Automotive Supply Chain Insights: Spring Washer Selection Guide: Ensuring the Reliability of Automotive Braking System Connections-Zhejiang Zhongrui Auto Parts Co., Ltd.

Spring washers in automotive braking systems are typically placed between the wheel bolt and the wheel hub, or between the wheel bolt and the wheel nut. Their main purpose is to provide continuous elastic pressure after the bolt is tightened, resisting vibrations generated during vehicle operation and braking, preventing the bolt from loosening, and thereby ensuring the reliability and safety of the connection between the wheel and the brake disc.

Specifically, when the wheel bolt is tightened, the spring washer is compressed. Due to its inherent elasticity, it continuously exerts an axial reaction force on the bolt, increasing the friction between the threads, thus effectively preventing the bolt from self-loosening when subjected to vibration or impact.

This guide will refer to the key loads and environmental factors experienced by wheel bolts to guide you in selecting the appropriate spring washers.

Load Capacity: Matching the Strength Grade of Bolts
While spring washers do not directly bear the main tensile and shear loads, their resilience affects the preload of the bolted connection, thereby indirectly affecting the overall strength of the connection. Therefore, the resilience of the spring washer should match the strength grade of the wheel bolts used.

According to DIN 127 B standards, common spring washers are suitable for bolts with strength grades up to 8.8. For higher strength grade wheel bolts (such as 10.9 or 12.9), it is recommended to use heavy-duty spring washers with higher resilience (such as DIN 127 A or Belleville spring washers according to DIN 6796).

Vibration Resistance: Maintaining Preload and Preventing Loosening
The strong vibrations generated during vehicle operation are one of the main factors causing wheel bolts to loosen. Suitable spring washers can provide continuous elastic force, compensating for small movements caused by vibration, thereby maintaining the preload of the bolts.

According to DIN 6796 standards, Belleville spring washers exhibit excellent vibration resistance due to their high elasticity and load-bearing capacity, making them particularly suitable for wheel connections subjected to large dynamic loads. Compared to ordinary split lock washers, Belleville spring washers can provide higher axial force under the same compression deformation, more effectively resisting preload reduction caused by vibration.

Fatigue Resistance: Adapting to Frequent Stress Cycles
The braking system frequently experiences alternating stress during vehicle operation, and long-term repeated loading and unloading can cause metal fatigue in wheel bolts and spring washers.

Spring steel is a common material for manufacturing high-quality spring washers due to its high elastic limit and fatigue strength. For example, spring steel conforming to EN 10270-1 standards can achieve fatigue strengths of several hundred megapascals after proper heat treatment. Selecting spring washers with excellent heat treatment and surface treatment, such as phosphating or Dacromet coating, can further improve their fatigue resistance, ensuring stable performance during long-term frequent braking.

Material Compatibility: Preventing Galvanic Corrosion
When dissimilar metals come into contact, especially in humid or road salt-containing environments, galvanic corrosion may occur. When selecting spring washers, it is necessary to consider the compatibility of their material with the wheel bolts, brake discs, and wheel components (usually steel or aluminum alloy) to avoid using incompatible metals that could lead to corrosion and weaken the connection strength.

For aluminum alloy wheels, it is generally recommended to use steel spring washers with special anti-corrosion treatments, such as Dacromet coating or zinc-nickel alloy coating. These coatings can provide salt spray resistance of over 1000 hours, effectively preventing galvanic corrosion between steel and aluminum. In addition, for stainless steel wheel bolts, it is recommended to use stainless steel spring washers to ensure the overall corrosion resistance of the connection.

Corrosion Resistance: Adapting to Harsh Environments
The wheel and brake disc connection area is often exposed to harsh environmental conditions, including rain, snow, road salt, and other corrosive substances. Selecting spring washers with sufficient corrosion resistance is crucial for ensuring long-term performance and safety.

Common anti-corrosion treatments for spring washers include zinc plating, hot-dip galvanizing, and Dacromet coating. Depending on the coating thickness and passivation process, zinc plating can provide salt spray resistance ranging from dozens to hundreds of hours. Dacromet coating and zinc-nickel alloy coating offer higher corrosion resistance and are suitable for more demanding environments. For applications requiring extremely high corrosion resistance, it is recommended to use spring washers made of 304 or 316 stainless steel, which can provide excellent rust resistance.

This guide aims to provide a basic selection framework, and in practical applications, please be sure to choose the appropriate spring washers based on the specific vehicle model, operating environment, and working conditions.

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