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A view of China's high-end bolt manufacturing technology from the passenger plane C919

The C919, a domestic passenger jet, took off from Shanghai's pudong airport. It is a high-tech aircraft in terms of aerodynamic shape and fuselage materials, so it has won many orders from airlines in the past two years.

But the origin of on the C919 has always been a controversial topic, some people think that the C919 is a total assembly platform, also some people think that he is self-independence of domestic, this small make up to has examined the distribution table, the supplier material such as the nose fuselage, the tail and wings are from China's chengdu sac and the shoulders, etc., a key part of the other are from foreign enterprises, such as engine, avionics, flight control, landing gear, etc., but the C919 remains a localization of the plane.

Because its overall design is completed by Chinese engineers, from the initial drawing design, aerodynamic shape, computational experiments to the final manufacturing and including system integration.Why does China have its own property rights?Because no one company can fully independent production in the world the various parts of the aircraft parts, including the famous Boeing and airbus, the industry's standard is: which country as long as the overall design, the manufacture of aircraft have self-independence of domestic, but the C919 is not without flaws, because he is adopted more than the counterparts of imported parts and materials, even the bolts are not domestic.

Why can't China make high-end bolts?

Bolt is the most widely used component in mechanical equipment at present, the commonly used bolt performance grade is divided into 10 kinds, among which the high-end bolt is also known as high strength bolt in 4 kinds, generally used in military industry, aviation, navigation and other fields.

China as a manufacturing power, the annual production and export large quantities of mid-range bolt, but high-end bolts are basically rely on imports, and imports also bolt price is 4 to 10 times, in Britain, for example, China's imported from Britain bolt unit price for $20718 a ton, but exports to the UK low-end bolt is only $1840 a ton, the unit price is 10 times.

This is because China has not yet mastered the technology of high-end bolts, so the import price is very high. The technology requirements of high-end bolts have four characteristics: corrosion resistance, high strength, small tolerance and the same tightening torque.

First of all, the processing technology is not good, the tolerance range is too large.The tolerance of high-end bolts should be controlled at 0.01 mm;Secondly, the surface treatment is not in place, the same type and specification of fasteners, even can not be replaced;

In the aviation industry, for example, planes can experience severe vibrations during takeoff and landing, and temperatures in the sky can reach nearly 100 degrees Celsius, accompanied by wind, frost, snow and turbulence, which could pose major safety risks if the bolts are not up to scratch.

What are the problems in the manufacture of high pressure bolts?It begins with his manufacturing techniques:

Bolt manufacturing, first of all to the diameter of the steel from the steel procurement standard, and then drawing processing, according to the different models and sizes of the bolt drawing to different diameter, in this respect China currently do not have what problem, domestic baosteel, taigang group can provide the high quality raw materials, in addition, the drawing mould and process don't is a world leading level.

The next step is the cold heading process for the bolts, which requires the use of a cold header, which breaks the bolts according to their length, and then goes through several steps to make the bolts unthreaded.These processes need to control key dimensions such as length and diameter, and the error needs to be controlled at the level of 0.01 mm.

This puts forward the superhigh request to the cold block machine, not only the accuracy is high, but also maintains the stability, it is equivalent to the bolt mold.However, the current situation in China is basically domestic, but the performance requirements can not meet the current high-end cold header, the Netherlands, the United States, Japan and Germany basically monopolized, the domestic cold block machine basically monopolized the low-end market.

The third process is the screw thread, will use the screw machine, this is also a key process, precision requirements are particularly high, but the high-end screw machine has been Europe and America and Japan monopoly, and heat treatment process, heat treatment related to the mechanical properties of bolts, so the temperature control requirements are very high, but also by foreign monopoly.

Finally, the bolt surface treatment, generally using electroplating, at present some professional domestic electroplating manufacturers can meet the specification requirements.

Above four working procedure, China currently only have two kinds, the remaining two working procedure, because there is no high precision equipment, furthermore China actually has the ability to make high precision bolt, but not for mass production, our country in the field of military aircraft carrier aircraft are bolts localization, this is because the demand is small, military field and high output, the traditional mechanical industry bolt demand is high, mass production can not be sure.

The C919 can also be made with domestic bolts, but China's aviation sector is still at the beginning stage, not afraid of 10,000, just in case, so simply import, China's industry started late, and there will be a certain gap with the west.In addition, the import of high-end bolts does not reflect the problem that Chinese standard parts cannot be manufactured,

However, many high-end industry precision equipment is still in the hands of the west, which will take a long time to make up for. Of course, China's high-end bolt manufacturing still needs to be paid attention to, so we can't stay in the middle and low-end industries, but move to the high-end field.

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