U.S. patent application number 10/864156 was filed with the patent office on 2005-01-20 for recuperator burner including recuperator.
Invention is credited to Harbeck, Wolfgang, Riehl, Ingo, Weiss, Karl.
Application Number | 20050014102 10/864156 |
Document ID | / |
Family ID | 33185799 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050014102 |
Kind Code |
A1 |
Harbeck, Wolfgang ; et
al. |
January 20, 2005 |
Recuperator burner including recuperator
Abstract
A recuperator burner comprising a recuperator is disclosed,
comprising a tube section serving as a heat exchange surface with
flowing fluids, the tube section having a plurality of pleats wound
spirally about the longitudinal axis of the recuperator. The
recuperator allows an intensive heat exchange between fluids
streaming on the inner side and the outer side and can be
manufactured using slip casting, due to its simple geometric
shape.
Inventors: |
Harbeck, Wolfgang;
(Leubsdorf, DE) ; Riehl, Ingo; (Freiberg, DE)
; Weiss, Karl; (Freiberg, DE) |
Correspondence
Address: |
SHOOK, HARDY & BACON LLP
2555 GRAND BLVD
KANSAS CITY,
MO
64108
US
|
Family ID: |
33185799 |
Appl. No.: |
10/864156 |
Filed: |
June 9, 2004 |
Current U.S.
Class: |
431/215 ;
126/91A |
Current CPC
Class: |
Y02E 20/348 20130101;
F23D 14/66 20130101; F23L 2900/15043 20130101; Y02E 20/34 20130101;
F23L 15/04 20130101 |
Class at
Publication: |
431/215 ;
126/091.00A |
International
Class: |
F23D 011/44 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 12, 2003 |
DE |
103 26 951.7 |
Claims
What is claimed is:
1. A recuperator burner comprising: a burner head; a burner tube
having a first and a second end, said first end being supported by
said burner head; a burner chamber provided at said second end of
said burner tube; an exhaust gas guide tube coaxially enclosing
said burner tube from the outside and being supported by said
burner head; and a ceramic recuperator supported at one end thereof
by said burner head and being located between said burner tube and
said exhaust gas guide tube; an outer gap defined between said
exhaust gas guide tube and said recuperator; an inner gap defined
between said recuperator and said inner tube; and a plurality of
undulated pleats extending along a tube section of said recuperator
along an outer surface thereof and along an inner surface thereof
and being spirally wound about a longitudinal axis of said
recuperator, said undulated pleats serving as a heat exchanger
between said outer and said inner surfaces of said recuperator;
wherein at least one of said outer and inner gaps has a radial
extension which corresponds to at least a wall thickness of said
recuperator multiplied by 0.3.
2. The recuperator burner of claim 1, wherein at least one of said
outer and inner gaps has a radial extension which substantially
corresponds to half of a wall thickness of said recuperator.
3. The recuperator burner of claim 1, wherein said pleats of said
recuperator define a helix angle with a longitudinal axis of said
recuperator that is between 5.degree. and 85.degree..
4. The recuperator burner of claim 1, wherein said pleats of said
recuperator define a helix angle with a longitudinal axis of said
recuperator that is between 30.degree. and 80.degree..
5. The recuperator burner of claim 1, wherein adjacent wave crests
of said undulated pleats define a distance that corresponds to at
least twice the thickness of a wall of said tube section.
6. The recuperator burner of claim 1, wherein adjacent wave crests
of said undulated pleats define a distance that corresponds to
about for times the thickness of a wall of said tube section.
7. The recuperator burner of claim 1, wherein an amplitude defined
by a difference between a radius of a circle touching an outer
surface of the pleats and between a circle touching an inner
surface of the pleats is larger than a thickness of a wall of said
tube section.
8. The recuperator burner of claim 1, wherein an amplitude defined
by a difference between a radius of a circle touching an outer
surface of the pleats and between a circle touching an inner
surface of the pleats is about 2.5 times the thickness of a wall of
said tube section.
9. The recuperator burner of claim 1, wherein a ratio between the
number of pleats provided along a circumference of said tube
section and between an average circumference of said tube section
is at least 2 per 100 millimeters.
10. The recuperator burner of claim 1, wherein a ratio between the
number of pleats provided along a circumference of said tube
section and between an average circumference of said tube section
is at least 5 per 100 millimeters.
11. The recuperator burner of claim 1, wherein said recuperator is
made of a SiC ceramic.
12. The recuperator burner of claim 1; wherein said recuperator is
configured as a slip cast part.
13. A recuperator burner comprising: a burner head; a burner tube
having a first and a second end, said first end being supported by
said burner head; a burner chamber provided at said second end of
said burner tube; an exhaust gas guide tube coaxially enclosing
said burner tube from the outside and being supported by said
burner head; a ceramic recuperator supported at one end thereof by
said burner head and being located between said burner tube and
said exhaust gas guide tube; an outer gap defined between said
exhaust gas guide tube and said recuperator; an inner gap defined
between said recuperator and said inner tube; and a plurality of
undulated pleats extending along a tube section of said recuperator
along an outer surface thereof and along an inner surface thereof
and being spirally wound about a longitudinal axis of said
recuperator, said undulated pleats serving as a heat exchanger
between said outer and said inner surfaces of said recuperator.
14. The recuperator burner of claim 13, wherein at least one of
said outer and inner gaps has a radial extension which
substantially corresponds to half of a wall thickness of said
recuperator.
15. The recuperator burner of claim 13, wherein said pleats of said
recuperator define a helix angle with a longitudinal axis of said
recuperator that is between 5.degree. and 85.degree..
16. The recuperator burner of claim 13, wherein said pleats of said
recuperator define a helix angle with a longitudinal axis of said
recuperator that is between 30.degree. and 80.degree..
17. The recuperator burner of claim 13, wherein adjacent wave
crests of said undulated pleats define a distance that corresponds
to at least twice the thickness of a wall of said tube section.
18. The recuperator burner of claim 13, wherein adjacent wave
crests of said undulated pleats define a distance that corresponds
to about for times the thickness of a wall of said tube
section.
19. The recuperator burner of claim 13, wherein an amplitude
defined by a difference between a radius of a circle touching an
outer surface of the pleats and between a circle touching an inner
surface of the pleats is larger than a thickness of a wall of said
tube section.
20. The recuperator burner of claim 13, wherein an amplitude
defined by a difference between a radius of a circle touching an
outer surface of the pleats and between a circle touching an inner
surface of the pleats is about 2.5 times the thickness of a wall of
said tube section.
21. The recuperator burner of claim 13, wherein a ratio between the
number of pleats provided along a circumference of said tube
section and between an average circumference of said tube section
is at least 2 per 100 millimeters.
22. The recuperator burner of claim 13, wherein a ratio between the
number of pleats provided along a circumference of said tube
section and between an average circumference of said tube section
is at least 5 per 100 millimeters.
23. The recuperator burner of claim 13, wherein said recuperator is
made of a SiC ceramic.
24. The recuperator burner of claim 13, wherein said recuperator is
configured as a slip cast part.
25. A recuperator burner comprising: a burner head; a burner tube
having a first and a second end, said first end being supported by
said burner head; a burner chamber provided at said second end of
said burner tube; an exhaust gas guide tube coaxially enclosing
said burner tube from the outside and being supported by said
burner head; a ceramic recuperator supported at one end thereof by
said burner head and being located between said burner tube and
said exhaust gas guide tube; and a plurality of undulated pleats
extending along a tube section of said recuperator along an outer
surface thereof and along an inner surface thereof and being
spirally wound about a longitudinal axis of said recuperator, said
undulated pleats serving as a heat exchanger between said outer and
said inner surfaces of said recuperator.
26. A recuperator arrangement for a recuperator burner, said
recuperator arrangement comprising; a ceramic recuperator, said
ceramic recuperator comprising: a first tubular end section and a
second tubular end section, one of said first and second tubular
end sections being configured for attachment to a burner head of
said recuperator burner; a tube section being arranged between said
first and second end sections and serving as a heat exchanging
surface between an outer surface and an inner surface of said
recuperator; and a plurality of pleats arranged along said tube
section and being spirally wound about a longitudinal axis of said
recuperator, said pleats being undulated at said outer and said
inner surfaces, said inner and said outer surfaces replicating a
contour of each other; an outer tube enclosing said recuperator and
being arranged at a distance to said recuperator defining an outer
gap between said recuperator and said outer tube; and an inner tube
arranged within said recuperator at a distance there from and
defining an inner gap between said recuperator and said inner
tube.
27. The recuperator arrangement of claim 26, wherein at least one
of said outer and inner gaps has a radial extension which
corresponds to at least a wall thickness of said recuperator
multiplied by 0.3.
28. The recuperator arrangement of claim 26, wherein said at least
one of said outer and inner gaps have a radial extension which
substantially corresponds to half of a wall thickness of said
recuperator.
29. The recuperator arrangement of claim 26, wherein said pleats of
said recuperator define a helix angle with a longitudinal axis of
said recuperator that is between 5.degree. and 85.degree..
30. The recuperator arrangement of claim 26, wherein said pleats of
said recuperator define a helix angle with a longitudinal axis of
said recuperator that is between 30.degree. and 80.degree..
31. The recuperator arrangement of claim 26, wherein adjacent wave
crests of said undulated pleats define a distance that corresponds
to at least twice the thickness of a wall of said tube section.
32. The recuperator arrangement of claim 26, wherein adjacent wave
crests of said undulated pleats define a distance that corresponds
to about for times the thickness of a wall of said tube
section.
33. The recuperator arrangement of claim 26, wherein an amplitude
defined by a difference between a radius of a circle touching an
outer surface of the pleats and between a circle touching an inner
surface of the pleats is larger than a thickness of a wall of said
tube section.
34. The recuperator arrangement of claim 26, wherein an amplitude
defined by a difference between a radius of a circle touching an
outer surface of the pleats and between a circle touching an inner
surface of the pleats is about 2.5 times the thickness of a wall of
said tube section.
35. The recuperator arrangement of claim 26, wherein the ratio
between the number of pleats provided along a circumference of said
tube section and between an average circumference of said tube
section is at least 2 per 100 millimeters.
36. The recuperator arrangement of claim 26, wherein a ratio
between the number of pleats provided along a circumference of said
tube section and between an average circumference of said tube
section is at least 5 per 100 millimeters.
37. The recuperator arrangement of claim 26, wherein said
recuperator is made of a SiC ceramic.
38. The recuperator arrangement of claim 26, wherein said
recuperator is configured as a slip cast part.
39. A ceramic recuperator for a recuperator burner, said ceramic
recuperator comprising; a first tubular end section and a second
tubular end section, one of said first and second tubular end
sections being configured for attachment to a burner head of said
recuperator burner; a tube section being arranged between said
first and second end sections and serving as a heat exchanging
surface between an outer surface and an inner surface of said
recuperator; and a plurality of pleats arranged along said tube
section and being spirally wound about a longitudinal axis of said
recuperator, said pleats being undulated at said outer and said
inner surfaces, said inner and said outer surfaces replicating a
contour of each other.
40. The recuperator of claim 39, wherein said pleats of said
recuperator define a helix angle with a longitudinal axis of said
recuperator that is between 5.degree. and 85.degree..
41. The recuperator of claim 39, wherein said pleats of said
recuperator define a helix angle with a longitudinal axis of said
recuperator that is between 30.degree. and 80.degree..
42. The recuperator of claim 39, wherein adjacent wave crests of
said undulated pleats define a distance that corresponds to at
least twice the thickness of a wall of said tube section.
43. The recuperator of claim 39, wherein adjacent wave crests of
said undulated pleats define a distance that corresponds to about
for times the thickness of a wall of said tube section.
44. The recuperator of claim 39, wherein an amplitude defined by a
difference between a radius of a circle touching an outer surface
of the pleats and between a circle touching an inner surface of the
pleats is larger than a thickness of a wall of said tube
section.
45. The recuperator of claim 39, wherein an amplitude defined by a
difference between a radius of a circle touching an outer surface
of the pleats and between a circle touching an inner surface of the
pleats is about 2.5 times the thickness of a wall of said tube
section.
46. The recuperator of claim 39, wherein the ratio between the
number of pleats provided along a circumference of said tube
section and between an average circumference of said tube section
is at least 2 per 100 millimeters.
47. The recuperator of claim 39, wherein the ratio between the
number of pleats provided along a circumference of said tube
section and between an average circumference of said tube section
is at least 5 per 100 millimeters.
48. The recuperator of claim 39, wherein said recuperator is made
of a SiC ceramic.
49. The recuperator of claim 39, wherein said recuperator is
configured as a slip cast part.
50. A ceramic recuperator for a recuperator burner, said ceramic
recuperator comprising; a first tubular end section and a second
tubular end section, one of said first and second tubular end
sections being configured for attachment to a burner head of said
recuperator burner; a tube section being arranged between said
first and second end sections and serving as a heat exchanging
surface between an outer surface and an inner surface of said
recuperator; and a plurality of pleats arranged along said tube
section and being spirally wound about a longitudinal axis of said
recuperator, said pleats being bent gradually.
Description
RELATED APPLICATIONS
[0001] This application claims Convention priority of German patent
application serial no. 103 26 951.7 filed on Jun. 12, 2003.
BACKGROUND OF THE INVENTION
[0002] The invention relates to a ceramic recuperator for a
recuperator burner, comprising a tube section, the inner surface
and the outer surface of which serving as a heat exchanging surface
with flowing fluid and that comprises a plurality of pleats.
[0003] In addition, the invention relates to a recuperator burner
comprising a burner head, whereon a burner tube yielding into a
burner chamber and an exhaust gas guide tube being coaxial to the
burner tube are received, wherein between the burner tube and the
exhaust gas guide tube a ceramic recuperator having a plurality of
pleats is received.
[0004] Such a recuperator burner comprising such a recuperator is
known from DE 40 11 190 A1.
[0005] In recuperator burners the efficiency is improved by
increasing the heat exchange between the burner feed air and the
exhaust gas current of the burner. To this end the recuperator is
used that effects a heat exchange between the two flowing gases. In
the recuperator burner as mentioned at the outset the recuperator
is made of a ceramic material and, for increasing the heat exchange
surface, comprises pleats that extend in longitudinal direction of
the recuperator.
[0006] For effecting a further increase of the heat exchange
according to EP 0 803 696 A2 a recuperator is used the heat
exchange surface of which is increased by providing naps.
[0007] According to EP 0 773 407 A2 protrusions and recesses that
are oriented in a certain manner are used for increasing the heat
exchange surface.
[0008] All in all an effective heat exchange can be reached when
using such recuperators. Due to the high thermal load such
recuperators usually consist of a ceramic material. A manufacture
using a cast process, in particular a slip cast process, is
preferred because of the complicated shaped surface.
[0009] However, herein a problem arises with the generation of
delicately structured surfaces, such as necessary for the known
recuperators. Delicately structured outer surfaces became rounded
more or less and loose their desired delicate structures.
SUMMARY OF THE INVENTION
[0010] Therefore, it is a first object of the invention to provide
a ceramic recuperator that effects a good heat transfer.
[0011] It is a second object of the invention to disclose a ceramic
recuperator that allows a simple, precise and cost effective
manufacture.
[0012] It is a third object of the invention to disclose a ceramic
recuperator that is highly efficient as a heat exchanger.
[0013] It is a forth object of the invention to disclose a
recuperator burner comprising a ceramic recuperator providing a
high efficiency.
[0014] It is a fifth burner object of the invention to disclose a
recuperator burner comprising a ceramic recuperator that allows a
simple, precise and cost effective manufacture.
[0015] These and other objects of the invention are achieved by
designing the pleats of a recuperator to be spirally wound about
the longitudinal axis of the recuperator.
[0016] In addition, the object of the invention is achieved by a
recuperator burner comprising a burner head, whereon a burner tube
yielding into a burner chamber and an exhaust gas guide tube being
coaxial to the burner tube are received, wherein between the burner
tube and the exhaust gas tube a ceramic recuperator having a
plurality of pleats is received, wherein the pleats are spirally
wound about the longitudinal axis of the recuperator.
[0017] The object of the invention is thus fully achieved.
[0018] The recuperator according to the invention comprises a large
heat exchange surface for the fluids transferring heat. The outer
shape of the recuperator is designed in a simple way, thereby also
it substantially duplicates the inner shape of the inner wall.
[0019] In this way the manufacture using a casting process, in
particular a slip casting process, is particularly facilitated,
wherein a precise design of the desired surface is guaranteed. By
making the pleats spirally wound on the tube section of the
recuperator serving as a heat exchange surface, the flow path of
the media transferring heat is enlarged, thereby improving
effiency.
[0020] Preferably, the pleats are bent gradually, in particular,
are shaped undulated.
[0021] In this way a simple manufacture together with a large heat
exchange surface can be guaranteed.
[0022] According to a further design of the invention the tube
section together with an outer tube and an inner tube defines an
outer space and an inner space for guiding the fluids, wherein at
least between the outer tube and the pleats or between the inner
and the pleats there remains a gap.
[0023] The gap which, preferably is formed between the outer tube
and the pleats as well as between the inner tube and the pleats,
preferably is at least 0.3 times the wall thickness of the tube
section, preferably about half of the wall thickness of the tube
section.
[0024] By these measures an increased turbulence is effected,
whereby, the heat exchange is improved. When the fluids enter into
the pleats, a part of the media flows along the wave troughs, while
an other part flows above the wave crests through the remaining gap
between the recuperator and the outer tube and the inner tube,
respectively, thus through the respective area contractions that
result at the crests. After the crests there are cross sectional
enlargements, and thereby the current separates, and secondary
currents are generated. This part also mixes with the part of the
current that can be found within the next wave trough. In this way
the generation of interface layers is considerably impaired, and
the efficiency is considerably improved.
[0025] According to a further feature of the invention the pleats
with respect to the longitudinal axis of the recuperator form a
helix angle .alpha. that is between 5.degree. and 85.degree.,
preferably between 30.degree. and 80.degree..
[0026] Using such a helix angle depending on the current velocity
of the flowing fluids an optimized heat transition can be reached.
It will be understood that the helix may extend clockwise or
counter clockwise with such a helix angle.
[0027] According to a further preferred embodiment of the invention
the pleats define a distance L between a wave crest and an adjacent
wave crest that is at least twice the thickness d of the tube
section, preferably about four times the wall thickness d.
[0028] In addition, preferably the amplitude A defined by the
difference between the radii of a circle touching the outer surface
of the pleats and a circle touching the inner surface of the pleats
is larger than the wall thickness of the tube section and is
preferably about 2.5 times the wall thickness d.
[0029] In this way by designing the pleat shape the pleat number
can be derived and depending thereon an optimized heat transfer can
be reached.
[0030] According to a further preferred design of the invention for
about 100 mm of an average circumference of the tube section, there
is/there are provided at least one pleat, preferably at least two
pleats, particularly preferred at least five pleats. Herein with an
increase of the average diameter also the pleat number increases
accordingly.
[0031] In this way by adjusting the pleat number and the rotation
angle of the pleats depending thereon an optimized heat transfer
can be reached.
[0032] Preferably, the recuperator is made of a SiC ceramic.
[0033] As mentioned before, preferably, the recuperator is designed
as a cast part, particularly preferred as a slip cast part.
[0034] It will be understood that the above-mentioned and following
features of the invention are not limited to the given
combinations, but are applicable in other combinations or taken
alone without departing from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Further features and advantages of the invention will become
apparent from the following description of a preferred embodiment
taken in conjunction with the drawings. In the drawings show:
[0036] FIG. 1 a longitudinal sectional view through a recuperator
burner according to the invention, shown in simplified
representation;
[0037] FIG. 2 a perspective view of the recuperator according to
the invention, shown in FIG. 1;
[0038] FIG. 3 a longitudinal sectional view through the recuperator
according to FIG. 2, shown in enlarged representation;
[0039] FIG. 4 a cross-sectional view through the recuperator
according to FIGS. 3;
[0040] FIG. 5 a cross-sectional view through a pleat section;
and
[0041] FIG. 6 a simplified representation of the recuperator,
showing the definition of the helix angle .alpha..
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0042] In FIG. 1 a recuperator burner according to the invention is
shown in longitudinal sectional view and designated in total with
numeral 10.
[0043] The recuperator burner 10 comprises a burner head 12,
whereon an air guide tube, the so-called burner tube 14, is
supported at one end. The burner tube 14 yields into a burner
chamber 16. An outer tube or exhaust gas guide tube 24 is supported
by the burner head 12 coaxially to the burner tube 14. Between the
burner tube 14 and the exhaust gas guide tube 24 a recuperator 30
is received.
[0044] Combustion air is fed to the burner head 12 via a lateral
channel 26, as indicated by arrow 28 and passes into an inner space
or cavity 32 defined between the burner tube and the recuperator,
and finally, after passing there through, it reaches the burner
chamber 16 via through openings (not shown) of the burner tube.
Fuel is fed via a channel 22 arranged within the burner head 12
into a gas lens 20, as indicated by arrow 23, and reaches the
burner chamber 16 via a swirl plate 21. In addition, for igniting
the fuel/air mixture an igniting electrode 18 is provided which
also protrudes with its free end into the burner chamber 16.
[0045] Between the recuperator 30 and the exhaust gas guide tube 24
an outer space or cavity 38 is defined. As shown by arrows 44, the
combustion gases or flue gases flow through the outer space 38 into
the exhaust gas channel 46 of the burner head 12 and thereby heat
up the recuperator 30. The combustion air fed via channel 26 flows
in opposite direction into the inner space between recuperator 30
and burner tube 14, as indicated by arrows 40. In this way there is
a heat exchange between the combustion gases streaming within the
outer space 38 and the combustion air streaming within the inner
space 32, using the counter current principle.
[0046] As can be seen from FIGS. 2 to 6 in more detail, the
recuperator comprises a tube section 50 serving as a heat exchange
surface, whereon a plurality of pleats 36 are provided that are
spirally wound about the longitudinal axis 58 of the recuperator.
The tube section 50 which makes up about three quarters of the
length of the recuperator 30 is received at its end facing the
burner head 12 by a hollow cylindrical section 52 having a collar,
and at the opposite end is also enclosed by a hollow cylindrical
section 54 which tapers at its free end and wherein an opening 56
is provided. This opening 56 is designed so as to be able to
receive the burner tube 14 at its exit end 49 for the flame
gases.
[0047] As can be seen in particular from FIGS. 4 and 5, the pleats
36 are configured wave-shaped so that at the inner surface as well
at the outer surface of the recuperator 30 alternatingly troughs
and crests result.
[0048] The recuperator 30 consists of ceramic, for example of a SiC
ceramic and is preferably prepared using a slip casting
process.
[0049] The pleats 36 are shaped spirally or helically so that for a
length of the tube section 50 of e.g. 400 mm they are rotated by
180.degree., this corresponding to a helix angle .alpha. of
65.degree..
[0050] The number of the pleats 36 and the helix angle .alpha.
depend on the distance L between adjacent wave crests 59 and on the
amplitude A (cf. FIG. 5), as well as on the respective case of
application, in particular on the current velocity of the fluids,
i.e. of the combustion air and of the exhaust gases.
[0051] When using an average recuperator diameter of about 120 mm,
for example there could be provided 21 pleats. Herein the pleat
distance L e.g. could be 24 mm using an amplitude A of 13 mm and a
wall thickness d of 6 mm.
[0052] During operation hot flame gases exit from burner chamber 16
via its exit opening 49 and heat up the exhaust gas guide tube 24.
From the end facing the burner combustion air streams into the
helically located pleats 36 of the inner surface 32, while
simultaneously flue gases enter into the spirally shaped pleats 36
of the outer space 38 from the outer end. Herein the helical
arrangement effects an enlarged current path along the recuperator
30. In addition, continuously parts of the combustion air steam
against the provided pleats on the inner side, as well as exhaust
gases on the outer side. A portion of the media, respectively,
flows through the gaps 34 and 39, respectively, between the pleats
36 and the burner tube 14 and the exhaust gas guide tube 24,
respectively. Thus secondary currents are generated by the mixture
between the media flowing along the spirally wound pleats 36 and of
the media flowing through the gaps 34 and 39, respectively. To this
end the gaps 34 and 39, respectively, may be dimensioned to have
about half the wall thickness of the tube section, in the present
case it could be about 3 mm for example. Thus a good mixture of the
streaming media results and turbulences are generated so that the
generation of stable interface layers is impeded or avoided to a
large extent, respectively, thus leading to an intensive heat
contact with the surfaces of the tube section 50.
[0053] In this way a very good heat exchange between the flue gases
and the combustion air is reached.
[0054] Due to its simple geometrical shape the recuperator 30 can
be manufactured with high precision using slip casting
processing.
* * * * *