We often say that hot-expanded pipe refers to a steel pipe with a relatively low density but a strong shrinkage, the China National Standards Association stipulates that the hot-expanded steel pipe should be a larger-diameter steel pipe expanded and deformed after the overall heating of the blank steel pipe.. Thermal expansion technology is to expand the diameter of the pipe through radial deformation, that is, non-standard, special models of seamless pipes can be produced using standard pipes, and the cost is low and the production efficiency is high. It is a common processing method for seamless pipes. Due to the high-parameter development of power plant boilers and the large-scale development of petrochemical plants, the demand for large-diameter seamless pipes is also increasing, and it is difficult for pipe rolling units to produce the seamless tube that diameters greater than 508mm, ratio of outside diameter to wall thickness(D/S)>25, thermal expansion technology, especially the relatively cost-effective medium frequency thermal expansion technology has gradually developed thus it.
The two-step propelling pipe expander used for hot-expanded steel pipes combines cone die diameter expansion technology, digital intermediate frequency induction heating technology, and hydraulic technology in one machine. With its reasonable process, lower energy consumption, lower construction investment, and good The product quality, wide range of raw materials and product specifications, flexibility and low input production batch adaptability have replaced the traditional pull-type diameter expansion technology of the steel pipe industry.
It should be noted that the mechanical properties of hot-expanded steel pipes are generally slightly worse than hot-rolled steel pipes.
The general process of thermal expansion of the pipe is to fix the pipe on the lead screw, place a cone-shaped top anvil with a diameter larger than the diameter of the pipe into the other end of the pipe, and link and fix the other screw in the pipe. The connection between the pipe and the top anvil is at Below the intermediate frequency heating coil, in order to counteract the heating too fast and burst, you need to pass water in the tube first, start the coil heating, and after reaching the specified temperature, the screw that links the tube pushes the tube, so that the tube moves toward the top anvil and extends. The top anvil taper enlarges the pipe diameter. After the entire pipe passes, the pipe will not be straight because of the thermal expansion process, so he needs to straighten it.
The above is the basic content of thermal expansion technology.
The following is the relevant formula of thermal expanded pipe
Expanded weight:
carbon steel: (diameter-thickness) × thickness × 0.02466 = weight of one meter(kg)
alloy: (diameter-thickness) × thickness × 0.02483 = weight of one meter (kg)
number of meters after hot expanded：
original tube Diameter ÷ hot expanded diameter × 1.04 × length *
original tube meters：
expanded length × (diameter ÷ original tube diameter ÷ 1.04)
speed:
100000 ÷ (original diameter-thickness × thickness)
thickness:
expanded thickness (1 time) ) = Original tube thickness × 0.92
Expanded thickness (2 times) = Original tube thickness*0.84
Diameter :
Expanded diameter = mould size + expanded thickness × 2
Mould size: expanded diameter—2 * expanded walls Thickness
Diameter tolerance：
Diameter ＜426mm, tolerance ±2.5
Diameter426-630mm,tolerance ±3
Diameter＞630mm, tolerance ±5
Ellipticity:
Diameter ＜426mm, tolerance ±2
Diameter＞426mm, tolerance ±3
Thickness:
thickness ≤20mm, tolerance ﹢2 ，—1.5
thickness ≤40mm，﹢3 ，—2
Pipe for making Pipe fitting
﹢5 ，—0
Inside and outside of scratch：
Scratch deepth : 0.2mm,length:2cm, it is called scratch. Not allowed
Straightness: ≤6meter,bend is 5mm，≤12meter,bend is 8mm
For expample:
Original tube 610*19 hot expanded 660*16
Original pipe length:12.84meter
Expanded thickness:19*0.92=17.48(1time)
19*0.84=15.96（2times）
Expanded length of pipe:610÷660*1.04*12.84=12.341962
Expanded diameter:625+17.48*2+1=660.96(1time)
625+15.96*2+1=657.92(2times)
Module Size:660-2*16=628
