[0001] The present invention relates to a burner for a combustion unit, e.g., for gas boilers.
[0002] Prior-art combustion units comprise a combustion chamber with a heat exchanger, a
burner connected to the combustion chamber for generating heat through the combustion
of a mixture of combustible gas and combustion air in the combustion chamber, and
a supply conduit for supplying the gas and air mixture to the burner.
[0003] The known burner comprises:
- a framework made of impermeable material, connectable to the combustion chamber and
supporting a diffuser made of gas permeable material, and
- a combustion surface (the so-called combustion head) formed by a portion of the diffuser
and intended to face the combustion chamber and be surrounded by the framework, so
that a gas mixture conveyed through the diffuser can be combusted in the form of a
flame pattern on the combustion surface.
[0004] In a known solution, the combustion surface and the framework are made of a single
piece of sheet metal which is resistant to high temperatures, perforated at the combustion
surface, and impermeable at the framework. This solution is disadvantageous due to
the formation of breaks caused by high temperature gradients between very hot zones
and relatively cold zones.
[0005] Similar breaks have also been observed in a further known solution, where the perforated
sheet metal combustion surface and the impermeable sheet metal framework were assembled,
for example, by welding spots.
[0006] In order to obviate breaks due to thermal stresses, it is known to the inventors
to position a flexible porous layer on the perforated sheet metal, for example a fabric
or a metal fiber mesh which acts both as a combustion surface and flame spacer which
spaces the combustion zone apart from the perforated sheet metal, and insulating material
which shields the sheet metal from the high temperatures of the gases present in the
combustion chamber, at the cost of needing to provide for and assemble an additional
expensive component.
[0007] It is also known to perforate the perforated sheet metal of the diffuser with circular
pinholes and through slots, arranged in alternate groups, for the purpose of obviating
the formation of localized breaks between two adjacent perforations. In this case,
the through slots still have very small dimensions, of the same order of magnitude
as the circular pinholes.
[0008] In addition to thermal stresses and localized thermal breaks (between adjacent perforations),
sheet metal diffusers are subject to buckling (uncontrolled deformations of instability
from a modal form to another modal form of the diffuser) due to the high rigidity
of the sheet metal in the plane thereof and the impossibility to fully extend freely
according to the thermal stresses. This results in uncontrolled mechanical stresses
combined with thermal stresses which increase the risk of premature breakage of the
diffuser.
[0009] Mesh diffusers are easily deformable both in the extension plane and outside the
extension plane and do not have the aforesaid buckling problem. On the other hand,
metal meshes for burners are very expensive, the porosity thereof is subject to statistical
variations which cannot be controlled with certainty, and the manufacturing of burners
with diffusers made of metal mesh is more complex, slower and expensive than the manufacturing
of burners with diffusers made of perforated sheet metal.
[0010] Publication EP3412967A1 describes a burner with:
- a framework made of impermeable sheet metal having an outer peripheral connection
portion,
- a perforated sheet metal diffuser, the diffuser forming a combustion surface surrounded
by the framework and having an extension in a longitudinal direction and an extension
in a transverse direction, orthogonal to the longitudinal direction, where the extension
of the combustion surface in the transverse direction is less than the extension of
the combustion surface in the longitudinal direction,
where the combustion surface is intended to face a combustion space so that a gas
mixture conveyed through the diffuser can be combusted in the form of a flame pattern
on the combustion surface,
where the diffuser forms a plurality of perforated sheet metal diffusor segments,
separated from one another by partial separation slits, and where the partial separation
slits extend in the transverse direction over at least half of the extension of the
combustion surface in the transverse direction.
[0011] This known burner achieves within certain limits an uncoupling of the thermal deformations
of the individual segments formed by the diffuser and reduces the onset of buckling
due to thermal expansion. In order to reduce or eliminate an undesired notching effect
at the ends of the partial separation slits, one or both of the ends of the partial
separation slits of the diffuser forms/form relaxation grooves or holes, which are
rounded and enlarged as compared to the width of the partial separation slit.
[0012] The critical features of known burners, which were designed for traditional combustion
gases such as methane, propane, butane and mixtures thereof, for example, are further
accentuated with the use of hydrogen or mixtures of combustible gases containing significant
percentages of hydrogen gas. Examples of particularly accentuated negative phenomena
with the use of hydrogen gas are overheating, flash back, light back, excessively
high combustion speed, and higher temperature gradients which result in greater thermal
stresses on the components of the burner.
[0013] When using the burner described in
EP3412967A1 with gas mixtures having high combustion speed, an undesired light back tendency
occurs from the combustion surface towards the inside of the burner exactly at the
partial separation slits between the diffuser segments, since to date is has not been
possible or at least is not easy and inexpensive to make such partial separation slits
narrow enough to avoid light back even with high and very high combustion speeds.
In simple terms, for the use of hydrogen gas, the gas path through the sheet metal
layer of the diffuser at the slits is too short, too wide and not suitable for preventing
light back. Furthermore, due to higher temperature gradients, the end zones of the
slits of the burner described in
EP3412967A1 are subject to the onset of fatigue fractures.
[0014] However, for reasons of environmental protection, containment of greenhouse gas production,
and increase of the efficiency of energy resources, the need is felt to also use hydrogen
as a combustible gas or as a part of combustible gas mixtures for generating heat.
[0015] Therefore, it is the object of the present invention to provide an improved burner
having features such as to obviate at least some of the drawbacks of the prior art.
[0016] It is a particular object of the invention to provide a burner with a diffuser made
of perforated sheet metal, having features such as to withstand even better the mechanical
and thermal stresses, and to reduce the risk of flash back in the presence of gases
and gas mixtures having high combustion speed.
[0017] Further objects of the invention relate to the simplification and the manufacturing
precision of the burner.
[0018] At least some of the objects are achieved by a burner according to claim 1. Dependent
claims are directed to preferred and advantageous embodiments.
Summary description of the invention
[0019] According to an aspect of the invention, a gas burner, for example a premixed gas
burner, for example suitable for gases and gas mixtures having high combustion speed,
e.g., hydrogen gas and mixtures thereof, comprises:
- a framework made of impermeable sheet metal, having an outer peripheral portion connectable
to a combustion chamber,
- a perforated sheet metal diffuser, supported by the framework, the diffuser forming
a combustion surface possibly surrounded by the framework and having an extension
in a longitudinal direction and an extension in a transverse direction, orthogonal
to the longitudinal direction, where the extension of the combustion surface in the
transverse direction is less than the extension of the combustion surface in the longitudinal
direction,
where the combustion surface is intended to face a combustion space of the combustion
chamber, so that a gas mixture conveyed through the diffuser can be combusted in the
form of a flame pattern on the combustion surface,
where the diffuser is formed by a plurality of diffuser segments made of perforated
sheet metal not belonging to the same piece of sheet metal and completely separated
from one another by means of separation slits and placed side-by-side along said separation
slits, and where the separation slits extend in the transverse direction over the
entire extension of the diffuser, where on an inner side of the diffuser, opposite
to the combustion surface, a plurality of covering strips made of sheet metal is arranged,
and each covering strip extends along respectively one of the separation slits overlapping
and at least partially in contact with both the free edges of the two diffuser segments
which are bordering and delimiting said separation slit, so as to cover each of said
separation slits.
[0020] The construction of the diffuser with a plurality of diffuser segments completely
separated from one another, but only connected indirectly by further components of
the burner not belonging to the same sheet metal thereof, further improves the uncoupling
of the thermal deformations of the individual segments, the thermal resistance, the
resistance against the onset of fatigue fractures, and obviates the onset of thermal
expansion buckling, also in the presence of higher temperature gradients.
[0021] The complete separation of the individual diffuser segments and their juxtaposition
side-by-side at a freely definable and lockable distance further allows creating,
in an easy, inexpensive and industrially repeatable manner, a much narrower gap than
a minimum cutting width obtainable using traditional sheet metal cutting technologies.
Moreover, the juxtaposition of diffuser segments completely separated from one other
allows creating freely definable and not necessarily uniform slit profiles in an easy
and inexpensive manner, while remaining within a very small slit width range. This
possibility to create very narrow separation slits reduces per se the risk of light
back even when the burner is supplied with gas, e.g., hydrogen, having high combustion
speed.
[0022] In addition, the covering of the separation slits with the covering strips further
extends the gas path through the diffuser at the separation slits and reduces the
overall passage section and thus the local porosity. This further reduces the risk
of light back. On the other hand, the covering strips stabilize the position of the
free edges of the diffuser segments, thus obviating undesired, unplanned thermal or
mechanical deformations. This leads to a synergetic anti-light back and thermal resistance
effect.
Brief description of the drawings
[0023] In order to better understand the invention and appreciate the advantages thereof,
some non-limiting exemplary embodiments will be described below with reference to
the accompanying drawings, in which:
figure 1 is a top perspective view of a burner according to an embodiment,
figure 2 is a bottom perspective view of the burner in figure 1,
figures 3 and 4 are exploded perspective views of the burner in figure 1,
figure 5 is a sectional view of the burner in figure 1,
figure 6 shows an enlarged detail of the burner in figure 2,
figure 7 shows a further enlarged detail of the burner in figure 2,
figure 8 is a perspective view of an assembly of a diffuser and a covering framework
of a burner according to an embodiment,
figure 9 is a perspective view of a covering framework of a burner according to an
embodiment, figure 10 shows an enlarged detail of the covering framework in figure
9,
figure 11 is a plan view of a diffuser of a burner according to an embodiment,
figure 12 is a perspective view of an individual segment of the diffuser of the burner
according to an embodiment,
figure 13 is an enlarged view of a separation slit between two diffuser segments of
the burner according to an embodiment,
figure 14 is a perspective view of an assembly of a distributor also acting as a covering
framework of the burner according to an embodiment,
figure 15 is a sectional view of a burner according to figure 1, but containing the
distributor and covering framework in figure 14.
Detailed description of embodiments
[0024] The figures show a gas burner 1 suitable for a combustion unit of the type having
a first housing part (combustion housing) which internally delimits a combustion space,
a second housing part (gas supply housing) which internally delimits a gas supply
space, and indeed the burner 1 connected between the first housing part and the second
housing part.
[0025] The burner 1 comprises:
- a framework 2 made of impermeable sheet metal, having an outer peripheral portion
3 connectable to a combustion chamber 9,
- a diffuser 4 made of perforated sheet metal supported by the framework 2, the diffuser
4 forming a combustion surface 5 having a longitudinal extension in a longitudinal
direction 6 and a transverse extension in a transverse direction 7, orthogonal to
the longitudinal direction 6, wherein the transverse extension of the combustion surface
5 is less than the longitudinal extension of the combustion surface 5.
[0026] The combustion surface 5 faces an outer side 8 of the burner 1 (the outer side 8
defines the combustion space 8 of the combustion chamber 9) so that a gas mixture
10 conveyed through the diffuser 4 can be combusted in the form of a flame pattern
on the combustion surface 5.
[0027] The diffuser 4 is formed by a plurality of diffuser segments 11 made of perforated
sheet metal not belonging to the same piece of sheet metal and completely separated
from one another by means of separation slits 12 and placed side-by-side along the
separation slits 12, and wherein the separation slits 12 extend in the transverse
direction 7 over the entire transverse extension of the diffuser 4.
[0028] On an inner side 13 of the diffuser 4, opposite to the combustion surface 5, a plurality
of covering strips 14 made of sheet metal is arranged, and each covering strip 14
extends along respectively one of the separation slits 12 overlapping and at least
partially in contact with both the free edges 15 of the two diffuser segments 11 which
are bordering and delimiting the separation slit 12, so as to cover each of said separation
slits 12. The diffuser segments 11 are preferably not connected directly to one another,
but individually with the framework 2.
Detailed description of diffuser 4
[0029] According to an embodiment, the combustion surface 5 or the entire diffuser 4 can
be substantially flat and the separation slits 12 can be substantially straight and,
possibly, parallel to one another.
[0030] According to a further embodiment, the part of the diffuser forming the combustion
surface 5 can be in the shape of a shell rounded towards the combustion side 16, advantageously
a half-cylinder or a portion of cylinder, preferably with a constant cross section
(in a transverse plane orthogonal to the longitudinal direction 6) with the exception
of local interruptions due to the separation slits 12 and perforation.
[0031] In this embodiment, the separation slits 12 are advantageously straight in the top
view and shaped like an arc of a circle in the cross-section view, as shown in figures
1, 3, 8, 11, 12. The separation slits 12 are advantageously parallel to one another.
[0032] According to an embodiment, the separation slits 12 have a maximum width 16 in the
longitudinal direction 6 of less than 1 mm (figure 13).
[0033] According to an embodiment, the separation slits 12 have a gradually converging shape
from a central region 17 (about half the central length or a third of the central
length of the separation slit 12) towards the two opposite ends 18 (figure 13).
[0034] According to an embodiment, the separation slits 12 form zero-thickness contact sections
or points 19 where the free edges 15 of the bordering diffuser segments 11 abut in
contact with one another. This allows a certain relative positioning between consecutive
diffuser segments 11, without any need to measure distances or adjust the position
of the diffuser segments 11 during the assembly of the burner 1.
[0035] Advantageously, the contact sections 19 are positioned at opposite ends 18 of the
separation slits 12.
[0036] According to an embodiment, the diffuser 4 or the diffuser segments 11 are formed
from (obviously heat resistant) sheet steel having a thickness of the individual sheet
metal in the range from 0.3 mm to 3 mm, preferably from 0.5 mm to 1.5 mm, for example
0.9 mm.
[0037] According to an embodiment, the diffuser 4 or the diffuser segments 11 are stacked
steel sheet metal multi-layer structures, wherein the thickness of the individual
sheets (individual layers) is preferably within the thickness values and ranges described
above for the individual sheet.
[0038] According to an embodiment, the perforation 20 of the diffuser 4 does not extend
as far as the separation slits 12. The separation slits 12 are delimited by the free
edges 15 of the diffuser segments 11 preferably smooth or with a continuous shape
to obviate the onset of notching effects and the formation of cracks.
[0039] The diffuser segments 11 advantageously have a substantially constant and/or substantially
equal length 22 in the longitudinal direction 6, to facilitate manufacturing, storage
and assembly and for the purpose of ensuring that properties of thermal capacity,
temperature distribution, and thermal and mechanical stresses, as well as the distribution
of gas mixture permeability are as uniform as possible, and thus to obtain burner
operating properties which are as uniform, certain and predictable as possible.
[0040] According to an embodiment, the diffuser segments 11 advantageously have a length
22 in the longitudinal direction 6 which is less than a width 23 thereof in the transverse
direction 7. This means that the individual diffuser segments 11 are "locally" elongated
in the transverse direction 7, while the entire combustion surface 5 is "globally"
elongated in the longitudinal direction 6. In this way, the thermal expansions of
the individual diffuser segments 11 in the longitudinal direction 6 cannot be added
together due to the separation slits 12, and the thermal expansions of the individual
diffuser segments 11 in the transverse direction 7 can be absorbed thanks to an out-of-plane
bulging of the framework 2. Such a bulging will systematically take place in the direction
of the combustion space (outer side 8 of the burner 1) due to the thermal bending
of the diffuser 4 towards the hotter side thereof.
[0041] In accordance with an embodiment (figures 11, 12), the diffuser segments 11 consist
of or are formed by a plate bent in an arc shape, where opposite ends 27 of the plate
form two arc bases and are bent towards the outside and, preferably, oriented in a
common plane parallel to a plane of the framework 2. The opposite ends 27 of the plate
form connection ends 27 for connecting the diffuser segment 11 to the framework 2.
[0042] In accordance with another embodiment, the diffuser 4 is a planar diffuser, the diffuser
segments 11 consist of or are formed by an elongated planar plate, wherein opposite
ends of the plate are oriented in a common plane parallel to the plane of the framework
2 and form connection ends 27 of the diffuser segment 11 to the framework 2.
[0043] In accordance with a further embodiment, the diffuser 4 is tubular, e.g., cylindrical
or frustoconical, the diffuser segments 11 consist of or are formed by an elongated
plate bent in a closed loop or a continuous tubular wall, and connected by a small
connection frame or one or more appendices of the framework 2 of the burner.
[0044] According to an embodiment (figures 3, 4), the burner 1 comprises two closing portions
24 made of sheet metal which extend outside the plane of the framework 2 and close
longitudinal end zones 25 between the combustion surface 5 and the framework 2.
[0045] This allows simplifying the manufacturing of the diffuser 4, due to the easier forming
of the perforated sheet metal by calendering or simple bending (about a single longitudinal
axis), e.g., in a press, and the use of simple "cap" portions made of preferably impermeable
sheet metal for closing the burner 1 in the longitudinal end zones 25.
[0046] In the embodiment shown in the figures, the two closing portions 24 are made of unperforated
sheet metal.
[0047] The closing portions 24 can be shaped (e.g., by a press) as a part (e.g., a quarter)
of a spherical cap for creating a gradual transition between the plane of the framework
2 and an apical region of the combustion surface 5. Alternatively, the closing portions
24 can be shaped like flat portions with or without stiffening ribs.
[0048] It is particularly advantageous to form at least one or both of the closing portions
24 together with the framework 2 using a single piece of sheet metal, e.g. by forming
or bending the closing portions 24 outside the plane of the framework 2 along transverse
edges 21 of a front opening 22 of the framework 2 (figures 3, 4).
[0049] This saves on material and connection costs and increases the tightness of the connection
between the combustion surface 5 and the framework 2.
The perforation or piercing of the diffuser 4 can comprise, by way of advantageous
but non-limiting example, holes having diameters in the range from 0.2 mm to 0.7 mm
and/or slots with lengths in the range from 5 mm to 50 mm and width less than 0.5
mm.
Detailed description of covering strips 14
[0050] According to the shape of the diffuser 4, e.g., planar, convex, cylindrical, frustoconical,
half-cylinder shaped, etc., the covering strips 14 can be separate pieces of sheet
metal connected individually to the framework 2, or the covering strips 14 are portions
of a covering framework 28 formed by a single piece of sheet metal (figures 3, 4,
9, 10).
[0051] According to an embodiment, the covering strips 14 are made of continuous sheet metal,
without perforation, in order to really ensure a deviation of the gas flow at the
separation slits 12 and to facilitate manufacturing and reduce the manufacturing cost
of the burner 1.
[0052] According to an embodiment, the covering strips 14 form:
- two outer strip portions 29 extending along the separation slit 12 and forming a contact
surface 30 facing the diffuser 4 (i.e., towards the outer side of the burner 1) and
having a smooth shape complementary to the shape of an inner surface 31 of the diffuser
segments 11 (to create a wide contact support between the two surfaces 30, 31),
- a central rib 32 extending centrally between the two outer strip portions 29 and projecting
towards the inside of the burner 1 for stiffening the covering strips 14 without creating
an undesired spacer effect (Figures 6, 10).
[0053] According to an embodiment, the covering framework 28 forms an outer frame 33, consisting
for example of two opposite sheet metal strips, which supports and positions the covering
stripes 14. Advantageously, the outer frame 33 lies in a plane parallel to the plane
of the framework 2.
[0054] According to an embodiment, the outer frame 33 forms one or more local stiffening
ribs 34, e.g., a plurality of bosses equidistant from one another (figures 4, 7).
[0055] According to an embodiment, the covering strips 14 are formed from sheet steel having
a thickness of the individual sheet metal in the range from 0.3 mm to 1.5 mm, preferably
from 0.5 mm to 1.0 mm, for example of 1 mm.
Description of framework 2
[0056] According to an embodiment, the framework 2 is formed by a flat metal sheet, preferably
substantially elongated and rectangular, which delimits a passage opening 35 at which
the diffuser 4 is arranged.
[0057] The framework 2 can be made of sheet steel having a thickness of the individual sheet
metal in the range from 0.5 mm to 2 mm, preferably from 0.8 mm to 1.5 mm, for example
of 1 mm.
Description of the distributor
[0058] According to a further embodiment, the burner 1 can comprise a distributor 36, preferably
made of perforated sheet metal with larger openings than the perforation openings
of the diffuser 4. The distributor 36 is placed on the side of the diffuser 4 opposite
to the combustion side and can have a similar shape to that of the combustion surface
5, e.g., a planar or convex shape or a portion of a cylinder, or half-cylinder, or
a tubular, e.g., cylindrical or frustoconical shape.
[0059] In accordance with an embodiment, the covering strips 14 can be formed by unperforated
portions of sheet metal of the distributor 36 which protrude with respect to perforated
portions 37 of the distributor 36 towards the outside of the burner 1 and which rest
in contact against the diffuser segments 11 (figures 14, 15). The perforated portions
37 of the distributor 36 are instead spaced apart from the diffuser 4 so as to be
able to correctly perform the task of distributing the gas mixture towards the diffuser
4.
[0060] According to an embodiment, the diffuser 36 can be made from the covering framework
28.
Assembly of burner 1
[0061] According to an embodiment, the diffuser 4 is sandwiched and held between the framework
2 and the covering framework 28.
[0062] Advantageously, the outer strip portions 29 of the diffuser segments 11 are sandwiched
between an edge of the framework 2 and the outer frame 33 of the covering framework
28.
[0063] For example, the framework 2 and the covering framework 28 can be connected to each
other by welding spots or by mechanical fixing without welding, e.g., Tox clinching,
in a plurality of discrete connection positions, spaced apart from one another.
[0064] The diffuser segments 11 can be fixed into the burner 1 only by friction interlocking
or clamping or welding or Tox clinching.
[0065] When fixing the diffuser segments 11 by friction interlocking between the framework
2 and the covering framework 28, the direct fixing between the framework 2 and the
covering framework 28 may not involve the diffuser segments 11, allowing the diffuser
4 and the individual segments thereof to have greater freedom of deformation and movement
to accommodate thermal expansions.
Reference numerals
[0066]
- 1 burner
- 2 framework
- 3 connection portion
- 4 diffuser
- 5 combustion surface
- 6 longitudinal direction
- 7 transverse direction
- 8 outer side of the burner, combustion space
- 9 combustion chamber
- 10 gas mixture
- 11 diffuser segments
- 12 separation slits
- 13 inner side
- 14 covering strips
- 15 free edges of segments 11
- 16 maximum width
- 17 central region
- 18 end
- 19 contact sections
- 20 perforation
- 21 transverse edges of segments
- 22 segment length
- 23 segment width
- 24 closing portions
- 25 longitudinal end zones
- 26 transverse edges of the framework
- 27 connection ends of segments 11
- 28 covering framework
- 29 outer strip portions
- 30 contact surface of the covering strips
- 31 inner surface of the diffuser
- 32 central rib of the strips
- 33 outer frame of the covering framework
- 34 local stiffening ribs
- 35 passage opening of the framework
- 36 distributor
- 37 perforated portions of the distributor
1. A gas burner (1), in particular a premixed gas burner, comprising:
- a framework (2) made of impermeable sheet metal, having an outer peripheral portion
(3) connectable to a combustion chamber (9),
- a diffuser (4) made of perforated sheet metal supported by the framework (2), the
diffuser (4) forming a combustion surface (5) and having a longitudinal extension
in a longitudinal direction (6) and a transverse extension in a transverse direction
(7), orthogonal to the longitudinal direction (6), wherein:
- the transverse extension of the combustion surface (5) is less than the longitudinal
extension of the combustion surface (5),
- the combustion surface (5) faces an outer side (8) of the burner (1) so that a gas
mixture (10) conveyed through the diffuser (4) can be combusted in the form of a flame
pattern on the combustion surface (5),
- the diffuser (4) is formed by a plurality of diffuser segments (11) made of perforated
sheet metal not belonging to the same piece of sheet metal and completely separated
from one another by means of separation slits (12) and placed side-by-side along the
separation slits (12), and wherein the separation slits (12) extend in the transverse
direction (7) over the entire transverse extension of the diffuser (4),
- on an inner side (13) of the diffuser (4), opposite to the combustion surface (5),
a plurality of covering strips (14) made of sheet metal is arranged, and each covering
strip (14) extends along respectively one of the separation slits (12) overlapping
and at least partially in contact with the free edges (15) of the two bordering diffuser
segments (11), delimiting the separation slit (12), so as to cover each of said separation
slits (12).
2. A burner (1) according to claim 1, wherein:
a) the combustion surface (5) is substantially flat and the separation slits (12)
are substantially straight and parallel to one another, or
b) the combustion surface (5) is in the shape of a shell bulged towards the outer
side (8).
3. A burner (1) according to claim 1, wherein:
- the combustion surface (5) is in the shape of a half-cylinder or a cylinder portion,
with constant cross-section, with the exception of the local interruptions due to
the separation slits (12) and the perforation, and
- the separation slits (12) are straight in a top view and are in the shape of an
arc of a circle in cross-section,
- the separation slits (12) are parallel to one another.
4. A burner (1) according to any one of the preceding claims, wherein the separation
slits (12) have a maximum width (16) in the longitudinal direction (6) of less than
1 mm.
5. A burner (1) according to any one of the preceding claims, wherein the separation
slits (12) have a shape gradually converging from a central region (17) towards two
opposite ends (18) of the separation slit (12).
6. A burner (1) according to any one of the preceding claims, wherein the separation
slits (12) form zero-thickness contact sections (19) where the free edges (15) of
the bordering diffuser segments (11) abut in contact with one another.
7. A burner (1) according to claim 6, wherein the contact sections (19) are positioned
at opposite ends (18) of the separation slits (12).
8. A burner (1) according to any one of the preceding claims, wherein the diffuser segments
(11) are formed from sheet steel having a thickness of the single sheet metal in the
range from 0.3 mm to 3 mm, or in the range from 0.5 mm to 1.5 mm, or of 0.9 mm.
9. A burner (1) according to any one of the preceding claims, wherein the diffuser segments
(11) are multi-layer structures made of stacked sheet steel.
10. A burner (1) according to any one of the preceding claims, wherein:
- the diffuser segments (11) consist each of a plate bent in the shape of an arc,
- opposite ends (27) of the plate form two arc bases and are bent towards the outside
of the arc and oriented in a common plane parallel to a plane of the framework (2),
- the opposite ends (27) of the plate form connection ends for connecting the diffuser
segment (11) to the framework (2).
11. A burner (1) according to any one of the preceding claims, wherein the covering strips
(14) are portions of a covering framework (28) formed from a single piece of sheet
metal.
12. A burner (1) according to any one of the preceding claims, wherein the covering strips
(14) form:
- two outer strip portions (29) extending along the separation slit (12) and forming
a contact surface (30) facing the diffuser (4) and having a smooth shape complementary
to the shape of an inner surface (31) of the diffuser segments (11), the contact surface
(30) and the inner surface (31) being in wide contact with each other,
- a central rib (32) extending centrally between the two outer strip portions (29)
and forming a relief towards the inside of the burner (1) so as to stiffen the covering
strips.
13. A burner (1) according to claim 11, wherein:
- the covering framework (28) forms an outer frame (33), consisting of two opposite
sheet metal strips, from which the covering strips (14) extend and which lies on a
plane parallel to the plane of the framework (2), or
- the diffuser (4) is sandwiched and held between the framework (2) and the covering
framework (28).
14. A burner (1) according to claim 13, wherein the outer frame (33) forms one or more
local stiffening ribs (34).
15. A burner (1) according to any one of the preceding claims, comprising a distributor
(36) made of perforated sheet metal with larger openings than the perforation openings
of the diffuser (4), wherein the distributor (36) is placed on the inner side (13)
of the diffuser (4),
wherein the covering strips (14) are formed by unperforated portions of the distributor
(36) which protrude with respect to perforated portions (37) of the distributor (36)
towards the outside of the burner (1) and which rest in contact against the diffuser
segments (11).