Brief Discussion on the Sealing Force of 200 L Closed Steel Barrel
Shanghai Mechanical and Electrical Design Research Institute Shi Zhougang
introduction
The 200-liter closed steel drum has a wide range of uses as packaging containers for petroleum, chemical, paint, dye and edible oil products. With the development of the national economy, the demand for steel drums in foreign trade is increasing. However, most of the domestic barrel factories have poor equipment, backward technology and poor product quality, especially the key equipment that is closely related to the quality of steel drums. Most of the steel drum production line equipment is quite old and needs to be updated.
I. Analysis of the forming force of the crimping machine
The quality of the crimping seal directly affects the quality of the steel drum. If the sealing performance is not good after the sealing of the crimping, the leakage of the liquid packaging material will be leaked out, and the product will be lost and polluted, and the seriousness will endanger the personal safety and cause a major accident. However, what kind of crimping force should be used to make the barrel and the bottom of the barrel, the barrel cover is well sealed and does not leak. When we design the first steel barrel production line equipment in China, it is almost nothing. When known, there is no ready-made data for reference. In order to obtain the necessary design basis, a dynamic stress-strain field test of a US-made crimping machine of a factory in the forties was carried out, and the crimping force of the crimping machine was measured up to 18 tons.
According to the actual curling forming force of the crimping machine, the method of pressing the crimping by the hydraulic cylinder is used when designing the crimping machine to form the pressure roller. In order to ensure sufficient forming pressure, reduce the power of the hydraulic device and reduce the energy consumption, a pressurized cylinder is adopted in the hydraulic system, which not only satisfies the requirements of the forming pressure, but also avoids the use of the high pressure oil pump and its hydraulic components. Not only reduces the requirements for oil and piping, but also reduces manufacturing costs and ease of maintenance.
From the structural design of the crimping machine, the stroke from the start of the pressing wheel to the forming of the crimping is 72 mm. When the crimping is performed, the production rhythm is ensured and the processing time is shortened. The design of the hydraulic system adopts "fast forward" and "work advance". In the hydraulic system, the double vane pump is used for oil supply in the hydraulic system. When the fast forward and retreat are fast, the double pump is used for oil supply at the same time, and the small flow pump is separately supplied with oil during the work. The designed crimping forming pressure is based on the user's proposed process parameters and the pressure data obtained from the field test. The maximum pressure of the pressurized cylinder of the hydraulic system of the machine is 170kg/cm2, which can be used to derive the thrust of the cylinder. That is, the pressure of the crimping forming roller is:
Q=Ï€/4(D2-d2)P = 100013.82kg
Where: Q - the thrust of the cylinder (kg); D - the cylinder cylinder light (cm); d - the diameter of the piston rod (cm); P - the working pressure of the cylinder (kg / cm2)
It can be seen from the above calculation that the designed crimping forming pressure value is only 55.5% of the originally measured pressure data value. If considering the seal loss and friction loss when the cylinder is working, the actual forming pressure is:
Q real = Q・ηk = 90012.43kg
Where: Q - the actual thrust of the cylinder (kg); ηk - the mechanical efficiency opposite the seal loss and friction loss, (take ηk = 0.9)
It can be seen from the above formula that the theoretical pressure value of the actual design is 50% smaller than the pressure value obtained by the field test. However, in the commissioning after the manufacture of the crimping machine, it was found that even the forming pressure which is half the test value is much larger than the actual crimping force required. Firstly, it is found that when the gauge pressure reaches 65kg/cm2, the hemming forming pressure roller has a significant lag effect when the spindle is pressed by the hand pressure roller during the pressing process, and even the spindle stalls when the pressing speed is too fast. When the speed control valve is adjusted to slow down the feed rate of the pressure roller, the influence of the spindle speed is not obvious. In addition, it was found that when the gauge pressure was 55kg/cm2, the barrel body and the bottom of the bucket and the lid of the bucket were completely formed, and the cutting edge inspection was performed on the curling edge. The barrel body and the bottom of the bucket were well engaged. In this way, the supercharged cylinder used in the original design can be completely eliminated, and in actual use, the speed of the spindle can not be used due to excessive pressure. It is converted into a crimping forming force of 3,240 kg from a gauge pressure of 55 kg/cm 2 , which also includes a pressure loss caused by leakage inside the hydraulic component.
The data obtained from the test is far from the value of the crimping forming pressure obtained by on-site commissioning. There is only one reason, that is, the value obtained by the test is not true, because the design basis of the crimping force of the machine is determined based on the repeated field test of the original equipment of the user's factory, due to the test conditions, Test factors such as various characteristics and environmental conditions of the test instrument, the test results inevitably produce errors. Moreover, in the test of the strain gauge, if the temperature change occurs during the measurement, the resistance of the resistor will also change, and this change comes from two aspects: one is the temperature versus the resistivity of the wire. Direct influence, the second is the effect of the linear expansion coefficient of the material between the resistive film and the measured object (that is, the same temperature change amount produces unequal temperature deformation). If there are these factors in the test process, the measured results will produce a large error, and even these measurements are not true. During the sealing process of the barrel body and the bottom of the bucket and the lid of the bucket, the heat is generated at the curling edge due to the mutual friction of the forming pressure roller. At this time, the temperature change at the crimping edge is quite large, even if it is not considered. At this time, the influence of ambient temperature and noise on the instrument, only the temperature change at the crimping edge, is enough for the instrument to affect the accuracy of the measurement results. In addition, the measurement results are also affected by the sensitivity of the instrument, and the sensitivity of the instrument is usually only constant over a certain range. When this “linear range†is exceeded, the sensitivity will change. Therefore, at the same time of various factors Under the action, the actual forming pressure required is greatly different from the test forming pressure.
Through the debugging of the crimping machine, the crimping force and test value of the crimping machine were verified, and the actual data of the crimping forming force was obtained, which provided a reliable method for designing and developing a new crimping machine. The design parameters have also created favorable conditions for upgrading and renovating the production line equipment of the middle section of China's 200-liter closed steel drum.
Second, the analysis of mechanical and hydraulic crimping machines
After obtaining the actual data of the crimping force of the crimping machine, we designed a second 200-liter closed-end steel drum production line equipment. The crimping machine adopts a mechanical (cam) structure. The pressing of the original design of the crimping forming roller completes the engagement of the barrel with the bottom of the barrel and the lid of the barrel through the action of the cylinder. The newly designed crimping machine uses a cam mechanism instead of the action of the cylinder. See the diagram below.
There is a big problem in the commissioning of the crimping machine which is pressed down by the cylinder to complete the hemming forming. That is, the second pressure roller can fast forward only when the pressure roller completes the work feeding, that is to say, the pressure roller works. When given, the second pressure roller can't quickly approach the bottom of the bucket and the lid of the bucket. The second pressure roller must wait for a pressure roller to complete the work and start fast rewinding. This is determined by the hydraulic structure.
The pressure in the hydraulic system is based on the hydraulic oil in the system being pushed forward. Under such a motion condition, that is, the front side of the hydraulic oil is blocked by the load resistance, and the latter is caused by the movement condition of the oil pump's non-stop oil supply. Therefore, when a pressure roller is in the working feed state and at the same time requires the second pressure roller to fast forward, the characteristic of the oil flowing easily determines that the oil must flow from a high pressure to a low pressure, and the second pressure roller is fast. The resistance of the incoming working load is large, and the load resistance of the second pressing wheel is much smaller. The oil must flow from a pressure cylinder to a two-pressure cylinder with low load resistance. Therefore, the working feed pressure of the forming of a pressure roller is not enough, and the movement of the whole mechanism is confusing, and it is impossible to complete the desired crimp forming. This characteristic of the hydraulic structure determines that its processing time is relatively long and the production rhythm cannot be too fast. If these two problems are solved, the design of the hydraulic system of the machine is much more complicated and uneconomical.
The mechanical crimping machine replaces the hydraulic structure with a cam mechanism, which solves the problem of long processing time. The main advantage of the cam mechanism is that the follower can be arbitrarily expected to move as long as the appropriate cam profile is designed. We have utilized this feature of the cam mechanism to have a relatively free choice and combination of the design of the cam's corner and the working stroke and the relative motion and stroke of a press wheel and the second press wheel. Therefore, when the cam is designed, the second pressure roller advances when the pressure roller is fed, and when the pressure roller starts to retreat, the second pressure roller enters the working state. This avoids the waiting time for each other, so that the processing time can be shortened, which shows its advantages in the design of the higher productivity crimper.
The hydraulic crimping machine is somewhat incapable of completing a higher production rhythm due to the mutual waiting time of the two forming rollers. Moreover, in the hydraulic system, when the reversing valve is quickly reversed or because some components in the system are not sensitive enough, the inertia of the moving liquid or the inertia of the moving parts will cause a drastic change in the pressure in the system. High pressure, resulting in hydraulic shock. The hydraulic impact will cause the feed of the crimping forming roller to be uneven, which will affect the quality of the crimping seal. Especially when the feed is small, the hydraulic impact will have a great influence on the feed.
The pressure roller controlled by the cam mechanism does not cause a hydraulic shock or the like as long as the relationship between its rotation angle and the feed amount of the pressure roller is determined when the cam profile is designed. The cam contour curve is designed to make the feeding amount of the pressure roller smaller, so that the machining deformation can be made relatively slow, so as to reduce the influence of the deformation speed on the deformation resistance, and it is advantageous for improving the quality of the crimping door. When designing the cam profile of a pressure roller and a two pressure roller of a mechanical crimper, we consider both the waiting time for reducing the work of the two pressure rollers to meet the production rhythm as much as possible, and They have a smaller amount of work in the later stages of the work feed to ensure smooth work feed and uniform curling.
Of course, from the point of view of processing and installation, the hydraulic crimping machine is simpler in structure than the mechanical corona machine, so the maintenance of the mechanical part is much easier.
Third, the conclusion
At present, most of the steel barrels produced by domestic barrel factories are still five-layer flat-rolled type. Because of their low strength, poor impact resistance and high leakage rate, most of them can only meet the "International Maritime Dangerous Class III" standard. In order to implement the International Rules for the Transport of Dangerous Goods by Sea, some domestic barrel factories have begun to explore the production process of triple-layer and seven-layer round crimping. The triple seven-layer round bead has been widely used in foreign countries because of its high strength, good impact resistance and low leakage rate. According to tests conducted by some domestic barrel factories, the steel barrels manufactured by this process have high bite strength with the bottom of the barrel and the bottom of the barrel, which can make the steel drum meet the "International Maritime Dangerous Class I" standard. What we have done before is only limited to the verification of the five-layer flat-edged bead forming of the 200-liter closed steel drum. As for the seven-layer round crimping of the 200-liter closed-door steel drum, how much crimping force is required. Another new topic before us requires us to conduct more in-depth analysis and research.
Reference material
(1) "Simplified design of the production line of the middle section of 200 liter steel drum" (for review); Shanghai Mechanical and Electrical Design and Research Institute
(2) "Mechanical Principles" Huang Xiyu; Zheng Wenwei Editor of Higher Education Press
(3) "Mechanical Design Handbook"; Petrochemical Industry Press
(4) "Basic Engineering Machinery Dynamics"; edited by Wang Tiemin; China Railway Publishing House
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