Application and assumptions of engineering machinery sealing technology

At present, China’s construction machinery industry has introduced a large number of host design and manufacturing technologies from developed countries, and gradually adopted internationally advanced sealing system design concepts and sealing device application technologies. However, due to the constraints of the domestic industrial manufacturing level of seals, the application level of engineering mechanical sealing technology still lags behind the international advanced level by about 20-25 years. The normal working hours of the main engine without leakage are only about 400 hours, which is less than 1/10 of the international advanced level.

Application status: The product variety and quality of domestic seals still cannot meet the development and supporting needs of engineering machinery that introduces advanced manufacturing technology. In fact, there are nearly a thousand rubber and plastic seal manufacturers serving the construction machinery industry in China, but there are only more than 40 companies with good production conditions and technical capabilities. Among them, only 40 companies have strong technical capabilities and complete sets of advanced equipment. There are 7-8 (professional research institutes engaged in the production of military sealing products are not included). Despite this, the quality and service life of the sealing products produced by these enterprises still lag behind the advanced foreign levels. After the construction machinery and medium and high-pressure hydraulic parts industries introduced manufacturing technologies from world-renowned manufacturers such as Linde, Carter, Komatsu, Ceres, and Rexroth, the product variety and quality of domestic seals cannot meet the development of products with advanced manufacturing technologies. and supporting needs are examples. Secondly, there is a large demand for small-section U-shaped sealing rings (AU) for the lifting devices of dump trucks. Due to the poor quality of domestic sealing products, both OEMs and users purchase them from foreign companies.

Existing problems: The quality of seal products and the design and application level of sealing systems need to be improved.

1. Seal product quality Over the past 20 years, through the joint efforts of domestic scientific research and technical personnel, a complete national standard system for various seal installation cavities that is in line with ISO/TC131/SC7 has been established. At the same time, a national standard system for seals such as seal size series, seal performance indicators, seal appearance quality, seal packaging, storage, and transportation that is in line with international standards for various types of seals has been established. This facilitates the design and selection of seals for sealing systems of engineering machinery and other medium and high-pressure hydraulic machinery products. However, there are still many shortcomings in actual operation. The main reasons are that the industrial foundation is too weak, the quality and variety of raw materials are unsatisfactory, management work is not standardized, etc. The gap is particularly wide in the quality of products used for rotating oil seals for hydraulic pumps, hydraulic motors and gearboxes, and reciprocating seals for hydraulic cylinders. Regarding the service life of the drive axle wheel oil seal of the ZL50C loader, the author once conducted an installation comparison test. The inner frame oil seal with an auxiliary lip developed by a domestic unit was tested on the road after installation and began to leak after only 50 kilometers. At the same time, The BABSL oil seal of a foreign company that was used for installation assessment has not leaked after nearly 3 years of use. Another example: the quality of dynamic sealing components of engineering machinery hydraulic cylinders, foreign standards can meet 5,000 operating hours without leakage, while the service life of domestic seals is generally 1/10 of that, and some even less than 100 operating hours.

2. The design and application level of the sealing system The design and application level of the sealing system depend on the development capabilities of sealing products, which are mainly reflected in three aspects.

(1) Rotary dynamic sealing system At present, ordinary standard oil seals are still widely used. For rotary sealing devices with pressure requirements, only pressure-resistant oil seals with a pressure resistance of 1-3 MPa can be provided, while the international advanced level is 10 MPa. The application of hydrodynamic return oil seals has not been popularized in rotating sealing devices of engineering machinery.

(2) Hydraulic cylinder reciprocating dynamic sealing system At present, most domestic engineering machinery hydraulic cylinder dynamic sealing system designs still use U-shaped sealing rings as the main seal. The dynamic sealing system of engineering machinery hydraulic cylinders designed and produced in the mid-1990s began to adopt the composite design of coaxial sealing components and U-shaped sealing rings. The production process of the 5-component (or 3-component) hydraulic cylinder piston combined sealing assembly with a support ring, which is commonly used internationally, is relatively complex. At present, it is still in the stage of small batch production in China, and the quality stability is poor.

(3) Static sealing system In the static sealing system, although asbestos and plant fiber sealing products have been eliminated, the use of polymer liquid sealing gaskets is not yet popular. At present, such products used in China are still mainly various sealant products produced by Loctite Company. There are few product brands of domestic liquid sealants and anaerobic adhesives used for piping connections in hydraulic systems, and there are certain gaps in coating processes and quality performance. Outlook: China’s scientific research and medical seal manufacturing industry in sealing technology will face severe issues raised by engineering machinery and other medium and high-pressure hydraulic machinery industries. With the introduction of international advanced science and technology and manufacturing technology and the development trend of the national economy after 2000, China’s construction machinery industry, which relies on the introduction of advanced technology, will have greater development. The working pressure of the hydraulic system of engineering machinery and the advanced nature of the system ensure reliable operation. It will definitely promote the development of sealing system design and sealing component manufacturing technology. Therefore, China’s scientific research on sealing technology and seal manufacturing industry will face severe issues raised by the engineering machinery and other medium and high-pressure hydraulic machinery industries. It can be expected that by then, China’s sealing industry system will no longer be a small-scale farmer economy-style business model with high energy consumption, low efficiency, and complex structure, but will be a highly intensive, large-scale, low energy consumption, and high-efficiency business system. . By then, 60% of the main varieties of China’s seals will have reached the international quality level of the late 1980s and early 1990s, and another 15% of the product varieties will have reached the contemporary quality level of international seal products. The design and application level of sealing systems for China’s construction machinery and medium and high-pressure hydraulic machinery products will reach the international technical level in the mid-1990s. Background information: Four stages of application of engineering machinery sealing technology in China. The development process of engineering machinery sealing technology with rubber and plastic seals as the main application can be roughly divided into four stages.

1. Initial stage (1960-1970) During this period, the working pressure of the hydraulic system of China’s construction machinery products was roughly 12-14 MPa. The seals used in the sealing system include: 0-shaped rubber sealing ring (NBR); iron shell-cowhide rotating oil seal; corrugated steel skin + cork + metal spring end seal; asbestos packing; asbestos + rubber sealing gasket; V-shaped Sealing ring (cowhide + phenolic + bakelite); V-shaped sealing ring (NBR + fabric): soft sealing gasket, etc.

2. Entrepreneurship stage (1971-1980) The working pressure of the hydraulic system of the main products of China’s construction machinery produced during this period was roughly 14-3.5 MPa. The seals used in its sealing system are mainly rubber and plastic seals, eliminating the end face seals of cowhide, asbestos fiber, corrugated steel and cork. The main types D are: 0-shaped sealing ring (NBR, FKM); floating oil seal for crawler D chassis (metal ring dry 0-shaped diagram); D inner skeleton rotating oil seal Sichuan BR, FKM, ZACM). Hydraulic and pneumatic reciprocating seals include 0-shaped sealing rings (NBR, FKM); U-shaped dense shooting rings (NBR, AU, BU): V-shaped sealing rings (NBR ten-clip fabric); cup-shaped sealing rings ( NBR ten-clip fabric), etc. During the past 10 years, in order to meet the development needs of medium and high-pressure hydraulic technologies such as engineering machinery and forging machinery, the former Machinery Department established seven professional rubber and plastic seal production plants. In addition, in order to promote the development of China’s sealing technology, the “National Hydraulic and Pneumatic Standardization Technical Committee” and the “National Hydraulic and Pneumatic Standardization Technical Committee Rubber and Plastic Sealing Standardization Sub-Technical Committee” were established in 1975 and 1979 (similar to the old ISO/TCI3 /SC7 corresponding) and the Fluid Sealing Sub-Technical Committee of the Tribology Society.

3. Consolidation and development stage (1981-1990) The working pressure of the hydraulic system of the main products of domestic engineering machinery has reached 16-40MPa, and the seals used in the sealing system are still mainly rubber and plastic sealing products. The main types are: O-ring seals (NBR, FKM); floating oil seals for crawler chassis (O-shaped metal rings); sealing components for lubricated and sealed crawler tracks (NBR + AU): inner and outer skeleton rotating oil seals (NBR, FKM, ACM, EPDM); combined sealing gasket (NBR+metal); hydraulic cylinder piston and piston rod dynamic seal. Coaxial seal assembly for sealing (PTFE+NBR); dynamic hydraulic return oil seal for rotating shaft (NBR, FKM, ACM); and pressure-resistant rotary oil seal (NBR, FKM) with working pressure of 1-3 MPa; bidirectional medium rotary oil seal ( NBR, FKM), double-acting reciprocating D dynamic seal assembly with support ring for hydraulic cylinder piston (NBR + PTFE + POM), etc.

4. In the rapid development stage (after 1991), engineering machinery and other medium and high-pressure hydraulic industries have successively introduced a large number of product manufacturing technologies, promoting the entry of foreign seal merchants into the Chinese seal market. The entry of foreign funds and technology has improved the overall level of my country’s sealing industry.