GB1587020A

GB1587020A - Furnaces

Info

Publication number: GB1587020A
Application number: GB2082078A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-05-19
Filing date: 1978-05-19
Publication date: 1981-03-25

Description

(54) FURNACES (71) I, ALBERT GEORGE DOCX, a British subject of 70 Ellesmere Road, Altrincham, Cheshire, do hereby declare the invention, for which I pray that a Patent may be granted to me, and the method by which is is to be performed to be particularly described in and by the following statement: The present invention relates to furnaces and in particular to furnaces having a muffle housed in an open topped cup-shaped enclosure which can be closed by a lid.

Furnaces of the type described above are known from the Applicant's German Offenlegungsschrift 27 18 596 which describes a furnace having a disc-shaped lid pivoted about a horizontal axis between furnace open and furnace closed positions. This known arrangement requires a lid catch for securing the lid in the closed position which catch must be verv accurately positioned relative to the lid if reliable operation is to be obtained. It is desirable to have a furnace which opens automatically. and with the known furnace this required the provision of a solencid-releasable catch. Such solenoid operated devices are difficult to adjust and relatively unreliale.

It is an object of the present invention to provide a furnace having a lid which can be opened automatically without it being necessary to provide a mechanical lid catch.

According to the present invention. there is provided a furnace comprising a muffle housed in a container. a lid pivotal between a position in which it closes an opening in the container and a position in which the lid is located away from the opening to permit access to the interior of the container. and a vacuum pump for evacuating gas from the interior of the chamber. characterised in that the lid is movable manually to the closed position. such movement actuating a switch which starts the vacuum pump and thereby generates a pressure difference across the lid which maintains the lid in its closed position, means being provided to enable the release of the vacuum within the container and to automatically move the lid to its open position when the vacuum is released.

Preferably the release means comprises a solenoid controlled valve. The valve is a normally open bleed valve such that when the valve is open and the pump operates a reduced pressure exists within the container to maintain the lid closed but air is drawn through the furnace to scavenge gassed off vapours from within the container.

Means are preferably provided to automatically shut the bleed valve when the furnace reaches a first predetermined temperature and to reopen the bleed valve and stop the pump when the furnace reaches a second predetermined temperature.

In the furnace described in Offenlegungsschrift 27 18 596, as the furnace lid pivots about a horizontal axis its mounting must be relatively heavy whilst the lid itself must be relatively light; i.e. of spun aluminum.

Furthermore, when the lid is open heat is radiated from its underside directly towards a user of the furnace, and the lid projects a considerable distance above the upper surface of the furnace. This exposes it to damage. To avoid these problems. the present invention further proposes that the furnace lid be mounted to pivot about a vertical pivot axis.

Preferably the muffle is housed in an open topped cup-shaped container and the lid is pivotal about a vertical axis between a position in which the lid is located over the container and a position in which the lid is located to one side of the container the lid being mounted on a pivot mounted in bearings supported bv the container the pivot being slidable parallel to its pivot axis between an upper position and a lower position. Means may be provided for pre venting the pivot assuming the lower position except when the lid is located over the container.

This arrangement is more robust than horizontally pivoted arrangements. Furthermore the lid moves perpendicular to its seating during the final closing movement.

An attractive low profile appearance is also achieved. Furthermore, the weight of the lid is less critical and therefore the lid may be cast.

The pivot may support a pin eccentrically mounted relative to the pivot axis which pin is located over a plate supported by the container when the lid is not located over the container. When the pin is located over the plate the pivot cannot assume its lower position. Rotation of the pivot causes a corresponding movement of the pin over the plate, and when the lid is located directly above the container the pin is located beyond the edge of the plate. The pivot can then assume its lower position and the lid can be lowered onto the container.

Preferably. the pivot is spring biased to the upper position and the lid is spring biased to swing away from the position in which it located over the container.

An embodiment of the invention will now be described. by way of example. with reference to the accompanying drawings, in which: Figure 1 is a front view of a furnace embodying the invention, with its lid in the closed position; Figure 2 is a front view of the furnace of Figure 1 with its lid in the open position; Figilre 3 is a schematic sectional view through the muffle container of the furnace of Figures 1 and 2; and Figure 4 is a schematic perspective view of the lid support mechanism shown in Figure 3.

Referring to Figures 1 and 2, the illustrated furnace comprises a casing fabricated from an upper sheet metal panel 1 in the shape of an inverted U and a front sheet metal panel 2. Control devices and indicators 3. 4 and 5 are mounted on the front panel 2 but will not be described in detail.

The casing is of course completed by rear and base panels (not shown).

A furnace container is mounted in the left hand half (as seen in Figures 1 and 2) of the casing. A lid 6 may be located in the position shown in Figure 1 in which it seals the container or in the position shown in Figure 2 away from the container. The lid is supported by a member 7 rigidly secured to a pivot 8 (Figure 2).

Referring now to Figures 3 and 4. details of the container and the lid mechanism are shown. The container comprises a cupshaped vessel 9 receiving a muffle 10 incorporating a heating element I I . The muffle 10 is located between upper and lower members 12 and 13, the lower member supporting a pin 14 for receiving a workpiece support (not shown). The container has a flanged lip 15 which bears on the upper panel 1, an elongated outlet 16 and short inlet 17, both outlet 16 and inlet 17 passing through the container base. The lid 6 comprises an outer casing 18 supporting an insulating member 19. A sealing ring 20 is supported on the lower face of the lid. An aluminum ring 21 is located over member 12. Members 10, 12, 13 and 19 are fabricated from a ceramic fibrous material in known manner.

The pivot 8 is mounted in bearings defined by a bracket 22 rigidly secured to the container. The pivot supports a pin 23 against which a compression spring 24 bears to bias the pivot and thus the lid 6 upwards.

The pivot 8 also supports a plate 25 in which a further pin 26 is supported and a disc 27 against which the actuating lever of a microswitch 28 (Figure 4) bears.

In addition to supporting the pivot 8. the bracket 22 is provided with a lower edge on which a plate 29 is mounted. The plate 29 is slidable in the direction perpendicular to the plane of Figure 3 and may be locked in position by a screw 30. In Figures 3 and 4, the mechanism is shown in the position in which the lid is closed on the container 9. In this position, the pin 26 extends below plate 29 closely adjacent the edge thereof.

If it is desired to open the lid by turning the pivot 8, the pivot 8 must be turned such that pin 26 which is mounted eccentrically relative to the pivot axis of pivot 8 moves anticlockwise (Figure 4). A stop (not shown) prevents the turning of the pivot in the opposite direction. Thus, before the lid can be opened, the pivot 8 must be raised until the lower end of the pin 26 is above the plate 29. Turning can then take place with the pin 26 moving across the upper surface of the plate 29. A spring 31 (Figure 4) connected between the pin 26 and a bracket 32 automatically opens the lid as soon as the pin 26 rises above the edge of the plate 29.

In operation, the user places workpieces in the muffle and swings the lid so that it is located above the container. The lid is then pressed down against the force of spring 24 until the sealing ring 20 bears against the lip 15. Downward movement of the lid 6 and pivot 8 actuates switch 28 which turns on a vacuum pump (not shown) connected to outlet 16 and energises the heating element 11. Air is bled into the container 9 through a solenoid controlled bleed valve (not shown) via inlet 17. The resulting pressure differential across the lid 6 is sufficient to maintain the lid closed.

The air bled in via inlet 17 passes diametrically across the container. scavenging gas sed off vapours in the process. When the temperature in the furnace reaches a first predetermined temperature the solenoid controlled bleed valve is shut to give a full vacuum. When a second predetermined temperature is reached, the bleed valve is reopened to release the vacuum and the pump is stopped. Thus air is bled into the container via inlet 17. The pressure differential across the lid 6 falls and the spring 24 raises the lid so that pin 26 rises above plate 29. The lid 6 then swings sideways automatically under the influence of the spring 31 connected to the pin 26 and fired workpieces can be removed and placed on an insulating pad (not shown) located on the upper casing panel 1 to the right hand side (Figures 1 and 2) of the furnace.

The switch 28 is so connected as to prevent energisation of the muffle until the lid is closed.

The screw 30 enables the position at which the lid can drop to close the container to be easily and accurately adjusted.

WHAT I CLAIM IS: 1. A furnace comprising a muffle housed in a container, a lid pivotal between a position in which it closes an opening in the container and a position in which the lid is located away from the opening to permit free access to the interior of the container, and a vacuum pump for evacuating gas from the interior of the chamber, characterised in that the lid is movable manually to the closed position, such movement actuating a switch which starts the vacuum pump and thereby generates a pressure difference across the lid which maintains the lid in its closed position, means being provided to enable the release of the vacuum with the container and to automatically move the lid to its open position when the vacuum is released.

2. A furnace according to Claim 1, wherein the vacuum release means comprises a solenoid controlled valve.

3. A furnace according to Claim 2.

wherein the valve is a normally open bleed valve such that when the valve is open and the pump operates a reduced pressure exists within the container to maintain the lid closed but air is drawn through the furnace to scavenge gassed off vapours from within the container.

4. A furnace according to Claim 3, comprising means to automatically shut the bleed valve when the furnace reaches a first predetermined temperature.

5. A furnace according to Claim 4, comprising means to automatically reopen the bleed valve and stop the pump when the furnace reaches a second predetermined temperature.

6. A furnace according to any preceding claim, wherein the muffle is housed in an open topped cup-shaped container and the lid is pivotal about a vertical axis between a position in which the lid is located over the container and a position in which the lid is located over the container and a postion in which the lid is located to one side of the container, the lid being mounted on a pivot mounted in bearings supported by the container, the pivot being slidable parallel to its pivot axis between an upper and a lower position.

7. A furnace according to Claim 6, comprising means for preventing the pivot assuming the lower position except when the lid is located over the container.

8. A furnace according to Claim 7, wherein the pivot supports a pin eccentrically mounted relative to the pivot axis and a plate is supported by the container, the plate being located such that it prevents downwards movment of the pin and thus movement of the pivot to its lower position unless the lid is located over the container.

9. A furnace according to Claim 8, wherein the orientation of the plate relative to the container is adjustable.

10. A furnace according to any one of claims 6 to 9, wherein the pivot is spring biased to the upper position.

11. A furnace according to any preceding claim, wherein the lid is spring biased to swing away from the position in which it closes the container.

12. A furnace substantially as hereinbefore described with reference to the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. sed off vapours in the process. When the temperature in the furnace reaches a first predetermined temperature the solenoid controlled bleed valve is shut to give a full vacuum. When a second predetermined temperature is reached, the bleed valve is reopened to release the vacuum and the pump is stopped. Thus air is bled into the container via inlet 17. The pressure differential across the lid 6 falls and the spring 24 raises the lid so that pin 26 rises above plate 29. The lid 6 then swings sideways automatically under the influence of the spring 31 connected to the pin 26 and fired workpieces can be removed and placed on an insulating pad (not shown) located on the upper casing panel 1 to the right hand side (Figures 1 and 2) of the furnace. The switch 28 is so connected as to prevent energisation of the muffle until the lid is closed. The screw 30 enables the position at which the lid can drop to close the container to be easily and accurately adjusted. WHAT I CLAIM IS:

1. A furnace comprising a muffle housed in a container, a lid pivotal between a position in which it closes an opening in the container and a position in which the lid is located away from the opening to permit free access to the interior of the container, and a vacuum pump for evacuating gas from the interior of the chamber, characterised in that the lid is movable manually to the closed position, such movement actuating a switch which starts the vacuum pump and thereby generates a pressure difference across the lid which maintains the lid in its closed position, means being provided to enable the release of the vacuum with the container and to automatically move the lid to its open position when the vacuum is released.

3. A furnace according to Claim 2.