Views: 0 Author: Site Editor Publish Time: 2022-07-12 Origin: Site
Large-diameter steel pipes are steel pipes with an outer diameter of more than 1000MM. Large-diameter seamless steel pipes are made of steel ingots or solid tube blanks through perforation to make capillaries, and then hot-rolled, cold-rolled, or cold-drawn.
1. Chain cooling bed. In the past, a chain cooling bed with a simple structure was mostly used, which is simple in structure and low in cost. However, because it is easy to produce chain dislocation, the large-diameter steel pipe is bent, and the large-diameter steel pipe cannot be freely collected from the input roller table to the cooling bed population, so it is rarely used.
2. Step-by-step cooling bed. This cooling bed is composed of walking beams and fixed beams. The cooled large-diameter steel pipe is lifted by the walking beam, moved forward a distance, and then placed in the tooth groove of the fixed beam. Properly adjusting the stroke of the rack can make the large-diameter steel pipe roll twice for each step, to achieve the effect of straightening the large-diameter steel pipe. At present, almost all of the newly-built tube rolling mills use stepping rack cooling beds.
3. Spiral cooling bed. This cooling bed is cooled by the helical wire on the screw rod to push the large-diameter steel pipe on the cooling bed to move forward for cooling. With the rotation of the screw rod, in addition to the forward thrust, the large-diameter steel pipe also receives a lateral thrust, so it moves laterally while advancing, just forward.
When the cooling rate is faster, the carbon content and alloy composition are higher, the uneven plastic deformation caused by thermal stress during the cooling process is larger, and the residual stress formed later is larger. On the other hand, due to the change of the structure of the steel during the heat treatment process, that is, the transformation of austenite to martensite, the increase of the specific volume will be accompanied by the expansion of the volume of the workpiece, and the various parts of the workpiece will undergo phase transformation, resulting in inconsistent volume growth and structure. stress. The final result of the change of tissue stress is tensile stress on the surface and compressive stress on the core, which is just the opposite of thermal stress.