Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 The present invention relates to a bushing for
glass fiber spinning apparatus and~ more particularly,
to an improvement in bushing having a bottom orifice
plate provided with a number of extremely densely arranged
orifices consisting of plain holes.
According to a current technique of manufactur-
ing glass fibers, a bushing is used to contain molten
glass which is the material o~ the glass fiber. The
bushing is provided at its bottom with an orifice plate
having 400 to 2000 orifices. The molten glass in the
bushing is forced out through the orifices, by the static
head-and viscosity, to assume a form of number of glass
cones which are then mechanically drawn to be turned '
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into fibers.
This method, however, has been found inconvenient
in that the orifice plate is apt to be bent and deflected
to cause the lower surface convexed downwardly, &S the
time elapses, due to a combined effect of weight of the
molten glass in the bushing, spinning tensile force,
high spinning temperature which well reaches 1100 to
1300C This deflec-tion of orifice plate '
causes a difference in the rates of heat radiation from i
the glass cones suspended from the orifice plate,
especially between the orifices located near the periphery
of the orifice plate and the orifices located near the
center of the orifice plate, resulting in an unstable
spinning. ~
In addition, the deflection of the orifice ~j
plate badly affectSthe stability of the glass cones to
incur the breakdown of the later, due to an incre~scd
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1 component of force to pull the glass cones laterally
along the orifice plate. Moreover, the deflection of the
orifice plate tends to cause so-called "flooding" in
which the cones creep through capillary action along the
underside of the orifice plate to join adjacent cones.
Once the flooding takes place, it is quite difficult to
resume the separate flows of glass cones.
~ n order to avoid th~is inconvenience, various
methods have been proposed and actually used, such as
increasing the distance between adjacent orifices, thicken-
ing of the orifice plate itself and provision of
reinforcing ribs on the orlfice plate. However, these
proposed methods have been found unsatisfactory because
the size of the bushing becomes unacceptably large to
15 deteriorate the uniformly heated condition of the molten ;
glass held by the bushing, which renders the nature of the ,
glass flow i:rregular to incur the breakdown of the fibers,
resulting in a deteriorated yield, or, even if the fibers ;
- are not broken, the diameter of the fibers inconvelliently ~
20 fluctuate to reduce the strength of the prc~uced fibers. i
In addition~ since the orifice plate is made of platinu~, ,
the larger size of the bushing inevitably leads to a
drastically raised cost of installation which can be
compensated only by the raised price OI the produced f~x~s.
Recently, deman~s for increase of yield through increasing
the nu*~r of orifices and reduction of cost of ins ~ - l
lation through minimizing the size of the bushing are ¦
notable, as a fruit of which, nowadays, a bushing is uscd
having an orifice plate provided with 2000 to 6000 plain -
~0 hole orifices which are so densely arranged, e.~. at an
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1 interval of 3 mm or smaller, that the glass cones from the
plain hole orifices join one another to cause the afore-
mentioned flooding condition, if suitable means are not .
provided for preserving the separate flows of glass
cones.
Thus in order to obtain a good spinning fromsuch bushing having densely arranged plain hole orifices,
it is strictly required to avo`id the flooding at the
underslde of the orifice plate by the flowing glass, l.e.
unde$irable joining of the glass cones with one another.
To this end, Specification of U.S.P. No. 3905790
discloses the use of air nozzles adap-ted to jet out
cooling air upwardly to cool the underside of the orifice
plate and the surfaces of the flowing glass cones, so as
to increase the viscosity of the glass cones, thereby to
prevent them from joining. However, in the apparatus as
disclosed in this U.S. Patent specificationj the plain
hole orifices are so densely provided that the orifice
plate assumes almost a form of a net to exhibit too
large deflection due to the reduced rigidity. Consequent-
ly, the upward flow of the cooling air toward the orifice
plate provides an uneven cooling effect on the glass
; cones, resulting in a fluctuation of the diameter of the
fibers and, i.n the worse case, the breakdo~m of the fibers,
which considerably deteriorates the working efficiency
and the yield.
It has been proposed, in order to overcome
the drawback attributable to the deflection of the
bushing, to provide stiffening ribs on the orifice plate
~0 by means of, for example, welding. However, in th.e
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1 modern bushing having an orifice plate provided with a
greàt number of plain hole orifices arranged extremely
densely, the orifice plate cannot have enough space for
fixing the stiffening ribs thereto. Thus, the provision
of the stiffening rib is possible only at a cost of
enlarged space between adjacent rows of plain hole orifices
at portions of the orifice plate where the ribs are to
be secured, undesirably enlarging the area of the
orifice plate, which is quite incompatible with the
current demand for as large a number of orifices as pos-
sible in a small area.
Moreover, when such stiffening ribs are provided,
the glass cones at the underside of the orifice piate are
inevitably divided into a plurality of sections by these
ribs. Consequently, the heat radiating conditions are
different for the glass cones at the inner and the outer
sides of each group, such that the glass cones at the
outer side perform larger heat radiation than those
located at the inner side of each group, to exhibit
correspondingly lowered temperature, causing an eneven
temperature distribution over the orifice plate, which
also badly affects the production efficiency.
It is therefore an object of the invention to
provide an improved bushing for spinning glass fibers
having an orifice plate provided with an increased number
of plain hole orifices per unit area, and sufficiently
reinforced against deflectionO
According to the invention there is provided
a bushing for a glass fiber spinning apparatus
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having at its bottom an orifice plate provided with a great
number of orifices consisting of holes arranged so densely
that molten glass cones associated with the respective
orifices tend to join so as to cause a flooding condition at
the downside of said orifice plate, said bushing further
comprising at least one beam member disposed in said bushing
and connected at both ends to opposing walls of said bushing,
each such beam member extending in parallel with and spaced
from said orifice plate, and at least one rod member extending
substantially perpendicularly to said orifice plate and
affixed at one end to a beam member and affixed at the other
end to said orifice plate, each rod member having a diameter
substantially equal to the diameter of one of said holes.
Such a bushing can be sufficiently reinforced
without adversely affecting the quality of the produced
fibers or the production efficiency, and can be provided at
relatively low cost.
These and other objects, as well as advantageous
features of the invention will become clear from the
following description of the preferred embodiment taken
in conjunction with the attached drawings in which:
Fig. 1 is a sectional side elevational view of a
bushing in accordance with the invention,
Flg. 2 is a partial enlarged sectional front
elevational view taken along the line II-II of Fig. 1,
and
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1 Fig. 3 is a partial plan view of the bushing
as viewed from the upper side thereof, showing the detail
of the internal structure of the bushing.
The invention will be described hereinafter
with specific reference to the attached drawings.
Referring at first to Figs. 1 and 2, a bushing
in accordance with the invention is provided at its
bottom with an orifice plate 2 in which are formed a
great number of orifices 1 in the form of extremely
densely arranged plain holes. The bushing has opposing
walls 3, 3' to which respecti~e ends of beam members 4,
4 ... are secured by means of, for example, welding.
~hese beam members 4, 4 ... extend in parallel with and
spaced from the orifice plate 2. The beam members 4,
4 ... are connected to the orifice plate 2 through rod
members 5 having a small diameter. ~he beam members 4
and the rod members 5 in combination constitute stiffen-
ing or reinforcing members for the orifice plate.
As will be seen from Fig. 3, the beam members
4 are disposed to extend at right an~le to the longitudil~al
direction of the bushing when the latter has a rectangular
profile, and the number of beam members is
selected depending on the size of the bushing, while the
number ofrod members is suitably selected in
accordance with the length of the beam member.
Needless to say, the beam members may be
disposed to extend radially -from the center of a circle
or may be arranged in parallel with one another, when
a cylindrical bushing is used, and any other pattern of
the arrangement of the beam members can be adopted, e.g.
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1 in the form of a lattice.
The dist~ce between the beam member and the
orifice plate is preferably within a range of between
1.5 to 10 mm. A too small distance would adversely
affect the supply of the molten glass to the orifices,
while a too large distance wouid cause an excessively
large elongation or strain of the rod members to
deteriorate the stiffening effect on the orifice plate.
The beam member can have any deslred shape
such as flat plate, rod, and is preferably
made of platinum. Thus, in order to minimize the
expense, the beam members are made small, insofar as they
can ensure sufficient stiffening effect. Also, the rod
members connectlng the beam members to the orifice plate ~
15 should be made as small as possible. ~or the same reason, i
the number of beam members employed in a bushing, as well
as the number of the r~d members for one beam member,
should be made as small as possible, as far as they l
promise the good stiffenin~ effect. I ,
~ The pitches at which the beam members and the
rod members are disposed, respectively, are typically
10 to 50 mm, and 5 to 20 mm, although they depend on the
si7e of the orifice plate and the mlmber of plain hole
orifices formed in the latter. tl
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~hanks to the structural features as stated
above, the orifice plate of the bushing in acco~dance ~¦
with the invention is rendered free from the force which
would cause the downward d~flection of the orifice plate,
since.the force is convenicntly born by the reinforcing
members consisting of ~the beam and the rod members. In - ¦
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1 addition, the reinforcing members occupy only a very
limited area on the orifice plate. More specifically,
the number of the orifices rendered invalid or useless
by the provision of the reinforcing members is very small
for the total number of the orifices, so that the -tempe-
rature differential between the glass cones from
respective orifices is conveniently reduced. Thus,
according to the inventionS the entire area of the
orifice plate can be effectively used for densely and
uniformly locating the orifices, in good contrast to the
conventional arrangement in which the distance between
the adjacent orifices is made large at portions where the
reinforcing members are located, or the orifices are
arranged in a plurality of separate groups.
However, it is to be noted that the present
invention is applicable also to those bushings as having
an orifice plate provided with orifices arranged in groups
separated by the reinforcing members, to effectively
preven-t the orifice plate from being deflected at
portions thereof where the groups of orifices are located.
Another advantage of the invention resides in
that the separation of the joining glass cones into
respective independent cones can be performed efficiently.
As mentioned before, this separation of the joining
cones is usually effec-ted by upward flow of air jetted
from air nozzles toward the underside of the orifice
plate, so as to cool the orifice plate to facilitate the
separation of the molten glass in the flooding condition
from the orifice plate 9 thereby to promote the separation
~0 of the joining glass cones. However, as the separation
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1 is performed to some extent, the temperature of the
orifice plate is caused to rise again, as a result of the
increased flow rate of the molten glass through the
orifices and the correspondingly increased amount of
heat brought out by the molten glass. This temperature
rise undesirably causes rejoining of the glass cones.
~his tendency renders the separation work considerably
difficult, especially when thè number of the orifices
employed is large.
Hcwever, according to the invention, the separation of the joining
glass cones is o~enced at first at p~rtions of the underside of the orifioe
plate, where no orifioes are opened due to the provision of the rod mem~ers
affixed to the orifioe plate, so that molten glass flooding over the under-
side of the orifice~plate is separated into a plurality of
groups of jolning glass cones. ~he separation then goes
on in each group. It will be understood that such a ¦
procedure of the separation is less likely to cause the
rejoining of the glass cones, greatly contributing to
improve the separation efficiency.
In fact, according to the invention, the ti~e
can be reduced to almost a half of that required by the
conYentional technique, in separating thé joining glass
cones.
~he advantageous features of the invention
will be more fully understood from the following descrip-
tion of examples of bushing in accordance with the
invention.
Example 1
Glass fiber spinning was carried out by means
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1 of a bushing having at its bottom an orifice plate having
2000 orifices arranged at a constant pitch of 1.80 mm and
reinforced by three reinforcing ribs directly attached
thereto. The bushing could endure only 0.8 month, while
another bushing having the same orifice plate but seven
reinforcing members was found to be able to sustain for
2 months, but exhibited a bad spinning performance due
to uneven temperature distribùtion over the orifice
plate.
In good contrast to the above, it has been
confirmed that a bushing in accordance with the invention
incorporating 11 reinforcing members can endure for 12
months ? suffering no uneven temperature distribution over
the orifices. The relnforcing members incorporated
three rod members for each beam member, so that the
orifice plate was supported at three points by each of
the relnforcing member.
Example 2
Glass fiber spinning was conducted employing a
bushing hav~ng at its bottom an orifice plate reinforced
by five reinforcing members directlyfixed to the orifioe plate
andprovided with 4,000 orifices disposed at a constant pitch ~!
of 1.80 mm. Due to the deflection of the orifice plate, ¦'
this bushing could be used only for 0.6 months, and !
some uneven temperature distribution was observed, while
a bushing of the invention incorporatinV 17 reinforcing
members could be used for 10 mon-ths, exhibiting almost '
no uneven temperature distribution. The reinforcing i'
members incorporated each had three rod members for each
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1 beam member, similarly with the Example 1.
As has been described, the present invention
ensures a stable spinning of glass fibers, through
avoidi.ng the deflection of orifice plate provided at a
bushing, by a provision of reinforcing members each of
~Ihich consisting of beam members fixed at both ends to
the wall of the bushing and rod members through which
the beam member is connected to the orifice plate.
