Working principle and process parameters of seamless steel pipe cold drawing machine

Seamless pipe cold drawing machine is an important equipment for the production of high-precision and high-surface quality seamless steel pipes. Its working principle is based on the cold deformation processing of metal. The steel pipe is applied to the mold to cause plastic deformation, thereby achieving the purpose of reducing diameter, wall reduction or improving performance. Cold-drawn seamless steel pipes are high-precision steel pipe materials, also known as cold-rolled precision seamless steel pipes. Its characteristics are small outer diameter, high precision and mass production, high precision of cold-drawn finished products, good surface quality, etc.

• How it works

The cold drawing machine fixes one end of the seamless steel pipe in front of the pulling mold (such as the pulling mold, core rod) through the clamping device, and the other end is exerted by the traction mechanism (such as chain type, hydraulic type). The steel pipe passes through the mold under the action of the tension to achieve diameter reduction, wall or diameter reduction. The deformation amount of a single pulling is limited by the plasticity of the material, and usually requires multiple pulling (multiple pass processing). Pull-outhourThe pipe pulling mold controls the outer diameter of the steel pipe, and the mandrel controls the inner diameter (used to reduce walls or sizing diameters). The steel pipe is radially compressed and axially stretched through the conical holes of the mold, reducing its cross-section and increasing its length. After extraction, straightening, flaw detection, heat treatment (such as annealing, normalizing) and surface treatment may be carried out to meet the accuracy and performance requirements.

• Cold drawing method

Cold drawing methodgenerallyThere are two types of them. According to the reduction diameter and the reduction wall, it is divided into empty steel pipes and mandrel extrusion pipes. Those with only reduced diameters are called empty pulls, while those with reduced diameters and walls are called mandrel extrusion pipes.

Air pulling is also called coreless rod pulling. The molding tool required during drawing is only one air pulling mold, so it is the simplest way to pull, as shown in the figure. inRIt is the arc radius of the working cone of the arc mold, α is the half-cone angle of the cone mold, the arrow shows the direction of drawing, and the steel pipe is formed from left to right through the inlet area, the reducer area, the sizing area and the outlet area in turn..

The tool for the fixed short mandrel pulling method is simple to manufacture and easy to adjust and operate. Therefore, among the drawing methods with the mandrel, the use of the fixed short mandrel pulling is the most widely used.

• Main process parameters

The process parameters of the cold drawing machine directly affect the dimensional accuracy, surface quality and production efficiency of the steel pipe, and must be reasonably set according to the material, specifications and equipment model.

1.Deformation parameters

Diameter reduction: The difference between the outer diameter of the steel pipe before and after the extraction.

Wall reduction: The difference between the wall thickness of the steel pipe before and after the pull-out.

Extension coefficient: The ratio of the length of the steel pipe before and after the pull-out reflects the overall deformation degree.

2.Mold parameters

Extraction die angle: The cone angle of the mold inlet cone affects metal flow and friction. The angle range of the pipe extraction die is generally8°~15°. If the angle is too small, it will increase friction, and if it is too large, it can easily lead to metal accumulation or uneven wall thickness.

Mandrel position:The relative position of the mandrel and the pull-out mold determines the deformation state of the inner wall of the steel pipe, and it needs to be adjusted accurately to control the uniformity of the wall thickness. Common types of mandrel positionsforFixed mandrel (for wall reduction)andFloating mandrel (for continuous pulling).

3.Speed ​​and tension parameters

Drawing speed: Chain cold drawing machine is usually0.5~3 m/s, hydraulic cold drawing machine can reach5 m/sabove. The pull-out speed may lead to insufficient lubrication, mold heating or scratches on the steel pipe surface, and the lubrication conditions must be matched.

Pull the force:Determined by factors such as material strength, deformation amount, mold friction, etc., the calculation formula can be referred to as empirical formulas or finite element simulation. When selecting equipment, make sure that the pulling force does not exceed the rated pulling force of the cold drawing machine (such as100~2000 kN).

4.Materials and lubrication parameters

Material properties:The yield strength, elongation and work hardening index of the material need to be considered, and the hard material needs to reduce the amount of single deformation.

Common lubricating media: saponified liquid, phosphated membrane+Lubricants (such as industrial greases) require the lubricating film to withstand high pressures and high temperatures. Poor lubrication can lead to increased mold wear, rough surface of the steel pipe or even cracks.

• Summarize

Cold drawing processing is highly employed by relevant industries for its high production efficiency, good surface quality, high body strength and high utilization rate of chipless processing materials. For example, cold-drawn seamless pipes, cold-drawn stainless steel pipes, cold-drawn round steel, cold-drawn rolled pipes, etc. all have broad market space.Especially in the fields of automobile manufacturing, aerospace, petrochemicals, precision instruments, etc., it has shown huge application potential. With the continuous advancement of technology, cold drawing processing technology is also continuing to innovate, such as using advanced lubrication technology and mold design to further optimize process parameters to improve production efficiency and product quality. Therefore, cold drawing processing technology not only occupies an important position in the current market, but will continue to maintain its competitiveness and development prospects in the future.