The traditional form of the strip spring is the power spring.
The special feature of the MAXIMO power spring is that the combination of winding forward and then back increases the power density, making maximum use of the available material properties.
A large number of different cuts and shapes are available for the design of the inner and outer ends of the springs. Their selection depends on various factors, such as the amount of load on the spring end or the installation conditions.
There are three main variants:
• Stretched spring end with hole / cut-out
• Curved spring end / hook / eyelet
• Fitting of an end piece by welding or riveting
A range of different hook and eyelet designs can be fitted to both the inner and outer ends . In addition to a large number of standard designs, special shapes are of course also possible, although they may involve the manufacture of new tailor-made tools and tool inserts, which in turn involves additional costs.
As a rule, power springs are manufactured with a curved spring end for easy installation.
The thicker the material cross-section of the spring strip, the more stable the spring ends must be. High torque values increase the stress on the spring ends.
To allow the spring-hard steel strip to be formed into a hook, the spring ends must first be soft annealed, as the hard strip material can otherwise form cracks or even break, either during the manufacturing process itself or at the latest after a few applications.
To ensure easy installation and perfect spring function, the design of the spring ends on the mounting point in the spring installation space must be coordinated during the design phase.
Ideally, the outer end of the spring runs over a support. The spring support has a positive influence on the running behavior and the service life of the power spring.
In special cases, stretched spring ends with different hole patterns can also be used to fix the mounting point. Final installation of power springs with spring ends of this kind is usually much more complex than mounting with a hook or eyelet. To simplify the mounting of a spring end with a hole, the punched end can also be bent slightly. This makes it easier to fit it into an existing pin or to fix it to the wall of the housing with a screw.
The inner end of the power spring is hooked into the matching opposing contour on the spring axis or on the spring core. This means that the design of the spring inner end must be well coordinated.
To achieve better formability of the spring strip, it may be necessary to soft anneal the end in the area of sharp bends.
Thanks to the standard tools we have at our disposal, many different geometries can be produced. A curved spring end, including for example 90-degree hooks, parallel hooks or step hooks has proven effective in numerous applications.
The special shapes available include variants such as rolled eyelets, which are often used for large, heavy-duty power springs or springs for timepieces. However, this type of mounting requires more installation work, so that mounting of the inner end of the spring using a hook or eyelet is the most cost effective solution. Before deciding on a special shape, the costs should always be weighed against the benefits.
From a purely technical point of view, a wide range of special shapes is possible.
Special designs must however always be assessed individually with regard to tool and cost-effectiveness.
The hook shapes shown are only a small selection. Depending on the spring dimensions and the application, they can be manufactured as standard products .
For MAXIMO power springs, these hook designs are common:
