Basic Knowledge of Continuous Casting Mold

 This article describes the design and principles of continuous casting molds and their main features, the characteristics of different types of large molds and related knowledge about molds.

Key words: continuous casting; crystallizer; characteristics; method

Design principles for the shape of the inner cavity of the mold copper tube of the high-efficiency billet continuous casting machine

The shape of the inner cavity of the mold copper tube of the high-efficiency billet continuous casting machine is designed according to the solidification characteristics of the continuous casting billet. Two aspects are mainly considered: one is near the meniscus, due to the high heat flux density and heat concentration, the heat deformation of the mold copper tube. The second is the shrinkage of the billet shell during the solidification process. The design principle is that the shape of the inner cavity of the copper tube of the crystallizer is consistent with the shrinkage law of the solidified billet shell, so as to reduce the thermal resistance of the air gap.

The main characteristics of high-efficiency continuous casting mold copper tube material

The requirements for the material of high-efficiency continuous casting molds are good thermal conductivity, high recrystallization temperature, thermal fatigue resistance, high strength, good wear resistance, and long service life. The main characteristics of high-efficiency continuous casting mold copper tube materials are the above-mentioned The overall performance of the performance is the best.

Hot top crystallizer

The surface quality of the slab largely depends on the uniformity of the primary slab shell at the meniscus, and the uniformity of the primary slab brightness depends on the heat flux density and the uniformity of heat transfer at the meniscus. The heat flux density is high, and the growth of the primary shell is too fast, which will increase the depth of the vibration mark, and at the same time make the shell shrink in advance, which enhances the unevenness of the shell thickness. Depression occurs locally, the tissue is coarsened, and obvious crack sensitivity is produced. For this reason, low thermal conductivity materials are inlaid in the meniscus area of the crystallizer to reduce the heat flux density and delay the shrinkage of the billet shell, that is, the hot top mold. The test shows that when casting low carbon steel, the casting speed is 1.3m/min, and the heat flux density at the meniscus is 2MW/m2 for common crystallizer and 0.5MW/m2 for hot top mold. The heat flow of the hot top crystallizer is reduced by 75%, the vibration marks are reduced by 30%, and the surface quality is obviously improved.

Characteristics of explosively formed mold copper tubes

The mold copper tube with taper can be manufactured by profiling or pressure forming with inner core and outer mold. Profiling will destroy the copper structure and affect the service life. Processing complex tapers requires special processing equipment, which improves the manufacturing cost. Pressure forming will produce larger cutting head and tail cutting, and the yield of copper is low. Explosively formed crystallizer copper tubes can be made into multi-taper and small angles of the inner cavity, which is especially beneficial to the repair of scrapped old crystallizers.

Explosive mold water jacket characteristics

With the development of high-efficiency continuous casting, high-efficiency narrow-slot water-jacketed crystallizers have been widely used at home and abroad. The narrow-slit water-jacketed crystallizer puts forward high requirements on the precision and form of the diversion water jacket. The deviation of the water gaps on the four sides of the crystallizer will have a great impact on the water flow rate, resulting in uneven cooling on the four sides. It is difficult to completely eliminate the influence of the weld seam by welding the water jacket after machining or welding after overall extrusion. The mold water jacket formed by explosion has the characteristics of no weld seam processing and high manufacturing precision. Foreign stainless steel water jackets are mostly made by explosive forming technology.

Characteristics of spray crystallizer

The spray crystallizer is to change the isolation water gap of the tubular crystallizer into spray water cooling, that is, the spray water sprayed from the nozzle is directly sprayed on the copper tube of the crystallizer to realize cooling. High cooling efficiency and significant water saving effect. The spray mold has a simple structure and low requirements for sealing, which avoids the problems of non-adjustable cooling intensity at the corner of the copper tube of the water seam mold, relatively weak cooling intensity, and uneven temperature distribution. Spray mold has been widely used in billet continuous casting machine. Theoretically speaking, the spray crystallizer can use general cooling water, but the accidents caused by problems such as fouling and nozzle blockage in actual production have affected the use of the spray crystallizer.

“Water seam” crystallizer features

Both the “water slot” crystallizer and the spray crystallizer belong to the tubular crystallizer. “Water seam type” crystallizer adds a water jacket to the copper tube of the crystallizer, and the water gap formed between the copper tube of the crystallizer and the water jacket is cooled by water. The “water gap” crystallizer is stable in use and not prone to blockage. At present, high-efficiency continuous casting generally uses narrow water-slit crystallizers with water gaps less than 4mm to increase the flow rate of cooling water, and with parabolic taper copper tubes, good results have been achieved.

Slab online width adjustment crystallizer

In order to meet the needs of producing slabs of various specifications and shorten the time for mold replacement, the width of the mold can be adjusted online. Slab online width adjustment crystallizer means that the two narrow sides of the crystallizer can move inwards or outwards in small steps for many times until the predetermined width is adjusted, and the adjustment of the crystallizer width is completed during the production process. In order to produce slabs of various specifications, the width of the crystallizer needs to be changed. The on-line width adjustment of the crystallizer can continuously cast billets of different widths, which saves downtime and improves production efficiency; it can reduce the loss of billet trimming and increase the yield; it can cast molten steel with similar composition without Downtime is required.

Commonly used methods for crystallizer liquid level detection

Commonly used methods for crystallizer liquid level detection include: eddy current method, electromagnetic induction method, thermocouple method, infrared method, radioactive source method, etc. Currently the most widely used method is cobalt 60 or cesium 137 radioactive source detection method.

Crystallizer non-sinusoidal vibration

The most commonly used method to realize the non-sinusoidal vibration of the mold is through the hydraulic servo system, which can realize online adjustment of the amplitude and frequency, and set the waveform according to the process requirements. The hydraulic servo system realizes the non-sinusoidal vibration of the crystallizer with relatively high precision, and has been well applied in production practice, but the equipment cost is relatively high. The non-sinusoidal vibration of the crystallizer can also be realized by mechanical methods, and a device for realizing non-sinusoidal vibration of the crystallizer by mechanical methods has been developed in China. According to reports, foreign countries have developed and used digital hydraulic cylinders instead of hydraulic servo systems to realize non-sinusoidal vibration of the crystallizer, which greatly reduces costs and has broad market prospects.

Advantages of the plate spring mold vibration system

Traditional crystallizer vibration systems mostly use four-eccentric and short-arm four-link mechanisms. It is generally believed that this mechanism has a flaw in the guide design, that is, uncontrollable motion deviation due to wear. Therefore, a flexible body crystallizer vibration guide mechanism-leaf spring crystallizer vibration system has emerged. The vibration system in which the upper arm of the four-link mechanism is replaced by a spring steel plate is called a half-leaf spring crystallizer vibration device, and the vibration system in which all four-link mechanisms are replaced by spring steel plates is called a full-leaf spring mold vibration device. Since the vibration system of the plate spring crystallizer is a vibration mechanism without bearings, there is basically no wear and tear, and it has the advantages of stable performance, high motion precision, and long life. At present, a new generation of all-leaf spring vibration devices has appeared in China, with enhanced overall rigidity and higher precision.

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