Conical Springs: Progressive Rate Design and Uses

A conical spring is a compression spring wound into a tapered (cone) shape, with a large coil at one end and a smaller coil at the other. Two things make it different from an ordinary straight cylinder spring. First, its stiffness rises as it is compressed, so it is a progressive-rate spring. Second, it can telescope into a very short solid height, which saves axial space. This guide covers how the progressive rate works, how the spring is designed, and where the shape earns its place.

What makes a conical spring different

In a standard cylindrical compression spring every active coil has the same diameter, so the number of active coils is fixed and the spring rate is constant: the same force is added for every millimetre of travel. In a conical spring the coils have different diameters, so they do not all touch down at the same time. The smaller coils, which sit at the top of the cone, deflect first. As the load grows they bottom out on the coil below, and each coil that lands is no longer active. Because the rate depends on how many coils are still working, the effective rate rises step by step — the spring feels soft at the start of its travel and firm toward the end.

The math behind the progressive rate

The rate of a helical compression spring made from round wire is calculated as:

k = G d⁴ / (8 D³ n)

where G is the shear modulus of the material, d is the wire diameter, D is the mean coil diameter and n is the number of active coils. In a conical spring, as coils bind in sequence, the effective number of active coils n falls. Since n sits in the denominator, a smaller n means a larger k — a stiffer spring. That is the whole principle of the progressive rate in one relationship. You can work the numbers for a constant-diameter spring with our compression spring calculator and see how strongly k depends on D and n.

Design rules

Spring index D/d — the ratio of mean coil diameter to wire diameter is normally kept between 4 and 12 so that the spring remains manufacturable. In a conical spring each coil has its own index, so the design must be checked coil by coil; the smallest coil is usually the one that governs stress.
Stress and travel — because the rate rises as coils bind, the force-versus-deflection curve is not a straight line. The load at the installed height, not just the rate, is what usually has to be specified.
Standards — EN 13906-1 covers the design calculation of cylindrical helical compression springs made from round wire and bar, which is the basis from which tapered variants are analysed. EN 15800 defines quality specifications for cold coiled compression springs made of round wire.

Where conical springs are used

Conical springs are chosen for two families of reasons. The first is variable load: applications that need a light initial force but a much higher force near full compression. The second is space and stability: because the coils nest into one another, solid height is much shorter than a straight spring of the same wire, and the tapered form resists lateral buckling better than a narrow cylinder. Typical service includes vibration-damping mounts, clutches and overload devices, and any assembly where a short, telescoping, load-rising spring is needed.

Materials and manufacture

Small and medium conical springs are cold coiled from wire supplied to EN 10270-1 (cold drawn patented, grades SL/SM/SH/DH) or EN 10270-2 (oil hardened and tempered, grades FDC/TDC/VDC), then stress-relieved. Larger conical springs are hot coiled from alloy spring steels such as 60Si2Mn and 51CrV4 and receive a full hardening and tempering cycle. Stainless grades per EN 10270-3 (for example 1.4310 and 1.4401) are available when corrosion resistance matters. Our shop handles wire from 0.1 mm up to 80 mm, so both routes are covered.

Frequently asked questions

Q: What is the difference between a conical spring and a straight compression spring?
A: A straight spring has a constant rate; a conical spring has a progressive rate because its coils bind in sequence as it is compressed.

Q: Why does the rate increase?
A: As coils touch down they stop being active, so the active coil count n falls, and since k = G d⁴ / (8 D³ n), the rate rises.

Q: Why choose a conical spring?
A: For a rising load curve, a short telescoping solid height, or better lateral stability than a narrow cylinder spring.

Q: What spring index should I use?
A: Keep D/d between about 4 and 12 so the spring stays manufacturable, and check each coil in a tapered design.

Q: What standards apply?
A: EN 13906-1 for design calculation of helical compression springs, and EN 15800 for cold coiled compression spring quality.

Related resources

Have a conical or progressive-rate spring requirement? Send the drawing or the load curve to liu@chenjisprings.com or call / WhatsApp +86 158 5311 1612.