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Analysis of screw anti-loosening program. Washers are not a panacea
Do I have to use washers to prevent the screws from loosening?
Ms. Wan told the author that in early September 2011, she spent more than 2,400 yuan to buy a Lijie brand electric car in an electric car store on Hongcheng Road, Nanchang.
On May 10, 2012, when she was riding on Yingbin Avenue, the front of the car suddenly jumped forward, and she fell down immediately. After she got up, she found that her mouth was full of blood and her teeth were tingling. After returning to her senses, she realized that three teeth had been broken. The next day, accompanied by her family, she came to the hospital for treatment. The doctor told her that dentures can be installed after the swelling is reduced, and the cost is about 4,500 yuan.
Why did the accident happen suddenly? The Lijie electric car after-sales staff who came to the door later gave the answer and the front fork was loose. Later, Ms. Wan and others discovered that none of the front fork screws of the Lijie electric vehicle had spring washers installed. They believe that the manufacturer did not install anti-loosening spring washers for the front fork, which caused the screws to loosen very easily.
This car is indeed not equipped with a spring washer at the front fork position, and the pad is ugly. The relevant person in charge of the Lijie electric vehicle manufacturer stated that there is no need to install gaskets, and the effect is actually no difference. It has been 8 months, and the car has not been maintained at any time. The person in charge said that there is a process for screw loosening. If the after-sales department maintains it in time, accidents will not occur.
However, will the spring pad be sure to prevent it from loosening? Let’s take a look at the anti-loosening principle of the spring washer: Since the spring is not flat, elasticity is produced by squeezing and flattening. An axial force is exerted on the connecting body of the nut and bolt to increase the friction between the threads to prevent loosening. Effective, but in the case of vibration, the inclined surface of the thread forms a cut surface, and the nut and bolt move relative to each other, so that the anti-loosening of the spring washer fails.