When considering a spring design it can sometimes be important to discuss the edge condition of the steel. There is a vast amount of technical information concerning the edges of slit strip, but in this blog we will only discuss the basic characteristics and some of the benefits of each edge condition.
Vulcan produces springs with two edge condition options; de-burred edge (#5) and round edge (#1). Let’s take a look at the characteristics of each.
#5 de-burred edge – This is the standard for most springs. It could be called the default edge and is widely utilized throughout all of the industries Vulcan serves. This edge is burr free and the edges are square. Below is a magnified photo of this edge:
Below is a graphical representation of the # 5 edge:
To achieve a #1 round edge the strip must undergo an additional processing step before we use it to manufacture springs. This additional processing removes the square edges and provides a smooth, round edge. Here are similar photos and graphics of the round edge:
Descriptions, photos and graphics are great but why do we need to discuss this issue at all? Well, both edges have their benefits and costs. The #5 de-burred edge is a practical option for standard applications. Any burrs from the slitting process have been removed and the material has undergone the least amount of processing necessary to be ready to be made into a spring. The benefit of this edge is mainly lower cost. Since it has less processing to go through it is more inexpensive than the #1 edge. A spring with a #5 edge will operate reliably in many applications although it can feel sharp to the touch.
Specifying springs with a #1 edge increases the part cost slightly since the spring material is processed further than if a #5 edge was required. However, there are a few advantages that make this edge condition a necessity in certain situations. For instance, when making a power spring the round edge is preferred because it will maximize the cycle life of the design. Additionally, the round edge will not damage a plastic housing during regular use.
A spring with unprocessed edges can cut grooves into a plastic housing or even cause the housing to fail by sawing through it. In either instance flakes of plastic material are created that are detrimental to the spring’s performance as these flakes contaminate the spring and increase inter-coil friction. This increase in friction will degrade the design torque and shorten cycle life. The round edge may also be preferred in constant force extension spring and constant torque spring designs as a safety consideration if the edges are exposed and may be touched.
The protection of other sensitive components of the design may also dictate the need for a spring with rounded edges. The information provided here can be used as a guideline for discussing the edge condition of a spring design. The final determination should be made and agreed upon prior to the quotation of a spring.