GB2032076A - Crucible furnace - Google Patents

Abstract

A crucible furnace (10) comprises a crucible (11) mounted within a cylindrical holder (12) arranged for pivotal movement relative to a supporting steel frame (21). The crucible (11) is held within the holder (12) by a refractory ring (13) having radially inwardly projecting lugs (31) which extend into depressions (32) in the crucible (11). A gas burner nozzle (27) is mounted on the frame (21) and is operative to direct a gas flame through an aperture (26) in the holder (12) and onto the crucible (11). A handle 25 is attached to the holder (12) to facilitate controlled pouring of the molten contents of the crucible (11) through a spout (34) by pivoting the crucible (11) and holder (12) about the common axis of two studs (19) in respective bearing brackets (20). <IMAGE>

Description

SPECIFICATION Furnace The invention relates to furnaces and particuiarly concerns crucible furnaces of a size and type suitable for use in schools and other educational establishments.

One problem associated with crucible furnaces for use in schools concerns the provision of adequate safety margins to the use of such furnaces. In known furnaces it is usual to melt a metal, for example aluminium, in a crucible, and then to transport the crucible and molten metal with the aid of tongs to a mould into which the molten metal is poured. This procedure clearly presents a safety hazard especially where children or inexperienced persons are involved and it is the aim of the present invention to provide a crucible furnace which is considerably safer in use and which may be used without substantial risk by relatively inexperienced persons.

According to the present invention there is provided a crucible furnace comprising a crucible mounted within a holder, a frame about which the crucible and holder are together pivotable, and means for heating said crucible.

The holder may comprise a substantially cylindrical metal (e.g. aluminium) container closed at a base and lined with a lightweight fibre or refractory material, such as a vacuum-formed ceramic fibre material. The crucible may be held in place by a ring disposed at the open end of the container and the ring is preferably fixed relative to the container by means of a flexible circumferential member threaded through a passageway formed between the metal container and the ring.

Preferably the crucible has a radially extending spout which projects beyond the outer circumference of the metal container, for example through a gap or aperture through the container, liner and refractory ring.

Means, such as a handle, may be provided for tilting the crucible and holder in the frame when molten metal is to be poured from the crucible. A single handle attached to the container or, for example, to a ring surrounding the container may be sufficient. When, however, the crucible and holder is to be detachable from the frame, it is desirable to provide handles on diametrically opposite sides of the container for example a single radially extending handle on one side to act as a held pivot during pouring, and two circumferentially spaced handles on the other side to enable the crucible and holder assembly to be tilted.

Means for heating the crucible and its contents may comprise a gas nozzle disposed so as to be operative to direct a jet of burning gas through an aperture in the side of the crucible holder and on to the crucible itself. In this case the crucible is left free for tilting or for lifting clear of the frame or housing to which it is mounted. However, other ways of heating the crucible are, of course, possible, and a nozzle or gas ring may be provided within the holder and supplied with gas by way of a flexible tube.

Releasable locking means may be provided to prevent the furnace being lifted during tilting from the bearings about which tilting takes place. Such means may comprise a spring clip, one arm of which normally engages the upper portion of a stud of the furnace and about which tilting takes place, which clip may be disengaged to allow the furnace to be lifted clear of its tilting bearings if required.

Conceivably means may also be provided for automaticaily cutting off the gas supply when the crucible and holder are tilted in the frame or are lifted from the frame. Deflection means may also be provided for the deflection of burnt heating gases over the upper portion of the crucible to prevent or reduce oxidation of the melt in the crucible.

The present invention will hereinafter be further described by way of example with reference to the accompanying drawings in which: Fig. 1 is a perspective view of a crucible furnace constructed in accordance with the present invention; Fig. 2 is a plan view (from above) of the furnace of Fig. 1; and Fig. 3 is a cross-section taken along the line Ill-Ill of Fig. 2.

Referring first to Fig. 1, the furnace 10 can be seen to comprise a crucible 11 mounted within a housing or holder designated as a whole by the numeral 12 and held in place by a refractory ring 13. The holder 1 2 comprises a substantially cylindrical spun aluminium container 14 provided with an internal lining 1 5 of a vacuum formed ceramic fibre material.A metal (aluminium) ring 1 6 fastened tightly round the container 14 by means of a nut and bolt arrangement 1 7 (Fig. 2) and further held in by two diametrically opposite screws 40 carries two brackets 1 8 on each of which is disposed a respective integral cylindrical stud 1 9. Each stud 1 9 lies in a respective Ubracket 20 attached to vertical arms of a steel frame 21, and the crucible and holder are pivotable together, relative to the frame 21, with the studs 1 9 in their brackets 20 acting as bearings. In the normal, rest position, the crucible holder 1 2 sits on a cross bar 22 of the frame.A releasable locking device is provided at one of the brackets 20 and comprises a steel spring clip 41 with a flat blade 42 which extends through a solt in one arm of the U-bracket. A lower curved blade 43 of the clip 41 extends below the bracket 20. When the spring clip is in position, the crucible and holder are constrained in the vertical direction to prevent upward movement during pouring. The clip 41 may be removed when the crucible 11 and holder 1 2 are to be lifted away from the frame.

The ring 1 6 is also provided with radially outwardly extending diametrically opposed solid bars 23 and 24 of square cross-section. Each of the screws 40 extends radially outwardly through casing 14 and into a respective one of the bars 23, 24 thereby securing the ring 1 6 to the casing 14.

Bar 24 has a handle 25 attached to it by means of which the handle 25 is fixed to the bar 24 by means of a tube 44 of square cross-section fixed to one end of the handle. The tube 44 is slipped over bar 24 and attached to bar 24 by means of a screw 45 preferably adapted for manual tightening and release. Bar 23 is provided so that a handle similar to handle 25 may be attached if necessary for tilting the crucible and holder from the other side. In this case also a screw 45 is provided so that the handle may be fixed to the bar. If the crucible and holder is to be lifted from the frame 21 prior to tilting and pouring the melt from the crucible then preferably two handles are provided on opposite sides of bar 24, and a further handle is attached to and coaxially with bar 23.In this case the crucible and holder are lifted by two persons, one on each side, and the assembly is tilted by means of the two handles on bar 24 with the handle on bar 23 serving as a pivot (hand held) about which the tilting takes place.

The holder 12 has an aperture 26 disposed in the side and a nozzle 27 is arranged opposite the hole and is operative to direct a jet of burning gas through the hole 26 and onto the crucible. The nozzle 27 is supplied with gas by means of a flexible tube 28, the gas supply being controilable by means of a valve 29 with control handle 30.

As may be seen most clearly from Fig. 2, the refactory ring 1 3 has three inwardly radially projecting lugs 31 which abut against the upper surface of corresponding depressions 32 in the crucible 11. The ring 13 also has a gap 33 in its circumference through which a spout 34 of the crucible 13 projects. The refractory ring 11 is attached to the aluminium container 14 by means of a helical spring 35 threaded in a circumferential passage way of circular cross-section formed between the container 14 and ring 13 and in fact, comprising a groove 36 in the ring 13 and a depression or channel 37 in the container 14, both of semi-circular cross-section. The crucible is thus held firmly against axial or angular displacement in the holder 12. As will be seen from Fig. 3 the crucible 11 is supported on a ring 38 also of vacuum formed ceramic fibre material.

The furnace is operated by first placing the metal to be melted in the crucible 11 after which lever 30 of valve 29 is turned to allow throughflow of gas which is ignited at the mouth of nozzle 27 by means of Piezo-electric crystal operated ignitor device 39 (Fig. 1). The stream of burning gases passes through aperture 26 and surrounds the crucible 11 to heat it and thus melt the metal therein. When the metal is in a sufficiently molten state the gas supply is switched off and the holder 12 and crucibel 11 are tilted together by means of handle 28 and the molten contents of the crucible are poured by way of spout 34 for example into a mould suitably disposed adjacent to frame 21 and beneath spout 24. It will be seen that the whole operation requires no transportation of a crucible from one part of a workshop to another with the obvious attendant dangers. Furthermore, the crucible 11 and holder 12 are supported by the ring 16 in the frame 21 and the tilting movement is predetermined within the frame. Should the operator let slip the handle 24 at any stage during metal pouring, the crucible and container will pivot in the reverse direction under the action of gravity to the upright position shown in Fig. 1.

Claims (14)

1. A crucible furnace comprising a crucible mounted within a holder, a frame about which the crucible and holder are together pivotable, and means for heating the crucible.

2. A furnace as claimed in claim 1 in which the holder comprises a substantially cylindrical metal container.

3. A furnace as claimed in claim 2 in which the metal container is lined with a ceramic fibre material.

4. A furnace as claimed in claim 2 or 3 in which the crucible is supported in the holder on a ceramic ring at the base of the holder.

5. A furnace as claimed in any of claims 2 to 4 in which the crucible is held in place by a ring disposed at an upper end of the container.

6. A furnace as claimed in claim 5 in which the ring is fixed relative to the container by means of a flexible circumferentially extending member threaded through a passageway of compiementary cross-section formed between the metal container and the ring.

7. A furnace as claimed in any preceding claim in which the crucible has a spout which extends radially beyond the holder.

8. A furnace as claimed in any preceding claim in which handle means are provided for tilting the crucible and holder relative to the frame when molten metal is to be poured from the crucible.

9. A furnace as claimed in claim 8 in which the handle means comprises respective handles on opposite sides of the holder.

10. A furnace as claimed in any preceding claim in which the holder is provided with pivot rods, adapted to engage bearing elements on the frame, to facilitate said pivotal movement of the crucible and holder relative to the frame.

11. A furnace as claimed in claim 10 in which the pivot rods are so disposed relative to the crucible and holder that the crucible and holder are urged by the action of gravity to return to an initial upright position after pivotal movement to pour the contents of the crucible.

12. A furnace as claimed in claim 10 or 11 in which the bearing elements are U-shaped brackets, the rods resting in said brackets such that the crucible and holder may, when required, be lifted free of the frame.

13. A furnace as claimed in any of claims 10 to 12 in which the frame comprises a base portion, adapted to support an underneath portion of the crucible holder, and two upwardly extending parallel arms on which said bearing elements are provided.

14. A furnace as claimed in any preceding claim in which the means for heating the crucible comprises a gas burner.

1 5. A furnace as claimed in claim 14 in which the crucible hölder has an aperture in the side thereof through which a gas flame provided by the gas burner may be diverted on to the crucible.

1 6. A furnace as claimed in claim 1 5 in which the gas burner is mounted on the frame, a nozzle of the burner being directed towards said aperture but spaced therefrom so as not to interfere with subsequent tilting of the crucible holder and crucible.

1 7. A furnace as claimed in any of claims 14 to 16 in which means are provided whereby a gas supply to the gas burner is automatically shut off on tilting or lifting of the holder and crucible.

1 8. A crucible furnace substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.