Optimization of oil and gas lubrication system of rolling mill, rolling mill technology (187)
Abstract: In view of the deficiencies in the design of the oil and gas lubrication system of the rolling mill, the system pressure loss is large, the equipment lubrication is prone to failure, and the oil consumption is high. The bearing lubrication is designed to be controlled by different oil and gas branches and oil and gas distributors, which solves the problems of low system pressure, frequent bearing burning and high oil consumption, while reducing pollution and improving the environment.
0、Introduction
The rolling mill used in the 750,000-ton/year bar production line of Xuangang Section Bar Plant is the Italian POMINI rolling mill, and the rolling mill bearings and guide bearings of the 18 rolling mills in the whole line are lubricated by oil and gas. The so-called oil-air lubrication is the process of mixing lubricating oil and compressed air into a turbulent two-phase oil-air mixed fluid and sending it to the friction surface that needs to be lubricated. The advantage of oil-air lubrication is that it can maximize the service life of the bearing and is not limited by the viscosity of the oil. The important thing is that the compressed air has small specific heat, high flow rate, easy to take away frictional heat, and the air has a certain pressure. Can play a sealing role.
1. Operating condition of oil and gas lubrication system
1.1. Working process
The lubricating oil output from the oil pump station is supplied to the tertiary distributor through the primary distributor and the secondary distributor (both the secondary distributor and the tertiary distributor are set on the rolling mill body), and mixed with air on the tertiary distributor After that, the oil-air mixture is formed and supplied to the lubricating parts such as rolling mill bearings and guide bearings, as shown in Figure 1. The function of the primary distributor is to evenly distribute the flow of the pressure lubricating oil output by the oil pump; the secondary distributor is to quantitatively supply oil to the five tertiary distributors on each rolling mill, and the five oil outlets are connected to four A rolling mill bearing distributor and a guide distributor: The three-stage distributor distributes the lubricating oil quantitatively and mixes it with the compressed air and then delivers it to each lubrication point.
1.2, The existing problems
During the operation of the oil and gas lubrication system of the rolling mill, there are the following problems: First, the compressed air and the lubricating oil are mixed outside the station. Before mixing in the three-stage distributor of the rolling mill, oil and gas are independent pipelines, with many pipelines, many joints, and large transmission pressure loss. The oil pressure supplied by the system from the station is 18MPa, and the pressure when it reaches the lubrication point is often difficult to ensure normal. bearing lubrication. The high system pressure also often causes damage to the joints and distributors of various parts, resulting in oil leakage, causing various alarms and affecting the normal operation of production and equipment. Second, the fuel consumption is high and the production cost is high. The average monthly oil consumption of the system is more than 40 barrels. The main reasons for the high oil consumption are: the 18 rolling mills in the whole line, the oil and gas of the rolling mill bearings and guide bearings of each rolling mill are provided by the same primary distributor and secondary distributor. During use, the amount of oil and gas obtained by the guide bearing is not as good as that of the rolling mill bearing. This leads to frequent burning of the guide and guard bearings, which seriously affects the rhythm of the steel. However, the oil supply to the rolling mill bearings also increases, resulting in high oil consumption and high production costs. In addition, when the oil supply interval is set to zero, although the oil supply of the guide bearing is guaranteed, the oil supply of the rolling mill bearing also increases, causing excess oil to overflow from the rolling mill roll box, causing environmental pollution.
2. Transformation plan
2.1. The oil and gas mixing outside the station is changed to the mixing inside the station
The reformed oil and gas lubrication system consists of a main oil pipeline, two sets of air source treatment devices (two main air source pipelines), a main lubrication station, six lubricating substations, and primary and secondary oil and gas distributors. . Two sets of air source processing devices include air pressure relay, pneumatic pressure reducing valve, air filter, shut-off valve, solenoid valve, pressure gauge, etc. Two main gas source pipelines, all the way to send 1 to 12 rolling mills and their ancillary equipment, namely the 1# substation. 3# substation; another way to send 13 to 18 rolling mills and their ancillary equipment, namely wrong substation - 6# substation. The main lubricating station is responsible for supplying lubricating oil to the sub-stations. It is mainly composed of fuel tank, gear pump and electronic control detection device. The oil supply part of the lubricating substation is composed of stop valve, pressure gauge, solenoid valve, throttle valve, progressive distributor, oil and gas mixing block, etc. Progressive distributors are responsible for the precise distribution of lubrication to the oil-air mixing block in the required amount. And mixed with the treated compressed air to form a stable gas-liquid two-phase fluid. Oil and gas mixing blocks, progressive distributors, etc. are integrated and assembled in the substation. The primary and secondary oil and gas distributors are installed on the intermediate pipeline from the outlet of the oil and gas mixing block to the lubrication point. The point lubricates the bearing, and at the same time, when the compressed air overflows from the bearing seat, it takes away the friction heat of the bearing and generates a slight positive pressure inside the bearing seat to prevent the intrusion of external dust and water.
The working principle of the system: the main station filters the lubricating oil and transmits it to each sub-station through the main oil pipe. The compressed air is mixed in the mixing block to form an oil flow into the oil and gas pipeline. The oil flow is distributed through the two-stage oil and gas distributor, and is sprayed into the lubrication points of the equipment in a fine continuous stream of oil droplets. After the dry from the sub-station, it is the mixed oil flow. The pipeline is simple and the joints are few, which ensures the pressure of the lubrication part, and each sub-station does not affect each other (see Figure 2 for the schematic diagram of the oil-gas lubrication system after the transformation).
2.2. The rolling mill bearing and the guide bearing share a distributor
The lubrication of rolling mill bearings, brackets and guide bearings is designed to be controlled by different oil and gas branches and oil and gas distributors. The oil supply can be adjusted and set according to the characteristics of the equipment, and the lubrication of different equipment does not affect each other. In addition, a ball-seat structure leakage-free electromagnetic reversing valve is arranged upstream of the progressive distributor in the substation, through which the pressure oil supplied to the progressive distributor can be turned on or off. A proximity switch is installed on the progressive distributor to count the number of working strokes of the distributor. Once the stroke number reaches the set value, the ball seat reversing valve will be closed, and then the work will be suspended until the next working cycle. According to the characteristics of production and equipment, the working cycle of the progressive distributor is reasonably designed to achieve accurate oil supply, that is, to give as much lubrication as needed, never under-lubricated or over-lubricated, so that it can achieve economical efficiency while ensuring lubrication. purpose of oil.
2.3. Improvement of observation points
The oil and gas pipes of the original lubrication system at the lubrication point of the rolling mill are all opaque rubber pipes, and it is impossible to find out whether the oil and gas flow is interrupted in time. Aiming at this drawback, two improvements have been made: First, the oil and gas pipes at the outlet of the mixing block in the sub-station are designed to be transparent oil and gas pipes that are easy to observe. Through this small section of oil and gas pipe, it can be seen that the oil on the pipe wall is flowing in waves. If a pipe is blocked, this flow cannot be seen or the oil flow is very small, so that the fault point can be found intuitively and quickly. which branch. The second is to change the rubber tube at the lubrication point of the rolling mill to a high temperature resistant transparent hose, so that the oil and gas working conditions can be observed intuitively at the lubrication terminal of the equipment. No matter which lubrication point is interrupted, it will be found through the connected transparent hose, so that it can be judged in time. The specific fault points should be dealt with in time to avoid the expansion of faults.
2.4. Design of electronic control system
(1) The electric control system of oil and gas lubrication is designed as a set of independent electric control system. The control system does not enter the PLC system of the rolling line, but only sends 3 points to the PLC system of the rolling line. That is, "running", "minor failure" and "major failure". The detailed failure prompts are reflected in the host computer. The lubrication of each substation can be individually controlled to start and stop, and it will not be interlocked when there is a problem with the lubrication of a substation. Affect the normal operation of other equipment;
(2) The electronic control system adopts Siemens PLC system and sets the upper computer on the Pl console for monitoring, operation and related parameter settings, and uses WINCC to generate a visual operation monitoring screen, and the entire system workflow is clear at a glance. Through the alarm prompt to find the fault location in time, the oil tank level, oil supply and oil distribution, compressed air pressure, oil and gas flow, etc. are all monitored;
(3) Oil level monitoring: The oil level of the main station oil tank is monitored by the liquid level switch. When the lubricant in the oil tank is only 113, the liquid level switch will send an alarm signal. The alarm signal and prompt can be clearly seen on the operation screen of the upper computer:
(4) Compressed air pressure monitoring: The pressure switch in the substation is used to monitor the compressed air pressure after decompression. If the pressure is lower than 2bar, the pressure switch will send a fault signal;
(5) Monitoring of oil delivery: When the system is turned on, the total monitoring time function of the progressive distributor is enabled. Each time the progressive distributor works for one stroke (all pistons in the interior move once), the proximity switch installed on the distributor will send out a corresponding induction signal, and the signal will be converted into the monitoring time of each stroke after processing.
3. Effect
The reformed oil and gas lubrication system completely solves the problems of low pressure in the original system and easy failure of equipment lubrication, and improves the operation rate; because the oil and gas lubrication system can provide suitable oil supply amount and oil supply time for rolling mill bearings and guide bearings , The phenomenon of burning bearings is reduced, and the fuel consumption is significantly reduced (the fuel consumption is reduced from more than 40 barrels to 13 barrels), which greatly reduces the production cost and maintenance workload, and improves the on-site environment. The successful transformation of the oil-air lubrication system proves that the oil-air lubrication system has unparalleled advantages [41, reducing costs, saving manpower, reducing maintenance, and being environmentally friendly. With the continuous improvement of rolling speed and automation level, the application field of oil and gas lubrication more and more expansive.
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