Glass manufacturing – Apparatus made of special material – Metallic
Reexamination Certificate
1999-08-02
2001-08-21
Zimmerman, John J. (Department: 1775)
Glass manufacturing
Apparatus made of special material
Metallic
C065S374100, C428S605000
Reexamination Certificate
active
06276173
ABSTRACT:
BACKGROUND
The invention relates to a contact member for covering structures that come into contact with glass objects during their moulding process: in general, during the transport of the glass throughout the entire process, and more in particular also during the phase involving the actual moulding and tempering of the moulded glass.
The contact member or covering according to the invention can for example be used to cover the support rings (pressure and tempering rings) used for shaping and/or tempering car glass sheets, i.e. windows for vehicles. In addition, the covering can also be used for covering the means by which the glass (or glass object) is lifted to move it, for example, between the different phases of the forming process. The actual moulding means, such as for example the pressure moulds, can also be covered with the covering. These applications will be explained below, with emphasis on the numerous advantages offered by the use of a covering according to the invention in the different situations.
In essence there are three basic process phases or steps that can be distinguished in the glass forming process as a whole: the actual shaping of the glass, in particular of glass plates, the transport, and the tempering of the glass after it has been shaped.
Different processes are known. The glass is heated in an oven to the shaping temperature. The shaping itself then occurs, for example, by pressing the glass using a form or mould and a ring, or using two moulds that are mounted either horizontally or vertically. Next, the glass—often supported by a ring—can be transferred to the tempering zone, where the glass, whether supported by the same ring or not, is cooled by air.
Another process consists in producing the forming or shaping of the glass through the mere action of gravity on the hot glass, which again is supported by a ring. This method is referred to as “gravitational bending” or “gravitational sag” method.
In what follows, the pressure and tempering rings referred to above will be designated hereafter in general as support rings. The term “support ring” should therefore be broadly interpreted in the present description: it relates to any ring which comes into contact with the glass, even if only for a brief time and no matter what the position of the ring may be in relation to the glass.
The support rings are often provided with a covering to avoid the adverse effects of direct contact between the glass and the steel ring. Such coverings are subject to a great diversity of requirements. For example, the covering must be sufficiently thermally insulating, and during the hot moulding process the covering should leave as few imprints or marks on the glass as possible, and preferably none at all. Moreover, the (perforated) covering should have a large air permeability in order not to shield the glass too much during tempering.
The support ring is conventionally covered, for example, with one or more layers of metal mesh, as described in the American U.S. Pat. No. 3,741,743. Although the ring is often serrated/toothed or perforated in order not to shield the glass too much from the air during tempering, the air permeability of the covered ring is often still insufficient because the perforations or the serrated gaps are closed by the covering. In addition, the deformability and thermal resistance of the aforementioned meshes also turn out to be insufficient in practice. Thus the covering can be fitted only with great difficulty to certain complex mould forms and only a brief glass/ring contact can be permitted. However the shapes that manufacturers want to impart to glass are becoming increasingly complex, so that—as a consequence—the required contact time between glass and ring during pressing is increasing.
In the European patent EP 0312439 a metallic covering is proposed which is constructed of oriented metal fibres and has an essentially mesh-shaped structure. Thus, for example, a woven or knitted metal fibre cloth is used which is fixed on the (perforated or serrated) support ring, either directly on the support ring or with a metal mesh interbetween.
SUMMARY OF THE INVENTION
Some disadvantages are associated with the use of such a covering for a broad range of moulding requirements. The stitches, the crossings of the yarns and the like, which are intrinsically present in the fabric, can press into the glass surface during the hot moulding process, which results in imprints and defects. As a result of the very open structure of the fabric, it can also happen that the underlying metal mesh or the ring itself can come into contact with the glass which is being shaped through the mesh holes of the fabric. Again this can result in marks on the glass surface.
Furthermore, the metallic covering—and also the mesh, when present—cover the perforations or serrated teeth of the ring, so that they partially lose their function, which is to promote the flow of air during the tempering process. The use of a coarser mesh has a positive effect on the air permeability, but in turn results in an even more frequent contact between mesh and glass. In the covering of the support ring with the fabric, it is stretched over the ring. Due to unevenness in the tension, the porosity (and hence the permeability to air) of the covering is modified in a fairly uncontrollable manner, which could give rise to irregular tempering properties. Indeed, two identical coverings can never be stretched over the ring entirely in the same manner.
The pressure moulds for the shaping of the glass are also provided with a covering. The American U.S. Pat. No. 4,678,495 describes the use of a needle felt for covering the press moulds. The layered structure proposed contains fibres made of at least two different materials, namely steel and composite fibers, as well as aramid or carbon fibers.
The use of a needle felt for covering moulds involves a few significant drawbacks. For example, a non compressed needle felt according to the state of the art is so soft that after a number of pressing operations it never recovers its original volume. The pressing thus changes in an irreversible manner the thickness of the covering so that the characteristics of each moulded glass object are different and deviate from the preset design characteristics. Moreover, the fibers in a non precompressed needle felt are held together only by mutual entanglement, which makes a needle felt much less wear resistant, for example, than a precompressed or sintered web.
The glass transportation means can also be provided with a covering in order to avoid the adverse effects of direct contact with the glass (or glass object). By creating an underpressure or vacuum, the glass is sucked up against the underside of the transportation means in order then to move it, for example, to a subsequent phase of the shaping or forming process. A perforated ceramic or cast steel block which is extremely flat along the side where it is in contact with the glass is often used as a transportation means here. Conventionally, this block is covered on this side with fiberglass paper, a fiberglass fabric or a fabric made of stainless metal fiber yarn. Stone particles that have come loose from the block can then, for example, get stuck between the fabric and the underside of the block. These trapped stone particles result in an embossed surface or imprints during the hot moulding of the glass. This problem is totally avoided through the use of the contact member according to the invention that, because of its substantial rigidity, fits closely to the surface of the mould.
It is an object of the invention to avoid these drawbacks by providing a contact member for covering structures that come into contact with glass objects in the course of their moulding process. The contact member consists of a relatively compact eg. a sintered web composed of randomly oriented fibers which by preference are made of stainless steel. In particular the invention relates to a covering for moulding members for glass objects comprising a relatively compact non woven fiber
Van Steenlandt Wim
Vanhuysse Boudewijn
Foley & Lardner
N.V. Bekaert S.A.
Zimmerman John J.
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