1. Classification and composition of hydraulic cylinders
According to the structure, hydraulic cylinders can be divided into four categories: piston cylinders, plunger pump cylinders, shaking cylinders and unique hydraulic cylinders; according to the rated pressure, they are divided into high-pressure and high-pressure hydraulic cylinders, medium-high-pressure hydraulic cylinders and medium-low voltage hydraulic cylinders. The single-rod double-effect piston hydraulic cylinder is a kind of simple structure and common use. The basic structure of the hydraulic cylinder is explained by taking the single-rod double-effect piston hydraulic cylinder as an example.
1. Cylinder: The cylinder is the main part of the hydraulic cylinder.
It forms a closed cavity with the cylinder head, piston and other parts to promote the fitness movement of the piston. There are 8 types of common cylinder structures, which are generally adopted according to the connection method between the cylinder and the cover. The raw materials are generally required to have sufficient compressive strength and fracture toughness. For electric welding, they also need to have excellent electric welding characteristics. Therefore, common raw materials are: 25, 45, ZG200~400, 1Cr18Ni9 these. Cylinder barrel blanks are mostly cold-drawn or hot-rolled seamless tubes, so the process is generally heat treatment (to ensure the compressive strength of the cylinder barrel, so that it can bear the air pressure and not easily deform and destroy) → honing or boring extrusion ( Ensure the surface roughness, concentricity, cylindricity and parallelism of the inner diameter of the cylinder, so that the tightness of the piston will not change after long-term repeated movement) → Car (ensure the length of the cylinder and other design specifications) → Drill ( Produce and process the oil outlet hole to ensure access to the oil channel) → pliers.
2. Piston: Piston is a key component that converts hydraulic function into mechanical kinetic energy. Its total area during work immediately affects the efficiency and movement rate of the hydraulic cylinder. There are various forms of connection between the piston and the piston rod, the common ones are the snap ring, the coupling type and the nut type. When there is no guide ring, the piston uses high-toughness pig iron HT200~300 or ductile casting; when there is a guide ring, the piston uses high-quality alloy steel No. 20, No. 35 and No. 45.
3. Piston rod: Piston rod is the key component of hydraulic cylinder transmission force. Select low carbon steel (such as No. 45 steel) as the raw material. When the hydraulic cylinder is working, the piston rod is subject to driving force, tensile force or bending torque, etc., it is necessary to ensure its compressive strength; and the piston rod often rolls in the guide sleeve, and the mutual cooperation should be suitable and very tight. The sliding friction is large and too loose, which is very easy to cause jamming and unilateral damage, which requires its surface roughness, parallelism and concentricity to be suitable. Therefore, the machining process of the piston rod is generally rough turning → heat treatment → half boring → heat treatment → pre-plating grinding → stainless steel → post-plating grinding → boring.
4. Cylinder head: The cylinder head is installed on the two hydraulic cylinders and forms a close oil cavity with the cylinder barrel. Generally, there are various interface methods such as electric welding, external threads, anchor bolts, card keys and support rods, which are generally selected according to factors such as the working pressure, the interface method of the hydraulic cylinder, and the application environment.
5. Guiding sleeve: The guiding sleeve plays the role of guiding and supporting point for the piston rod. It stipulates high precision of mutual cooperation, small friction resistance, good wear resistance, and can bear the pressure, bending force and impact of the piston rod. shock. There is a sealing device inside to ensure the sealing of the cylinder and rod cavity, and there are dust rings on both sides to prevent the residue, dust and water from being sent to the sealing device and damaging the sealing. Metal guide sleeves are generally made of brass, gray cast iron, ductile cast iron and air-oxidized pig iron with low friction resistance and good wear resistance; non-metal guide sleeves can be made of polytetrafluoroethylene and polychlorotrifluoroethylene, etc. .
6. Cache equipment: The piston and piston rod have a very large projectile motion when exercising under the push of hydraulic pressure. When they enter the cover and bottom of the hydraulic cylinder, it will cause mechanical equipment to hit and cause a very large impact. Sexual stress and noise. The choice of caching equipment is to better prevent such impacts. The principle is that the oil (part or part) in the low-voltage chamber of the cylinder can convert kinetic energy into energy according to the throttle valve, and the energy is sent out of the hydraulic cylinder by the oil in the circulation system. The structure of the cache device is divided into two types: constant throttle total area cache device and wild manifold cache device.
Second, the basic parameters of the hydraulic cylinder
The basic parameters of the hydraulic cylinder include pressure, total flow, specifications and models, piston stroke arrangement, fitness movement rate, push and pull force, and hydraulic cylinder output power.
1. Pressure: Pressure is the gas pressure of the oil effect on the total area of the enterprise. The calculation method is p=F/A, that is, the load on the piston divided by the total working area of the piston. From the above equation, the creation of the pressure value is caused by the existence of the load. On the total active area of the same piston, the greater the load, the greater the pressure necessary to release the load. That is to say, if the total area of the piston is constant, the greater the oil pressure, the greater the interaction force caused by the piston. The rated pressure that everyone usually refers to is the pressure at which the hydraulic cylinder can work for a long time. According to the rated pressure, the hydraulic cylinder pressure is divided into the following: (enterprise MPa) pressure range 0-2.5 is low voltage, 2.5-8 is high pressure, 8-16 is medium high pressure, 16-32 is high pressure, > 32 is high pressure, The allowable pressure refers to the limited pressure that the hydraulic cylinder can bear in an instant; the AC pressure test pressure refers to the experimental pressure to be borne when checking the quality of the hydraulic cylinder. Most of these two pressures are required to be no more than 1.5 times the rated pressure.
2. Total flow: The total flow is the volume of oil in a unit time according to the section of the cylinder. The calculation method Q=V/t=vA, in which V indicates the oil volume consumed by the hydraulic cylinder piston sub-stroke arrangement, t indicates the time required for the hydraulic cylinder piston sub-stroke arrangement, v indicates the fitness movement rate of the piston rod, A Indicates the total working area of the piston.
3. Piston stroke arrangement: The piston stroke arrangement refers to the distance that the piston steps in between when the piston moves repeatedly. Generally, after the reliability requirements of the hydraulic cylinder are reached, the itinerary arrangement is selected according to the specific work schedule, which is the same as the normative itinerary arrangement.
4. The fitness movement rate of the piston: The fitness movement rate is the distance that the pressure oil promotes the movement of the piston per unit time, which can be expressed as v=Q/A.
5. Specifications and models: The specifications and models mainly include the inner and outer diameter of the cylinder, the diameter of the piston, the diameter of the piston rod and the size of the cylinder head. force and its itinerary to measure, design and proofread.
