SPRING MATERIALS

This section will tell you about the different kinds of material that springs are made out of. It will also tell you where to get your wire -- make sure you read the Safety section so you know how to handle it safely once you've got it.

Types of Wire

Springs are usually made from alloys of steel. The most common spring steels are music wire, oil tempered wire, chrome silicon, chrome vanadium, and 302 and 17-7 stainless. Other materials can also be formed into springs, depending on the characteristics needed. Some of the more common of these exotic metals include beryllium copper, phosphor bronze, Inconel, Monel, and titanium. The following table summarizes the more important properties of each material:

Material	Common Sizes	Properties and Uses
Music Wire	.003-.250	A high-carbon steel wire used primarily for applications demanding high strength, medium price, and uniformly high quality. Guitar and piano strings are made from this material, as are most small springs. Music wire will contract under heat, and can be plated.
Oil Tempered Wire (OT)	.010-.625	This is the workhorse steel spring wire, being used for many applications in which superior strength or uniformity is not crucial. Will not generally change dimensions under heat. Can be plated. Also available in square and rectangular sections.
Chrome Silicon, Chrome Vanadium	.010-.500	These are higher quality, higher strength versions of Oil Tempered wire, used in high-temperature applications such as automotive valve springs. Will not generally change dimensions under heat. Can be plated.
Stainless Steel	.005-.500	Stainless steels will not rust, making them ideal for the food industry and other environments containing water or steam. 302 series stainless will expand slightly under heat: 17-7 will usually not change. Cannot be plated.
Inconel, Monel, Beryllium Copper, Phosphor Bronze	.010-.125	These specialty alloys are sometimes made into springs which are designed to work in extremely high-temperature environments, where magnetic fields present a problem, or where corrosion resistance is needed in a high-temperature working environment. They are much more costly than the more common stocks and cannot be plated. Generally will not change dimensions under heat.
Titanium	.032-.500	Used primarily in air- and spacecraft because of its extremely light weight and high strength, titanium is also extremely expensive and dangerous to work with as well: titanium wire will shatter explosively under stress if its surface is scored. Generally will not change dimensions under heat. Cannot be plated.

Titanium is the strongest material, but it is very expensive. Next come chrome vanadium and chrome silicon, then music wire, and then oil tempered wire. The stainless and exotic materials are all weaker than the rest.

Buying wire

Spring wire is made in common sizes (see table above) and in special sizes to order. The common sizes that are manufactured are available within the ranges specified at intervals ranging from a couple of thousandths of an inch (for the smaller sizes) to sixteenths of inches (for the larger sizes). Metric-measure sizes are available outside the US.

These spring wire materials may be bought from steel suppliers in two forms: coils and straightened-and-cut bars. Unless you are dealing with extremely close tolerances, exotic materials, or need a stock size that is not commonly manufactured, you'll probably find it most economical to buy your stock in coils.

Bought in coils, spring steel is generally sold by the pound: the coils range in size from about 6 inches (for wire under .005') to 7 feet (for wire in the .437-.500' range) in diameter. The smaller coils are generally shipped UPS, while the larger sizes require truck transport as well as special unloading and storage facilities.

Finding a source of supply is as easy as looking in the phone book: if you're in a rural area, try the local library which will have Yellow Pages for the major metropolitan areas -- try Detroit or Los Angeles for starters. You can also contact the Spring Manufacturers' Institute and ask them for a copy of Springs magazine, which is filled with suppliers' advertisements (as well as technically interesting articles). The Addendum also lists some wire manufacturers and suppliers. By the way, this link will take you to a guide of how many feet of wire you'l get per pound of material ordered (thanks to Jeff for this).

One caution: you should not order straightened-and-cut wire until you're SURE you know what you want. Once you get your material, you'll find it impossible to return if the bars are an inch too short.

And one note: when spring wire is made, it develops what's known as a 'cast' from being tied into round coils. If you strip wire from a coil, it will likely not be perfectly straight: the 'natural' curvature of the wire is 'cast'. The cast of the wire will introduce an extremely small variance in the physical dimensions of the springs made from the wire -- it's only a problem when you're working with very close dimensional tolerances. Cast is why wire is also available in straightened-and-cut bars.

Forward to Safety.