Frequently asked questions about Disc Springs

What is the difference between a disc spring and a belleville or pressure washer?

Disc springs are pieces manufactured for dynamic works. This is why the type of steel used and treatments they are submitted to during the manufacture process are aimed at conferring elastic properties to be maintained over time. On the other hand, pressure washers are pieces for static applications, which must be highly resistant to compression, but whose recovery capacity for new compressions is very low.

What is the useful life for a disc spring?

Useful life of these pieces depends on many factors and cannot be precisely determined. It is possible to carry out an estimate, which will help us decide between two or more possible solutions for the same application. Depending on the work (force and displacement) the piece is submitted to, the number of cycles the piece can withstand can be calculated. In this respect, it is essential at which points of the piece travel the work is going to be made, ideally to be pre-compressed at least 15% and the travel is not over 75% of the total travel. Aspects such as friction, temperature and corrosive environment vary this estimation drastically, therefore they should always be considered. Finally, these aspects are valid for springs which are manufactured in compliance with the standard (DIN 2093), as the use of lower-quality steels as well as incomplete thermal treatments reduce the piece useful life. “Austenising”, combination of “tempering-hardening” and “shot peening” are the treatments which ensure the longer duration of disc springs.

Which is better, stainless steel material or anticorrosive coating?

Both solutions offer advantages and disadvantages. The answer depends on the type of anticorrosive agent to withstand and the use. Generally, stainless steels show higher protection to most corrosive agents, however, in some cases such as magnesium chloride, coatings are more efficient. On the other hand, in dynamic applications the different characteristics of the material can make a standard material with better elastic properties and good coating is more lasting than stainless steel. Each situation should be individually analyzed and factors such as delivery time or cost of the solution may be decisive.

How long can disc springs stacks be?

There is no limit for the length of stacks, but some aspects should be considered. Buckling of stacks may increase if the length is longer, with the subsequent friction with the guidance system. In order to avoid it, it is recommended to insert separator flat washers in the stack. These washers should be inserted in such a way that sections among them do not exceed three times the external diameter of the disc springs conformed by the group. It should also be considered that, even with separator washers, the longer the stack is the more friction is increased.

Do disc springs loose force over time?

Disc springs as they are under a constant load, suffer relaxation that produces a decrease in force, over time. The loss is produced at the beginning and afterwards tends to remain stable. This loss cannot be precisely determined as it depends on different factors. In any case, it is possible to estimate that a stack will lose its force by 5% during the first two weeks being the loss of force insignificant from then. Depending on the spring quality (material and manufacture), this loss may vary. In order to ensure correct performance of the piece in relaxation, pre-setting treatment is of great importance. This treatment is to flatten the spring completely and to discard those pieces which are not able to recover their initial height.

Which temperature range can a standard disc spring work within?

Elastic properties of disc springs are affected by temperature. In our calculation program, it is one of the values to be considered when calculating the behavior of stack because the elasticity module varies depending on the temperature. For standard material ASTM 6150 (50CrV4), the range of temperature to operate under normal conditions ranges from 120ºF to 212ºF, taking into consideration that elasticity will vary within this range. For higher or lower temperatures, pieces manufactured with materials which are resistant to these temperatures should be used. Materials such as 17-7PH (1.4568), which works from -400ºF to 600ºF , or Inconel 718, whose thermal range is between -400ºF and 1.250ºF, are the most common in these cases.

Do elastic properties of disc springs vary depending on the material?

Yes, they do. Each material has a different elasticity module therefore, when carrying out calculations on stack; we should consider what kind of material it is, as the result will be different. Besides, for the same material the elasticity module varies depending on the working temperature as explained in the question above.

Why some disc springs life is longer than other ones?

Material quality and manufacture process of disc springs are decisive for their resistance to fatigue and consequently their useful life. DIN 2093 standard establishes which type of steels is suitable for the manufacture. However, not all manufacturers carry out correct quality controls of steels they use. A high level of impurities in the material results in a higher breakage rate in the pieces. With regard to the thermal treatment, which is a decisive factor for the piece elasticity, the standard establishes a tempering and hardening treatment. However, there are complementary treatments which improve this aspect significantly. Austenising is a treatment superior to tempering and hardening, which provides steel with improved characteristics. A similar quality is obtained when carrying out shot peening treatments, after tempering and hardening.

What is the difference between flange washers and a disc spring DIN 2093 or Belleville (USA)?

Flange washers are a type of disc springs. The main difference is the ratio OD / ID. For flange washers this ratio is about 1.75. This allows the flange washers to be used in places where the attachment bolts are very close to each other.
On the other hand, as a general rule, the force in 100% compressed position for a flange washer type is greater when compared with other DIN 2093 same outer diameter and thickness. This is to meet the demand of force required in most applications where they are used.

Do I have to use one or two disc springs for each bolt?

The answer to this question depends on the application. In most cases it is sufficient to use a single spring. In other applications with high dilatation forces you can put two springs, one on each side. Consult our technical department for calculating the number of springs.

Are flange disc springs manufactured in non-magnetic material?

The answer is yes, using standard materials such as Inconel 718 and Inconel X750

Which stainless steel should I use?

It depends on the application. AISI 301 and 17-7PH are the most common stainless steel material for these springs. In applications where it is necessary a good corrosion resistance in special temperature conditions, the 17-7PH uses to be the best solution due to its greater range of allowed temperature. The steel AISI 301 is cheaper but it is manufactured using stamping material condition: work hardened. For this reason it is not recommended for springs with a thickness greater than 0,1 inch. In other way the mechanical properties of 17-7PH are better.

What does mechanically Zinc Plate mean?

This is a method we use apply zinc on the disc springs to protect them against corrosion. The process is to rotate the spring in a mixture of particles of zinc and glass stones. The function of the stones is that zinc is securely attached to the springs. This provides corrosion protection for all our steel parts and eliminates the risk of fracture due to the presence of hydrogen which is very common when this procedure is performed using a deposition method using electricity. (Electroplated).

What types of anti-corrosive protection are available for this type of elastic flange washers?

Apart from zinc plating, we offer other methods of protection such as nickel plating, yellow chrome, phosphate (black), oil coating, etc.

How many times can a flange washer be used?

Indefinitely, as long as during its use the limits are not exceeded and no damage is caused by good or bad use. They can be damaged by excessive fatigue cycles, long exposure to high temperatures or by exposure in highly corrosive environments, etc.