WO1994016845A1

WO1994016845A1 - Casting metal tubes having one closed end

Info

Publication number: WO1994016845A1
Application number: PCT/GB1994/000105
Authority: WO
Inventors: Martin Richard Boland; Lee Jenkins
Original assignee: Jennings Winch & Foundry Co., Ltd.
Priority date: 1993-01-19
Filing date: 1994-01-19
Publication date: 1994-08-04
Also published as: AU5841394A

Abstract

Metal tubes having an integral closed end (2), for example to contain a pyrometer thermocouple, are cast with a preformed silica tube (5) defining the central bore of the tube. The silica tube has a domed closed end (6) formed by fusing. Each metal tube (1) is cast in a vertical mould cavity with the upper open end of the silica tube (5) held in the upper end of the mould. A lower portion of the silica tube (5) is located in the mould cavity by a chaplet clip (17). The molten metal flows upwards in the cavity from the bottom thereof.

Description

Casting- Metal Tubes Having One Closed End

The present invention relates to the casting of metal tubes having a closed end cast integrally with the tube. One example of such a tube is a pyrometer tube which contains a thermocouple junction and is mounted so that the portion containing the thermocouple, as well as the closed end, is immersed in a liquid, such as molten metal, the temperature of which is to be measured.

Such pyrometer tubes may be required to be from one to two or even three metres long and 25mm to 75mm in diameter. Conventionally, they are sand-cast with a sand core which involves stabilising the core during pouring by means of a large number of chaplets spaced along the length of the core to hold the core firmly in position. The use of many chaplets in conjunction with sand casting can result in one or more of the chaplets not fusing properly into the molten iron with the result that the molten material in which the tube is subsequently immersed may penetrate into the interior of the tube. Thus for example where the pyrometer is to measure the temperature of a bath of molten aluminium and the thermocouple includes a platinum/rhodium wire, the latter wire will be irreparably damaged by the molten aluminium.

In accordance with the present invention there is provided a method of casting a metal tube with a closed end, characterised in that the interior of the tube is defined by a preformed tube having a closed end, the preformed tube being formed of ceramic or other refractory material capable of maintaining its shape during casting of the metal, the preformed tube is supported vertically in an upright mould cavity and the cavity is filled with molten metal from the bottom of the cavity.

Also according to the invention there is provided a cast metal tube which is closed at one end, characterised in that the interior of the tube is defined by a preformed tube around which the material of the remainder of the tube is cast, the preformed tube being formed of ceramic or other refractory material capable of maintaining its shape during casting.

Particularly where the outer part of the tube is of cast iron or steel, the preformed tube may consist of a length of fused silica tubing.

Advantageously, during casting, the upper end of the preformed tube is secured in the mould at the upper end of the cavity and a lower portion is centralised in the mould cavity by a chaplet clip having ends supported by the mould.

The invention will now be further described by way of example with reference to the accompanying drawings in which:

Figure 1 is a view in longitudinal section of a pyrometer tube;

Figure 2 is a view in longitudinal section of the ends of a cast metal pyrometer tube showing the position of the chaplet used during the casting of the tube;

Figure 3 is a vertical sectional view on the parting plane of a mould in which five tubes are cast simultaneously; and

Figure 4 is a cross section, on an enlarged scale, of one of the mould cavities of Figure 3 on the line IV-IV of Figure 3.

The thermocouple or pyrometer tubes 1 shown in Figures 1 and 2 each has an end portion 2, for example 60 mm in length, which is solid in cross section and has a hemispherical lowermost end surface 3. Within the remainder of the tube 1 is a cylindrical space 4 up which extend insulated electrical connecting wires leading from a thermocouple junction (not shown) in the lowermost part of the space 4.

The space 4 is defined by a length of ceramic tubing or fused silica tubing 5, the lower end of which is closed, for example, by fusing at 6. The tubing 5 may be of the kind which is commercially available for enclosing helical electric radiant heating elements. Suitable tubing is available from TSL Group PLC, P.O. Box 6, Wallend, Tyne and Wear NE28 6DG, United Kingdom.

The wall thickness of the tubing 5 may be 2 mm and its internal diameter in the range 8 to 22 mm.

The tube 1 is cast vertically around the tubing 5 in a sand mould, or in a metal die the internal mould-forming cavity of which is precoated with a suitable release agent such as graphite. The tubing 5 forms a core for the casting and can be left in the casting after the latter solidifies.

In the arrangement shown in Figure 3, five tubes are cast simultaneously. The half mould shown in Figure 3 consists of a moulding box 11 containing moulding sand 12 in the surface of which patterns have formed a half-cavity 13 for each tube, and half-cavities for a feed runner 14 and a distribution runner 15 connecting the feed runner 14 to the ends of the half-cavities corresponding to the closed ends of the tubes.

A core-forming tube 5 (not shown in Figure 3) is placed in each half-cavity 13 with its open end suitably supported (for example in a print in the end portion 16 of the sand) and with its opposite, closed end portion supported and located by a chaplet clip 17 bridging the half-cavity 13, for example at 120 mm to 350 mm from the closed end of the half-cavity.

As is shown in Figure 4, each chaplet clip 17 is formed from a pair of strips of austenitic stainless steel (e.g. 1.5 mm thick) tack- or spot-welded together at one end 18. Each strip is shaped with a central transverse trough 19 to make frictional contact with the core tube 5 and two further transverse troughs forming locating projections 20 to engage the sides of the half-cavity 13.

A second mould half is formed as a mirror-image of that shown in Figure 3 and secured thereto to form a complete mould which is then mounted vertically. Molten cast iron is then poured into an in-gate 22.and flows down the feed runner 14 through a foamed ceramic "sponge" filter F, along the distribution runner 15 and thence upwardly in each mould cavity around the core tubes 5.

During the casting process, the tubing 5 is accurately located in position and centralised in the mould near its lower end by the chaplet clip 17. An advantage of using stainless steel for the clip 17 is that it does not evolve gases when the molten metal rises into contact with the chaplet clip 17. Accordingly, the iron can unite cleanly with the chaplet clip without forming voids at the interface between the iron and the chaplet clip.

After casting, the end portion 7 of the tube is formed with internal screwthreads 8 (Figs. 1 and 2) and the end portions 17a, 17b of the chaplet clip protruding from the cast tube, as well as the runner sprues, are removed.

The tube length may be in the range 900 to 2,000 mm or even 3,000 mm with an outside diameter, for example of 44 mm. Particularly, where the diameter of the core tube 5 is small, it may be found necessary to use a second chaplet set, for example from 200 to 350 mm above the first chaplet set.

After casting, the core tube may be left in place except at the open end, although it may become broken up as the metal solidifies. Alternatively, it may be removed mechanically or chemically, for example with hydrofluoric acid.

In use, the chaplet, or lowermost chaplet is preferably positioned above the surface of the bath of molten metal, the temperature of which is to be measured.

Claims

1. A method of casting a metal tube with a closed end, characterised in that the interior of the tube is defined by a preformed tube having a closed end, the preformed tube being formed of ceramic or other refractory material capable of maintaining its shape during casting of the metal.

2. A method according to claim 1, wherein the preformed tube is supported vertically in an upright mould cavity and the mould cavity is filled with molten metal from the bottom of the cavity.

3. A method according to claim 2, wherein the open end of the preformed tube is held at the upper end of the mould cavity and a lower portion of the preformed tube is located relative to the mould wall by a chaplet means.

4. A method according to claim 3, wherein the chaplet means comprises a clip engaged with the preformed tube.

5. A method according to claim 4, wherein the clip is made of stainless steel.

6. A method according to any preceding claim, wherein the preformed tube is formed of fused silica.

7. A cast metal tube which is closed at one end, characterised in that the interior of the tube is defined by a preformed tube around which the material of the remainder of the tube is cast, the preformed tube being formed of ceramic or other refractory material capable of maintaining its shape during casting.

8. A cast metal tube according to claim 7, in which the preformed tubing is of fused silica.

9. A cast metal tube according to claim 7 or 8 , having incorporated in the metal thereof portions of a chaplet clip extending between the preformed tube and the outer wall of the cast tube in a position nearer to the closed end than to the open end of the performed tube.

10. A pyrometer comprising a cast metal tube according to any of claims 7 to 9, a thermocouple junction in the interior of the tube adjacent the closed end and leads extending within the tube from the thermocouple junction to the exterior.

11. A core assembly for use in casting a metal tube having an open end and an integrally closed end and a bore of predetermined diameter, the said core assembly comprising a refractory tube having an open end and an outwardly domed closed end, the refractory tube having an external diameter corresponding to the said predetermined diameter, and a chaplet clip frictionally engaged on the refractory tube.