Glass manufacturing – Processes – Reshaping or surface deformation of glass preform
Reexamination Certificate
1999-02-03
2001-02-27
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
Reshaping or surface deformation of glass preform
C065S114000, C065S253000, C065S273000, C065S287000
Reexamination Certificate
active
06192710
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bending method and a bending apparatus for glass sheets. In particular, the present invention relates to a bending method and a bending apparatus for glass sheets wherein glass sheets heated to a bending temperature by a heating furnace are conveyed and the glass sheets are bent in a shape along a conveyer path under their own weight.
2. Discussion of the Background
As an apparatus for bending glass sheets during conveyance by rolls, there have been known roll-formed conveyor apparatuses (for instance, U.S. Pat. No. 4,311,509). Such roll-formed conveyor apparatuses include a plurality of conveyer rolls which are bent so as to have arbitrary curvatures. The conveyor rolls are provided at equal distances. The conveyor rolls provide a conveyor path having arbitrary curvatures in the apparatuses. The glass sheets which have been heated to a softening temperature in a heating furnace are conveyed on the conveyor path from an outlet of the heating furnace toward a certain direction. The glass sheets which are conveyed on the conveyor path are bent in a shape along the conveyor path under their own weight during conveyance.
However, the conventional conveyor rolls cause striped defects on a surface of the glass sheets after forming. The striped defects are optical distortion caused during bending the glass sheets, and the distortion degrades the quality of the glass sheets.
The causes of the optical distortion will be explained, referred to FIG.
7
.
FIG. 7
is a transitional view showing how a glass sheet
1
which has been delivered from an outlet of a heating furnace is conveyed by a plurality of conveyer rolls
2
A,
2
B,
2
C,
2
D forming a conveyor path. The glass sheet
1
is bent in a certain shape, being conveyed by the conveyor rolls
2
A,
2
B,
2
C,
2
D.
As shown in FIG.
7
(B), when the glass sheet
1
has a leading portion
1
A contacted with the conveyor roll
2
A, the leading portion
1
A has heat removed to the conveyor roll
2
A. Such removal of heat causes a conveyor roll side of the glass sheet
1
to be thermally shrunk, making the leading portion
1
A sag downwardly (C). As shown in (D), the sagged leading portion
1
A runs onto the conveyor roll
2
B when passing on the conveyor roll
2
B. This creates a state that the entire glass sheet
1
is slightly lifted. As shown in (E), when the leading portion
1
(A) has passed the conveyor roll
2
B, the entire glass sheet
1
returns to a position before being lifted, and contacts with the conveyor rolls
2
A,
2
B. (F) and (G) are viewes showing a repeat of the operations in (D) and (E). As explained, the glass sheet
1
is conveyed on the conveyor rolls
1
A,
2
B,
2
C,
2
D . . . , being slightly vibrated in a vertical direction because of the presence of such sagging motion of the leading portion
1
A.
In (C)-(G), attention is directed to arbitrary points a and b on the glass sheet
1
(actually, lines perpendicular to a conveyance direction). The point a rises (D) after contacting with the conveyor roll
2
A, and contacts with the conveyor roll
2
B after lowering of the glass sheet
1
(E). Next, the point a rises (F) and contacts with the conveyor roll
2
C when having lowered (G). In other words, the glass sheet
1
sequentially contacts with the conveyor rolls
2
A,
2
B,
2
C,
2
D . . . , during conveyance.
On the other hand, the point b is located above the conveyor roll
2
A as shown in (D) when the glass sheet
1
is lifted. After that, the point b is located between the conveyor roll
2
A and the conveyor roll
2
B in (E) wherein the glass sheet
1
has lowered. This motion prevents contact with the conveyor roll
2
A. Repeats of such motion prevent contact with the conveyor rolls
2
B,
2
C,
2
D as well. In other words, the point b does not contact with the conveyor roll
1
A,
2
B,
2
C,
2
D . . . at all during conveyance of the glass sheet
1
.
When the conventional conveyor rolls are used, portions (e.g. the point a) which are cooled by contact with the conveyor rolls and portions (e.g. the point b) which are not cooled by the conveyor rolls not at all coexist on formed glass sheets. This creates differences among these portions in terms of thermal shrinkage, and the differences are exhibited as striped defects in the formed glass sheets. This is the causes of the optical distortion.
SUMMARY OF THE INVENTION
The present invention has been conceived, considering these problems, and it is an object of the present invention to provide a bending method and an bending apparatus for glass sheets capable of forming glass sheets having good quality and free from any optical distortion.
In order to attain the object, the present invention provides a method for bending glass sheets wherein glass sheets are conveyed in a heating furnace to be heated to a certain bending temperature, the heated glass sheets are conveyed on a conveyor path including a plurality of conveyor rolls provided from an outlet of the heating furnace toward a downstream direction and having certain curvatures given thereto by the rolls, and the glass sheets are bent in a shape along the conveyor path under their own weight, characterized in that the conveyor rolls are provided to set at least some of distances between adjoining conveyor rolls so as to be different from the other distances, and that the glass sheets are conveyed on the conveyor path.
The present invention also provides an apparatus for bending glass sheets which comprises a heating furnace to heat glass sheets to a bending temperature, a conveyor for conveying the glass sheets in the heating furnace, and a conveyor path including a plurality of conveyor rolls provided from an outlet of the heating furnace toward a downstream direction and having certain curvatures given by the rolls, wherein the heated glass sheets are conveyed on the conveyor path to be bent in a desired shape; characterized in that the conveyor rolls are provided to set at least some of distances between adjoining conveyor rolls so as to be different from the other distances.
As explained, the present invention is based on finding that the rout cause of the optical distortion stated earlier is the equality in the distances between the conveyor rolls, and the present invention sets some of the distances between the conveyor roll so as to be unequal in order to improve the optical distortion. When the distances between the conveyor rolls are equal, portions which are cooled by contact with the conveyor rolls and portions which are not cooled by the conveyor rolls at all coexist in formed glass sheets. This phenomenon causes optical distortion in the glass sheets. On the other hand, when at least some of the distances between the conveyor rolls are set to be unequal in accordance with the present invention, glass sheets can contact with the conveyor rolls at any portions thereof. This prevents striped defects from being caused in the glass sheets, improving the quality of the glass sheets.
REFERENCES:
patent: 4226608 (1980-10-01), McKelvey
patent: 4311509 (1982-01-01), Reader et al.
patent: 4381933 (1983-05-01), Schultz et al.
patent: 4957528 (1990-09-01), Letemps et al.
patent: 4966618 (1990-10-01), Letemps et al.
patent: 5094679 (1992-03-01), Letemps et al.
patent: 8-188431 (1996-07-01), None
Ohtsubo Nozomi
Takeda Takashi
Asahi Glass Company Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Vincent Sean
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