Spring washers are widely used in both load-bearing and non-load-bearing structures of general mechanical products. Their characteristics include low cost, easy installation, and suitability for frequently assembled and disassembled components.
Spring Washers Introduction
In the screw industry, spring washers are commonly referred to as “elastic pads” or “spring pads”. They are made of either stainless steel or carbon steel (which is essentially iron). The commonly used sizes for spring washers are M3, M4, M5, M6, M8, M10, M12, M14, and M16. These sizes are widely used in the industry. The national standard for spring washers is GB/T 94.1-87, which specifies the standard type of spring washers with sizes ranging from 2mm to 48mm.
Main Material of Spring Washers
Typically made from 65MN spring steel or 70# carbon steel, 3Cr13, materials such as stainless steel SUS304 or SUS316, as well as phosphor bronze can also be used.
Main Applications of Spring Washers
Spring washers are used to prevent nuts from loosening and this is specified in the national standard. Hexagon slotted nuts are specifically designed to be used with bolts that have holes at the end, so that a cotter pin can be inserted from the nut’s slot into the hole in the bolt, preventing the nut from automatically loosening. This type of nut is mainly used in situations where there are vibrational or alternating loads.
In mechanical design and manufacturing, there are several methods to prevent nuts (or bolts) from loosening automatically:
- Adding spring washers (simple and easy to do)
- Using hexagon slotted nuts with cotter pins (adds extra processing steps)
- Adding anti-loosening washers (adds extra processing steps)
- Inserting a steel wire into the hexagon head of a hexagonal bolt (adds extra processing steps)
Spring washers are commonly used to prevent loosening, for example, bolts that connect motors to machine bases generally require spring washers because if there is no spring washer, the nut will loosen due to motor vibrations.
Fasteners on equipment that is subject to vibration generally have spring washers installed on them, while flanges typically do not require washers. Whether or not to use spring washers on flanges depends on the fluid medium being used. If there is a risk of pulsation or if the fluid is flowing at high speeds or if there are frequent changes in diameter, spring washers should be used.
It is important to note that this may not apply in all cases, as some valves and filler box pressure cover flanges may require spring washers. Quick and easy selection of spring washers is available through the Fastener Expert automated system.
Spring washers can prevent loosening and increase preload force, whereas flat washers do not have this function. Flat washers are used to increase the contact area of the fastening and prevent friction between bolts and workpieces, protecting the surface of the connection and preventing scratches when tightening bolts and nuts.
However, for some important connections that rely mainly on compression to transmit frictional force, spring washers cannot be used as they reduce the rigidity of the connection and may lead to accidents. In such cases, flat washers or flange bolts can be used to increase the contact area. When there is vibration, pulsation, or large temperature fluctuations in the medium, spring washers must be used.
Causes of Spring Washer Fracture
- Spring washers experiencing “swelling” is generally not an issue with the spring washers themselves.
- A spring washer that experiences swelling has necessarily been subjected to a radial outward force, which comes from the axial clamping force produced by the tightening torque.
- The outer chamfer on the nut support surface produces a radial splitting force, causing the opening of the spring washer to enlarge. The smaller the diameter of the chamfer, the greater the likelihood of swelling occurring.
- Placing a flat washer between the nut and spring washer helps to slow down or prevent swelling, but if the flat washer is too thin or soft, it may not prevent swelling.
- The cause of hydrogen embrittlement fracture in spring washers is generally due to an unreasonable heat treatment process or failure to perform hydrogen removal treatment after zinc plating.
Extensive testing and long-term practical experience have confirmed the above analysis.
Classification of Spring Washers
Internal toothed elastic washer, external toothed elastic washer
There are many sharp elastic teeth on the circumference, which pierce the supporting surface and prevent the fastener from loosening. The internal toothed elastic washer is used under the smaller head size of the bolt; the external toothed elastic washer is mostly used under the bolt head and nut. The toothed elastic washer has a smaller volume than the ordinary spring washer, and the fastener is subjected to uniform force, which can prevent loosening reliably, but it is not suitable for frequent disassembly.
Wave spring washer
National Standard: GB/T 7246-1987
Wave spring washers are divided into WG, WL, and WN types.
WG type wave spring washer
WG type wave spring washer is an open-type elastic washer, which can usually be installed in a small space, such as applying preload to bearings, reducing the noise of bearing operation, improving the running accuracy and stability of bearings. In addition, it is widely used in electronics and electrical appliances, with materials such as carbon steel, stainless steel, and copper alloy.
WL type wave spring washer
WL type wave spring washer is a lap joint elastic washer, which can usually be installed in a small space, such as applying preload to bearings, reducing the noise of bearing operation, improving the running accuracy and stability of bearings. In addition, it is widely used in electronics and electrical appliances, with materials such as carbon steel, stainless steel, and copper alloy.
WN type wave spring washer
WN type wave spring washer is a multi-layer wave peak overlapping elastic washer. Compared with the WL type, this series is composed of multiple layers of material, so the K value curve under the same compression stroke is flatter than the WL type, which is suitable for situations where the elasticity is larger, and the entire working stroke requires uniform release of elasticity. Materials used include carbon steel, stainless steel, and copper alloy.
Disc spring washer
Disc spring washer, also known as Belleville spring washer, was invented by Frenchman Belleville. The DIN6796 disc spring washer (HDS series) is designed for anti-loosening washers for bolt and screw connections.
It is designed and manufactured according to DIN 6796 and is used for connecting medium or high-strength bolts and screws. The large supporting load and elastic recovery make the HDS series very effective. The bolt tension can withstand relaxation caused by wear and tear of vulnerable parts, creep, relaxation, thermal expansion, shrinkage, or tightening of sealing parts.
The HDS series increases the elastic effect of bolts several times, and it can effectively replace ordinary spring washers, but it is not suitable for use as a locking washer or a flat washer combination. As the HDS series is a disc spring that can be matched or overlapped, matching can increase the deformation of the disc spring group, and overlapping can increase the spring force of the disc spring group.
The ideal installation method is to press it as flat as possible. The closer it is to the flat state, the faster the tightening torque will increase. An appropriate bolt tension can be obtained without a torque wrench.