In order to save cost, many people want to avoid flat washer or spring washer. In fact, flat washer and spring washer respectively play an indispensable role in the use of bolts. Today let’s introduce flat washer and spring washer to you.
Left flat washer, right spring washer

Flat washer, the shape is a flat washer commonly, there is a hole in the middle, basically is to use iron plate stamping out, so how to use flat washer and specific effect have you done understanding?

Flat washer how to choose?
Flat washer is used as a part to prevent bolt and nut from locking. Flat washers are used where fasteners are used. How to choose suitable flat washers? Flat washer is a kind of flat washer, mainly to increase the contact area of screws and some large equipment and fastening, in the use of flat washer, often suitable for nuts and nuts with each other, in the flat washer storage must be in the most effective sealing time, there are necessary important characteristics:
1, in the harsh environment, should be said to seal the flat washer, when a certain temperature and pressure in the working time is not easy to leak.
2, in the flat gasket and contact surface connection, to better ensure the sealing, just like the good effect.
3, when the gasket receives pressure under the influence of temperature, the anti-wrinkle ability should be better, otherwise it will make the screw damaged, there will be hard gas leakage.
4. Do not get infected when using flat washers.
5, the use of flat washer can be very good disassembly, which is the biggest role of the choice of flat washer.
6. Remember to use flat washers to ensure normal use at relative temperature.
In order to better use the flat washer, when choosing the flat washer, we should try to choose the flat  of washer-rust and anti-corrosion material immersion, which not only saves time and effort, but also can play a good role in the flat washer.
When used with bolts and nuts, the selection criteria of flat washers are as follows:
1. When choosing gasket materials, attention should be paid to the electrochemical corrosion of different metals in contact. The material of the flat washer is generally the same as that of the connected piece, usually steel, alloy steel, stainless steel, aluminum alloy, etc. Copper and copper alloys can be used when the electrical conductivity is required.
2. The inner diameter of the flat washer is selected according to the larger diameter of the thread or screw. The connected material is softer (such as composite material) or matches the larger diameter of the spring washer.
3. When the W washer is placed under the bolt or screw head, flat washer with inner hole chamfering can be used to avoid interference between the fillet under the head and the washer.
4. Steel washers should be used for important bolts with large diameters or to increase extrusion resistance. Tensile bolts or tensile shear composite bolts shall be connected with steel washers.
5, special gasket applied to special requirements of the parts, such as conductive copper gasket available; Available gaskets with air tightness requirements.
Function of flat washer:
1. Increase the contact area between screws and machines.
2, eliminate the spring washer when removing screws on the machine surface damage. The use must be: spring washer a flat washer, flat washer next to the machine surface, spring washer between the flat washer and the nut. Flat washer is to increase the force surface of the screw. Spring washer in order to prevent screw loose, the force plays a certain amount of buffer protection. Although flat MATS can make sacrifice MATS.
3. But more often it is used as a supplementary washer or flat washer.
Advantages:
(1) By increasing the contact area, parts can be protected from damage;
② By increasing the contact area, reduce the pressure between the nut and the equipment, so as to play a protective role.
Disadvantages:
(1) flat washer can not play the role of seismic;
(2) Flat washer also has no anti-loosening effect.
The role of spring washer
1. The function of the spring washer is to tighten the nut, and the spring washer gives the nut a spring force to tighten the nut, so that it is not easy to fall off. The basic function of the spring is to exert a force on the nut after tightening it, increasing the friction between the nut and the bolt.
2, generally do not use flat washer with spring washer, (in addition to the fastener and installation surface to protect the surface only consider using flat washer and spring washer).
3, flat washer is generally used in the connection of a soft texture, one is hard and brittle, its main role is to increase the contact area, disperse the pressure, to prevent the soft texture of the crushed.
Advantages:
The spring washer has good anti-loosening effect; ② Spring washer has better seismic effect; (3) Low manufacturing cost; The installation is very convenient.
Disadvantages: the spring washer is greatly affected by the material and process. If the material is not good, the heat treatment is not good or other processes are not done, it is easy to crack, so we must choose a reliable manufacturer.
When to use flat washers and when to use spring washers?
1, under normal circumstances, in the case of relatively small load, and do not bear vibration load, can only use flat washer.
2. In the case of large load and vibration load, flat washer and spring washer must be used.
3, the spring washer is basically not used alone, are used in combination.
In the actual use of the process, due to the different focus of the flat washer and spring washer, in many occasions the two are cooperate with each other, used together, so at the same time to protect parts, prevent nut loosening, reduce the advantages of vibration, is a great choice.
Application and failure form analysis of flat pad assembly bolt
According to statistics, there are hundreds and thousands of various types of fasteners used in an automobile, among which various types of flat washer combination screws are widely used in automobile fasteners.
1. Main functions of flat washer in assembly
1) Provide a bearing surface
When the bolt or nut support surface is not sufficient to cover the connector, the washer can provide a larger bearing surface;
2) In order to reduce the pressure of the supporting surface or make it uniform
When the area of the supporting surface is too small or the pressure of the supporting surface is too high, the washer can reduce the pressure of the supporting surface or make it more uniform.
3) Friction coefficient of stable supporting surface
When the flatness of the supporting surface of the connecting piece is poor (such as stamping parts), so that it becomes sensitive to the bite caused by local contact, which leads to the increase of the friction coefficient of the supporting surface, and the washer can stabilize the friction coefficient of the supporting surface;
4) Protect the supporting surface
When tightening bolts or nuts, there is a risk of scratching the surface of the connected parts, the gasket has the function of protecting the supporting surface;
2, flat pad bolt failure form
Failure mode of flat washer assembly bolt — interference between washer and round corner under bolt head
1) Failure phenomenon
An important failure mode of flat washer assembly bolt in application is the interference between washer and round corner of bolt head, which leads to abnormal torque and bad washer following during assembly.
The most intuitive manifestation of the interference between the washer and the fillet under the bolt head is that there will be an obvious gap between the washer and the support surface under the bolt head, which will lead to the failure of the bolt and the washer to fit properly when the bolt is tightened.

2) Failure reasons
The main reason for the interference between bolt washer and bolt head fillet is that the fillet under bolt head is too large or the design of washer inner aperture is too small and unreasonable. Lead to interference between gasket and bolt assembly.

3) Improvement measures
In order to reduce the risk of interference after bolt and washer combination, the design of bolt head can refer to the ISO 10644 standard for type U design under the head. In this way, interference problems caused by excessive fillet under bolt head or small washer aperture can be avoided.