Common technical parameters and selection requirements of cylinders

Common technical parameters of cylinders 1

1) The output force of the cylinder. The design calculation of the theoretical output force of the cylinder is similar to that of the hydraulic cylinder. Please refer to the design calculation of the hydraulic cylinder. For example, the thrust of a double-acting single-piston rod cylinder is calculated as follows:
Theoretical thrust (piston rod extended)
Ft1＝A1p                              
Theoretical tension (piston rod retracted)
Ft2＝A2p                                
In the formula, Ft1, Ft2——theoretical output force of the cylinder (N);
A1, A2——Piston area of ​​rodless cavity and rod cavity (m2);
p — cylinder working pressure (Pa).

In practice, due to the inertial force of moving parts such as the piston and the friction of seals and other parts, the actual output force of the piston rod is less than the theoretical thrust. This thrust is called the actual output force of the cylinder. The efficiency n of the cylinder is the ratio of the actual thrust of the cylinder to the theoretical thrust, that is,

so


The efficiency of the cylinder depends on the type of seal, the state of the cylinder's inner surface and piston rod machining, and the state of lubrication. In addition, the cylinder's movement speed, exhaust chamber pressure, external load conditions and pipeline conditions will all have a certain impact on efficiency.





Common technical parameters of cylinder 2


2) Load rate β From the study of cylinder operating characteristics, it can be seen that it is difficult to accurately determine the actual output force of the cylinder. Therefore, when studying cylinder performance and determining cylinder output, the concept of load rate is often used. The load rate β of the cylinder is defined as







The actual load of the cylinder is determined by the actual working conditions. If the cylinder load rate θ is determined, the theoretical output force of the cylinder can be determined by definition, and the cylinder bore can be calculated.

For resistive load, if the cylinder is used as a pneumatic fixture, the load does not generate inertial force, and the load rate β is generally selected to be 0.8;for inertial load, if the cylinder is used to push the workpiece, the load will generate inertial force, and the value of load rate β is as follows

β＜0.65 When the cylinder moves at low speed and v＜100 mm/s;
β<0.5 When the cylinder moves at medium speed, v=100~500 mm/s;
β＜0.35 When the cylinder moves at high speed and v＞500 mm/s.



3) Cylinder air consumption The air consumption of the cylinder is the volume that the piston moves per minute. This volume is called compressed air consumption. Generally, the air consumption of the cylinder refers to the free air consumption.





Technical parameters of cylinder 3


4) Characteristics of the cylinder The characteristics of the cylinder are divided into static characteristics and dynamic characteristics. The static characteristics of the cylinder refer to the minimum working pressure, maximum working pressure, friction resistance and other parameters that are closely related to the output force and air consumption of the cylinder. The dynamic characteristics of the cylinder refer to the changes with time of air pressure, temperature, piston speed, displacement and other parameters in the two chambers of the cylinder during the movement of the cylinder. It can truly reflect the working performance of the cylinder.





Cylinder selection and calculation 1





1. Cylinder selection steps
The selection of the cylinder should be based on the working requirements and conditions, and the type of cylinder should be selected correctly. The following takes a single-piston rod double-acting cylinder as an example to introduce the cylinder selection steps.
(1) Cylinder bore. The output force of the cylinder is determined according to the load force of the cylinder, and the bore diameter of the cylinder is calculated from this.
(2) The stroke of the cylinder. The stroke of the cylinder is related to the use occasion and the stroke of the mechanism, but the full stroke is generally not selected.
(3) Calculation of cylinder strength and stability
(4)