Tightening solutions for high-strength bolts in automobile chassis

Tightening solutions for high-strength bolts in automobile chassis

The automobile chassis is an integral part of the car and plays a crucial role in supporting the car, forming the overall shape of the vehicle, and accepting the engine power. Currently, the production and assembly of automobile chassis use many high-strength bolts, and the connection quality of these bolts is directly related to the safety of automobile driving. If the high-strength bolts appear loose, the vehicle will likely be damaged, overturned, and other accidents, jeopardizing the personal safety of passengers and drivers.

The various fasteners in the chassis are generally performance level 8.8 and 10.9-grade bolts or performance level 8 and 10-grade nuts. The critical connection points must use 10.9-grade bolts or performance level and 10-grade nuts. The surface treatment is generally chrome-free zinc-aluminum coated class. At the same time, anti-loosening bolts/nuts are often chosen, or anti-loosening measures are taken to design the connecting vice.

Factors affecting the anti-loosening performance of automobile chassis high-strength bolts.
High-Strength Steel Hex Head Screws with Material Certification： These screws come with a traceable lot number and a physical and chemical test report. Made from Grade 8 steel, they can be used in high-stress applications, such as valves, pumps, motors, and automotive suspension systems. They are at least 25% stronger than medium-strength steel screws. The zinc yellow-chromate plating resists corrosion in wet environments. The material meets SAE J429 specifications for quality. Dimensions meet ASME B18.2.1 specifications. Grade 8 steel hex head screws are marked with six radial lines. Length is measured from under the head.

Steel Heavy Hex Head Screws for High-Pressure Applications： These Grade B7 steel screws are nearly twice as strong as our stainless steel screws for high-pressure applications. Also known as pressure bolts, they meet the high-pressure and high-temperature regulations of ASTM A193 and are used to secure pressure tanks, valves, and flanges. Length is measured from under the head. Screws should be used with ASTM A194 nuts.

Partially threaded screws come with precise threaded and unthreaded portions, allowing you to place only the more muscular unthreaded portion (grip) in joints subjected to sideways forces.

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1. Bolt head structure

Automobile chassis threaded fasteners are more types according to the bolt in the form of anti-loosening that can be divided into ordinary hexagonal head bolts, hexagonal flange bolts, hexagonal head bolts, flat washer assemblies, hexagonal head bolts, spring washers, hexagonal head bolts and flat washer spring washer assemblies of five kinds. Due to the different head structures, the heads of the various bolts and connectors have a more significant difference in contact with the outer diameter. In general, the larger the outer diameter of the threaded head, the larger the contact surface area and the greater the friction torque of the bolt. There are fewer types of plate connections on the chassis, but the following design points should be noted.

a) The fitting dimensions of the plate thickness t and the shoulder distance a of the bolt should meet the requirements of the clamping thickness;

b) A sufficient supporting surface is required to ensure complete contact between the fastener and the connected part.

2. Spring washers

 Through mechanical simulation experiments on bolts with spring washers, it is found that spring washers are prone to slight local contact, small support surface, and easy pressure feed at the open end in threaded connections, which ultimately cause the axial force of the bolt to drop and the anti-loosening performance of the spring washer to decline. At the same time, the spring washer has an elastic effect that can, to a certain extent, compensate for the deformation of the connecting parts due to the reduction of the axial force; it can be seen that the spring washer for the automobile chassis high-strength bolts can play a specific role in preventing the loosening of the role of the spring washer.