1.1 Overview of Hydraulic Transmission and Control
Hydraulic transmission and control is to realize the output of various mechanical quantities (force, displacement or speed, etc.) by using a liquid (oil, high water-based hydraulic oil, synthetic liquid) as a medium. It is compared with the simple mechanical transmission, electrical transmission and pneumatic transmission, has a large transfer power, small structure, fast response and other characteristics, and therefore is widely used in a variety of mechanical equipment and precision automatic control system. Hydraulic transmission technology is a new discipline technology, its development history is relatively short, but the speed of development is very fast. Since 1795 made the first press, hydraulic technology into the field of engineering; 1906 began to be used in defense weapons.
During World War II, hydraulic servo control systems appeared as a result of the military industry's urgent need for fast-responding, high-precision automatic control systems. From the 60's onwards, due to the development of atomic energy, space technology, large ships and electronic technology, and constantly put forward new requirements for hydraulic technology, from civil to national defense, from the general transmission to the control system with high precision, this technology has been more widely developed and applied.
In the defense industry: sea, land, air and all kinds of weapons of war are hydraulic transmission and control. Such as aircraft, tanks, ships, radar, artillery, missiles and rockets.
In the civil industry: machine tool industry, metallurgical industry, engineering machinery, agriculture, automotive industry, textile industry, shipping industry.
In addition, in recent years and the emergence of the sun tracking system, wave simulation device, aircraft driving simulation, ship driving simulator, earthquake reproduction, rocket boost launchers, aerospace environment simulation, high-rise building earthquake prevention systems and emergency braking devices, etc., are used in hydraulic technology.
In short, all engineering fields, where there are mechanical equipment, can be used in hydraulic technology. Its development is so fast, the application of such a wide range of reasons is that hydraulic technology has excellent characteristics, summed up the hydraulic power transmission method has significant advantages: its output power per unit weight and output power per unit size; hydraulic transmission device is small in size, compact structure, flexible layout, easy to achieve stepless speed regulation, speed range is wide, easy to realize automation in conjunction with the electrical control; easy to realize overload protection and pressure preservation, safe and reliable! Protection and pressure, safe and reliable; components are easy to achieve serialization, standardization, generalization; hydraulic and microcomputer control is easy to combine with new technologies, constituting a "machine-electricity-liquid-optical" integration to facilitate the realization of digital.
1.2 The development of hydraulic press and process characteristics
Hydraulic press is one of the most widely used equipment in the production of molding products, since its inception in the 19th century since the rapid development of hydraulic presses in the work of a wide range of adaptability, so that it is widely used in all sectors of the national economy. As the hydraulic system and the entire structure of the hydraulic press, has been relatively mature, the current development of hydraulic presses at home and abroad is not only embodied in the control system, but also mainly in the high-speed, high efficiency, low energy consumption; electromechanical-hydraulic integration, in order to fully and reasonably use the advanced technology of mechanical and electronic to promote the improvement of the entire hydraulic system; automation, intelligence, to achieve automatic diagnosis and adjustment of the system, with fault Pre-processing function; hydraulic components integration, standardization, in order to effectively prevent leakage and pollution and other four aspects.
As the two main components of the hydraulic machine host and hydraulic system, due to the technological development tends to mature, domestic and foreign models without a large gap, the main difference lies in the processing technology and installation. Good technology to make the machine in the filtration, cooling and prevention of shock and vibration, there is a more significant improvement. In the oil circuit structure design, hydraulic machines at home and abroad tend to be integrated, closed design, cartridge valves, stacked valves and composite components and systems in the hydraulic system has been more widely used. Especially integrated blocks can be specialized production, its quality, reliable performance and design of the cycle is relatively short.
In recent years on the basis of the development of integrated blocks of new hydraulic components composed of the circuit also has its unique advantages, it does not require additional connectors and its structure is more compact, the volume is also relatively smaller, lighter weight without the need for tubing connections, thereby eliminating the leakage caused by the tubing, joints, vibration and noise. Logic cartridge valve has a small size, light weight, good sealing performance, small power loss, fast action, easy to integrate the characteristics of the early 1970s began to appear, so far has been a rapid development. Our country from 1970 began to research and production of this valve, and has been widely used in metallurgy, forging and other equipment, showing great superiority.
Hydraulic press process has a wide range of uses, applicable to bending, flanging, stretching, molding and cold extrusion and other stamping process, the press is a kind of hydrostatic pressure to process products. It is suitable for the press molding process of metal powder products and non-metallic materials, such as plastics, glass fiber reinforced plastic, insulating materials and abrasive products, and it can also be applied to the process of calibration and press fitting.
Because of the need to carry out a variety of processes, hydraulic presses have the following characteristics:
(1) a larger worktable and a longer stroke of the slide to meet the requirements of a variety of processes;
(2) there is an ejector device to facilitate ejection of the workpiece;
(3) hydraulic presses with point, manual and semi-automatic work mode, easy to operate;
() (4) The hydraulic press has the functions of pressure preservation, time delay and automatic return, and can carry out the operation of fixed-pressure molding and fixed-pressure molding, which is especially suitable for the pressing of metallic and non-metallic powder;
(5) The working pressure, pressing speed and stroke range of the hydraulic press can be adjusted arbitrarily, with great flexibility.
Two 150t hydraulic press hydraulic system working condition analysis
This machine (see Figure 1.1) is suitable for the pressing process of malleable materials. Such as stamping, bending, flanging, thin plate stretching and so on. It can also be engaged in calibration, press fitting, wheel forming, cold extrusion metal parts forming, plastic products and powder products pressing and forming. This machine has independent power mechanism and electrical system. It adopts push button centralized control, which can realize three operation modes of adjustment, manual and semi-automatic. The working pressure, pressing speed, no-load rapid downward and deceleration stroke range of the machine can be adjusted according to the needs of the process, and can complete the general pressing process. This process is divided into two kinds of process actions for choice: fixed pressure and fixed range. The process action of fixed-pressure molding has the actions of pressure preservation, time delay, automatic return, automatic return after time delay, etc. after pressing. The machine is rectangular in shape, novel and beautiful, the power system adopts hydraulic system, simple and compact structure, sensitive and reliable action. The machine is also equipped with a foot switch, which can realize the cycle of semi-automatic process action.
2.2 Analysis of working conditions
This design in the graduation internship survey on the basis of the preliminary determination of the analogical method of the vertical installation of the main hydraulic cylinder piston rod drives the slide and the moving beam in the column sliding down, the mass of the moving parts is 500Kg.
1. Work load The workpiece's compression resistance that is, the work load:
2. friction Load Static frictional resistance:
Dynamic frictional resistance:
3. Inertial load
Self-weight:
4. Load value of hydraulic cylinder at each working stage:
Where:
--Mechanical efficiency of the hydraulic cylinder is generally taken as =0.9-0.97. working load Composition Thrust F/
2.3 Drawing of load and speed diagrams:
Load diagrams are drawn according to the values above, and speed diagrams are drawn according to the given conditions, as shown in Figure:
Three Hydraulic Pressure Hydraulic System Schematic Design
3.1 Design of Pressure Maintaining Circuit for Automatic Oil Replenishment
Considering the design requirements, the holding time should be up to 5s, and pressure Stability is good. If the hydraulic check valve circuit holding time is long, high pressure stability, the design of the use of directional valves can hold pressure in the neutral position, the design of the automatic replenishment circuit, and the holding time by the electrical components of the time relay control, in the 0-20min can be adjusted. This circuit is fully suitable for high pressure system with high pressure holding performance, such as hydraulic presses.
Automatic replenishment of the holding pressure circuit system diagram of the working principle:
Press the start button, solenoid 1YA energized, reversing valve 6 access circuit, the upper chamber of the hydraulic cylinder becomes the pressure chamber, in the pressure to reach the predetermined upper limit value of the pressure relay 11 issued a signal to make the reversing valve to switch into the neutral position; this time, the hydraulic pump is unloaded, the hydraulic cylinder by the reversing valve M-type median function to hold pressure. When the hydraulic cylinder upper chamber pressure drops to a predetermined lower limit value, the pressure relay sends a signal to make the reversing valve right position to take over the circuit, then the hydraulic pump to the hydraulic cylinder upper chamber replenishment, so that its pressure back up. Return trip when the solenoid valve 2YA energized, the reversing valve left position to take over the circuit, the piston quickly returned upward.
3.2 pressure release circuit design:
The function of the pressure release circuit is to make the high-pressure large-capacity hydraulic cylinders in the storage of energy slowly release, so as not to produce a large hydraulic shock when she suddenly released. General hydraulic cylinder diameter greater than 25mm, the pressure is higher than 7Mpa, its oil chamber in the oil discharge before the pressure release.
According to the design of the actual production needs, choose to use the throttle valve pressure release circuit. Its working principle: press the start button, the reversing valve 6 of the right position on, the hydraulic pump output oil through the reversing valve 6 of the right position flow to the upper chamber of the hydraulic cylinder. At the same time the pressure of the hydraulic oil affects the pressure relay. When the pressure reaches a certain pressure, the pressure relay sends a signal to return the directional valve 5 to the neutral position, and the electromagnetic directional valve 10 is turned on. Hydraulic cylinder in the upper chamber of the high-pressure oil in the reversing valve 5 in the neutral position (hydraulic pump unloading) through the throttle valve 9, reversing valve 10 back to the tank, the release of pressure by the throttle valve to adjust the speed. When this cavity pressure drops to the pressure relay regulator pressure, reversing valve 6 switch to the left position, the hydraulic check valve 7 open, so that the hydraulic cylinder cavity of the oil discharged through the valve to the top of the hydraulic cylinder in the secondary tank 13. The use of this pressure release circuit can not be held before the release of pressure, the release of pressure before the pressure holding requirements of the reversing valve can also be used in the M-type, and is equipped with other components.
Machine in the work of the machine, if the machine is outside the debris or workpiece jammed, this is the pump work, the output pressure oil with the work of time and increase, and can not make the hydraulic oil to reach the hydraulic cylinder, in order to protect the hydraulic pump and hydraulic components of the safety of the pump out of the oil to add a direct-acting relief valve 1, play the role of the safety valve, when the pump pressure reaches the pressure of the relief valve on the pressure, the relief valve opens, the hydraulic oil to reach the pressure, the pressure of the hydraulic oil, the hydraulic oil to reach the pressure, the relief valve opens, the hydraulic oil to reach the pressure, the hydraulic oil to reach the pressure. When the pump pressure reaches the pilot pressure of the relief valve, the relief valve opens and the hydraulic oil flows back to the tank. Play a protective role. In the hydraulic system, generally use the relief valve connected to the hydraulic pump near, but also can increase the stability of the hydraulic system. Make the parts of the machining accuracy increase.
3.3 Hydraulic machine hydraulic system schematic drawing
Upper hydraulic cylinder work cycle
(1) rapid downward movement. Press the start button, the solenoid 1YA energized, the oil circuit at this time is:
The oil circuit for the oil supply of the upper chamber of the hydraulic cylinder
Variable pump 1-directional valve 6 right position-throttle valve 8-pressure relay 11-hydraulic cylinder 15
The oil return line to the lower chamber of the hydraulic cylinder
The lower chamber of the hydraulic cylinder 15-hydraulic control check valve 7-directional valve 6 right position-solenoid valve 5-backpressure valve 4-tank
Oil circuit analysis: The hydraulic oil from the variable pump 1 passes through the right position of the directional valve 6, and the oil return line from the lower chamber of the hydraulic cylinder is connected to the oil return line of the hydraulic cylinder. Hydraulic oil through the right position of the directional valve 6, the hydraulic oil is divided into two oil paths: one oil path through the throttle valve 7 flows through the relay 11, the other path flows directly to the upper chamber of the hydraulic cylinder and the pressure gauge. The upper chamber of the hydraulic cylinder is pressurized. The lower chamber of the hydraulic cylinder 15 flows through the right position of the reversing valve 6 through the hydraulic control check valve 7 and then flows to the tank through the back pressure valve. Because this is the back pressure generated by the back pressure valve to connect the secondary tank next to the hydraulic check valve 7 open, so that the hydraulic oil in the secondary tank 13 through the secondary tank next to the hydraulic check valve 14 to the hydraulic cylinder 15 upper chamber refill. Make the hydraulic cylinder fast downstream, in addition to the back pressure valve connected to the system return line, resulting in a certain return resistance, in order to improve the smoothness of the movement of the executive element.
(2) the oil circuit at the time of pressure preservation:
Oil circuit analysis: when the upper chamber quickly down to a certain time, the pressure relay 11 signal, so that the solenoid 1YA of the reversing valve 6 disconnecting, reversing the valve back to the neutral position, the use of variable pump plunger holes from the suction state of the transition to the state of the discharge of the oil, and the change in its volume from large to small, and in the process of the change from increasing to shrinking, there must be a volume change rate of zero. There must be a zero rate of change in volume of a moment, which is the plunger hole movement to its own center line and the dead center of the face of the moment of coincidence, when the plunger hole of the inlet and outlet in the oil distribution plate on the position, known as the dead center position. Plunger in this position, neither suction nor discharge oil, but from the suction to discharge the transition state. The hydraulic system retains pressure. And hydraulic pump 1 in the neutral position, directly through the back pressure valve directly back to the tank.
(3) the return of the oil circuit:
hydraulic cylinder lower chamber of the oil supply of the oil circuit:
variable pump 1 - directional valve 6 left position - hydraulic check valve 7 - - hydraulic tank 15 lower chamber. -The lower chamber of the hydraulic tank 15
The return oil circuit of the upper chamber of the hydraulic cylinder:
The upper chamber of the hydraulic cavity - hydraulic control check valve 14 - sub-tank 13
The upper chamber of the hydraulic cavity -Throttle valve 8 - directional valve 6 left position - solenoid valve 5 - back pressure valve 4 -Tank
Oil circuit analysis: When the pressure to a certain time, the time relay sends a signal, so that the reversing valve 6 solenoid 2YA energized, the reversing valve is received in the left position, the variable pump 1 hydraulic oil through the reversing valve next to the hydraulic check valve to the hydraulic cylinder's lower chamber, while at the same time, the hydraulic oil of the cylinder's upper chamber through the throttle valve 9 (solenoid 6YA on), the upper chamber oil through the reversing valve 10 (solenoid 6YA), the oil through the hydraulic cylinder's upper chamber (solenoid 6YA). The oil in the upper chamber is connected to the oil tank through the reversing valve 10 to realize the pressure release, and the other part of the oil flows to the reversing valve 6 through the throttle valve of the main oil circuit, and then flows back to the oil tank through the solenoid valve 19 and the back pressure valve 11. To realize the pressure release.
The working cycle of the lower hydraulic cylinder:
When ejecting upward, solenoid 4YA is energized and 5YA is de-energized.
Inlet oil circuit:
Hydraulic pump--directional valve 19 left position--one-way throttle valve 18--lower hydraulic cylinder lower chamber
Return oil circuit:
Lower hydraulic cylinder upper chamber - reversing valve 19 left position - tank
When the piston touches the upper cylinder head, it stays in this position.
The downward return is generated when 4YA is de-energized and 3YA is energized.
Inlet circuit:
Hydraulic pump - reversing valve 19 right position - one-way throttle valve 17- -lower hydraulic cylinder upper chamber
Return circuit:
Lower hydraulic cylinder lower chamber - reversing valve 19 right position - tank
In-situ stop is in the solenoid 3YA, 4YA are de-energized, reversing valve 19 is in the neutral position. and the reversing valve 19 is in the neutral position.
Four Hydraulic System Calculation and Component Selection
4.1 Determine the main parameters of the hydraulic cylinder:
According to the type of hydraulic machine tools, the initial selection of the hydraulic cylinder working pressure of 25Mpa, according to the requirements of the fast-forward and fast-backward speed, the use of single-rod piston hydraulic cylinder. Fast forward using differential connection, and through the liquid replenishment method to achieve, in this case the hydraulic cylinder rodless chamber working area should be 6 times the working area of the rod chamber, that is, the piston rod diameter and cylinder diameter to meet the relationship.
Fast forward, the hydraulic cylinder must have back pressure on the return line to prevent the upper pressure plate due to self-weight and automatically slide down, according to the "Hydraulic System Design Manual" Table 2-2, can be taken = 1Mpa, fast forward, the hydraulic cylinder is to do the differential connection, but due to the pressure drop in the oil pipe The existence of a rod cavity pressure must be greater than the rodless cavity, the estimate can be taken, fast back, back to the oil cavity is a back pressure, this time, but also by 2Mpa to estimate. According to 2Mpa to estimate.
1) Calculate the area of the hydraulic cylinder
Can be calculated according to the following graph
-- Hydraulic cylinder working chamber pressure Pa
-- Hydraulic cylinder return chamber pressure Pa
Therefore.
When these diameters are rounded into standard values according to GB2348-80, we get: ,
The actual effective area of the hydraulic cylinder area is obtained as follows:
2) Calculation of the actual required flow rate of the hydraulic cylinder
1) the required flow rate when the working fast empty range
The volumetric efficiency of the hydraulic cylinder is taken as follows
2) the required flow rate when the working cylinder is suppressed Required flow rate
③ work cylinder return flow rate
4.2 selection of hydraulic components
4.2.1 Determine the specifications of the hydraulic pump and drive motor power
From the previous analysis of the working conditions, by the maximum compression force and the type of hydraulic mainframe, initially set on the working pressure of the hydraulic pump is taken as , taking into account the inlet and outlet of the oil valve and the piping of the pressure loss for the (including the return) (including the return oil pressure loss into the oil chamber), the maximum working pressure of the hydraulic pump for
The above calculation is the static pressure of the system, taking into account the system in a variety of conditions in the transition phase of the dynamic pressure often exceeds the static pressure, in addition to a certain amount of pressure reserve, and to ensure that the pump's life, the normal operating pressure for the pump's rated pressure of about 80%, so the selection of the rated pump pressure should meet the following requirements:
Hydraulic pumps should be used in the hydraulic system to ensure that the pressure is not too high. Pressure should meet:
The maximum flow rate of the hydraulic pump should be:
The maximum flow rate of the hydraulic pump
Maximum value of the flow rate of the implementation of the action at the same time the maximum value of the flow rate of the sum of the flow rate required, if the relief valve at this time is working, must be added to the relief valve of the minimum relief flow rate .
System leakage coefficient, generally take , now take .
1. Select the specifications of the hydraulic pump
Since the hydraulic system has a high working pressure, high load pressure, high power. Large flow. So choose axial piston variable pump. Plunger variable pump is suitable for large load, high power machinery and equipment (such as gantry planer, broaching machine, hydraulic machine), plunger variable pump has the following characteristics:
1) High working pressure. Because the plunger and cylinder hole processing is easy, dimensional accuracy and surface quality can reach high requirements, oil leakage is small, high volumetric efficiency, the working pressure that can be achieved, generally ( ) , the highest can reach .
2) larger flow range. Because as long as the appropriate increase in plunger diameter or increase the number of plungers, the flow rate becomes larger.
3) Changing the stroke of the plunger can change the flow rate, easy to make a variety of variable type.
4) The main parts of the piston oil pump are subjected to pressure, so that the strength of the material is fully utilized, long life, unit power weight is small. But the plunger variable pump structure is complex. Material and machining precision requirements, high processing volume, expensive.
According to the above calculation and in the review of the relevant manual "Machinery Design Manual" into a large first P20-195 got: now choose , displacement 63ml/r, rated pressure 32Mpa, rated speed 1500r/min, drive power 59.2KN, volumetric efficiency, weight 71kg, volumetric efficiency of 92%.
2. Selection of the motor matched with the hydraulic pump
By the previous, the maximum power of this hydraulic system appeared in the work cylinder pressing stage, when the hydraulic pump supply pressure value of 26Mpa, the flow rate has been selected for the flow rate value of the pump. The total efficiency of the hydraulic pump. Piston pump for , take 0.82.
Select 1000r/min motor, the drive motor power is
Select motor , its rated power is 18.5KW.
4.2.2 Valve Components and Auxiliary Components Selection
1. The basic requirements for hydraulic valves:
(1). Sensitive action, reliable use, low impact and vibration during operation. Small pressure loss when the oil flows through.
(2). Good sealing performance. Compact structure, installation, adjustment, use, maintenance is convenient, versatility
2. According to the working pressure of the hydraulic system and through the various valve components and auxiliary components models and specifications
The main basis is based on the valve in the system work of the maximum working pressure and through the valve's actual flow rate, and other considerations need to be made of the valve's mode of operation, the way the installation is fixed, the value of the pressure loss, the work of the performance parameters and working life and other conditions to Performance parameters and working life and other conditions to choose the specifications of standard valves:
Serial number Name of components Estimated flow rate
Model
1 Swash plate piston pump
156.8 63SCY14-1B 32Mpa, drive power 59.2KN
2 WU mesh type Oil filter 160 WU-160*180 40 pass, pressure loss 0.01MPa
3 Direct-acting relief valve 120 DBT1/315G24 10 pass, 32Mpa, plate coupling
4 Back pressure valve 80 YF3-10B 10 pass, 21Mpa, plate coupling
5 2-position 2-way manual solenoid valve 80 22EF3-E10B
6 3-Way Solenoid Valve 100 34DO-B10H-T 10-Way, 31.5MPa
7 Pilot Operated Check Valve
80 YAF3-E610B 32-Way, 32MPa
8 Throttle Valve
80 QFF3-E10B 10-Way. 16 MPa
9 Throttle Valve
80 QFF3-E10B 10 O.D., 16 MPa
10 2-Position 2-Way Solenoid Valve
30 22EF3B-E10B 6 O.D., 20 MPa
11 Pressure Relay
- DP1- 63B 8 pass, 10.5-35 MPa12 Gauge Switch
- KFL8-30E 32Mpa, 6 measuring points
13 Oil Tank
14 Pilot Operated Check Valve YAF3-E610B 32 pass, 32 MPa
15 Upper Hydraulic Cylinder
16 Lower Hydraulic Cylinder
17 Unidirectional Throttle Valve
48 ALF3-E10B 10 bore, 16MPa
18 Unidirectional Check Valve
48 ALF3-E10B 10 bore, 16MPa
19 Three-way four-way solenoid valve 25 34DO-B10H-T
20 Pressure reducing valve 40 JF3-10B
4.2.3 Determination of piping size
There are many types of piping used in the oil piping system, such as steel, copper, nylon, plastic, rubber, etc., and they have to be selected correctly according to the installation location, working environment and working pressure. The oil pipe in this design is made of steel pipe. The design of the oil pipe using steel pipe, because the pressure required in this design is high pressure, P = 31.25MPa, steel pipe can withstand high pressure, low price, oil resistance, corrosion resistance, good rigidity, but the assembly can not be arbitrarily curved, often in the installation and dismantling of conveniently used as a pressure pipe in a high-pressure seamless pipe, low-pressure welded pipe. This design in the bending place can use the pipe joint to realize the bending.
Nylon tube used in low-pressure systems; plastic pipe is generally used in the return pipe with oil.
The hose is used as a pipeline between two relatively moving parts. Hose is divided into high and low pressure two kinds. High-pressure hose is a steel wire braided body for the skeleton or steel wire winding body for the skeleton of the hose, can be used for higher pressure in the oil circuit. Low-pressure hose is hemp or cotton silk braid for the skeleton of the hose, mostly used for lower pressure in the oil circuit. Because the hose is more difficult to manufacture, the cost is very high, so non-essential generally do not use.
1. Selection of pipe fittings:
Pipe fittings is a detachable coupling between the oil pipe and the oil pipe, oil pipe and hydraulic parts, it must have easy to install and disassemble, connect firmly, sealing and reliable, small external dimensions, flow capacity, small pressure drop, good workmanship and other conditions.
There are many types of pipe fittings, hydraulic system tubing and pipe fittings in the common connection:
Welded pipe fittings, tube fittings, flared pipe fittings, buckling pipe fittings, fixed hinged pipe fittings. The connection threads for the screwed-in end of the pipeline adopt international standard metric cone thread (ZM) and ordinary fine thread (M). Taper thread rely on their own cone screwing and the use of polytetrafluoroethylene and other sealing, widely used in medium and low-pressure hydraulic systems; fine thread sealing, commonly used in high-pressure systems, but requires the use of a combination of gaskets or O-rings for the end sealing, and sometimes also use copper washers.
Most of the leakage problems in the hydraulic system appear in the joints in its pipe system, for the selection of pipe materials, joints to determine the form (including joint design, gaskets, seals, hoop, anti-leakage coatings, etc.), the design of the pipe system (including the design of the bends, pipe support points and support forms of selection, etc.) and the installation of pipelines (including the correct transportation, storage, cleaning, assembly, etc.) All should be considered clearly, so as not to affect the quality of the entire hydraulic system.
Foreign research work on the material of the tube, joint forms and connection methods never stop, recently appeared a special nickel-titanium alloy made of pipe joints, which can make the deformation that occurs after the low-temperature force in the temperature elimination - that is, the pipe joints into liquid nitrogen with a mandrel to expand its inner diameter, and then remove it to the end of the tube quickly! Set on the end of the pipe, it can make it at room temperature to get a solid, close combination. This kind of "heat-shrinkable" connection has been applied in aviation and some other processing industries, and it can guarantee no leakage under the working pressure of 40~55Mpa. This design is based on the need to select the tube fitting. Requirements for the use of cold-drawn seamless steel pipe.
2. Calculation of the inner diameter of the pipe:
(1)
In the formula Q - the flow rate through the pipe
v - the allowable flow rate in the pipe , see table:
Allowable flow rate recommendation
Pipes through which the oil flows Recommended flow rate m/s
Hydraulic pump suction pipe
Hydraulic system pressure pipe 3~6, high pressure, short pipeline viscosity is small to take the larger value
Hydraulic system return pipe 1.5~2.6
(1). Hydraulic pump pressure oil pipe diameter:
Take v=4m/s
According to "Mechanical Design Manual" into a large first P20-641 to find: take d=20mm, the outer diameter of the steel pipe D=28mm;
Pipe connector coupling thread M27 × 2.
(2). Hydraulic pump return pipe diameter:
Take v=2.4m/s
According to "Mechanical Design Manual" Cheng Daxian P20-641: take d=25mm, the outer diameter of the steel pipe D=34mm;
Pipe connector coupling thread M33×2.
3. Calculation of the wall thickness of the pipeline
In the formula: p --Maximum working pressure in the pipe Pa
d --Inner diameter of the pipe m
--Permissible stress of the pipe material Pa,
-- tensile strength of piping material Pa
n -- safety factor, for steel pipe, when, take n=8; when,
take n=6; when, take n=4.
Based on the above parameters, we can get:<
We choose the material of steel pipe is 45# steel, from which we can get the tensile strength of the material = 600MPa;
(1). Hydraulic pump pressure oil pipe wall thickness
(2). Wall thickness of hydraulic pump return pipe
So the selected pipe is applicable.
4. Calculation of hydraulic system
It has been calculated above that the inner diameter of the inlet and return pipes in this hydraulic system are 32mm and 42mm respectively.
But because the specific piping arrangement and length of the system have not been determined, so the pressure loss can not be calculated.
4.2.4 Calculation of temperature rise of the system
In the whole working cycle, the work-in phase takes up the longest time and generates heat. the longest time and generates the largest amount of heat. In order to simplify the calculation, the main consideration is the heat generation at the time of work-in. Generally speaking, the power loss of the work done during the work-in phase is large and causes the heat generation to be larger, so only the heat generation during the work-in phase is considered, and then its value is taken for analysis.
When V=10mm/s, that is, v=600mm/min
that is
This time the efficiency of the pump is 0.9, the pump's outlet pressure is 26MP, then there are
that is
The power loss at this time:
Assuming that the system's heat dissipation is general, take ,
The tank's heat dissipation area A
The temperature rise of the system is
According to the Mechanical Design Manual, Cheng Daxian P20-767: the temperature in the tank is generally recommended to be 30-50
So the calculation shows that the temperature rise of the system is within the permissible range.
V Structural Design of Hydraulic Cylinder
5.1 Determination of Main Dimensions of Hydraulic Cylinder
1) Calculation of Hydraulic Cylinder Wall Thickness and Outer Meridian
Hydraulic cylinder wall thickness is calculated by the strength conditions of the hydraulic cylinder.
The wall thickness of the hydraulic cylinder generally refers to the thickness of the thinnest part of the cylinder structure. From the mechanics of materials can be seen, bear the internal pressure of the cylinder, its internal stress distribution law should be different wall thickness and different. General calculation can be divided into thin-walled cylinder and thick-walled cylinder.
Hydraulic cylinder bore D and its wall thickness of the ratio of the cylinder is called thin-walled cylinder. Engineering machinery hydraulic cylinder, generally seamless steel pipe material, most of the thin-walled cylinder structure, its wall thickness according to the thin-walled cylinder formula
Design calculation process
In the formula -- hydraulic cylinder wall thickness (m);
D -- hydraulic cylinder bore diameter (m);
D -hydraulic cylinder inner diameter (m);
-Test pressure, generally take the maximum working pressure (1.25 ~ 1.5) times;
-The permissible stress of the cylinder material. Seamless steel pipe: .
= = 22.9
Then In the low and medium pressure hydraulic system, the wall thickness of the hydraulic cylinder calculated according to the above formula is often very small, so that the cylinder stiffness is often very insufficient, such as deformation in the cutting process, installation deformation, etc. caused by the working process of the hydraulic cylinder jammed or oil leakage. Therefore, generally do not make calculations, selected by experience, if necessary, according to the above formula for calibration.
Hydraulic cylinder wall thickness is calculated, you can find the cylinder body of the external longitudinal 2) hydraulic cylinder working stroke determination
Hydraulic cylinder working stroke length, according to the maximum stroke of the actuator's actual work to determine, and refer to & lt; & lt; Hydraulic System Design Handbook & gt; & gt; P12 Table 2-6 in the series of dimensions to select the standard value.
Hydraulic cylinder working stroke selection
The determination of the thickness of the cylinder head
Generally hydraulic cylinders are mostly flat-bottomed cylinder head, the effective thickness t according to the strength requirements can be used in the following two formulas for the approximate calculation.
No holes
With holes
The effective thickness of the cylinder head (m);
--cylinder head stop inner diameter (m);
--cylinder head stop diameter (m);
--cylinder head hole diameter (m);
--cylinder head hole diameter (m). - diameter of cylinder head hole (m).
Hydraulic cylinder:
Without hole
take t=65mm
With hole
take t'=50mm
3)Determination of minimum guiding length
When the piston rod is fully extended outward, the distance from the midpoint of piston bearing surface to the midpoint of the cylinder head sliding bearing surface H is called the minimum guide length (shown in Figure 2 below). If the guiding length is too small, the initial deflection of the hydraulic cylinder (clearance caused by deflection) will increase, affecting the stability of the hydraulic cylinder, so the design must ensure that there is a certain minimum guiding length.
For general hydraulic cylinder, the minimum guiding length H should meet the following requirements:
Design Calculation Process
In L - the maximum stroke of the hydraulic cylinder;
D - the inner diameter of the hydraulic cylinder.
The width of the piston B is generally taken as B=(0.6~10)D; the length of the sliding bearing surface of the cylinder head is determined according to the inner diameter of the hydraulic cylinder D;
When D<80mm, it is taken;
When D>80mm, it is taken.
In order to ensure that the minimum guide length H, if too much increase and B are not suitable, if necessary, in the cylinder head and piston between a spacer K to increase the value of H. The length of the spacer C is determined by the length of the cylinder head and piston, and the length of the spacer C is determined by the length of the piston. The length of the spacer C is determined by the minimum guiding length H, that is
Sliding hydraulic cylinder:
Minimum guiding length:
Take H=200mm
Width of piston: B=0.6D=192mm
Length of sliding bearing surface of the cylinder head:
Length of the spacer: So there is no spacer.
Hydraulic cylinder cylinder body internal length should be equal to the sum of the piston stroke and the width of the piston. Cylinder body profile length should also take into account the thickness of the end caps at both ends. General hydraulic cylinder cylinder length should not be greater than 20-30 times the internal diameter.
Hydraulic cylinder:
Internal cylinder length
When the hydraulic cylinder support length LB (10-15)d, need to consider the stability of the piston rod curvature and calculation. This design does not need to carry out stability calculations.
5.2 Structural design of hydraulic cylinder
After the main dimensions of the hydraulic cylinder are determined, the structural design of each part. Mainly includes: cylinder and cylinder head connection structure, piston and piston rod connection structure, piston rod guiding part of the structure, sealing device, exhaust device and hydraulic cylinder installation connection structure. Due to different working conditions, the structure of different forms. Design according to the specific circumstances of the choice.
Design and calculation process 1) cylinder block and cylinder head connection form
Cylinder block and cylinder head connection form and working pressure, cylinder material and working conditions.
The outer half-ring connection is used in this design, as shown in Fig.1 below:
Fig.1 Advantages of the outer half-ring connection between cylinder block and cylinder head:
(1) Simple structure
(2) Convenient processing and assembling
Disadvantages:
(1) Large external dimensions
(2) Cylinder cylinder grooved, which weakens the strength and increases the cylinder wall thickness. Increase the cylinder wall thickness 2) piston rod and piston connection structure
Refer to & lt; & lt; Hydraulic System Design Manual & gt; & gt; & gt; P15 Table 2-8, the use of threaded connections in the combined structure. As shown in Figure 2 below:
Figure 2 Piston rod and piston threaded connection
Features:
Simple structure, easy to loosen under the vibration of the working conditions, must be used to lock the device. More applications, such as combined machine tools and engineering machinery on the hydraulic cylinder.