Improvements in Screw Pulley Blocks and other Lifting or Hoisting Apparatus.
Year: 1889

page_text: *Date of Application, 17th May, 1889
Complete Specification Left, 17th Mar., 1890-Accepted, 17th May, 1890
*
PROVISIONAL SPECIFICATION.
Improvements in Screw Pulley Blocks and other Lifting or
Hoisting Apparatus.
I, JOHN MACKENZIE, of Egglescliffe Yarm-on-Tees, Durham, Engineer, do hereby
declare the nature of this invention to be as follows:-
My invention relates to improvements in Pulley Blocks or other hoisting or lifting
apparatus, wherein the power is obtained through the medium of a worm and worm
wheel and known as screw pulley blocks.
The objection to screw pulley blocks as at present constructed, is that the thrust of
the worm or screw has to be taken by the frame or bearing in which the worm works,
and necessitates not only a very strong frame, but various collars and other devices to
diminish the friction due to this thrust.
The object of this invention is to obviate this, and is accomplished in the following
manner. I employ a worm or screw with a right handed thread and a left handed
thread, cut or cast one across the other, and instead of a single worm wheel, I use
two worm wheels arranged to work side by side on one spindle or shaft, in the rim of
one of these wheels I arrange cogs or teeth to suit the pitch and angle of the right
handed thread on the worm, and in the rim of the other wheel I arrange cogs or
teeth to suit the pitch angle of the left handed thread on the worm, the result of this
arrangement is that when the worm is put into position, it engages with both wheels,
and when the worm is rotated the wheels will move in opposite directions, and the
thrust is taken by the wheels themselves and not by the frame. To apply this motion
to pulley blocks, I use a suitable frame provided with a hook to support the block,
the frame is also provided with suitable bearings & pivots for the worm and worm
wheels. I arrange on the outside of each of the worm wheels, a chain wheel with
beds cast or cut in to suit the size and pitch of the chain used. Two chains are put
on to the chain wheels, and the weight to be lifted is attached to the two ends of the
Lifting and
chain hanging from the opposite side of each of the worm. wheels.
lowering are accomplished by revolving the worm in opposite directions..
JOHN MACKENZIE.
COMPLETE SPECIFICATION.
Improvements in Screw Pulley Blocks and other Lifting or
Hoisting Apparatus.
I, JOHN MACKENZIE, of Egglescliffe, Yarm-on-Tees, in the County of Durham,
Engineer, 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 :—
My Invention has reference to hoisting or lifting apparatus of the screw pulley block
type, in which the power to raise and lower weights is obtained from the combined action
of two wheels or pulleys which carry the lifting chains and which are forced round in
opposite directions by the rotation of a specially constructed or double acting worm
which gears into a couple of combined worm and chain wheels and rotates them in
opposite directions.
Pulley blocks constructed with this combination of moving parts are capable of
sustaining a suspended load in any position, the tendency to run down being prevented
by the worm interlocking with the worm wheel, the interlock being more or less
reliable according as the angle at which the worm is pitched is less or greater.
In screw pulley blocks as hitherto constructed the worm wheels have been rotated

page_text: by single acting worms only, and the reacting thrust of the worm has consequently
been communicated direct to the frame or fixed parts of the blocks, causing unnecessary
strain and friction to provide for which the frame or fixed parts of the block have
been made of greater strength than is required in blocks constructed according to my
invention and sleeves and collars or other devices which I dispense with have been
employed to diminish the friction.
Apparatus constructed according to my invention consists as follows: a worm
which I term a double acting worm that is provided with both a right hand thread
and a left hand thread pitched to the same angle intersect each other, the threads
being intermittent to leave the requisite spaces at the points of intersection of the two
threads. This double acting worm engages with two worm wheels rotating on the
same shaft which is of course.placed at right angles to the shaft of the worm; cast in
one piece with or otherwise attached to each worm wheel is a wheel or pulley to carry
the lifting chains. The worm is caused to rotate by a hand wheel which is usually
actuated by an endless rope or chain.
.
As the worm rotates its right hand thread forces one worm wheel round in one
direction whilst the left hand thread forces the other worm wheel round in the opposite
direction thus making the worm double acting, consequently the lifting chains which
are slung from opposite sides of the chain wheels are simultaneously raised or lowered
by turning the worm one way or the other as required.
The essential feature of my invention is the particular construction of the worm to
make it double acting and the mode in which it forces two worm wheels round in
opposite directions; and in order that my invention may be fully understood and
readily carried into effect, I will now proceed to describe the same and for that
purpose shall refer to the accompanying drawings which illustrate a screw pulley
block constructed to work with an arrangement or combination of moving parts to
which my invention is especially applicable.
In the drawings Figures 1 and 2 are corresponding views of a screw pulley block
with all its parts fitted together in working order. Figures 3 and 4 are drawn to a
larger scale, Figure 3 illustrating in sectional view the manner in which the worm
and worm wheels are geared together, and Figure 4 is a detail view of the
worm.
In the Figures a is the worm, b1 62 are the worm wheels with which are combined
the chain wheels c¹ c², that is worm wheel and chain wheel care in one piece or
casting, similarly worm wheel 2 and chain wheel c³ are in one piece or casting; these
combined worm and chain wheels rotate on the same axis or shaft
which passes
through the fixed parts or frame of the block, the lifting chains e are slung from
opposite sides of the chain wheels in the usual manner so that they are drawn up or
let out simultaneously by rotating the chain wheels in opposite directions, the slack
ends of the chains being united to form the usual loop below the apparatus. By
turning the hand wheel to the right or left as required the lifting chains are raised
or lowered at will. Referring to Figure 4 which illustrates a worm constructed
according to my invention, that is with right hand and left hand threads intersecting
each other, it will be observed that the usual continuous thread of a single acting
worm such as would follow the lines X X for the right hand thread and the lines Y Y
for the left hand thread is cut away where such threads would intersect, leaving inter-
secting but continuous tracks between lozenge shaped projections a¹ for the reception_
or passage of the teeth of the worm wheels, the tapered sides of which projections
correspond to the angle of inclination of the intersecting tracks. When the worm
and worm wheels are geared together and put in operation, the sides of the lozenge
shaped projections corresponding to lines X X engage with the teeth of the right
hand worm wheel and force it round in one direction whilst the other sides of the
said projections corresponding to lines Y Y similarly engage with the teeth of the
left hand worm wheel and force it round in the opposite direction in the manner
required.
It must be understood that I do not restrict myself to the particular form of
hoisting apparatus illustrated in the drawings which are only intended to show a

page_text: useful application of my invention, as the general construction and arrangement of
details of hoisting and lifting apparatus of the screw pulley block type can be varied
to adapt them to various purposes or positions without departing from the essential
feature of my invention so long as the worm wheels which actuate the lifting gear are
forced round in opposite directions by a double acting worm constructed and operating
in the manner hereinbefore described.
Having now particularly described and ascertained the nature of my invention and
in what way the same is to be performed, what 1 claim is :-
:-
Firstly In the construction of hoisting or lifting apparatus of the screw pulley
block type. the employment of a double acting worm provided upon a worm shaft and
actuating the lifting gear by rotating two worin wheels in opposite directions, substan-
tially in the manner and for the purpose as hereinbefore described and illustrated by
way of example in the accompanying drawings.
Secondly-The general arrangement of parts combined, fitted and operating
together to constitute a lifting or hoisting apparatus of the screw pulley block type,
substantially as described with reference to the accompanying drawings.
1000
G. J. CLARKSON,
Stockton-on-Tees, Agent for the Applicant.