Glass manufacturing – Product cooling means
Patent
1996-01-30
1997-04-15
Czaja, Donald E.
Glass manufacturing
Product cooling means
65351, 65115, 239DIG7, C03B 2700
Patent
active
056204922
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to thermal treatment of glass.
As is well-known, a sheet of glass may be toughened by heating it until it reaches its transition temperature and then cooling it rapidly. The most commonly used method of cooling is air quenching, in which a large quantity of turbulent cooling air is blown onto each surface of the sheet. The quantity of air must be large enough to create a steep temperature gradient between the surfaces and the median plane of the sheet so that the glass cools inwardly from its surfaces to its median plane. This causes stresses to be set up within the sheet, as it cools, such stresses having a beneficial effect on the toughness of the glass.
Conventional glass toughening apparatus comprises quenching apparatus in which the air required to quench the glass is provided by a large fan which generates a stream of air of high volume but low pressure. The air stream is typically carried by ducts to plenum chambers mounted adjacent both surfaces of a sheet of glass to be toughened. The plenum chambers have jets from which the air issues and impinges on the sheet of glass. The fan is typically driven by an electric motor.
A major disadvantage with such known quenching apparatus is that the power consumption of the fan is typically very large. For example, in a typical apparatus for toughening architectural glass, the power required to drive the fan may be as high as 700 kW. Such high power consumption not only makes the plant expensive in use, but also makes installation expensive, special provision often being necessary to supply the required electrical power. Furthermore, the required fan and its associated ducting are often very large.
Quenching apparatus is also known, from GB-A-2 185 476, which provides quenching air from a body of compressed air contained within an air receiver. A compressor supplies air to the receiver, the receiver being connected to a plenum having jets as described above through a closable valve. A sheet of glass to be quenched is placed adjacent the jets, and the valve is opened. This results in a rush of air into the plenum and then out of the jets to quench the glass. A disadvantage with this system is that the compressor must supply the entire of volume of air required to quench the glass, and is consequently large, expensive, and power-hungry.
It is the aim of the present invention to provide apparatus for quenching glass which overcomes or at least ameleorates the disadvantages of known apparatus.
According to a first aspect of the invention there is provided apparatus for quenching a sheet of glass undergoing heat treatment comprising a source of compressed air, a plurality of air flow amplifiers adapted to receive from the source of compressed air a flow of compressed air and to amplify that flow to provide a flow of cooling air for quenching the sheet of glass.
The large flow of air required to quench the glass can be generated by such apparatus from only a comparatively small flow of compressed air. The compressed air source can, therefore, be of smaller size then would be the case if it had to supply all of the quenching flow.
The air amplifiers are preferably arranged in an array to provide multiple air streams distributed over a surface of the sheet of glass to be quenched. More preferably, the apparatus comprises two of such arrays each arranged to direct air onto a respective surface of the sheet of glass.
Each air flow amplifier may comprise an air ejector. Such devices have been found to provide a particularly advantageous amplification of air flow. The air amplifiers may be individually adjustable such that the volume of cooling air produced thereby may be controlled. By this arrangement, the volume of air applied to quench the sheet of glass may be varied from one region of the sheet to another, so allowing the degree of toughening (and therefore the fracture properties) of the glass to be varied across the sheet.
Typically, the apparatus further comprises air distribution means for conducting air from the source of pressure
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patent: 3607173 (1971-09-01), McMaster et al.
patent: 3743186 (1973-07-01), Mocarski
patent: 3890063 (1975-06-01), Spafford
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patent: 4336442 (1982-06-01), Starr
patent: 4867380 (1989-09-01), Sibbertsen
patent: 5334234 (1994-08-01), Anttonen et al.
patent: 5407135 (1995-04-01), Jeffs
Czaja Donald E.
Ruller Jacqueline A.
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