Coil Compression Springs for Auto-Injector Syringes


A preloaded helical spring used specifically inside of an auto-injector syringe to inject a single or multiple dose of a particular medication by people who are in need of these injections.

Auto-injector syringes are an advanced device in the medical industry which has helped unexperienced patients administer injected medications in the commodity of their homes or on the go. These devices are spring-operated and operate similar to a ball-point pen. The needle remains inside the device for safety reasons and is pushed out by the pre-loaded spring by the click of a button. Once the needle is pushed out, the medication is also administered automatically.

Diagrams and Examples


This is one of the devices which Acxess Spring has proudly been able to work with. The spring inside the device is a coil compression spring. The material type which is usually utilized for these types of applications is stainless steel. Our spring company works with three different types of stainless steel; stainless steel 302 A313, stainless steel 316 A316, and stainless steel 17-7 A313.

To design a spring for an auto-injector syringe, you will need to know the pre-loaded length of the spring, the amount of pre-load that will be applied to keep it at that length, and how much distance the spring will need to travel in order to reach that pre-loaded length. You can calculate the distance traveled by subtracting the pre-loaded length of the spring from the free length. Knowing the distance travel and the applied load will help you calculate the spring rate. Spring rate is the constant increase of force proportional to the increase of distance traveled. It is measured in pounds of force per inch (lbf/in) or newtons per millimeter (N/mm).

In terms of physical dimensions, you will need to know the inside diameter of the device so that you know your limitations on the helical compression spring’s outer diameter. In case your spring will be going over a shaft, you need to know the outer diameter of that shaft to make sure that the inner diameter of the coil compression spring will not be too tight around it.

Diagrams and Examples