Research Papers: Design of Mechanisms and Robotic Systems

Effect of Ramp Angle on the Anti-Loosening Ability of Wedge Self-Locking Nuts Under Vibration

[+] Author and Article Information
Jianhua Liu

School of Mechanical Engineering,
Beijing Institute of Technology,
5 South Zhongguancun Street, Haidian District,
Beijing 100081, China
e-mail: jeffliu@bit.edu.cn

Hao Gong

School of Mechanical Engineering,
Beijing Institute of Technology,
5 South Zhongguancun Street, Haidian District,
Beijing 100081, China
e-mail: gongh0220@163.com

Xiaoyu Ding

School of Mechanical Engineering,
Beijing Institute of Technology,
5 South Zhongguancun Street, Haidian District,
Beijing 100081, China
e-mail: xiaoyu.ding@bit.edu.cn

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received September 28, 2017; final manuscript received April 19, 2018; published online May 23, 2018. Assoc. Editor: David Myszka.

J. Mech. Des 140(7), 072301 (May 23, 2018) (8 pages) Paper No: MD-17-1661; doi: 10.1115/1.4040167 History: Received September 28, 2017; Revised April 19, 2018

Recently, the wedge self-locking nut, a special anti-loosening product, is receiving more attention because of its excellent reliability in preventing loosening failure under vibration conditions. The key characteristic of a wedge self-locking nut is the special wedge ramp at the root of the thread. In this work, the effect of ramp angle on the anti-loosening ability of wedge self-locking nuts was studied systematically based on numerical simulations and experiments. Wedge self-locking nuts with nine ramp angles (10 deg, 15 deg, 20 deg, 25 deg, 30 deg, 35 deg, 40 deg, 45 deg, and 50 deg) were modeled using a finite element (FE) method, and manufactured using commercial production technology. Their anti-loosening abilities under transversal vibration conditions were analyzed based on numerical and experimental results. It was found that there is a threshold value of the initial preload below which the wedge self-locking nuts would lose their anti-loosening ability. This threshold value of initial preload was then proposed for use as a criterion to evaluate the anti-loosening ability of wedge self-locking nuts quantitatively and to determine the optimal ramp angle. Based on this criterion, it was demonstrated, numerically and experimentally, that a 30 deg wedge ramp resulted in the best anti-loosening ability among nine ramp angles studied. The significance of this study is that it provides an effective method to evaluate the anti-loosening ability of wedge self-locking nuts quantitatively, and determined the optimal ramp angle in terms of anti-loosening ability. The proposed method can also be used to optimize other parameters, such as the material properties and other dimensions, to guarantee the best anti-loosening ability of wedge self-locking nuts.

Copyright © 2018 by ASME
Topics: Vibration , Wedges , Thread
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Fig. 1

Schematic diagram of engagement between: (a) a wedge self-locking nut and a regular bolt and (b) a regular nut and bolt

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Fig. 2

Thread profile of a typical wedge self-locking nut along the axis within a pitch

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Fig. 3

Key dimensions of the wedge self-locking thread and the regular thread

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Fig. 4

Finite element mesh: (a) a wedge self-locking nut, regular bolt, and moving plate and (b) cross section of the threaded part

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Fig. 5

Relationship between residual preload and vibration cycle

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Fig. 6

Relationship between λt and vibration cycle

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Fig. 7

Change in preloads with an increase in vibration cycle under different initial preloads

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Fig. 8

Building different ramp angles: (a) the thread profile for a wedge self-locking nut and (b) nine typical types of ramp angle

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Fig. 9

Relationship between the threshold value of the initial preload and the ramp angle obtained based on FE models (it should be noted that the curves for sets 1 and 2 are identical)

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Fig. 10

Nine types of manufactured screw tap and wedge self-locking nut

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Fig. 12

Change in the preload with an increase in vibration cycles for three specimens with 30 deg wedge ramp (initial preload was 7 kN)

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Fig. 11

Junker test apparatus: (a) picture of the apparatus and (b) schematic of the test

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Fig. 15

Experimental results on the relationship between the threshold value of initial preload and ramp angle

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Fig. 14

Relationship between the slope value and initial preload

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Fig. 13

Experimental results of the preload change with an increase in the vibration cycle for different initial preloads



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