FIELD OF INVENTION
The invention relates to an extrusion mould and an extrusion method for
manufacturing ceramic tubes with an end collar.
BACKGROUND OF INVENTION
Ceramic tubes of uniform cross-section are commonly produced by extrusion. But
when tubes with varying diameters such as ceramic candles used for Hot gas
filtration are to be produced, the conventional extrusion method cannot be used.
Unlike plastic material, the ceramic materials cannot be moulded to complex
shapes due to its stiffness. Thus, the only method available to produce tubes of
2 different diameters is by extrusion and joining. But this joining makes the
product week at the joint and there are chances of breakage at the collar when
tensile load is applied. These candles in actual use are hanged at the collars and
any crack or breakage at the joint will results in failure of hot gas filter. Other
alternatives for production of such complex ceramic product are isostatic
pressing and casting technique which are completely different complex
fabrication methods, yet to be established for production. Hence a novel method
of producing tubes with collars by extrusion using a novel extrusion mould and a
2-step extrusion process is disclosed.
Various porous ceramic materials are used as a filter, a catalyst carrier, a
substrate of gas separation membrane for temperature gas filtration of

particulates from hot flue gases or coal gases. The use of ceramic filters for
filtering hot flue gases or coal gas or like is well known and use of such filter
elements is known for ex: in US Patent No. 4,713,174. Ceramic filters have been
tested in processes such as coal gasification and coal combustion to remove
particulates from hot flue gases to protect down-stream equipment from
corrosion and erosion. Ceramic filters in tubular (candle) form, with one end
closed and the other end open have been shown to remove the particulates
efficiently (EP1772178). Ceramic hot-gas candle filters known in the art are
generally fabricated from either porous monolithic materials or porous fiber-
composite materials (US Patent No. 5,075,160).
Ceramic filter elements are generally of tubular products with one end closed and
another end with collars. These collars are required for hanging the candles in
the hot gas filtration system. Hence these collars need to be integral part of the
tubes and should have sufficient strength and integrity, some time more than the
strength of the tubes and integrity to bear the load of the tubes while hanging
inside a system which experience high pressure up to 30 bar and high
temperature up to 1000°C. The ceramic candles may be made by molding,
casting extrusion, as well as other methods known to those of skilled in the art.
Most preferably by extrusion to provide tubes that have uniform thickness,
density and strength throughout the tube length. But this complicated shape of
having collar at one end makes the manufacturing process more difficult.
The ceramic material usually comprises a ceramic oxide powder such as Silicon

carbide and a binder. The ceramic oxide powder/binder system is typically made
into a formable paste, and firstly extruded through a die to form a tube in a
"green" state, thereafter the tube is thermally treated to partially remove the
binder to leave a bisque fired body, followed by sintering and densification of the
tube through high temperature heat treatment. If the tubes are to be with collar
at one end, they are either made by joining the collar part at green stage or
after firing. The former method is preferred having a strong joint.
US Patent No. 4,629,483 a method of manufacturing ceramic filter elements in
moulding operation, in which isostatic pressing is used. This requires a special
isostatic press and rubber mould which makes the manufacturing more complex.
Casting methods using epoxy resins, gel casting etc have also been attempted in
the prior art. A process of forming silicon carbide bodies is disclosed in US Patent
No. 4,127,629. However, all these casting methods generally fail to provide a
stronger and uniform microstructure, and further prove to be expensive due to
high level of costly organic binders required for the casting.
US 200816441 discloses an extrusion mold having an outer mold, for molding a
ceramic membrane having an one-end closed tube structure which is easily
integrated and has a high gas separation efficiency, and a fabrication method of
a ceramic membrane tube using the extrusion mold. EP 1075916 describes a
process and a die for forming an end cap in a ceramic tube in which the ceramic
tube is extruded into an end cap forming cavity defined in the die.

Although various means are known for forming open-ended ceramic tubes and
joining the collars but forming a collar as an integral part of the ceramic tube
during extrusion is not disclosed in the prior art.
JP 11230512 provides a method for producing a ceramic long tube with flange in
which cracking and deformation of a molded body can be prevented by obtaining
a higher yield for higher producibility. But this patent does not disclose the
length of the tubes with collars which can be extruded. CN 101406782 discloses
a method for preparing a silicon carbide porous ceramics filtering element and
squeezing equipment. In this method a silicon carbide paste is filled inside the
tube in a squeezing equipment; two ends of the tube are pressurized to form a
flange at one end of the silicon carbide porous ceramics plastic tube, and an end
enclosure is formed at the other end the die is removed to obtain any dried
silicon carbide porous ceramics filtering unit blank; and the tube is baked at
certain temperature to obtain the silicon carbide porous ceramics filtering
element. But this method requires a separate squeezing equipment, fails to
produce an uniform compaction, and generates stresses in the collar area.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a method for
manufacturing of ceramic tubes with an end-collar adaptable as ceramic candles
in Hot gas filtration, which eliminates the disadvantages of prior Art.

Another object of the present invention is to propose a method for
manufacturing of ceramic tubes with an end-collar adaptable as ceramic candles
in Hot gas filtration, which constitutes a two-step extrusion process.
A still further object of the present invention is to propose an extrusion mould
with split die inserts attached next to a main die for manufacturing of ceramic
tubes with end collar adaptable as ceramic candles in hot gas filtration.
A still another object of the present invention is to propose a method for
manufacturing of ceramic tubes with an end-collar adaptable as ceramic candles
in hot gas filtration, which is enabled to produce the ceramic tubes with integral
collar.
A further object of the present invention is to propose a method for
manufacturing of ceramic tubes with an end-collar adaptable as ceramic candles
in Hot gas filtration, which exhibits sufficient strength and contains uniform
microstructure and adaptable as ceramic candles for hot gas filtration or similar
applications.
Another object of the present invention is to propose a method of handling the
extruded tubes with varying diameter during the extrusion.
SUMMARY OF INVENTION
According to the present invention, an extrusion mould and a two-step extrusion

process is disclosed for the manufacture of tubes with collar at one end. The
disclosed mould consist of a main mould with dimension corresponding to an
outer diameter of the tube, and a mandrel with dimension corresponding to an
inner diameter of the tube, the mandrel extended along a length of a split mould
having dimension and profile corresponding to a collar to be formed and
attached to a compaction plate. The spilt mould can optionally have inserts and
can be detachable from main mould and can be split into two halves.
In this invention, the split mould with the inserts for forming the collars are
attached next to the main mould and a compaction plate is attached to other end
of the split mould. A paste is made to fill the mould and is compacted by a
compaction plate through advancement of a ram in an extruder at a pre-
determined speed. Then the compaction plate is detached and an extrusion
through the split mould is first carried out till the required length of the collar.
The Split mould and the inserts are then removed and the extrusion is continued
through the main mould to produce the tubes with a smaller diameter which are
integral to the collar having a higher diameter.
The invention thus describes a mould and an extrusion method to manufacture a
ceramic tube with varying diameter such as collar at one end which can be used
as a ceramic candle in hot gas filtration of particulates from hot flue gases or
coal gases.
Moreover, according to the present invention, there is provided a method of
handling the extruded tubes of varying diameter using a steel pipe which

supports the inner surface of the tubes instead of the outer surface of the tube.
The extruded products are made to pass over this steel pipe and then the
product is carried along with the pipe to an oven or a drier to stiffen the product
for further heat treatment process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The above and other objects, features and advantages of the present invention
will become more readily apparent from the following description, reference
being made to the accompanying drawing in which:
Figure 1: Schematic diagram showing extrusion mould for extruding tubes
with collar according to the invention
DETAILED DESCRIPTION OF THE INVENTION
As shown in figure-1, the mould according to the invention comprises a main
mould (1) having dimensions corresponding to the outer diameter of the tube, a
mandrel (2) having dimension corresponding to inner diameter of the tube, and
the mandrel (2) is extended up to the length of a spilt mould (3) having
dimension and profile in registration with the dimension of a collar to be formed,
and attached to a compaction plate (4). The spilt mould (3) can optionally have a
plurality of inserts (5) and detachable from the main mould (1) and can be
configured in two halves. The inserts (5) are preferably made of Polypropylene

or Teflon material to reduce the weight of the spilt mould (3) and easy to
remove without causing damage to the extruded collar part. Moreover the outer
profile of the collar can be formed easily by changing the inserts (5).
According to the present invention, a paste for extrusion is made from ceramic
materials such Alumina, mullite, Silicon carbide with suitable binder and water
and filled inside a piston extruder and de-aired and compacted. Then the split
mould (3) along with the inserts (5) for forming the collars are attached next to
the main mould (1). A compaction plate (4) is attached to the other end of the
split mould. The paste is made to fill the main mould (1) and get compacted by
the compaction plate (4) by advancement of a ram in the extruder at a
predetermined speed. Then the compaction plate (4) is detached and an
extrusion through this split mould (3) is carried out first till the required length of
the collar is attained. The Split mould (3) and the inserts (5) are then removed
and a further extrusion is carried-out through the main mould (1) to produce the
tubes with a smaller diameter which are integral to the collar with a higher
diameter.
Moreover, according to the present invention, there is provided a method of
handling the extruded tubes with varying diameter using a steel pipe to support
the inner surface of the tubes instead of the outer surface of the tubes. The
extruded products are made to pass over this pipe and then the product is
carried along with the pipe to an oven or drier to stiffen the product for further
heat treatment process. The pipes used is preferably made of steel and having
an outer diameter equal to or slightly lower than the inner diameter of tubes.
Example:
Silicon carbide (SiC) ceramic candles of 1.6 m long with 40 mm ID, 60 mm OD
and 80 mm OD collar of 27 mm long are produced by this method. After dying
and firing the formed integral collar are strong and found withstanding burst
strength of 50 bar.

WE CLAIM
1. A method for manufacturing of ceramic tubes with an end-collar adaptable
as ceramic candle in hot gas filtration, comprising the steps of:
- providing an extruder having at least one mandrel, and a ram operable at
different speeds by an actuator;
- providing a main mold detachably attached to the mandrel of the
extruder, the main mold having cavity to receive a paste made of ceramic
materials;
- providing a split-mold releasably attached to the main mold via a first end,
a second end of the split mold is attached to a compaction plate;
- filling the main mold with the paste and compacting the paste by
advancing the ram against the compaction plate;
- detaching the compaction plate and extruding the compacted paste in the
extruder by adapting the split mold till the collar achieves the required
length;
- removing the split-mold from the extruder and continuing the extrusion by
adapting the main mold to produce a ceramic tube the ceramic tube
having a first end with a smaller diameter, and a second end with higher
diameter with the inbuilt collar.
2. The method as claimed in claim 1, optionally comprising the step of
providing a plurality of inserts to the split mold for enabling extrusion of
different diameter of tubes with end-collar.
3. The method as claimed in claim 1 or 2, comprising a step of providing a
metal pipe to support the produced tubes for transferring the tubes from
the extruder to an oven or drier.
4. The method as claimed in claim 1, wherein the main mould is selected to
have a dimensions corresponding to the outer diameter of the mandrel,
and wherein the mandrel is selected to have dimensions in registration
with the inner diameter of the tube.
5. The method as claimed in claim 1 or 4, wherein the split mold is selected
to have dimensions matching with the profile of the end collar.
6. The method as claimed in claim 1, wherein the split mold is configured in
two-halves.
7. A method for manufacturing of ceramic tubes with an end-collar adaptable
as ceramic candle in hot gas filtration as substantially described and
illustrated herein with reference to the accompanying drawings.

The invention relates to a method for manufacturing of ceramic tubes with an
end-collar adaptable as ceramic candle in hot gas filtration, comprising the steps
of providing an extruder having at least one mandrel, and a ram operable at
different speeds by an actuator; providing a main mold detachably attached to
the mandrel of the extruder, the main mold having cavity to receive a paste
made of ceramic materials; providing a split-mold releasably attached to the
main mold via a first end, a second end of the split mold is attached to a
compaction plate; filling the main mold with the paste and compacting the paste
by advancing the ram against the compaction plate; detaching the compaction
plate and extruding the compacted paste in the extruder by adapting the split
mold till the collar achieves the required length; removing the split-mold from the
extruder and continuing the extrusion by adapting the main mold to produce a
ceramic tube the ceramic tube having a first end with a smaller diameter, and a
second end with higher diameter with the inbuilt collar.