Copper mould tube life

Description:

The copper mould tube is the core equipment of the continuous casting machine, which is responsible for the solidification and forming of molten steel. During the continuous casting process, the inner surface of the copper tube of the copper mould tube is in contact with the high-temperature molten steel, and is subject to the combined effects of chemical corrosion, thermal erosion, and friction between the molten steel and the shell, and the copper tube is prone to thermal deformation and surface scratches. , affecting the continuous casting production and deteriorating the quality of the slab.

Keyword: Copper mould tube life

copper mould tube life

The life of the mold is usually calibrated by the amount of steel passing through the mold. The judgment of the life of the mold copper tube is mainly based on two important parameters, namely the reverse taper and the amount of wear. In fact, these two parameters also affect each other.

In order to eliminate or reduce the influence of the air gap, the cavity of the copper mould tube should be designed with a certain reverse taper according to the different shrinkage characteristics of the steel and the degree of thermal deformation of the copper plate of the  mould tube . The selection of  mould tube  reverse taper should follow the following principles: the solidification shrinkage characteristics of the steel grade, the shape of the inner cavity of the  mould tube  should be adapted to the actual shape of the solidified billet shell in the  mould tube  to the greatest extent, so that the thickness of the air gap in the entire  mould tube  can be minimized , to improve the heat transfer effect of the copper mould tube to ensure the uniformity of the shell thickness in the mold and the thickness of the shell at the bottom of the mold. After the copper tube is used, if the overhaul span can no longer repair the reverse taper of the mold to the standard range required by the steel mill, it is determined that the life of the copper tube of the mold has expired.

The existence of the reverse taper improves the heat transfer efficiency of the mold, but at the same time increases the friction between the casting slab and the copper tube at the lower part of the mold, which requires that the inner surface of the copper tube should have good wear resistance. A nickel-based coating with a thickness of 0.06~0.08mm is added to the inner surface of the copper tube, and the life of the copper mould tube is considered to be expired when the wear amount of the lower mouth exceeds 1mm.

The main reasons restricting the service life of copper pipes

Copper mould tube vibration stand

The billet continuous casting machine in the steelmaking plant adopts a semi-leaf spring type imitation positive rotation vibration system. However, due to the occurrence of steel leakage accidents in actual production, the vibration frame exposed to the lower mouth of the mold is most susceptible to adhesion by molten steel or residual steel residue entering the vibrating machinery parts. It affects the accuracy of vibration parameters and even produces polarization phenomena. In severe cases, it can cause the leaf spring to break, which brings great hidden dangers to the quality of the casting billet and the normal use of the copper tube.

When the vibrating leaf spring has a long service life, the leaf spring produces linear plastic extension, and the arc of the copper tube in the mold does not coincide with the basic arc of the casting machine. This results in excessive resistance during drawing, resulting in transverse cracks and shortening the service life of the copper tube.

Assembly of tension leveling machine

The tension and leveling machine system of the billet continuous casting machine mainly consists of a set of tension and leveling upper and lower rollers, a set of free rollers, a set of despindle upper and lower rollers, a frame, a base, a transmission system, a hydraulic cylinder, etc. It is a five-roller two-point straightening structure. However, due to the weak maintenance force and limited technical level of our factory, it often happens that the dummy rod deviates from the lower mouth of the mold when feeding the dummy ingot, which cannot ensure the accuracy of arc alignment, artificially increases the drawing resistance, and increases the wear of the chromium plating layer of the copper tube.

Copper mould tube assembly

The key parameter of the copper mould tube assembly is the adjustment of the water seam. Whether the water seam is uniform on both sides directly affects the quality of the slab and the service life of the copper mould tube. When the water seams on both sides are uneven, the molten steel is easily prone to quality accidents such as deformation, corner cracks, etc. due to uneven heating. In severe cases, single-stream production accidents such as steel leakage occur, which seriously restricts production and affects the quality of the slab and the service life of the mold copper tube.

Copper mould tube reverse taper

The taper size of the mold must be appropriate. Excessive taper will cause the mold to squeeze the billet shell, causing the corners to be dented. The friction between the billet shell and the copper tube of the mold will increase, aggravating the wear of the copper tube. There will also be copper increase on the surface, and hot spots will be formed in the corner areas due to the air gap, resulting in thinning and cracks of the billet shell. A small taper will increase the air gap, reduce the heat flow, thin the shell, and easily cause steel breakouts. In addition, an excessively small taper will intensify the rotation of the corners, resulting in subcutaneous cracks and longitudinal depressions.

Corresponding measures taken

(1) Strengthen the inspection of the copper mould tube vibration device. Every time the copper mould tube is replaced or overhauled, a dedicated person will check the gap between the leaf spring and the stand to prevent the entry of protective slag, cold steel, etc., causing polarization of the copper mould tube. In addition, after the copper mould tube replacement is completed, the copper mould tube anchor bolts are tightened in place.

(2) Strengthen the training of maintenance-related knowledge and operational abilities within the workshop and the factory to ensure that basic data such as the longitudinal centerline and outer arc reference line of the continuous casting machine can be accurately identified during continuous casting maintenance and overhaul.

(3) Copper mould tube assembly.

a. For the offline copper mould tube, confirm the inner wall of the copper tube, dismantle and inspect it, check the aging of the sealing rubber ring, whether there are any abnormal changes in the water seam between the copper tube and the water jacket, whether there are foreign objects in the copper mould tube, etc. Analyze the specific reasons for offline operations and keep records.

b. The new copper tubes and water jackets are inspected strictly in accordance with the drawing requirements. All spare parts of the copper mould tube are measured and can be put online only if they meet the requirements. Ensure spare parts accuracy during copper mould tube repair.

c. During the disassembly and installation of copper pipes, two key points must be ensured: stability and accuracy. This prevents pits from appearing due to local stress on the copper pipe and deformation of the water seam adjustment device, which ultimately affects the assembly accuracy of the copper pipe. It is strictly forbidden to use sharp tools when installing the sealing rubber ring to prevent the rubber ring from being damaged easily.

d. The adjustment of the water gap is the core content of the copper mould tube repair operation. The upper water seam of the copper pipe should be positioned with matching copper pipes and water jackets before assembly. The deviation of the upper water seam is not allowed to exceed 0.5mm, and the deviation of the lower water seam of the copper pipe is not more than 0.2mm to ensure the accuracy of the water seam during assembly. Avoid casting defects caused by uneven cooling in the copper tube due to uneven water seams.

e. After the assembled copper mould tube has been tested and maintained for 30 minutes, if there is no leakage or pressure loss, it can be used online and records should be kept.

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