METHOD AND APPARATUS FOR PRODUCING EXTRUDED CERAMIC PRODUCTS

Abstract: A method of producing ceramic products by extruding a ceramic material (10) through an extruding opening, includes the step of coating with a liquid (8), which is nonvolatile at ordinary room temperatures, on a surface of the extruded product. An apparatus for producing extruded ceramic products includes a forward end portion (1) having an extruding opening for extruding the ceramic mater­ ial, a guide passage (19) for introducing the ceramic forming material into the extruding opening, and a liquid supply section (4) provided on the forward end portion for supplying a liquid, which is nonvolatile at ordinary room temperatures, to the outer surface of the product.

Description: This invention relates to a method and an apparatus for producing extruded ceramic green products, and more particularly to a method and apparatus for producing ceramic honeycomb structures as catalyst carriers. In order to produce, for example, ceramic honeycomb structures in a known manner, a ceramic material is mixed and kneaded in a kneader, the kneaded product is extruded to column-shaped bodies in suitable sizes from a vacuum auger machine, the column-shaped bodies are supplied into a plunger molding machine from which the bodies are extruded. Fig. 1 illustrates in section a vacuum auger machine suitable for the purpose above described. The vacuum auger machine includes a vacuum kneading section having a screw-type mill 23 and a vacuum chamber 24 for kneading the ceramic material to obtain ceramic batches for forming the products, a ceramic batch transfer section having an auger 25 for transferring the ceramic batches in the vacuum chamber 24, and a green product forming section having a forming column ring 1 for forming the ceramic batches transferred by the auger 25 into column-shaped green products. These sections are located on a frame 27. The screw-type mill 23 is used for transferring the ceramic material supplied from a ceramic material supply opening 22 into the vacuum chamber 24, while the ceramic material is being kneaded. In the vacuum chamber 24, bubbles and the like in ceramic batches supplied as kneaded batches for forming are removed. The ceramic batches are loosened when falling by gravity and are then supplied to the ceramic batch transfer section. The ceramic batches supplied into the ceramic batch transfer section are transferred while being compressed by the auger. As the ceramic batches are transferred through the auger, they pass through a grid drum 9 to be crushed and loosened so as to remove laminations included in the ceramic batches. Thereafter, the ceramic batches pass through a guide passage 19 of the forming column ring 1, forming then into a column-shaped green product which is then extruded at an extruding opening 11 shown by an arrow A in Fig. 1. The resultant column-shaped green product is cut in predetermined lengths by a cutter (not shown) provided on a side of the outlet of the forming column ring 1. The column-shaped products of the predetermined lengths are then supplied to a plunger molding machine (not shown) preparatory to a subsequent process. In this case, the column-shaped products must have diameters and lengths permitting the products to be inserted into a cylinder of the plunger molding machine. These column-shaped products are then caused to pass through an extruding die of the plunger molding machine, thereby producing honeycomb structures. The above explained method is a so-called "batch process", wherein the column-shaped products extruded from the extruding opening 11 of the vacuum auger machine shown in Fig. 1 have to be loaded one by one into the plunger molding machine for the next process by means of a movable loading machine. During this loading process the column-shaped products conventionally stay in a stock yard for a period of time until they are locaded into the plunger molding machine. During such a waiting period, moisture tends to evaporate from surfaces of the column-shaped products causing local drying and hardening. Moreover, such a drying may take place until they are extruded from a plunger cylinder of the plunger molding machine in the next process. The dried outer surfaces of the column-shaped products detrimentally affect resultant products having a predetermined shape obtained through an extruding die by an actuation of a ram head by means of a hydraulic plunger. Specifically, the hardened surfaces make rough outer surfaces of extruded honeycomb structures, or the hardened portions of ceramic batches mix with inner material of the formed structures to cause strains therein, or forming grooves of a forming die are partially clogged with the hardened ceramic material to cause defects in the extruded honeycomb structures. In the batch process, moreover, the honeycomb structures extruded from the plunger molding machine are left as extruded until the next drying process. In the same manner as above described, therefore, the honeycomb structures are partially dried and suffer cracks, or uniform construction of the structures can not be obtained in the next drying and firing processes so that strains inevitably remain in the structures. In generally, the outer surfaces of the extruded products are considerably dried by frictional heat caused by contact resistance between ceramic batches and extruding dies. In the prior art, CH-A-629414 (Gerhaher) describes reducing deformation of an extruded ceramic strip, due to evaporation from its surface regions, by coating an oil, varnish or fat onto the top surface of the strip after it emerges from the extrusion opening. The coating is done by a sponge applicator replenished by a drip. According to the present invention, in a first aspect we provide a method of making an extruded ceramics product in which a ceramics forming material is extruded from an extrusion opening and a liquid, non-volatile at room temperature, is coated on a surface of the emerging extruded material, characterised in that the non-volatile liquid is applied to the peripheral surface of the material at the extrusion opening and spreads around the peripheral surface by capillarity between the opening and the material. The liquid which is nonvolatile at room temperatures used herein is preferably a liquid having a low vapor pressure at ordinary room temperatures, for example, a mineral oil such as kerosene, light oil, spindle oil or a mixture of them. In coating, the oil is caused to spread on the surface of an extruded product with the aid of the capillarity to form a film of the oil. The term "ceramic forming material" used herein is intended to include both a ceramic batch and an extruded ceramic green product once formed in a predetermined shape (for example, a cylindrical formed body). The "extrusion opening" used herein may be a simple opening, but may be an opening such as an extrusion die having forming grooves. In a second aspect, we provide apparatus for providing an extruded ceramics product, comprising a forward end portion having an extrusion opening from which a ceramics-forming material is extruded in use, and a guide passage leading to the extrusion opening, characterised by liquid application means provided at the forward end portion for applying a liquid which is nonvolatile at room temperature to the peripheral surface of extruded material at the extrusion opening, such that the liquid can be distributed around the material peripheral surface by capillarity between the material surface and the opening. In a third aspect, we provide a coating device for coating a liquid, non-volatile at room temperature, onto an extruded ceramic product, comprising an extrusion opening through which ceramics-forming material is extruded and a guide passage for guiding the material into the opening, characterised by means for applying said liquid at the extrusion opening to the surface of material extruding therefrom such that said liquid can be spread around said surface by capillarity between the material and the opening. Preferred features are set out in the claims. In the method aspect of the invention for producing extruded ceramic formed products, as a liquid, which is nonvolatile at ordinary room temperatures, is coated on surfaces of extruded ceramic formed products, films of the liquid are formed thereon to prevent the moisture in the proximity of the surfaces of the ceramic products from evaporating therefrom. Therefore, the films can prevent local drying, hardening and change of properties of the surfaces of the products so that uniform ceramic products can be obtained. According to the apparatus of the invention for producing extruded ceramic products, the apparatus comprises at its forward end a liquid supply means to which a liquid, nonvolatile at ordinary room temperatures, is supplied so that the surface of the extruded ceramic product is coated with the liquid by capillary action as the product is being extruded from the extrusion opening of the apparatus. The invention will be more fully understood by referring to the following detailed description and claims taken in connection with the appended drawings. Fig. 1 is a sectional view of a vacuum auger machine of the prior art; Fig. 2 is a partially removed perspective view illustrating a part in the proximity of the extruding opening of a vacuum auger machine embodying the invention; Fig. 3 is a sectional view illustrating the part shown in Fig. 2; Fig. 4 is a sectional view taken along the line IV-IV in Fig. 3; Fig. 5 is a perspective view illustrating jetting an oil against an end face of a column-shaped ceramic product; Fig. 6 is a sectional view illustrating a part in the proximity of the extruding opening of the plunger molding machine embodying the invention, and Figs. 7a and 7b illustrate a quadrangular pyramid aperture and Figs. 7c and 7d illustrate a conical aperture as versions of a liquid supply device embodying the invention. An embodiment will be explained, which is an application of the invention to the vacuum auger machine shown in Fig. 1. Fig. 2 is a perspective view illustrating a forward end of a column forming ring 1 partly broken away and Fig. 3 is a sectional view of the column forming ring 1. Fig. 4 is a sectional view of the column forming ring 1 taken along the line IV-IV in Fig. 3. In this embodiment, the column forming ring 1 is formed with a triangular pyramid-shaped notch 2 at an edge of a forward face 3. One end 2a of the notch 2 is at an edge of an extrusion opening 11 of the column forming ring 1. A pair of jet nozzles 6 are provided in the proximity of the extrusion opening 11. Above the notch 2 is fixed a constant amount oil supply means 4 from whose lower end an oil 5, which is a mixture of kerosene, light oil and spindle oil, is supplied at a constant velocity to the notch 2 under stable conditions. A ceramic batch 10 is extruded from an auger (not shown) and crushed and loosened by a grid drum 9. The loosened ceramic batch 10 is caused to pass through a guide passage 19 in the column forming ring 1 and then extruded out of the column forming ring 1 as shown by an arrow A. During such an extrusion, the oil 5 supplied from the constant amount oil supply means 4 onto the notch 2 flows down in the notch 2 and arrives at the end 2a of the notch 2. As shown in Fig. 4, on the other hand, when the ceramic batch 10 is extruded from the extruding opening 11, there is a clearance 40 (not shown in Figs. 2 and 3) between an inner wall of the guide passage 19 and the ceramic batch 10. Therefore, the oil 5 extends over the cylindrical outer surface of the ceramic batch 10 with the aid of capillarity and is attached to the outer surface. An oil film 8 is thus formed and coated on the entire outer surface of the formed product 7, while the ceramic batch 10 is being extruded in the direction of the arrow A. When the ceramic formed product 7 has been extruded to a predetermined length, it is cut with cutting means such as a wire saw or the like (not shown) to obtain column-shaped products 7a as shown in Fig. 5. The extruding machine and the like are omitted in Fig. 5. Moreover, an oil is jetted onto an end face 7b of the column-shaped formed product 7a by means of injection nozzles 6 as shown by arrows B, so that the end face 7b is also coated with an oil film. When an oil film is formed on the forward end face 7a of the column-shaped product 7A (Fig. 2), the oil may be sprayed onto the forward end face by the injection nozzles 6. According to this embodiment, as the entire column-shaped product 7A is coated with the oil films 8, the moisture included in the column-shaped product 7A is prevented from evaporating so that drying, hardening and change of properties are prevented. Therefore, in forming and treating the column-shaped product 7A in the plunger molding machine, there is no risk of the outer surface of the treated formed product roughening or of hardened ceramic batch mixing in the formed product to cause strains therein, or of forming grooves of an extruding die being clogged with the hardened ceramic batch. Moreover, as the oil films 5 are formed preferably with the aid of the capillarity and spraying, so that thin and uniform oil films can be readily formed in a reliable manner. Furthermore, it is only required to provide a notch 2, so that the requisite function can be easily obtained in a simple manner without modifying the existing machine. Moreover, as the oil 5 is supplied to the notch 2 under the stable condition, the oil films 5 are uniform in thickness so that the control for forming the oil films is simply effected. In addition, the lubricating performance between the ceramic batch 10 and the proximity of the extruding opening 11 is improved by the oil films 5 so that the extruding is effected more smoothly. In the above embodiment, the inclined notch 2 is provided in the proximity of the extruding opening 5. Instead of such a notch 2, different oil supply means may be provided at the column forming ring 1. For example, the column forming ring 1 may be provided with a small aperture 42 tapered inwardly (for example, in the form of a quadrangular pyramid or cone as shown in Figs. 7a-7d ) and the oil 5 supplied into a wider end of the small aperture on an outer side to feed the oil through the tapered end of the aperture into the guide passage 19 so that an oil film is formed with the aid of the capillarity in the same manner as above described. Another embodiment will be explained which is an application of the invention to a plunger molding machine. Fig. 6 illustrates the proximity of an extruding die of the plunger molding machine. A ram head 16 is accommodated in a plunger cylinder 15 so as to be movable, interacting with a hydraulic cylinder (not shown) so as to pressurize a column-shaped product 7A. The column-shaped product 7A is moved in a guide passage 19 in a forward end of the plunger cylinder 15 by the pressurizing action of the ram head 16 in a direction shown by arrow C, so that the column-shaped product 7A is formed into a predetermined shape through an extruding die 18 attached to a forward and of the plunger cylinder 15 to obtain a honeycomb formed product 17. It is preferable to provide a grid drum 9 immediately before the extruding die 18 in order to crush and loosen the column-shaped product 7A. Die 18 and product 17 are not shown in detail. The extruding die 18 is formed with a triangular pyramid-shaped notch 2a similar to that shown in Fig. 2. Above the notch 2a is arranged a constant amount oil supply means 4. An oil 5 is supplied from an end 2a of the notch 2 onto an outer surface of the honeycomb formed product 17 by capillarity, to form an oil film on the outer surface of the product 17 in the same manner as above described. Oil films may also be formed on both end faces of the ceramic honeycomb formed product 17 by spraying the oil 5 by the use of injection nozzles above described. According to this embodiment, the local drying of the surfaces of the honeycomb formed product 17 can be prevented so that uniform contraction in the honeycomb product can be obtained in next drying and firing processes without strains remaining in a sintered product. In the above embodiment, after column-shaped formed products have been formed, they are loaded one by one into the plunger cylinder to produce the honeycomb formed products. However, after ceramic batches have been kneaded, the kneaded batches may be directly caused to pass through the extruding die continuously to produce honeycomb formed products which are then dried and fired. In this case, by the use of the arrangement as shown in Fig. 2 or 6, the same effect similar to that shown in Fig. 6 can be obtained. According to the method described above for producing extruded ceramic formed products, as a liquid, which is nonvolatile at ordinary room temperatures, is coated on surfaces of extruded ceramic formed products, films of the liquid can prevent the moisture in the proximity of the surfaces of the ceramic products from evaporating therefrom. Therefore, the films can prevent local drying, hardening and change of properties of the surfaces of the products so that uniform ceramic products can be obtained. As a result, roughness and peeling of hardened portions can be prevented. Moreover, upon applying drying or firing treatment to the extruded ceramic product, it exhibits uniform contraction in its entirety so that strains do not remain in the product. According to the apparatus of the invention for producing extruded ceramic products, the apparatus comprises at its forward end the liquid supply means to which the liquid, nonvolatile at ordinary room temperatures, is supplied so that the surface of the extruded ceramic product is coated with the liquid as the product is being extruded from the extruding opening of the apparatus. According to the liquid coating device of the invention, moreover, there is provided coating means capable of coating a liquid, which is nonvolatile at ordinary room temperatures, on surfaces of a ceramic product extruded from the extruding opening of the device, so that even after the product has been extruded, the liquid can be coated on surfaces of the extruded ceramic product.

Claims: A method of making an extruded ceramics product in which a ceramics-forming material is extruded from an extrusion opening (11) and a liquid (5), non-volatile at room temperature, is coated on a surface of the emerging extruded material, characterised in that the non-volatile liquid is applied to the peripheral surface of the material (7,17) at the extrusion opening (11) and spreads around the peripheral surface by capillarity between the opening and the material. A method according to claim 1 in which the entire outer surface of the extruded material (7,17) is coated with the liquid (5). A method according to claim 1 or claim 2 in which the extruded material (7) is cut into lengths downstream of the extrusion opening (11). A method according to any one of claims 1 to 3 in which a liquid, non-volatile at room temperature, is sprayed onto at least one end face (7a,7b) of the extruded material. A method according to any one of the preceding claims in which the extruded material (7,17) is cylindrical. A method according to any one of the preceding claims in which the extruded material comprises honeycomb-structure ceramics (17). A method according to any one of the preceding claims in which the non-volatile liquid (5) is an oil. Apparatus for producing an extruded ceramics product, comprising a forward end portion (1,18) having an extrusion opening (11) from which a ceramics-forming material is extruded in use, and a guide passage (19) leading to the extrusion opening (11), characterised by liquid application means provided at the forward end portion (1,18) for applying a liquid (5) which is non-volatile at room temperature to the peripheral surface of extruded material at the extrusion opening, such that the liquid can be distributed around the material peripheral surface by capillarity between the material surface and the opening (11). Apparatus according to claim 8, in which the liquid application means comprise a notch (2) formed in the forward end portion (1) adjacent the extrusion opening (11). Apparatus as claimed in claim 9 in which the notch (2) is of triangular pyramid shape. Apparatus as claimed in claim 9 in which the liquid application means comprise a small, inwardly tapering aperture (42) of either quadrangular pyramid or cone form, in the forward end portion (1) adjacent the extrusion opening (11). A coating device for coating a liquid, non-volatile at room temperature, onto an extruded ceramic product, comprising an extrusion opening (11) through which ceramics-forming material is extruded and a guide passage (19) for guiding the material to the opening (11) characterised by means for applying said liquid (5) at the extrusion opening (11) to the surface of material extruding therefrom such that said liquid (5) can be spread around said surface by capillarity between the material and the opening (11). A coating device according to claim 12 in which said means for applying the liquid (5) comprise a notch (2) formed at the extrusion opening (11). A coating device according to claim 13 in which the notch (2) is of triangular pyramid shape.

Inventors: ARAI, KENJI, KATSURAGAWA, YASUJI
Applicants: NGK INSULATORS, LTD.
Application year: 1990
Main classification: B28B3
IPC codes: B28B3