Cylinder selection method
F' : output force at 85% efficiency (KGF)--(F' = F×85%)
D: Cylinder diameter (mm)
P: Working pressure (KGF /cm2)
When determining the size of output force in engineering, you can refer to experience Figure 1-1 and Figure 1-2 directly.
FIG. 1-1
Figure 1-2
Example: diameter 340mm cylinder, working pressure is 3kgf/cm2, its theoretical output force is what? What is the bud output force?
Connect P and D, find the point on F and F', get:
F = 2800 KGF; F '= 2300 KGF
Select the cylinder diameter based on the service pressure and theoretical thrust or pulling force, as shown in Table 1-1.
Example: there is a cylinder with a working pressure of 5kgf/cm2 and a thrust of 132kgf when the cylinder is pushed out (cylinder efficiency is 85%).
● From the cylinder thrust 132kGF and cylinder efficiency 85%, the theoretical thrust of the cylinder can be calculated as F = F'/85% = 155(KGF)
● According to the use of pressure 5kgf/cm2 and the theoretical thrust of the cylinder, it can be found out from experience table 1-1 that the cylinder diameter of 63 can meet the use requirements.
(2) Length of cylinder stroke:
The stroke of the cylinder depends on the occasion and the stroke ratio of the mechanism (Figure 1-3). It can be seen from Figure 1-3 that the stroke ratio of cylinders varies with different installation forms. The maximum calculated length (L) of the piston rod in the figure can be obtained from empirical data in Table 3-2. In engineering design, the cylinder diameter is selected by the size of the force. According to the actual use of the occasion to check the strength of the piston rod whether longitudinal bending.
For example, there is a cylinder QGBQ125×4000 with a load of 600kgf. It can be found from Table 1-2 that the maximum calculated length of the piston rod L = 2300.
● When the inner diameter of the cylinder is 125, the diameter of the piston rod is 35, and the load is 600kgf, the maximum calculated length of the piston rod L = 2300 can be found in Table 1-2.
● In the form of fixed --(a) diagram structure installation, the cylinder allowed stroke is 2L = 2×2300 = 4600.
● Because the actual stroke of the cylinder is 4000 < 4600.
● So the cylinder does not produce longitudinal bending.
Table of theoretical thrust and tension
Table 1-1 Unit: KGF
1 hinge - hinge 1 hinge - hinge
3 fixed - hinge 4 fixed - fixed
(3) Movement speed of piston (or cylinder) :
Piston speed is closely related to air source pressure, load, friction, inlet and exhaust pipe joint diameter, etc. Among them, exhaust velocity has the greatest influence. If the piston rod is required to move at high speed, the inlet and exhaust ports and conduits with large inner diameters should be selected. Usually, in order to get slow and smooth piston rod movement speed, the cylinder with throttle device or gas-liquid damping device can be selected. Throttle speed control methods are: when the horizontally installed cylinder to push the load, it is recommended to use the exhaust throttle; If the vertical installation of the cylinder when lifting heavy objects, the use of a buffer device with the cylinder.
From the following figure 1-4 1-5 "the effective cross-sectional area of the valve and cylinder speed" relationship, according to the cylinder diameter and speed to choose the control element used to control the cylinder - the effective cross-sectional area of the valve, and thus to judge the size of the valve.
The vertical axis represents the speed of the cylinder, from which the horizontal line is drawn, and the intersection point with the planned cylinder size is found, from which the vertical line is drawn, and the required effective cross-sectional area can be obtained from the intersection point of the horizontal axis. Choose a more suitable valve according to the effective load area.
The cylinder speed is calculated by considering only the effective cross-sectional area of the solenoid valve. Please note that loop factors such as governor, piping, pipe joint and load rate of cylinder are not considered here.
The relation between piston rod diameter and maximum calculated length (L) of piston rod
Figure 1 is shown in figure 1-4-5
(4) Selection of installation form:
It is determined by installation position, purpose and other factors. In general, the use of fixed cylinder. In need of continuous rotation with the working mechanism (such as lathe, grinder, etc.) should choose rotary cylinder. In addition to the piston rod is required to do linear motion, and the cylinder is required to make a large arc swing, then choose the pin cylinder. Only need in 360° or 180° reciprocating swing, should choose a single blade or double blade swing cylinder, there are special requirements, should choose the appropriate phase of the special cylinder and combined cylinder.
Air consumption is a part of the operating cost. Figure 1-6 shows the air consumption calculated according to the following formula.
D: Piston or piston rod diameter (mm)
S: Cylinder stroke (in addition, constant 10mm)
P: Operating pressure (KGF /cm2)
The air consumption calculated using this formula is approximate, because sometimes the supply air in the cylinder chamber is not fully discharged (especially at high speed), and the actual consumption may be slightly lower than the data read on the drawing.
Example: Cylinder QGBQ50×500, piston diameter 50mm, piston rod diameter 20mm, stroke 500mm, operating pressure 4.5bar.
Demand: air consumption.
Solution: the diameter of the piston given is selected, and the intersection of the horizontal line and the operating pressure line is determined. The air consumption is then read from the horizontal coordinate and multiplied by the stroke (cm) of the cylinder. The value read in the above steps is 0.091 /cm stroke, then the air consumption of single stroke is 4.51. For the return trip, the volume of the piston rod must be deducted from the 20mm diameter of 0.0141 /cm stroke ×50cm stroke = 0.71. Therefore, the air consumption of the return trip is 3.8 and the air consumption of the round trip is 8.3.
Figure 1-6
Two, the use of cylinder requirements
(1) The normal working conditions of the cylinder: the medium and ambient temperature are generally -20 ~ 80℃, and the working pressure is generally 0.1 ~ 1.0mpa. See technical parameter table of various cylinders for specific conditions.
(2) Before installation, the test should be carried out under 1.5 times the working pressure, and there should be no air leakage.
(3) Oil mist should be set at the inlet of the installed air source to facilitate lubrication during work. Reasonable lubrication of the cylinder is very important, often due to poor lubrication and crawling, even can not work normally.
(4) when installing, pay attention to the direction of action. The piston rod is not allowed to bear eccentric load or transverse load.
(5) When the load changes in the stroke, a cylinder with enough output force should be used, and a buffer device should be attached.
(6) Do not use full stroke, especially when the piston rod is extended, do not make the piston and cylinder head collide. Otherwise easy to cause piston and cylinder head and other parts damage.