An Automatic Screw Brake for Screw Pulley Blocks, Oranes, Screw Jacks, and such like.
Year: 1893

page_text: Date of Application, 16th Dec., 1893-Accepted, 3rd Feb., 1894
COMPLETE SPECIFICATION.
An Automatic Screw Brake for Screw Pulley Blocks, Oranes, Screw
Jacks, and such like.
We, ANDREW MATTHEW of 12 Sussex Street, Glasgow, Engineer, and
ALEXANDER LEITH of 29 Eaglesham Street, Glasgow, 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 :-
This invention relates to an automatically acting screw brake for screw pulley
blocks, cranes, screw jacks and such like and it has for its object to utilize to the
fullest extent the power of the worm or screw whilst retaining its self-sustaining
quality.
And in order that the invention may be properly understood we have hereunto
appended an explanatory sheet of drawings, showing, by way of example, a double
speed screw pulley chain block.
On the drawings:-
Fig. 1 is a side view of the pulley block-partly in section.
Fig. 2 is a plan.
Fig. 3 is an end view, partly in section. The section is taken on the line x-x
Fig. 1 and looks into the back strap.
Fig. 4 is a section on the line y-y Fig. 1 looking towards the back strap.
a is the usual chain pulley for turning the worm spindle b. o is the load chain
pulley. The worm d on the spindle may be double threaded as shown. d¹ is a
collar on the spindle and this collar is reduced at and ends with a journal and
step d³. e is a hollow bearing thimble fitted loosely into the back strap f and its.
collar or shoulder f¹ bears against said strap. The end of the spindle and the
part of the collar turn freely within the thimble e which is bored out for their
reception. 9 is a pawl which is fitted loosely into a recess in the reduced part d
of the collar and so that it cannot move either backward or forward but only in an
upward direction as shown in the sectional views at Figs. 3 and 4. The internal
surface of the shoulder f¹ of the thimble is made with four or other number or
recesses which correspond with the pawl and into which the latter can at certain
times, as hereinafter explained, enter.
A small spiral or other suitable spring i may be fitted underneath the pawl for
the purpose of normally pressing it upwards. The spring, if a spiral one, can be
inserted in a hole j made in the collar part of the spindle in order to prevent it
being displaced. If a plate spring is used it may be secured at one end to the
spindle.
k is a pin which is fitted firmly into the back of the thimble e, and acts as a
centre or pivot for the worm spindle to bear against and turn on.
The action of the device is as follows:-
When the worm is turned to the right, the thimble e is stationary, as the spindle
turns freely within it and the pawl g over-rides the inclined ends h¹ of the recesses h;
but when the worm is turned in an opposite direction, the spring i, forces the pawl
into one or other of the recesses h, (see Fig. 3) and, as a consequence, the thimble e
is turned simultaneously with and at the same speed as the worm spindle. As the
worm presses with considerable pressure against the pivot k, when it is turned to
the left hand, the shoulder of the thimble e is also pressed against the back strap f.
The friction resulting from the grinding or working of the face of the shoulder f',
against the back strap gives sufficient brake power to make the pulley block self-
sustaining.

page_text: The pulley block is so constructed, that, when it is lifting a load the worm spindle
turns to the right and when the load is being lowered the worm spindle turns to
the left.
The friction surfaces between the shoulder f¹ and the strap f, may be increased
or diminished as desired by simply enlarging or reducing the size of the strap and
shoulder.
In some cases the shoulder f¹ may be dispensed with and the strap f made with
a recessed solid end into which the end of the thimble e enters. In this case the
frictional surface would be between the end of the thimble and the interior face of
the recess in the back strap.
If desired the spring i, may be dispensed with as the pawl will always catch,
whether acted upon by a spring or not, in the lower recesses of the thimble. Its
gravity, when it turns round to the lower side, is sufficient to cause it to fall into
these recesses.
The invention may, with equal advantage, be applied to cranes, screw jacks, etc.
If desired two or more pawls may be fitted on the spindle, and in some cases, if
so desired, the action may be reversed, that is to say, the pawl or pawls may be
fitted to the thimble and the spindle or its collar be recessed for their reception.
The following are some of the advantages claimed for this invention.
1. Safety against running down, as the shoulder can be made as large as
required to sustain the load, whilst the lifting power is not interfered with.
Previously, in, say, a double speed screw pulley-block the friction collar which was
solid with the worm had to be made too large for the lifting power to be of any
great benefit.
2. The tear and wear in this invention is reduced more than half because the
worm spindle does not work in the same journal each way.
When heaving up
the
load the wear is at d³, k, and when lowering the load the wear and friction is
at f¹, f.
3. From its construction it is self protective as shown at Fig. 2. Nothing can
get out of place and it is not so liable to be damaged as other arrangements.
4. The worm, whilst retaining its sustaining power, is made to give the highest
possible efficiency.
The parts of the apparatus can be modified or altered to suit the various
appliances to which it may be fitted.
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 consider novel and desire to claim is :-
1. The general arrangement and combination of parts of the automatic screw
'brake, substantially as hereinbefore described with reference to the drawings
annexed.
2. The combination with the worm spindle, of a thimble or bearing in which
said spindle turns and of one or more pawls for locking the spindle to the thimble
at certain times, substantially as and for the purpose hereinbefore set forth.
Dated this 15th day of December 1893.
H. D. FITZPATRICK,
70, Wellington Street, Glasgow, Agent.