Analysis of Spring Washers

In the connection of mechanical components, spring washers play a crucial role, especially in preventing fasteners from loosening due to vibration. As a professional enterprise in the fastener industry, Jiaxing Haina Fastener Co., Ltd. has conducted in-depth research into the performance and applications of spring washers. Spring washers provide constant pressure to bolts and nuts, maintaining their tightened state and ensuring the stability of mechanical components during operation. Moreover, spring washers can handle impact loads, effectively cushioning shocks generated during mechanical operations and protecting components from damage. To help fastener professionals better understand and apply spring washers, this article presents a detailed analysis of spring washer deformation phenomena.

Force Analysis of Spring Washers During Bolt Tightening and Loosening

During the bolt tightening process, the bearing surface under the bolt head presses point A on the spring washer in the tightening direction. Simultaneously, the flat washer applies a clockwise force to point D of the spring washer in the same direction. Under the combined action of these forces, points A and C, as well as points B and D on the spring washer, eventually align on the same plane. At this point, the spring washer is flattened, indicating that the axial force applied to the bolt and flat washer by the spring washer has reached its maximum.

Conversely, during the bolt loosening process, the bearing surface under the bolt head pushes point A in the opposite direction of loosening, causing point A to embed into the bearing surface. Meanwhile, the flat washer pushes point D in the opposite direction of loosening, leading to point D embedding into the flat washer. Continued loosening is likely to result in the spring washer deformation phenomenon known as "washer expansion."

Causes of Spring Washer Expansion

1. Clearance Between Bolt and Spring Washer Hole Diameter:
   During manufacturing, the inner diameter of a spring washer typically exceeds the nominal diameter of the bolt thread, creating a gap. If the washer's inner diameter is on the high tolerance side and the bolt diameter is on the low tolerance side, the resulting clearance can lead to positional instability during installation. This contributes to washer expansion. Jiaxing Haina Fastener Co., Ltd. emphasizes the need to control this gap during production to mitigate the risk of instability.

2. Installation Orientation of the Connection Assembly:
   Spring washers installed horizontally are more prone to eccentric force due to gravity and gap issues. This increases the likelihood of washer expansion compared to vertical installations. Haina's technical experts recommend selecting the appropriate installation orientation to minimize risk.

3. Size of the Bearing Surface:
   If the diameter of the bolt or nut’s bearing surface closely matches the outer or inner diameter of the spring washer, outward forces during tightening can lead to washer failure. Haina optimizes the bearing surface dimensions to improve compatibility and reduce such risks.

4. Burrs at the Washer Cut:
   Burrs formed during the cutting process may embed into components during tightening, causing uneven stress and washer deformation. Haina utilizes advanced machining techniques to minimize burr formation.

5. Width of the Washer Cut:
   Excessive cut width can increase the likelihood of expansion during installation. Haina ensures strict control over equipment and tooling adjustments to maintain consistent cut widths.

6. Thickness of the Washer Cut Edge:
   Improper blade angles during cutting can cause thicker edges, making the washer prone to embedment and rotation during tightening. Haina controls cut edge thickness to avoid such issues.

7. Hardness of Flat Washers:
   Using low-hardness flat washers with high-hardness spring washers can exacerbate embedding and deformation. Haina advises matching flat washer hardness to the bolt grade for reliability.

8. Excessive Applied Load:
   Exceeding the load capacity of the spring washer can lead to deformation. Haina advises selecting appropriate bolts and tightening torque to prevent overloading.

9. Use of Pneumatic or Electric Tools:
   High-speed tools can cause increased impact forces, contributing to washer expansion. Haina recommends adjusting tool settings to reduce installation speed.

10. Interface Shape of the Washer Section:
    Different sectional shapes, such as "outer thick, inner thin," may increase expansion risks compared to standard "uniform thickness" designs. Haina ensures compliance with standard requirements for sectional shapes.

11. Surface Treatment of the Washer:
    Different surface treatments, such as galvanization, may influence washer performance. Haina advises selecting treatments based on the specific application environment.

The above factors often act together to cause washer expansion. This analysis, partially excerpted from the Fastener Standards Implementation Guide, 2nd Edition, aims to provide practical insights to reduce washer expansion issues and enhance the reliability and safety of mechanical connections.

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