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The basic knowledge of forklift

Publisher:hyder Date:2017-07-26

The basic knowledge of forklift
Hydraulic transmission equipment is usually composed of power, execution, control and auxiliary four components. hydraulic cylinder as the realization of linear reciprocating motion or less than 360. Hydraulic mechanism, reciprocating motion has the advantages of simple structure, reliable operation, the main actuator hydraulic system is widely used, it is the original motivation to mechanical energy to drive the hydraulic pump to form liquid pressure which can then become, can directly drive the load reciprocating or less than 360. An energy conversion device for mechanical energy that swings back and forth. To understand the hydraulic cylinder, we must know the following basics.

Classification and composition of hydraulic cylinders

According to the structure of the hydraulic cylinder, it can be divided into four categories: piston cylinder, plunger cylinder, swing cylinder and special cylinder. According to the rated pressure, the hydraulic cylinder can be divided into high pressure and extra high pressure hydraulic cylinders, middle and high pressure hydraulic cylinders and middle and low pressure hydraulic cylinders.

1)   Cylinder:     the cylinder is the main part of the hydraulic cylinder, which forms a closed chamber with the cylinder head, piston and other parts to push the piston movement. The commonly used cylinder structure has 8 kinds, usually according to the cylinder and the end cover connection form choice. Materials generally require sufficient strength and impact toughness, and also have good welding performance, so the commonly used materials are: 25, 45, ZG200~400, 1Cr18Ni9 and so on. The cylinder blank by cold drawing or hot rolling seamless steel tube, so the process is usually tempered (ensure cylinder strength, which can withstand the pressure without deformation and damage), honing or boring and rolling (ensure the inner diameter of cylinder roughness, roundness, cylindricity and straightness, make the piston seal in the same long after the car (to) the reciprocating motion of the cylinder is designed to ensure the size requirements), drilling (processing oil outlet hole, to ensure oil import, clamp)

2)    Cylinder head:     the cylinder head is arranged at both ends of the hydraulic cylinder and forms a tight oil cavity with the cylinder. Usually there are welding, thread, bolt, card key and pull rod and other connections, generally according to the working pressure, cylinder connection, the use of environmental factors such as choice.

3)    Piston rod:     the piston rod is the main component of the transfer force of the hydraulic cylinder. The material is usually medium carbon steel (such as steel No. 45). When the oil cylinder piston rod, the thrust, tension or bending moment, solid is necessary to ensure its strength; and the piston rod in the guide sleeve in sliding fit should be appropriate, too tight, too loose, friction, easy to cause the clamping phenomenon and unilateral wear, which requires surface roughness, straight line and roundness as appropriate. Therefore, the piston rod is usually made of coarse material, Quenched and tempered, semi refined, quenched, plated, polished, chrome plated, plated, polished and refined.

4)    Piston:     piston is the main component that transfers hydraulic energy to mechanical energy. Its effective working area directly affects the force and speed of the hydraulic cylinder. The piston is connected with the piston rod in many forms, such as clamp ring type, shaft type and nut type. In the absence of a guide ring, the piston is made of high strength cast iron, HT200~300 or ductile iron; when used with guide rings, pistons are made of high-quality carbon steel No. 20, No. 35 and No. 45.

5)    Guide sleeve:     the guide sleeve plays a guiding and supporting role to the piston rod. It requires high coordination precision, small friction resistance, good wear resistance, and can bear the pressure of the piston rod, bending force and impact vibration. A sealing device is arranged to ensure the sealing of the cylinder cavity of the cylinder, and the outer side is provided with a dustproof ring, so as to prevent impurities, dust and moisture from being brought to the sealing device and to damage the sealing. The metal guide sleeve usually adopts the bronze and gray iron, nodular cast iron and oxide cast iron with small friction coefficient and good wear resistance, and the non-metal guiding sleeve can be made of polytetrafluoroethylene and poly three fluorine vinyl chloride, etc..

6)    Buffer device:     piston and piston rod under the driving force of liquid pressure, the movement has a great momentum, when entering the end of the cylinder and the bottom of the cylinder, it will cause mechanical impact, and produce great impact pressure and noise. A buffer device is used to avoid such a collision. Its working principle is to make the oil tank in the low-pressure chamber (all or part of) through the throttle to change kinetic energy into heat energy, and the heat energy is carried by the circulating oil liquid to the hydraulic cylinder. The structure of the buffering device is divided into two kinds of constant throttling, area buffer device and variable flow type buffer device.

main technical sheet of hydraulic cylinder

The main parameters of the hydraulic cylinder include pressure, flow, size, piston stroke, movement speed, thrust force, efficiency and hydraulic cylinder power, etc.

1)    Pressure:     the pressure is the pressure acting on the unit area of the oil. The formula p=F/A, that is, the load acting on the piston, is divided by the effective working area of the piston. From the upper model, the establishment of the pressure value is caused by the existence of the load. On the effective working area of the same piston, the greater the load, the greater the pressure required to overcome the load. In other words, if the piston's effective working area is constant, the greater the oil pressure, the greater the piston's force. Normally we say the rated pressure is the pressure that the hydraulic cylinder can work for a long time. According to the rated pressure, the hydraulic pressure grading table MPa maximum allowable pressure to the limit pressure of hydraulic cylinder at the moment can withstand the test pressure; and test pressure is refers to when the need for quality inspection of hydraulic cylinder, the two pressure countries most of the provisions of less than or equal to 1.5 times rated pressure

2)    Flow rate:     the flow rate is the volume of the effective cross sectional area of the cylinder through unit cylinder in unit time. The calculation formula of Q=V/t=vA, which V said the oil consumption volume of the hydraulic cylinder piston in one stroke of the hydraulic cylinder piston, t said a time required for a trip, V said the velocity of piston rod, the piston A said the effective working area.

3)    Piston stroke:     piston stroke means the distance traveled between the poles during reciprocating motion of the piston. Generally, after meeting the requirements of the stability of the cylinder, the standard stroke corresponding to the actual working stroke is selected.

4)    Piston movement speed:     the movement speed is in the unit time pressure, the oil liquid pushes the piston movement distance, may indicate v=Q/A.

5)    Dimensions:     internal and external dimensions including cylinder diameter and piston diameter, the diameter of the piston rod and the cylinder head size, the size of the hydraulic cylinder according to the use of the environment, the installation form, to provide the force and stroke calculation, design and check.

Common problems and maintenance of hydraulic cylinder
The hydraulic cylinder as an element, a working device, like all mechanical equipment, in the long run the process inevitably in the structure of parts will produce fatigue, wear, corrosion, loosening, aging deterioration and damage phenomenon in different degree, the technical conditions of hydraulic cylinder performance, deterioration, which directly caused the fault the whole hydraulic equipment, and even failure. Therefore, it is very important to remove and repair the common problems in the daily operation of the hydraulic cylinder.

Development trends of hydraulic cylinders          

With the popularization and application occasions, hydraulic technology is growing, the working performance of the hydraulic cylinder, the structure, scope, precision, appearance, material, manufacturing method of test are put forward new requirements, and constantly promote the development and progress of hydraulic cylinder.
Its general trend is:

1, High pressure, miniaturization. Pressure is reduced to the size and weight of the hydraulic cylinder, and reduce the volume of the whole hydraulic device effective way.         
2, New materials, lightweight. With the high pressure, miniaturization, the use of the hydraulic cylinder test, new materials, lightweight has become one of the solutions.
3, Novel structure composite. In order to adapt to the expansion of the application scope of hydraulic cylinder, all kinds of new structure of hydraulic cylinder appear continuously, such as automatic control hydraulic cylinder, self-locking hydraulic cylinder, cable type hydraulic cylinder, creeping hydraulic cylinder and compound hydraulic cylinder, etc..     
4, High performance, variety.          

5, Energy saving and corrosion resistance.