With the development of shipbuilding, petrochemical, boiler, pressure vessel, and other industries, ultra-large CNC marine plate rolling machine has become one of the important development directions of plate rolling machine. The work roll is the crucial part of the ultra-large CNC marine plate rolling machine. One upper roll and two lower rolls are integrally forged, and after heat treatment in a pit furnace, they are processed and shaped, requiring sufficient toughness and high surface hardness. , can not produce indentation on the surface of the roller when rolling the plate, and can meet the requirements of long-term rolling of the steel plate. Therefore, its processing quality accuracy (referring to processing accuracy and surface roughness) directly affects the accuracy and service life of the entire equipment.
Analysis of processing technology characteristics of ultra-long coiling machine roll
Generally, the length-to-diameter ratio of the roll shaft of the plate bending machine is greater than 20~25 (ie L/d≥20~25), which is called a slender shaft, and when the working roll of the plate rolling machine has a length of 24400mm and a diameter of about 430mm, the ratio of length to diameter is about 60, which belongs to the ultra-slender axis. Figure 1 is a schematic diagram of the experimental blank.
The technological characteristics of ultra-slender long-axis turning are as follows:
The rigidity of the ultra-slender long shaft is very poor, and it is easy to bend and deform due to the cutting force and gravity, and generate vibration, which affects the machining accuracy and surface roughness. The traditional clamping method used for turning the slender shaft on the lathe mainly adopts the clamping method of one clamp and one top, and its mechanical model is shown in Figure 2.
The reason for the bending deformation of the slender shaft caused by turning is analyzed and studied. In the turning process, the cutting force generated can be decomposed into main cutting force PZ, back force PY, and feed force PX. Different cutting forces have different effects on bending deformation when turning slender shafts.
The influence of back force PY
The back force acts vertically in the horizontal plane passing through the axis of the slender shaft. Due to the poor rigidity of the slender shaft, the radial force will bend the slender shaft to make it occur in the horizontal plane.
Influence of feed force PX
The feed force acts parallel to the axial direction of the slender shaft. For general turning, the axial cutting force has little effect on the bending deformation of the workpiece and can be ignored. However, due to the poor rigidity of the slender shaft, its stability is also poor. When the axial cutting force exceeds a certain value, the slender shaft will be bent to cause longitudinal bending deformation. Under the action of rotating centrifugal force, the deformation is aggravated, caused a vibration.
The cutting heat generated by ultra-slender long-axis turning can cause thermal elongation of the workpiece. In the turning process, if both ends of the shaft are fixed supports, the chuck and the top of the tailstock are fixed, so that the distance between the two is also fixed, so that the axial elongation of the slender shaft after heating The amount is limited, resulting in bending of the slender shaft due to axial compression.
Long continuous cutting time
Due to the long continuous cutting time, the tool is constantly worn during the machining process, and it is not easy to obtain good machining accuracy and surface quality if it is not compensated in time.
Due to the use of the tool holder, if the pressure of the supporting workpiece is too small or does not contact the part, it will not work, and the rigidity of the part cannot be improved: if the pressure is too large, the part is pressed against the turning tool, the cutting depth increases, and the turning out The diameter is small. When the tool holder continues to move, the support block is supported on the outer circle of the small diameter, and the support block is separated from the workpiece. The cutting force makes the workpiece move outward, the cutting depth decreases, and the diameter of the machine becomes larger. The tool holder follows the large diameter circle, and presses the workpiece against the turning tool to make the turning diameter smaller. Such continuous and regular changes will turn the slender workpiece into a “bamboo” shape. The poor rigidity of the machine tool, workpiece, and tool technology system brings difficulties to the cutting process, and it is not easy to obtain good surface roughness and geometric accuracy.
Marine plate rolling machine
Marine plate rolling machines can be mainly divided into two categories – symmetrical type and horizontal downward adjustment type. Among them, the earliest marine plate rolling machine developed in China is a symmetrical plate rolling machine. The three rolls of the plate rolling machine are symmetrically distributed, and the upper roll and the lower roll are equipped with beams and support rolls. Generally, each of the two lower rollers is equipped with a set of independent driving devices. Generally, the symmetrical marine plate rolling machine can roll conical or arc-shaped workpieces with a central angle of 180 degrees. The length of the workpiece must be controlled between 8 meters and 21 meters, and it cannot be rolled into a full circle. The disadvantage of this bending machine is that there is no pre-bending function, and the remaining straight sides are large.
The ultra-large marine plate rolling machine is the necessary equipment for manufacturing large ships, and it is currently the world’s largest CNC marine plate rolling machine. Only a few large foreign companies such as Switzerland and the United Kingdom can manufacture the plate rolling machine in the world. Due to high technical content, many technical difficulties, and large research and development funds, domestic forging machine tool manufacturers do not have the strength to break through the technology of ultra-large marine plate rolling machines. There is a technological gap in the industry. Domestic shipbuilding enterprises can only rely on imports, and import a machine of this specification. The plate rolling machine in China needs more than 8 million US dollars, and the delivery period is at least two years.
PRV marine plate rolling machine
The PRV marine plate rolling machine came into being. This plate rolling machine makes up for the shortcomings of the previous generation of symmetrical marine plate rolling machines. It has a pre-bending function and higher working accuracy. The upper roller of the horizontal downward adjustment marine plate rolling machine rises and falls vertically, and the lower roller moves horizontally. The upper and lower rollers are equipped with beams and supporting rollers, and are not equipped with dumping bearing bodies. Generally, the two lower rollers are equipped with a set of independent driving devices. It can roll arc-shaped or tapered workpieces with a central angle of less than 180 degrees. The length of the workpiece is controlled between 8 meters and 21 meters, and the remaining straight sides are small.