Improvements in Pug Mill Knives.
Year: 1891

page_text: Date of Application, 12th June, 1891
Complete Specification Left, 10th Mar., 1892-Accepted, 16th Apr., 1892
PROVISIONAL SPECIFICATION.
Improvements in Pug Mill Knives.
I, JOHN WILLIAM CRAVEN of Roundwood Brick Works Wakefield in the
County of York, Engineer do hereby declare the nature of this invention to bé as
ollows:-
This invention relates to knives for pug-mills such as are employed in connection
with brick making machines being more particularly intended for use in conjunction
with the machines known as Craven's Patent Brickmaking Machines.
By means of this invention the clay after being acted upon by the pugging
knives is forced out of the mill more effectually than is possible with the
arrangement heretofore employed and the parts are so constructed as to be less
liable to wear.
With these objects the double knife at the delivery end of the shaft is made of
peculiar form as hereinafter described. The front or cutting edge of the first
blade which forms a continuation of the screw or helix formed by the ordinary
pugging knives is straight but the under surface or surface that acts upon the clay
to expel it from the delivery orifice is of concave form so as to counteract the
centrifugal force and tend to drive the clay from the periphery towards the centre.
The rear edge is curved in the plane of rotation the curve being of shorter radius
near the centre than at the periphery and at the central part forms a ridge
extending to the centre or axis of rotation.
The front or cutting edge of the second or extra blade of the knife is curved
upwards in about an arc of a circle so as to project above the plane of rotation of
the cutting edge of the first blade. This enables the second blade to act upon the
clay that has escaped the action of the first knife and effectually assist in expelling
it from the delivery orifice. This second blade is made of concave form on its
under or acting surface in a similar manner to the first blade and its rear edge is
likewise curved in the same way.
Dated this 19th dox of 1001
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C., Agents.
COMPLETE SPECIFICATION.
Improvements in Pug Mill Knives.
I, JOHN WILLIAM CRAVEN of Wakefield in the County of York Engineer do
hereby declare the nature of my 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 relates to knives for pug mills such as are employed in
connection with brick making, machines being more particularly intended for
use in conjunction with the machines known as Craven's Patent Brick Making
Machines.
By means of this invention the clay after being acted upon by the pugging
knives is acted upon and forced out of the mill more effectually than is possible
with the arrangement heretofore employed and the parts are so constructed as to
be less liable to wear.
With these objects the knife at the delivery end of the pug mill shaft is made of
peculiar form as hereinafter described. The front entering or cutting edge of the

page_text: first or leading blade which constitutes a continuation of the screw or helix formed
by the ordinary pugging knives is straight or nearly straight but the under surface
or surface that acts upon the clay to expel it from the delivery orifice is concave
so as to counteract the centrifugal force and tend to drive the clay from the
periphery towards the centre. The rear edge is curved in the plane of rotation
the curve being of shorter radius near the centre than at the periphery and at
the central part forms a ridge extending to or towards the centre or axis of
rotation.
The front cutting or entering edge of the second or extra blade of the knife is
curved upwards in about an arc of a circle so as to project above the plane of
rotation of the cutting or entering edge of the first blade. This enables the second
blade to act upon the clay that has escaped the action of the first blade and
effectually assist in expelling it from the delivery orifice.
This second blade is made of concave form on its under or acting surface
in a similar manner to the first blade and its rear edge is likewise shaped in the
same way.
And in order that my invention may be fully understood I shall now proceed
more particularly to describe the same and for that purpose shall refer to the
several figures on the annexed sheet of drawings the same letters of reference
indicating corresponding parts in all the figures.
Figure 1 of the accompanying drawings represents a knife with a pair of
blades formed according to this invention viewed from the front edge of the second
blade.
Figure 2 represents the knife in plan.
Figure 3 represents the knife viewed from the front edge of the first blade and
Figure 4 represents the knife viewed from the under side.
A represents the pug mill shaft, B that part of the knife termed the first
blade and C that part of the knife termed the second blade. The front or entering
edge of the first blade B is straight as represented at d and the under or acting
surface (as shewn in Figures 3 and 4) is concave which prevents the clay from
being compressed against the sides of the delivery orifice or passage through which
it is forced by the rotation of the knives. The rear edge e is curved as represented
in Figures 2 and 4 and forms a curved ridge projecting beyond the end of the
boss (Figure 4).
The second blade C likewise presents a concave acting surface, as represented in
Figures 1 and 4, its front or entering edge f projecting above the plane of rotation
of the front or cutting edge d of the first blade B as represented in Figures 1 and 3
thus enabling it to cut into or enter the clay left at the back of the said first
blade. The rear edge g of the blade C is similar to that of the blade B as herein-
before described and represented in Figures 2 and 4.
In place of both blades being formed of the shape hereinbefore described with
reference to the drawings the second blade may be so formed the first blade being
of any other suitable or ordinary shape.
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. A pug mill knife for the delivery end of a pug mill the said knife being con-
structed with two blades the second or extra blade being concave on its under or
acting surface and being provided with a cutting or entering edge projecting above
the plane of rotation of the cutting or entering edge of the first or leading blade
and having a curved rear edge projecting beyond the end of the boss in combina-
tion with a first or leading blade having a concave acting surface and a curved rear
edge projecting beyond the end of the boss all substantially as hereinbefore
described and illustrated in the accompanying drawings.
2. A pug mill knife having in combination with a first blade a second blade

page_text: concave on its under or acting surface and having a cutting or entering edge
projecting above the plane of rotation of the cutting or leading edge of the first
blade and having a curved rear edge projecting beyond the end of the boss as.
herein before described and shewn in the accompanying drawings.
Dated this 10th day of March 1892.
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C., Agents.