Improvements in Machinery and Processes for Grinding Cement and other materials.
Year: 1892

page_text: Date of Application, 15th June, 1892
Complete Specification Left, 15th Mar., 1893-Accepted, 10th June, 1893
PROVISIONAL SPECIFICATION.
Improvements in Machinery and Processes for Grinding Cement and
other materials.
WILLIAM WALTER HEWITT Engineer Greenhithe Kent. I do hereby declare
the nature of this invention to be as follows:-
The grinding of cement clinker has been done by millstones from the commence-
ment of its manufacture and with but slight improvements-to assist the grinding,
crushers, rollers, disentegrators, pulverizers, and breakers have been introduced by
which means the material is very greatly reduced in size before entering the stones-
only quite recently with the demand for a more finely ground cement have
sieves &c. been introduced to get this result.
It is
Other systems have been tried to take the place of stones but up to the present
they have made but little progress-it is agreed that the action upon cement
clinker by millstones in producing a granular cement is the right one.
reported that in a large roller mill put up at very great expense that this the
action of the rollers being a crushing, pressing or squeezing action the material
ground when put under a microscope was found to be globular instead of granular
and thus retarded the setting of the cement-whether this was so or whether it was
thro' the finer particles or flour of the cement not being fine enough I am not
able to say, but it is just possible that if the cement altho' ground to such
fineness as would all just pass thro' a 40 or 50 mesh sieve when tried thro' a much
finer sieve only a very small portion is fine enough to pass thro' it is quite in
evidence that this residue altho' very fine does not in itself posses any setting
qualities at all in its then state and would produce a very slow setting and low
tensile strength of cement.
Assuming this to be the correct view to take of it the fact of grinding by any
other means that produced the same action upon the clinker the result will be the
same.
By the roller system with suitable rolls going at differential speeds the action
produced is a cutting, crushing, rolling and yet grinding motion.
The clinker in the first instance is or may be reduced in any of the many
different kinds of crushing, pulverizing, or disentegrating machines, and it may be
put thro' a sieve, centrifugal, or separator between the passing of it thro' each set
of rollers.
By this system the grinding takes place by what I term gradual reduction as it
is easier to reduce the clinker gradually by means of a series of rolls, sieves &c.
than by one operation of any kind.
Instead of crushing the clinker at one operation and compelling it to remain
under severe pressure several minutes the roller does the work required of it in
an instant at one point of contact and then the cement escapes without unnecessary
friction and in a positively cool condition.
Instead of grinding the cement down to the required fineness at one operation
and then separating the mass and returning the residue to be reground the roller
system grinds gradually by a series of continuous operations in small quantities
and the quality of the cement thus ground is finer, stronger, and more uniform.
The power required is much less in the roller system than in the stone system
for a given quantity.
The reason why a rough roll with differential speeds is used is that if the cement
is passed between two smooth rollers made of any substance it will be crushed into

page_text: a series of flakes, to prevent the latter it is necessary that one of the rollers should
run ahead of the other, that is it must revolve at a greater speed.
If both rollers are smooth when they are brought very near together the cement
will not be drawn in.
With rollers of equal diameter and speed the cement acted upon is made into
flakes or cakes whereas with differential speed a rubbing or grinding action is
obtained which separates the particles.
It is of great importance not to use more pressure between the rollers than is
absolutely necessary for the disintegration of the cement as unnecessary pressure
means extra wear and tear and power irrespective of the fact that any flakes
produced by it must necessarily be again reduced at a further expense of power in
the following operations.
On theoretical considerations the power consumed in crushing cement by direct
pressure that is between smooth rollers without differential motion is exactly
double that required to reduce cement between rough rolls with differential
motion.
This approximately coincides with the result obtained in practice and
experiments have proved that direct pressure without differential speed produces
about one third less result than the same pressure with it.
All rolls have a tendency to wear in the centre leaving them hollow in the middle
whilst in contact at the ends-this tendency increases in proportion with the length
of the roll-when they become thus worn it is evident with metal rolls that no
amount of pressure will enable them to do good work and they must be taken out
at once and made true-but in my invention they can either be trued up with a
diamond or they will grind each other true whilst running in the same way as two
grindstones running face to face to keep each other true the rolls may be reversed
or speeds changed.
To get proper and good grinding it is advisable that the peripheral speed should
be kept the same, so that as the roll wears away the speed can be increased.
The difficulty has been to find a material that can be made into rolls of great
grinding power and that will not require trueing up or comparatively speaking
none.
Now by the use of emery or what I most prefer corundum great grinding
power is obtained with the ability of being able to true them up at a small
expense.
The rolls may be made up of any composition that has a grinding capacity but
I prefer corundum, it is usual in the grinding of flour to have corrugated metal,
smooth metal, and porcelain rolls-but for cement these would be useless as in the
first place there is no grinding power in porcelain for cement and with metal the
great difficulty would be to keep them true and if with corrugations the difficulty
is increased.
The construction of the mills is of the ordinary roller mill or bone mill type but
with rough rolls or breakers going at differential speeds placed above the com-
position rolls in any case they must have a powerful frame and base with the
ability to adjust them to the greatest nicety it is preferable to drive them with belts
instead of gearing as they must be free from jarring.
The corundum or composition should be of that mixture or manufacture that is
cemented and burnt together with earths, clays, minerals or the like that will not
fuse when working under pressure-instead of with glues or other sticky material
that becomes soft when heated-my reason for laying great stress upon this is the
fact that when grinding them together face to face the tendency is for them to heat
and stick together and spoil each others faces.
There may be one or more rolls or discs going at differential speeds and running
in the same or opposite direction, one or more rolls within each other, or the roll
or rolls running against a stationary or movable face-the rolls or discs may be
straight, grooved, corrugated, fluted, convexed or concaved.

page_text: The rolls, discs, or wheels may be made in one piece or a series, solid hollow
cylindrical, in segments, concentric rings, or built up with a series of pieces
longitudinally or the reverse.
It is equally well adapted for wet, dry or plastic grinding and for any class of
work that is usually done by millstones.
Dated this 14th day of June 1892.
WILLIAM WALTER HEWITT,
Greenhithe, Kent, Engineer.
COMPLETE SPECIFICATION.
Improvements in Machinery and Processes for Grinding Cement and
other materials.
WILLIAM WALTER HEWITT Engineer Greenhithe Kent. I do hereby declare
the nature of this invention and in what manner the same is to be performed, to
be particularly described and ascertained in and by the following statement :-
This invention has for its object improvements in the construction of machinery
and processes for grinding cement and other materials.
For this purpose I employ rolls of emery, corundum, or any composition that
has a grinding capacity but I prefer corundum which rolls may travel in the same
or opposite directions at the same or differential speeds and the material to be
operated upon may be passed through one or more of such sets of rolls placed in
suitable positions for that purpose.
The construction of the mills is of the ordinary roller mill or bone mill type,
but with rough rolls or breakers going at differential speeds placed above the
composite rolls-in any case they must have a powerful frame and base with the
ability to adjust them to the greatest nicety-it is preferable to drive them with
belts instead of gearing as they must be free from jarring.
By the roller system with suitable rolls going at differential speeds the action
produced is a cutting, crushing, rolling and yet grinding motion.
The clinker in the first instance is or may be reduced in any of the many
different kinds of crushing, pulverizing, disintegrating, or grinding machines and
may be put through a sieve, centrifugal, or separator between the passing of it
through each set of rollers.
By this system the grinding takes place by what I term gradual reduction as it
is easier to reduce the clinker gradually by means of a series of rolls sieves &c. than
by one operation of any kind.
Instead of crushing the clinker at one operation and compelling it to remain
under severe pressure several minutes the roller does the work required of it in an
instant at one point of contact and then the cement escapes without unnecessary
friction and in a positively cool condition.
Instead of grinding the cement down to the required fineness at one operation
and then separating the mass and returning the residue to be reground the roller
system grinds gradually by a series of continuous operations in small quantities
and the quality of the cement thus ground is finer, stronger and more uniform.
The power required is very much less in the roller system than in the stone
system for a given quantity.
The reason why a rough roll with differential speeds is used is that if the cement
is passed between two smooth rollers made of any substance it will be crushed into
a series of flakes, to prevent the latter it is necessary that one of the rollers should
run ahead of the other that is it must revolve at a greater speed.
If both rollers are smooth when they are brought very near together the cement
will not be drawn in.
With rollers of equal diameter and speed the cement acted upon is made into

page_text: flakes or cakes whereas with differential speed a rubbing or grinding action is
obtained which separates the particles.
It is of great importance not to use more pressure between the rollers than is
absolutely necessary for the disentegration of the cement as unnecessary pressure
means extra wear & tear and power irrespective of the fact that any flakes so
produced by it must necessarily be again reduced at a further expense of power in
the following operations.
On theoretical considerations the power consumed in crushing cement by direct
pressure that is between smooth rollers without differential motion is exactly
double that required to reduce cement between rough rolls with differential motion.
This approximately coincides with the result obtained in practice and experiments
have proved that direct pressure without differential speed produces about one
third less result than the same pressure with it.
All rolls have a tendency to wear in the centre leaving them hollow in the
middle whilst in contact at the ends-this tendency increases in proportion with
the length of the roll-when they become thus worn it is evident with metal rolls
that no amount of pressure will enable them to do good work and they must be
taken out at once and be made true-but in my invention they can either be trued
up with a diamond or they will grind each other true whilst running in the same
way as two grindstones running face to face to keep each other true-the rolls may
be reversed or speeds changed.
To get proper and good grinding it is advisable that the peripheral speed should
be kept the same, so that as the rolls wear away the speed can be increased.
The difficulty has been to find a material that can be made into rolls of great
grinding power and that will not require trueing up or comparatively speaking
none.
Now by the use of emery or what I most prefer corundum great grinding power
is obtained with the ability of being able to true them up at small expense.
The rolls may be made up of any composition that has a grinding capacity but I
prefer corundum, it is usual in the grinding of flour to have corrugated metal,
smooth metal, and porcelain rolls-but for cement these would be useless as in the
first place there is no grinding power in porcelain for cement and with metal the
great difficulty would be to keep them true and if with corrugations the difficulty is
increased.
The corundum or composition should be of that mixture or manufacture that is
cemented and burnt together with earths, clays, minerals or the like that will not
fuse when working under pressure-instead of with glues or other sticky materials
that become soft when heated-my reason for laying great stress upon this is the
fact that when grinding them together face to face the tendency is for them to heat
and stick together and spoil each others faces.
There may be one or more rolls or discs going at differential speeds and running
in the same or opposite directions, one or more rolls within another roll, or a roll
or rolls running against a stationary or movable face, the rolls or discs may be
straight, grooved, corrugated, fluted, convexed or concaved.
The rolls discs or wheels may be made in one piece or a series, solid, cylindrical,
hollow, in segments, concentric rings, or built up with a series of pieces
longitudinally or the reverse.
It is equally well adapted for wet, dry or plastic grinding and for any class of
work that is usually done by millstones.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is;
(1) The use of one or more rolls which may be straight, grooved, corrugated,
fluted, convexed, or concaved composed of emery, corundum (preferably corundum)
or any composition that has a grinding capacity going at differential speeds

page_text: and running in the same or opposite directions substantially as hereinbefore
described.
(2) One or more rolls within another roll or a roll or rolls running against a
stationary or movable face substantially as herein before described.
(3) The grinding of cement (or other wet, dry, or plastic materials) by gradual
reduction consisting of a series of continuous operations substantially as herein-
before described.
Dated this Fourteenth day of March 1893.