for high - end manufacturing through precision processing and strict quality control. As the accuracy requirements of industrial equipment continue to increase, the application scope of this product is gradually expanding to emerging fields such as semiconductor equipment and medical machinery.