Structure and Characteristics of Cantilever Mill

1. Preface

With the rapid development of continuous rolling technology for small and medium-sized bars, as the requirements for output, quality and efficiency are getting higher and higher, the requirements for rolling mills are also getting higher and higher, which are mainly reflected in the following aspects:

First, the rolling mill is required to have extremely high stability, so the rolling mill must have high rigidity;

Second, it is required to have a faster spoke changing speed to improve the operation rate of the rolling mill, so the function is required to realize simple, fast, and reliable replacement;

Third, the rolling mill is required to have a compact structure in order to realize the compact layout of the rolling line and save investment;

Fourth, the rolling mill operation is required to be easy to use and have a very low accident rate.

Therefore, the new generation model – cantilever rolling mill shows its advantages. In the 1980s and 1990s, advanced continuous rolling bar production lines all over the world adopted cantilever rolling mills in roughing mills. In the 1990s, many of the dozens of continuous rolling production lines built in China chose this type of machine.

Facts have proved that this rolling mill is advanced, practical and reliable, and has been well received by users. This paper introduces the structure and characteristics of this rolling mill.

2. The structure of the cantilever rolling mill

2-1 Main drive system

The system consists of a motor, a gear coupling with a safety shear pin and a compact reducer. Due to the continuous rolling process and the requirements of multi-product rolling, the second flow of each rolling mill must be adjustable , the second flow is equal to the speed of the rolling piece multiplied by the pass area. Therefore, in order to flexibly adjust the second flow, the speed must be adjusted. Therefore, at present, the cantilever rolling mill generally uses a DC motor or a variable frequency motor, and the system is also equipped with an electrical drive that meets the process requirements. systems and control systems.

2-2 Gearbox System

Since the rolling speed of the roughing mill is relatively slow and a large speed ratio is required, the system is relatively complicated, through which torque transmission, seam adjustment and deceleration are realized.

2-3 stick ring shaft and its ring locking system

The system is the main component of the cantilever rolling mill, and the ring drop is fixed on the ring rolling shaft by means of the ring rolling locking device. The parts and functions of the ring shaft are as follows:

2- 3.1 Root Ring Locking Device

The device mainly includes several major components such as ring rolling, conical sleeve, cap, flange, etc. Through these components, the spoke ring can be quickly and safely fixed on the root ring shaft, and the stability under large rolling load can be ensured sex.

(1) Conical sleeve

The part is made of aluminum bronze, which is tapered along the axial direction and inserted into the hole of the spoke ring. For the centering of the rolling ring on the shaft, four slits with a width of 3mm are symmetrically and evenly opened around the conical sleeve to accommodate the elastic deformation during rolling. There are small holes at the top of the slits to reduce stress concentration. The spoke rings are fixed and released through a hydraulic system using tapered sleeves, thereby realizing the disassembly and assembly of the spoke rings.

(2) hat

Its main function is to transmit the torque from the phase ring shaft. The flat head of the shaft cooperates with the flat hole with the spacer in the cap to transmit the torque. The various hydraulic circuits required when changing the spoke ring are passed through the circuit inside the cap. The hydraulic connector is also installed on the hat. The hat is equipped with two shapes of intermeshing teeth, which can fix the spoke ring and the conical sleeve.

(3) Flange and center large bolt

Its main function is to compress the cap and rolling ring on the spoke shaft and maintain the pressure of the hydraulic medium between the cap and the conical sleeve. The large central bolt is screwed on the spoke ring shaft. In order to protect the inner wire of the ring rolling shaft from being damaged by the axial impact load, the inner wire is provided with a wire protector.

(4) Sealing support ring

This part is a ring with an inner hole and an outer wire. It is connected with the cap by a screw thread. The inner hole is matched with the conical sleeve – there is a sealing ring at the mating place. A closed hydraulic working chamber is formed between the ends to prevent the leakage of hydraulic medium and maintain the pressure, so as to ensure that the working parts such as the conical sleeve and the phase ring are not loosened during operation.

2- 3.2, spoke shaft

Also called a mandrel, the rolling ring is mounted on its head, a gear is machined in the middle of the shaft, and the shaft is supported by two liquid sliding bearings. The axial thrust adopts double round tapered roller bearings.

2.4. Radial adjustment device of ring shaft

Since the shaft is axially fixed and stable, there is no common axial adjustment device for rolling mills. However, due to the wear of the rolling stock and the need to change the area of ​​the rolling stock, radial adjustment is required. The mill has an eccentric sleeve adjusting device. The device consists of an eccentric sleeve worm gear, a worm, a hydraulic motor, an encoder, and a locking cylinder. The hydraulic motor drives the worm and the worm gear to rotate the eccentric sleeve. At the same time, a manual adjustment mechanism is also configured to realize the change of the center moment of the ring rolling shaft. The locking cylinder is used to prevent loosening during normal rolling, and the encoder is used for digital display of rolling seam value.

2.5, guide beam

The device is used to fix the inlet and outlet guides. It fixes the guides through dovetail grooves and fixing brackets with bolts, and the guide beams are fixed on the axle box body.

3. Features of cantilever rolling mill

3.1. Realize the quick replacement of tungsten

Due to the adoption of the cantilever shaft and the special design of the device, the spoke ring can be disassembled only by loosening the large central bolt with a pneumatic wrench. The entire spoke ring disassembly and assembly process is very simplified, easy to operate, and the work rate is greatly improved.

3.2, has a good degree and stability

The use of oil film bearings makes the shaft diameter of the ring rolling shaft large enough. Compared with the shaft diameter of ordinary rolling bearings, the diameter is increased by 30%, and the load area is increased by 65%, thus ensuring the strength of the spoke ring shaft, and the elastic deformation is extremely small, which can withstand Large rolling load.

3.3, has good safety protection performance

3- 3.1 Coupling with safety shear pin for mill overload protection.

3- 3.2 The oil film bearing has a unique design. During the normal rolling process, only 4bar pressure oil film can be formed, and the lubrication system has low pressure and power loss protection, and is equipped with the function of automatic oil temperature adjustment, so that the rolling mill can run safely and reliably.

3- 3.3 Adopt special labyrinth seal and compressed air seal in the axle box, which can effectively prevent water and iron oxide skin damage.

3- 3.4 All gear meshing parts in the axle box are automatically lubricated, and are equipped with small flow alarm protection, so as to ensure that the transmission box works under normal temperature.

3.4 The rolling mill has a compact structure

It can be seen from the introduction that the structure of the rolling mill is very compact and reasonable, and it is alternately arranged horizontally and vertically to realize twist-free rolling, which creates conditions for the compact layout of the roughing mill.

3.5 Greatly shorten the accident handling time

The eccentric sleeve oil film bearing, the thrust bearing and the phase ring shaft form an integral part of the rolling shaft assembly, which can be replaced as a whole in case of failure, which greatly shortens the accident handling time.

3.6 The stick ring is easy to replace

The frame is easily accessible for easy ring roll replacement, troubleshooting, repairs and replacement of guides, and more.

3.7 Various media safety

The various media are distributed in pipes inside the frame without any external lines or connections exposed and therefore not damaged.

4 Conclusion

From this, it can be seen that the cantilever rolling mill is very ideal for the application of small and medium-sized bar and wire roughing mills. It makes large-scale, fast-paced and high-efficiency production possible. Of course, this kind of rolling mill also has a one-time cost. High, poor flexibility, high manufacturing precision requirements, complex maintenance and other shortcomings.

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