Step 1: Master the basic concepts and formulas
1) Basic parameters of oil cylinder
Cylinder diameter D (cylinder inner diameter), rod diameter d (piston rod diameter), stroke S, operating pressure P, installation method, installation size.
The most important ones are the cylinder diameter, stroke and working pressure. The cylinder diameter is available in standard series, and the working pressure is also divided into several gears.
2) F = PS
It can be known from the calculation formula of force: F = PS (P: pressure; S: pressure area - determined by the cylinder diameter and rod diameter of the oil cylinder)
For example: the thrust of the oil cylinder needs to reach 10 tons, that is, F=10, then there are various combinations of P and S.
100-bore cylinder, when the operating pressure reaches 14MPA, it can reach 10 tons
80-bore cylinder, the operating pressure can reach 21MPA and can also reach 10
Step 2: Determine the system pressure P
1. Primary hydraulic working pressure:
The choice of pressure depends on the size of the load (ie F) and the type of equipment. It is also necessary to consider the limitations of the assembly space of the actuator, economic conditions and component supply.
Generally speaking, for equipment that is not too limited in size, the pressure can be selected to be lower, and the pressure of the equipment for mobile machinery should be higher.
Step 3: Preliminary selection of cylinder diameter D/rod diameter d
After selecting the design pressure, that is, P is known, and the load size F is known, then the S force area is obtained by the formula, and then the cylinder diameter of the cylinder is calculated according to the force area.
Re-select rod diameter d
1) P≤10, d=0.5D
2) 2) P=12.5～20,d=0.56D
3) 3) P>20, d=0.71D
Step 4: Select the itinerary S
According to the requirements of the overall design of the equipment or device system, the installation method and stroke S are determined. The specific determination principles are as follows:
Stroke S = actual maximum working stroke Smax + stroke allowance △S;
Stroke margin △S=travel margin △S1+travel margin △S2+travel margin △S3.
5
Step 5: Installation method, that is, in what form is the oil cylinder connected to the equipment. After determining the installation method, determine the installation size.
The principle of determining the installation method
1) Flange installation
2) Hinge installation
a) Tail single (double) earring installation
b) End, mid or tail trunnion mounting
c) The installation of the tail trunnion is similar to the installation of the tail double clevis.
Step 6: Selection of end buffer
The following conditions should be considered to choose two-end buffer or one-end buffer:
1) When the hydraulic cylinder piston runs in full stroke and its reciprocating speed is greater than 100mm/s, buffers at both ends should be selected.
2) When the one-way (return) speed of the hydraulic cylinder piston is greater than 100mm/s and runs to the end of the stroke, one or both ends should be buffered.
3) Other specific conditions.
7
Step 7: Port type and diameter selection
1) Port type:
The selection of internal thread type, flange type and other special types is determined by the way of connecting pipes in the system.
2) Selection principle of port diameter:
Under the condition that the medium flow rate in the connecting pipeline between the system and the hydraulic cylinder is known, the medium flow rate through the oil port is generally not greater than 5mm/s. At the same time, pay attention to the factor of the speed ratio to determine the oil port diameter.
Step 8: Condition selection for specific working conditions
1) Working medium
The normal medium is mineral oil, and other media must pay attention to its influence on the sealing system, material properties of each component and other conditions.
2) Ambient or medium temperature
The normal working medium temperature is -20°C to +80°C. If the working temperature exceeds this temperature, attention must be paid to its influence on the sealing system, the material properties of each component and the setting of the cooling system.
3) High running accuracy
For servo or other hydraulic cylinders with low starting pressure requirements such as medium and high pressure, attention must be paid to its influence on the sealing system, material properties of each component and detailed design.
4) Zero leakage
For hydraulic cylinders with specific pressure holding requirements, attention must be paid to their influence on the sealing system, material properties of each component and other conditions.
5) Working pressure and speed, working conditions such as
a) Medium and low pressure system, piston reciprocating speed ≥70~80mm/s
b) Medium and high pressure, high pressure system, piston reciprocating speed ≥100~120mm/s
It is necessary to pay attention to the influence on the sealing system, material properties of each component, connection structure and matching accuracy.
6) High-frequency vibration working environment: attention must be paid to its influence on the material characteristics of each component, the connection structure and the detailed design.
7) Low temperature freezing or polluted working environment, working conditions such as
a, high dust and other environments;
b. Environments such as water drenching, acid mist or salt mist.
Attention must be paid to its influence on the sealing system, the material properties of the components, the surface treatment of the piston rod and the protection of the product.
Step 9: Selection of seal quality
Case 1. There is no specific working condition and specific quality requirements, and the standard sealing system is adopted.
Situation 2. There are specific working conditions as mentioned above and no specified quality requirements, which are adopted according to the specific sealing system;
Situation 3. There are specific working conditions as mentioned above and specified quality requirements. It is recommended that the sealing system be recommended by professional engineers;
Situation 4. The failure of the sealing system of the hydraulic cylinder has serious consequences (such as affecting safety, difficult to replace, large economic losses, etc.), it is recommended that the sealing system be recommended by the professional engineer;
Situation 5. For the hydraulic cylinder sealing system for export, it is recommended that professional engineers recommend the use of well-known sealing quality with good interchangeability and easy procurement according to the working conditions.
Step 10: Selection of other features
(1) Exhaust valve
According to the working position of the hydraulic cylinder, it is normally set at the highest point of the final air accumulation in the end chambers of the two chambers. After the air is exhausted, it can prevent crawling, protect the seal, and slow down the deterioration of the oil.
In the working environment where oil leakage is strictly prohibited, due to the long stroke of the hydraulic cylinder or certain working conditions, the oil accumulates behind the dust ring during the round-trip work to prevent leakage after long-term work. Leakage ports are set at the location where the oil accumulates.
