An Improved Single Chain Grab.
Year: 1898

page_text: Date of Application, 28th May, 1898-Accepted, 30th July, 1898
COMPLETE SPECIFICATION.
An Improved Single Chain Grab.
I, SAMUEL WILLIAM BOYER, of 1, Amberley Wharves, Paddington, London, W.,
Contractor, 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 relates to an improved grab for dredging or excavating and lift-
ing materials and it consists of a single chain grab having a jaw closing and open-
ing chain barrel working in a single central guide frame forming part of the main
frame of the grab to which the bucket jaws are pivoted, the suspension chain
winding on a central barrel of large diameter and the jaw closing chains working
on small barrels forming lateral prolongations of the central barrel and being
connected to a sliding crosshead also working in the said frame and connected by
links to the bucket jaws.
The chain barrel axis is provided with a stirrup link adapted to engage with
a catch on the frame in order to retain the barrel in its lowest position in the frame
during the closing operation and whilst the load is carried, and the invention
consists essentially in the combination with a grab so constructed, of releasing
mechanism as hereafter described whereby the release of the stirrup piece from the
catch is automatically effected immediately the suspension chain is relieved of the
load of the grab, the said gear being adapted by the change of relative position of
the parts of the grab when in the closed and open positions, to act in the reverse
way whilst the grab is open during the descending motion of the chain barrel
preparatory to closing the grab, the said gear then tending to force the stirrup
link into engagement with its catch as soon as it reaches its lowest position.
The invention will be described with reference to the accompanying drawings
wherein Figure 1 is a sectional elevation and Figure 2 is a front elevation of the
grab closed and ready to be raised, and Figure 3 is a side elevation of the grab
open.
A is the central vertical guide frame rising from a cross frame A¹ to which the
jaws B of the grab bucket are pivoted in the usual manner.
C is the sliding cross-
head working in the guides of the frame A and connected to the bucket jaws by
the pairs of links D. E is the chain barrel of large diameter to which the suspen-
sion chain is attached and on which it winds, and F F are lateral extensions of
small diameter forming chain barrels to which are attached the chains G con-
nected to the crosshead C, these barrels being spirally grooved to receive the links
of the chain. These barrels F turn in die blocks fitted to slide up and down in
the guides of the frame A and form the axis of the main barrel and to the said
barrels the stirrup link H is connected by eyes pivoting freely thereon so that the
link is free to swing within limits determined by bosses h upon it abutting against
the guides of frame A. K is a fixed hook or detent rising from the cross frame A¹
in position to be engaged by the stirrup piece H when the chain barrel descends
in the frame and reaches its lowermost position. The engagement of the stirrup
piece with the catch is ensured and its disengagement therefrom is effected at
proper times by the pull of a weight L (or it may be a spring) attached to a cord 7