GB2112317A

GB2112317A - Making a reinforced refractory article

Info

Publication number: GB2112317A
Application number: GB08235342A
Authority: GB
Inventors: David Mills; Anthony Thomas Lindahl
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1981-12-10
Filing date: 1982-12-10
Publication date: 1983-07-20
Also published as: FR2518083A1; JPS58104076A; DE3245828A1

Abstract

A method of reinforcing a Silica core (8) by locating an Alumina rod (2) therein, comprises initially coating the reinforcing rod (2) with a fugitive coating material (6) of precise thickness, Fig. 2, forming the Silica core around the coated rod in a mould (not shown), and dispelling the fugitive coating when firing the core. The rod (2) is a slidably close fit in the core. The fugitive coating (6) can be a heat shrinkable plastic sheath or an adhesive low melting point material. <IMAGE>

Description

SPECIFICATION Reinforced refractory article making This invention relates to the making of reinforced refractory articles.

U.K. Patent Application No.8102598 relates to reinforced refractory articles and discloses a method of making such articles by inserting into a hollow member a reinforcing member which is sized to be a slidably close fit within the hollow member.

This method of providing a slidably close fit requires high dimensional accuracy in the manufacture of the members, especially in the case of small articles which increases production costs.

It is an object of the present invention to provide a method of making a reinforced refractory article wherein the above disadvantage may be overcome.

According to the present invention a method of making a reinforced refractory article comprises coating a reinforcing member with a predetermined thickness of fugitive coating material; forming the article around the coated reinforcing member; and dispelling the fugitive coating to leave the reinforcing member with a slidably close fit within the article.

One method in accordance with the invention of making a reinforced refractory core for use in defining a passage in a casting will now be described, by way of example only, with reference to the accompanying drawings, which show fragmented cross-sectional views of various stages in the making of the core.

Referring now to the drawings, a rod 2 (Fig. 1) of recrystallised alumina of length approximately 12 inches and diameter approximately 0.1 inches in inserted into a loose-fitting sleeve 4 of Mylar (Trade Mark) extending all along its length and having a thickness of approximately 0.003 inches.

The rod 2 may be solid (as shown) or tubular, as desired, and if tubular may typically have an internal diameter of approximately 0.045 inches.

The rod 2 may also be straight or of any desired shape, depending on the shape of the article to be reinforced.

The rod 2 and its loose-fitting sleeve 4 are heated to approximately 60 C to heat-shrink the sleeve 4 onto the rod to produce an intimate coating 6 (Fig. 2). The coated rod 2 is positioned in a mould (not shown) for casting a core 8 for use in defining a passage in a casting, and a slurry of core material (in this example silica) is injected into the mould to form the core 8 around the coated rod 2. The core 8 is then allowed to solidify and is removed from the mould (Fig. 3). In this case the core 8 is unfired or "green" and in order to make it suitable as a refractory component it must be fired. This firing is performed in known manner by maintaining the core 8 at a temperature of 1 0000C-1 2000C for a period sufficient to form ceramic bonds and to drive out all volatile components.

Under these conditions the Mylar (Trade Mark) coating 6 acts as a fugitive coating. The fugitive coating 6 is thus dispelled in the firing process to leave the rod 2 with a slidably close (approximately 0.003 inches) fit with the core 8 (Fig. 4). It will be appreciated that since recrystallised alumina is a far more refractory material than silica, the alumina rod 2 reinforces the silica core 8, the slidably close fit being necessary to take up differential thermal expansion between the core 8 and the rod 2.

It will also be appreciated that if the rod 2 is wholly enclosed within the core 8 a gap must be left at each end to accommodate longitudinal expansion; such gaps may conveniently be formed by wax, which will be removed during firing.

It will also be appreciated that in making the core in the above described way, the reinforcing effect of the alumina is present during the firing process, resulting in greater dimensional stability in the fired core.

It will also be appreciated that although in the above example the core is formed around the coated reinforcing member by injecting a slurry into a mould containing the coated reinforcing member, other methods of forming the core around the coated reinforcing member may be used. For example, the core may be pre-formed with a recess therein, and the coated reinforcing member may be inserted into the recess, the remainder of the recess then being filled with core material.

Other materials may be used for the fugitive coating material instead of the Mylar (Trade Mark) which is a polyester resin sold by Stone Industrial Division of U.S.A. For example, another heat shrinkable material which has proved satisfactory is a polyvinylchloride material sold by Thomas Ness Limited of Cheltenham but other heat shrinkable plastics could be used, for example a polyolefin, P.T.F.E., or fluoro-polymers.

In addition, in place of a heat shrinkable material, an adhesive fugitive material could be used and one which has given a good bond is an adhesive sheet sold under the trade name of WAFER MOUNT 562 by AREMCO Products Inc. of the U.S.A.

A still further alternative material is an adhesive low melting point tape, for example, a polythene or vinyl tape coated with an acrylic or rubber resin adhesive.

1. A method of making a reinforcing refractory article comprising: coating a reinforcing mcmber with a predetermined thickness of fugitive coating material; forming the article around the coated reinforcing member; and dispelling the fugitive coating to leave the reinforcing member with a slidably close fit within the article.

2. A method according to Claim 1 wherein the article is a core for use in defining a passage in a casting.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Reinforced refractory article making This invention relates to the making of reinforced refractory articles. U.K. Patent Application No.8102598 relates to reinforced refractory articles and discloses a method of making such articles by inserting into a hollow member a reinforcing member which is sized to be a slidably close fit within the hollow member. This method of providing a slidably close fit requires high dimensional accuracy in the manufacture of the members, especially in the case of small articles which increases production costs. It is an object of the present invention to provide a method of making a reinforced refractory article wherein the above disadvantage may be overcome. According to the present invention a method of making a reinforced refractory article comprises coating a reinforcing member with a predetermined thickness of fugitive coating material; forming the article around the coated reinforcing member; and dispelling the fugitive coating to leave the reinforcing member with a slidably close fit within the article. One method in accordance with the invention of making a reinforced refractory core for use in defining a passage in a casting will now be described, by way of example only, with reference to the accompanying drawings, which show fragmented cross-sectional views of various stages in the making of the core. Referring now to the drawings, a rod 2 (Fig. 1) of recrystallised alumina of length approximately 12 inches and diameter approximately 0.1 inches in inserted into a loose-fitting sleeve 4 of Mylar (Trade Mark) extending all along its length and having a thickness of approximately 0.003 inches. The rod 2 may be solid (as shown) or tubular, as desired, and if tubular may typically have an internal diameter of approximately 0.045 inches. The rod 2 may also be straight or of any desired shape, depending on the shape of the article to be reinforced. The rod 2 and its loose-fitting sleeve 4 are heated to approximately 60 C to heat-shrink the sleeve 4 onto the rod to produce an intimate coating 6 (Fig. 2). The coated rod 2 is positioned in a mould (not shown) for casting a core 8 for use in defining a passage in a casting, and a slurry of core material (in this example silica) is injected into the mould to form the core 8 around the coated rod 2. The core 8 is then allowed to solidify and is removed from the mould (Fig. 3). In this case the core 8 is unfired or "green" and in order to make it suitable as a refractory component it must be fired. This firing is performed in known manner by maintaining the core 8 at a temperature of 1 0000C-1 2000C for a period sufficient to form ceramic bonds and to drive out all volatile components. Under these conditions the Mylar (Trade Mark) coating 6 acts as a fugitive coating. The fugitive coating 6 is thus dispelled in the firing process to leave the rod 2 with a slidably close (approximately 0.003 inches) fit with the core 8 (Fig. 4). It will be appreciated that since recrystallised alumina is a far more refractory material than silica, the alumina rod 2 reinforces the silica core 8, the slidably close fit being necessary to take up differential thermal expansion between the core 8 and the rod 2. It will also be appreciated that if the rod 2 is wholly enclosed within the core 8 a gap must be left at each end to accommodate longitudinal expansion; such gaps may conveniently be formed by wax, which will be removed during firing. It will also be appreciated that in making the core in the above described way, the reinforcing effect of the alumina is present during the firing process, resulting in greater dimensional stability in the fired core. It will also be appreciated that although in the above example the core is formed around the coated reinforcing member by injecting a slurry into a mould containing the coated reinforcing member, other methods of forming the core around the coated reinforcing member may be used. For example, the core may be pre-formed with a recess therein, and the coated reinforcing member may be inserted into the recess, the remainder of the recess then being filled with core material. Other materials may be used for the fugitive coating material instead of the Mylar (Trade Mark) which is a polyester resin sold by Stone Industrial Division of U.S.A. For example, another heat shrinkable material which has proved satisfactory is a polyvinylchloride material sold by Thomas Ness Limited of Cheltenham but other heat shrinkable plastics could be used, for example a polyolefin, P.T.F.E., or fluoro-polymers. In addition, in place of a heat shrinkable material, an adhesive fugitive material could be used and one which has given a good bond is an adhesive sheet sold under the trade name of WAFER MOUNT 562 by AREMCO Products Inc. of the U.S.A. A still further alternative material is an adhesive low melting point tape, for example, a polythene or vinyl tape coated with an acrylic or rubber resin adhesive. CLAIMS

3. A method according to Claim 1 or 2 wherein the article is made of silica and the reinforcing member is made of recrystallised alumina.

4. A method according to Claim 1, 2 or 3 wherein the step of forming the article around the coated reinforcing member comprises forming the article in an unfired state around the coated reinforcing member and the step of dispelling the coating occurs in firing the article.

5. A method according to Claim 1, 2, 3 or 4 wherein the fugitive coating material is heat shrinkabie and the step of coating comprises arranging a sleeve of fugitive coating material around the supporting member and heating the sleeve so as to shrink the fugitive coating material onto the supporting member.

6. A method according to any preceding claim wherein the fugitive coating material is Mylar (Trade Mark).

7. A method according to any one of Claims 1 to 6 wherein the step of forming the article around the coated reinforcing member comprises injecting a slurry of material into a mould surrounding the coated reinforcing member and hardening the material.

8. A method according to any one of Claims 1 to 6 wherein the step of forming the article around the coated reinforcing member comprises inserting the coated supporting member in a recess in a pre-formed article and filling the remainder of the recess with article material.

9. A method of making a reinforced refractory article substantially as hereinbefore described.