Why do seamless pipes need to shrink and expand?

Some seamless pipes require shrinking and flaring to produce products. The shrinking and flaring of seamless steel pipes is a forming process that shrinks and expands the mouth of a preformed steel pipe through a shrinking and flaring die.

Seamless pipe hot extrusion expansion technology

(1) Shrinkage and expansion hot extrusion refers to heating the steel pipe to a temperature above a specified temperature, and the plasticity is good in its hot state. Equipment used: super audio, forging press, shrinking machine, expanding machine and other extrusion molding.
(2) Heat shrinkage process: Port heating → rough forging → rolling extrusion compression → natural cooling → port turning (this is shrinking at one end, shrinking at both ends and repeating the above process).
(3) Thermal expansion process flow: port heating → rolling extrusion expansion → natural cooling → car port (this is the expansion at one end, and the above process is repeated at both ends).

Cold contraction and expansion cold extrusion process

(1) The contraction and expansion cold extrusion process uses hydraulic pressure to push the mold and directly squeeze the nozzle to form.
(2) Equipment used: double-station shrinking and expanding machine, shrinking mold, and mold expanding.
(3) One end shrinking and expanding process: Lubricate the mold and nozzle → squeeze the short tube, expand → turn the mouth.
(4) The process flow of shrinkage and expansion at both ends: Apply lubricating oil to the mold and ports → Extrusion and expansion → Rotary fine-tuning positioning block (the length has a certain extension and shortening) → Apply lubricant to the mold and ports → Extrusion and expansion →Car port.
(5) The number of shrinks is determined by the material. Enabling the duplex bit takes two seconds.

Confirmation of shrinkage and expansion times

(1) Due to the lack of effective calculation formulas, the principles of shrinkage and expansion times can be determined based on actual experience. The axial pressure required for shrinkage and expansion deformation does not cause the material to yield or plastic deformation, and it is completed in one go. The axial pressure required for deformation causes the material to yield, plastic deformation occurs, and the material bulges out of shape. It should be divided into two times, and the differentiated axial pressure is less than the yield of the material. This principle is also used to judge whether a material meets the craftsmanship.

(2) Considering factors such as material work hardening, increased production frequency, equipment cost, etc., the number of shrinks should not be too many, only two at most.

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