Wednesday, August 19, 2015

Steel belt, metal belt tracking by crown pulley

Today we further refer to tracking by crown pulleys.

Fig. 1 Crown pulley for steel belt, metal belt

As shown in Fig. 1 , crowning process is done on pulleys when steel belt is used.  'Crown' is a circular arc of curvature radius.  Due to this arc tracking is done.
We often receive questions like 'how much curvature radius is required for a metal belt?'
We reply R=W2/(8×h)
where W is belt width and h= crown height.
Then how can we describe curvature radius like this?
This is led by the Pythagorean theorem.
Please refer to a crown pulley in Fig. 2.
Here a half of W (belt width) is applied to a triangular on the right.

This is deformed to

h2 is much smaller than R.
R is several meters to several hundreds meters, while h is just 1mm or less.
So h2 is described as h2≒0
Then, h=W2/(8×R)

Curvature R is found here.
But how much is the value of h?

In case of plastic belts and rubber belts, pulley d\crown height is set to 0.3mm to several millimeters, depending on belt width and belt thickness.
However, this h is quite limited, quite low in case of steel belts.
It is just 100~200μm when belt with is 500mm.  Curvature radius here is 150 meters!  It requires sophisticated level of process.

However this crowning does not secure tracking.  Sometimes this crown pulley cannot control tracking of metal belts.  This is the very point that metal belt users find difficulty in controlling tracking.
In such cases Dymco listens how the belt is used and present recommendation to each case.
So be free to contact us.