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How to make innersprings (steel, wire, coils)


Leggett & Platt owns North America’s largest electric furnace, located in Sterling, Illinois. There we melt scrap and transform the molten liquid into rod. Rod is drawn into wire. Our high-carbon wire is formed into a variety of gauges we can shape into unique coil designs. 

How to change a coil's feel

There are four primary ways to change the feel of a coil. You can change the tensile strength, number of turns, gauge, and how the coil is connected to other springs. 

When you consider the variety possible within all of those factors, the possibilities for unique combinations to create distinct feels is almost limitless. Here are explanations for those four factors.

Tensile Strength
Tensile strength is a wire’s capacity to stretch without breaking and its ability to withstand compression. At Leggett & Platt, we use high-tensile wire to create coils that are supportive and longer lasting than our competitors and those offering cheap imports. Testing data that proves our product’s superiority is available to customers.

If you take a straight piece of wire and create a turn, you will add a weak point. Turn that wire a few times and you’ll see a coil spring begin to form. The more turns, the softer the coil. A coil turn is defined as a complete rotation. Most coils have between five and eight turns. If you have two separate pieces of wire and their gauges are the same, a coil with a higher number of turns should be softer because each turn creates a point of weakness, making the coil easier to compress. Fewer turns means fewer weak points, resulting in a firmer coil.

Wire gauges typically run from 12 to 19. A lower number corresponds to thicker wire. That means 12-gauge wire is fatter than 19-gauge. You can increase firmness by lowering the wire gauge. One way mattress makers can create a softer sleep surface is by using higher-gauge wire, which is thinner and has more give. Units with thinner wire gauges are usually softer and springier.

For innerspring units using Bonnell and offset innersprings, the coils are connected using a helical lacing technique that involves a long spiral of high-gauge wire binding the rows together and bordering the entire unit. This method keeps the unit together while allowing the coils to move independently and conform to the shape of the body.

Explore the entire process to learn more.


See related articles: innersprings, manufacturing

Mark Kinsley

Mark Kinsley is Leggett & Platt's Staff Vice President of Marketing for the Bedding Group. Outside the office he enjoys spending time with family, mountain biking, hiking, and snow skiing. Connect with Mark on Twitter via @markkinsley.