Material Types
In general, springs can be made from many types of materials with a spring property. RSM is here to help determine what is best for your application. Materials selected will depend upon many different factors, but the main considerations are atmospheric conditions of installation, the imposed stress levels, the fatigue life required, or the relaxation properties desired. Ultimately the main consideration, however, is always cost, and an effective balance between mechanical properties and unit cost must always be achieved.
The most common materials used at RSM are:
Carbon Spring Steels
Alloy Spring Steels (such as Silicon Chromes and Chrome Vanadium)
Stainless Steels and Hastelloys
Non-Ferrous Alloys (Generally copper based, Phosphor Bronzes, Brass, Beryllium Coppers)
Titaniums
Heat Resisting Alloys (Nimonics and Inconel)
Should you be uncertain as to the type of material required for a specific application, we would welcome a call at the onset of any design, so details may be incorporated into any calculation of stress levels and fatigue analysis.
Plain Carbon Steels – generally known as “Spring Steel”. It is a cheap material, commonly available, and is readily available in differing grades and most common diameters and gauges. It has very good spring qualities, but like most High Carbon Steels, it readily corrodes, and a whole number of protective finishes are now available to minimise this. Carbon Steels have a restricted range of temperature operation of up to 100 degrees centigrade without excessive relaxation, but beyond this temperature long term relaxation may become an issue where stress levels are high. Due care must be undertaken when specifying corrosion preventing finishes, as these materials are susceptible to embrittlement. To ensure that hydrogen embrittlement is not introduced, springs are often “de-embrittled” to boil off any residual hydrogen. This issue has resulted in an increasing number of organic coatings reaching the market to ensure no such issues can occur. If in doubt, RSM can help to specify a suitable protective coating to suit your needs.
Some grades of plain Carbon Steels are available pre-coated, such as Zinc coated (or Galvanised), or Zinc-Aluminium which can be useful where a spring design does not allow a coating to permeate between the coils, or where it gets electronically repelled by the coating process.
Alloy Spring Steels (Silicon Chromes, Chrome Vanadium etc)
These are spring steels which are more stable for use at high fatigue levels, and elevated temperature and stress levels, such as engine valve springs. Their performance can be greatly enhanced by the introduction of some post forming processes such as shot peening, where considerable gains in fatigue life may be achieved. Our ability to coil and heat treat in process is beneficial to reducing of the spring notch embrittlement effect, which may occur in the manufacture of some tight index springs manufactured from these materials. Materials of this type, usually have a more prolonged lead time due to material availability. Indeed, most requirements are drawn to order only. Minimum material draws and costs are therefore a consideration, and so the manufacture of springs from this type of material is usually for those designs requiring higher volumes, or very specialised requirements needing extreme fatigue life or low relaxation levels at elevated temperatures.
Stainless Steels – Spring quality Stainless Steels are generally referred to as types “302”, “301” and “316” materials. Duplex Stainless Steels and Hastelloys are also often referred to within this class of material but are not so commonly drawn and therefore are not so readily available. In general, they are more expensive than Carbon Steels with a higher and more volatile price structure due to their high Nickel content. Each grade is engineered for differing physical and mechanical properties, locations and environments. In most cases they have good corrosion resistance to normal environmental conditions, although each grade has its own strengths and weaknesses. They are more resistant to relaxation than Carbon Steels at elevated temperatures and can be used from cryogenic temperatures up to 400 degrees centigrade. These are often the preferred option due to their relatively low costs compared to more exotic materials such as Inconel and Nimonics. Their relaxation and corrosion properties are particularly good.
Type 302 Stainless Steel is the most commonly available spring quality Stainless steel and is generally available in commonly drawn sizes up to 12.5mm diameter and even larger. It can be specified where mechanical stresses are high and good corrosion resistance and relaxation performance are required. It is not recommended in an environment where Chlorine is present. Type 302 Stainless Steels are often used in saltwater environments where good mechanical properties are required, but a layer of whiteish oxidation initially builds up on the surface. Where a good cosmetic appearance is required in these environments, 316 materials are generally specified, but they have poorer mechanical properties.
Type 316 Stainless Steel is often referred to as “J” type Stainless, and has very good corrosion resistant properties, especially in the presence of chlorine or in a “Saltwater” environment.
316 Stainless Steel, when polished, retains the bright shiny surface for long periods.
Exotic Materials
Materials such as Monels, Hastelloy, Titanium, Inconel X750, Elgiloy, Phynox, MP35 and Nimonics etc are generally given the term “Exotic”.
They have been developed for operating in specialist working environments. They are often used in the Aerospace, Nuclear and similar industries. We have experience in working with them, and over the years we have established good working relationships with Companies which manufacture these raw materials.
Let us have your requirements, and we can quote accordingly, helping you through design and development if required, and advising you of any pitfalls which may be considered. The
Black Country has over the years developed a wealth of Industries with experience in the use of these materials, and Reliable Spring is at the forefront of them.
Non-Ferrous Materials
This term is usually used for materials which contain Copper and Brass as major constituents. They are not used a great deal in modern designs due to their cost, lack of high yield stress and weight. They do however play a part in designs where there are few other alternatives. Phosphor Bronze is perhaps the most useful material of this type, where it can be aged. These materials have very low magnetic permeability, so Phosphor bronze is often used where a magnetic component cannot be used. They are also very good electrical conductors, so may be used to fulfil dual roles of springing and conduction of some fairly high currents. They are often used in saltwater environments, where once oxidised on the surface, very little further corrosion takes place.
Titanium
This material is used in springs where weight is of a primary consideration. It is also used where resistance to oxidation and corrosion is a major factor; as a consequence, it is often used in the aerospace industry. We have experience in the manufacture and supply of springs made from Titanium and careful consideration to the process of manufacture and grinding is required at all times throughout manufacture when using these materials due to their individual behaviour.