เวลาอ่านโดยประมาณ: 60 นาที

How to Design Hydraulic Cylinder

The combination of a hydraulic cylinder and mechanism

For the situation that the motion form of the main machine working mechanism is more complicated, the ไฮดรอลิค actuator can be organically matched with other mechanisms to form a hydraulic mechanical working mechanism to meet the activity requirements. For hydraulic motors and swing hydraulic motors, the working mechanism can be driven to move through the gear mechanism and the screw nut mechanism. For hydraulic cylinders, the working mechanism can be driven in horizontal, vertical, and inclined directions. The schematic diagram and characteristics are shown in 1-1. How to Design Hydraulic Cylinder

Diagram of a hydraulic cylinder

Combination working structure of common hydraulic cylinders How to Design Hydraulic Cylinder

1. Direct drive mechanism

Feature: The piston rod of hydraulic cylinder 1 is directly connected with moving object 2, and the hydraulic cylinder drives the moving object to make horizontal reciprocating linear. How to Design Hydraulic Cylinder

Surface grinder table, combined machine tool power sliding table reciprocating motion, etc. How to Design Hydraulic Cylinder

Feature: The piston rod of hydraulic cylinder 1 is directly connected with the moving object 2, and the hydraulic cylinder drives the moving object to make a vertical reciprocating linear motion.

Press slider and ejector device, hydraulic elevator lifting device, harvester header lifting, etc. How to Design Hydraulic Cylinder

Feature: The piston rod of hydraulic cylinder 1 is directly connected with the moving object 2, and the hydraulic cylinder drives the moving object to make a reciprocating linear motion in an inclined direction.

Mining and metallurgical machinery, etc. How to Design Hydraulic Cylinder

2. Force-increasing clamping mechanism How to Design Hydraulic Cylinder

Feature: The piston rod of the vertical hydraulic cylinder 1 is connected with the connecting rod mechanism 2, and the workpiece 4 is clamped in the horizontal direction by clamp 3, and a hydraulic cylinder with a smaller thrust is used to achieve a larger clamping force, and the clamping force varies with the clamped workpiece Changes in size.

Machine tool fixtures, manipulators, etc. How to Design Hydraulic Cylinder

3. Telescopic extension mechanism How to Design Hydraulic Cylinder

Feature: The piston rod of the horizontal hydraulic cylinder 1 is connected with the connecting rod mechanism 2, and the horizontal movement of the hydraulic cylinder is converted into vertical lifting movement of platform 3, which can expand the range and increase speed. How to Design Hydraulic Cylinder

Lifting stage, large-stroke scissor telescopic frame, automobile maintenance lifting platform, etc. How to Design Hydraulic Cylinder

4. Pulley lifting mechanism How to Design Hydraulic Cylinder

Feature: Hydraulic cylinder 1 is installed obliquely, and its piston rod is connected with the steel cable 2 wound on pulley 3 to realize the lifting movement of lift 4. How to Design Hydraulic Cylinder

Hoist, blast furnace feeding device. How to Design Hydraulic Cylinder

5. Swing mechanism How to Design Hydraulic Cylinder

Feature: The piston rod of hydraulic cylinder 1 is connected with the rocker mechanism 2 which converts the telescopic motion of the hydraulic cylinder into the swing of the rocker.

Construction machinery, construction machinery working mechanism. How to Design Hydraulic Cylinder

6. Rack-gear mechanism How to Design Hydraulic Cylinder

Feature: The piston rod of hydraulic cylinder 1 is connected with rack 2 to convert the reciprocating linear motion of the hydraulic cylinder into the rotary motion of gear 3.

Intermittent feeding mechanism, feeding mechanism. How to Design Hydraulic Cylinder

7. Sector gear-rack mechanism How to Design Hydraulic Cylinder

Feature: The piston rod of hydraulic cylinder 1 connected at the end is connected with the sector gear 2 to convert the horizontal reciprocating linear motion of the hydraulic cylinder into the vertical reciprocating linear motion of rack 3.

Short-stroke working device. How to Design Hydraulic Cylinder

8. Linear motion mechanism How to Design Hydraulic Cylinder

Feature: The piston rod of hydraulic cylinder 1 is connected with rod system 2, which converts the vertical movement of the hydraulic cylinder into positive and negative adjustable bidirectional horizontal reciprocating linear movement.

Periodic motion mechanisms in various types of machinery. How to Design Hydraulic Cylinder

9. Moving cam mechanism How to Design Hydraulic Cylinder

Feature: The piston rod of hydraulic cylinder 1 is connected to the moving cam 2, which can make follower 3 perform vertical reciprocating motion according to the predetermined motion law under the cam drive. The structure is simple and compact, and the required cam profile can be easily obtained by CNC machine tools. How to Design Hydraulic Cylinder

Automatic feeding device, etc. How to Design Hydraulic Cylinder

10. Tension and compression clamping mechanism How to Design Hydraulic Cylinder

Feature: The piston rod of hydraulic cylinder 1 is connected with the tapered jacket 2 and the clamping is realized by stretching movement of the piston rod.

Machine tool fixtures, etc. How to Design Hydraulic Cylinder

11. Double-cylinder rigid synchronization mechanism How to Design Hydraulic Cylinder

Feature: The oil circuits of the two hydraulic cylinders 1 are connected in parallel, and their piston rods establish a rigid connection through the rigid member 2 to achieve displacement synchronization.

Press, blast furnace feeder, planter fertilizer box lifting device, harvester header, etc. How to Design Hydraulic Cylinder

Calculation of hydraulic cylinder parameters

Question 1: Calculation of motion parameters

• The movement of the main engine’s actuators can be represented by the displacement cycle diagram (L-t), the velocity cycle diagram (v-t), and the overall machine working cycle diagram, to analyze the movement law. How to Design Hydraulic Cylinder

Displacement cycle diagram วิธีการออกแบบกระบอกไฮดรอลิก

• Figure 2-1 is a hydraulic cylinder displacement cycle diagram of a hydraulic machine. The ordinate L represents the displacement of the piston, the abscissa t represents the time from the start of the piston to the return to the original position, and the slope of the curve represents the movement speed of the piston. Figure 2-1 clearly shows that the working cycle of a hydraulic press is composed of six stages: fast down, decelerated down, compression, pressure retention, pressure relief, slow return, and fast return. How to Design Hydraulic Cylinder

Speed cycle diagram

Analysis of motion parameters

• The movement of the main engine’s actuators can be represented by the displacement cycle diagram (L-t), the velocity cycle diagram (v-t), and the overall machine working cycle diagram, to analyze the movement law. How to Design Hydraulic Cylinder

Displacement cycle diagram

• It is a hydraulic cylinder displacement cycle diagram of a hydraulic machine. The ordinate L represents the displacement of the piston, the abscissa t represents the time from the start of the piston to the return to the original position, and the slope of the curve represents the movement speed of the piston. Figure 2-1 clearly shows that the working cycle of a hydraulic press is composed of six stages: fast down, decelerated down, compression, pressure retention, pressure relief slow return, and fast return. How to Design Hydraulic Cylinder

Speed cycle diagram

• According to the working cycle diagram of the whole machine, the stroke or speed of the actuator, and the acceleration change law, the speed cycle diagram (v-t or v-L) of the actuator can be calculated and drawn. According to the characteristics of the movement form of the hydraulic cylinder in the project, it can be summarized as three types. How to Design Hydraulic Cylinder

• It is the speed cycle diagram of the three types of movement of the hydraulic cylinder.

• As shown by the solid line 1 in Figure1-2, the hydraulic cylinder starts to move at a uniform acceleration, then moves at a constant speed, and finally decelerates to the endpoint; as shown by the dotted line 2 in Figure 2-2, the first half of the total stroke of the hydraulic cylinder is done Perform uniform acceleration movement, and finally perform uniform deceleration movement, and the acceleration values are equal; as shown in the double-dotted line 3 in Figure 2-2, the hydraulic cylinder moves at a small acceleration during the majority of the total stroke, and then uniformly decelerates to the end of the stroke. The three-speed curves in the figure not only clearly show the movement laws of the three types of hydraulic cylinders but also show the dynamic characteristics of the three working conditions.

Working cycle diagram of the whole machine วิธีการออกแบบกระบอกไฮดรอลิก

• In a complex system with multiple hydraulic actuators, the actuators usually work in cycles according to a certain program. Therefore, it is necessary to reasonably arrange the working sequence and working time of each actuator according to the working mode and productivity of the host and draw the working cycle diagram of the whole machine. How to Design Hydraulic Cylinder

Question 2: Calculation of the maximum load force of the hydraulic cylinder

• For the actuators that drive the working mechanism of the machine tool, the focus is on the time relationship between the load and each working condition; for the actuators that drive the working mechanism of the construction machinery, the focus is on the gravity at each position, and the load diagram uses the position as a variable. The external load of hydraulic actuators includes three types: working load, friction load, and inertial load. How to Design Hydraulic Cylinder

• Figure 1-1 shows the calculation diagram of the hydraulic cylinder, where Fe is the external working load acting on the piston rod, Fm is the seal of the hydraulic cylinder (between the piston and the inner wall of the cylinder, and between the piston rod and the guide sleeve on the cylinder head The internal sealing resistance of the seal).  How to Design Hydraulic Cylinder

Workload Fe

• The working load has resistance load (the load that is opposite to the direction of movement and prevents movement, also called positive load) and overrun load (the load that promotes movement in the same direction of movement, also called negative load). The common working loads of hydraulic cylinders include gravity, cutting force, squeezing force, and so on. The resistance load is positive, and the overrun load is negative.

Mechanical friction load FF

• Friction load refers to the mechanical friction resistance load to be overcome when the hydraulic actuator drives the working mechanism. There are two types of static friction load and dynamic friction load. How to Design Hydraulic Cylinder

• Mechanical friction load Ff; for machine tools, it is the frictional resistance of the guide rail. Flat guide rail. The frictional resistance of the flat guide rail varies with the way the guide rail is placed.
• Flat rails placed horizontally (see Figure 1-2)
• Static friction resistance How to Design Hydraulic Cylinder
• Ffs-us(G＋Fn) How to Design Hydraulic Cylinder
• Dynamic friction resistance
• Ffd=ud(G + Fn) How to Design Hydraulic Cylinder
• Flat guide rails placed obliquely (see Figure 1-2)
• Static friction resistance
• Ffs—us (Gcosβ+Fn) How to Design Hydraulic Cylinder
• Dynamic friction resistance
• Ffd=pd(Gcosβ＋Fn)
• V-shaped guide rail (see Figure 1-3).
• Static friction resistance How to Design Hydraulic Cylinder
• Ffs-us(G + Fn)/sin(a/2)
• Dynamic friction resistance
• Fd=ud(G＋Fn )/ sin(a /2) How to Design Hydraulic Cylinder
• In the formula, G—gravity of moving parts, N;
• Fn——The vertical component of the working load on the guide rail, N;
• β——Inclination angle of the plane guide rail, (°); How to Design Hydraulic Cylinder
• α——The included angle of the V-shaped guide rail, (°); How to Design Hydraulic Cylinder
• Us, Ud-static and dynamic friction factors, selected according to the material and properties of the friction surface. Generally, for sliding guide rails, us=0.1~0.2, Ud=0.05~0.12 (large value at low speed, and small value at high speed); for rolling guide rail, Ud=0.003~0.02 [cast iron to ball (column) takes the larger value, Steel to roller takes the small value]; for cast iron hydrostatic guide rail, Ud=0.005.

Question 3: Checking the effective area of the hydraulic cylinder

• The effective working area of the hydraulic cylinder affects the thrust and speed of the hydraulic system. Therefore, the effective working area calculated according to the load must be checked according to the speed to verify that it can meet the requirements of the minimum stable flow of the throttle or speed control valve. The minimum operating speed of the system is required. After the effective working area meets the minimum working speed requirements of the hydraulic system, it needs to be rounded to ensure that standard sealing elements can be used. How to Design Hydraulic Cylinder

• For example, for hydraulic cylinders with a very low working speed, such as the feed cylinder of a precision boring combined machine tool, after calculating the size of the cylinder according to the load force. How to Design Hydraulic Cylinder
• Minimum working speed check cylinder size, How to Design Hydraulic Cylinder
• A≥q min/v min How to Design Hydraulic Cylinder How to Design Hydraulic Cylinder
• Where A is the effective working area of the hydraulic cylinder, m2; V min’; How to Design Hydraulic Cylinder
• The minimum working speed of the hydraulic cylinder, m/s;q min; How to Design Hydraulic Cylinder
• The minimum stable flow of the system, m3/s, the throttle speed control system depends on the minimum stable flow of the flow control valve; How to Design Hydraulic Cylinder
• The volumetric speed control system depends on the minimum stable flow rate of the variable pump, and the sample is checked according to the component selection.
• If the effective area after verification cannot meet the minimum working speed requirement, the cylinder’s size must be determined at the minimum stable speed. How to Design Hydraulic Cylinder

Question 4: Compile working condition diagrams of hydraulic cylinders or hydraulic motors

• The working condition diagram includes a pressure cycle diagram (p-t diagram or p-L diagram), a flow cycle diagram (q-t diagram or q-L diagram), and a power cycle diagram. Diagram (P-t diagram or P-L diagram), which reflects the pressure, flow, and power requirements and changes of a hydraulic system in a cycle. How to Design Hydraulic Cylinder

• The situation and the location of the peak are the basis for drawing up hydraulic systems, comparing schemes, adjusting or modifying design parameters for equalizing power distribution, and selecting and designing hydraulic components. p-t diagram (or p-L diagram). How to Design Hydraulic Cylinder

• According to the final size of the actuator structure, according to the actual load, it can be calculated that the hydraulic actuator is in its action. How to Design Hydraulic Cylinder

• The working pressure at each stage of the cycle is shown in Figure 1-5 and then drawn into a p-t diagram (or p-L diagram). How to Design Hydraulic Cylinder

• If multiple actuators working at the same time in the system, the q-t diagram (or q-L diagram) of each actuator should be stacked.
• Plus, draw the total q-t diagram (or q-L diagram) of the system;
• P-t diagram (or P-L diagram); How to Design Hydraulic Cylinder
• P-t diagram (or P-L diagram) can be drawn from the p-t; How to Design Hydraulic Cylinder
• Graph (or p-L graph) and q-t graph (or q-L graph) root; How to Design Hydraulic Cylinder
• According to the hydraulic power, P=pq plotted.How to Design Hydraulic Cylinder

• Figure 1-6 is an example of a working condition diagram of a hydraulic cylinder. The working condition diagram of the hydraulic cylinder is to select other elements in the system. Components and hydraulic basic circuits, for the drafting of the hydraulic system; Both the system and the comparison of schemes play an important role.

• The maximum pressure and maximum flow in the working condition diagram determine the maximum working pressure and the maximum working pressure of hydraulic components such as hydraulic pumps and hydraulic valves. Maximum working flow. How to Design Hydraulic Cylinder

• The main parameter values of the hydraulic system determined according to the working condition diagram reflect the rationality of the original design parameters and are the main parameters of the system. The revision and finalization provided the basis. How to Design Hydraulic Cylinder

• By analyzing the change law of pressure and flow in each stage of the working condition diagram, the hydraulic circuit and oil can be selected reasonably. The structural form of the source, a perfect hydraulic system plan is drawn up. When the actuator in the hydraulic system is a hydraulic motor, because the hydraulic motor is a series of design products, this step becomes an option. Determine the working pressure p, displacement Vm, maximum speed max, and maximum flow max of the hydraulic motor, and then perform rounding to determine the specifications of the hydraulic motor. As for drawing the pressure diagram, flow diagram, and power diagram of the hydraulic motor according to the load and speed, it is the same as that of the:How to Design Hydraulic Cylinder

Question 5: Calculation of cylinder length of hydraulic cylinder

Calculation of the length of hydraulic cylinder

• The cylinder length L1 of the hydraulic cylinder is determined by the maximum working stroke length plus various structural requirements, namely.
• L1=L+B+A+M +C How to Design Hydraulic Cylinder
• In the formula, L is the maximum working stroke of the piston;How to Design Hydraulic Cylinder
• B-Piston width, generally (0.6~1)D;How to Design Hydraulic Cylinder
• A-Piston rod guide length, take (0.6~1.5)D;
• M-The sealing length of the piston rod is determined by the sealing method;
• C-Other lengths.How to Design Hydraulic Cylinder

Pay attention to the problem

• Generally, the length of the cylinder should not exceed 20 times the inner diameter. In ensuring that the conditions of movement stroke and load force can be met. Next, the outline size of the hydraulic cylinder should be reduced as much as possible.How to Design Hydraulic Cylinder

• Special problems of high-pressure long hydraulic cylinders. When the length of the hydraulic cylinder is particularly large and the working pressure is high, a special structure should be adopted to ensure the deformation of the hydraulic cylinder. Not too big. The specific solution is to install a reinforcing hoop in the middle of the cylinder tube of the hydraulic cylinder, as shown in Figure 1-7.

• Calculation of minimum guide length of hydraulic cylinderHow to Design Hydraulic Cylinder
• When the piston rod is fully extended, the distance from the midpoint of the piston bearing surface to the midpoint of the sliding surface of the guide sleeve is called the minimum guide length H (Figure 1-8). For general hydraulic cylinders, the minimum guide length should meet the following formula: How to Design Hydraulic Cylinder
• HL /20+D/2
• Where L is the maximum working stroke of the hydraulic cylinder, m;
• D-Inner diameter of cylinder, m. How to Design Hydraulic Cylinder
• The length A of the sliding surface of the general guide sleeve, when D<80mm, take A=(0.6~1.0)D; when D>80mm, take A=(0.6~1.0)d.

• The width B of the piston, take B=(0.6~1.0)D. To ensure the minimum guide length, it is not appropriate to increase A and B excessively. It is best to install a spacer K between the guide sleeve and the piston. The spacer width C is determined by the required minimum guide length, namely: How to Design Hydraulic Cylinder

• The use of spacers can not only ensure the minimum guide length but also improve the versatility of the guide sleeve and the piston.

Pay attention to the problem

• The guide length of the piston rod should not be too small. If the guide length is too small, the initial deflection (deflection caused by the clearance) of the hydraulic cylinder will increase, which will affect the stability of the hydraulic cylinder. Therefore, a minimum guide length must be ensured in the design. The length A of the guide sleeve generally varies with the size of the hydraulic cylinder and the type and purpose of the piston rod seal, but the general size should be more than 0.6 times the diameter of the piston rod to ensure sufficient stability of the piston rod, as shown in Figure 1- 9 shown.

•  The guide sleeve of the high-speed and long-stroke hydraulic cylinder should adopt a special structure. For hydraulic cylinders with a speed greater than 1000mm/s and a stroke greater than 4000mm, local overheating caused by high-speed action will cause significant wear of the guide sleeve and the appearance of metal powder. This not only requires forced lubrication on the surface of the guide sleeve from the structural point of view but also requires special treatment such as high-frequency quenching on the surface of the piston rod. At the same time, hydrostatic bearings may also be considered. How to Design Hydraulic Cylinder

Question 6: Determining the tolerance of cylinder shape and position

• The cylinder must ensure the necessary shape and position tolerances. To ensure that the hydraulic cylinder has a lower starting pressure and does not occur “unusual” during movement, sufficient attention should be paid to the shape and position tolerance of the cylinder. How to Design Hydraulic Cylinder

• Under normal circumstances, the roundness, and cylindricity error of the cylinder diameter cannot be greater than half of the cylinder diameter tolerance.

• The circular runout of the cylinder end facing the cylinder axis is not more than 0.04mm per 100mm.

• The position error of the earring hole of the earring type hydraulic cylinder to the axis of the cylinder barrel is not more than 0.03mm.

• The axis position tolerance of the pin type hydraulic cylinder pin is not more than 0.1mm, and the perpendicularity error is not more than 0.1mm on the length of 100mm.

• The straightness error of the cylinder axis is not more than 0.03mm per 500mm length.

Question 7: Calculation of piston parameters

Piston length calculation

• Although the piston is not expected to bear radial force from the perspective of design thinking, due to the limitation of the actual structure, the piston of the hydraulic cylinder. How to Design Hydraulic Cylinder

• It is inevitable to bear a considerable part of the radial external force; for this reason, the length of the piston of the hydraulic cylinder must be appropriate, generally, 0.6 to 1.0 times the outer diameter of the piston, to increase the guiding effect of the piston and increase the supporting surface area, to reduce wear, The purpose of improving the service life of the hydraulic cylinder, as shown in Figure 1-10. How to Design Hydraulic Cylinder

The shape and position tolerance of the piston is determined.

• The quality of the hydraulic cylinder largely depends on the quality of the piston, so the machining of the piston should be required to have sufficient precision geometric tolerances. Generally speaking, the error of the outer diameter of the piston, the roundness of the inner hole, and the cylindricity cannot be greater than half of its dimensional tolerance; the tolerance of the concentricity of the outer diameter of the piston to the inner hole and the sealing groove should be within 0.02mm. How to Design Hydraulic Cylinder

Determination of the tolerance of the piston rod shape and position

• Generally, the straightness tolerance of the piston rod is required to be less than 0.02mm/100mm; the roundness and other geometric accuracy tolerances are not greater than the outside.

• 1/2 of the diameter tolerance; the concentricity tolerance between the shaft diameter and the outer circle matching the inner hole of the piston is not more than 0.01~0.02mm; the piston is installed.

• The perpendicularity tolerance between the shaft shoulder and the axis of the piston rod is not more than 0.04mm/100mm. How to Design Hydraulic Cylinder

Hydraulic Cylinder Structure Design

Question 1: Problem with the connection structure of the cylinder end 

1. Flange connection

Flange connection at the end of the cylinder, as shown in Figure 1-11. The cylinder block of Figure 1-11(a) and Figure 1-11(b) is a steel pipe and the end welding method; Figure 1-11(c) the cylinder body is a steel tube with thick end titanium; Figure 1-11(d) the cylinder body is forging or casting, this structure is the most widely used, and its advantage is that the structure is relatively simple; Processing; easy to load and unload; high strength, able to withstand high pressure.

Pay attention to the problem

The weight is larger than the threaded connection but smaller than the tie rod connection; the outer diameter is larger.

2. External thread connection

The external thread connection of the cylinder end is shown in Figure 1-12.

3. Internal thread connection

The internal thread connection at the end of the cylinder is shown in Figure 1-13. The advantage is that the weight is small and the outer diameter is small.

Pay attention to the problem

• Special tools should be used when the end structure is complicated. When screwing the end, it is possible to twist the sealing ring, as shown in Figure 1-13(a).
• When the end cover and the cylinder barrel are connected by a thread (internal thread of the cylinder, external thread of the end cover), special care should be taken not to damage the sealing ring during the assembly process. This requires the diameter of the inner thread tip on the cylinder barrel to be larger than the outer diameter of the sealing ring placed on the end cover. Otherwise, the sealing ring will be damaged in the process of assembling the end cover, as shown in Figure 1-14(a).
• Since the initial pressure point of the seal ring after entering the cylinder barrel cannot be grasped, a proper guiding transition zone should be machined at the end of the internal thread on the cylinder barrel to avoid damage to the seal ring during the assembly process, as shown in Figure 1-14(b) Shown.

4. External snap ring connection

The outer snap ring connection at the end of the cylinder, as shown in Figure 1-15, has the advantages of smaller weight than tie rod connection, compact structure, and small size.

Pay attention to the problem

The outer diameter of the cylinder body needs to be machined, and the half-ring groove weakens the cylinder body, and the cylinder body wall thickness must be thickened accordingly.

5. Internal snap ring connection

The snap ring connection at the end of the cylinder body, as shown in Figure 1-16, has the advantages of compact structure and lightweight.

Pay attention to the problem

When installing, the end is deeper into the cylinder, and the sealing ring may be scratched by the edge of the oil inlet.

6. Tie rod connection

The tie rod connection at the end of the cylinder is shown in Figure 1-17. This mechanism is widely used. The advantages are that the cylinder body is easy to process, easy to install and unload, and the structure is versatile.

Pay attention to the problem

• The weight is relatively large and the overall size is relatively large.
• Tie rod structure should be avoided for long hydraulic cylinders. When the length of the hydraulic cylinder is greater than 1500～2000mm, the tie rod structures should not be adopted. Although the tie rod hydraulic cylinder has the characteristics of good manufacturability and maintenance performance, due to the action of hydraulic pressure, it is easy to elongate the tie rod and cause leakage, as shown in Figure 1-18.
• Hydraulic cylinders with tie rod structures should not be used in harsh working environments. In the occasions where the use conditions are too bad and the seal ring and guide sleeve of the piston rod needs to be replaced frequently, and the equipment using the hydraulic cylinder does not allow the hydraulic cylinder to be removed, the hydraulic cylinder should not adopt a tie-rod structure. The reason is that when replacing the seal ring and guide sleeve of the piston rod of the tie rod hydraulic cylinder, the hydraulic cylinder must be removed first, and then the four tie rods can be removed before the replacement, which is very inconvenient. In this case, use The core barrel structure is better.

7. Welding

The end of the cylinder is welded as shown in Figure 1-19. Its advantages are simple structure and small size.

Pay attention to the problem

• The cylinder body may be deformed; the inner diameter of the cylinder after welding is not suitable for reprocessing, and it is locally hardened.
• The end welding seam should be at a certain distance from the working surface of the hydraulic cylinder. When using the hydraulic cylinder with end welding, the distance between the welding part and the working surface of the hydraulic cylinder should not be less than 20mm, as shown in Figures 1-20. This is because the inner surface of the hydraulic cylinder barrel after the end is welded, that is, the working surface is no longer processed after welding, and the welding process will cause the cylinder barrel to deform to a certain extent. If the distance is too close, the friction force of the hydraulic cylinder will increase or even get stuck when it moves near the end.

8. Steel wire connection

The steel wire connection at the end of the cylinder body, as shown in Figure 1-21, has the advantages of a simple mechanism, lightweight and small size.

Pay attention to the problem

• It is inconvenient to assemble and disassemble, and the wire is difficult to assemble and disassemble.
• When there are no special requirements on the size and weight of the fixed machinery, it is recommended to adopt the form of a flange or tie rod connection mechanism.
• When there are special requirements for the size and weight of the movable machinery, it is recommended to adopt the form of a flange, external thread, or external snap ring connection mechanism.

Question 2: Cylinder body material selection

Cylinder body materials are commonly used seamless steel pipes of 20 steel, 35 steals, and 45 steals. The cylinder body of the hydraulic cylinder whose working temperature is lower than -50℃ must be made of 35 steel and 45 steal, and it must be quenched and tempered. The cylinder body welded to the end is made of 35 steel, which is mechanically pre-processed and then quenched and tempered. The cylinder body that is not welded to other parts uses quenched and tempered 45 steel. Cylinder body materials are also useful for forged steel, cast steel, and aluminum alloy.

Question 3: Technical requirements for cylinder block design

• The cylinder inner diameter D adopts an H9 fit.
• Heat treatment: quenching and tempering, hardness 241～285HB.
• The conicity and ovality of diameter D are not more than half of the diameter tolerance.
• The curvature of the axis is not more than 0.03mm in the length of 500mm.
• The non-perpendicularity of the end face T is not more than 0.04mm on the diameter of 100mm.
• When the cylinder body and the end are connected by thread, the thread adopts a 2a precision metric thread.
• When the tail of the cylinder body is earring shape or the cylinder body is shaft pin type:
• The deviation of the axis of the hole d1 from the cylinder diameter D is not more than 0.03mm;
• The non-perpendicularity of the axis of the hole d1 to the cylinder diameter D is not more than 0.1mm in the length of 100mm;
• The disjoint degree of the axis of the shaft diameter d: to the cylinder diameter D is not more than 0.1mm;
• The non-perpendicularity of the shaft diameter d2 to the cylinder diameter D is not more than 0.1mm in the length of 100mm.

Question 4: End cap design

• The end cap should not be too thin. The end cover of the hydraulic cylinder bears the hydraulic pressure is relatively large. If the end cover is too thin and the bolt spacing is too large, local gaps will easily occur under the action of hydraulic pressure, which will cause oil leakage, as shown in Figures 1-23.
• The geometric tolerance of the end face of the hydraulic cylinder. General requirements the perpendicularity tolerance of the end of the hydraulic cylinder facing the axis of the hydraulic cylinder should be less than 0.04mm/100mm.
• When there is a severe impact during work, the cylinder tube and end cover of the hydraulic cylinder cannot be made of brittle materials, such as cast iron.

Question 5: The connection between the piston and the piston rod is formed

• Under normal working conditions of the hydraulic cylinder, the piston, and the piston rod are connected by thread, as shown in Figure 1-24.
• When the working pressure of the hydraulic cylinder is large and the working machinery is vibrating, the half-ring connection is adopted, as shown in Figure 1-25. According to the specific situation, the piston and the piston rod are also made into a whole.

Question 6: Selection of piston material

• Wear-resistant cast iron; gray cast iron (HT150～HT200); steel (some wear-resistant rings with outer diameter sleeve nylon 66 or nylon 1010); aluminum alloy.
• The friction pair in the hydraulic cylinder should avoid using the same material. The friction coefficient of the friction pair of the same material is relatively large, and all the two surfaces that need to be lubricated in relative motion should be avoided. The same is true for hydraulic cylinders, pistons, and cylinders Piston rod and guide sleeve Avoid using the same material between them to facilitate lubrication and reduce friction.

Question 7: Technical requirements for piston design

The non-perpendicularity of the end face shall not be greater than 0.04mm on the diameter of 100mm; the ovality and conicity of the outer diameter d shall not be greater than half of the diameter tolerance.

Question 8: Piston rod structure design

• Avoid stress concentration at the transition of the piston rod shaft diameter 

When using a long-stroke hydraulic cylinder, it is necessary to comprehensively consider selecting a piston rod with sufficient rigidity and installing a spacer ring.

• Consider the selection of piston rod and spacer

When using a long-stroke hydraulic cylinder, it is necessary to comprehensively consider selecting a piston rod with sufficient rigidity and installing a spacer ring.

• Consider using a piston rod protective sleeve

When the working environment is seriously polluted and there are more impurities such as dust, sand, moisture, etc., a piston rod protective sleeve is required.

Question 9: Exhaust the hydraulic cylinder

When the hydraulic system stops working for a long time, the oil in the system will flow out due to its weight and other reasons. At this time, it is easy for air to enter the system. If there is air in the hydraulic cylinder or mixed with air in the oil, the hydraulic cylinder will not move smoothly. Therefore, the air in the system should be discharged before the hydraulic system starts to work. For this reason, an exhaust device can be installed at the highest part (often where air collects) at both ends of the cylinder. There are two types of exhaust devices.

One is to open an exhaust hole at the highest part of the hydraulic cylinder and connect the exhaust valve with a pipe for exhaust; the other is to place an exhaust plug on the highest part of the hydraulic cylinder. The device is opened when the hydraulic cylinder is exhausted and closed after the exhaust is completed.

1. The contact surface angle of the steel ball exhaust valve seat

The exhaust valve on the hydraulic cylinder is most of the steel ball type, and the valve seat is generally drilled directly with a drill bit. The angle of commonly used drills is generally 120°. Experience has proved that the tightness of this angle is not optimal. The angle is small, it is easy to guide the steel ball, but the sealing performance is not good; the angle is large, it is easy to seal, but the guiding performance is poor. According to experience, the best angle is about 160°, as shown in Figure 1-27.

2. Leakage problem of poppet type exhaust valve

The cone valve type exhaust valve is composed of a sealed cone valve and a plug sleeve. The rod of the cone valve passes through the middle hole of the plug sleeve. When the axis of the screw plug sleeve is too large, it will cause the cone valve and valve seat. One-sided contact, leakage occurs. 

Also, if the axial dimension of the screw plug sleeve is too small, the poppet valve cannot be compressed when fully screwed in, it will also cause leakage. The cone angle of the poppet valve head is between 60°and 90°, as shown in Figure 1-28. When it is too large because the contact surface is enlarged and widened, it is not easy to obtain an ideal sealing line with the same tightening force, and it is easy to be blocked if it is too small.

3. The problem of exhaust air

The exhaust valve needs to be installed at the highest point of the oil cavity of the กระบอกไฮดรอลิก to discharge air.

Installation form of hydraulic cylinder

The hydraulic cylinder installation requirements are as follows:

• The installation of the hydraulic cylinder should be solid and reliable. To prevent the influence of thermal expansion, one end of the cylinder must be kept floating when the stroke is large and the working conditions are hot. The piping connection must not be loose.
• The installation surface of the hydraulic cylinder and the sliding surface of the piston rod should maintain sufficient parallelism and perpendicularity.
• The center axis of the moving cylinder should be concentric with the centerline of the load force, otherwise, it will cause lateral force, which is easy to wear out the seal and damage the piston. The greater the distance between the support points of the piston rod, the less wear. For the hydraulic cylinder of the moving object, the cylinder should be kept parallel to the moving object during installation, and the non-parallelism is generally not more than 0.05mm/m.
• Do not install the sealing ring too tightly, especially the U-shaped sealing ring, which has very high resistance.
• The fuel tank should be cleaned carefully, dried with compressed air, and then checked with kerosene for the quality of the weld.

Problem 1: Fixed axis installation skills

The position of the axis of the hydraulic cylinder of this type of installation is fixed when it is working. The vast majority of hydraulic cylinders on machine tools adopt this type of installation.

1. Tie rod type

Drill through holes on the cylinder heads at both ends, and use a double-headed screw to tighten the connection between the cylinder and the mounting seat.

Pay attention to the problem

Generally used for hydraulic cylinders with short strokes and low pressure.

2. Flange type

Use the flange on the hydraulic cylinder to fix it to the machine.

The flange is set on the cylinder head of the piston rod, and the outer side is tightly attached to the mechanical installation surface. This is the head outer flange type.

Pay attention to the problem

• Due to the action of the reaction force when the hydraulic cylinder is working, the mounting bolts bear the tensile action of hydraulic pressure, the diameter of the mounting bolts is relatively large, and the strength calculation is required.
• The flange is arranged on the cylinder head at the end of the piston rod, and the inner surface is tightly attached to the mechanical mounting surface. This is the head inner flange type. When the hydraulic cylinder is working, the mounting bolts are not stressed, and they are mainly supported by the mounting supporting surface, so the flange diameter is small and the structure is more compact. This type of installation is the most widely used in a fixed installation.
• The flange is set at the bottom of the cylinder and is fastened with bolts on the mechanical mounting surface. This is a tail flange type. Pay attention to the problem. This type of installation makes the hydraulic cylinder cantilever, the installation length is large, and the stability is poor.
• Note that the force and the support center should be on the same axis. The connection between the flange and the support seat should make the flange surface bear the force, and should not make the fixing screw bear the tension E.g. front flange. For installation, if the acting force is thrust, the structure is shown in Figure 1-29(a) should be adopted, and the structure is shown in Figure 1-29(b) should be avoided; if the acting force is pulling force, vice versa.
• For rear flange installation, if the acting force is thrust, the structure is shown in Figure 1-30(a) should be adopted, and the structure is shown in Figure 1-30(b) should be avoided; if the acting force is pulling force, the reverse is true.

3. Base installation

• Fasten the flanges at the head and tail ends of the hydraulic cylinder with the base. The base can be placed in the radial and tangential directions of the left and right of the hydraulic cylinder, and can also be placed in the front and rear ends of the axial bottom. In the radial installation, the installation surface is on the same plane as the axis of the piston rod. When the hydraulic cylinder is working, the installation bolts only bear the shearing force.
• When installing tangentially and axially, there is a certain distance between the axis of the piston rod and the bottom surface of the base, and the mounting bolt is subjected to both shearing force and bending force due to the overturning moment. The tilting moment of tangential installation is smaller than that of axial installation.

Pay attention to the problem

• For the base type installation form, GB/T 3766-2015 stipulates: If the base type hydraulic cylinder does not use keys or pins to bear the shear stress, the anchor bolts must withstand all the shear stresses without causing danger.
• The front base needs to use positioning screws or positioning pins, and the rear base uses loose screw holes so that the cylinder can expand and contract when the hydraulic cylinder is heated, as shown in Figure 1-31. When the axis of the hydraulic cylinder is high and the distance H from the supporting surface is large (see Figure 1-31(b)), the base screws and base rigidity bear the effect of the overturning moment F×H.

Problem 2: Axis swing type installation skills

When the hydraulic cylinder is reciprocating, due to the interaction of the mechanism, its axis swings to meet the requirements of adjusting the position and direction. To install this type of hydraulic cylinder, the only way to install it can be to make it swingable. The hydraulic cylinders used in construction machinery, agricultural machinery, dump trucks, and ship deck machinery are mostly used in this type of installation.

1. Trunnion installation

• The dumpling shaft fixed on the hydraulic cylinder is installed in the shaft seal of the machine, so that the axis of the hydraulic cylinder can swing freely in a certain plane, and the force is in the same plane.
• The trunnion set on the head of the hydraulic cylinder is ahead of the trunnion type. With this type of installation, the swing amplitude of the hydraulic cylinder is smaller, but the stability is better.
• The trunnion set at the tail of the hydraulic cylinder is a tail trunnion type. The hydraulic cylinder of this type of installation has a larger swing, but its stability is poor.
• The trunnion set in the middle of the hydraulic cylinder is a middle trunnion type, and its swing amplitude and stability are average.
• Usually, the front trunnion and the middle trunnion are more commonly used. The rear trunnion is only used on small short-stroke hydraulic cylinders. Because of its large supporting length, it affects the bending stability of the piston.
• The trunnion of the trunnion hydraulic cylinder must be at right angles to the axis of the hydraulic cylinder. When installing a trunnion hydraulic cylinder, it must be ensured that the axis of the cylinder body is at right angles to the swing direction, as shown in Figure 1-32. If there is a deviation, the two trunnions cannot share the load evenly, and in severe cases, the hydraulic cylinder trunnion may break.
• For trunnion mounted hydraulic cylinders, attention should be paid to the load direction. Similar to hydraulic cylinders with single ring installation, hydraulic cylinders use trunnions. During installation, the load is also allowed to swing in one direction. However, it is not allowed to swing or move in the other direction perpendicular to it, otherwise, the hydraulic cylinder will be subjected to bending load and cause the thread to break. Moreover, due to the lateral force, it is easy to strain the inner surface of the cylinder, causing uneven wear of the guide sleeve, resulting in uneven sealing, resulting in leakage, as shown in Figure 1-33.
• The trunnion support should be as close as possible to the root of the trunnion. The inner side of the trunnion support should be as close as possible to the root of the trunnion, preferably without leaving a gap. If it is really necessary, the maximum distance cannot be greater than 1mm, as shown in Figure 1-34. This is for reducing the bending moment of the single bearing. The larger the above distance, the greater the total stress on the lug bearing.

• Spherical bearings are not suitable for trunnion hydraulic cylinders. When the hydraulic cylinder is installed with a trunnion, the bearing on the trunnion cannot be a spherical bearing. This kind of bearing can fine-tune itself when its centerline is tilted, which is beneficial to the bearing itself. But it is disadvantageous for the trunnion of the hydraulic cylinder. The reason is: if a sliding bearing is used, the trunnion only bears shear stress; if a spherical bearing is used, the trunnion must bear the same shear stress, but also an additional bending moment caused by the tilt of the trunnion axis. The stress condition has deteriorated significantly, so spherical bearings cannot be installed on the trunnion.

2. Taboo for earring installation

Connect the earrings of the hydraulic cylinder with the earrings on the machine with a pin, so that the hydraulic cylinder can swing freely in a certain plane. The acting force is in a plane, such as earrings with ball dumplings, they can change direction within ±4°cone angle.

The earrings are at the tail of the hydraulic cylinder and can be single earrings or double earrings, and can also be made into single earrings or double earrings with joint bearings.

Pay attention to the load direction of hydraulic cylinders installed in earrings. As shown in Figure 1-34, when the hydraulic cylinder is installed in the earring type, the load is allowed to have a considerable swing range in one direction. However, it is not allowed to swing or move in the other direction perpendicular to it, otherwise, the hydraulic cylinder will be subjected to the bending load with the earring as the fulcrum. Sometimes the thread of the rod end may be broken due to the bending of the piston rod.

Moreover, because the piston rod reciprocates when the piston rod is in a bent state, it is easy to damage the inner surface of the cylinder, causing uneven wear of the guide sleeve, resulting in imperfect sealing. Evenly, leading to leakage, these must be avoided.

3. Taboo for ball head installation

Connect the ball head at the tail of the hydraulic cylinder with the ball seat on the machine, so that the hydraulic cylinder can swing freely within a certain spatial cone angle range. This type of installation has a large degree of freedom, but its stability is poor. This type of hydraulic cylinder is often used for ship lifting booms.

Pay attention to the problem

Hydraulic cylinders installed with swing axis are often inclined when they work. As the piston rod gradually extends, the angle between the axis and the horizontal plane also gradually changes, and its working displacement changes with the angle. Therefore, calculate the hydraulic pressure The effective working force of the cylinder must be based on the load pushed when the included angle is at the minimum.

Problem 3: Installation Taboos of Hydraulic Cylinders

1. The position arrangement of the hydraulic cylinder should consider the convenience of disassembly and assembly

The location of the hydraulic cylinder is generally determined by the structure of the equipment. When designing the main equipment, the needs of the installation and disassembly of the hydraulic cylinder should be considered, and at least enough operating space should be left to facilitate the operation of the hydraulic cylinder. In the project, there are indeed cases where the hydraulic cylinders are arranged in an unreasonable position, which leads to very difficult maintenance and overhaul, which must be considered in the overall equipment design.

2. Correctly determine the installation and fixing method of the hydraulic cylinder

For example, the piston rod subjected to bending cannot be connected with threads, but must be connected with a spigot; the hydraulic cylinder cannot be positioned with keys or pins at both ends, but can only be positioned at one end, so as not to hinder its thermal expansion; impact load makes the piston rod For compression, the positioning piece must be set at the end of the piston rod; for tensile load, the positioning piece must be set at the end of the cylinder head.

3. Avoid fixing both ends of the hydraulic cylinder during fixed installation

Generally speaking, the temperature of the hydraulic oil flowing in the hydraulic cylinder always changes, and there is no problem when the temperature changes not too much. However, when the oil temperature changes greatly, the cylinder body of the hydraulic cylinder will always expand and contract in different degrees. If the hydraulic cylinder is installed fixed at both ends at this time, it may cause very large stress on the cylinder body, and even damage the structure of the hydraulic cylinder. Therefore, when installing a fixed hydraulic cylinder, try to avoid the installation of fixed at both ends. The fixed installation method of the hydraulic cylinder is shown in Figure 1-35.

4. Large hydraulic cylinders should not be loaded by mounting bolts

The output force of a large hydraulic cylinder is generally relatively large, and the main function of the mounting bolt of the hydraulic cylinder is to fix the hydraulic cylinder in the working position. Of course, the bolt can bear a certain load. However, when the hydraulic cylinder is large and the load is heavier, the mounting bolts of the hydraulic cylinder should not be used to bear the load, because the load at this time is very large and requires a larger number of bolts or bolts with a larger diameter to be installed. Cause structural irrationality. Other mechanical methods can be used to fix the hydraulic cylinder, such as adding a stopper.

5. The mounting base of the hydraulic cylinder must have sufficient rigidity

The installation base of the hydraulic cylinder must be firm and rigid. If the installed base is not strong, no matter how the installation method is correct, the hydraulic cylinder body will bend upwards in a bow shape when working, as shown in Figure 1-36. In severe cases, the piston rod will bend, jam, and break the piston rod.

6. Piston rod of hydraulic cylinder

Try to make the piston rod of the hydraulic cylinder bear the maximum load under tension or have good stability under pressure.

7. The plunger cylinder should not be placed horizontally

Although the plunger cylinder has the advantage of simple processing of the inner wall of the cylinder because the plunger cylinder can only withstand pressure, the cylinder rod is generally thicker in terms of rigidity; at the same time, its radial support point is also somewhat different from that of ordinary hydraulic cylinders.

Because of the difference, the cylinder base cylinder is generally heavy and heavy. When installed in a horizontal position, the plunger is easy to press on one side, causing the guide sleeve and the sealing ring to wear back. If the right hand is installed horizontally, a plunger bracket needs to be installed to prevent the plunger from sagging, causing bending and increasing initial deflection, and causing jamming.

8. Hydraulic cylinders with synchronization requirements should not be simply connected in parallel

Theoretically speaking, when the effective working area of the two hydraulic cylinders is the same and the input flow is equal, synchronization can be achieved. However, due to unbalanced load distribution, unequal friction, manufacturing differences, and different leakage rates, etc. Can make them out of sync. Therefore, hydraulic cylinders with synchronization requirements should not be simply connected in parallel. To overcome the influence of the above factors, a positive displacement, servo-type synchronization control loop is generally used, as shown in Figure 1-38.

Design of hydraulic cylinder buffer device

The hydraulic cylinder is equipped with a buffer device mainly to buffer the huge impact generated by the piston of the hydraulic cylinder when it suddenly stops at the end of the stroke. There are many types of cushioning devices, and the cushioning principle is the same, that is when the piston reaches a certain distance before the end of the stroke,

it tries to seal part or all of the oil in the oil cylinder drain cavity so that it can pass through a small throttle (or Seam>Discharge, to generate appropriate back pressure (buffer pressure) from the enclosed hydraulic oil, which acts on the oil discharge side of the piston to oppose the inertial force of the piston to achieve the purpose of deceleration and braking.

Question 1: Applicability of the cushioning device

• When the hydraulic cylinder has a working pressure of ≤10MPa and a piston speed of ≤0.1m/s, the buffer device may not be considered; otherwise, a hydraulic cylinder with a buffer device or other buffer methods should be used. This can only be a reference condition, and it is mainly determined by the specific situation and the purpose of the cylinder.
• Short-stroke hydraulic cylinders should not use buffer devices at both ends. When the stroke of the hydraulic cylinder is short (<100mm), in principle, a hydraulic shed without buffer devices should be used. If it is very necessary, only one buffer device can be placed in one direction of movement. Otherwise, the non-buffering stroke will be too short, or even there will be no non-buffering stroke, as shown in Figure 1-39.

• Low-speed hydraulic cylinders do not need to use buffer devices. The function of the buffer device is to reduce the speed of the piston rod at the end of the stroke to avoid impact. When the hydraulic cylinder speed is low (<100mm/s), the buffer device has lost its meaning.
• It is generally believed that ordinary hydraulic cylinders should adopt buffer devices or other buffer methods when working pressure>10MPa and piston speed>0.1m/s. This is only a reference condition, and it is mainly determined by the specific situation and the purpose of the hydraulic cylinder. For example: For hydraulic cylinders that require slow speed changes, when the piston speed is ≥0.05～0.12m/s, a buffer device is also required.
• The quick-acting hydraulic cylinder should be equipped with a buffer device. When the hydraulic cylinder moves fast, due to the large mass of the load and the hydraulic cylinder piston and the piston rod itself, the momentum of the movement is large, so it is easy to stop suddenly at the end of the stroke. A great impact and noise are generated. This impact will not only cause damage to the hydraulic cylinder but also cause damage to various valves, piping, and related mechanical parts, which is very harmful. To eliminate such impacts, corresponding components can be set in the hydraulic circuit to control the speed of the hydraulic cylinder, or a buffer device (such as a fixed or adjustable hydraulic cylinder buffer device, etc.) can be set on the hydraulic cylinder.

Question 2: Type of buffer device structure

For the requirements of the cushioning device, the ideal situation is to move the piston uniformly decelerate during the entire cushioning process, without peaking inadmissible cushioning brake pressure, and minimizing the load on the cylinder. The buffer device of the hydraulic cylinder can be arranged inside the hydraulic cylinder or in the external circuit of the hydraulic cylinder.

1. Internal buffer device of the hydraulic cylinder. There are many structural types of buffer devices inside hydraulic cylinders. According to the flow area of the orifice (or gap) and whether it can be automatically changed during the buffering process, it can be roughly divided into two types: constant throttle area buffer device and variable throttle area buffer device class.

2. Constant throttling area buffer device. In the buffering process of this kind of buffering device, since its throttle area is unchanged, the buffering braking force generated at the beginning of buffering is very large. But it was quickly lowered, and it didn’t work in the end, and its cushioning effect was not very good. However, in the general series of standard oil cylinders, because it is impossible to know the movement speed of the cylinder piston and the movement part. The quality and the load to bear, so to simplify the structure, facilitate the design, and reduce the manufacturing cost, this kind of throttling and buffering method is often used.

3. Variable throttle area buffer device. During the buffering process of the oil cylinder piston, the flow area of the throttle hole (slit) automatically changes with the stroke, so that the buffer pressure in the buffer oil chamber is kept uniform or changed regularly, to obtain a satisfactory buffer effect. It can only adapt to a certain cylinder load and work movement, so this kind of buffer device can be designed for general special cylinders.

Question 3: Cushioning device for the external circuit of the hydraulic cylinder (buffer circuit)

• The function of the buffer circuit is to pre-decelerate the working part before the end of the stroke, delay its stop or reversing time, and delay the unloading and boosting process of the pressure regulating unloading circuit to achieve the purpose of mitigating the impact. To eliminate or reduce hydraulic shock, in addition to taking certain measures on the structure of the hydraulic component itself (such as setting a buffer device at the end of the hydraulic cylinder and setting damping on the overflow valve spool), buffering can also be used in the system design Loop.

• The ordinary standard oil cylinder is equipped with buffer devices at both ends of the stroke so that the oil cylinder can stop smoothly at the ends of the stroke. However, when the piston stops or reverses in the middle of the stroke, the kinetic energy of the moving parts will cause a violent impact. For this reason, a small relief valve is installed at the end of the cylinder to eliminate the impact. Take A and Y/safe that the piston stops during the stroke as shown in Figure 1-40. Set sensitive small direct-acting safety valves on the two oil paths of the cylinder to eliminate the impact that occurs when the piston stops or changes direction during the stroke. The one-way valve in the valve is used as a supplementary valve. This circuit is suitable for occasions with large moving parts and high positioning accuracy.

• The buffer circuit adopts the stroke throttle valve. As shown in Figure 1-41, a stroke throttle valve is connected to one side of the hydraulic cylinder. When the piston reaches a predetermined position, the stopper presses down the stroke throttle valve to gradually decelerate the moving parts until they stop, thereby avoiding Shock. The buffer effect of this circuit is better, but the buffer stroke is fixed, which is suitable for occasions with fixed working conditions. This method is also applicable to the treatment of hydraulic motors.

• Adopt the buffer circuit of the electro-hydraulic directional valve, as shown in Figure 1-42. It controls the movement speed of the spool of the hydraulic directional valve by adjusting the opening of the throttles 1 and 2, to make the hydraulic cylinder stable and free. Reversing shockingly. This kind of buffer circuit is suitable for small impact occasions.

• Using a combined buffer circuit of an overflow valve and an electro-hydraulic directional valve, as shown in Figure 1-43, the control pressure oil of the electro-hydraulic directional valve is drawn from the remote control port of the overflow valve. When reversing, the electro-hydraulic reversing valve and the two-position valve are energized at the same time because only after the action of the hydraulic valve spool is completely stopped, the oil pressure entering the hydraulic cylinder can rise and push the piston to move. When the hydraulic cylinder is not working, the pump Uninstall. The backpressure valve can maintain a certain pressure when the system is unloaded for operating the electro-hydraulic valve. This loop is suitable for high-power systems.

• The hydraulic pump unloading buffer circuit, as shown in Figure 1-44, in the remote control oil circuit of the overflow valve 1, a damper 2 is connected in series to control the movement speed of the overflow valve spool and extend the opening or closing of the overflow valve Time, thereby reducing the hydraulic shock in the process from holding pressure to unloading or from unloading to boosting.

• To reduce the impact of the circuit, the pipelines between the valves, pumps, and cylinders should be shortened as much as possible to reduce unnecessary pipeline bending. Experience believes that when noise is generated due to the complexity of the pipeline, it is a very simple and effective method to connect the hose at the place of vibration.

• It is very good to use a suitable accumulator to alleviate the impact. The accumulator should be placed near the place where the impact is generated. A bladder-type accumulator can be used. It has small inertia and is suitable for eliminating the impact.

Question 4: Buffer calculation of hydraulic cylinder

The buffer calculation of the hydraulic cylinder is mainly to estimate the maximum impact pressure that appears in the cylinder during buffering, to check whether the strength of the cylinder barrel and the braking distance meet the requirements. In the buffer calculation, if it is found that the hydraulic energy in the working chamber and the kinetic energy of the working parts cannot be absorbed by the buffer chamber, the piston and the cylinder head may collide during braking.

Hydraulic cylinder working medium requirements

Question 1: Ambient temperature requirements

1. Hydraulic cylinders working at room temperature (-20~60°C) generally use petroleum-based hydraulic oil.
2. Hydraulic cylinders working at high temperatures (>60°C) need to use flame-retardant fluids and hydraulic cylinders with special structures.

Question 2: Viscosity and filtration accuracy requirements

1. Viscosity requirements of the working medium. Most manufacturers require that the viscosity of the working medium used in their hydraulic cylinders is 12~28cSt, and individual manufacturers allow it to reach 2.8~380cSt.
2. Requirements of the working medium filtration accuracy.

Hydraulic cylinders with general elastic seals: 20~25μm;

Servo hydraulic cylinder: 10μm;

Hydraulic cylinder with piston ring: 200μm.

Difference between single acting and double acting cylinder

Double action cylinder: the piston can move back and forth

Single saction cylinder: the piston can only move out.