Glass forming apparatus

A glass rod used as a molding material is inserted into a cylinder, pressed and heated with a temperature gradient in which the tip side of the glass rod is at a higher temperature. The glass rod is melted on the tip side thereof, and it is solidified on the rear side in the vicinity of the inlet of the cylinder, the solid portion functioning as a plunger when the rear side is pushed. When the glass rod is forwardly moved, the molten glass on the tip side is injected from an injection nozzle and is filled in the cavity of a forming mold. Since the glass rod itself is made of a molding material and functions as a plunger, when the tip side is melted and consumed, the solid portion on the rear side is forwardly moved and melted. It is thus possible to perform continuous mold forming without complicating the mechanism and steps and to improve the quality of the molded product.

BACKGROUND OF THE INVENTION 
The present invention relates to a glass forming apparatus and method. 
When a glass optical element, e.g., a glass lens, is formed, a forming 
method is generally employed in which a glass lump is ground and polished 
to form a desired final shape. 
However, since this forming method comprises the complicated steps of 
grinding and polishing and requires much time for the steps, the cost is 
increased. Particularly, when an aspherical lens which has been greatly in 
demand in recent years is formed, the work becomes difficult because the 
steps are further complicated, and it is necessary for a skilled worker to 
finish the product in a final step. 
On the other hand, a forming method which enables the omission of the final 
finishing step has been proposed. 
For example, in a reheat press method, a preform (a glass preformed 
product) having a predetermined shape and mass is previously formed by 
grinding and is pressed with heating at a high temperature in a forming 
mold having high-precision surfaces. This method is capable of directly 
forming a glass lens having a desired shape. 
However, in order to attain surface accuracy and dimensional precision 
which are required of a glass lens as a final product, it is necessary to 
sufficiently adjust the weight of the preform and to sufficiently finish 
the surfaces in the step of grinding and the like. This makes the work of 
forming the preform troublesome and increases the cost. 
A direct press method of directly pressing molten glass without forming a 
preform has thus been proposed. 
In this case, a glass flow is formed by the molten glass caused flow out or 
pushed out from an outflow orifice, is cut in a required amount by a 
cutting edge and is filled in a forming mold. In this case, the forming 
mold comprises a pair of left and right or upper and lower parts so that 
softened glass is directly held between the parts of the forming mold and 
pressed (Japanese Patent Laid-Open No. Hei 1-203234). 
The direct press method generally uses a pair of cutting edges for cutting 
the glass flow. In this case, if the glass does not have proper viscosity 
(10.sup.3 to 10.sup.5 poise) a sound product can not be easily formed. 
Namely, for example, when the viscosity is high, a nonuniform cutting mark 
occurs at the front end and rear end of the cut glass flow and remains as 
a defect in a formed product. Conversely, when the viscosity is low, the 
glass flow cannot be easily cut, and defects such as bubbles, striae or 
the like easily occur. 
Although various techniques of cutting and supplying a glass flow are 
proposed for solving the above problems, satisfactory results are not 
always obtained. 
In addition, it is necessary for obtaining good forms by the direct press 
method to hold and press molten glass maintaining proper viscosity 
(10.sup.3 to 10.sup.5 poise) in the forming mold. 
Although it is thus necessary to press the forming mold with high precision 
while controlling it in an appropriate high-temperature state, it is very 
difficult to control such a forming mold having a complicated mechanism in 
an appropriate high-temperature state. Further, since glass is excessively 
supplied to the forming mold, excess glass is extruded from the forming 
mold. A mechanism for removing the extruded glass is thus necessary, 
thereby further complicating the structure of the forming mold. 
A forming method is thus proposed in which glass is filled in the cavity of 
a forming mold under pressure instead of pressing by moving the forming 
mold (Japanese Patent Laid-Open No. 49-81419 and 1-249630). 
In this case, molten glass is filled in the cavity of the forming mold 
under pressure, and pressing is continued until the glass is solidified in 
order to prevent a shrink mark from occurring by shrinkage during 
solidification of the glass. 
However, in this forming method, since the molten glass is supplied to the 
forming mold by sliding a plunger in a cylinder which is filled with the 
molten glass, the plunger and the cylinder are eroded by the glass, and 
abrasion or galling thus occurs thus making it difficult to stably supply 
the glass for a long time. 
In the forming method disclosed in the Japanese Patent Laid-Open No. 
49-81419, since a glass lump as a raw material must be inserted into a 
transfer chamber for each forming step, forming cannot be continuously 
performed, with reduction in efficiency. 
In the forming method disclosed in the Japanese Laid-Open Application No. 
1-249630, although forming can be continuously performed, the heat 
resistant structure and the temperature control of the overall forming 
apparatus are significantly complicated because the molten glass in a 
molten glass bath is supplied to the cylinder through a supply tube and 
injected by the plunger. In addition, since the raw material glass is held 
in a high-temperature melt state for a long time, the glass becomes 
heterogeneous in quality, and impurities are easily mixed therein. 
In all the above methods, the complicated mechanism and steps increase the 
cost, and the quality of the formed product cannot be improved. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to solve the problems of the 
conventional glass forming apparatuses and forming methods and to provide 
a glass forming apparatus and method which are capable of continuously 
forming molten glass by a mold forming method without complicating the 
mechanism or steps and which is capable of improving the quality of the 
formed product. 
In order to achieve the above object, in the present invention, a glass rod 
made of glass used as a molding material is inserted into a heating 
cylinder and pressed by a glass rod pressing device disposed at the rear 
end of the glass rod. 
Heating means is provided on the heating cylinder so as to heat the glass 
rod with a temperature gradient in which the front end of the glass rod is 
at a higher temperature. The glass rod is thus melted at the front end, 
and it is solidified in the vicinity of the inlet of the heating cylinder. 
When the glass rod is forwardly moved, the molten glass on the front end 
side is injected from an injection nozzle disposed at the tip of the 
heating cylinder and filled in the cavity of a forming mold disposed in 
front of the injection nozzle. 
Since the glass rod itself is made of molding material, and the rear end 
side of the glass rod is solidified and thus functions as a plunger, when 
the solidified portion on the rear side is pushed by the glass rod 
pressing device, the glass on the front end side is consumed, so as to be 
successively moved forward and melted. It is thus possible to continuously 
form the glass. 
Since only the front end portion of the glass rod may be heated at a high 
temperature by the heating means, the glass forming apparatus has a simple 
structure, and only the front end portion of the heating cylinder may need 
be made heat resistant, thereby decreasing the cost. 
In addition, since the molten glass does not slide on a metal or ceramic, 
the life of the heating cylinder is increased. The glass is filled in the 
forming mold immediately after melting, thereby reducing contamination and 
heterogeneity.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Embodiments of the present invention are described in detail below with 
reference to the drawings. 
FIG. 1 is a conceptual drawing of a glass forming apparatus and method of 
the present invention. 
In the drawing, reference numeral 10 denotes a melting and injection 
portion comprising a heating cylinder 12 and an injection nozzle 14 
provided at the front end of the heating cylinder 12. The melting and 
injection portion 10 is connected to a glass rod pressing device 16 so 
that a glass rod 18 is inserted into the heating cylinder 12 and pressed 
by the glass rod pressing device 16. The glass rod 18 is made of glass and 
is melted and consumed in itself, as well as forming a self-consumable 
plunger for pressing molten glass. In the present invention, the glass 
used includes glass and a glass matrix composite. Any one of hydraulic, 
pneumatic, electric, electromagnetic and mechanical driving devices may be 
used as the glass rod pressing device 16. 
Glass generally shows viscosity changes within a wide range of several 
poise to 10.sup.18 poise as temperature changes. A heater 20 is thus 
disposed over the whole peripheral region of the injection nozzle 14, and 
a heater 22 is disposed over the whole peripheral region of the heating 
cylinder 12. A heater 24 is also disposed in a portion of the heating 
cylinder 12 near the injection nozzle 14. These heaters are operated and 
controlled so as to form a suitable temperature gradient in the region 
from the portion near the injection nozzle 14 to the inlet 26 of the 
heating cylinder 12. It is thus possible to establish the state where the 
tip portion (near the injection nozzle 14) of the glass rod 18 has low 
viscosity, and the portion near the heating cylinder inlet 26 has high 
viscosity. In this case, the heaters are set so that the viscosity of the 
glass in the tip portion is 10.sup.5 poise or less (preferably 10.sup.2 to 
10.sup.4 poise), and the viscosity of the glass near the heating cylinder 
inlet 26 is 10.sup.13 poise or more. The glass rod 18 is heated into the 
heating cylinder 12 and pressed. 
The glass heated and softened in the heating cylinder 12 by the heaters 22 
and 24 is further heated in the injection nozzle 14 by the heater 20. The 
glass is pressed and injected from the injection nozzle 14 by the force of 
the glass rod pressing device 16 to press the glass rod 18, and is filled 
in a cavity 32 of a forming mold 30. Since the portion near the injection 
nozzle 14 is easily cooled and the glass in the injection nozzle 14 is 
easily solidified, the glass is thus further heated by the heater 20 in 
order to prevent the clogging of the injection nozzle 
Although the forming mold 30 used is provided with the cavity 32 and can be 
divided into two parts, a forming mold which can be divided into many 
parts may be used. 
The nozzle opening of the injection nozzle 14 can also be opened and closed 
by turning the heater 20 on and off. Namely, when the heater is turned on, 
the glass in the injection nozzle 14 is melted and is filled in molten 
condition in the cavity 32 of the forming mold 30, and the molded product 
can be held under pressure. After dwelling is completed, when the heater 
20 is turned off, the glass in the injection nozzle 14 is solidified. Even 
if the injection nozzle 14 is separated from the forming mold 30 in the 
next cooling step or discharge step, it is thus possible to prevent the 
glass from drooling from the nozzle opening of the injection nozzle 14. 
In order to improve the molten condition of the glass filled in the cavity 
32, a heater 34 is buried in the forming mold 30, and mold temperature 
control medium holes 36 are provided in the forming mold, and a 
temperature control medium is supplied to the forming mold temperature 
control medium holes 36. 
Since the glass rod 18 is continuously pushed by the glass rod pressing 
device 16 after filling the glass in the cavity 32 of the forming mold 30, 
the molded product is held under pressure, thereby preventing the 
occurrence of shrink marks during cooling. 
In the present invention, the viscosity of the glass in the portion near 
the injection nozzle 14 is 10.sup.5 poise or less, and the viscosity in 
the vicinity of the heating cylinder inlet 26 is 10.sup.13 poise or more. 
This is because the work point which enables the forming of glass is about 
10.sup.4 poise, and because glass with a viscosity of 10.sup.13 poise or 
more assumes the state where it has sufficient rigidity and is not 
plastically deformed. The viscosity is not always limited to the above 
values so long as the above-described function is satisfied. 
When the glass rod 18 is consumed and becomes short, a new glass rod 18 
having the same dimensions may be added to the rear end of the short glass 
rod 18, whereby glass can be continuously supplied. In this case, both 
glass rods 18 can be fused to each other if required. 
The glass rod 18 is preferably a round rod from the viewpoint of the 
structure of the forming apparatus. 
Although the heaters 20, 22, 24 are disposed in the heating cylinder 12 and 
the injection nozzle 14 so that the glass rod 18 is heated and melted by 
the heaters 20, 22, 24, the heating method is not limited to electric 
heating by the heaters 20, 22, 24, and another heating method such as 
high-frequency heating, microwave heating, plasma heating or the like can 
be employed. A temperature control mechanism (a cooling system) can also 
be provided on the heating cylinder 12 for forming an optimum temperature 
distribution in the glass rod 18 if required. 
The steps of the glass forming method of the present invention are 
described below. 
The glass rod 18 made of the glass used as a molding material is first 
inserted into the heating cylinder 12. A temperature gradient is formed by 
driving the heaters 20, 22, 24 so that the viscosity of glass in the 
vicinity of the injection nozzle 14 is a value of 10.sup.5 poise or less, 
which allows forming, and the viscosity of glass in the vicinity of the 
heating cylinder inlet 26 is a value of 10.sup.13 poise or more, which 
produces no plastic deformation of glass. 
In the state wherein the tip of the injection nozzle 14 closely contacts to 
the forming mold 30, the glass rod 18 is then forwardly moved by pressure 
by the glass rod pressing device 16. The molten glass in the heating 
cylinder 12 is thus pressed and filled in the cavity 32. 
In order to prevent the occurrence of a shrink mark in the molded product, 
the glass rod 18 is continuously pressed for an appropriate time, and thus 
the glass filled in the cavity 32 is held under pressure. 
After dwelling is completed, the molded product is cooled in the forming 
mold 30 and is then removed by the ejector after opening the mold. 
Annealing can also be made if required. When annealing must be made for a 
long time in the state wherein the molded product is placed in the forming 
mold 30, multiple forming molds 30 may be prepared and successively used. 
After cooling (annealing), the injection nozzle 14 which closely contacts 
to the forming mold 30 is separated therefrom. At this time, the tip of 
the injection nozzle 14 must be sealed. The heater 24 disposed in the 
heating cylinder 12 is thus turned off so that the glass in the injection 
nozzle 14 is solidified, thereby preventing drooling of the glass from the 
nozzle opening of the injection nozzle 14. 
On the other hand, when the molten glass is supplied under pressure, the 
glass is filled in the cavity 32 through the gate of the forming mold 30. 
However, since the gate has a small size, the glass is first solidified in 
the gate due to precedence of cooling. Although it is thus necessary to 
supply the glass at a sufficiently high temperature to prevent the 
coagulation in the gate, the viscosity decreases with an increase in the 
temperature, and drooling of the glass from the nozzle opening occurs when 
the forming mold 30 is separated from the injection nozzle 14. 
A description will now be made of a glass forming apparatus which is 
capable of freely setting the viscosity of glass and which prevents the 
occurrence of drooling of glass from the nozzle opening of the injection 
nozzle 14 after injection. 
FIG. 2 is an enlarged view of the injection nozzle of the glass forming 
apparatus of the present invention. 
In the drawing, reference numeral 12 denotes a heating cylinder; reference 
numeral 14, an injection nozzle; reference numeral 40, the nozzle opening 
of the injection nozzle 14; and reference numeral 42, a nozzle body. A 
heater 44 is buried in the heating cylinder 12, and a heater 46 is 
disposed around the nozzle body 42 in close proximity to it. 
Reference numeral 30 denotes a forming mold, the nozzle opening 40 being in 
close contact with the forming mold Reference numeral 48 denotes a cooler 
or a temperature control device which is buried in the nozzle body 42 so 
as to surround the nozzle opening 40. A controller 50 selectively operates 
the cooler 48 and heaters 44 and 46. 
In the injection nozzle 14 configured as described above, when the glass is 
filled in the cavity 32 of the forming mold 30, the glass is heated by the 
heater 46 so that the viscosity is sufficiently decreased. After the glass 
is filled in the cavity 32 of the forming mold 30 and sufficiently held 
under pressure, the heating of the injection nozzle 14 is stopped by 
turning the heater 46 of the injection nozzle 14 off, and the injection 
nozzle 14 is cooled by the temperature control device 48 so that the 
viscosity of the glass in the injection nozzle 14 is increased. 
After the cooling by the temperature control device 48 is completed, and 
after the viscosity of the glass in the injection nozzle 14 is a value 
suitable for cutting, the forming mold 30 is transversely moved, whereby 
the glass can be directly cut by shearing force. Alternatively, after the 
forming mold 30 is downwardly moved, the glass can be cut by moving 
scissors (not shown). 
In other words, the viscosity of the glass is sufficiently lowered by the 
heater 46 until the glass is filled in the cavity 32 of the forming mold 
30 so that the sufficient amount of glass is diffused over the whole 
cavity 32. After the fill of the glass is completed, the viscosity of the 
glass is subsequently increased by cooling by the temperature control 
device 48, whereby the glass can easily be cut. During molding and cutting 
of the glass, any desired value of the viscosity of the glass can be 
selected, and the times of supply and stop can be arbitrarily controlled. 
It is also possible to prevent drooling of the glass from the nozzle 
opening 40 of the injection nozzle 14 and the occurrence of defects in the 
cut position of the glass. 
The heater 46 is capable of rapid heating by high-frequency induction 
heating. The injection nozzle 14 is thus made of-a conductive material 
such as a metal or the like, and the heater 46 comprises a coil and is 
disposed around the nozzle body 42 in close proximity to it. When the 
injection nozzle 14 is made of an non-conductive material such as ceramics 
or the like, microwave heating is used. A usual hot-wire heater may be 
employed. 
The temperature control device 48 is preferably capable of rapid cooling. 
The temperature control device 48 is thus formed at the tip of the nozzle 
body 42 so as to surround the nozzle opening 40, whereby a temperature 
control medium (for example, gas such as argon, nitrogen or the like or a 
liquid such as cooling oil or the like) can be supplied. Another cooling 
method may be employed in which a temperature control medium such as gas 
or the like is directly sprayed on the nozzle body 42 from the outside or 
a lump of a metal such as copper or the like is put into contact with the 
nozzle body 42 instead of the formation of the temperature control device 
48. When the viscosity of the glass can be sufficiently increased by 
cooling by spontaneous heat radiation after the heating of the injection 
nozzle 14 is stopped, the temperature control device 48 need not be 
provided. 
The operation of the injection nozzle 14 configured as described above is 
described below. 
The glass rod 18 is first supplied under pressure and is heated by the 
heater 44, and the molten glass is supplied to the injection nozzle 14. 
After the forming mold 30 is placed an appropriate position of the 
injection nozzle 14 so as to closely contacts to the nozzle 14, the 
injection nozzle 14 is rapidly heated by operating the heater 46 so that 
the glass is heated until it has desired viscosity. 
The glass is then supplied into the cavity 32 of the forming mold 30 by the 
glass rod pressing device 16 (FIG. 1) for pressing the glass rod. After 
the passage of the optimum supply time which is determined by the relation 
between the amount of the glass supplied and the amount of the glass 
filled in the cavity 32 of the forming mold 30 the heating of the 
injection nozzle 14 is immediately stopped and cooling by the temperature 
control device 48 is started. 
After the viscosity of the glass in the vicinity of the nozzle opening 40 
of the injection nozzle 14 is a value suitable for cutting, the glass is 
cut by moving the forming mold 30, and a next forming mold 30 is placed. 
The forming mold 30 filled with glass is annealed according to demand, and 
the molded product is then taken out. The forming mold 30 may be 
previously heated to a necessary temperature. 
Since the nozzle body 42 is put into close contact with the forming mold 
30, glass can be supplied not only downwardly but also transversely or 
upwardly. 
A description will now be made of a glass forming method which does not 
produce defects such as breaking, bubbles or the like. 
FIG. 3 is a sectional view of a forming apparatus in which glass is 
upwardly filled. 
In the drawing, reference numeral 18 denotes a glass rod, and reference 
numeral 12 denotes a heating cylinder containing the glass rod 18. The 
heating cylinder 12 comprises a low-temperature side cylinder portion 52, 
a heat insulating cylinder portion 54 made of a material such as ceramics 
or the like which has high heat insulation, and a high-temperature 
cylinder portion 56 made of a heat resistant metal or conductive ceramics. 
These portions are continuously formed from the lower side to the upper 
side. In this way, the heat insulating cylinder portion 54 is provided in 
the heating cylinder 12, thereby preventing the heat in the 
high-temperature cylinder portion 56 from being transmitted to the 
low-temperature cylinder portion 52, and forming a great temperature 
gradient in the axial direction of the glass rod 18. This permits 
efficient pressure and injection of the glass rod 18. 
Reference numeral 14 denotes an injection nozzle formed at the tip of the 
high-temperature cylinder portion 56 and made of a heat resistant metal or 
a conductive ceramics. The glass is injected through the injection nozzle 
14. 
The glass rod 18 is pressed by the glass rod pressing device (FIG. 1) and 
is upwardly moved in a plunger room 58 formed by the heating cylinder 12. 
The glass rod pressing device 16 is controlled by a controller (not shown) 
so as to upwardly move the glass rod 18 at a set speed. 
Reference numeral 60 denotes a high-frequency induction heating coil which 
is disposed around the high-temperature cylinder portion 56 in close 
proximity to it. The high-frequency induction heating coil 60 generates a 
high-frequency induced current in the high-temperature cylinder portion 56 
by the driving current received from a high-frequency source device 61 so 
that the high-temperature cylinder portion 56 is heated by high-frequency 
induction heating. In this case, the high-frequency source device 61 
receives a signal from a controller so as to supply a set driving current 
to the high-frequency induction heating coil 60. Since the high-frequency 
induction heating coil 60 heats only the vicinity of the injection nozzle 
14, the portion of the glass rod 18 which is surrounded by the 
high-temperature cylinder portion 56 is rapidly melted. 
The glass rod 18 is then upwardly moved by the glass rod pressing device 16 
so as to press the molten glass at the tip thereof. The pressed glass is 
thus injected from the injection nozzle 14. When the driving current is 
continuously supplied to the high-frequency induction heating coil 60, the 
unmelted portion of the glass rod 18 is continuously melted. 
Reference numeral 30 denotes a forming mold made of a heat resistant metal 
or ceramics and having a fixed side and a movable side which are put into 
contact with and separated from each other at a parting line by a forming 
mold opening/closing device (not shown). The forming mold 30 has a runner 
62 which is opened at a position corresponding to the injection nozzle 14 
and a cavity 32 communicating with the runner 62. Namely, the gate 64 
disposed between the runner 62 and the cavity 32 is located at the lower 
side of the cavity 32. A vent 66 which communicates with the outside of 
the forming mold 30 is formed at the upper end of the cavity 32 in order 
to exhaust the air in the cavity 32 through the vent 66 when the glass is 
filled in the cavity 32. 
The glass is thus upwardly made to flow in the runner 62 in the forming 
mold 30 and then the flow front of the glass is moved into the cavity 32 
through the gate 64. Even after the glass enters the cavity 32, the glass 
is constantly upwardly moved so that the space of the cavity 32 is filled 
with the glass. 
Hence the glass is gradually upwardly moved in the cavity 32 thereby 
preventing the occurrence of defects such as breaking, bubbles or the like 
in the molded product. 
In addition, the viscosity of glass in the portion near the inlet of the 
cavity 32, for example, in the gate 64, is 10.sup.2 to 10.sup.5 poise, and 
the supply speed of glass is as low as about 10 (cm/sec), preferably about 
0.1 to 1 (cm/sec), whereby the quality of the molded product can be 
improved. 
The controller controls the high-frequency source device 61 so as to supply 
the set driving current to the high-frequency induction heating coil 60. 
The glass in the high-temperature cylinder portion 56 is heated to the set 
temperature on the basis of the conditions such as the glass composition, 
the structure and temperature of the forming mold 30 and so on so that the 
viscosity of the glass in the gate 64 is within the above range. The 
controller also controls the glass pressing device 16 so as to upwardly 
move the glass rod 18 at the set speed. At this time, the glass supply 
speed in the gate 64 is set to be within the above range. 
Since the glass in the tip portion melted in the nozzle opening 40 in an 
initial stage has nonuniform viscosity, and since defects easily occur in 
the portion, the portion is discharged to a slug reservoir (not shown) and 
is not supplied to the cavity 32 during filling. 
Although, in FIG. 3, the injection nozzle 14 is opened to the upper side, 
even if the injection nozzle 14 is opened to the lower side, the glass can 
be upwardly filled in the cavity 32 of the forming mold 30 by providing a 
U-shaped runner 62 in the forming mold 30. In this way, the opening 
direction of the injection nozzle 14 is not particularly limited. 
A description will now be made of a glass forming apparatus in which can 
prevents the deformation of an intermediate portion of the glass rod. 
FIG. 4 is a conceptual drawing of a glass forming apparatus in which a 
groove is formed in the glass rod in the axial direction thereof so as to 
prevent the deformation of the glass rod. 
In the drawing, reference numeral 10 denotes a melting injection portion 
comprising a heating cylinder 12 and an injection nozzle 14 provided at 
the tip of the heating cylinder 12, a plunger room 70 being formed in the 
heating cylinder 12. The melting injection portion 10 is connected to a 
glass rod pressing device 16 which functions to insert a glass rod 72 in 
the plunger room 70 and press it. 
It is necessary that the tip portion of the glass rod 72 is melted, and the 
root portion thereof near the heating cylinder inlet 26 is maintained in a 
solid state in order to press the molten glass. When the glass rod 72 is 
pressed in this state, the glass rod is radially deformed in a semi-fluid 
region or a viscoelastic region which forms an intermediate portion of the 
glass rod 72. This causes the occurrence of galling between the glass and 
the inner wall of the heating cylinder 12 and thus makes it impossible to 
fill the glass in the cavity 32 under appropriate pressure. In order to 
prevent the phenomenon, it is necessary that the temperature region which 
produces galling of the heating cylinder 12, which is caused by unsound 
deformation of the glass rod 72, is decreased as much as possible by 
increasing the axial temperature gradient of the glass rod 72. 
A heat insulating layer 80 is thus interposed between the high-temperature 
cylinder portion 73 provided with the heaters 20, 24 and the 
low-temperature cylinder portion 71 on the rear end side in the heating 
cylinder 12 so that-the axial temperature gradient of the glass rod 72 is 
increased by increasing the axial temperature gradient of the heating 
cylinder 12 as much as possible. A cooling pipe 82 may be also disposed in 
the low-temperature cylinder portion 71 of the heating cylinder 12 near 
the heat insulating layer 80 so as to further cool the glass rod 72 with 
the cooling medium supplied to the cooling channel 82. 
Although the above method has remarkable effects, a groove 74 in one of 
various shapes is formed in the surface of the glass rod 72 in order to 
further prevent the deformation of the glass rod 72 and achieve the sound 
supply of glass. The formation of the groove 74 in the surface of the 
glass rod 72 permits the groove 74 to absorb the radial deformation of an 
intermediate portion of the glass rod 72, thereby preventing the 
occurrence of galling. 
The dimensions of the groove 74, such as the width, the depth and the like 
thereof, are not limited, and the shape of the groove 74 is appropriately 
determined in accordance with the composition, viscosity, melting 
temperature of glass, the pressure applied, the temperature gradient of 
the glass rod 72 and so on. 
Cooling gas is caused to flow from the root portion of the glass rod 72 to 
the tip thereof so as to force the intermediate portion of the glass rod 
72 to cool. 
A cooling gas inlet 76 and a cooling gas outlet 78 both of which are passed 
through the heating cylinder 12 and opened to the plunger room 70 are thus 
provided. The cooling gas inlet 76 and the cooling gas outlet 78 are 
formed so as to open at positions corresponding to the root portion and an 
intermediate portion, respectively, of the glass rod 72. Cooling gas is 
supplied from the cooling gas inlet 76, sent to the cooling gas outlet 78 
through the groove 74 and is discharged to the outside from the cooling 
gas outlet 78. During this time, the cooling gas cools the glass rod 72, 
thereby suppressing deformation of the intermediate portion. 
Although the cooling gas is preferably discharged from a position close to 
the heat insulating layer 80, the discharge position is not limited to 
this, and the cooling gas may be caused to flow from a position near the 
root portion to a position near a deformation portion. 
Inert gas such as Ar gas or the like is generally preferable as the cooling 
gas, and conditions such as the flow rate and the like are determined by 
forming conditions (particularly, the melting temperature, the viscosity 
of glass and the like). 
In this way, the occurrence of galling on the inner wall of the heating 
cylinder 12 can be further suppressed by forcing the glass in the 
intermediate portion of the glass rod 72 to cool with the cooling gas. 
Namely, in FIG. 4, character a shows the viscosity distribution of the 
glass rod-72 when the glass was not cooled, and character b shows the 
viscosity distribution of the glass rod 72 when the glass was cooled. 
Character c shows a viscosity region (about 10.sup.5 to 10.sup.9 poise) in 
which glass is easily deformed, and galling easily occurs because of the 
large friction with the inner wall of the heating cylinder 12. 
As shown in FIG. 4, since the viscosity distribution is changed from a to b 
by cooling glass, the portion corresponding to the viscosity region c is 
decreased by cooling glass. 
As a result, the glass in the intermediate portion of the glass rod 72 is 
not easily deformed, and the absorption of deformation by the groove 74 
prevents the occurrence of galling. 
The cooling gas may be caused to flow from the tip of the glass rod 72 to 
the root portion thereof. 
FIG. 5 is a conceptual drawing of another glass forming apparatus of the 
present invention which is capable of preventing deformation of a glass 
rod. 
In this case, a groove 86 opened to a plunger room 70 is formed within the 
region from an inlet 26 of a heating cylinder 12 to an intermediate 
portion thereof in the inner wall of the heating cylinder 12 so that a 
portion of a glass rod 18 within the region is forced to cool by the 
cooling gas flowing through the groove 86. A large temperature 
distribution is consequently formed in the axial direction of the heating 
cylinder 12. 
A cooling gas inlet 88 and a cooling gas outlet 90 both of which are passed 
through the heating cylinder 12 and communicate with the groove 86 are 
thus provided. The cooling gas inlet 88 and the cooling gas outlet 90 are 
formed so as to open at positions corresponding to the heating cylinder 
inlet 26 and an intermediate portion, respectively, of the cylinder 
cylinder 12. Cooling gas is supplied to the cooling gas inlet 88, sent to 
the cooling gas outlet 90 through the groove 86 and is discharged to the 
outside from the cooling gas outlet 90. During this time, the cooling gas 
cools the glass rod 18 and suppresses deformation of the intermediate 
portion thereof. Even if the cooling gas is sent in the reverse direction, 
the same effect can be obtained. The direction of the groove 86 is not 
limited to the axial direction of the heating cylinder 12, and the heating 
cylinder 12 may be formed in the peripheral direction thereof and may have 
any desired shape. 
The present invention is not limited to the above embodiments, various 
changes can be made on the basis of the gist of the present invention 
within the range of the invention.