IMPROVEMENTS IN THE PROCESS OF PREPARING COMPOUNDS OF NITRO-CELLULOSE OR PYROXYLINE, AND IN APPARATUS FOR THE CONDUCT OF SUCH PROCESS
Year: 1881

page_text: LETTERS PATENT to Sydney Pitt, of Sutton, in the County of Surrey, for
an Invention of "IMPROVEMENTS IN THE PROCESS OF PREPARING COMPOUNDS
OF NITRO-CELLULOSE OR PYROXYLINE, AND IN APPARATUS FOR THE CONDUCT
OF SUCH PROCESS." A communication from abroad by John W. Hyatt, of
Newark, in the County of Essex and State of New Jersey, United States
of America.
«
COMPLETE SPECIFICATION filed by the said Sydney Pitt at the Office of
the Commissioners of Patents on the 6th September 1881.
SYDNEY PITT, of Sutton, in the County of Surrey. IMPROVEMENTS IN THE
PROCESS, OF PREPARING COMPOUNDS OF NITRO-CELLULOSE OR PYROXYLINE, AND
IN APPARATUS FOR THE CONDUCT OF SUCH PROCESS." A communication from
abroad by John W. Hyatt, of Newark, in the County of Essex and State of
New Jersey, United States of America.
.
My Invention relates more immediately to the manufacture of plastic
compositions, which are susceptible of being moulded in forms or shapes of the
solid material, or upon forms, skeletons, or foundations of wood, metal, or other
substances or compositions; but my improvements extend only to the preparation
of the compounds for the subsequent treatment by which they are converted into
the plastic composition. I contemplate applying my Invention to various com-
pounds that are not, strictly speaking, the bases of plastic compositions, but will
proceed to describe it in connection with certain compounds of nitro-cellulose or
pyroxyline, as the most comprehensive exemplification of the principles involved.
In the manufacture of compounds of nitro-cellulose or pyroxyline, vegetable
fibre which has been treated with nitric and sulphuric acids, as is well understood,
is mixed with solvents of such converted fibre, and with pigments, and with foreign
matters, such as bone dust, for example, and this mixture is subjected to a
treatment by which the plastic composition is produced. Such plastic compositions
are generally designated as solid collodion.

page_text: In the manufacture of that kind of solid collodion which is characterized by the
name of celluloid, it is also well understood that the peculiarity of the process by
which it is made consists in the use of solvents (of the nitro-cellulose), which are
mechanically mixed with it in such a way that the action of the solvent is left
dormant or restrained until the mixture is subjected to heat and pressure, the
great advantage of such restraint upon the converting action of the solvent being
due to the fact that an intimate mixture of the ingredients of the compound is
ensured before the converting action begins, so that when that action does begin, it
operates upon every atom of the nitro-cellulose, and produces a more perfect and
thorough conversion than can be obtained where active liquid solvents are applied
in the old way.
In the manufacture of celluloid the nitro-cellulose has heretofore been ground
into a pulp in a beating engine, the camphor (used as the latent solvent) was
crushed between rolls, and then mixed with the ground pulp, and this mixture was
then again ground in a Bogardus mill. The pigments and the foreign matters
when any were employed were separately prepared, but were mixed with the pulp
at the same time as the camphor.
To recapitulate, the process of preparing the compound consisted of the following
several separate steps or stages-1st, grinding the nitro-cellulose into pulp;
2nd, comminuting the camphor; 3rd, the preparation of the pigments and foreign
matters when any were employed; 4th, the mixing together of the pulp, the
camphor, and the other ingredients; 5th, the grinding together of these ingredients;
and 6th, the application of powerful pressure to the ground compound for the
purpose of thoroughly compacting the ingredients, and of removing the excess of
aqueous moisture.
At each of these separate stages there is unavoidably a greater or less accretion
of extraneous matters, such as dust or dirt, grit, and the like, incident to the
repeated handling of the ingredients, and their exposure to the liability of such
accretions.
Now it is the 'object of my improvements to simplify this preparation of these
compounds, and to this end my Invention consists as to the process in simul-
taneously reducing and thoroughly mixing together all of the ingredients, so that
the entire operation is completed and perfected at one stage, and in about the same
time which was formerly required for the simple reduction of the nitro-cellulose to
pulp; and it then only remains to press out the excess of aqueous moisture to
bring the compound to the same condition of readiness for the converting process
to which it was previously brought only by the six steps or stages above enumerated,
and I conduct-this-operation-so-as-to-prevent-any-accretions-of-dust, dirt,-grit, and
other impurities from the atmosphere or from the floors of the work-room.
In my improved process I take the hydrated nitro-cellulose after the converting
acids have been thoroughly washed out, and place it in a strong metal drum which
can be slowly rotated upon its axis; into this drum I charge with the hydrated
nitro-cellulose the proper relative quantity of camphor in lumps, or just as it is
purchased in the market, and such pigments and foreign matters as are to be
incorporated in the compound just as such materials are supplied for such uses.
I then close the drum securely and rotate it slowly, say, ten to twenty revolutions
per minute. Within the drum I provide knives or beaters secured to a shaft
passing through the drum and driven at a very high speed, so that they will act
upon the respective ingredients of the charge with the required effect of reducing
and intermixing them, while the slowly rotating drum constantly throws the
charge towards the centre, and presents the -ingredients to the reducing edges of
the knives or beaters in a constantly changing relation. In this way I simul-
taneously reduce the nitro-cellulose to pulp, comminute the camphor and other
ingredients, and thoroughly mix them altogether in the most thorough and effectual
manner; this intermixture being progressively more and more rapidly promoted as
the reduction of the ingredients progresses until the charge is brought to the
required condition, all of the ingredients being thoroughly reduced and the

page_text: compound being mixed homogeneously, while by conducting the process in a closed
vessel and completing it at one operation I avoid the repeated handling of the
ingredients or compound, and prevent the accretion of impurities incident to such
repeated manipulation and exposures.
As the nitro-cellulose when charged into the drum is comparatively very light,
and the camphor and other ingredients comparatively heavy, it will be seen that
it is essential to have the speed at which the knives or beaters rotate high enough
to ensure their proper action upon the lightest and least friable ingredients of the
charge, and also to have their surfaces adapted to their proper action upon the
heaviest ingredients. For the particulars of the construction of the knives I refer
to the description hereinafter given, but as to their rate of rotation I give as the
practical rule which I have adopted in use the following, to wit, in a drum of five
feet interior diameter with knives or beaters projecting from their shaft twenty
one inches on each side, I drive the shaft carrying the knives eighteen hundred or
two thousand revolutions per minute, so that the end of each blade or beater travels
say from eighteen to twenty thousand feet per minute. The speed of rotation of
the drum is as already stated very slow, and only requires to be such, relative to
that of the knives, as will ensure the turning over of the charge and its constant
return from the circumference towards the centre or within the range of the knives
or beaters fast enough to maintain a constant supply for their action.
Having now described my improvements in the process of preparing these
compounds, I will proceed to describe my improvements in the apparatus for the
conduct of my improved process.
In the preparation of compounds of pyroxyline, such as hereinbefore referred to,
the reduction of the ingredients cannot be satisfactorily effected by the ordinary
operation of grinding, since the mills usually employed for such purposes soon
become clogged with the camphor and other ingredients, and their reducing action
is at once retarded and very soon practically ended. In addition to this difficulty
the grinding surfaces of these mills and the materials ground in them are so acted
upon by each other that the grinding surfaces are reduced by attrition, and there
is consequently a considerable amount of pulverized metal thus introduced into
the compound. Moreover the beating engine in which the nitro-cellulose was
reduced has its revolving knives necessarily working past its fixed knives very
closely, and these knives are acted upon by the slightest residuum of acids in the
nitro-cellulose and are more or less abraded, so that in the beating engine as in the
grinding mills there is an appreciable quantity of triturated metal incorporated
with the pulp, and an equally appreciable oxidating effect producing a discoloration
which must be dissolved and washed out by a subsequent process.
It is the object of the second branch of my improvements to obviate these
difficulties, and to this end my Invention consists in an improved reducing and
mixing apparatus in which the simultaneous reduction of the different ingredients
of the compound is made practicable by due provision for the differences between
the specific gravities of the ingredients and their respective conditions in other
respects, and this reduction is effected without discoloring the charge, thus obviating
the necessity of a subsequent treatment to remove such discoloration.
In the accompanying Drawings which form part of this Specification, Figure 1
is a vertical transverse section through the apparatus on the line x, x, of
Figure 2; and
+
Figure 2 is a vertical longitudinal section on the line y, y, of Figure 1.
Two strong uprights A, A, properly secured to the bed plate or foundation B
afford bearings for the hollow trunnions of the drum C which is rotated on these
trunnions, as will presently be more particularly described.
Bracket arms a, a,
projected from the uprights afford bearings for the shaft D which passes through
the drum and through the hollow trunnions, as seen in Figure 2 of the Drawings.
On one of the projecting ends of the shaft D its driving pulley J is mounted.
The drum C is a strong hollow cylinder of metal, of say five feet diameter, with
a plain interior surface, and with a gate or door E through which the ingredients

page_text: '
are charged or removed. This door is closed and secured in place by bolts or other
suitable fastenings, and may be raised or lowered as required in opening or closing
the cylinder by means of a chain suspended on pulleys. The opening at each end
of the drum C is reinforced by flanges on the trunnions which serve to attach them
to the drum, strengthening the shell at that point. A driving pulley G is mounted
on a hub attached at one end of the drum and serves to rotate it.
The shaft D carries the knives or beaters E, E, E, which are flat blades of fine
steel, a quarter of an inch thick, and tapering from a width of four inches near the
shaft to one inch at the point, which is rounded off. These knives are fitted to
the shaft in any suitable manner and at some distance apart. In the instance
shown the plates or blades are swelled at the centre and tapered towards each
end, the centre being bored out so that the blades can be slipped on the shaft into
their proper positions, and projecting in this instance about twenty one inches on
cach side of the shaft. They are placed spirally on the shaft so that these edges
and points form a series of reducing surfaces acting successively upon the charge
at different points in the drum as the shaft rotates. They are distanced apart and
kept in place longitudinally by collars e, e, interposed between two adjacent blades
and screw nuts ff, interposed between the outer surface of the blades and the ends
of the drum, a space being left between the collars of the screw nuts and the drum
in which I place packing for the purpose of preventing the charge from wasting or
being thrown out through the annular spaces between the shaft and the hollow
trunnions.
Instead of mounting the drum upon trunnions as herein described and shown, I
contemplate supporting it upon rollers placed under it and rotating the rollers so
that they will rotate the drum at the required slow speed; I also contemplate
placing on the interior of the drum cleats or other irregularities of the surface in case
any of the ingredients to be reduced are of such weight or character as to make the
smooth interior surface inefficient to prevent slipping.
The operation is as follows:-The drum is charged with the washed nitro-
cellulose, the camphor, the pigments, and any other substance that is to be
incorporated in the compound.
The drum is then closed, the door or gate E secured fastened in place, and the
charged drum slowly rotated on its trunnions, so as to constantly turn the charge
over and throw it towards the shaft and within the range of the knives or beaters.
The shaft D meanwhile is driven at a speed such as herein before mentioned, so that
the beaters will act constantly upon the ingredients of the charge, reducing them
and mixing them thoroughly together, and when this reduction and intermixing
has been effectually completed, the machine is stopped and the charge removed
from the drum and submitted to pressure, so as to free it from the excess of aqueous
moisture when it is ready for the first stage of the converting process.
The knives or beaters act separately but in concert, and their action differs
essentially from that of the moving and fixed knives of the beating engine, or the
moving and fixed teeth of the grinding mills herein before mentioned, as in my
improved apparatus there are no stationary knives or beaters or teeth against
which the revolving blades act, but these blades exert their reducing force entirely
of themselves, deriving their efficiency from the high speed at which they are
driven, and thereby effecting of themselves what has heretofore involved the use
of opposing reducing surfaces. By this means I avoid the clogging to which the
grinding mill is subject, and the abrasion of the teeth or knives to which both the
inil and the beating engine are liable as already stated, and accordingly do not
encounter the oxidating or rusting effect of such accretions in the charge.
To counteract any tendency to become over heated during the operation, I
maintain a circulation of water about the outer surface of the drum, upon which
the water can be sprayed or sprinkled and allowed to trickle down into a receptacle
placed underneath, and from which it is led off by a waste pipe, or I may have a
double shell for the drum, and a water circulation between the two shells, as in
puddling machines. I propose having in some cases simply a trough of water

page_text: placed underneath the drum, so that the lower portion of the drum as it rotates
will be immersed in water. I also contemplate using a circulation of air for the
same purpose, that is, to prevent any overheating of the apparatus.
Having thus described the nature and objects of my Invention, what I claim as
new and desire to secure by Letters Patent is,―
First. The hereinbefore described process of preparing compounds of nitro-
cellulose for the converting process by charging the ingredients together into the
reducing and mixing apparatus, and simultaneously reducing and mixing the
charge, substantially as set forth.
Second. The combination with the drum rotating on its axis of the independently
revolving knives or beaters within the drum, substantially as and for the purposes
described.
Third. The knives or beaters arranged upon the independent shaft and driven
at a high velocity to reduce and mix the ingredients of the charge in combination
with the drum independently rotated at a low speed to throw the charge within
the range of the knives, substantially as described.
In witness whereof, I, the said Sidney Pitt, have hereunto set my hand and
seal, this Twenty third day of August, in the year of our Lord One
thousand eight hundred and eighty one.
SIDNEY PIII.
(L.S.)