Practical Application and Prospect of Sealing Technology for Construction Machinery

At present, China's construction machinery industry has introduced a large number of mainframe design and manufacturing technologies from developed countries, and gradually adopted the international advanced design concepts of sealing systems and application technologies of sealing devices. However, due to the constraints of the domestic manufacturing level of sealing parts, the application level of sealing technology for construction machinery still lags behind the international advanced level by about 20 to 25 years. The normal operating hours of the main unit without leakage are only about 400 hours, which is less than one-tenth of the international advanced level.

Application status: The product variety and quality of domestic sealing parts still cannot meet the development and matching needs of construction machinery that has introduced advanced manufacturing technologies.

In fact, there are nearly a thousand rubber and plastic sealing parts manufacturing enterprises serving the construction machinery industry in China. However, only about 40 of them have good production conditions and technical capabilities. Among them, only 7 to 8 enterprises have strong technical capabilities and complete sets of advanced equipment (professional research institutes engaged in the production of military sealing products are not included). Despite this, the sealing products produced by these enterprises still have more or less gaps compared with the advanced levels abroad in terms of quality and service life. After the construction machinery and medium and high-pressure hydraulic components industry introduced manufacturing technologies from world-renowned manufacturers such as Linde, Caterpillar, Komatsu, ZAI, and Rexroth, the fact that the variety and quality of domestic sealing parts could not meet the development and matching needs of the introduced advanced manufacturing technology products is a case in point. Secondly, for the small-section U-shaped sealing rings (AU) used in the lifting devices of dump trucks with considerable demand, due to the poor quality of domestic sealing products, both the main engine manufacturers and users purchase them from foreign companies.

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

1. Quality of sealing parts products

Over the past 20 years, through the joint efforts of domestic scientific research and technical personnel, a complete national standard system for various types of sealing installation cavities in line with ISO/TC131 / SC7 has been established. At the same time, a national standard system for sealing parts has also been established, which is in line with various international standards for sealing parts, including the size series of sealing parts, performance indicators of sealing parts, appearance quality of sealing parts, packaging, storage and transportation of sealing parts. Thus, it facilitates the design and selection of sealing components for the sealing systems of construction machinery and other medium and high-pressure hydraulic machinery products. However, there are still many drawbacks in actual operation. The main reasons are the overly weak industrial foundation, the unsatisfactory quality and variety of raw materials, and the non-standard management work, etc. The gap is particularly significant in the quality of rotary oil seals for hydraulic pumps, hydraulic motors and gearboxes, as well as reciprocating dynamic seals for hydraulic cylinders. Regarding the service life of the wheel edge oil seal of the drive axle of the ZL50C loader, the author once conducted an installation comparison test. The oil seal with a secondary lip and an inner skeleton developed by a domestic unit began to leak after being installed and tested on the road surface for only 50 kilometers. Meanwhile, the BABSL oil seal of a foreign company that was also installed and tested at the same time had not leaked after nearly three years of use. For instance, the quality of dynamic sealing components in hydraulic cylinders of construction machinery can meet the requirement of no leakage for 5,000 working hours at the international level, while the service life of domestic sealing parts is generally one-tenth of that, and some are even less than 100 working hours.

2. The design and application level of the sealing system

The design and application level of the sealing system depend on the research and development capability of sealing products, which is mainly reflected in three aspects.

(1) Rotating dynamic sealing system

At present, the common standard type 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 10MPa. The application of dynamic hydraulic return oil seals in the rotary sealing devices of construction machinery has not yet been widely adopted.

(2) Reciprocating dynamic sealing system for hydraulic cylinders

At present, the dynamic sealing system design of most domestic construction machinery hydraulic cylinders still adopts U-shaped sealing rings as the main seal. In the mid-1990s, the dynamic sealing systems for hydraulic cylinders of construction machinery designed and produced began to adopt a composite design of coaxial sealing components and U-shaped sealing rings. The 5-component (or 3-component) hydraulic cylinder piston combined sealing assembly with support rings, which is widely used internationally at present, has a relatively complex manufacturing process. Currently, in China, it is still at the stage of small-batch production, and the quality stability is poor.

(3) In static sealing systems, although asbestos and plant fiber sealing products have been eliminated, the use of liquid sealing gaskets made of high molecular materials is still not widespread. At present, the products of this type used in China are still mainly various sealant products produced by Loctite Company. There are relatively few domestic brands of liquid sealants and anaerobic adhesives used for pipe connections in hydraulic systems, and there are certain gaps in coating processes and quality performance.