With the improvement of industrialization and automation level, mechanical equipment needs a large number of high performance and high reliability of hydraulic pneumatic and sealing components. According to preliminary calculation, it is estimated that the total domestic demand for hydraulic, hydraulic, pneumatic and sealing products will increase from 20 billion yuan in 2005 to about 35 billion yuan by 2010. Among them, hydraulic products increased from more than 10 billion yuan to 20 billion yuan, hydraulic products from more than 1 billion yuan to more than 2 billion yuan, pneumatic products from nearly 3 billion yuan to more than 5 billion yuan, and sealing products from more than 3 billion yuan to 7 billion yuan. Among them, construction machinery is the largest user of hydraulic products, accounting for 42.3 of the industry sales, and the proportion will be expanded in the future. Every year, the imported hydraulic parts for excavators, road machinery and cement mixer trucks produced by domestic enterprises amount to more than 150 million US dollars. In a word, the market of hydraulic and sealing parts for construction machinery and maintenance will face a new period of great development. In this trend of large demand, hydraulic and sealing parts need to have a better level of technology and innovation.
Because the hydraulic seal is immersed in the hydraulic oil for a long time, it is easy to swell, dissolve or embrittlement and harden, which makes it lose the sealing function. Therefore, it is required that the hydraulic seal has good compatibility with the hydraulic oil.
Low friction resistance
In order to avoid or reduce the low-pressure creeping and other undesirable phenomena of hydraulic equipment, the hydraulic seals are required to have low static friction resistance and dynamic friction resistance, and their friction coefficient should be very stable.
Long service life
Hydraulic seals should have good elasticity, heat resistance, cold resistance, pressure resistance, wear resistance and certain physical and mechanical strength, and have a long service life.
The hydraulic sealing parts should be easy to manufacture and install, and the corresponding sealing groove should be easy to process and manufacture. The machining accuracy of the sealing surface should be low and low-cost.
Hydraulic and pneumatic seals are molded according to operating temperature, cylinder speed, cylinder working pressure, working application and medium. They are usually non-metallic, very soft rings placed in the housing, or a mixture of rings arranged in a sealed unit. This is the separation or plugging of liquids in applications involving reciprocating motion. Hydraulic seal is very important in mechanical equipment. When liquids are converted to linear motion, their use is critical.
The wiper seal (also known as the scraper seal) is usually used in conjunction with other sealing components. Through a reciprocating rod hole, they are still allowed to pass through a reciprocating fit.
The piston seal ensures that liquid or other media will not flow around the piston because the system pressure pushes the piston down during the stress process. They are usually single acting seal, that is, the stress only acts on one side; double acting seal is that the stress acts on both sides.
Rod seal is considered as the most important part of cylinder seal structure. When the rods rotate back and forth, they prevent fluid leakage from the inside of the cylinder to the outside (dynamic stress seal). As a result, the rod seal works with the wiper seal to protect the hydraulic configuration from external contaminants, including dust, dirt, and the external atmospheric environment.
The wear ring is used to hold the piston in the center position. This makes the seal wear and stress distribution uniform. Wear rings are used for piston rod and piston unit.
Hydraulic technology has penetrated into many fields, and has been widely applied and developed in civil industry, machine tool, engineering machinery, metallurgical machinery, plastic machinery, agricultural and forestry machinery, automobile, ship and other industries, and has developed into a complete automation technology including transmission, control and detection. Nowadays, the degree of using hydraulic transmission has become one of the important signs to measure the industrial level of a country. For example, 95% of construction machinery, 90% of CNC machining centers and more than 95% of automatic lines in developed countries adopt hydraulic transmission technology.
Notes for maintenance users: when choosing the seal for maintenance, most users will purchase according to the size and color of the sample, which will only increase the difficulty of purchasing, and may not be able to select the appropriate product. The following procedures are recommended to improve the accuracy of purchased seals:
1. Direction of movement - determine the direction of movement of the seal location first, such as reciprocating, rotating, spiral or fixed.
2. Key points of sealing - for example, the rod seal with the moving point at the inner diameter or the piston seal with the movable point at the outer diameter, etc.
3. Temperature grade - check the operating temperature from the original machine instructions or evaluate the working temperature according to the actual working environment to determine the materials to be used. For the description of the temperature class, please refer to the following precautions for production users.
4. Pressure rating - refer to the relevant data from the original machine instructions, or infer the working pressure level by observing the soft hardness and structure of the original seal. For the description of the pressure level, please refer to the following precautions for production users.
5. Size - most users will choose from the used old samples, but the original size of the seal will be greatly affected by the factors such as temperature, pressure and wear after using for a period of time. The selection according to the sample can only be used as a reference. A better method is to measure the metal groove size of the seal location, which will have higher accuracy.