The welding core is the metal core of the welding rod, in order to ensure the quality and performance of the welding seam of Hexagon Socket Head Bolt.

The welding process performance of the electrode refers to the various characteristics of the electrode during the entire welding process. The welding process performance of the electrode has the following requirements:

(1) The welding arc can burn continuously and stably, and it is easy to start the arc again.
(2) The coating of the electrode can be evenly melted during the welding process, and there will be no lumps or falling off. The sleeve formed at the front end of the coating should not hinder the uniform melting of the welding core.
(3) The slag has good fluidity, can evenly cover the weld, the weld is well formed, and the weld slag is easy to remove.
(4) There should be no excessive smoke or excessive splash during welding.
(5) When the electrode is welded within the specified current range, there is no phenomenon of cracking, serious redness and generation of pores in the coating.
(6) The weld metal of China Fasteners Suppliers is not allowed to have cracks, continuous or dense pores and inclusions.

1. Users of Hexagon Socket Head Bolt must be trained before using the product. The main purpose is to be able to use the product correctly and ensure safety;

2. In different occasions and different application scenarios, it is necessary to reasonably select the correct model, grade and length of Hexagon Socket Head Bolt, and select the appropriate product reasonably;

3. Each Hexagon Socket Head Bolt must be carefully inspected before use to check whether it is damaged or deformed. If there is damage or deformation, it must be replaced immediately;

4. The Hexagon Socket Head Bolt must be screwed to closely fit the supporting surface, tools are not allowed to be tightened, and the thread and threaded mouth must be tightly matched;

5. For different models of Hexagon Socket Head Bolt, the lifting direction should be designed within the range of the force direction. For details, please refer to its standard. For example, Hexagon Socket Head Bolt has different standards such as national and American standards, as well as different material grades. So make sure it is within its force range;

6. The maximum lifting weight of the Hexagon Socket Head Bolt is the rated load, and it cannot be overloaded, otherwise it will have other serious consequences;

7. If the Hexagon Socket Head Bolt of China Fasteners Suppliers is found to wear more than 10% of the interface diameter during use, it must be stopped. If it continues to be used forcibly, various safety accidents are prone to occur, so special attention must be paid.

Heat treatment refers to a metal hot working process in which the material is in a solid state, through heating, heat preservation and cooling to obtain the desired structure and performance. In the process from the Stone Age to the Bronze Age and the Iron Age, the role of heat treatment is gradually recognized. The following China Custom Bolt Wholesaler - Zhejiang Weigao introduces the following four points in the heat treatment of standard parts, so the products produced must be of high quality.

1. Hardness and strength

In the detection of Hexagon Socket Head Bolt, it is not easy to check the relevant manual based on the hardness value and convert it to the strength value. There is an influence of hardenability factors. Because the national standard GB3098.1 and national standard GB3098.3 stipulate that the arbitration hardness is measured at 1/2 radius of the cross section of the part. The tensile sample is also taken from the 1/2 radius. Because it is not excluded that there are low hardness and low strength parts in the center of the part. Generally, the hardenability of the material is good, and the hardness of the cross section of the screw can be evenly distributed. As long as the hardness is qualified, the strength and guaranteed stress can also meet the requirements. However, when the hardenability of the material is poor, although the hardness is qualified according to the specified parts, the strength and guaranteed stress often fail to meet the requirements. Especially when the surface hardness tends to the lower limit. In order to control the strength and ensure the stress within the acceptable range, the lower limit of hardness is often increased. For example, the hardness control range of grade 8.8: 26-31HRC for specifications below M16, 28-34HRC for specifications above M16; 36-39HRC for grade 10.9. Level 10.9 or higher is another matter.

2. Decarburization and carburization

In the production process of mass heat treatment, the metallographic method or the micro-hardness method can only be selected at regular intervals. Because of its long inspection time and high cost. In order to judge the carbon control situation of the furnace in time, spark detection and Rockwell hardness test can be used to make a preliminary judgment on decarburization and carburization. Spark detection is to harden the hardened parts and grind the sparks on the grinder from the surface and the inside to determine whether the carbon content of the surface and the core is the same. Of course, this requires operators to have skilled skills and spark identification capabilities. Rockwell hardness testing is performed on one side of the hexagon bolt. First, lightly polish a hexagonal plane of the quenched parts with sandpaper, and measure the first Rockwell hardness. Then grind the surface to about 0.5mm on the grinder, and measure the Rockwell hardness again. If the hardness values ​​of the two are basically the same, it means neither decarburization nor carburization. When the previous hardness is lower than the latter hardness, it indicates that the surface is decarburized. When the hardness of the previous time is higher than that of the latter time, it indicates that the surface is carburized. Under normal circumstances, when the hardness difference between two times is within 5HRC, when the metallographic method or microhardness method is used to check, the decarburization or carburization of the part is basically within the acceptable range.

Nanjing Standard Parts

3. Inspection of hydrogen embrittlement

The sensitivity of hydrogen embrittlement increases with the strength of the standard parts. After plating, external Hexagon Socket Head Bolt or surface hardened self-tapping screws and combination screws with hardened steel washers should be dehydrogenated. Hydrogen removal treatment is generally carried out in an oven or tempering furnace at 190-230°C for 4 hours or more to allow hydrogen to diffuse out. The Hexagon Socket Head Bolt can be screwed on a special fixture and screwed to a tensile force that allows the screw to bear a considerable guarantee stress for 48 hours. After loosening, the Hexagon Socket Head Bolt does not break. This method serves as an inspection method for hydrogen embrittlement.

4. Re-tempering test

The bolts, screws and studs of grades 8.8-12.9 shall be subjected to the re-tempering test according to the actual production with a minimum tempering temperature lower than 10℃ and holding for 30 minutes. On the same sample, the difference between the average of the three-point hardness before and after the test shall not exceed 20HV. The re-tempering test can check the incorrect operation due to insufficient quenching hardness and tempering with too low temperature to barely reach the specified hardness range to ensure the comprehensive mechanical properties of the parts. Especially Hexagon Socket Head Bolt made of low carbon martensitic steel adopts low temperature tempering. Although other mechanical properties can meet the requirements, the residual elongation fluctuates greatly when measuring the guaranteed stress, which is much larger than 12.5um. Moreover, under certain conditions of use, a sudden fracture may occur. In some automotive and construction bolts, sudden fractures have occurred. When the lowest tempering temperature is adopted for tempering, the above phenomenon can be reduced. However, when making 10.9 grade bolts with low carbon martensitic steel, special care should be taken.

Hexagon Socket Head Bolt is a common Hexagon Socket Head Bolt connection part in our lives, ranging from small screws on watches to large mechanical parts or aircraft bolt and nut connections. The use range of Hexagon Socket Head Bolt is very extensive, but in the process of using it, will you encounter some misunderstandings, for example, if we don't have fine-tooth bolts, can we replace coarse-tooth bolts? When using Hexagon Socket Head Bolt, the common misunderstandings are mainly the following, I hope to help everyone.
What are the misunderstandings when using Hexagon Socket Head Bolt, how much do you know?

1. Use coarse teeth instead of fine teeth

There are many important connectors on the machine, such as the drive shaft, etc. Most of the bolts are fine-threaded. If parts are missing during maintenance, some maintenance personnel will use coarse-tooth bolts instead, which should be avoided.

Because the fine-diameter bolt has a large inner diameter, a small pitch and an external angle, high strength, good self-locking performance, and strong ability to withstand shock, vibration and exchange loads. Once replaced with coarse-tooth bolts, it is easy to loosen or disengage, disassemble, and even cause mechanical accidents.

2. Poor pores

The bolts on the machine that are subjected to lateral loads and shear forces, such as drive shaft bolts and flywheel bolts, have a transitional fit with the bolt holes. The assembly should be strong and reliable, and can withstand lateral forces. Someone did not pay attention to the inspection during the assembly process, and continued to install when there was a large gap between the bolt and the bolt hole, which was easy to loosen or cut off the bolt.

3. Thick nuts increase connection reliability

Some people mistakenly believe that thickening the nut can increase the number of working cycles of the thread and improve the reliability of the coupling. But in fact, the thicker the nut, the more uneven the load distribution among the threads of the circle, the easier the coupling is to loosen.

4. One mother and more pads

After the installation is completed, sometimes the bolts are too long, so some people will install additional spring washers on the bolts.In this case, the spring washers will be unevenly broken during the process of solidification, which will cause the bolts to be pre-prepared. Decreased tightening force may also produce eccentric loads, reducing the reliability of bolted connections.

5. The tighter the better, the better

Many staff members have the misunderstanding that they think that the bolts should be “tightened rather than loosened”, so they deliberately increased the tightening torque, which resulted in the bolt slipping. In addition, there are some important bolts that need to be tightened with torque, but some people use an adjustable wrench to save the trouble. As a result, the torque is insufficient, resulting in loose bolts and even causing mechanical failure.

6. The washer is too large

Sometimes a properly sized washer is missing, and some workers will replace it with a larger inner diameter washer.In this case, the contact area between the bolt head and the washer is small, which will reduce the bearing pressure or locking force of the washer. There is vibration and shock in it, and the bolt is easy to loosen.

7. Improper locking

Important bolts should be locked with anti-loosening devices after assembly. There are four cases to illustrate here. If cotter pins are used for locking, do not use too thin cotter locks or half-piece cotter locks for locks; if spring washers are used for locks, the gap of the gasket openings must not be too small; if lock plates are used for locks, the lock plates must not be locked at The corners of the nuts; if double nuts are used for locking, the thinner nuts must not be installed outside.

8. False and strong

If the bolts, nuts or threads of China Fasteners Suppliers are rusted, or impurities such as scale, iron filings, etc., they must be cleaned before assembly; the joint surface of the coupling parts have burrs, sediment and other impurities should also be removed. Otherwise, when tightening the bolts, the surface seems to be tightened, but in fact the coupling is not really compressed. Under such false solidity, if the vibration, load shock and temperature change occur, the bolt will quickly loosen.

The plastic index required by Hexagon Socket Head Bolt, the higher the performance level, only the higher grade materials can achieve. The lower grade materials can only meet the strength requirements by reducing the tempering temperature, but they cannot meet the plasticity and toughness requirements. In the test, the brittle fracture was judged as unqualified. The steel structure bolt also stipulates the highest tensile strength, which is to ensure the plastic toughness of the bolt. According to the construction process, it is divided into torsion-shear type high-strength bolts and large hexagon high-strength bolts. The large hexagonal high-strength bolt belongs to the high-strength level of ordinary screws, while the torsional shear type high-strength bolt is an improved type of the large hexagonal high-strength bolt, for better construction. The construction of high-strength bolts must be first tightened and then finalized. The initial tightening of high-strength bolts requires impact-type electric wrenches or torque-adjustable electric wrenches; while the final tightening of high-strength bolts has strict requirements, the final twisting of high-strength bolts must use torsional shear Type electric wrench, torque type high-strength bolts must be used to finalize the torque type electric wrench. Ordinary bolts can be divided into three grades A, B, and C according to manufacturing accuracy. Grades A and B are refined bolts, and grade C is rough bolts. For connecting bolts for steel structures, unless otherwise specified, they are generally ordinary coarse grade C bolts. ①The bolts of class A and B bolts are processed by lathes with smooth surface and accurate size. The material performance level is 8.8. The production and installation are complicated and the price is relatively high. It is rarely used; ②C class bolts are made of unprocessed round steel The size of the material is not accurate enough, and the material performance level is 4.6 or 4.8. The deformation during shear connection is large, but the installation of China Custom Bolt Wholesaler is convenient and the production cost is low. It is mostly used for temporary connection during tensile connection or installation.