Shrinking and flaring process of seamless steel tubes
The shrinking and flaring of the seamless steel tube is a forming process in which a preformed steel pipe is narrowed and enlarged by a shrinking and flaring die.
 
 
1. Seamless steel tube shrinking and flaring hot extrusion process
(1) Shrinking and flaring hot extrusion are materials that are heated to above the specified temperature, and use the hot state to have good plasticity. The equipment used is extrusion molding such as super audio, forging machine, shrinking machine, flaring machine, etc. The product is shown in Figure 1.

(2) Heat shrinking process: port heating → rough forging → rolling compression port → natural cooling → car port (this is a shrinking at one end, and the above process is repeated at both ends).
(3) Thermal flaring process: port heating → roll extrusion flaring → natural cooling → car port (this is a flaring at one end, the flaring at both ends repeats the above process).
 

2. Cold pipe shrinking and flaring cold extrusion process
(1) Shrinking and flaring The cold extrusion process is hydraulically pushing the die and directly extruding the nozzle. The product is shown in Figure 2. (2) Equipment used: double-station shrinking tube, expanding machine (see Figure 3), shrinking mold (see Figure 4), expanding mold (see Figure 5).
(3) Shrinking and flaring at one end Process flow: Lubricating oil on the mold and nozzle → squeeze and compress, flaring → car port. The process of shrinking and flaring at both ends: mold, port lubricating oil → squeeze compression port, flaring → appropriately adjust the positioning block (the length has a certain length extension and shortening) → lubricant on the mold, port-squeeze compression port, Flaring → car port.
(4) The number of shrinking is determined by the material. Requires two times, using double stations.
 
Comparison and analysis of the shrinkage, flaring cold extrusion process and the shrinkage, flaring hot extrusion process have their own advantages (see Table 1). Cold extrusion compression port, flaring quality requirements:
①Non-destructive testing of magnetic particles without cracks on the surface.
② Good surface roughness.
③ The metal flow lines in the extrusion deformation section are reasonable and no fracture occurs.
④ After the fatigue test of the tension rod, the loading force and the number of times of tension and compression exceeded the standard QC / T 648-2000. No abnormalities such as cracks in the shrinking and flaring were found.
⑤ Work hardening, improved tensile strength and yield strength.
 
 
Table 1 Comparison of shrinking, flaring cold and hot extrusion processes

Shrinking and flaring cold extrusion process	Shrinking and flaring hot extrusion process
Good cold extrusion surface roughness is good for paint layer adhesion	Many oxide scales on the surface, poor surface quality Affects the quality of paint, needs to be polished to remove oxide
No air pollution	The presence of anti-rust oil on the surface of the raw materials forms a lot of harmful fumes during heating The working environment is extremely poor, although there is a smoke exhaust device, the workshop is still full of smoke
Smooth surface	The mold is not adjusted in place The surface layer is easy to superimpose to form tiny cracks, which are not easy to find under the oxide layer
1 operator 1 device can complete No heating required	At least 3 operators More equipment Super audio heating power consumption
Simple process Uniform size of extrusion die	Cumbersome Poor uniformity of processing dimensions
Port turning removal 2mm	The steel port is easily overheated and melted Need turning turning 10 ~ 15mm Material waste
Direct turning operations	Need to cool naturally before turning Long waiting time and low productivity
Mold only needs 1 operator to install	Large amount of mold installation work, need 2 people to complete
The inner core is high-quality tungsten steel, Slightly higher mold manufacturing cost long lasting	The mold surface is easy to wear and needs mold repair Short use time

 
 
3. Confirmation of shrinking and flaring times
(1) Due to the lack of effective calculation formulas, the principle of shrinking and flaring times can be determined based on actual experience: The axial pressure required for the deformation of the flaring and flaring has not yielded the material, no plastic deformation has occurred, and it is completed at one time; Axial pressure is required to yield the material, plastic deformation occurs, and the material bulges (see Figure 6). It should be divided twice, after which the axial pressure is less than the material yield. This principle also determines whether a material conforms to the process. (2) Considering factors such as material hardening and increased production, equipment costs, and other factors, the number of shrinkings should not be too much. Our company only considers it at most twice.