A High-precision cold-drawn tubes offer exceptional dimensional accuracy, typically achieving IT8–IT9 tolerance grades or better, with surface roughness as low as Ra 0.4 μm. The cold-drawing process strengthens the material, increasing hardness and strength while retaining good toughness. This makes them ideal for high-pressure hydraulic systems like construction machinery cylinders. The process enables continuous mass production with higher speed, shorter cycles, and significantly improved material utilization compared to traditional cutting, effectively reducing costs. Additional benefits include excellent straightness and surface finish, reducing downstream machining needs across automotive, electronics, and medical device industries.

A Production begins with selecting high-quality carbon structural steel or alloy steel that passes strict chemical and physical inspection. The material is cut, heated, and pierced to form a tube blank. After rolling to achieve the required wall thickness and outer diameter, the tube undergoes acid pickling to remove scale, oil, and impurities. The core step is cold drawing, where the tube is continuously pulled through a die at low temperature to further reduce dimensions and improve precision and surface finish. Finally, the tube receives heat treatment, finishing, and thorough inspection to ensure it meets all quality standards.

A The complete process includes: tube stock supply using hot-finished, semi-finished, extruded, or welded tubes as raw material; tube preparation involving inspection, bundling, acid pickling, cleaning, rinsing, neutralizing, drying, and lubricant coating; cold working via cold rolling or cold drawing; and finished product finishing including final heat treatment, straightening, sampling, end cutting, manual and non-destructive inspection, hydrostatic testing, oiling, packaging, and warehousing. Because multiple cold deformation passes are typically required, the overall production cycle is long with many reciprocating steps and relatively low output volumes.

A Special treatments include acid pickling and cutting to remove surface oxides and impurities from the raw material. Cold drawing then gradually reduces the tube's diameter while increasing length and improving surface finish and dimensional accuracy. Annealing follows to release internal stresses and enhance strength and toughness. After these core steps, the tubes undergo finished product heat treatment, straightening (both hot and cold with strictly controlled temperatures), sampling, end trimming, comprehensive inspection, hydrostatic testing, oiling, and final packaging before entering storage.

A Deformation is controlled through multiple measures. Select materials with good plasticity and deformation capacity. Maintain a suitably low cold-drawing temperature to reduce excessive plasticity. Control the drawing speed; too fast causes localized overcooling, while too slow leads to inadequate deformation. Apply proper lubrication to reduce friction. Optimize the cold-drawing ratio—the degree of deformation per pass—to stay within design limits. Use well-designed dies with correct geometry and surface quality. Control drawing force and tensile ratio precisely. Apply intermediate heating or annealing when needed to relieve stress and restore plasticity.

A The initial rolling reduction rate is the percentage by which the original hot-rolled tube billet's diameter is reduced during the first rolling stage. It is calculated from the difference between the tube's outer diameter after drawing and the original billet diameter. This rate is typically small, generally below 5%, though it varies with specific requirements. Its purposes are to reduce the tube diameter for precision, control dimensions within specified tolerances, improve surface quality by reducing irregularities and internal stress, and help set proper rolling mill parameters such as radial force and speed.

A Accuracy is ensured by using high-quality raw materials that provide stable mechanical properties and good processability. Processing temperature must be strictly controlled—too high causes softening and deformation, too low increases brittleness. Optimal process parameters including pressure, number of drawing passes, and drawing speed are selected based on material characteristics. The precision and stability of the drawing equipment itself are critical and require regular maintenance. Finally, rigorous quality inspection throughout the process detects and resolves issues promptly, ensuring the finished product consistently meets dimensional and quality specifications.

A During cold drawing, plastic deformation activates multiple slip systems within the metal crystals. Dislocation movements intersect and impede each other, causing many dislocations to become pinned and pile up. Dislocation sources then cease operating. This results in significantly reduced dislocation mobility and a sharp increase in dislocation density. As deformation continues, increased stress forces pinned dislocations to move again, with screw dislocations undergoing cross-slip and edge dislocations creating more immobile jogs. The increased density and reduced mobility of dislocations make the material harder and stronger.

A Before cold treatment, immerse the tube in boiling water for about 30 seconds to reduce internal stress by approximately 15%. Then perform conventional cold treatment, typically starting at -60°C followed by deep cooling at -120°C. Lower temperatures transform more retained austenite to martensite, though about 2% austenite usually remains to provide a buffering effect. After cold treatment, immediately transfer the tube to hot water for gradual warming, which reduces cold-treatment stress by roughly 40%. Follow with prompt tempering to further relieve stress and prevent cracking, ensuring stable properties and preventing future distortion during storage and use.

A Precise temperature control during annealing and cooling is critical; incorrect temperatures can cause thermal and structural stresses leading to cracking or warping. Internal stresses from machining must be relieved after rough processing. During cooling, white, hard, and brittle structures can form on surfaces and in certain sections, making machining difficult. Standard annealing or normalizing occurs at 850–950°C, held for 1–2 hours to allow cementite to decompose into graphite and austenite. Slow furnace cooling then further decomposes secondary and eutectoid cementite into graphite, resulting in a ferrite-plus-pearlite matrix with reduced hardness and improved machinability.