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Advanced fasteners are the basis of high-end machinery manufacturing, and their functions can be described as "four or two." The value of fasteners on the surface only accounts for a few percent of the machinery industry. In essence, it adds much more value to key components and equipment. For example, automotive fasteners are fasteners with high economic value. Due to the high requirements for quality and reliability, China's production cannot fully achieve localization; the engine is used for key parts of engine connecting rod bolts and flywheel bolts. Wheel bolts, suspension bolts, etc., are important fasteners that are related to life and property safety. At present, 30% to 50% rely on imports. Although their manufacturing techniques have some similarities with general fasteners, their manufacturing and testing techniques, equipment, materials, management controls, etc. are all very different, and they are the highest and most concentrated embodiment of fastener technology. .
Heat treatment is the key technology to control fastener performance, ensure long life and safety and reliability, and is the core element of the competitiveness of advanced materials and high-end mechanical equipment. International fastener manufacturers that produce brand-name products have always attached great importance to the research and development of heat treatment technology. Through extensive investment, long-term accumulation and continuous improvement, we have mastered the unique heat treatment technology and kept it secret, and others can create geometric elements and precision. The same imitation, but the service life and reliability are hard to come by.

China has become a big manufacturing country. Although the scale of heat treatment has grown rapidly in the past 20 years, there are still decades of gaps in technology heat treatment technology with the world's advanced level, which has led to the emergence of bottlenecks in domestic high-end fasteners behind the mainframe.

Such as 10.9 high-strength bolts, quenching and tempering can greatly improve the tensile strength of the material, the specified non-proportional extension stress, improve the yield ratio and impact toughness, so that the material has a good fit of strength and plastic toughness. Due to the improvement of fatigue strength and impact toughness, a smaller material cross section can be used in the design of high-strength bolts, thereby reducing the overall weight of the whole machine and saving component space and energy consumption.

Commonly used low and medium carbon structural steels, low alloy structural steels, 20, 35, 45, 20MnTiB, 10B21, 10B33, 35CrMo, 40Cr, 42CrMo and 40CrNiMo steels can only fully exert the role of alloying elements through quenching and tempering treatment, not adjusted Quality is a waste of valuable resources.

GB/T3098.1-2010 "Fastener mechanical properties bolts, screws and studs" new standard release, stressing that the material requirements for grade 8.8 and above should have sufficient hardenability to ensure fastener thread cross section The core obtained about 90% of the martensite structure in the hardened state and before tempering. In fact, for fasteners with a diameter of 8.8 thread over 20 mm to ensure good hardenability, it is necessary to quench and temper the alloy steel material specified in the standard. For this reason, the metallographic examination has been rapidly developed in the fastener industry. The metallographic examination is not only to study the internal structure of the metal material by means of a metallographic microscope, but also to perform macroscopic inspection under the naked eye or a low magnification magnifying glass.

The main failure mode of high-strength bolts is fatigue, which is characterized by sudden failure without significant deformation. The key to solving the fatigue failure problem is heat treatment technology. Heat treatment not only gives the material ultimate performance and endurance performance of high-strength bolts, but also guarantees the service of high-strength bolts. Therefore, heat treatment of fasteners is very important. When some enterprises have problems with product quality in heat treatment, they think of the importance of heat treatment and the improvement of technology. It is not too late to make up for it.

After the quenching and quenching of the bolt, the performance can not meet the technical requirements, and the influencing factors can be multi-faceted. The quality analysis is a complicated process. It is only emphasized that the metallographic examination should pay attention to the adverse factors affecting the toughness, such as coarse grains, non-metallic inclusions, reticulated cementite, reticular ferrite, non-martensitic structures in quenched structures, and Tissue inhomogeneity caused by microsegregation in low-power detection, and the like.

The research on the relationship between the microstructure of steel materials and materials, processes and performance is a major issue that people have been working hard for over the past 100 years. The identification and analysis of organizational morphology (ie metallographic examination) is a highly practical discipline that requires practical experience, reference and reference. However, the microstructures of many materials are very similar, such as ferrite, carbide and retained austenite, low carbon lath martensite and feathery upper bainite, high carbon flake martensite. And needle-shaped lower bainite, etc., although the electron microscope can accurately judge and distinguish, but the rapid test of the actual requirements of production is often not allowed, which brings certain difficulties to the inspection work of the microstructure. In fact, many microscopic organizations will find their independent features under the light microscope as long as they are carefully and carefully observed. The purpose of the metallographic examination is to determine whether the quality of the finished bolts meets the relevant standards; on the other hand, to observe the distribution and nature of various defects, to analyze the causes of the defects and the various process factors for the quality. Impact, providing data for improved process and experimental research, is currently an indispensable means.

Do you know the importance of heat treatment of fasteners? Do you understand the relationship between metallographic examination and heat treatment? Will you analyze the fastener failure case by metallographic examination? September 27, 2013 (Friday) 9 am to 12 am, 2 pm to 5 pm; September 28 (Saturday) 9 am to 12 am. Hangzhou Golden Spider Training Center will hold a special seminar on “metallographic inspection technology and fastener failure cases”, which will be given by Zhang Xianming senior engineer.

Zhang Gong has been engaged in metal materials and metallurgical heat treatment processes in state-owned enterprises and private enterprises for a long time; he is especially good at technical work of mechanical basic parts such as fasteners, has rich experience in heat treatment field, and has certain unique views on the development and application of new materials and new processes. He has published more than 250 papers in national and provincial professional magazines, and has won several third prizes for provincial technical achievements. He is a special consultant for Golden Spider Fastener Network.

Contents of the special seminar: 1. Metallographic inspection technology and organization analysis (basis); 2. Metallographic examination of quenched and tempered; 3. Initial failure form and reasons of fasteners; 4. Discussion of high-strength bolt fracture cases; Interpretation of the latest metallographic inspection standards for fasteners; 6. Heat treatment of fasteners.

Questions that the course can solve:

1. Metallographic inspection technology, heat treatment defect analysis and product failure analysis preliminary

1. Metallographic examination basis

2. The basic technical basis of steel

3. Metallographic inspection technology and equipment

4. Metallographic examination of non-metallic inclusions of steel raw materials, basic organization in carbon steel and low alloy steel

5. Metallographic examination of structural steel

6. Metallographic analysis of fastener carburized surface after heat treatment

7. Analysis of heat treatment defects and preliminary analysis of failure analysis

Second, the metallographic inspection technology and heat treatment practice hotspot questions

1. Identification of ferrite and cementite

2. Identification of martensite and its tempering products

3. The difference between undissolved ferrite and pro-eutectoid ferrite

4. Identification of quenched torsite and tempered torsite

5. Identification of ferrite and retained austenite

6. Identification of carbides and retained austenite

7. Identification of lath martensite and upper bainite

8. Identification of flaky martensite and lower bainite

Time is not waiting for me, technological innovation is rare. For details, please pay attention to the Golden Spider Fastener Training Seminar held on the 27th of this month.

Do a good job in industrial planning, promote industrial upgrading

This article is transferred from: China Machine Network


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