Whether To Add Washers For Bolted Connection?

Bolted connection -- without washer, as shown in Figure 1

      

When the bolts need to be removed frequently, in order to protect the surface of the connected parts from scratches, it is generally necessary to place flat washers at the positions of the nuts or bolt heads to prevent the surface of the connected parts from being scratched, especially for the surfaces that are precisely machined.

In some joints where the friction coefficient is required to be more accurate, there is no separate test requirement for the friction coefficient. For example, in wind power bolt connection, the connection mode of (bolt connection pair) is generally adopted (one bolt, one nut, two washers).

In this case, the bolts, nuts and washers are all provided by the same manufacturer. The bolt manufacturer needs to treat the nuts and washers accordingly to ensure the consistency of the friction coefficient between the nuts and washers. At the same time, the supplier is required to test the torque coefficient to meet the technical requirements.

When the bolt strength is high and the allowable compressive stress of the connected piece is low. For example, the requirements for lightweight of automobiles are becoming higher and higher. Lightweight connection technologies and structures are widely used on vehicle bodies and even chassis structures. In order to reduce the compressive stress of the pressure bearing surface of the connected parts in bolted joints and prevent crushing and permanent plastic deformation, flat washers are generally required.

In addition, in bolted connection, the pressure transmission on the pressure bearing surface of the bolt head or nut is gradually expanded in a trumpet shape. The larger the pressure bearing surface is, the smaller the compressive stress will be. Therefore, the addition of flat washers can reduce the compressive stress on the contact surface of the connected parts to ensure the effectiveness of bolted connection.

For the connection requiring sealing, the stress distribution diameter of the stress cone on the joint surface is increased. In this way, the sealing effect can be ensured by adding gaskets, as shown in Fig. 4.

Figure 4

     

In some cases, for example, most cars use stamping parts and welding parts, and the position of the hole between the two parts cannot match accurately.

In order to ensure that the bolt holes between two connectors can be one-to-one corresponded, we need to increase the diameter of the hole to compensate for the position deviation of the hole. When the bolt hole exceeds the standard requirements, the compressive stress exceeds the strength of the material, in this case, flat washers need to be added.

Sometimes, for the convenience of installation and adjustment, for example, when the control arm bracket is connected with the control meter, one of the bolt holes of the two bolt connections will be made into a long hole, so that the installation position of the workpiece can be adjusted within a certain range. When using a long hole, a thickened flat washer must be used, more specifically, or even a special washer or multiple washers can be used.

      

The main purpose of spring washer is to relax, and it is generally used in situations where the pre tightening force of bolts is not high and the dynamic load is small. At present, a large number of tests have confirmed that the spring washer is not effective in preventing looseness. Therefore, it is not recommended to use spring washers for tightening occasions with high preload and important connections.

However, for the electrical connection connector, the spring washer still has a certain effect when it is finally completely loosened, especially when it is loosened to a certain extent, and there is still a certain preload when the preload is small. At this time, it can still play a certain role compared with the effect without the spring washer.

When the clamping length of the bolt is short, the stress relaxation of the bolt is obvious, and the spring washer can compensate for the stress relaxation. Of course, at this time, it can be considered to use the belleville spring instead of the spring washer, and the belleville spring can be more evenly distributed in the axial pressure.

Some experiments show that under the dynamic load condition, the spring washer of high-strength bolt connection has almost no anti loosening effect, and will also cause the rapid attenuation of bolt clamping force. Therefore, spring washer has been rarely used in high-strength bolt connection abroad.

• The connection of shear stress bearing bolts (reamed bolts) generally does not require washers. First, the shear stress bearing bolts do not require too much preload, and do not bear axial force during operation. In this case, the bolt holes are generally small, and the bearing surface of nuts or bolt heads is generally large, so the connected parts can bear without reducing the compressive stress.

  
  

• When flange nuts or bolts are used, because the contact area of flange bolts or nuts is large, gaskets are usually no longer needed to increase the contact area and reduce the compressive stress.

For Jinrui, whether you are a fastener demander/dealer/supplier, you can visit the official website of Jinrui for more information:http://www.jinruibolt.com/

Part of Jinrui's product display

      

Jiangsu Jinrui Metal Products Co., Ltd. is the production base of Shanghai Jinrui standard parts. The factory covers an area of more than 20000 square meters, with a registered capital of 50 million yuan, a total investment of more than 100 million yuan, and an annual output of more than 20000 tons. Its products are exported to more than 40 countries.

Since its establishment in 2001, Jinrui Company has developed into a new layout with Hai'an in Jiangsu as its production base and Baoshan in Shanghai and Nanyang in Henan as its sales centers after more than 20 years of unremitting efforts.

At present, Jinrui's main products include the following six categories:

1. The main products of bolts include metric and American round head oval neck bolts (also called fishtail bolts), internal and external hexagon bolts, hexagon flange bolts, carriage bolts, wheel hub bolts, etc

2. Stud products: full thread thread, double head studs, etc

3. Nut products: hexagon nut, flange nut, heavy nut, square nut, butterfly nut, etc

4. Screw products: self tapping screws, self tapping self drilling screws, wood screws, various machine screws, etc

5. Washer products: flat washer, spring washer, square washer, lock washer, etc

6. Fastener related non-standard products

The wire drawing plant under Jinrui Company also provides processing services such as fine drawing, rough drawing and spheroidizing of wire rods, and supplies finished wire rods of various domestic famous steel mills.

Adhering to the business philosophy of "pioneering and innovation, pursuing excellence", Jinrui has successively introduced multiple types of heading and forming machines, thread rolling machines, nut machines, hot heading and rolling machines, lathes, large hot heading machines and their supporting testing equipment, such as magnetic particle flaw detectors, metallographic analyzers, salt spray testing machines, direct reading spectrometers and optical screening machines, tensile machines, Vickers hardness meters, Rockwell hardness meters, etc., and has set up independent research and development departments, It can produce all kinds of high-quality fasteners such as GB, DIN, ANSI, JIS and ISO international standards. The products are widely used in petroleum, chemical industry, boiler, wind power generation, highway guardrail board, elevator guide rail, machinery manufacturing, construction sites, auto parts, medical equipment and other fields.

Jinrui has been developing vigorously since its establishment. It integrates the advantages of each company, carefully designs and strictly selects materials to make the products more durable, and is highly praised by the majority of users. Jinrui won the ISO9001: 2000 international quality system certification in 2001, the special equipment manufacturing license in 2010, and the TS16949 automobile quality management system certification in 2012. The People's Insurance Company of China underwrites the "Global Product Liability Insurance" for its products, ensuring that every screw can be used with confidence, determination, and peace of mind!

Whether now or in the future, Jinrui will always adhere to the core service concept of "quality first, science and technology for enterprise development, customer first, and considerate service", sincerely provide you with high-quality services and high-quality products, and Jinrui will also become your most loyal long-term partner

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