Rubber Bellows

- Dec 10, 2019-

Rubber Bellow Geometry:
The design of a custom-molded rubber bellow follows five steps:

  1. Understanding the direction of travel required

  2. Understanding the length of travel required

  3. Understanding the interface between the two rubber bellow ends and the mating components

  4. Understanding the outside constraints or the envelope within which the rubber bellow has to function

  5. Understanding the environment in order to select the right material


1. Understanding the direction of travel required:
There are two types of convolutes used in molded rubber bellows; concentric and spiral.  It's important to understand the advantages of both to ensure the right choice is made.  

When the motion in question is straight up and down or out and back, concentric convolutes work best.  They are simpler to the machine in the mold and they tend to maintain their shape as they flex back and forth.
When the motion has any articulation to it at all, spiral convolutes are the best.  Spiral convolutes do not kink or pop out of shape when bent in the middle - as concentric convolutes tend to do.

2. Understanding the length of travel required:
The length of the stroke required by the application can be accommodated in two basic ways and the choice is dependent on the constraints of the surrounding environment.  First, the delta between the peak and valley of the convolutes can be large, with fewer numbers of convolutes - this requires more available space around the application.  Second, the delta between the peak and valley of the convolutes can be smaller, with more convolutes - this is the direction to go if the surrounding area is constrained.
In short, the design has to ensure that there is enough material between the peaks and valleys of the rubber convolutes so that when fully extended, the shape is still convoluted - if any rubber bellows is stretched beyond it's designed maximum, the rubber peaks tend to buckle inward and then when the bellows is compressed, the part doesn't collapse back properly.

3. Understanding the interface between the two rubber bellow ends and the mating components:
In order for rubber bellows to perform their role properly, they have to be secured at both ends of the apparatus in question.  There are innumerable ways to accomplish this, some include:
hose clamp on rubber bellows

  An extended straight section with a retaining bead and a hose clamp 



grommet feature on rubber bellows 
A locking grommet feature that secures the bellows into a panel or sheet metal




rubber bellows with square mounting flange
An integrated flange that extends out beyond the convolutes with mounting holes



rubber bellows with solid cap
When the bellows are protecting something that simply goes up and down, there may not be a need to secure one end - it may be completely enclosed.