Application and practice of fixed-length shearing in high-quality bar production line

1 Overview of production status
Xuangang's high-quality bar production line was officially put into production in March 2012. This production line is currently a professional production line in domestic technology and automation level. The main drive of the entire production line adopts fully digitally controlled AC motors. The raw material adopts the new technology of hot charging and hot feeding, full continuous high-speed rolling, and the rolling speed can reach 18 meters per second. Mainly in the production of rebar-based. The types of rolled products mainly include ∮10×4, ∮12×4, ∮14×3, ∮20×2, ∮22×2, ∮25, ∮36, ∮40. The cold shear on the production line is responsible for all finished products. For the shearing task of the material, the double ruler shears the finished material into a finished steel of 6-15m. The sizing machine is located above the cold shear output roller table, and a hydraulic motor drives it to run left and right. The production line adopts stationary cold shears, with a shearing capacity of 1,300 tons and a shearing blade width of 1,700mm. The cold shearing equipment mainly includes the main motor of cold shearing, brake fan, clutch fan, thin oil lubrication, dry oil lubrication, inlet pressure roller, flush baffle, and outlet lifting roller table. The function of the sizing machine is to change the length of the finished product by sizing and moving after determining the size of the finished product. In production, the length of the finished product is often limited and adjusted by the sizing machine. When rolling 15m, 12m, and 9m finished products, it is necessary to move the sizing machine to control the length of the finished product.
After the exit bar of the finishing mill is cut in sections by the double ruler flying shear, it is accelerated by the cooling bed and input to the roller table, so as to widen the distance from the head of the next bar. When the tail of the bar is about to reach the steel parting point The brake apron begins to descend to divide the steel. When the brake apron reaches the low position, the bar on the roller table slides into the brake apron along the slope of the roller table to start braking, and the head of the next bar reaches the dividing point. Before the brake skirt rises to the middle position to block the next steel, when the bar material in the brake skirt stops running, the brake skirt rises to the high position and throws the bar material into the straightening plate, the brake skirt is made of steel Finished moving. After the brake apron reaches the high position, the moving teeth of the cooling bed are delayed and started, and the bars are transported to the discharge side of the cooling bed for a distance of one tooth pitch. The bar material is transported to the steel row chain, and forms a material layer on the steel row chain. The new material layer forms the rear steel chain and takes a big step to separate the material layer from the next material layer. After that, the material transport trolley will discharge steel. The material layer on the chain is lifted and transported to the cooling bed output roller table, the cooling bed output roller table is started, the material layer is transported to the fixed-length baffle for alignment, and then cold-cut to make a single cut, and the fixed-length baffle is raised. After the cold shearing, the roller table runs, and the sheared rod layer is transported to the collection area.

2 The principle of operation of the sizing machine
2.1 Main operations
The length of the fixed length is set, the hydraulic station of the fixed length starts and stops, and the fan of the hydraulic station starts and stops. Sizing machine encoder calibration.
2.2 Local operation
The sizing machine can be moved left and right in the BM05LCB2 on-site operation box, the baffle is lifted, the lock is released, the hydraulic station starts and stops, and the fan starts and stops.
2.3 Centralized operation
Centralized and controllable movement of the sizing machine left and right, the sizing baffle is lifted, locked and released, and the sizing machine is automatically positioned.
Automatic calibration of the sizing machine: when the sizing machine is at a high position, press the automatic positioning button. If the deviation between the position of the sizing machine and the set position exceeds 2mm, the locking device of the sizing machine will be automatically released, and the sizing machine will automatically run to the setting position. After the fixed length position, it will automatically stop and the locking device will be re-locked. Position calibration of the sizing machine: When the running error of the sizing machine is too large, the sizing machine needs to be re-calibrated. The specific steps are as follows: stop the sizing machine at a fixed position, lower the sizing baffle, and measure the cold shear. The distance from the cutting edge to the fixed-length stop, enter this distance into the HMI, and then press the calibration button.
Automatic fixed-length baffle: When the fixed-length baffle is at a low position, transport the bar to the fixed-length baffle to align it, and then press the single cut. The roller table runs after shearing. When the cut double ruler leaves the 3# grating after the cold shearing, the fixed-length baffle automatically descends after a delay.

3 Cold shear clutch assembly
Clutches are used for coupling and separation between the main and driven shafts of various machines and to transmit motion or power. In addition to being used for mechanical starting, stopping, reversing and shifting, it can also be used for overload protection of mechanical parts. The bar shop clutch is pneumatic, the air pressure is 0.6～0.9MPa, 0.7MPa is the suitable working pressure, and the working clearance of the clutch is 9～11mm.
(1) Before assembly, remove the debris inside the clutch body, especially the residue attached to the side wall teeth, and use an angle grinder to grind the inner teeth of the steel plate, the expansion joint chamfering and the burr trimming of the friction plate, especially if the old one is reused. When rubbing the disc, the outer teeth must be ground;
(2) During the installation of the friction plate, the heat dissipation groove of the friction plate should be aligned with the heat dissipation hole of the clutch body to achieve a good heat exchange effect. The installation position of the release spring should avoid the heat dissipation hole of the clutch body to ensure the stability of the release spring;
(3) When placing the steel sheet, adjust the position of the steel sheet to ensure that the steel sheet is in the clutch position, without affecting the placement of the release spring, and at the same time, the installation and release must ensure that the spring is stable and free from skew;
(4) After the clutch and brake are replaced online, the working clearance must be measured. If the clearance exceeds the range, online adjustment must be performed.

4 Problems existing in the operation of the equipment
4.1 Problems existing in cold shearing
4.1.1 Insufficient pressure leads to unstable operation of the equipment.
Bar wire cold shearing relies on the opening and closing of pneumatic clutches and brakes to achieve work. The working pressure of cold shear clutches and brakes is required to be no less than 0.65MPa. When the system pressure is lower than 0.65MPa, the power source transmitted to the clutches and brakes is not enough, resulting in increased internal friction of the clutches and brakes, so that the temperature is too high and the clutch is burned. In the initial design of the clutch, the internal friction plate uses a release spring to release the friction plate, but in actual use, the reciprocating action of the release spring can easily lead to the failure of the spring itself. When the friction plate needs to be opened and released, the release spring not only does not help effect. The pressure of the compressed air system required for the normal use of the cold shear clutch and brake should be 0.65 ~ 0.9MPa. Due to the low and unstable compressed air pressure of the original pipe network, the cold shear clutch and brake are frequently overheated and caused to burn out.
4.1.2 It is inconvenient to check the internal structure.
The original two-bar cold shear clutch and brake need to remove the overall protective cover to realize the clearance inspection. Only when the shutdown time exceeds 30 minutes, the cold shear can be stopped to check, so that the real-time monitoring of the cold shear cannot be realized.
4.1.3 The cold shear brake is overheated.
The cold shear system of the second bar line is the key system of the whole finishing area. Its operation is related to the production capacity and stability of the entire production line, and the cold shear brake is one of the important equipment in the cold shear system, so ensure the brake operation. Stable, the cold shearing system can be stable, and the entire production line can be produced in an orderly manner. The brake is greatly affected by temperature. Once the temperature rises above 80°C, the internal friction plate of the brake will be locked due to overheating, which will cause the brake to fail and must be repaired and replaced. The brake cooling fan is equipped to cool down the brake. However, due to the design error of the factory, the brake fan is designed to be placed in a suspended position. Since the cooling fan is running all day, it is very easy to be damaged. This placement method causes the fan to be damaged. It is very troublesome to replace, and there is a risk of being hit by the fan, which not only delays time, but also brings a heavy workload to workers.
4.2 Problems existing in the sizing machine
Due to the small fuel tank of the designed sizing machine, poor environment and dirty oil, the sizing machine itself has its own cooling system, which cannot fully achieve the cooling effect, and the pipeline of the sizing machine itself is complicated and difficult to replace, etc., which lead to the normal use process. The production has been affected many times due to the inaction of the sizing baffle of the sizing machine and the low pressure of the sizing machine. The main problems encountered in production are as follows:
4.2.1 The pressure of the sizing machine is insufficient. Because the environment where the sizing machine is located is dirty, the phenomenon that the baffle of the sizing machine cannot be lifted and cannot move forward or backward has occurred many times because the oil clogs the hydraulic valve.
4.2.2 The fixed-length oil tank is small, and the built-in cooling system is air-cooled. When the fixed-length machine moves back and forth, the air-cooled machine cannot play a good cooling effect, and the oil temperature of the oil tank is too high, which causes the seal to be damaged. Happened multiple times.
4.2.3 The position of the valve table and the oil pipe of the fixed-length machine are not suitable. When the oil leaks due to the damage of the sealing oil pipe, the disassembly and assembly of the oil pipe is inconvenient, which affects the replacement efficiency.
4.2.4 When rolling steel grades of different lengths, the sizing machine needs to move its position. During the moving process, sometimes the car slips and moves automatically.
4.2.5 The valve table of the sizing machine is completely fixed by the bottom plate welded on both sides of the valve table through connecting bolts, and the sizing machine is subjected to tens of thousands of impacts of the finished product every day, resulting in the valve table without buffer elements and its fixing bolts It is easy to loosen or break, and each control valve on the valve table is damaged and scrapped many times.

5 Problem solving
5.1 Eliminate unstable operation of cold shear
5.1.1 Install the air compressor to stabilize the air source.
The transformation has been carried out by adding steam drums, modifying routes and other measures, but the expected effect has not yet been achieved. When the air pressure is lower than 0.55MPa, the number of shears must be reduced for cold shearing, and the temporary measures are taken to automatically stop it when the air pressure is lower than 0.5MPa. Seriously restrict the production rhythm. By adding an air compressor, an independent air source is provided to stabilize the air pressure, and the pressure is stabilized at 0.68-0.73MPa to ensure the normal use of the cold shear. Due to the unstable air pressure in the air path, the high and low air pressure affects the normal opening and closing of the brake and clutch, resulting in the damage of the clutch and brake airbag, resulting in a large number of accident shutdowns. Since the brake reversing valve is located on the upper part of the roller table, the inspection and monitoring of the equipment cannot be realized when the equipment is running. The air pressure monitoring device is installed on the gas path, which realizes the real-time monitoring of the equipment, facilitates the judgment of equipment failures, and shortens the downtime.
5.1.2 Add a peephole to facilitate observation.
Use electric welding to open a 150*300mm peephole on the protective cover of the clutch and brake, and use a hinge to fix a 150*300mm iron sheet on the peephole, and weld nuts on the iron sheet and the protective cover body to achieve iron Fixing of the sheet. In this way, the inspection of the cold shear clutch and brake clearance can also be realized when there is a short-time shutdown.
5.1.3 Self-made air exhaust cooling brake.
The self-made air exhaust replaces the fan to provide cooling for the brake, using a 6" seamless pipe and evenly distributing many small air holes on one side of the pipe, leaving only the air inlet and fixing it to the setter, the small air holes are facing the brake, so that As long as the cold shear air bag is connected to the air exhaust air inlet, a steady stream of air will be blown from the air exhaust to the brakes, which will play a cooling role.
5.2 Removing the fuel tank and rebuilding the valve table to stabilize the operation of the sizing machine
The oil tank of the sizing machine is removed, and the two inlet and return oil pipes of the cooling bed hydraulic station are connected with the general inlet and return oil pipes of the sizing machine, which solves the problem of insufficient pressure caused by dirty oil in the sizing machine and sealing caused by high oil temperature. Damage, and the problem that the sizing machine cannot move and lift due to insufficient pressure; the original oil pipe and valve table of the sizing machine were renovated, and the original valve table position was moved to the position after the oil tank was removed, which solved the valve table position. Inconvenience during replacement due to inappropriateness; adding a cut gate to the moving oil pipe of the sizing machine solves the problem of inaccurate sizing caused by the sizing machine sometimes moving by itself. Use 10mm thick steel plate to remake the base, drill holes on the base, use 250mm long bolts to make a small gantry frame and insert it into the holes of the base and fasten with bolts, press the valve table through the gantry frame, and put the waste conveyor belt on the valve table. The bottom of the table acts as a buffer, and the valve table is well fixed, which protects each control valve, prolongs the service life of each valve, and ensures the normal operation of the sizing machine.

6 Conclusion
After the renovation of the equipment in this area, it has the advantages of long service life and easy maintenance, which effectively reduces the maintenance cost of the equipment and the labor intensity of maintenance personnel, and ensures the normal production. After the project is put into operation, the production indicators of the production line have reached the domestic level, and various technological transformation measures can be promoted and applied to other similar production lines.