Glass manufacturing – Processes – With program – time – or cyclic control
Reexamination Certificate
1999-01-11
2001-06-05
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
With program, time, or cyclic control
C065S029190, C065S104000, C065S107000, C065S160000, C065S162000, C065S273000
Reexamination Certificate
active
06240746
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for bending glass sheets.
2. Discussion of the Background
Glass sheets are heated to a bending temperature (normally around 600° C.-700° C.) to be formed into a bent shape from a flat shape. The forming can be carried out by several measures. As one example of the measures, there is a method wherein glass sheets carried on ring molds are conveyed into a heating furnace to sag under their own weight so as to be bent, following the profile of the molds (hereinbelow, referred to as the gravity using bending method).
EP-A-621244 contains a reference to a forming apparatus with the gravity using bent method applied thereto. The forming apparatus for glass sheets controls a conveyance commencing position of molds in a heating furnace into an annealing zone when glass sheets are conveyed into the annealing zone provided subsequently to the heating furnace. Such control can adjust the degree of deformation of the glass sheets between the heating furnace and the annealing zone and provide the glass sheets with a certain bent shape.
On the other hand, the bent shapes of glass sheets for automobile windows are required to be suited to small-quantity of multi-product production in order to cope with the tendency that automobiles are manufactured in small-quantity of multi-product production. Since a heated and softened glass sheet follows the profile of its related mold, the bent shape of each glass sheet is changed by changing its related mold. The glass sheets are deformed even when the glass sheets are conveyed from the heating furnace into the annealing zone. This means that the shape of each glass sheet can be also changed by modifying the conveyance commencing position that each of the glass sheets starts moving toward the annealing zone in the heating furnace and thereby modifying the period wherein each of the glass sheet is moving.
However, in order to use the apparatus disclosed in the publication to cope with the demand for small-quantity of multi-product production, the conveyance commencing position of the molds from the heating furnace into the annealing zone is required to be modified, depending on a desired shape of the glass sheets. Modifying the conveyance commencing position as required involves complication in the driving device for the modification. In addition, since the glass sheets are successively conveyed into the heating furnace, a preceding glass sheet interferes with the moving of the succeeding glass sheet if the conveyance commencing position is modified for each of the glass sheets. In case of the apparatus and the method disclosed in the publication, it has been difficult to cope with frequent modification of the shape of the glass sheets, which are required for the small-quantity of multi-product production of the glass sheets.
The heating temperature in the heating furnace for bending the glass sheets has been experientially set based on a targeted degree of curvature of the glass sheets. Before bending glass sheets in mass-production, sample glass sheets are formed in a bent shape in the heating furnace, and the bent shape of the formed sample glass sheets is compared to a targeted degree of curvature. When the bent shape is out of an acceptable range, the heating temperature is modified by feedback.
Such method for bending glass sheets requires to check on an actual apparatus whether the bent shape of glass sheets is in the acceptable range since the heating temperature in the heating zone has been experientially set. The conventional method for bending glass sheets has a disadvantage in that considerable labor is involved until glass sheets are actually mass-produced. In particular, unlimited considerable labor is involved to cope with the small-quantity of multi-product production since checking on an actual apparatus is required for each of targeted shapes. It takes a lot of time to change the shape of the glass sheets to another one (job change).
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the disadvantage of the conventional technique, and to provide a novel method and apparatus for bending glass sheets which have not been known.
The present invention has been provided to solve the problem, and provides a method for bending glass sheets wherein a plurality of molds are provided, the respective molds have glass sheets carried thereon and the molds are successively conveyed into a heating furnace to bend the glass sheets; and wherein the heating furnace includes a plurality of divided heating zones which heat the glass sheets to a forming temperature and an annealing zone which is provided downstream of the heating zones to anneal the glass sheets, and the molds are successively conveyed into the heating furnace from upstream of the heating zones to downstream of the annealing zone through the divided heating zones and the annealing zone to bend the glass sheets, following the molds, so as to successively bend the glass sheets; characterized in that the molds are intermittently conveyed between the respective heating zones such that the molds stay for a certain period T
0
in the respective heating zones except the heating zone thereamong just before the annealing zone; and that a period T
1
wherein the molds stay in the heating zone just before the annealing zone is variable to not longer than T
0
, and the molds are intermittently conveyed between the heating zone and the annealing zone such that the molds stay for the period T
1
dependent on a targeted curvature of the glass sheets.
The present invention also provides a method for bending glass sheets wherein a plurality of molds are provided, the respective molds have glass sheets carried thereon and the molds are successively conveyed into a heating furnace to bend the glass sheets; and wherein the heating furnace includes a plurality of divided heating zones which heat the glass sheets to a forming temperature and an annealing zone which is provided downstream of the heating zones to anneal the glass sheets, and the molds are successively conveyed into the heating furnace from upstream of the heating zones to downstream of the annealing zone through the divided heating zones and the annealing zone to bend the glass sheets, following the molds; characterized in that before conveying the glass sheets into the heating furnace to actually bend the glass sheets, a simulated shape of a glass sheet is found by calculating a degree of curvature of a glass sheet in its entirety in accordance with a method for calculating a degree of curvature of the glass sheet including a first step for setting dimensions of the glass sheet and preset temperatures of heaters provided in the respective heating zones, a second step for dividing the glass sheet into a plurality of elements and calculating a glass temperature in each of the elements in the respective heating zones based on a heating quantity received by each of the elements in the respective heating zones and a staying period of the glass sheet elements in the respective heating zones, a third step for calculating a degree of sag of each of the elements of the glass sheet in the respective heating zones based on the calculated glass temperature in each of the elements in the respective heating zones in consideration of a relationship between sagging speeds and glass temperatures of the glass sheet preliminarily found and a fourth step for calculating a degree of curvature of the entire glass sheet conveyed through the entire heating zones based on the calculated degree of sag of each of the elements of the glass sheet in the respective heating zones; and that the simulated shape of the glass sheet is compared to a preset desired design shape of the glass sheet and set temperatures of the heaters are determined by modifying the preset temperatures of the respective heaters so as to bring the simulated shape of the glass sheet near to the desired design shape, and that the molds with the respective glass sheets carr
Konishi Masaaki
Maeda Kenji
Saito Katsuki
Ueno Yasuichi
Yajima Toshimi
Asahi Glass Company Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Vincent Sean
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