Overview of Hydraulic Cylinders

Hydraulic cylinders (also called a linear hydraulic motor) are mainly used in machinery. They are the most important components of construction machinery and are mainly important core components that provide power for machinery. Hydraulic cylinders are widely used in various construction machinery, ships, machine tools, and even defense equipment industries.

A hydraulic cylinder is a hydraulic actuator that converts hydraulic energy into mechanical energy and performs linear reciprocating motion (or swing motion). The hydraulic cylinder has simple structure and reliable operation. When it is used to realize reciprocating motion, the deceleration device can be eliminated, and there is no transmission gap, and the motion is stable. Hydraulic cylinders are widely used in hydraulic systems of various machines. 

Features of Hydraulic Cylinders

1. The hydraulic cylinder is exquisitely shaped like a flashlight, but compared with the cylinder, it can withstand a pressure of 15 tons with a working pressure of 100MPA.

2. The hydraulic cylinder is made of No. 45 high-quality carbon steel, which has the characteristics of skin fatigue resistance, impact resistance, and non-magnetic properties, and its own weight is reduced by 2/3.

3. The operating temperature range of the hydraulic cylinder can reach -60~200 degrees, and its super long life will not cause any failure after 6000 hours of operation.

4. The hydraulic cylinder is a masterpiece of hydraulic components and hydraulic technology, so its new structure and multiple working methods are the biggest features of the hydraulic cylinder.

Disadvantages of hydraulic cylinders:

1. The design formula of the hydraulic cylinder is unreasonable, and a large safety factor cannot be obtained. Therefore, the structure and strength design theory of the hydraulic cylinder is relatively lagging behind, resulting in certain limitations in its motion characteristics.

2. The stress on the hydraulic cylinder is underestimated, and unsafe situations will inevitably occur, for example, the piston rod in the cylinder is broken.

3. Compared with air cylinders, hydraulic cylinders are prone to oil leakage (working medium hydraulic oil is not a small consumption.) 

Types of Hydraulic Cylinders

According to the structure of hydraulic cylinders, hydraulic cylinders can be divided into five categories. Each type of hydraulic cylinder has the following characteristics:

1. Telescopic hydraulic cylinder

Telescopic hydraulic cylinders have two-stage or multi-stage pistons. The order in which the pistons extend in telescopic hydraulic cylinders is from large to small, while the order of retraction without load is generally from small to large. The characteristic of this type of hydraulic cylinder is that it can realize a long stroke, and its length is relatively short when stretching, and its structure is more compact. changes happened. Based on this feature, this type of hydraulic cylinder is usually used in construction machinery and agricultural machinery.

2. Swing hydraulic cylinder

The swing hydraulic cylinder is an actuator that outputs torque and realizes reciprocating motion. It is also called a swing hydraulic motor. It generally has several forms such as single blade, double blade, and spiral swing. The so-called vane type, that is, the stator block is fixed on the cylinder body, and the vane is connected to the rotor. According to the direction of oil inlet, the vane will drive the rotor to reciprocate and swing; the so-called spiral swing can be further divided into single spiral swing and double spiral swing , the current double-helical swing is more common, relying on the linear motion of the piston in the two helical auxiliary down-hydraulic cylinders to transform into a compound motion of linear motion and rotation motion, thereby realizing the swing motion.

This type of hydraulic cylinder is characterized by a compact structure and a large output torque, but it is difficult to seal, so it is generally only used for reciprocating motion, indexing or intermittent motion in low and medium pressure systems.

3. Piston hydraulic cylinder

Piston hydraulic cylinders can be divided into single-rod and double-rod structures. The fixing methods are fixed by the cylinder body and the piston rod. According to the action of the hydraulic pressure, it is divided into single-acting and double-acting. In the single-acting hydraulic cylinder, the pressure oil is only supplied to one cavity of the hydraulic cylinder, and the hydraulic pressure makes the hydraulic cylinder move in one direction, and the reverse direction is realized by external force (such as spring force, self-weight or external load, etc.); The acting hydraulic cylinder tends to move in two directions, alternately feeds oil through the oil chamber, and completes the corresponding action through the action of hydraulic pressure.

In terms of application characteristics, the single-piston rod hydraulic cylinder only has a piston rod at one end, so the effective area of the two chambers is different. When the oil supply is the same, the movement speed of the piston is different when the oil is supplied to different chambers; When the load force is the same, the required oil supply pressure is also different when the oil enters different chambers. If the system pressure is adjusted, such as the movement of the hydraulic cylinder on the sanitation garbage truck in both directions can overcome the difference in load force, and the two ends Both the inlet and outlet oil ports can realize two-way movement through pressure oil or return oil. This type of hydraulic cylinder is called a double-acting cylinder.

Both sides of the piston of the double-rod piston hydraulic cylinder protrude. When the diameters of the piston rods on both sides are the same and the oil supply pressure and flow are constant, the movement speed of the piston (or cylinder) in both directions and the thrust F are equal.

4. Plunger hydraulic cylinder

The precision requirements of the inner hole of the plunger hydraulic cylinder are quite high, and it is relatively difficult to process when the stroke is long. In this case, the plunger cylinder can be used as a single-acting cylinder, and its return stroke can be realized by external force or by itself. Processing provides more convenience.

In terms of application characteristics, the plunger does not contact the inner wall of the cylinder, so the inner hole of the cylinder does not need to be finished, the manufacturability is improved, and the cost is also reduced. Since the plunger is always under pressure, the component rigidity is also large enough. In addition, the plunger cylinder also has the characteristics of simple structure and convenient manufacture. The large weight requires it to be used vertically. Hydraulic cylinders are often used in long-stroke machine tools, such as gantry planers, guide rail grinders, and large broaching machines.

5. Combined hydraulic cylinder

We can roughly divide this type of hydraulic cylinder into three categories: booster cylinder, rack-piston cylinder and multi-stage cylinder. We will explain these three types respectively.

①The booster cylinder, also known as a supercharger, can convert the input low-pressure oil into high-pressure oil for use in the high-pressure branch in the hydraulic system.

②Rack-piston cylinder, which is composed of a double-piston cylinder with a rack and pinion and a rack-and-pinion machine. When the reciprocating motion of the oil cylinder is changed to the reciprocating rotation of the pinion shaft through the rack-and-pinion mechanism, it is mostly used for automatic lines, combined machine tools, etc. In bit or indexing mechanism.

③Multi-stage cylinder, also known as telescopic cylinder, is composed of two-stage or multi-stage piston cylinders. This type of cylinder is mostly suitable for construction machinery and other walking machinery, such as crane telescopic arm hydraulic cylinder, dump truck weightlifting hydraulic cylinder wait. 

Hydraulic Cylinders consist of

1. Cylinder

The commonly used materials are No. 20, 35, and 45 seamless steel pipes. The steel pipes are honed or rolled to meet the roughness requirements within 0.4 μm. The low-pressure cylinder can use No. 20 steel pipe, and the high-pressure cylinder can use No. 45 steel pipe.

2. Piston rod

There are two kinds of piston rods: solid rod and hollow rod. The hollow piston rod needs to leave a vent hole for welding and heat treatment.

The material of the solid piston rod is 35, 45 steel, and the material of the hollow piston rod is 35, 45 seamless steel pipe.

After rough machining, the piston rod is quenched and tempered to 229~285HB in India, and if necessary, it is subjected to high-frequency quenching to reach a hardness of 45~55HRC.

3. Cylinder head

Castings for low pressure, HT300 gray iron for medium and low pressure, No. 35 and 45 steel for medium and high pressure.

When the cylinder head itself is the guide sleeve of the piston rod, the cylinder head is made of cast iron. At the same time, brass, bronze or other wear-resistant materials should be welded on the guide surface. If the structure of pressing the guide sleeve into the cylinder head is adopted, the guide sleeve should be wear-resistant cast iron, bronze or brass.

4. Piston

Commonly used materials are wear-resistant cast iron, gray cast iron (HT300, HT350), steel and aluminum alloy.

The concentricity tolerance of the piston and piston rod should be 0.03mm. 

Applications of Hydraulic Cylinders 

Hydraulic cylinders are everywhere around us, we see them so often in our daily life, we may not even realize it if we are not paying special attention: In excavators, trucks, forklifts, tractors, aerial work platforms, mining equipment - Everything you need. A hydraulic cylinder is one of the four main components of a hydraulic system, which is a technology in which a fluid (most commonly hydraulic oil) is used to move energy from an electric motor to an actuator: most commonly a hydraulic cylinder.

A hydraulic cylinder is an actuating device in a hydraulic system. Hydraulic cylinders are used in hydraulic jacks, lifting devices for dump trucks, and lifting devices for bulldozer (snow) machine loader buckets. Hydraulic cylinders are also widely used in automobile cranes.

A hydraulic cylinder is a hydraulic actuator that produces linear motion by converting hydraulic energy back into mechanical motion. A hydraulic cylinder can be likened to a muscle, and it creates movement with the help of a machine's hydraulic system - so it's like a muscle. In hydraulic transmission, the medium is a liquid, usually oil. The pressure in a hydraulic system is determined by the load induced by the hydraulic cylinders or valves, which resists the flow of fluid induced by the hydraulic pump. 

Working principle of Hydraulic Cylinders

The principle of hydraulic transmission is to use oil as the working medium, and the power is transmitted through the pressure inside the oil.

1. Power part - converts the mechanical energy of the prime mover into the pressure energy (potential energy) of the oil. For example: hydraulic pumps.

2. Executing part - convert the oil pressure energy input by the hydraulic pump into the mechanical energy driving the working mechanism. For example: Hydraulic cylinders, hydraulic motors.

3. Control part - used to control and adjust the pressure, flow and flow direction of oil. For example: pressure control valves, flow control valve.

4. Auxiliary part - connect the first three parts together to form a system for oil storage, filtration, measurement and sealing and so on. For example: soft and hard pipelines, joints, oil tanks, oil filters, accumulators, seals and display instruments, etc. 

Price of Hydraulic Cylinders

The Hydraulic Cylinders Price will change randomly with factors such as production cost, transportation cost, international situation, exchange rate, market supply and demand of raw materials. Sino Mechanical aims to provide you with high quality and best price Hydraulic Cylinders. If you are looking for Hydraulic Cylinders or Hydraulic Cylinders spares, please kindly contact us to get the latest Hydraulic Cylinders price. 

Hydraulic Cylinders Supplier

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