1, the choice of type
According to the work requirements and conditions, the type of cylinder is correctly selected. It is required that the cylinder reaches the stroke terminal without impact phenomenon and impact noise should choose buffer cylinder; light weight is required, light cylinder should be selected; required installation space is narrow and stroke is short, optional thin cylinder; lateral load, optional with guide rod cylinder; High braking accuracy, should choose to lock the cylinder; do not allow the piston rod to rotate, optional cylinder with non-rotating function; heat-resistant cylinder should be used in high temperature environment; corrosion-resistant cylinder should be used in corrosive environment. In the harsh environment such as dust, it is necessary to install a dust cover on the protruding end of the piston rod. When no pollution is required, it is necessary to select a cylinder that has no oil supply or no oil lubrication.
2, the installation form
It is determined by factors such as the installation location and the purpose of use. In general, fixed cylinders are used. Rotary cylinders should be used when continuous rotation with the working mechanism (such as lathes, grinding machines, etc.) is required. In addition to the linear movement of the piston rod, if the arc swing is required, the shaft pin type cylinder is selected. When there are special requirements, the corresponding special cylinder should be selected.
3, the size of the force
That is, the choice of bore diameter. The thrust and tension of the cylinder output are determined according to the magnitude of the load force. Generally, according to the external load theory, the required cylinder force is balanced, and different load rates are selected according to different speeds, so that the cylinder output force has a slight margin. The cylinder diameter is too small, the output force is not enough, but the cylinder diameter is too large, making the equipment bulky, the cost is increased, the gas consumption is increased, and the energy is wasted. When designing the fixture, the expansion mechanism should be used as much as possible to reduce the size of the cylinder.
4, piston stroke
It is related to the occasion of use and the stroke of the mechanism, but generally does not select the full stroke to prevent the piston and the cylinder head from colliding. If used for clamping mechanisms, etc., the amount of 10 to 20 mm should be increased by the required stroke.
5, the speed of the piston
It mainly depends on the cylinder input compressed air flow, cylinder inlet and outlet size and the inner diameter of the pipe. High speed motion is required to take large values. The cylinder movement speed is generally 50 to 800 mm/s. For high-speed moving cylinders, the inner diameter of the intake pipe should be selected; for the case of a change in load, in order to obtain a slow and smooth movement speed, a throttle device or a gas-liquid damping cylinder can be selected, which makes it easier to achieve speed control. It is necessary to select the throttle valve to control the cylinder speed. When the horizontally mounted cylinder pushes the load, it is recommended to use the exhaust throttle to adjust the speed. When the vertically installed cylinder lifts the load, it is recommended to use the throttle throttle to adjust the speed; When avoiding impact, use a cylinder with a buffer.
Cylinder selection
Procedure 1: Select the cylinder type according to the operating form:
The cylinder operation mode has three modes: single action spring press and single action spring press.
Procedure 2: Select other parameters:
1. The cylinder size of the selected cylinder is determined according to the relevant load, air pressure and direction of action.
2, selected cylinder stroke workpiece moving distance
3, selected cylinder series
4, the selected cylinder installation type different series have different installation methods, mainly basic type, foot type, flange type, U type hook, shaft type
5, selected buffer unbuffered, rubber buffer, gas buffer, hydraulic shock absorber
6, the selected magnetic sensor is mainly used for position detection, requires the cylinder built-in magnetic ring
7, selected cylinder accessories including related joints
Second, the choice of directional valve
1. The applicable range of the selection valve should be consistent with the conditions at the site of use.
That is, the valve should be used reliably under such conditions according to the source pressure, the power supply conditions (AC, DC, voltage and fluctuation range), medium temperature, humidity, ambient temperature and humidity, dust, vibration, etc.
2. The function and control mode of the selected valve should meet the requirements of the system.
That is, the valve that meets the required function and control mode should be selected according to the requirements of the number of positions, the number of passages, the memory, the on-off state and the control mode of the components of the pneumatic system.
3. The flow capacity of the selected valve should meet the requirements of the system.
That is, the diameter of the valve should be calculated according to the instantaneous maximum flow rate of the component of the pneumatic system according to the average airflow velocity of 15 to 25 m/s, and the flow capacity of the required valve C (or KV), CV value, and rated flow rate should be found. Pressure drop, standard rated flow rate and S value, etc., according to which the valve that meets the requirements of the system's circulation capacity is selected.
4, the performance of the selection valve should meet the system work requirements
That is, the valve that meets the required performance index should be selected according to the minimum working pressure or minimum control pressure of the pneumatic system, dynamic performance, maximum operating frequency, continuous energizing capability, valve power consumption, life and reliability.
5. The installation method of the selected valve should be based on the quality level of the valve, the space occupied by the system and the ease of maintenance.
At present, the widely used reversing valve in China is a plate type installation method. Its advantage is that it is easy to assemble and disassemble and repair. The ISO standard also adopts the plate type installation method, and the development of the package plate type is developed. Therefore, it is recommended to use the panel installation method first. However, due to the continuous improvement of component quality and reliability, the tubular installation valve has a small space and can also be assembled and installed, so it has also been applied. Therefore, when selecting, it should be determined according to the actual situation.
6, try to use standardized products
Since the standardized products adopt mass production methods, the quality is stable and reliable, the degree of generalization is high, and the price is low.
7. The price of the optional valve should be compatible with the system level and reliability requirements.
That is, the price of the valve should be considered in accordance with the advanced level and reliability requirements of the pneumatic system. Under the premise of ensuring the system is advanced, reliable and easy to use, we strive to make the price reasonable and not to pursue low cost regardless of quality.
8. When designing a large control system, consider the bus control type that uses integrated valves and signals whenever possible.
Directional control valve selection
1, the choice of directional control valve series
Valves of different functional series should be selected according to the different actuators
2, the choice of directional control valve specifications
The flow capacity of the selector valve should meet the system's operational requirements, ie the valve's diameter should be calculated based on the pneumatic system's requirement for the instantaneous maximum flow of the component.
3. Choice of control method
The appropriate directional control valve control method should be selected according to the work requirements and the operation mode of the cylinder.
4, the choice of the use of voltage
Third, the choice of pressure reducing valve
1. According to the highest working pressure of the pneumatic control system, the pressure reducing valve should be selected. The pressure of the air source should be 0.1Mpa larger than the maximum working pressure of the pressure reducing valve.
2. The outlet pressure of the pressure reducing valve is required to fluctuate little. If the outlet pressure fluctuation is not more than ±0.5% of the maximum working pressure, a precision pressure reducing valve is selected.
3. If remote control is required or the diameter is more than 20mm, the external pilot type pressure reducing valve should be used as much as possible.
Pressure reducing valve selection
1. Select the valve size according to the maximum flow rate through the pressure reducing valve.
2. According to the functional requirements, choose the valve type. Such as voltage regulation range, voltage regulation accuracy (whether to choose precision pressure reducing valve), remote control required (remote control should choose external pilot type pressure reducing valve), with or without special function requirements (whether to choose large flow pressure reducing valve or compound Functional pressure reducing valve).
Fourth, the choice of relief valve
1. Select the diameter of the relief valve according to the required overflow.
2. For the relief valve, it is hoped that the valve will be immediately vented as soon as the pneumatic circuit exceeds the set pressure, and the valve can be closed immediately after the pressure is slightly lower than the set pressure. The smaller the pressure change in the pneumatic circuit from the opening to the closing of the valve, the better the overflow characteristics. In general, a relief valve with a set pressure close to the maximum service pressure should be used.
3. If the pipe diameter is large (such as the diameter of 15mm or more) and is operated at a long distance, a pilot-operated relief valve should be used.
Fifth, the selection of filters
1. Select the type of filter. Select different types of filters depending on the filter object.
2. Select the filter of the corresponding specification according to the required air flow QV (converted to the standard state). The selected filter rated flow rate QO and the actual treated flow rate Qr should have the following relationship: Qr ≤ QO.
Sixth, the choice of oil mister
The specifications of the oil mister should be selected according to the requirements of the maximum output flow rate and the minimum drip flow rate through the oil mister. When passing the maximum output flow, the pressure drop at both ends should not be greater than 0.02Mpa.
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