A spring is usually the cheapest part in an assembly, and its failure stops the entire line. In an automated machine it runs through millions of cycles, often at elevated temperature or in contact with cleaning agents, and it decides whether the gripper releases the part at the right moment. This article explains the criteria used to select springs for industrial automation, and when an off-the-shelf part stops being good enough.
In automation a spring is rarely the primary component. It almost always handles one of five supporting functions, and which one it handles governs the entire selection:
Return to the home position. The actuator is driven pneumatically or electrically in one direction and returns on the spring. This is how most valves, single-acting grippers and ejector mechanisms work.
Constant contact force. The spring maintains force despite small dimensional changes, for example in pinch rollers, belt guides and locating nests.
Compensation for play and thermal expansion. Tensioners, bolted joints working across a temperature range, take-up for wear.
Damping of vibration and shock loads. Protecting the assembly when a part lands hard in its nest.
Safety function. The spring returns the mechanism to a safe state when power is lost, which is often a formal requirement rather than a designer's preference.
The same compression spring can serve as a return element in one machine and as a safety element in another. In the second case its failure has different consequences, so the durability margin is set differently.
A manufacturer does not need a finished spring from you. It needs the conditions the spring has to work in.
Rate and characteristic. A cylindrical compression spring has an approximately linear characteristic: force increases in proportion to deflection. If the application calls for a rising rate or a low solid height, that linearity stops being an advantage and another type is needed.
Installation space. This is the most common constraint in automation, where space is fought over in millimetres. Once the available length, the bore or rod diameter and the required stroke are known, the spring can be shaped to fit the space instead of the space being designed around the spring.
Number of cycles. A part that operates a few hundred times a day and a part that completes ten million cycles are two different designs, even at identical dimensions. For fatigue duty the working stresses are reduced, the surface finish is specified differently and shot peening is considered. Give the manufacturer the expected cycle count, because without it the selection rests on an assumption.
Operating temperature. Above roughly 80 °C ordinary spring steel begins to lose force through relaxation: the spring takes a permanent set even though nothing breaks. In ovens, soldering zones and drives with hot housings, a different grade is specified.
Environment. Moisture, oil mist, chemical washdown and food contact decide the material before strength does. In wet areas and in the food industry stainless steel is the standard, because a zinc-plated spring stops being what it was on the day of assembly after a few months of washing. Grade selection is covered separately in our article onstainless steel springs made to order.
Helical Cylindrical Compression Spring.
A full overview of the designs is collected in our article on the types of springs and their applications. The table below is narrowed down to jobs typical of automated machinery.
| Job in the machine | Spring type | What to watch |
| Return after compression | helical cylindrical compression spring | linear characteristic, risk of buckling when slender |
| Return within a limited height | conical compression spring | low solid height, resistant to buckling |
| High force over a short stroke | disc spring | stacking in series adds stroke, in parallel adds force |
| Return of rotary motion, levers | torsion spring | coiling direction must match the load direction |
| Near-constant torque, winding mechanisms | flat spiral and strip spring | near-constant torque over a large angle of rotation |
| Guards, catches, guiding elements | elastic wire forms | a formed wire part is often cheaper than an assembly |
| Return from extension | extension spring | the hooks are the weakest point and their shape must be agreed |
We have covered the applications of strip springs in industry separately, because in winding mechanisms and across large angles of rotation they are often the only sensible design.
Changing the spring type at the drawing stage costs very little; after production has started it costs a great deal. It is worth reviewing the selection before the design is frozen.
Repeatability comes from the material and from the document that certifies it. We go into more detail in our article on what materials springs are made from; in workshop practice three groups are enough to know:
Patented spring wire in grades SM and SH to EN 10270-1. The standard material for dry duty inside a machine, with a good strength-to-cost ratio.
Chromium-vanadium steel 50CrV4. Used at higher loads and elevated temperature, where patented wire starts to take a set.
Stainless steel 1.4310 to EN 10270-3. The choice for wet, chemically washed, food and medical areas, and for outdoor duty.
Then comes the acceptance document. A 3.1 inspection certificate to EN 10204 is issued by the material producer and tied to a specific heat, so the composition and properties of the input material can be traced years later. For disc springs there is a separate dimensional standard, DIN 2093, which governs dimensions and manufacturing groups so that a part can be replaced without redesigning its seat.
If an application calls for a material outside this list, manufacturing to the customer's specification is normal practice. The condition is that the grade is stated at the enquiry stage rather than after the batch has been made.
An off-the-shelf spring is available immediately, and that is its only advantage. It makes sense for a prototype, for an emergency repair and whenever the design can adapt to a catalogue dimension.
A spring made to order wins wherever installation space, cycle count or operating environment decide the outcome. Instead of adapting the machine to the available part, the part is made for the machine, and with repeat deliveries there is no risk that the next catalogue batch reaches the machine from a different works with a different characteristic. Across production runs the unit price difference usually disappears, because the set-up cost is spread over the quantity.
Reproducing a part that is no longer available is a case of its own, which we describe in our article on custom spring manufacturing.
The practical rule is simple. If the failure of a spring stops the line, have it made to order, with a documented material.
We have been manufacturing springs in Katowice since 1985, for customers in Poland and across the European Union. We make them to a drawing, a sample or technical data alone, from single pieces and prototypes through to long production runs.
| Parameter |
Range and options |
| Wire diameter (d) | 0.2 to 10.0 mm |
| Material | patented wire (SM/SH), 50CrV4, stainless steel 1.4310, others to specification |
| Certificate | 3.1 material inspection certificate |
| End types | closed ends, ground or unground, open ends |
| Coiling direction | right-hand or left-hand |
| Batch size | prototype, short and long production runs |
No drawing? A sample is enough, or a complete set of working conditions: available space, the force required at a given deflection, the number of cycles, the temperature and the environment. On that basis we will select the design and prepare a quote. Send an enquiry and we will reply with a proposed solution.