Glass manufacturing – Processes – Forming product or preform from molten glass
Reexamination Certificate
2000-08-11
2002-08-06
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
Forming product or preform from molten glass
C065S305000, C065S323000, C425S218000, C425S422000, C425S442000
Reexamination Certificate
active
06427490
ABSTRACT:
The invention relates to a method for producing funnels of picture tubes with adjustment bearing faces (pads) molded on by the pressing technique, having the following steps:
delivering a molten gob of glass to a mold corresponding to the outer contour of the blank,
pressing the gob of glass, by means of a die that predetermines the inner contour of the blank and by means of a ring resiliently secured to the die and resting on the mold, to form the funnel with a flat encompassing upper edge and molded-on pads.
The invention also relates to an apparatus for producing funnels of picture tubes with molded-on adjustment bearing faces (pads) by pressing, having
a mold, which has a mold surface corresponding to the outer contour of the blank, including recesses for the pads, and into which a molten gob of glass can be delivered,
a pressing die, which predetermines the inner contour of the blank and on which a ring, resting flatly on the mold, is resiliently retained for molding the flat upper edge of the funnel.
Picture tubes, especially television tubes or tubes for computer monitors, are composed in terms of glass of three separately made glass parts, namely the actual screen, then the back part of the picture tube, which is called a funnel, and finally the neck of the picture tube for receiving the beam system.
In the manufacture of the picture tubes, the funnel, on whose collar an encompassing plane connecting face—also known as the soldering edge—is formed, is joined to the screen, on which a corresponding soldering edge is formed, in vacuum-tight fashion with the aid of glass solder. The pastelike glass solder is applied to the soldering edge of the funnel. The funnel is placed in an obliquely disposed metal frame, with the soldering edge facing upward. The screen is placed with its soldering edge facing downward onto the glass solder. In the ensuing tempering process, the solder melts, and the funnel and screen join to make the tube.
For the function of the picture tube, an exact alignment of the funnel with the screen is necessary; a misalignment causes an offset of the beam system, located in the neck of the funnel, relative to the screen surface. To assure the alignment during the melting process, typically three raised bearing faces, so-called pads, are molded onto the funnel in the region of the collar. The screen is likewise provided with three bearing faces. The bearing faces on the screen and on the funnel are assigned bearing points in the metal frame. The inclined position assures that the screen and funnel will rest on the bearing faces, and thus that a defined alignment of the funnel and screen will be achieved.
After that, the picture tube neck is molded by known methods onto the other end of the funnel.
This technology of picture tube manufacture is prior art and is described in relevant publications, so that no further description of this is needed here.
The invention pertains to the production of the funnel. For manufacturing these funnels, the pressing technique is employed in a known manner, the world over. Molten gobs of glass are pressed into funnels, using the typical shaping tools of a mold, a ring, and pressing dies. Typically, round table presses are employed, in which from 11 to 15 structurally identical molds are mounted on the pressing table. The molds are transported to the next processing step with each increment of the press.
The outside of the funnel is shaped with the mold, and the inside is shaped with the pressing die.
For molding the terminal edge of the funnel, the third tool, the ring, is needed. The ring is placed on the mold before the pressing operation, and during the pressing is pressed onto the mold by spring force. Once the glass gob has been loaded into the mold, it is pressed out in the pressing station with the aid of the downward-moving die, under a strong pressing force. The die and the ring are manufactured to fit very precisely. Given a sufficient pressing force, the void of the three tools is completely filled with glass, and typically a mold seam forms between the ring and the mold. This mold seam must be located on the greatest circumference of the funnel, to allow both the ring and the mold to be unmolded. When the die is moved upward, the ring also takes on the function of stripping off the glass part.
At subsequent cooling stations, the pressed-out funnel is cooled enough that the product can be removed at the ensuing removal station without being deformed.
Before being removed, the ring, because it covers the funnel at the top, must be removed from the mold.
It is known to that end to mount the ring firmly with the pressing die in the pressing station via a spring plate. The ring is then pressed onto the mold in the downward motion of the die and in the upward motion, after the spring travel has been overcome, the ring is removed. In this technique, only one ring remaining in the pressing station is in use. In the European method, a ring that is flat toward the mold is placed on the mold. The mold seam is therefore created at the upper edge of the funnel. Since during the final machining following the hot shaping, the pressed upper edge of the funnel is ground and chamfered to make a plane surface known as the soldering edge, the mold seam is also ground in the process and is then no longer, present on the finished funnel. The potential risk that operational problems such as cracking or even implosion will originate in this mold edge is therefore absent in the picture tubes made by the European method.
As already noted, the so-called pads must be present on the funnel in its outer collar region. These raised pads are typically jointly molded on in the process of pressing the funnel. To that end, the mold has corresponding recesses in the region of the pads.
Because of the unmolding conditions described, it is absolutely necessary that the raised pads, in the funnels made by the European method, be drawn as far as the soldering edge, because otherwise undercuts would be made in the mold that would prevent unmolding.
A disadvantage of the pads drawn as far as the soldering edge is that the soldering edge in this portion is widened by the extent to which the pads are raised; that is, the soldering edge is no longer the same width all the way around. When the funnel is joined to the screen, surface effects can make the glass solder in these regions extend nonhomogeneously compared to the remaining soldering edge, thus creating a flaw, and increased stresses can arise.
FIG. 1
, in two fragmentary views, schematically shows this known shaping of the collar region of the funnel in the pressing process, specifically in part A in a sectional view in the collar free of pads and in part B with a sectional view in the pad region.
The glass funnel
4
is created between a mold
1
, the pressing die
2
that has entered it, and the ring
3
resting on the mold
1
. The shaping tools described are shown only schematically, for the sake of simplicity.
The ring
3
typically has an encompassing groove
3
a
, which serves to provide stability to the molded funnel while it is still in the plastic state; this groove is later ground away in the course of the plane grinding of the upper edge
4
a
of the funnel to the soldering edge, including the mold edge
4
b
that is necessarily created in this technology between the ring
3
and the mold
1
.
As can be seen from the comparison between parts A and B, the upper edge
4
a
in the region of the raised pads
4
c
(part B) is wider by the extent to which the pads are raised than in the pad-free collar region (view B); for the sake of better illustration, the pad region
4
c
is marked off by a dashed line from the contour of the funnel
4
. After the final machining, a so-called pad design as shown in
FIG. 5
, part A, results, with a raised pad
4
c on the soldering edge
4
a
without any mold seam.
A technique is also known—hereinafter called the Asiatic method—that in the pressing of the funnel
4
creates an upper edge
4
a
of the same width all the way around. The pressing operation b
Bordt Heinz-G.
Sparschuh Georg
Schott Glas
Striker Michael J.
Vincent Sean
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