1.Requirements of continuous casting production process for continuous casting equipment:
1) It must be suitable for the whole process of high-temperature molten steel changing from liquid to liquid solid and then to solid;
2) It must have high resistance to high temperature, fatigue strength and sufficient strength;
3) It must have high manufacturing and installation precision, easy maintenance and quick replacement, sufficient cooling and good lubrication, etc.
2.What types of continuous casting machines are divided into according to the running trajectory of continuous casting flow? Briefly describe the characteristics of each type?
1) Vertical continuous casting machine, vertical bending continuous casting machine, arc continuous casting machine, elliptical continuous casting machine and horizontal continuous casting machine.
2) A. Vertical continuous casting machine: The shell of this casting machine is cooled evenly and is not affected by bending and straightening, so it is not easy to produce internal and surface cracks, which is conducive to the floating of inclusions, but its equipment is high, inconvenient to operate, high investment cost, difficult equipment maintenance and accident handling, and the section, fixed length and pulling speed of the casting are limited. In addition, the casting is due to the high static pressure of molten steel, and the deformation of the slab belly is more prominent.
Vertical bending type continuous casting machine: the tundish, crystallizer, guide roller and dummy rod of the casting machine are distributed along the vertical line. The straightening machine and cutting machine are arranged horizontally, and the pouring and cooling solidification are completed in the vertical direction. After complete solidification, it is bent 90° and enters the bending section, and the billet is discharged in the horizontal direction. Its casting machine height is lower than that of the vertical type, which is convenient for transportation and can meet the requirements of longer fixed lengths. However, due to the addition of one bending and straightening, cracks are caused.
Arc continuous casting machine: divided into single-point straightening arc continuous casting machine, multi-point straightening arc continuous casting machine, and straight crystallizer arc continuous casting machine. a) Single-point straightening arc continuous casting machine: Advantages: The height is lower than that of the vertical and vertical bending types, so the equipment is light in weight, the investment cost is low, the installation and maintenance are convenient, the static pressure of molten steel on the billet is small, which can reduce the internal column and segregation caused by the belly, which is conducive to improving the pulling speed and improving the billet quality. Disadvantages: During the solidification of molten steel, non-metallic inclusions tend to focus inward, which causes uneven distribution of debris inside the billet. b) Multi-point straightening arc continuous casting machine: Advantages: The deformation rate of the solid-liquid interface is reduced. When the liquid core of the ingot is straightened, no internal cracks are generated, which is conducive to increasing the drawing speed. c) Advantages of the straight crystallizer arc continuous casting machine: It has the advantages of vertical type, which is conducive to the floating of large inclusions and the average distribution of inclusions in steel. It is higher than the vertical bending type and has low construction costs. Disadvantages: The outer arc side of the ingot shell is stretched, and the two-phase region is prone to crack defects. The equipment structure is complex and difficult to inspect and repair.
Elliptical continuous casting machine: Its advantages are that the height is greatly reduced compared to the arc type, the static pressure of the molten steel is low, the amount of the ingot belly is small, the internal crack center segregation is improved, and the investment is saved by 20%-30% (compared to the arc type). However, the inclusions in the molten steel in the crystallizer have almost no chance of floating, so the requirements for the molten steel are strict.
Horizontal continuous casting machine: Its advantages are the lowest equipment height, secondary oxidation of molten steel, improved quality of ingot, no bending and straightening, which is conducive to preventing cracks, simple equipment maintenance, and convenient accident handling, but the separation of the connection between the tundish and the crystallizer is expensive, the lubrication between the crystallizer and the ingot is difficult, and the crystallizer does not vibrate during billet drawing. It is suitable for small billet quantities, multiple castings, square billets below 200mm, round billets, and special steels.
3.Definition of continuous casting and rolling
The high-temperature defect-free billets produced by the continuous casting machine do not need to be cleaned and reheated (but need to be subjected to a short-term soaking and insulation treatment) and are directly rolled into products. In this way, the process of directly connecting “casting” and “rolling” into a production line is called continuous casting and rolling.
4.Methods for compact connection of continuous casting and continuous rolling
Hot charging and direct rolling of continuous casting billets. The hot charging process of continuous casting billets refers to the method of rolling the billets produced by the continuous casting machine into a heating furnace for heating without cooling. The direct rolling process of continuous casting billets refers to the method of directly sending the high-temperature billets from the casting machine to the rolling mill for rolling into products without heating or only slightly supplementing the edges.
5.Advantages of continuous casting and rolling
1) Simplified production process and short production cycle; 2) Small footprint; 3) Small fixed asset investment; 4) High metal recovery rate; 5) Good steel performance; 6) Low energy consumption; 7) Great reduction in factory staffing; 8) Good working conditions and easy automation.
6.Limiting factors for increasing billet drawing speed
1) Limitation of billet drawing force; 2) Influence of billet section; 3) Influence of billet thickness; 4) Limitation of heat conductivity of crystallizer; 5) Influence of speed on casting quality; 6) Influence of superheat of molten steel; 7) Influence of steel grade.
7.Second cooling zone position and cooling method
Foot roller section, support guide section and fan section.
Second cooling zone cooling method: 1) dry cooling; 2) water spray cooling; 3) water-air spray cooling (best effect).
8.Inverted taper
In order to reduce air gaps, accelerate heat transfer of molten steel and growth of billet shell, the lower section of the crystallizer is usually smaller than the upper section. Too small inverted taper will cause the billet shell to separate from the copper wall too early to produce air gaps, reduce the cooling effect, or make the billet shell thickness of the crystallizer insufficient to cause leakage accidents; too large inverted taper can easily lead to excessive extrusion pressure between the billet shell and the copper wall of the crystallizer, thereby accelerating the wear of the copper wall.
9.Crystallizer meets requirements
1) Simple structure and light weight; 2) Good thermal conductivity and water cooling conditions; 3) It should be reciprocated up and down and lubricant should be added; 4) The crystallizer has sufficient rigidity to avoid affecting the quality of the billet.
10.Crystallizer vibration mode
Synchronous, negative slip, sinusoidal vibration
11.Crystallizer width adjustment method:
1) Stop widening;
2) Translation widening;
3) Rotation plus translation widening (most representative).
12.Basic shape of vertical roller in vertical edge rolling mill:
1) Flat roller;
2) Conical roller;
3) Hole-shaped roller with flat or convex groove bottom surface;
4) Hole-shaped roller with inclined groove bottom surface.
13.Special roller type method in rolling width adjustment:
1) Scallop-shaped roller widening;
2) Roller widening with staggered roller rings;
3) Roller widening with middle protrusion;
4) Roller widening with variable ring-shaped protrusions, tapered roller widening;
5) Large crown roller widening;
6) Tapered roller widening.
14.Short hammer width adjustment presses are divided into:
1) Start-stop width adjustment presses;
2) Continuous width adjustment presses;
3) Swing width adjustment presses.
Features:
1) Start-stop width adjustment presses: the workpiece remains stationary during work, positioning is accurate, and the clamping rollers can prevent the slab from bending;
2) Continuous width adjustment presses: the compression of the workpiece is synchronized with the advancement of the work, the operation cycle is short, the efficiency is high, and the surface quality of the workpiece is high;
3) Swing width adjustment presses: the above two advantages are combined.
