An Improved Bakers' Hot Air Oven.
Year: 1895

page_text: Date of Application, 15th June, 1895
Complete Specification Left, 15th Apr., 1896-Accepted, 15th June. 1896
PROVISIONAL SPECIFICATION.
An Improved Bakers' Hot Air Oven.
I, MARK HENRY HURRELL, of Fairview New Brompton, Kent, Engineer do
hereby declare the nature of this invention to be as follows:-
A bakers oven to obtain any required temperature with equality over every part
of the sole, excepting that the front receives beat in excess of the back when the
oven is set with a peel; when set with the frame, to be described, the construction
is arranged to give equal temperature. An arrangement of flues and dampers to
permit of excess of "top" or "bottom" heat as desired.
All the flues are so arranged as to have each as much surface as the sole of the
oven and equalising plates are used to overcome such variations as may occur from
imperfect stoking.
I prefer to make the first flue above the fire with fire lumps supported on other
lumps so that any one may be removed and renewed without alteration to the
rest of the construction, and the flue case above and the uptakes are of iron
equalising plates; lining the sole and sides of the oven with thick tiles, or thin
tiles bedded on a mixture of slag and sand resting on the equalising plates; the
highly non-conducting material " slag" being used to check the heat where
desired.
I also prefer to make the whole front of the oven to open by several light doors,
the width of the peel, even where a setting plate is not used, closing them in again
by a covering door filled with slag, this allows the time of setting to be decreased
by more than one half.
The setting frame I make of steel ribbon or wire, the crossings being where the
green louf should be placed, when wire is used I prefer to place on the crossing a
disc of gauze not quite so large as the green loaf as I find all projecting material,
both metal and non conducting material, such as asbestos has a greatly deterrent
effect on the growing and shaping of the loaf. The frames are run in on rails and
dropped by a cam in the ordinary way.
M. H. HURRELL.
1 MARK HENRY HURRELL, Engineer of Fairview, New Brompton Kent 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 :-
A baker's oven to obtain any required temperature with equality over every
part of the sole excepting that the front receives heat in excess of the back when
the oven is set with a peel; when set with a frame the construction is arranged to
give equal temperature, also an arrangement of flues and dampers to permit of
excess of "top" or " bottom heat as desired.
"
In the accompanying drawings
Sheet 1. Fig. 1. is a sectional side elevation of an oven constructed according to

page_text: prau of the rurnace and lower пие.
Sheet 2. Figs. 5 and 6 plans of frames.
Fig. 7. section of frame and ribbon.
Fig. 8. front elevation of oven.
A. A. A. are the flues and A'A' and A" the uptakes through which the gaseous
products of combustion from the furnace F pass in the directions of the arrows
and the superficial area of each of these flues is the same as that of the sole of the
oven C.
The furnace gases pass equally over the top and bottom when the damper Dis
in about its mean position as shown; but by raising the counterweight E the
damper D may completely close the uptake A³ and therefore the passage of gases
through the bottom flue.
Reversing the action of the counterweight E closes the upper flue and
uptakes AA" while the amount of gases is governed by the position of the
ordinary damper D' in the chimney.
F is the furnace and F¹ the furnace chamber over which heat spreads with fair
uniformity, the fire-lumps directly over the fire being slightly thicker than the
others the excess of heat from the greater heat radiation directly over the
fire is thus nearly compensated such variation as occurs is quite neutralised by
the equalising plate G. The spaces 9g between the equalising plates G G¹
and the interior of oven C₁ are filled with a mixture of sand and slag in the
proportions required to give quite uniform temperature either on the top or bottom
of oven.
The equalising plates G G' are simply plates of iron preferrably not less than
inch thick their conductivity being so enormous compared with the nonconducting
sand and slag mixture that although the plate directly over the furnace may be
red hot the oven tiles directly over this do not become hotter than those at the
sides as most of this local heat in the plate is practically screened by the slag from
passing directly upwards, the plate conveying the heat so rapidly to its other
parts; the actual efficiency of the combination is best determined by actual
practice, that is, if any tiles in the interior of the oven get too hot then they
should be lifted and a small amount of slag put in the place of some of the
.sand.
As the latent heat of setting frames have a greatly deterrent. effect in the
growth of a loaf and the residual heat of the frame on the temperature of the
bakehouse when drawn out I make a frame to diminish these evils as far as
possible.
Fig. 5 is a plan of a setting frame H the rim of which is made of a slight steel band
or steel tube to which the ribbons or wires 1. I. are fastened when wires are used
I place on the crossing, which is adapted to the size of the loaf, a disc of gauze
about but not larger than the "green" loaf the wires and ribbons are as few as are
sufficient to carry the weight of the loaves without sheltering them from the
radient heat from the sole, on which heat their growth mainly depends.
Fig. 7. is a section about full size of a rim and attachment of a ribbon or
.wire.
Fig. 8 is an elevation of oven front which differs from an ordinary oven only in
having a second screening door K made of thin sheet steel filled with a non
conductor, preferably slag, to prevent the continuous loss of heat from the large
oven fronts passing out into the bakehouse, this second door I find it desirable to
hang horizontally so that a simple counterweight on the cord L (Fig. 1) carries it,
when opened, directly away from the setter.
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 a baker's oven an arrangement of flues and dampers which allow the

page_text: whole of the furnace gases to pass under the sole of the oven or over the top of
the oven or in any desired proportion both under and over substantially as and for
the purposes set forth.
2nd. A construction of flue and equalising plates which allows the whole of the
products of combustion to surround the oven without any undue heat at any part
substantially as described and shown.
3rd. A setting frame with a minimum amount of material substantially as
described and shown.
M. H. HURRELL.