Frequently asked questions about disc springs
and Belleville washers

Disc springs are parts manufactured for dynamic duty. For this reason, the type of steel used and the treatments applied during manufacture are intended to give them elastic properties that are maintained over time. Pressure washers, on the other hand, are parts geared towards static applications, which are required to have high compressive strength —which they are able to maintain— but whose ability to recover for further compressions is very low.

The service life of these parts depends on many factors and cannot be determined exactly. It is, however, possible to make an estimate, whose main value is to help us decide between two or more possible solutions for the same application. Based on the duty (force and travel) to which we are going to subject the part, we can calculate the number of cycles it can withstand. In this respect it is vitally important between which points of the part's travel the work will take place, the ideal being that it is pre-compressed at least 15% and that its travel does not exceed 75% of the total. Aspects such as friction, temperature and corrosive environments alter this estimate drastically, so they must always be taken into account. Finally, these aspects are valid for springs manufactured in strict compliance with the standard (DIN 2093 / DIN EN 16983), since the use of lower-quality steels, as well as incomplete heat treatments, greatly reduce the service life of the part. Austenitizing, or the combination of hardening and tempering together with shot peening, are the treatments that guarantee the longest life in disc springs.

Both solutions have advantages and disadvantages. The answer depends on the type of corrosive agent they must resist and the application they will be used in. In general, stainless steels offer better protection against most corrosive agents; however, in some cases such as magnesium chloride, coatings prove more effective. On the other hand, in dynamic applications, the different characteristics of the material may mean that a standard material with better elastic properties together with a good coating is more durable than a stainless steel. Each situation must be analyzed individually, and factors such as the lead time or the cost of the solution can be decisive.

There is no limit on the length of stacks, although some aspects must be taken into account. The greater the length, the greater the possibility of buckling of the stack, with the resulting friction against the guide. To avoid this, it is recommended to insert flat spacer washers into the stack. These washers must be inserted so that the sections between them do not exceed 3 times the external diameter of the disc springs that make up the assembly. In any case, it must be borne in mind that, even with spacer washers, the longer the stack, the more the friction increases.

When subjected to a constant load, a disc spring undergoes relaxation over time, which causes a decrease in its force. The loss occurs at the beginning and then tends to stabilize. This loss cannot be determined precisely, as it depends on several factors. Even so, it is possible to estimate that a stack will lose 5% of its force in the first two weeks, with any subsequent loss being negligible. Depending on the quality of the spring (material and manufacture), this loss may vary. To ensure good behavior of the part during relaxation, the pre-setting treatment during its manufacture is of vital importance. This treatment consists of completely flattening the spring and discarding any parts that are unable to recover their initial height.

The elastic properties of a disc spring are affected by temperature. In our calculation program it is one of the values taken into account to calculate the behavior of a stack, since the modulus of elasticity varies with temperature. For the standard material (50CrV4), the temperature range in which it can normally operate is considered to go from −50 °C to 100 °C, bearing in mind that within this range its elasticity will vary. For higher or lower temperatures, parts made of materials resistant to those temperatures should be used. Materials such as 17-7PH (1.4568), which works from −200 °C to 300 °C, or Inconel 718, whose thermal range is between −260 °C and 700 °C, are the most common in these cases.

Yes. Each material has a different modulus of elasticity, so when performing a calculation with a stack we must take into account which material it is, since the result will be different. In addition, for the same material, its modulus of elasticity also varies depending on the working temperature, as explained in the previous question.

Flange washers are a type of disc spring. The main difference lies in the De/Di ratio. For flange washers this ratio is around 1.75. This allows flange washers to be used in places where the joining bolts are very close together.

On the other hand, and as a general rule, the force in the 100% compressed position of a flange-type washer is greater compared with a DIN 2093 / DIN EN 16983 washer of the same external diameter and thickness. This is so in order to meet the force demand required in most applications where they are used.

The answer to this question depends on the application. In most cases, using a single washer is sufficient. In other applications with a lot of expansion, two washers can be fitted, one on each side. Consult our technical department for calculating the number of washers.

The answer to this question depends on the application. There are many situations where this is appropriate and many others where it is not. Our disc springs are designed not to be damaged even if they are compressed to 100% of their capacity. This does not mean they should be loaded to 100% in all cases. There are applications where the spring must be used at a load considerably lower than its maximum load. For example, when high temperature can damage the spring, it is necessary to use a strong spring to keep stresses at low levels and reduce the possibility of breakage.

This is a very common question. Determining the appropriate load for flange spring washers can be approximated by following these steps:

1. Decide what load or torque should be used to correctly seal the joint. If it is a joint between flanges, the gasket manufacturer must indicate the value. In the case of an electrical connection, the designer of that connection must provide it.
2. Decide what material should be used in producing the spring washer. A material similar to that of the bolts to be used in the joint is generally suggested.
3. If it is determined that the spring can be used at 100% of the load, simply select a spring from the list whose maximum load is similar to the design load of the joint. It may be necessary to use spring washers in parallel to reach the desired load value. Theoretically, the design load should be between 90% and 100% of the spring's maximum load.
4. Check that the selected spring or springs fit in the space available in the application.

Presetting is part of the manufacturing process of high-quality disc springs. This process momentarily brings the disc spring to the flat position (maximum possible compression). The part is first manufactured at a height slightly greater than the final height. During presetting, the springs yield to their design height. The purpose of this procedure is to improve fatigue life as well as the spring's general performance, such as relaxation or the accuracy of the force-versus-deflection values.

Some disc springs are not subjected to presetting because it is an impractical and costly procedure for small, thin springs. Flange spring washers are rarely preset, since they do not normally work in fatigue and must meet very tight manufacturing tolerances.

Many users complain that it is difficult to determine when 100% of the load the spring withstands has been reached, fearing an overload that would cause the opposite effect to the one desired (stiffening the joint).

The most suitable way to control the load on the joint is by controlling the torque applied to the screw at the moment of assembly. For this reason, one of the data items that appears in the listing of these washers is the tightening torque. By applying this torque to the joint and using a standard friction coefficient for steel of 0.2, the spring delivers its maximum load without exceeding it. This operation must be carried out with a wrench fitted with a torque meter.

Equation to use: T = K · Fi · d

• T — Torsional or tightening torque (N·m)
• K — Friction coefficient (≈ 0.2)
• Fi — Force generated in the bolt and therefore transmitted to the spring (N)
• d — Diameter of the bolt used, in meters (M10 = 0.01 m; M12 = 0.012 m; M20 = 0.02 m)

Yes. Using standard materials such as Inconel 718 and Phosphor Bronze 510.

The most common are AISI 301 and 17-7PH. AISI 301 is the least expensive and offers good corrosion resistance, but since it is manufactured by stamping in the «work hardened» condition, the available size range is more limited and it is not recommended for springs with a thickness greater than 2.5 mm. 17-7PH has better mechanical properties and resists higher temperatures (up to 300 °C), which makes it the best solution when good corrosion resistance is required under special temperature conditions.

It is the method we use to apply zinc to our springs in order to protect them against corrosion. The process consists of tumbling the springs in a mixture of zinc particles and glass beads. The function of the beads is to make the zinc adhere perfectly to the springs. This provides anti-corrosion protection for all our steel parts and eliminates the risk of hydrogen embrittlement, very common when zinc is applied by electrical deposition methods (electroplating).

This is because most manufacturers of DIN 2093 / DIN EN 16983 spring washers use the Almen and Laszlo formulas to calculate force as a function of deflection. This equation works very well as long as the assumption is maintained that the edges of the washers are straight and that the loads are applied at the edges of the external and internal diameters. However, in flange washers, as we approach the flat position, the forces are applied slightly inward of the points considered by Almen and Laszlo, which increases the actual force value. Therefore, the values given in our listing take this phenomenon into account.

In addition to mechanical zinc plating, we offer other protection methods such as nickel plating, yellow chromate, phosphating (black) and oil coating, among others.

All stainless steels are magnetic except for the austenitic group (300 series). Even those in the austenitic group can become magnetic if they are cold worked. Our springs are manufactured using cold-worked material, so they are noticeably magnetic.

Indefinitely, as long as its limits are not exceeded during use and no damage appears, whether from good or bad use. They can be damaged by excessive fatigue cycles, by prolonged exposure to high temperatures, or by being exposed to corrosive environmental conditions.