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Review and prospect of mechanical seal technology
Seals have a wide range of uses and are almost ubiquitous in various industries, so their varieties are particularly diverse. But in summary, it can be roughly divided into three categories, namely rubber seals, mechanical seals, and flexible graphite seals. In 1996, the total number of seals sold nationwide was about 1.4 billion, of which 457 million were rubber and plastic parts, accounting for 32.6%; The total sales revenue of seals is 545 million yuan, and rubber seals account for nearly half of the total sales revenue of seals. The construction machinery industry uses fewer mechanical seals and flexible graphite seals, with over 80% being rubber and plastic seals. Therefore, this article will focus on discussing rubber and plastic seals.
——The Development History of Sealing Technology in Chinese Construction Machinery——
The development history of China's engineering machinery sealing technology is basically the same as the entire development history of China's sealing technology, which can be roughly divided into three stages.
The first stage is the initial stage of the industry (1960-1980).
This period was also the initial development period of China's construction machinery. With the gradual formation and development of the construction machinery industry, the sealing technology and sealing component industry that are supporting construction machinery have also gradually formed and developed. From 1973 to 1979, sealing enterprises mainly engaged in supporting engineering machinery, such as Beijing Sealing Factory, Tieling Rubber Sealing Factory, Hebei Jingxian Plastic Sealing Factory, Shaanxi Xingping Sealing Factory, Jiangsu Yangzhong County Sealing Factory, Taicang Sealing Factory, Guangzhou Rubber Sealing Factory, Guanghan Changkong Rubber Sealing Factory, etc., were all established during this period, laying the foundation for the gradual formation of China's sealing industry. During this period, the sealing components of Chinese construction machinery were mainly rubber parts.
The second stage is the initial development period (1981-1990).
This period is the construction period of China's "Sixth Five Year Plan" and "Seventh Five Year Plan". During this period, there were two significant characteristics: firstly, China began to shift towards national economic construction as the center, and the speed of national economic construction gradually accelerated, driving the development of various industries such as construction machinery, and the demand for basic components such as seals rapidly increased. Secondly, this period coincided with China's reform and opening up since 1978. With the continuous opening of the country's borders, many products and technologies continue to enter China, and seals and sealing technologies are no exception starting to enter China. Polytetrafluoroethylene and rubber seals developed from this period. From then on, the development of engineering machinery seals mainly focused on rubber seals to rubber plastic seals. With the help of research institutions such as Shanghai Beijing Institute of Materials and Chemical Engineering, many manufacturers of polytetrafluoroethylene and rubber seals have rapidly emerged. Yangzhong County, Jiangsu Province is the most typical, with dozens of such seal production enterprises emerging successively. During this period, some larger and older seal production enterprises such as Qingdao Seal Factory and Nanjing 7425 Factory also began to produce large quantities of rubber and plastic seals. The largest seal production enterprise in China, Anhui Ningguo Zhongding Co., Ltd., was established during this period (1980-1981).
The third stage is the period of rapid and comprehensive development (1991 to present).
This period is the construction period of China's "Eighth Five Year Plan" and "Ninth Five Year Plan", as well as the high-speed development period of China's engineering machinery, automobile, and motorcycle industries. Not only has the demand for sealing parts increased exponentially, but also higher quality requirements have been put forward. The emergence of high-pressure hydraulic systems (above 20-40 MPa) and variable hydraulic systems has made it impossible for general seals to adapt. In this situation, many famous foreign sealing companies such as Xiaban Seal and Parker Seal from the United States, Honger Seal from Germany, and Freudenbeck Seal have successively entered the Chinese market. Chinese domestic enterprises have also joined ventures with well-known foreign sealing enterprises. So far, there are seven joint ventures in China's sealing industry. There are two largest companies among them: one is Anhui Ningguo Zhongding Co., Ltd., which formed a joint venture with Asia Strategic Investment Corporation in 1994 with 40% and 60% respectively. At present, the company has a relatively complete variety and specifications of sealing components, with annual sales exceeding 100 million yuan, ranking first in the industry. The other company is Qingdao Keeper Sealing Industry Co., Ltd., which is jointly established by "China Qingdao Sealing Industry Co., Ltd." (predecessor of Qingdao Sealing Factory), "Japan Keeper Co., Ltd." and "Japan Republic Materials Co., Ltd.". The company's annual sales of seals have approached 100 million yuan, making it one of the largest seal enterprises in China, second only to Zhongding Co., Ltd. At present, the annual sales revenue of these two joint ventures for seals accounts for a large portion of the market share in China's seal industry.
——The Current Status of Sealing Technology for Construction Machinery in China——
There are more than 1000 enterprises in China's sealing industry, including more than 300 rubber and plastic sealing production enterprises, including various forms of ownership such as state-owned, joint-stock, collective, and private, but only more than 40 have a certain scale. Among them, there are more than 10 large-scale enterprises, including Nanjing 7425 Factory, Guizhou Volkswagen Rubber Factory (mainly focused on brake seals), and Zigong Qinghua Seal Industry Company, in addition to the two largest backbone enterprises mentioned earlier, with annual sales revenue of over 30 million yuan. Among these more than 40 seal production enterprises, nearly 20 mainly produce rubber and plastic seals.
The product technology and quality level of these backbone enterprises are relatively high, but mainly for supporting automobiles and motorcycles. Due to its particularity, construction machinery mainly has large size specifications, high operating pressure, and harsh working conditions, which require special requirements for seals. Therefore, many enterprises mainly produce seals for construction machinery have emerged, including 11. In addition to the previously discussed Beijing Seal Factory and 8 others, there are also Zhejiang Haimen Rubber Seal Factory, Guangzhou Machine Tool Research Institute Seal Branch, and Shenyang Leather Assembly Factory, These enterprises have strong professionalism, but their scale is not as large as the top five backbone enterprises, and their annual sales revenue is generally between 3 million and 10 million yuan. These sealing enterprises have average technical level and cannot provide high-pressure and high-level sealing components, especially special sealing components with high requirements. For example, the combination skeleton oil seal required for the drive axle of LiuGong ZF joint venture company cannot be produced domestically in China.
——The Current Problems in China's Engineering Machinery Sealing Industry——
The sealing industry in China is a small industry that started relatively late. Although some have formed a certain scale after three five-year plans of technological transformation, technology introduction, joint venture and cooperative production, as well as the emergence of backbone enterprises mentioned earlier, due to China's thin foundation and poor foundation, coupled with the influence of the previous years of heavy emphasis on the main engine and light supporting equipment, the problem has not been fundamentally solved, far from keeping up with the development speed of various industries such as engineering machinery, There are many problems, mainly in the following aspects.
——Low technical level——
The entire sealing industry in China has a weak technical foundation and poor independent development capabilities. The several large-scale enterprises mentioned earlier have a certain level of technological foundation and development capabilities, but their focus is on the automotive and motorcycle industries. The dozen or so enterprises that mainly serve engineering machinery have relatively weak strength and low technical level.
The low level of technology is also reflected in scientific research. Most enterprises do not have any experimental equipment, let alone research on sealing mechanisms. Therefore, there is a technological disconnect between seal manufacturing enterprises and users. There are no decent samples or manuals that provide detailed information on the structural relationships and appropriate technical requirements of seals and accessories. While foreign companies provide seals, they also provide detailed installation and usage requirements. As long as they are done according to the requirements, the reliability and service life of the seals can be guaranteed. Some domestic seals also provide installation dimensions and requirements, but it may not be possible to do so according to their requirements, mainly because they have not undergone sealing mechanism research and reliability testing.
The low technical level is also reflected in the material aspect, with poor material assurance ability and lack of strong formula inspection and finished product inspection methods. Therefore, the material of the product is unstable, with good timing and time difference.
——Low product quality——
Chinese mechanical products, especially construction machinery, have long been plagued by oil leakage problems. Of course, the problem of oil leakage is complex and has many reasons, but the fundamental one is the quality of the sealing ring. The most commonly used sealing components for construction machinery include "O" type sealing rings, oil seals (mainly skeleton oil seals), and oil cylinder sealing rings (reciprocating motion). The "O" - shaped sealing ring has basically been in line with international standards through the GB3452.1 national standard formulated in 1982 and 1992, and domestically produced "O" - shaped sealing rings can basically meet the requirements. The biggest problem is the skeleton oil seal. Rotating skeleton oil seals for construction machinery are mainly used on gear oil pumps and transmission components. Taking loaders as an example, each machine requires at least 11 oil seals. Based on the annual production of 20000 loaders nationwide, more than 200000 skeleton oil seals are needed. Therefore, the amount of rotary skeleton oil seals used in the entire construction machinery industry is significant. At present, the vast majority of domestic loaders use domestically produced skeleton oil seals, which have poor reliability. During the six-month warranty period, about 7% of the pump's skeleton oil seals are damaged and need to be repaired and replaced due to oil leakage. During the six-month warranty period, almost all transmission components, especially the drive axle, have varying degrees of oil leakage. The host factory also wants to use imported high-quality skeleton oil seals, but due to the significant price difference, imported oil seals are about 5-10 times higher than domestic ones, which is difficult for the host factory to accept. With the continuous improvement of the level of construction machinery, domestic seals are no longer able to meet the requirements. Currently, users strongly demand that the "three leaks" issue be resolved as soon as possible. At the same time, China's exports of construction machinery are also increasing, so there is an urgent need for high-quality and reasonably priced skeleton oil seals. This kind of situation
In fact, the price is 1-2 times higher than the current domestic products, and the host factory can basically accept it.
The reciprocating sealing ring used in the oil cylinder is basically the same as the skeleton oil seal. Leakage of the oil cylinder sealing ring can cause downtime, increase costs, pollute the environment, and reduce production efficiency, which has received strong feedback from users. At present, many main engine manufacturers and large oil cylinder manufacturers that produce their own oil cylinders have gradually chosen imported or joint venture produced high-quality oil cylinder sealing rings. The sealing rings used for high-pressure and variable displacement pumps and variable displacement motors above 30MPa are currently mostly imported.
——Multiple, small, and scattered seal production enterprises——
As mentioned earlier, there are currently more than 1000 domestic seal production enterprises with an annual sales volume of 1.4 billion pieces, which is not as much as half of the annual sales volume of some world-class companies. However, the total annual sales revenue is only over 500 million yuan, with an average annual sales revenue of only 500000 yuan per company. The scale is too small to invest in technological transformation, let alone experimental research. We can only imitate each other, engage in price wars, and compete on low quality and low level. This situation urgently needs to be resolved.
