Variable Force Springs – Too Cool for School?

Lesson #2

We hope you enjoyed our first blog in this series that provided a general overview of flat steel springs as well as an introduction to constant force (aka Conforce®) springs.  

We will now spend some time talking about another very popular flat steel spring design – variable force (aka variable tension) springs. These springs are quite prevalent in the Point-of-Purchase, or POP, industry, especially in pusher trays and upfeed displays, therefore we will focus most of this session on these specific applications. 

Common Pusher Tray Design Common Upfeed Design

What are some of the reasons you would utilize variable force springs in POP display and what are they trying to achieve? 

  • Inventory controlVariable force springs are commonly used in trays that push product forward in a controlled manner. Variable force springs incorporated into pusher trays aid in front-facing the product, allowing shelves to look stocked at all timesThese trays allow for a more organized store inventory, as well as assist in keeping track of inventory needs. In today’s COVID environment, this is even more critical as it allows the customer to handle or touch only the item that they want to add to their cart.

 

  • Product integrityVariable Force springs are designed around the weight of the products they are pushing. This means that they are always designed in a way where the product never gets slammed or compromised while being selected. These springs allow for most any product to be pushed consistently, regardless of the weight. At Vulcan, we understand the importance of showcasing the product within premium retail space. Often, a low lip is needed on the front of the tray to show more of the product. It is critical to have the correct force to ensure the product does not tip over the front lip. This is taken into consideration with every design.

  • Customer satisfactionAllow for the product to be shopped hasslefree by the customer. Products include cosmetics, health/medicines, beverage, food and much more. 

What are some of the design aspects of variable force springs that you need to consider? 

  • ForceThe force of a variable force spring is variable (OK, maybe that was too easy!) When the spring is either extended or retracted, the force changes. With most retail applications, the spring is working in the retracting direction. However, Vulcan also design springs for both accurate pushing of the product as well as ease of loading. Unlike a constant force spring, these springs are designed to have a positive gradient change in force. This is required because the load or force changes as product is added or detracted from the tray or upfeed mechanism. A spring that produces less force as it is extended is said to have a negative gradient. Negative gradients up to 25% are possible. Positive gradient springs – a spring that produces more force as it is extended – is achievable up to 500%

  • ShapeUnlike Constant Force Springs, these springs are not as tightly wound and uniform in shape. The coil size changes throughout the body of the spring. This change in coil size is what allows Variable Force springs to be able to output multiple forces throughout its working extension!
  • End Detail: Like just about all flat steel springs, variable force springs are available in a wide variety of end details including, but not limited to

Consult with your Vulcan Spring Technical Sales Rep for more information. 

  •  Material Selection:  
    • The most common material is type 301 stainless steel. These variable force springs are able to handle a variety of environments required by retail customers, including ambient temperature store areas, as well as refrigerated and frozen packaging. 
    • Texture-rolled high carbon steel can be used when a lower cost is required for high volumes; Inconel 625 and Elgiloy are utilized for the most demanding applications, especially in harsh environments – they are rarely utilized in POP applications 
    • Material thickness generally runs from .002” – .031” and tensile strength range from 270,000 – 310,000 psi.  
    • Finally, our standard finish is a deburred edge but you can request a “round” finish for a smoother edge. Round edge material specifically works great in upfeed systems.
  • Cycle Life: The Vulcan Design Guide includes charts that range from 4,000 to 100,000 life cycles, measured as an extension and retraction of either the whole spring or a portion of it. Keep in mind that low design estimates will lead to early failure while high design estimates make the spring larger and more expensive than necessarySpecifically, for Variable Force Springs, cycle life is difficult to gauge due to the Coil size changing throughout the main coil body. Variable force springs often outlive the life of the display.
  • Mounting Methods: Space is oftentimes a limiting factor. The Vulcan Design Guide can help in determining the proper material size that will provide the load required while fitting into your mounting space 

Common Spring Mounting in a Pusher Tray

Thank you for taking a few minutes out of your busy day to learn more about different design considerations associated with variable forces springs. We hope you have found these blogs helpful so far! 

Please look for the next “Too Cool for School” training module in the upcoming weeks. In the meantime, if you have ANY questions whatsoever or would like to discuss one of your upcoming projects, please don’t hesitate to call Vulcan to speak with one of our very talented technical sales peopleAt Vulcan we go “Beyond the Spring” and we’re here to help! 

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