Processes for producing hollow ceramic articles

Abstract: Processes for producing hollow ceramic articles such as ceramic port liners are disclosed. Such ceramic articles are produced by using a water-absorbable mold (1) having water non-permeable faces (4) on an inner surface (3) of the mold at locations corresponding to valve holes. The thickness of a ceramic layer deposited on the inner surface of the mold is controlled by measuring an amount of a lowered liquid surface level of the slurry near a slurry-pouring opening of the mold. Open ends of a hollow ceramic article are formed by cutting corresponding closed ends after deposition of the slurry and firing. A uniform thickness of a slurry deposited onto the inner surface of the mold can be attained by rotating the mold around an arbitrary rotary axis at a rotation speed of 1 to 60 rpm. All ceramic material contained in the slurry fed inside the mold may be deposited on the inner surface of the mold while the mold is being rotated or swung.

Description: The present invention relates to a process for producing a ceramic port liner, to be used for lining inner surfaces of exhaust ports for gasoline engines, diesel engines and the like, by drain or slip casting. It is already known that purifying performances of a catalyst are improved and turbo lag of a turbo-charger is reduced by increasing temperatures of exhaust gases due to a heat insulating effect of a ceramic material lining the inner surface of an exhaust port in the form of a port liner. Such techniques are considered to be effective particularly for four valve type engines which are likely to reduce temperatures of exhaust gases. Such ceramic port liners may be shaped by a drain casting technique, in which a ceramic slurry is poured inside a water-absorbing mold made of gypsum or the like and an excess amount of the slurry is drained after a slurry material is deposited on the inner surface of the mold (For example, see "Ceramic Engineering Handbook" published by Gihoudo Co., Ltd. Dec. 25, 1966, pp. 1152-1159). However, in case of port liners, valve holes need to be bored at specific locations. Formerly, such valve holes have been formed by mechanical working using a drill or the like after the shaping or firing. However, since a surface of the port liner to be worked is a curved surface, many shortcomings arise, such as that the working takes much time, that locating is difficult, that accurate working needs a great number of steps, and that cracks are likely to be formed due to brittleness of the ceramics even after the firing. US-A-1,337,663 discloses a process for producing a ceramic article with a hole which is formed by covering a plaster surface with shellac at the hole position. DE-A-2657177 discloses a process for producing a ceramic article with a hole by using a separate impermeable mold part. It is the object of the present invention to overcome the above-mentioned problems. More particularly, it is an object of the present invention to provide a process for easily producing hollow ceramic articles, such as ceramic port liners, with accurately formed valve holes by drain or slip casting. The invention is set out in the claim. Features and advantages of the invention will be appreciated upon reading of the specification in conjunction with the attached drawings, with the understanding that modifications, changes and variations of the same could be made by the skilled person in the art to which the invention pertains. Embodiments of the invention are now described by way of example with reference to the attached drawings. Fig. 1 is a perspective view of a split type mold to be used in an embodiment of the present invention; and Fig. 2 is a perspective view of an example of a ceramic port liner obtained by the present invention. In Fig. 1 are shown water-absorbable mold sections 1 and 2 to be used for effecting the present invention. As the mold, a gypsum mold is ordinarily used, but a water-absorbing resin mold may be used. Water non-permeable faces 4 are formed on the inner surface 3 of the mold section 1 at locations corresponding to valve holes. The water non-permeable face 4 has a shape corresponding to that of the valve hole. The water non-permeable face is formed by any suitable method, such as, by attaching a water non-permeable seal, applying a water non-permeable resin, or burying a water non-permeable resin. After the water-absorbable mold sections 1 and 2 are shut together, a ceramic slurry is poured inside the mold. Although the ceramic slurry is not limited to any particular one, use of aluminum titanate based ceramic is preferred. This is because this material has heat resistance and a modulus of elasticity suitable for port liners. Water contained in a portion of the poured ceramic slurry which contacts the inner walls of the water-absorbable mold sections 1 and 2 is absorbed thereinto, and a slurry material is gradually deposited inside the mold sections 1 and 2. Since the water non-permeable faces 4 have no such water-absorbing effect, no slurry material is deposited thereon at all. Thus, after the slurry material deposits on the inner surfaces of the mold sections excluding the water non-permeable surfaces 4 in a desired thickness, the remaining slurry is drained. By opening the mold sections 1 and 2, a ceramic port liner 6 having holes corresponding to valve holes 5 as shown in Fig. 2 can be obtained. In the thus obtained ceramic port liner 6, peripheral edges of the holes have only to be slightly corrected, and the number of working steps can greatly be reduced as compared with a conventional process where valve holes are bored in a blank ceramic port liner body by mechanical working. Further, the port liner can be prevented from being cracked during the mechanical working. In addition, according to the process of the present invention, the valve holes can be preliminarily formed in accurate locations without need to locate valve holes 5 by mechanical working. Moreover, the valve holes 5 may freely be formed in any curved surface. In addition, the dimensional accuracy of the valve holes 5 can be attained with extremely high accuracy by adjusting the size of the water non-permeable face 4. As is clear from the aforegoing explanation, according to the present invention, the ceramic port liner having the valve holes accurately formed can easily be produced by a simple technique that the water non-permeable faces are formed in the inner surface of the water-absorbing mold corresponding to the valve holes. Thus, the present invention can substantially contribute to industrial development of the process for producing ceramic port liners.

Claims: A process for producing a ceramic port liner having at least one valve hole (5), which comprises pouring a ceramic slurry inside a water-absorbing mold (1) having at least one water non-permeable seal (4) adhered on an inner surface thereof at a location corresponding to the valve hole, and by absorption of water from the slurry depositing a ceramic raw material contained in the slurry to a given thickness, except at the water non-permeable seal or seals (4).

Inventors: HAMANAKA TOSHIYUKI, HARADA TAKASHI, HATTORI FUMIO, HAMANAKA, TOSHIYUKI, HARADA, TAKASHI, HATTORI, FUMIO
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1988
Main classification: B28B1
IPC codes: B28B1