Air motor selection

With the development of the economy, air motor in the field of industrial automation has been widely used, Gaston company long-term commitment to air motor, pneumatic equipment research and development, design, manufacturing, sales and service, we in the long-term manufacturing practice to master the structure, performance and characteristics of all kinds of air motor, we have a very rich experience in air motor selection, we are happy to share with you some experience in air motor selection and use.

Air motor selection depends on four factors: (1) power; (2) torque; (3) Rotational speed; (4) Air consumption

1. According to your actual application, you can choose motors with different power, different torque and speed, and the selection of some applications in this example increases the working pressure, and the output power, torque and speed of the motor are greatly increased; When the working pressure is unchanged, its speed, torque and power all change with the change of applied load, and all data and curves of the sample are measured when the motor supply pressure is 6 bar. The following chart shows the effect of pressure on speed, specified torque, power and air consumption. In the curve (Figure 1), start from the point of supply pressure used and look up at the power, torque and air consumption curves.

For example, at 4 bar supply pressure, the power is only 0.55 times, the torque is 0.67 times, the speed is 0.87 times, and the air consumption is 0.65 times at 6 bar.

This example shows how the power decreases if the supply pressure drops. Air must be supplied through a properly sized tube to reduce any latent pressure drop in the control loop.Throttling

The most common way to reduce the speed of an air motor is to install a flow control valve at the air intake. When the motor is used with air intake, it can also be used for exhaust port. Flow regulation is also used on the main exhaust port, which allows speed control in both directions.

Pressure regulation

Speed and torque can also be adjusted by installing a pressure reducing valve at the upstream air supply. When low-pressure air is continuously supplied to the motor and the motor decelerates, a low torque is generated on the output shaft. 

Operating torque

(Figure 2) When the load increases and the air motor stops, this is the stopping torque. When the load is reduced when the motor resumes work, the motor will not burn out, this is the biggest feature of the air motor, due to the influence of lubrication and friction, the starting torque is generally 75-80% of the stop torque, from the figure can be seen that the motor power becomes the maximum position, about half of the motor rotation speed. Therefore, the maximum power and torque of the motor can be obtained by reducing the motor speed, and the air supply consumption can be saved.

The motor slows down

If the air supply pressure is limited, high torque can be obtained by deceleration, such as 5:1, 10:1 deceleration, the performance curve becomes as shown in the table (Figure 3), the maximum horsepower remains unchanged, even when decelerating, the torque curve is the main tendency due to the torque deceleration amplitude curve varies greatly.

Running speed

1. The piston air motor is a low-speed and high-torque type. However, when it is considered pulsation becomes less restrictive than low speed rotation. Even with high torque, the horsepower becomes smaller. When the air motor accelerates and decelerates the structure, in this case used in parallel, it becomes large torque at low rpm and can be used almost at maximum horsepower. The recommended rotation range is (0.2-1) at the maximum output speed.

2. Vane air motor is high-speed type, but the life of the air motor is not comparable to the piston motor, if it is used with far more than the rotation at the maximum output speed, the efficiency of the motor becomes relatively low, it is best to alternate at low speed. At the maximum output (0.3-1) it is recommended to rotate the range.

Air supply for air motors

1. The air to be supplied to the motor must be filtered and depressurized. Directional control valves need to supply air to the motor and rotate the motor when needed. Such valves can be electronically controlled, mechanically controlled or pneumatically controlled.

2. When the motor is used in applications that cannot rotate directionally, it is sufficient to use a two-port two-position or three-port two-position valve to control it. For motors that can rotate in reverse, a five-port three-position or two-port valve is required to ensure that the motor has a compressed air supply and residual air exhaust.

3. If the motor is not used for directional rotation, the flow regulating valve can be installed in the air supply line to adjust the speed of the motor. If the motor is used for reverse rotation, a flow control valve with an internal one-way function needs to adjust the rotation in each direction. The valve with internal one-way function allows air to be discharged from the residual air vent of the motor to the exhaust port of the control valve and then discharged.

4. The compressed air supply must have a large enough pipe and valve to ensure the maximum torque of the motor. At any given time, the motor requires a supply pressure of 6 bar to 7 bar, and when the pressure is reduced to 5 bar, the power is reduced to 77%, and at 4 bar, the power is 55%.

Silencers

1.The noise generated by the motor includes mechanical noise, and also includes the pulsating noise of the air discharged from the exhaust port, and the installation of the motor has a considerable impact on the mechanical noise.

2. The motor should be properly installed to avoid mechanical resonance. There are many types of exhaust silencers that can be used to lower this standard. This is because the motor function causes the exhaust to pulsate. A good approach is to allow air to drain into one of the chambers to reduce pulsation before the exhaust reaches the silencer.

3. The device that can provide the best sound attenuation effect is connected to a large central silencer with a hose, the central silencer has the largest possible area, and the speed of air outflow is reduced as much as possible.

Note! Keep in mind that if a muffler is too small or clogged, it will create back pressure on the exhaust port side of the motor, which in turn will reduce the power of the motor.

Selection of gas supply elements

The important relationship between the air supply pressure of the motor inlet and power, speed and torque, then the following recommendations should be followed

The following data must be combined with the following criteria:

1. Motor supply pressure: 7bar

2. Pressure reducing valve pressure setting: 6.3bar

3. Medium: 40um filter, lubricate air

4. Pipe length between the air handling unit and the valve: up to 1m

5. Tube length between valve and air motor: up to 2m

The air motor is equipped with deceleration

The motor selection of reducer should consider its structure type, installation form, bearing capacity, output speed, working conditions and other factors.

    No-load torque t1 (nm): refers to the torque loaded onto the gearbox to overcome the friction in the gearbox

    Rated output torque tn (nm): refers to the torque that the motor or reducer can load for a long time (continuous work), and the load should be uniformly met under the rated air source pressure provided, and the safety factor is s=1

Maximum torque T2max (NM): Refers to the output torque that can be withstood under static conditions or high shutdown conditions, usually refers to the starting load or peak.

    Actual required torque t4 (nm): Refers to the torque required under the actual working conditions of the application, and the rated torque of the selected gearbox is greater than this torque.

   Calculation torque t5 (nm): When selecting a gearbox, you can use the actual required torque t4 and the reducer use coefficient, which can be according to the following formula:

T5=T4×fs

Transmission ratio (i): by the required output speed n2 and input speed n1 gear ratio:i=n1/n2

After determining the T5 and reduction ratio i, find the reducer rating table according to the input speed n1, and select the reducer with the transmission ratio closest to the calculated value that meets the following conditionsTn≥T5

The continuous output torque rating Tm of the air motor at the stable working speed under the stable air source pressure is obtained, and the torque Tr required for the reducer is calculatedTr=Tm×i×e

Select Calculate

Air motor performance depends on dynamic air inlet pressure measurement and air intake volume, using the correct chart we can get linear output torque and speed, you must know the required speed and torque, since the maximum power of the motor is reached at about half of the free speed of the motor, then the motor should be selected as close as possible to the maximum output point of the motor, in the selection of air motor it is necessary to choose the power or torque of the motor, according to the effective parameters refer to the following formula to select the required air motor.

At present, air motors with safety explosion-proof, stepless speed regulation and other characteristics have been widely used in the mixing industry, gaston company production of various types of high-precision air motors, stable performance and reasonable price has been widely used in various fields.