Reconstruction of high pressure molding automatic line hydraulic system

Key words: high-pressure molding line hydraulic system high-pressure molding automatic line is the key technical transformation project of Wuxi Diesel Engine Factory during the period of the Seventh Five-Year Plan. The size of the sand box is 1mm×850mm×400/400mm, and the design productivity is 45 integer/h. A total of 18 machines, hydraulically driven, controlled by the US GEIII programmable controller. The hydraulic system uses a centralized pumping station located in the basement next to the molding machine. There are 5 pumps in the pumping station, each with a flow rate of 160L/min, the motor power is 22kW, and the system working oil pressure is 5.0MPa. There are 4 valve boxes in the whole line, which are set in the binning machine, molding machine, boxing machine and 捅Next to the box machine. When the line was installed and commissioned, the hydraulic system was found to have the following problems: (1) The hydraulic system oil flow was insufficient, the cylinder movement was slow and there was mutual interference, and the actual productivity of the molding line was low.

(2) The temperature of the hydraulic oil is very high, and it can reach 70-80 °C in summer.

(3) The accumulator has a serious nitrogen leak and is mixed into the pressure oil circuit.

Therefore, the hydraulic system has been modified.

1 The pump station of the oil pump unit has 5 oil pumps, of which 1 are spare. In the trial production, it was found that the cylinders move slowly and interfere with each other. The most obvious is that the molding machine lifts up when it rises. After the movement of the mold conveyor is completed, it can continue to rise, and the casting conveyor has crawling during movement. phenomenon. After the standby pump was added to work, although the above phenomenon improved, it still existed. The actual productivity of the molding line was only 20 integer/h. This was mainly due to the serious internal leakage of the hydraulic system, resulting in insufficient flow at the pumping station.

According to the formula: N electric oil is Q oil electric oil: motor power N electric oil pump working pressure P oil motor efficiency η electric oil is calculated from the above: on the basis of keeping the motor power unchanged, the flow rate of the oil pump can be increased to L/min.

For this reason, when the oil pump unit was redesigned, the original motor was retained, and the original pump with a flow rate of 160 L/min was replaced with a 200 L/min vane pump. This can save the cost of retrofitting the electronic control system, and the second can shorten the transformation cycle. At the same time, the oil suction filter of the oil pump was also modified. The original oil suction filter of the pump uses a net oil filter, the flow rate is 480L/min (three times the pump flow rate), it is installed in the fuel tank, it is often blocked, and the cleaning is troublesome. . Now it is changed to a line gap type oil filter, which is installed on the suction pipe of the pump outside the fuel tank, and the flow rate is 1000L/min (5 times of the oil pump flow rate).

After the improvement, the problem of insufficient flow rate at the pumping station is basically solved. The actual productivity of the molding line is increased from 20 integers/h to 30 integers/h, the reliability is greatly improved, and the life of the oil filter is prolonged, and the cleaning is performed. Convenience.

2 The redesigned molding line of the oil cooling device produces oil temperature of the pumping station up to about 60 °C, which is higher than the maximum working oil temperature of 55 °C. In summer, the oil temperature can be as high as 70-80 °C. The increase in oil temperature causes the viscosity of the oil to drop drastically, which further increases the leakage of the hydraulic system, and at the same time accelerates the aging of the seal, shortens its service life, deteriorates the working condition of the system, and seriously affects the normal production of the molding line. . The internal leakage of the system accelerates the rise of the oil temperature, and the original oil cooler heat exchange area is only 4m 2 , and the cooling effect is poor.

First, the design calculation of the oil cooling device is performed.

Estimating the heat generated by the hydraulic system: the actual productivity of the molding line, the design of the production line, the productivity of the total electric system, the total power of the pumping station, the application technology of the total power of the pumping station, the transformation of the high-pressure modeling automatic line hydraulic system, 3/2000, China's foundry equipment and technology Electricity -- for motor efficiency, 0 .8 Wuxi area is hot in summer, so set the inlet temperature of cooling water t = 35 ° C set the oil temperature to 50 ° C, the cooler starts to work T = 50 ° C according to the technical parameters of the cooler , set the water outlet temperature = 38 ° C oil outlet temperature T = 45 ° C. Then the average temperature difference: the required heat exchange area: F = K in the formula - heat transfer coefficient, 349W / (m taking into account the formation of grease, scale and other factors, the heat transfer area is enlarged 30.

Select the type 2LQF W10/19 cooler, the heat transfer area of ​​the required cooling water flow of 19m: W water type C water pump with a flow rate of 15m / h.

The flow rate of the required cooling oil pump: The W oil type medium oil C oil cooling oil pump uses a flow rate of 18m 18/3 .6 gear type oil pump.

To enhance the cooling effect, the hot water flowing out of the cooler is sent directly to the cooling tower for cooling, and then flows back to the circulating pool. At the same time, increase the effective volume of the fuel tank from 4m to 6m 3, and connect the oil suction pipe and the return oil pipe of the cooling oil pump to the enlarged part of the oil circuit, so that the hot oil flows back to the oil suction part of the pressure oil pump as much as possible.

The temperature control instrument is also installed on the fuel tank. When the oil temperature reaches the set temperature, the cooling oil pump and the water pump are simultaneously opened. When the oil temperature drops to the required temperature, the two pumps are simultaneously turned off, and the oil temperature is automatically controlled.

After the transformation, the effect is very good. In the high temperature weather of 35 °C in summer, the molding line is continuously produced in two shifts every day. The oil temperature can still be controlled. The hydraulic principle of the accumulator before and after the transformation of the 3 accumulator device is shown in the figure below. . Before the transformation, the capacity of the piston accumulator is 60L. When it is half full, the NW signals and the XC loses power, so that one pressure oil pump is unloaded. When it is full, the NW signals, and the other pressure pump is unloaded. Not shown). The 550L pressure vessel consists of 11 50L nitrogen cylinders with many pipe joints and serious nitrogen leakage. It is both cumbersome and uneconomical to add a few bottles of nitrogen per day. And the nitrogen in the lower chamber of the piston can enter the pressure oil pipe through the sealing ring to generate hydraulic shock. This not only causes vibration, noise, but also damages the hydraulic components.

After the improvement of the hydraulic schematic before and after the improvement, the original piston accumulator was replaced by 12 50L bladder accumulators. It is used in combination with a conventional general bladder accumulator and an unloading relief valve. If the relief valve is replaced, one will take a long time to affect production, and the other must use an inlet valve. How to retain the original relief valve, and when the bladder accumulator is filled with 30L and 60L pressure oil, signal the oil pump to unload. For this purpose, two electric contact pressure gauges are installed in the pressure oil pipe when the accumulator is full. When 30L pressure oil is used, the I contact pressure gauge sends a signal to make XC lose power. When one pump is unloaded and filled with 60L pressure oil, the No. II electric contact pressure gauge sends a signal to make the other two unloading (because the spare pump also Join the work).

Set the system pressure to 5.0 MPa, the accumulator is filled with 60L pressure oil, then the pressure P of the P contact pressure gauge (filled with 30L pressure oil): (approximate isothermal process during production). The production line is confirmed by production. The reliability is greatly improved, the accumulator can be inflated for three months, and the nitrogen gas is not mixed into the pressure oil. The electric contact pressure gauge works reliably and has a long service life.

Application Technology--Reconstruction of High-pressure Modeling Automatic Line Hydraulic System 3/2000 China Foundry Equipment and Technology 4 Conclusion 4.1 On the basis of retaining the original motor, replace the original l60L/min with a vane pump with a flow rate of 200L/min. The oil pump solves the problem of insufficient oil flow in the hydraulic system, and the actual productivity of the molding line is increased from the original 20 integer/h to 30 integer/h, and the reliability is also greatly improved.

The oil cooling device designed by 4.6 can better control the temperature of the oil. Even in the continuous high temperature weather above 35 °C in summer, the molding line can be produced twice a day, and the oil temperature can still be controlled below 55 °C. The oil cooling device consisting of a large area heat exchanger and a large flow oil pump is an effective way to solve the high oil temperature.

4. 3 Replace the piston accumulator with a bladder accumulator, retain the original relief valve and electronic control. When the bladder accumulator is filled with pressure oil, the electric contact pressure gauge sends a signal, through the original electronic control, Unloading the oil pump is a good and reliable method. The device is reliable in operation, low in failure rate, low in investment, quick in effect, and has achieved good economic benefits.

1 mechanical design manual (5). Beijing: Mechanical Industry Press, 1992.

Checking the tensile strength of gray iron castings by wedge pressure test Yang Ronghuang Sun Liguo Tang Wei (450 Changchun First Automobile Group Corporation Second Casting Plant) Key words: wedge pressure test wedge strength tensile test tensile strength 1 tensile strength test The problem is currently in the foundry industry, generally only the tensile strength and hardness as a test indicator of the mechanical properties of gray cast iron materials. The tensile strength of gray cast iron is achieved by tensile testing of the mechanical properties of the cast. The general mechanical properties test bar can be obtained by casting a single casting test bar or a cast casting test bar. The so-called single-cast test bar separates the casting mechanical property test bar from the cast casting itself in time and space. The so-called cast-cast test bar refers to the casting mechanical property test bar and the cast casting on the same template. Whether it is a single-cast test bar or a cast-and-test test bar, although the mechanical properties of the cast bar are as similar as possible to the cooling conditions of the cast, it is still more or less due to production conditions and process factors. difference.

The second casting plant of First Automobile Group Co., Ltd. uses double-smelting of cupola and power frequency furnace. The chemical composition range is larger than that of single-frequency furnace melting. Therefore, the chemical composition of test bars and castings differs in time.

In addition, the use of the pouring process in the flow, so that the casting test bar and the casting itself have a greater difference in chemical composition, resulting in the performance of the test bar and the performance of the casting is inconsistent. Secondly, the sand type of the casting bar and the sand type of the casting have different cooling rates due to different compacting rates and different thicknesses of the molding sand, so that the performance reflected by the test bar does not represent the performance of the casting. In addition, even if the chemical composition and cooling rate of the test bar are consistent with the casting, the performance of the test bar does not truly represent the performance of the casting due to the difference in thickness between the test bar and the different castings.

This can be verified from everyday production. Free carbides were found in the metallographic structure of the test bars, but not in the castings corresponding to the package. This indirectly reflects the difference in performance between the test bar and the casting. In addition, the test rod and the camshaft casting were cast under the same chemical composition, and then the camshaft casting was made into a tensile test bar, which was compared with the mechanical property test. The results showed that the performance of the two was very different.

In addition, checking the tensile strength with a test bar is not only expensive, but also time consuming, it requires manual casting of the test bar, which requires a certain amount of energy and raw materials. When pouring cast test bars, for large modern foundries, there may be problems with the layout of the templates, affecting product quality and production tempo.

2 Wedge pressure test In response to the above problems, a wedge pressure test was proposed. The wedge pressure test is a fracture test used on a stationary process, similar to the tensile strength test. Two wedges are installed on the special device. The sample is clamped between the two wedges. The upper and lower pressures acting on the wedge break the specimen. The maximum breaking force per unit area of ​​the specimen is the wedge pressure. strength.

The wedge pressure test avoids the performance of the test rod in the tensile strength test, which does not represent the performance of the casting, and does not require manual application technology. - Check the tensile strength of the gray iron castings with the wedge pressure test. Equipment and technology