CAPACITY OF BREAKING




Capacity of Breaking 
Understanding a few detailed calculations is critical to enhancing quality.
The function of the breaking system in a flour mill is to remove
the bran from the endosperm, with maximum separation
but with a minimum release of bran powder, which has inferior
locity of slow roll, which deter-
The breaking process is perbaking
qualities.
mines the velocity of the fast roll
formed in stages, also sometimes
using the differential, and the
called passages.
roll diameter.
In modern mills, there are
four to five breaking passages,
Optimum Velocity
In any given breaking roller
fluted.
and the breaking roller mills are
mill, all the parameters usually
Many parameters influence
are fixed. Normally, the perforthe
performance of breaking mance of the roller mill is deterroller
mills, such as the details of Rami Flamer mined by adjusting the distance
the fluting (e.g., number of flutes between the rolls.
per centimeter), percentage of spiral (e.g., So, what is the optimum velocity of
the spiral angle), flute angles, land, dispo-the slow roll that will provide maximum
sition of rolls (e.g., dull-to-dull, sharp-to-capacity of the roller mill but without imsharp,
etc.), differential between rolls, ve-pairing the grinding performance and
raising the ash content of the throughs?
In his February 2009 article, “Congestion
in the Grinding Gap—Optimal Conditions
for a Selective Reduction in Flour
Milling” (published by Muhle &
Mischfutter), Josef Teich, drawing from
his own experience and knowledge in
milling, found an optimal maximum load
in terms of kg/m2. This was based on the
slow roll velocity for every passage.
Basically, Teich described or calculated
what happens in the gap between the rolls
(or the nip).
In looking at the first break, for example,
this is where the kernels are falling
from the feeding rolls to the nip.
In the nip, the slow roll is holding the
kernel, and the fast roll is cutting the kernel
to get the desired release.
Maximum Optimal Load
Teich found that the maximum optimal
load for the first break is:
Response No. 221 Response No. 222
22 Third Quarter 2010 MILLING JOURNAL



Ld = 0.5 kg/m2, related to slow roll Figure 1
velocity.
If, for example, the diameter of the
roll (Dr) is 0.25m, and the velocity of
the fast roll (Vf) is 550 rpm, and the
differential between rolls (Diff.) is
1:2.5, and the length of the rolls (L) is
1.0 m.
So, the maximum optimal
capacity(q) will be:
They travel from between the feeding
rolls through the nip of the grinding
rolls, which is represented by “h” or
the height.
As known in mechanical physics,
the velocity that a body gains in freefalling
(ignoring air resistance, in this
case) is independent of its weight.
Consequently, the calculation for the
velocity of the kernels, when they are
entering the nip, is:
As we can see from the equation
for q—or maximum optimal capac-
ity—the only parameter that can be
changed to generate a higher capacity in
an existing roller mill is the velocity of
the rolls.
Many experiments to increase
capacity by increasing velocity
and other parameters, such as
differential, etc., in existing
roller mills have failed, and the
reasons for the failure were not
understood fully.
If, for example, the bearings of the
rolls are strong enough, the capacity of
the feed rolls can be increased by 10%,
and this also will increase the velocity of
the fast roll to:
550 x 1.1 = 605 rpm.
Many experiments to increase the capacity
by increasing the velocity and other
parameters, such as differential, etc., in
existing roller mills have failed, and the
reasons for the failure were not understood
fully.
In many cases, there was a problem in
the grinding performance, and the ash
content of the products was higher.
As Teich said in his article: “If somebody
will find the reason for the phenomenon
and know how to solve it, this would
be a breakthrough and challenge the more
than 100 years of the undisputed practice
to use a 2.5-to-1 differential on break
rolls.”
For optimal grinding, the velocity of
the slow roll must be equal to the nip velocity
of the kernel. When this is achieved,
side angle photos have shown that the
kernels appear to be gripped or held by
the slow roll.
However, in practice, a roll cannot
hold a kernel. So, it’s assumed that in optimal
grinding, the nip velocity of the 
A Suggested Solution
So, in this column, an attempt will be
made to confront this challenge and suggest
and explain a solution.
In every roller mill, the setup of the
feeding system and the grinding system is
similar to what is shown in Figure 1 (see
above).
The kernels (or other breaking material)
fall freely through the grinding nip.
Response No. 231
MILLING JOURNAL Third Quarter 2010 23



kernel (or other breaking material) must
be equal to the peripheral velocity of the
slow roll.
This calculation (to the left) represents
the optimal velocity of an existing roller
mill to provide the best quality of products.
Under real conditions, if it needs to be
determined the roller mill is working optimally,
then examining the flutes of the
slow roll becomes necessary. If the flutes
look fairly new, that’s a good sign that the
nip velocity of the kernels is equal to the
peripheral velocity of the slow roll.
Response No. 241
24 Third Quarter 2010
not breaking optimally.
Against this background, it becomes a
little easier to answer the following question:
How can someone increase the capacity
of the breaking roller mills by increasing
the velocity of the rolls but without
breaking or damaging the product?
The answer may lie in the following
Under real conditions, if it
needs to be determined the
roller mill is working optimally,
then examining the
flutes of the slow roll becomes
necessary. If the flutes look
fairly new, that’s a good sign
that the nip velocity of the kernels
is equal to the peripheral
velocity of the slow roll.
calculation, which essentially concludes
that the feeding rolls should be set higher,
as represented by h.
For example, if someone wants to reach
a capacity that is 10% higher compared
to the previous example, then this calculation
would apply:
sec.
Basically, if the feeding rolls are set
higher by just 8cm than before, the capacity
should increase by 10% while still
maintaining optimal grinding conditions.
Technical Manager Rami Flamer has
been milling at the Shalom Flour Mill in
Petach Tikva, Israel since 1982. This column
has been edited for content and
length. 
MILLING JOURNAL