GB2175521A

GB2175521A - Manufacture of metal castings having chill-hardened zones

Info

Publication number: GB2175521A
Application number: GB08513730A
Authority: GB
Inventors: Frank Rowley
Original assignee: Perkins Engines Group Ltd
Current assignee: Perkins Engines Group Ltd
Priority date: 1985-05-31
Filing date: 1985-05-31
Publication date: 1986-12-03
Also published as: GB8513730D0

Abstract

A metal casting e.g. camshaft, having chill-hardened portions (4) is made by providing an outer mould support (1) composed of a thermally conductive material; providing a mould (7) composed of a material with higher thermal insulating property than the mould support, the mould (7) being located within the mould support (1) and having an internal recess or structure that cooperates with internal walls (6) of the mould support (1) to define a moulding cavity; and casting molten metal into the cavity so as to form a casting therein with those portions (4) thereof that are in contact with the internal walls (6) of the mould support being chilled by such contact. The mould (7) may be pre-formed with said internal recess and located within the mould support so as to align said recess with said internal walls (6). Alternatively however, a moulding pattern (3) may be used having the shape of the required casting and which is composed of a material, such as polystyrene, that will disperse when contacted with the cast metal. This pattern (3) is located within the mould support (1) in the required alignment relative to said internal walls (6), and mould material, such as sand, is poured around the pattern. <IMAGE>

Description

SPECIFICATION Manufacture of metal castings This invention relates to the manufacture of metal castings having chill-hardened portions.

Conventionally, metal castings are formed with chill-hardened portions by providing "chills" in the mould, that is, metal inserts that are located adjacent to those portions of the moulding only where the casting is to be chill-hardened. One difficulty with this process is the accurate location of the "chills" within the mould every time a casting is produced. For example, an engine camshaft with chill-hardened cam noses requires separate "chills" or set of "chills" to be inserted in the mould adjacent the nose of each cam. The "chills" are located by engagement with the mould pattern, but this requires care and time, and the loose "chills" have to be recovered for re-use. These factors increase the cost of production.

An object of the present invention is to provide a simpler method of manufacturing castings having chill-hardened portions.

The method according to the invention comprises providing an outer mould support composed of a thermally conductive material; providing a mould composed of a material with higher thermal insulating property than the mould support, the mould being located within the mould support and having an internal recess that cooperates with internal walls of the mould support to define a moulding cavity; and casting molten metal into the cavity so as to form a casting therein with portions that are chill-hardened by contact with the internal walls of the mould support.

It will be appreciated that this method avoids the use of "chills" and instead makes use of the outer mould support to define those parts of the moulding cavity where the cast metal is to be chilled. Internal walls of the mould support therefore have to be formed to define the chilled parts of the casting, and the mould has to be accurately located within the mould support so as to align its internal recess with said internal walls and produce the complete moulding cavity. However, this can be done relatively easily, and the problems associated with locating a plurality of loose "chills" are avoided.

The mould may be pre-formed with said internal recess and located within the mould support so as to align said recess with said internal walls. Alternatively, however, a moulding pattern may be used having the shape of the required casting and which is composed of a material, such as polystyrene, that will disperse when contacted with the cast metal. This pattern is located within the mould support in the required alignment relative to said internal walls, and mould material, such as sand, is poured around the pattern.

The invention will now be described by way of example with reference to the accompanying drawing in which; Figure 1 is an axial section through moulding apparatus employed according to one embodiment of the invention to manufacture an engine camshaft; Figure 2 and 4 are cross-sections through the apparatus of Figure 1, each taken through a cam forming portion of the apparatus; Figure 5 is an axial section through moulding apparatus employed according to a second embodiment of the invention to manufacture an engine camshaft; and Figure 6 and 8 are cross-sections through the apparatus of Figures 5, each taken through a cam forming portion of the apparatus.

The apparatus illustrated in Figures 1 to 4 comprises a mould support 1 in the form of a cast iron block split into two sections and formed with an internal cavity 2. A polystyrene pattern of a camshaft 3 is located within the cavity 2 and is aligned therein by engagement of the noses 4 of the cams 5 of the camshaft pattern in correspondingly machined recesses 6 in the side walls of the cavity.

Moulding sand is introduced into the cavity 2 around the camshaft pattern to form a mould 7 that surrounds the greater part of the pattern.

The casting process involves pouring molten metal into the mould and support block 1 so that it fills the space occupied by the pattern 3, the polystyrene of the pattern dispersing as the metal enters.

As the metal cools, the noses 4 of the camshaft cool more rapidly due to their contact with the cast iron block 1 and are therefore chill-hardened.

The split line between the two parts of the block 1 is arranged in relation to the cams 5, as shown in Figures 2 to 4, so as to allow the casting to be stripped from the block.

Also, the side faces of the camshaft are defined by the sand mould 7 rather than the metal block 1, as shown in Figure 1, so as to avoid the casting gripping the block as it contracts axially.

Preferably, the noses 4 of the camshaft pattern are of such a size as to be gripped by the recesses 6 in the block and thereby prevent or hinder loose sand from penetrating between the noses and the recesses.

Any tendency for the polystyrene camshaft pattern to become distorted in the process of fitting it into the support block 1, can be avoided by providing it with some internal reinforcement. For example, a metal bar or tube can be moulded into the polystyrene which can be withdrawn after assembly in the mould support block 1. Alternatively, the bar or tube can be left in place during casting so as to serve as a core forming an oil gallery.

The apparatus illustrated in Figures 5 to 8 is similar to that of Figures 1 to 4 except that the polystyrene camshaft pattern is omitted and instead the mould 7 is preformed with the recess 8 which, in cooperation with the recesses 6 for the cam noses, give the required form of the camshaft.

Molten metal is therefore cast directly into the empty moulding cavity. The mould 7 may be formed from bonded sand.

In both of the above described embodiments, the recesses 6 of the support block 1 can be formed in detachable portions of the block so that they can be replaced if they deteriorate through repeated contact with molten metal.

If required, the block can be water cooled to allow more rapid production cycles.

Claims

1. A method of manufacturing a metal casting having chill-hardened portions comprising providing an outer mould support composed of a thermally conductive material; providing a mould composed of a material with higher thermal insulation property than the mould support, the mould being located within the mould support and having an internal recess that cooperates with internal walls of the mould support to define a moulding cavity; and casting molten metal into the cavity so as to form a casting therein with those portions thereof that are in contact with the internal walls of the mould support being chilled by such contact.

A method as claimed in claim 1 in which the internal recess of the mould is formed by a moulding pattern composed of a material that disperses when contacted by the molten metal, the mould being formed within the moulding pattern by pouring material around the pattern.

3. A method as claimed in claim 1 or 2 in which those portions of the internal walls co-operating with said internal recess are formed on one or more detachable portions of the mould support.

4. A method as claimed in claim 2 in which portions of the moulding pattern engage recesses in the internal walls of the mould support.

5. A method as claimed in claim 4 in which said portions of the moulding pattern engaging said recesses are of such a size as to be gripped by said recesses.

6. A method as claimed in claim 4 or 5 in which said recesses are formed in one or more detachable portions of the mould support.

7. A method as claimed in claim 1 in which the mould is preformed with said internal recess.

8. A method as claimed in any one of the preceding claims in which the casting is a camshaft and in which noses of cams of the camshaft are chill-hardened.

9. A method as claimed in any one of the preceding claims in which the casting is elongate in the direction of an axis and has side faces extending radially of said axis, all of these faces being defined by the mould.

10. Apparatus for manufacturing a metal casting having chill-hardened portions comprising an out mould support composed of a thermally conductive material; and a mould composed of a material with higher thermal insulating property than the mould support, the mould being located within the mould support and having an internal recess that cooperates with internal walls of the mould support to define a moulding cavity.

11. Apparatus as claimed in claim 10 in which a moulding pattern occupies the moulding cavity, the moulding pattern being composed of a material that disperses when contacted by molten metal.

12. A method as claimed in claim 10 or 11 in which those portions of the internal walls co-operating with said internal recess are formed on one or more detachable portions of the mould support.

13. Apparatus as claimed in claim 11 in which portions of the moulding pattern engage recesses in the internal walls of the mould support.

14. Apparatus as claimed in claim 13 in which said portions of the moulding pattern engaging said recesses are of such a size as to be gripped by said recesses.

15. A method as claimed in claim 13 or 14 in which said recesses are formed in one or more detachable protioins of the mould support.

16. Apparatus as claimed in any one of claims 10 to 14 in which the moulding cavity taken the form of a camshaft with the noses of the cams of the camshaft being defined by said internal walls of the mould support.

17. Apparatus as claimed in any one of claims 10 to 16 in which the moulding cavity is elongate in the direction of an axis and has side faces extending radially of said axis, all of which are defined by the mould.

18. A method of manufacturing a metal casting having chill-hardened portions substantially as herein described with reference to the accompanying design.

19. Apparatus for manufacturing a metal casting having chill-hardened portions substantially as herein described with reference to the accompanying drawings.