Improvements in Pulley Blocks and in certain other Lifting Appliances.
Year: 1892

page_text: S
Date of Application, 3rd Dec., 1892
Complete Specification Left, 18th Mar., 1893-Accepted, 6th May, 1893
.PROVISIONAL SPECIFICATION.
Improvements in Pulley Blocks and in certain other Lifting
Appliances.
We, ROWLAND PRIEST and BENJAMIN MILLWARD, both of Pulley Block
Works, Cradley Heath, Staffordshire, Pulley Block Manufacturers, do hereby
declare the nature of this invention to be as follows:-
This invention has reference to that class of pulley blocks cranes and crabs in
which a worm wheel and worm are used to obtain the increase of power. It is well
known that in lifting appliances of this class the weight to be lifted, acting through
the chain which passes over the chain wheel cast with the worm wheel, thrusts the
worm and its shaft endwise against a bearing and thus causes considerable friction
and loss of power. This defect we overcome as follows:-
:―
We employ two worm wheels side by side that is a right hand worm wheel and a
left hand worm wheel both of the same diameter and mounted upon the same axle
and both gearing with the same worm which latter is of peculiar construction as it
is a right hand worm and a left hand worm in combination, that is to say, the
thread (or threads) is or are not continuous but is or are crossed at intervals by the
screw groove running in the opposite direction. To each of the two worm wheels
is cast a chain wheel over which the lifting chains pass in opposite directions so
that the weight tends to turn one worm wheel in one direction and the other worm
wheel in the opposite direction and as the worm wheels tend to thrust the worm in
opposite directions with the same pressure the result is that there is no end thrust
whatever upon the worm.
Our invention is equally applicable to " differential" pulley blocks and lifting
appliances as to those which lift direct.
£Decemben 1002
CHARLES BOSWORTH KETLEY,
Agent for the Applicants.
COMPLETE SPECIFICATION.
Improvements in Pulley Blocks and in certain other Lifting
Appliances.
We, ROWLAND PRIEST and BENJAMIN MILLWARD, both of Pulley Block
Works, Cradley Heath, Staffordshire, Pulley Block Manufacturers, 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 reference to that class of pulley blocks cranes and crabs in
which a worm wheel and worm are used to obtain the increase of power. It is well
known that in lifting appliances of this class the weight to be lifted, acting through
the chain which passes over the chain wheel cast with the worm wheel, thrusts the
worm and its shaft end wise against a bearing and thus causes considerable friction
and loss of power. This defect we overcome by our invention which we will
describe by referring to the accompanying drawings on which Figure 1 is a sectional
side elevation of a pulley block constructed according to this invention; Figure 2
is a sectional end elevation of the same; Figure 3 is a plan of the same and
Figure 4 shews the worm of the same on an enlarged scale separately; Figures 5,6
and 7 illustrate a modification of our invention.
The same letters of reference indicate the same or corresponding parts in all the
figures

page_text: Referring firstly more particularly to Figures 1, 2, 3 and 4, in carrying out our
invention we employ two worm wheels marked respectively A and B side by side
of which A is a right hand worm wheel and B is a left hand worm wheel. The worm
wheels A and B are both of the same diameter and pitch and are mounted to
revolve loosely (or one or them revolves loosely) upon the same axle C and they
both gear with the same worm D which is formed with the shaft E on the end of
which is fixed the usual chain wheel F provided with an endless hand chain G.
The worm D is of peculiar construction as it is a right hand worm and a left
hand worm in combination, the right hand worm part gearing with the right hand
worm wheel A, and the left hand worm portion gearing with the left hand worm
wheel B. To the worm wheel A there is a cast or otherwise fixed a chain wheel H
and there is a similar chain wheel I fixed to or cast with the worm wheel B and
over these chain wheels H and I the lifting chain passes or chains pass in opposite
directions as will be clear by an examination of Figures 1 and 3 where it will be
seen that the ends of the lifting chain are fixed to the hook K and that one
portion of the lifting chain passes over the worm wheel 1 from the right hand
side and down the left hand side and that the other portion J2 of the lifting chain
passes up and over the chain wheel H on the left hand side and down to the right
hand side. By this arrangement the weight which is being lifted tends to turn one
of the worm wheels in one direction and the other worm wheel in the opposite
direction and as the worm wheels A B thus tend to thrust the worm D in opposite
directions with the same pressure the result is that there is no end thrust what-
ever upon the worm or worm shaft.
The worm D and worm wheels A B are by preference made of a coarse pitch
double thread, otherwise when the two worms are formed together as shewn in
in Figure 4 the pieces d forming the portions of the worm thread become rather
small. In this worm the thread or threads is or are not continuous but is or are
crossed at intervals by the screw groove running in the opposite direction.
In the modification of our invention which is illustrated by Figures 5, 6 and 7
the two worms (in this case marked respectively D₁ D2) are not formed together
as in the example hereinbefore described and illustrated by Figures 1, 2, 3 and 4
but they are kept a short distance apart and the shaft E with which they are
formed is arranged slightly askew as shewn so that the worm D' which gears with
the worm wheel B does not touch the teeth of the worm wheel A. and similarly the
worm D² which gears with the worm wheel A does not come in contact with the
teeth of the worm wheel B. In other respects this pulley block is the same as that
herein before described and illustrated by Figures 1, 2, 3 and 4.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
In worm and worm wheel pulley blocks, cranes and crabs, the means herein-
described for lifting the load and neutralising the end thrust on the worm and worm
shaft, consisting of the combination of a right hand worm and a left hand worm
formed on or fixed to the same shaft and gearing respectively with a right hand
worm wheel and a left hand worm wheel mounted upon the same axle each of the
worm wheels having a chain wheel cast or otherwise fixed to it a portion of
the lifting chain being led over opposite sides of the chain wheels so that when the
worm shaft is turned to lift the weight the two worm wheels turn in opposite
directions and the end thrust on the worm and worm shaft is neutralised, all
substantially as hereinbefore described and illustrated by the accompanying
drawings.
Dated this 17th day of March 1893
CHARLES BOSWORTH KETLEY,
Agent for the Applicants.