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Selection of hydraulic transmission system

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Estimated reading time: 11 minutes

Occasions suitable for hydraulic transmission

  1. Hydraulic hash press,when the power-to-weight ratio is large, hydraulic transmission should be used.

Since the working pressure of the hydraulic system can be higher (for example, 32 MPa or higher), the ratio of the corresponding transmission power to the weight of the actuator 11 (hydraulic cylinder, hydraulic motor) is relatively large. And the power that can be transmitted by electric drive or pneumatic drive.

The weight ratio of the actuator (motor, cylinder) is small (for example the weight of the hydraulic motor is only 10% to 12% of the same power motor), so the hydraulic transmission should be used in situations where the power-to-weight ratio is required.

2. Hydraulic hash press,hydraulic transmission should be used when the load is large and the response is fast.

Since the pressure of pneumatic transmission cannot be too high (generally, the commonly used air pressure is not more than 1MPa), the load force of its drivers cannot be too large. In addition, because the gas is compressible and has a larger gas volume, its response is slower. Therefore, when the dynamic response is required to be fast, the hydraulic transmission can meet the requirements.

3. Hydraulic hash press, when infinitely variable speed and large speed range are required, hydraulic transmission should be adopted.

The hydraulic system can achieve the purpose of speed change as long as the flow is adjusted. Generally, the speed control valve can achieve step-less speed change, and the adjustment range is relatively large. For example, the speed adjustment range of the hydraulic system can reach more than 200, while the speed adjustment range of the electric motor is only about 20.

4. Hydraulic hash press,when low speed and high stability are required, hydraulic transmission should be adopted.

Because the pressure of pneumatic transmission is not high, the load cannot be too large. Relatively speaking, the proportion of friction 1 in the total load is greater than the proportion of hydraulic or electric transmission. Moreover, the friction force changes at low speeds (especially when dynamic friction and static friction are mutually (or repeatedly) converted). Therefore, at low speeds, pneumatic equipment is prone to crawl, and because of the compressibility of the gas, the crawling is even more aggravated. . Therefore, pneumatic transmission is not suitable for occasions requiring low speed and high stability, but hydraulic transmission is preferred.

5. For linear reciprocating motion, hydraulic transmission or pneumatic transmission should be used.

As shown in the figure below, since the output of the motor is rotary motion if the load is required to perform the linear reciprocating motion, a mechanical mechanism (such as a rack and pinion mechanism) must be added to convert the rotary motion output by the motor into linear motion, while the hydraulic cylinder or air cylinder Generally, it does linear reciprocating motion, so it can directly drive the load to do linear reciprocating motion, so the structure is simple.

6. Hydraulic transmission should be adopted for systems that require high rigidity.

Due to the large compressibility of the gas, the rigidity of the pneumatic system is smaller than that of the hydraulic system. Therefore, the system requiring high rigidity should not use pneumatic transmission, but hydraulic transmission should be used.

7. Where high positioning accuracy is required, hydraulic transmission should be used.

Due to the large compressibility of the gas, the accuracy of the flow control of the pneumatic system is poorer than that of the hydraulic system. In addition, the pneumatic system is prone to crawling in the low-speed range. However, it always runs in the low-speed range near the zero position, so the positioning accuracy of the pneumatic system is worse than that of the hydraulic system. It is not suitable to use pneumatic transmission on occasions that require high positioning accuracy.

8. Where there is an impact load, hydraulic transmission should be adopted.

The shock resistance of the electric drive is poor, and the hydraulic system can absorb the shock with an overflow valve, an accumulator, etc. so that the system pressure and movement speed are stable, so the shock resistance is strong. The hydraulic system should be selected on occasions with a large impact load.

9. For low-speed and high-torque occasions, pneumatic transmission and electric transmission should not be used, hydraulic transmission should be used.

For low-speed and high-torque occasions, it is difficult for pneumatic transmission to obtain large torque, while the electrical transmission is difficult to obtain stable low speed (reducer must be added). Only when low-speed and high-torque hydraulic motors are used in the hydraulic transmission system can the low-speed and large-torque requirements be achieved. The minimum stable speed can reach 1r/min, and the maximum torque can be greater than 4×10000N.m.

10. Where overload protection is required, hydraulic or pneumatic transmission should be adopted.

The hydraulic transmission and pneumatic transmission system can simply realize overload protection with safety valves, and can automatically continue to run after the overload are over, without restarting. The overload protection device of electric drive or mechanical drive is more complicated and often needs to be restarted after the end of the overload.

11. Actions that can be completed with ordinary hydraulic transmission systems do not use hydraulic proportional systems, and actions that can be completed with hydraulic proportional systems do not use hydraulic servo systems.

In terms of anti-pollution requirements, they are hydraulic drive system, hydraulic proportional system, and hydraulic servo system in sequence. As far as the system price is concerned, it also gradually increases in this order. Therefore, in terms of equipment investment or maintenance and operation costs, the hydraulic servo system is greater than the hydraulic proportional system, and the hydraulic proportional system is greater than the hydraulic transmission system. Therefore, the actions that can be completed by the hydraulic transmission system do not need the hydraulic proportional system, and those who can use the hydraulic proportional system do not need the hydraulic servo system.

Occasions not suitable for hydraulic transmission

  1. Hydraulic hash press,light-load high-precision position control, electric drive should be used as much as possible.

In the occasions where the load is not large and high control accuracy is required, it is best to use an electric drive, because the control accuracy of the electric drive is high, and the power supply is relatively easy to obtain (as long as the wire is used). Corresponding hydraulic transmission and pneumatic transmission require a hydraulic source or an air source. The establishment of a hydraulic source and an air source is much more complicated than the power supply, and the electric drive can also obtain higher control accuracy. Therefore, the electric drive should be selected first when the cargo load is not large and the accuracy is high.

2. The price is low, and the simple movement that can be realized by the simple mechanical mechanism can be driven by the electric motor. In the occasions where the load is not large and the control accuracy is not high, it is not suitable to use the hydraulic transmission in the occasions with high environmental pollution prevention requirements.

Because the hydraulic transmission needs to be equipped with a hydraulic source, the structure of the hydraulic source is more complicated and the price is higher, so the cost of the entire hydraulic system is also higher. It is not cost-effective to equip a set of oil source systems for a simple exercise. Relatively speaking, the cost of using a motor and a simple mechanical mechanism to achieve this simple movement is relatively low. However, if one oil source is used to supply multiple actuators, it is more appropriate to use a hydraulic system.

3. Hydraulic transmission is not suitable for occasions with high environmental pollution prevention requirements.

Since hydraulic systems often have oil leakage and other phenomena, cleaning up is more laborious and easy to pollute the environment, so hydraulic transmission is not suitable for occasions with high environmental pollution prevention requirements.

4. Hydraulic transmission and pneumatic transmission are not suitable for occasions requiring high efficiency.

Since the flow adjustment of the hydraulic system and pneumatic system is mostly throttled, the resistance loss is large, so the efficiency is low. Generally, the efficiency of the entire system does not exceed 50%. Even if the volumetric speed control is adopted, the total efficiency will not exceed 85%, and the total efficiency of the electric transmission and the gear transmission system can often reach more than 90%, so the electric transmission should be used in situations where high efficiency is required, and hydraulic transmission or pneumatic transmission should not be used.

5. It is not easy to obtain high control accuracy with hydraulic system in occasions with large temperature changes.

The viscosity of hydraulic oil is related to temperature. The higher the temperature, the lower the viscosity. Therefore, when the temperature changes greatly, the viscosity change is also large, and the corresponding system leakage change is also large. At the same time, the flow resistance of the pipeline also changes greatly (because the flow resistance is proportional to 1 viscosity). Therefore, the originally adjusted parameters change greatly when the temperature changes greatly, which is easy to produce more temperature drift, which reduces the control accuracy of the system accordingly.

6. In harsh environments such as flammable, explosive, dusty, and watery, hydraulic transmission is generally not suitable.

The general hydraulic medium is petroleum-based hydraulic oil (except for a special flame-resistant hydraulic medium), so it is not suitable for use in a flammable and explosive environment. The dusty environment can easily pollute the hydraulic medium and cause component wear, increased leakage, and even scrapped components. Inflammable, explosive, and dusty occasions, hydraulic transmission is not suitable.

7. For occasions with high requirements for noise reduction, hydraulic transmission, and pneumatic transmission are not suitable.

Hydraulic transmission (mainly hydraulic oil source and reversing valve, etc.) and pneumatic transmission (mainly air source and cylinder, air valve, etc.) are noisy at work (generally greater than 60dB). Therefore, hydraulic and pneumatic transmission is not suitable for occasions with high noise reduction requirements.

8. In addition to simple functions, it is not advisable to use a pure hydraulic or pure pneumatic system to complete the control function, and it is best to use an electro-hydraulic (pneumatic) integrated system to complete the control. function.

Hydraulic or pneumatic is generally used to drive the actuator to drive the load to complete linear or rotary motion. As for the positioning, speed change, signal transmission, and other functions of the movement, it is generally completed by the cooperation of electrical components. However, if you want to perform logic operations or control the dynamic characteristics of motion, it is more convenient to complete it with electronic components or computers. It is quite difficult to use hydraulic or pneumatic components to complete complex logic operations or dynamic characteristics control functions. The best solution is to combine electronic technology, computer technology, and hydraulic and pneumatic technology to complete the overall function of the equipment, the so-called electro-mechanical hydraulic integration technology.

9. Electric or hydraulic transmission is not suitable for ultra-high-speed rotation or reciprocating motion. Pneumatic transmission should be used.

To make the motor rotate at a high speed, a speed-increasing gear device is needed. When the speed-increasing ratio is large, the volume is large, the friction force is also large, and the hydraulic transmission is not easy to obtain too high operating speed. Only the pneumatic transmission can have a high flow rate due to the small gas viscosity and low resistance. [The movement speed can be very high. For example, the rotation speed of the pneumatic internal grinding head can reach 105r/min, and the impact of the pneumatic rock drill can reach reciprocating every 1 minute. 3500 time.

10. In occasions with strict transmission ratio requirements, hydraulic or pneumatic transmission is not suitable.

Since the internal and external leakage of the hydraulic system varies with the working pressure and temperature, it is difficult to maintain a constant transmission ratio. As for pneumatic transmission, it is more difficult to maintain a constant transmission ratio due to the large compressibility of air. Therefore, hydraulic and pneumatic transmission cannot maintain a strict transmission ratio like a mechanical transmission.

11. Hydraulic hash press, when transmitting power over long distances, hydraulic transmission is not suitable.

Since the power transmission of the hydraulic drive is realized by pipelines, the length of the pipeline will be very long during long-distance transmission, the installation and arrangement will be inconvenient and the cost will increase; in addition, the long pipeline has a large power loss, so the long-distance transmission power Electric drive.

12. Hydraulic hash press, hydraulic transmission should not be used in winter in severe cold areas and in the wild in the north.

In winter, the temperature reaches -25℃ or less, even if anti-coagulation hydraulic oil is used, hydraulic equipment for field operations cannot work reliably. If working under this condition, it will cause varying degrees of damage to the parts in the pump and the seals of the hydraulic cylinder.

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Grace Guo

In the last ten years, Grace has sold a third of our company’s hydraulic presses. She knows hydraulic presses as well as our engineers, and our customers trust her as much as we trust our own machines. If you need hydraulic presses and related products, you won’t be disappointed with Grace’s recommendations.

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This Post Has One Comment

  1. Abed

    Hello, I am very interested in your article. I would like to ask if you make a hydraulic press. I want to buy a hydraulic press.

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