Common materials are seamless steel pipes No.20, No.35 and No.45, and the steel pipes can meet the roughness requirements within 0.4μm m after honing or rolling .. 20 # steel pipes can be used for low-pressure oil cylinders and 45 # steel pipes can be used for high-pressure oil cylinders.

2 piston rod

There are two kinds of piston rods: solid rod and hollow rod. One end of the hollow piston rod needs an exhaust hole for welding and heat treatment.

The solid piston rod is made of 35 and 45 steels, and the hollow piston rod is made of 35 and 45 seamless steel pipes.

After rough machining, the piston rod is quenched and tempered to 229~285HB in India, and the hardness reaches 45~55HRC if necessary.

3 Cylinder head

Castings for low pressure, HT300 gray iron for medium and low pressure, and 35 and 45 steels for medium and high pressure.

When the cylinder head itself is the guide sleeve of the piston rod, it is best to use cast iron for the cylinder head. At the same time, brass, bronze or other wear-resistant materials should be fused on the guide surface. If the guide sleeve is pressed into the cylinder head, 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 value of piston and piston rod shall be 0.03mm..

Hydraulic cylinders have various structural forms and classification methods:

1 According to the motion mode, it can be divided into linear reciprocating motion and rotary swinging motion;

According to the function of hydraulic pressure, it can be divided into single-acting type and double-acting type;

According to the structural form, it can be divided into piston type, plunger type, multi-stage telescopic sleeve type, rack and pinion type and so on.

According to the installation form, it can be divided into pull rod, earring, foot, hinge shaft, etc.

5 According to the pressure grade, it can be divided into 16Mpa, 25Mpa, 3 1.5Mpa, etc.

Hydraulic cylinders are easy to use and maintain, so they are widely used.

Extended data:

Hydraulic cylinder is a hydraulic actuator that converts hydraulic energy into mechanical energy and makes linear reciprocating motion (or swinging motion). It has simple structure and reliable operation. When it is used to realize reciprocating motion, it can save the reducer, has no transmission gap and moves smoothly, so it is widely used in various mechanical and hydraulic systems.

The output force of the hydraulic cylinder is proportional to the effective area of the piston and the pressure difference between its two sides; Hydraulic cylinder is basically composed of cylinder body and cylinder head, piston and piston rod, sealing device, buffer device and exhaust device. Buffer device and exhaust device depend on the specific application, and other devices are essential.

It is generally believed that the reasons for the peeling of hard chromium coating on the inner surface of cylinder body are as follows.

A. the electroplating layer is not well combined. The main reasons for the poor adhesion of electroplating layer are: insufficient degreasing treatment of parts before electroplating; The surface activation treatment of the parts is not thorough, and the oxide film is not removed.

B. hard layer wear. The wear of electroplated hard chromium layer is mostly caused by the grinding action of piston rubbing iron powder, and the wear is faster when there is water in the middle. Corrosion caused by metal contact potential difference only occurs at the contact part of piston, and corrosion occurs at point.

As mentioned above, when there is moisture in the middle, it will promote the development of corrosion. Compared with castings, the contact potential difference of copper alloys is higher, so the corrosion degree of copper alloys is more serious.

C. corrosion caused by contact potential difference. The hydraulic cylinder is not easy to be corroded by contact potential difference when running for a long time; This is a common fault for hydraulic cylinders that stop for a long time.

Sliding or crawling of hydraulic cylinder piston will make the hydraulic cylinder unstable. The main reasons are as follows:

(1) The internal movement of the hydraulic cylinder is slow. Improper assembly of internal parts of hydraulic cylinder, deformation and wear of parts, or out-of-tolerance of shape and position, and excessive action resistance make the piston speed of hydraulic cylinder change with different stroke positions, resulting in sliding or crawling. Most of the reasons are due to the poor assembly quality of parts, surface scarring or sintering to produce iron filings, which increases the resistance and reduces the speed.

If the piston is not concentric with the piston rod or the piston rod is bent, the installation position of the hydraulic cylinder or piston rod on the guide rail is deviated, and the sealing ring is installed too tightly or too loosely. The solution is to repair or adjust again, replace damaged parts and remove iron filings.

(2) Poor lubrication or out-of-tolerance machining of hydraulic cylinder bore. Because the piston moves relative to the cylinder, guide rail and piston rod, if the lubrication is poor or the hole diameter of the hydraulic cylinder is out of tolerance, it will aggravate the wear and reduce the straightness of the cylinder center line.

In this way, when the piston works in the hydraulic cylinder, the friction resistance will increase or decrease, leading to sliding or crawling. The elimination method is to grind the hydraulic cylinder first, then prepare the piston according to the matching requirements, grind the piston rod and configure the guide sleeve.

(3) The hydraulic pump or cylinder enters the air. The compression or expansion of air will cause the piston to slide or crawl. The elimination measures are to check the hydraulic pump, set up a special exhaust device, and quickly operate the full stroke exhaust several times.

(4) The sealing quality is directly related to sliding or creep. When the O-ring is used at low pressure, compared with the U-ring, it is easy to slip or crawl because of the higher surface pressure and the larger difference between dynamic and static friction resistance.

The surface pressure of U-shaped sealing ring increases with the increase of pressure. Although the sealing effect is improved accordingly, the difference between static and dynamic friction resistance is also increased, and the internal pressure is increased, which affects the elasticity of rubber. As the contact resistance of the lip increases, the sealing ring will tip over and the lip will stretch, which is easy to cause sliding or crawling. In order to prevent it from falling over, a support ring can be used to keep it stable.

References:

Baidu encyclopedia-hydraulic cylinder