Open fire convector

A hot air generator is constituted by cast iron plates assembled together and sheets of steel cut out and bent in order to rest on elongated plane elements with which the plates are provided, perpendicularly to their surface, in such a manner as to form a closed shallow conduit. A first horizontal portion of the conduit, provided with a drawer which serves as an ash pan and as an adjustable member for leading in external air, forms the hearth and a chamber for preheating of the air. Two vertical portions serve as chambers for slowing down and for heating the air. The second vertical portion is constituted by the rear face of a throat of moulded cast iron which permits the conventional operation of the fireplace.

BACKGROUND OF THE INVENTION 
The invention relates to hot air generators intended to be mounted in an 
open fireplace and essentially constituted by a shallow closed conduit 
comprising on the ground a horizontal part forming a hearth and chamber 
for pre-heating of the air and, on the backwall of the fireplace, a 
vertical part in which the air is slowed down by baffles and achieves its 
final temperature. 
More precisely, the invention relates to hot air generators of the type set 
out above in which one of the faces of the shallow conduit is constituted 
by plates of cast iron assembled together. The cast iron has remarkable 
qualities in this situation, but also has the inconvenience of the 
difficulty of moulding complex forms without use of a core, and thus in 
practice one cannot consider the direct moulding by pouring of the 
portions of the closed shallow conduit. Also, in the prior art, the second 
face of the shallow conduit is constituted by a wall of masonry. As a 
result, this type of hot air generator cannot be installed in a fireplace 
which has already been constructed. Furthermore, this solution does not 
give perfect airtightness and thermal insulation. 
OBJECT OF THE INVENTION 
The invention proposes to avoid these inconveniences, to reduce the cost of 
transportation of the elements, and to economise in the installation, by 
making it possible to construct the shallow conduit by simple assembly "in 
the dry", without use of tools, which a non-professional can carry out. 
SUMMARY OF THE INVENTION 
The hot air generator according to the invention is principally 
characterised in that the plates are provided on their internal face with 
plane elongated elements for guiding and channelling the hot air, two of 
which elements form the narrow faces of the shallow conduit. A cut out 
sheet of steel is applied on the plate and is bent in order to form edges 
which bear on the said two plane elongated elements, the cast iron plates 
and the sheets of steel being assembled together by simple interengagement 
"in the dry". 
According to a preferred method of carrying out the invention, the closed 
conduit comprises a horizontal element forming a hearth, a first vertical 
element applied on the backwall of the fireplace, and a second vertical 
element constituted by the rear face of a smoke throat, itself formed by 
the assembly of elements of moulded cast iron, by interengagement in the 
dry, the said rear face being provided, at the external side of the 
throat, with plane elongated elements for guiding and channelling of the 
hot air. 
Further features and advantages of the invention will appear from the 
following description:

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1 there is shown a hot air generator having the general appearance 
of a box composed of three parts fitted into each other, that is to say: 
a horizontal element 1, seen from below in FIG. 2, and constituting the 
base of the hearth; 
a first vertical element 2, seen from the rear in FIG. 3 and constituting 
the back wall of the hearth; and 
a second vertical element 3, seen from the rear in FIG. 4 and made fast to 
a smoke throat 4. 
Each element is constituted by a plate of cast iron provided on one face 
with plane elongated elements serving as deflectors and/or partitions to 
form channels for the hot air, closed on the other face and on the edges 
by a sheet of steel applied on the plate and bent up to form edges which 
bear on two external longitudinal partitions, as will be seen from the 
following. 
It can be seen, in FIG. 2, that the element 1 is formed of a sheet 10 of 
cast iron provided with an element 11 forming a continuous bent strip 
having two central branches and two external branches 110-111. By way of 
example, the plate 10 has the dimensions 600.times.550 mm, the interval 
between the two central branches of the element 11 is 225 mm., and the 
interval between each external branch and the corresponding edge of the 
plate is 45 mm. Between the central branches, the plate 10 is provided 
with a rectangular opening 12, of dimensions 220.times.200 mm., the edge 
of which parallel to the transverse branch 112 is placed at 50 mm. 
therefrom. Each central branch is provided with two small elongated 
windows, such as 113, 114, having a length of for example 50 mm., and 
separated by an interval of 50 mm. The thickness of the plate 10 is, for 
example, 10 mm., and the height of the element 11 is 50 mm. The free 
extremities of the branches 110 and 111 extend by 50 mm. beyond the rear 
edge of the plate 10. 
Similarly, the element 2, FIG. 3, is formed of a cast iron plate 20 
provided with two external strips 21, 22, and with elements forming 
deflectors, certain of which, such as 23, have the shape of chevrons. By 
way of example, the plate 20 has for dimensions: 500.times.550 mm. The 
strips 21-22 are situated at 50 mm. from the edges of the plate and their 
lower extremity extends slightly beyond (by 15 mm. for example). Their 
upper extremity is bent twice, to form an "L" , of which the large 
horizontal branch, (in the actual position of the element 2, FIG. 1) has 
for example a length of 40 mm., and the small vertical branch (in FIG. 1) 
has for example a length of 12 mm. Thus, the distance between the two 
vertical branches of the two L's 210 and 220 is, in the example described, 
360 mm. 
In FIG. 4 it will be seen that the element 3 is composed of a plate 30 of 
cast iron in the form of a trapezium, the edges of which are shaped in 
such a manner as to constitute junction elements 301, 302, 303, and a 
fourth junction element, not visible in FIG. 4. 
In the preferred manner of construction described, this plate constitutes 
the rear element of the throat 4 (FIG. 1) and this latter is in conformity 
with the description given in the French Patent Application filed on 7th 
April 1978 by the present applicant, for "Prefabricated metal throat for a 
chimney". 
As in the example described in the said patent, the large base of the 
trapezium thus has a variable dimension according to the size of the 
throat, whilst its height measured between the two junction elements 301, 
and 303 is fixed, for all sizes, at 550 mm., and that the dimension of the 
small base is itself fixed at 300 mm. 
Nevertheless, the face of the plate 30 externally of the throat is provided 
with deflectors such as 31 and with an element in the form of a bent strip 
having two longitudinal branches 320-321 joined by a transverse branch 
322, the branches 320 and 321 being respectively interrupted by openings 
323 and 324 the upper edges of which are separated, in the example 
considered, by a distance of 265 mm. The branches 320 and 321 are 
separated at their lower extremities by a distance fixed at 375 mm., 
irrespective of the dimension of the large base of the plate. 
Referring now principally to FIG. 5, it will be seen that the plates 
10-20-30 seat one into the other. The plates 10 and 20 are rectangular and 
of the same width. The plate 10 comprises at its rear edge a junction 
element 101 (see also FIG. 2) which cooperates with a junction element 201 
with which the lower edge of the plate 20 is provided (see also FIG. 3). 
The junction thus formed is of the type illustrated in FIG. 3 of the 
patent mentioned above, and assures airtightness and compensation for the 
effects of expansion. 
The junction element 301 (see also FIG. 4) of the plate 30 cooperates with 
a junction element 202 (see also FIG. 3) with which the upper edge of the 
plate 20 is provided in order to form an airtight junction identical to 
the preceding one. 
A sheet of steel 13 is cut out and bent in order to form the first box 
portion 1 with the plate 10. It is provided at 130 with two openings 
serving for entry of external air, and at 131 (FIG. 1) with a forward 
opening which permits the introduction of a tray 14 which slides between 
the internal faces of the two internal branches of the element 11 (FIG. 
2). As can be seen in (FIG.) 1, the bent lateral edges 132 and 133 of the 
element 13 bear against the external faces of the branches 110 and 111 of 
the element 11 (FIG. 2). 
Similarly, a sheet of steel 24 (FIG. 5) is cut out and bent up to form the 
second box portion 2 with the plate 20. The principal face, parallel to 
the plate 20, of the sheet 24 rests at the lower part on the free 
extremities of the branches 110 and 111 (FIG. 2) and on the internal face 
of the bent edge of the element 13 (FIG. 5). The bent vertical edges 
perpendicular to the plate 20, of the sheet 24, rests on the external face 
of the elements 21 and 22 (FIG. 3). As the distance between the elements 
110 and 111 is slightly greater (by 5 mm. for the example described) than 
the distance between the lower extremities of the elements 21 and 22, 
these latter can become jammed, at a right angle, between the lower 
extremities of the elements 21 and 22. The putting into position and the 
joining of the two box portions 1 and 2 thus takes place with precision 
and without the need for use of any assembling instrument. 
Finally, a sheet of steel 33 (FIG. 5) is cut out and bent up to form the 
third portion of the box with the plate 30. The base of this sheet 33 is 
shaped at 333 to constitute a junction with the upper edge of the sheet 24 
and its inclined lateral edges press against the external faces of the 
elements 320 and 321 (FIG. 4). As has been indicated above, although the 
base of the rear and front faces of the throat have a variable dimension 
according to the size, the elements 320 and 321 form a trapezium of fixed 
dimensions, so that the sheet 33 can be shaped once and for all, and so 
that the interval between the two elements 320 and 321 is substantially 
equal to the interval, of 360 mm., between the vertical branches of the 
L's 210 and 220 (FIG. 3). As a result, as shown in FIG. 6, the said L's 
jam themselves between the extremities of the elements 320 and 321, 
thereby offering a continuous guidng surface for the positioning of the 
sheets 24 and 33. 
Two conduits 34 and 35, for the outlet of hot air, (FIG. 4-5) are mounted 
around openings formed in the sheet 33 and communicate with the interior 
of the portion 3 of the box through the openings 323 and 324 (FIG. 4). 
The throat 4 is only differentiated from that described in the 
above-mentioned patent by channelling and deflecting elements fast to the 
external face of its central rear panel 30. It is thus unnecessary to give 
a detailed description. It will be remembered nevertheless that it is 
characterised in that it is obtained by the assembly, by a single 
interengagement, of two identical elements of a first type (such as 41, 
FIG. 1) with two identical elements of a second type (such as 42) in order 
to constitute a principal body in the form of a frustum of a regular 
pyramid having a rectangular base, the elements of the first type having 
C-sections in planes parallel to the bases and each forming a terminal 
face and two return angles of the throat, whilst the elements of the 
second type join together the said return angles, in order to form front 
and rear faces of the throat, the said elements being of moulded cast iron 
and the element of the second type having the shape of a trapezium of 
which the oblique sides are more or less inclined with respect to the base 
as a function of the size of the chimney, in such a manner that the 
horizontal branches of the said C-sections have a length not exceeding a 
predetermined limit compatible with the moulding of the cast iron, without 
use of a core. Its principal body is capped by a cap 43 of moulded cast 
iron provided with a closure valve 44 (FIG. 1), an anti-return-flow plate 
45 (FIG. 5) and a control rod 46 for the closing of the closure valve. 
Returning to FIG. 1, it will be seen that a grille 15 is rested on the 
opening 12 of the plate 10, shown in FIG. 2. This grille supports the wood 
which serves as fuel and permits passage of the ashes which fall into the 
drawer 14. This latter, shown in open position in FIG. 1, comprises on 
each lateral face two openings 141-142 which can coincide with the 
openings 113-114 (FIGS. 2 and 5) when the drawer is slightly open (by 50 
mm. for the example described). In this position, the air which enters the 
drawer (principally through the openings 130, FIG. 5) can pass into the 
channel bounded by the element 11 (FIG. 2). The hot air generator can then 
be put into operation. To cut the feed, it is only necessary to close the 
drawer 14 completely. The opening 141 then comes into a position opposite 
to the space between the openings 113 and 114 and is thus masked, whilst 
the opening 142 is masked by the upper portion of the central branches of 
the element 11. It is thus possible to obtain an adjustment by placing the 
drawer in an intermediate position. 
The principle of operation of the generator described and shown in the 
following: the portion 1 of the box serves as a pre-heating chamber for 
the external air. The hot air follows the rising path shown by the arrows 
in FIG. 1 and is slowed down by the deflectors forming baffles. The 
vertical path has a considerable height, which improves the yield. When 
the drawer is closed, there is a slowing of the fierceness of the fire, 
and extinction. The exits of the conduits 34 and 35 are closed and the 
apparatus then operates like a normal fireplace, provided with the 
necessary throat. 
It will be noted that the apparatus forms a single unit, the box within 
which the hot air circulates being entirely closed without requiring the 
use of walls of masonry. As a result it can be installed in an existing 
fireplace, without having to carry out any demolition thereof. 
Nevertheless, if the latter already normally comprises a throat, use will 
then be made, in this case, of the simplified variant shown schematically 
in FIG. 7. 
The elements 1 and 2 are identical to those of the embodiment of FIGS. 1 to 
6, but the upper vertical element 5 is shaped to be lodged in the throat 
of an already constructed fireplace. It is composed, as is shown in FIGS. 
8, 9 and 10, of a plate 6 of cast iron provided, on its internal face, 
with deflector elements such as 60 and a casing 7 of sheet steel in the 
form of a truncated pyramid, provided with air outlet conduits 70-71. 
The plate 6 joins at its base to the plate of the element 2 by a junction 
of the same type as in the preceding embodiment, (junction 62, FIG. 8). 
The base of the casing 7 forms a frame which meets with the upper edges of 
the sheet of metal which closes the portion 2 of the box. 
The box portions 1 and 2 can be fitted into the base and back wall of the 
fireplace, if this latter is in the course of construction. If not, they 
can be applied in any manner on the existing walls, the shoulder formed by 
the sheet of metal and the projecting edges of the plates of cast iron 
being able to serve to engage a bonding layer of refractory cement or 
brick. 
The assembly of the elements takes place in the dry state and without the 
use of any fixing tool. The airtightness against dust and air is much 
better assured by the joints between the sheet metal elements and the 
plates of cast iron, than would be the case with shallow conduits 
constituted by plates of cast iron provided with projecting air 
channelling and deflecting elements directly embodied in a masonry wall.