HK1015345A - Oven for glass article - Google Patents

Description

Furnace for glass products

The present invention relates to a heat treatment furnace for glass products, and more particularly to a tunnel type furnace for continuous heat treatment of a cathode ray tube while evacuating the gas contained therein, which is generally called an "exhaust furnace".

An example of an exhaust gas furnace for the above purpose is described in US-A-4752268.

It is a critical operation to heat and cool the formed glass envelope forming the tube to minimize the stresses therein and to evacuate it so that the tube wall is subjected to significant external pressure. The demand for larger and flatter cathode ray tubes, particularly for domestic high definition "flat screen" television receivers, has increased the above-mentioned processing problems and has increased the need for heat treatment furnaces that can be economically produced and that minimize the consumption of such expensive components.

It is an object of the present invention to provide an exhaust gas furnace for a cathode ray tube which is extremely efficient and reliable in operation for economical and stable production.

According to an aspect of the present invention, there is provided an exhaust furnace for heat treating and simultaneously evacuating a cathode ray tube as defined in appended claim 1.

According to another aspect of the invention comprises a cathode ray tube as defined by claim 10.

An embodiment of the invention is described in more detail below with reference to the accompanying drawings, in which:

FIG. 1 is a side cross-sectional view of a heated zone of a CRT exhaust furnace;

FIG. 2 is a partial longitudinal cross-sectional view taken along line 2-2 of FIG. 1; and

fig. 3 is a schematic plan view of the furnace and its conveyor.

The exhaust gas furnace includes a tunnel structure 10 having an outer structural wall 12 lined with an insulating material 14 to form a channel 16 having a rectangular cross-section on one side.

The conveyor includes a track 18 having upper and lower rails 20, 22 spaced vertically apart and immediately below one side of the structure 10, and the track 18 extends in a continuous loop from a tunnel exit 24 to a tunnel entrance 26 (fig. 3). Outside the structure 10, along part of the rails 18, loading and unloading stations 28, 30 are provided.

Vacuum cars 32 run on rails 18, each car 32 being provided with an upwardly projecting support 34 which extends into the bottom of channel 16 through a longitudinal slot 36 in the bottom surface of structure 10. Each support 34 includes an exhaust tube and is operatively connected to a neck 38 of the glass envelope of a Cathode Ray Tube (CRT)40 so that the CRT can be conveyed along the tunnel 16 by movement of the vacuum cart with its large area panel 42 facing upwardly and generally maintained in a central portion of the lower half of the tunnel substantially spaced from the walls of the tunnel. Each tube is also supported and positioned by a respective bracket 44.

During transport through the exhaust oven, the vacuum trucks 32 automatically operate in a known manner to draw off gases within each CRT 40. The CRT to be processed is mounted on a cart 32 at a loading station 28 and unloaded at an unloading station 30 after processing.

The CRT40 is heat treated in three main steps within the furnace while being evacuated, for example, by successive zones A, B and C (fig. 3), although more or less than three zones may be provided and the order of treatment may be varied as desired. Typically, the first zone a is a heating zone, the temperature of the CRT is raised to anneal and relieve the stress in the glass envelope, and then controllably cooled down in the first cooling zone B, and terminated by the last cooling zone C for further cooling down.

Each CRT40 is carried within its respective cradle 44 for protection and safety support, but without any substantial restriction to the flow of air into and out of the enclosure itself.

The means for applying heat to the CRT at zone a will be described in detail below with particular reference to fig. 1. Fixed baffles 50 in the wall of structure 10, spaced apart therefrom, form an inner longitudinal enclosure surrounding and spaced apart from brackets 44 as brackets 44 and CRTs 40 are transported therethrough. The bottom 52 of the enclosure 50 defines a continuous central slot 54 of sufficient width to allow the support members 34 to pass therethrough, and the top surface 56 of the enclosure 50 defines a plurality of circular air inlet apertures 58 (only one shown) spaced longitudinally apart, each aperture being provided with a motor-driven fan impeller 60 for driving a flow of air downwardly into the enclosure.

A diffuser screen or other distribution device 61 is provided in the upper region of the baffle 50 between the top surface and the top of the support 44.

Each side arm 62, 64 of the enclosure 50 is spaced apart along its length to form outlet apertures 66, 68 in which are located shutters or other means for effectively adjusting its effective aperture size and/or its effective vertical or other orientation in the respective side wall.

The exit aperture 66 is located substantially at the same height as the side edge of the faceplate 42 of the CRT40, i.e. immediately adjacent the widest part of the tube envelope.

The space between the outside of enclosure 50 and the inside surface of the wall lining insulation 14 of structure 10 forms a circulation path for transporting heated air exiting after contact with CRT 40. A heating device, such as a radiant tube heater 17 of gas, is schematically shown in fig. 1, automatically controlled and regulated in a known manner to heat the circulating air to the desired temperature.

During operation, hot air is driven downwardly into the envelope 50 by the fan impeller 60 so that it impinges directly on the large upwardly facing face of the face plate 42 of the envelope and is distributed thereover as shown by the arrows in fig. 1 around its periphery for uniform heating thereof. The major part of this air flow is drawn out of the area at the sides of the panel and exits through the outlet openings 66, 68, and the minor part of this air flow is directed downwardly towards the neck, so that this particularly vulnerable part of the shell can be heated more gently. This further downward air flow is drawn through the slots 54 and circulated around the outside of the containment shell 50 by the fan impeller 60. Excess hot air is drawn through the exhaust duct 72 through the side walls of the tunnel 10.

The air flow around the cartridge can be selectively controlled and regulated to within close tolerances by monitoring the heating temperature, adjusting the speed of the fan wheel 60 to control its fan volume, and adjusting the dampers or other control devices of the outlet apertures 66, 68. The result of the adjustment is adapted to the specific size and shape of the CRT to be processed.

It will be appreciated that there are various means by which the air stream can be heated and effectively recirculated, minimising heat losses and providing maximum thermal efficiency, for example surplus hot air flowing at a lower temperature from zone a can be applied to zone B to determine whether to mix with cold air to effect the first stage cooling, depending on the temperature gradient required.

It should be appreciated that the above-described air circulation and application in zone a may also be used in one or more subsequent zones B and/or C to provide the desired temperature gradient through the exhaust furnace.

The use of the invention ensures a uniform temperature distribution over the glass envelope of the CRT throughout the entire heat treatment cycle, minimizing thermal gradients in the glass and thus reducing the risk of breakage thereof, even when the glass is subjected to additional stresses due to the degassing treatment. The apparatus of the present invention is suitable for handling all types of CRTs, but it is believed to be particularly suitable for large volume handling of large size "flat screen" CRTs required for television and computer monitors.

Claims (10)

1. An exhaust oven for heat treating and simultaneously evacuating a cathode ray tube (40), the exhaust oven comprising: a tunnel structure (10) forming a channel; temperature control means for controlled heating and/or cooling of the atmosphere contained in one or more longitudinal sections of the channel; a delivery device (32) for delivering the tube along the passageway and including an exhaust tube operatively connected to the neck (38) for drawing gas from the tube during delivery; and a baffle means (50) for circulating said atmosphere around the exterior of the tubes in at least one region of the passage, characterised in that said baffle means includes at least one inlet formation (58) which directs the atmosphere in operation to impinge on the large area of the shroud (42) of each tube, and one or more outlet formations (66, 68, 54) in adjacent spaced relationship relative to the sides of said panel and/or said neck for discharging said atmosphere from the baffle means.

2. The furnace of claim 1, wherein the conveyor (32) is arranged to carry the tubes (40) with their uppermost shroud (42), and the at least one inlet formation (58) is located at the top of the baffle (50) so that the incoming gas stream is directed downwardly over the shrouds of the tubes in use.

3. The furnace of claim 2, wherein at least some of the outlet structures (66, 68) open laterally to each side of the baffle means (50).

4. The furnace of any preceding claim, wherein some or all of the outlet structures (66, 68) are adjustable in effective cross-sectional area for selectively adjusting circulation around the tube (40) in use.

5. The furnace of any preceding claim, wherein some or all of the outlet structures (66, 68) are adjustable in their effective positions for selectively adjusting circulation around the tube (40) in use.

6. The furnace of any preceding claim, wherein the baffle means (50) is in spaced relationship to the outer walls (12, 14) of the tunnel structure to provide a circulation passage (16), the passage (16) being effective to distribute the flow of atmospheric gas to and from the inlet and outlet structures (58; 66, 68), respectively, without contact with the tubes (40).

7. The furnace of claim 6, wherein the baffles (50) and outlet structure (54) are arranged to direct a portion of the gas flow acting on the tubes (40) to and around the neck (38) as it exits the baffles (50).

8. The oven according to claim 6 or 7, characterized in that it comprises heating means (70) in said circulation channel (16) for heating the atmosphere before it enters the baffle means (50).

9. The furnace according to any of the foregoing claims, characterised in that the conveying means is a train of carts (32) driven through a continuous loop path provided with loading and unloading stations (28, 30) outside the tunnel structure for loading and unloading tubes.

10. A cathode ray tube, characterized in that it is processed by a furnace according to any one of the preceding claims.