Pushing Products with Variable Force

Variable Force Springs, also known as V-Springs, are commonly used to push products on shelves in retail shopping environments.  Research shows it is more likely a consumer will make an impulse purchase if the product is forward on the shelf than if placed back in the shadows of a display. The V-Spring is perfectly suited for this as it helps to keep products at the front of the shelf, visible and easy for the consumer to purchase.

The V-spring evolved from the more traditional “constant force” spring.  The constant force design used to be the standard in pusher applications, but they had a fundamental weakness.  Since the amount of product in a tray varies (say from 10 to 0), the weight that needs to be “pushed” varies as well.   A constant force spring must be designed to push the entire column or queue of product towards the front of the display.  Unfortunately, this means that the force becomes much stronger than the product weight as the quantity decreases.  The final few pieces of product could fly off the tray, and even customers fingers could get pinched due to this issue.

The variable force spring addresses these problems.  The tell-tale signature of a V- Spring is the openness of the coils throughout the length.  The changing diameters represent changes in the push force and usually mimic the change in total product weight as individual products are removed from the display.  In general, the spring will get stronger as products are loaded in the display and weaker as they are removed and pushed forward.

Let’s explore some variables to consider when designing a V Spring and discuss options when considering this type of spring pusher.

• Spring size – length of travel, maximum diameter, maximum available width for spring.  It is important to have at least 1-1/2 wraps of the spring remaining when the display is full.
• Product information – weight and dimensions of product.  It is also important to consider the sliding friction of the packaging when reviewing the product in a pusher display.
• Materials – Type 301 stainless steel typically produces the best part at the lowest cost.
• Life in total estimated number of cycles – the life of the variable force spring is very predictable and can be reviewed in our blog Life Cycles of a Variable Force “V” Spring.
• Force requirements – the force of the spring should be equal to the requirement of the application. The normal tolerance for a variable force spring is +/-10%
• End detail – Vulcan Spring has many standard dies to create the end detail for variable force springs. The image shows some that are available. Special end designs can be made for a nominal charge.
• Angle of Displacement – from 0° to 90°.  This is important to mention because it is often forgotten that the “V” Spring is the perfect solution for up-feed type displays.

The display track can also affect spring selection.   Testing is frequently performed using prototype trays that operate with high levels of friction.  However, once the tray is molded the friction is reduced and this can cause the spring force to appear stronger.  Tests using the actual production tray are recommended prior to manufacturing springs in volume, even if the spring has been selected during the prototype phase.

Choosing a Variable Force Spring may involve trial and error.  However, the result of the effort usually pays off with a smooth, functional display.

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