Discussion: Technical Application of China-made Seals in Construction Machinery Industry

In fact, there are nearly a thousand rubber and plastic seal manufacturing companies serving the construction machinery industry in China, but there are only 40 companies with better production conditions and technical capabilities. Among them, companies with strong technical capabilities and complete sets of advanced equipment are only There are 7-8 (specialized institutes engaged in the production of military seal products are not listed).

In spite of this, the sealed products manufactured by these companies still have a more or less disparity with the advanced foreign standards in terms of quality and service life. After the construction machinery and medium and high pressure hydraulic components industries introduced manufacturing technologies from world-famous manufacturers such as Linde, Carter, Komatsu, Ziezi, and Rexroth, the product variety and quality of domestic seals could not meet the development of advanced manufacturing technology products. And supporting needs are examples. Secondly, for the lifting devices of dump trucks with a large demand, small-section U-shaped sealing rings (AU) are used. Because of the poor quality of domestic sealing products, both OEMs and users purchase from overseas companies.

Existing problems: The quality of the seal product and the design and application level of the sealing system need to be improved1. In the past 20 years, with the joint efforts of domestic scientific and technical personnel, the seal product quality has established a complete national standard system for the installation of seals with ISO/TC131/SC7. At the same time, it has also established a national standard system for seals, such as seal size series, seal performance index, appearance quality of seals, seal packaging, storage and transportation. Thus, the design and selection of seals for sealing systems of construction machinery and other medium and high pressure hydraulic machinery products are facilitated. However, there are still many shortcomings in the actual operation. The main reasons for this are the excessively weak industrial base, unsatisfactory quality and variety of raw materials, and unregulated management practices. The disparity is particularly high in the quality of products with hydraulic pumps, hydraulic motors and gearbox rotating oil seals and hydraulic cylinder reciprocating dynamic seals. For the service life of the ZL50C loader drive axle wheel oil seal, the author once made a comparison test of the installed machine, which was developed by a domestic unit with the oil seal of the inner lip of the auxiliary lip. After the installation, the road surface was tested and only 50km began to leak. The BABSL oil seal of a foreign company evaluated has not leaked in the past 3 years. Another example: engineering machinery hydraulic cylinder dynamic sealing element quality, foreign level can meet 5000 hours without leakage, while the domestic seal life is generally 1/10, and some even less than 100 hours.

2. Design and Application of Sealing Systems The level of design and application of horizontal sealing systems depends on the ability of sealed products to be developed, and is mainly manifested in three aspects.

(1) The rotary seal system is still widely used as an ordinary standard oil seal. For a rotary seal device with pressure requirements, it can only provide a pressure resistant oil seal with a withstand pressure of l-3 MPa, and the international advanced level is 10 MPa. The application of hydraulic oil return seals has not been popularized in rotary seals for construction machinery.

(2) Hydraulic cylinder reciprocating dynamic seal system At present, most of the domestic engineering machinery hydraulic cylinder dynamic seal system design still uses the U-shaped seal ring as the main seal. In the mid-1990s, the dynamic sealing system for hydraulic cylinders of engineering machinery designed and produced began to adopt a composite design of a coaxial seal assembly and a U-shaped seal ring. When the five-component (or three-component) hydraulic cylinder pistons commonly used in the world are combined with a supporting ring assembly seal assembly, the manufacturing process is relatively complicated. At present, domestic production is still in the stage of small batch production, and the quality stability is poor.

At present, the Chinese construction machinery industry has introduced a large number of host design and manufacturing technologies in developed countries, and gradually adopted the international advanced sealing system design concept and application technology of sealing devices. However, due to the constraints of the industrial manufacturing level of domestic seals, the application level of construction machinery seal technology still lags behind the international advanced level by about 20-25 years. The normal working hours of the host without leakage is only about 400 hours, which is less than 1/10 of the international advanced level.

Application status: The product variety and quality of the domestically-made seals still cannot meet the development and supporting needs of the construction machinery that introduces advanced manufacturing technology.