Improvements in the Latch Mechanism of Furnace Doors.
Year: 1897

page_text: Date of Application, 22nd Feb., 1897-Accepted, 12th June, 1897
COMPLETE SPECIFICATION.
Improvements in the Latch Mechanism of Furnace Doors.
I, WILLIAM DOUGLASS, of Blaydon-on-Tyne in the County of Durham,
Engineer, do hereby declare the nature of said 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 certain improvements in the latch mechanism of furnace
doors in which the shorter arm of a pivoted lever latch is caused to act as, or
upon, a "pawl" engaging with slots in a circular ratchet fixed on the furnace
front, concentrically with the hinge bolt, by the action of which the furnace door
can be closed, fully opened, or opened to an intermediate extent, and there securely
held by the shorter arm or "pawl" of the latch entering one of the slots by the
automatic action of the longer arm. This automatic action works perfectly in
securing the door fully open, laid back against the furnace front, or open to an
intermediate extent but, owing to the heat of the furnace tending to slightly
warp
or twist the door and the effects of wear, it has been found difficult to
keep it perfectly airtight against the front when closed which, especially with
forced draught, is important.
"
1 therefore propose to supplement the automatic action of the shorter lever arm
by an extension of the longer arm so as, when closed, to cause it to enter into and
be securely held in a catch formed in a projecting stud in the furnace front, thus
with the "pawl" in the slot of the sector forming a "double-lock."
The accompanying drawing illustrates my invention in two forms of the door
and its mechanism.
Figs. 1, 2, and 3 shew respectively a front view, end view, and sectional plan of
the door and the latch mechanism, and Figs. 4 and 5 shew in sectional plan and
end section an alternative construction.
In the description of the figs. I will confine myself chiefly to those parts
which form the subject of the improvement in combination with such other parts
as are not part of my present invention.
Referring to Figs. 1, 2, and 3, A. is the door of flat plate, with the hinges B.
secured upon it externally and working upon the hinge pin C. supported by the
ratchet D. fixed to the furnace front plate E. The latch F. preferably of cast
steel or cast malleable iron of ☐ section is fulcrumed upon a stud G. in front of
the door, the longer end working through a guide H. and the shorter end
engaging with the "pawl" F¹ which enters the slots in the circular ratchet D.
the "pawl"F being (as I prefer) separate from the shorter arm of the latch, and
working in a guide box (as shewn in Figs. 1 and 3) to allow for adjustment in the
notches of the circular ratchet D. The latch is prolonged to engage with a slotted
catch K. projecting from the front plate E. and carries the heavy knob L. by
which the stoker raises it with his shovel, and the weight of which causes the
"pawl" F¹ to engage in the slots of the ratchet D. and also causes the outer end
of the latch to engage in the catch K. when the door is closed. The door A. is
provided with the usual regulating air grating and with a shield plate to protect
it from the beat of the furnace. When the door is closed it is not only kept so by
the "pawl" entering a slot in the circular ratchet, but it is additionally secured
and made airtight by the latch entering the slot in the catch K. which forces the
door tightly against the face of the front plate. In this arrangement the latch

page_text: mechanism is well protected from the heat of the furnace by being fixed upon the
outside of the door and the line of the hinges and of the latch and "pawl" is
direct to the hinge bolt and the slots in the ratchet.
Figs. 4 and 5 shew the mechanism in a modified form in which the door A. is
dished by stamping outward and a flat plate A' may form an inner door in which
are the air gratings to admit air entering from below between the outer and inner
doors, as shewn by the arrows, the bottom of the dished door being open for the
purpose as shewn on Fig. 5. Thus the latch and "pawl" are protected by being
enclosed in the space between the two doors and the guide H. (on Figs. 1, 2,
and 3) is not required, the latch being guided in the slot H. (through which the
knob L. passes out of the dished door) and falling into the slotted catch K.. is
secured perfectly close against the front plate E. In all the other positions as
"half open,
" 66 full open," or "laid back" against the front the door is held by the
"pawl" entering the slots in the ratchet D. until released and further opened or
closed by the stoker.
"
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 :-
1st. In furnace doors provided with lever latches engaging in slots in a fixed
circular ratchet, so operating as to retain the door in any required position, the
combination with such mechanism of a slotted catch fixed to the front plate into
which the prolonged end of the lever latch will engage in such manner as to cause
the door to be closed airtight against the front plate and to so secure it by a
"double lock."
2nd. The combination of parts forming such furnace doors comprising a front
plate E, a circular ratchet D, and catch K, secured on said front plate, a door A.
fitted with hinges B. working on a hinge pin C. in the circular ratchet, a lever
latch F. F' on a fulcrum G, a guide H. for the end of said latch F, prolonged to
engage in the slotted catch K. with knob L, all substantially as described and
shewn by Figs. 1, 2, and 3; or the modified construction shewn by Figs. 4 and 5,
with special provision for protecting the latch mechanism from heat, comprising
the front plate, circular ratchet and catch as above described, with an outwardly
dished door A. which may have an inner door or projecting plate A' attached to
it with gratings to admit air entering from below the door A. into the space
between the doors in which space is fitted the lever latch F. F' prolonged at F.
to engage in the slotted catch K.
Dated this 22nd dox of February 1897