Method of manufacturing a glass optical part

A method of pressing flowing-down molten glass from the opposite sides thereof by a pair of shaping mold members to thereby manufacture a glass optical part having surfaces corresponding to the shaping surfaces of the mold members is characterized in that a groove forming ring is provided around the shaping surface of at least one of the shaping mold members, a groove is formed in the molten glass by the groove forming ring during the press and the flowing-down molten glass is cut above that portion thereof which is being pressed, thereby obtaining a glass molded article having an ear protruding outwardly of the groove relative to an optical part body portion.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method of manufacturing a glass optical part, 
and in particular to a method of obtaining an optical part by pressing 
glass in its molten state from the opposite sides thereof by shaping mold 
members while causing the glass to flow down. 
2. Related Background Art 
As methods of obtaining an optical part from a glass blank by press 
molding, there are the so-called reheat press method and direct press 
method. 
In the reheat press method, a glass blank similar in shape to a final 
molded article is once formed, and this blank is contained in a shaping 
mold apparatus and heated and pressed to thereby obtain a final molded 
article corresponding to the shape of a cavity formed by the mold member 
of the mold apparatus. 
In the direct press method, molten glass is introduced into a shaping mold 
apparatus and pressed to thereby directly obtain a final molded article 
corresponding to the shape of a cavity formed by the mold member of the 
mold apparatus. 
Now, the glass blank used in the above-described reheat press method should 
preferably be good to some degree in shape accuracy and surface accuracy 
and therefore, the glass blank is ground and polished in some cases to 
obtain a final product of predetermined accuracy. However, this requires 
time and labor for grinding and polishing and thus, in some cases, the 
above-described direct press method is utilized to manufacture said glass 
blank. 
As the direct press method, there is a system as described, for example, in 
Japanese Laid-Open Patent Application No. 63-248727 and Japanese Laid-Open 
Patent Application No. 1-133948 wherein molten glass is sandwiched from 
the opposite sides thereof by the use of a pair of shaping mold members 
horizontally opposed to each other while the molten glass is caused to 
flow down from a nozzle, and the glass is cooled and cured in a cavity 
thus formed, thereby obtain a molded article of a predetermined shape. In 
this system, a ring-like cutting member is disposed around the optical 
surface shaping surface of one of the shaping mold members and this 
cutting member is moved forward simultaneously with or after the forward 
movement of the mold members to thereby cut and remove the protruding 
portion of the glass and form an optical part of a desired shape. This 
system is preferable in that an optical part can be obtained without the 
cutting traces of the flowing-down molten glass remaining on the optical 
surface. 
However, in the above-described system, when the glass is cut by the 
ring-like cutting member, dust may be created by the contact of the 
cutting member with the other mold member and such dust may adhere to the 
shaping surfaces of the mold members after the parting of the molded 
article and may further adhere to the glass surface which will provide the 
optical surface during the next press, thereby deteriorating the optical 
characteristic of the molded article. 
Further, as described above, the ring-like cutting member contacts with the 
other mold member and therefore is short in life and frequent replacement 
thereof is necessary, and this has hampered improvements in the 
manufacturing efficiency. 
SUMMARY OF THE INVENTION 
In view of the prior art as described above, the present invention has as 
its object the provision of a method of manufacturing a glass optical 
part, which method can obtain an optical part of good optical 
characteristic and can improve the manufacturing efficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first form in which the present invention is carried out will hereinafter 
be described with reference to the drawings. 
FIGS. 1A-1D are cross-sectional views schematically showing the steps of an 
embodiment of a method of manufacturing a glass optical part according to 
the present invention. 
In these figures, the reference numeral 2 designates a molten glass outflow 
nozzle connected to a glass melting apparatus, not shown, and the 
reference numeral 4 denotes molten glass caused to continuously flow down 
from the nozzle 2. The reference numeral 6 designates a shearing machine 
(cutting edge) disposed just beneath the nozzle 2 for cutting the 
flowing-down molten glass 4 at suitable timing. 
The reference numerals 12 and 12' denote a pair of shaping mold members 
disposed on the opposite sides of the flowing-down molten glass, and in 
the present embodiment, the shaping mold members 12 and 12' are for 
shaping a convex meniscus lens. The reference characters 12a and 12a' 
designate shaping surfaces for forming the optical surfaces of the convex 
meniscus lens. The shaping surfaces 12a and 12a' are finished as mirror 
surfaces. These mold members are of a rotation symmetrical shape and are 
disposed coaxially with each other with their shaping surfaces opposed to 
each other. A pair of mold sets are constructed including the mold members 
12 and 12'. 
In the left mold set, the shaping mold member 12 is fixed to a support 
member 14 which is mounted on a mounting member 16. A groove forming ring 
18 is mounted around the mold member 12. The end of this ring 18 is made 
into a cutting edge shape. The ring 18 is fixed to the mounting member 16 
by means of a bolt with a spacer ring 20 interposed therebetween. The 
projection amount of the cutting edge of the ring 18 from the shaping 
surface 12a of the mold member 12 is set in conformity with the thickness 
of the spacer ring. 
A heater 22 and a thermocouple 24 for temperature measurement are contained 
in the mold member 12. 
Although not shown, the mounting member 16 is supported by a base stand, 
not shown, for reciprocal movement in the directions of arrows A and B. 
This reciprocal movement is effected by driving means, not shown, and the 
foremost stop position in the direction A is set by a stopper, not shown. 
By making the position of this stopper variable and adjusting the position 
thereof, said stop position can be suitably set. 
While the left mold set has been described above, the right mold set is 
substantially the same as the left mold set except the shape of the 
shaping surface 12a' of the mold member 12', and corresponding members 
have a prime (') attached thereto. 
The manufacturing process will hereinafter be described with reference to 
the drawings. 
First, as shown in FIG. 1A, the left and right mold sets are opened at a 
predetermined interval and the molten glass 4 is caused to flow down from 
the nozzle 2 into the space between the mold members 12 and 12' while the 
shearing machine 6 is maintained open. Then, the arrival of the lower end 
of the molten glass 4 at the downstream of the space between the mold 
members as shown in FIG. 1A is detected by a sensor, not shown. 
Subsequently, on the basis of the detection signal, the right mold set is 
advanced in the direction B until it bears against the stopper. With a 
very slight delay relative to this advancement, the left mold set is 
advanced in the direction A until it bears against the stopper. Thereby, 
as shown in FIG. 1B, the molten glass is pressed correspondingly to a 
cavity formed by the pair of mold members 12, 12' and the pair of groove 
forming rings 18, 18'. At this time, as shown in FIG. 1B, the ends of the 
groove forming rings 18 and 18' are not in contact with each other but are 
spaced apart from each other by a spacing D and accordingly, on the left 
and right surfaces of the pressed molten glass, there are formed grooves 
around the portions thereof corresponding to the shaping surfaces 12a and 
12a' of the mold members. Thus, a glass optical part body portion 30 is 
formed inside the grooves. 
Subsequently, as shown in FIG. 1C, the shearing machine 6 is closed and the 
molten glass 4 is cut. Thereby, an ear 32 protruding outwardly of the 
grooves is formed around the glass optical part body portion 30. 
Then, as shown in FIG. 1D, the left and right mold sets are opened and 
further the shearing machine 6 is opened, and the molded article is 
removed. A take-out robot, not shown, is utilized for this removal. 
FIG. 2 is a front view showing the molded article obtained through the 
above-described steps, and FIG. 3 is a fragmentary schematic 
cross-sectional view thereof. 
In these figures, the reference numeral 30 designates the optical part body 
portion, the reference numeral 32 denotes the ear protruding outwardly 
thereof, and the reference numerals 34 and 36 designate grooves formed on 
the opposite surfaces of the body portion 30 between the body portion 30 
and the ear 32. The cross-sectional shape of the grooves is a wedge shape 
as shown in FIG. 3, and with respect to the direction parallel to the 
optic axis of the lens, the inner side and the outer side form angles 
.theta..sub.1 and .theta..sub.2, respectively, on the left surface side, 
and the inner side and the outer side form angles .theta..sub.1 ' and 
.theta..sub.2 ', respectively, on the right surface side. These angles 
are, for example, .theta..sub.1 =30.degree., .theta..sub.2 =15.degree., 
.theta..sub.1 '=45.degree. and .theta..sub.2 '=15.degree.. 
It is preferable in order to effect the break during the removal of the ear 
well that at least one of the depths d.sub.1 and d.sub.2 of the grooves 34 
and 36, respectively, corresponding to the projection amounts of the ends 
of the groove forming rings 18 and 18', respectively, be 0.3 mm or 
greater. Also, it is preferable in order to effect the maintenance of 
shape after pressing well that the spacing D between the ends of the 
groove forming rings 18 and 18', i.e., the thickness of the constricted 
portion formed by the grooves 34 and 36 in the boundary between the body 
portion 30 and the ear 32, be 0.3 mm or greater. Further, it is preferable 
in order to effect the break during the removal of the ear well that 
(d.sub.1 +d.sub.2) be 1/3 or greater of (d.sub.1 +d.sub.2 +D). 
In the above-described process, the mold members 12 and 12' are 
PID-controlled (proportional integral differential controlled) to a fixed 
point temperature on the basis of the result of the temperature 
measurement by the thermocouples 24 and 24', and this fixed point 
temperature is set to a temperature at which the molded article is cured 
to a viscosity at which it can be removed. The opening of the left and 
right mold sets shown in FIG. 1D is done after the molded article is cured 
to the viscosity at which it can be removed. 
The molded article formed in the manner described above has its ear 32 
removed thereafter. 
This removal can be mechanically accomplished with ease by producing a 
tensile stress at a desired location because the grooves 34 and 36 are 
formed. That is, the ear can be removed, for example, by applying a force 
thereto by fingers to thereby break the ear, or by a fall shock from a 
slight height, or by applying a force to the ear 32 while supporting the 
body portion 30 by the use of a jig for exclusive use therefor. 
FIG. 4 is a fragmentary schematic cross-sectional view showing the optical 
part body portion 30 having its ear 32 removed. 
As shown, the optical part body portion 30 has on the outer peripheral 
portion thereof inclined surfaces 35 and 37 which are parts of the grooves 
34 and 36 and a broken-away surface 40 formed during the removal of the 
ear. The broken-away surface is formed at a desired location because 
during the removal of the ear, break occurs stably from the bottom of the 
groove 34 to the bottom of the groove 36. 
The inclined surfaces 35 and 37 just perform the function as the chamfered 
portions of the both surfaces of the optical part body portion 30. 
FIG. 5 is a cross-sectional view showing a modification of the 
above-described embodiment of the method of manufacturing a glass optical 
part according to the present invention. This figure corresponds to FIG. 
1B, and in this figure, members similar to those in FIG. 1B are given 
identical reference numerals. 
This modification differs from the embodiment of FIG. 1 only in that the 
groove forming ring is not provided around the right mold member 12' and 
the outer diameter of the mold member 12' is large. 
Also, in FIG. 5, there is shown a stopper 50 for setting the foremost stop 
position of the right mold set in the direction B. 
FIGS. 6 and 7 are schematic cross-sectional views showing other examples of 
the groove forming rings 18 and 18'. 
As shown in these figures, the groove forming ring 18' of the right mold 
set is utilized to form a large chamfered portion of the concave surface 
of the optical part. 
The result of the manufacture of a specific glass optical part carried out 
by the use of the method as described above will be shown below. 
EXAMPLE 1 
By the use of the apparatus as shown in FIG. 1, a convex meniscus lens of 
both spherical surfaces having an outer diameter of 28.8 mm.phi., a 
maximum light ray effective aperture of 27.0 mm.phi., a marginal thickness 
of 2.38 mm and a thickness difference of 0.98 mm was manufactured as 
follows. 
The diameters of the mold members 12 and 12' were 28.8 mm.phi. and the 
projection amounts of the ends of the groove forming rings 18 and 18' were 
0.45 mm. 
Crown glass with a viscosity of 10.sup.3.7 poise was stabilized into a 
thickness of 20-22 mm and caused to flow down from the nozzle 2 made of 
platinum. 
The press conditions were: the mold member temperature was 
fixed-point-controlled to 550.degree. C., the pressing pressure was 20 
kg/cm.sup.2 and the pressing time was 5 seconds. Such press was 
continuously effected. 
The ear 32 of the molded article could be easily removed by breaking it by 
fingers. 
The thus obtained optical part body portion 30, although some drops were 
seen in the central portion thereof, had no surface flow and was good in 
its external appearance, and was sufficiently practically usable as a 
blank for reheat press. 
EXAMPLE 2 
By the use of the apparatus as shown in FIG. 5, a convex meniscus lens of 
both spherical surfaces having an outer diameter of 21.0 mm.phi., a 
maximum light ray effective aperture 20.0 mm.phi., a marginal thickness of 
1.98 mm and a thickness difference of 1.42 mm was manufactured as follows: 
The diameter of the mold member 12 was 21.0 mm.phi., and the projection 
amount of the end of the groove forming ring 18 was 1.30 mm. 
Flint glass with a viscosity of 10.sup.4.5 poise was caused to flow down 
from the nozzle 2 made of platinum. 
The press conditions were: the mold member temperature was 
fixed-point-controlled to 340.degree. C., the pressing pressure was 50 
kg/cm.sup.2 and the pressing time was 5 seconds. Such press was 
continuously effected. 
The ear 32 of the molded article could easily removed by breaking it by 
fingers. 
The thus obtained optical part body portion 30, although some drops were 
seen in the central portion thereof, had no surface flow and was good in 
its external appearance, and was sufficiently practically usable as a 
blank for reheat press. 
In the aforedescribed embodiments, the material of the ring member 18 and 
the shearing machine 6 was quenched high-speed steel. 
As described above, according to the present invention, grooves are formed 
in the molten glass by the groove forming rings during press and a glass 
optical part having an ear protruding outwardly of the grooves relative to 
the optical part body portion is obtained, whereby during press, no dust 
is created and therefore it does not happen that dust adheres to the 
shaping surface of the mold members to deteriorate the surface accuracy 
and thus, there is obtained an optical part of good optical characteristic 
and the groove forming rings do not contact with any other metallic 
members and therefore, the frequency of replacement of the rings is very 
low, and this is advantageous in improving the manufacturing efficiency of 
the optical part. Also, the ear can be easily removed by breaking the 
grooved portion of the molded article obtained, and an optical part of a 
desired shape can be easily obtained. 
When in the aforedescribed embodiments 1 and 2, grooves were formed under 
the conditions that .theta..sub.1 =.theta..sub.2 =0.degree. (no wedge) and 
.theta..sub.1 '+.theta..sub.2 '=45.degree. to 90.degree. and the depth of 
the grooves was set to 1/3 or greater of the lens thickness, the ear 32 
could be cleanly cut off even though the grooves were formed only on one 
surface. 
A second form in which the present invention is carried out will now be 
described. 
This form proposes a method of pressing flowing-down molten glass from the 
opposite sides thereof by a pair of shaping mold members and manufacturing 
a glass optical part having a surface corresponding to the shaping 
surfaces of said mold members, characterized in that said glass continues 
to be pressed without the space between said pair of shaping mold members 
being closed until the glass reaches a temperature below the strain point 
thereof, and the flowing-down molten glass is cut above the portion 
thereof being pressed to thereby obtain a glass molded article having an 
ear protruding outwardly relative to an optical part body portion formed 
between said shaping mold members. 
As an apparatus for this form, use is made of the apparatus for the 
aforedescribed first form shown in FIGS. 1 to 5. 
As the mold members 12 and 12', use can be made of Ni group super-heat 
resisting alloy base material having its shaping surface polished to 
surface roughness Rmax 0.01 .mu.m and desired shape accuracy and coated 
with a nitride ceramics coating layer having a thickness of about 0.8 
.mu.m. As the mold base material, use can also be made of Mo group heat 
resisting alloy, Fe group heat resisting alloy, stainless heat resisting 
alloy, Mo, Ta, carbon, carbon composite material or the like. The coating 
layer is used to make up for the hot strength of the base material, and 
besides nitrides such as BN, TiN and AlN, use can be made of carbides such 
as TiC, SiC and TaC, or C (diamond) and others. These can be attached by 
the use of various film forming techniques. The coating layer need not be 
a single layer, but can be provided with an intermediate layer to improve 
the contact strength and the heat resisting property. Also, in the case of 
a coating layer formed by the CVD method, treatment such as 
super-precision grinding or polishing can be applied thereto to provide 
good surface accuracy of the coating layer itself. Further, where the hot 
strength of the base material is great and the shape accuracy thereof can 
be maintained even if press shaping is effected a sufficient number of 
times, platinum, plutinum alloy, Ni or alloy thereof which is a soft 
material can be used as the coating layer. 
The manufacturing process will hereinafter be described with reference to 
the drawings. 
First, as shown in FIG. 1A, the left and right mold sets are opened at a 
predetermined interval and the molten glass 4 is caused to flow down from 
the nozzle 2 into the space between the mold members 12 and 12' while the 
shearing machine 6 is maintained open. Then, the arrival of the lower end 
of the molten glass 4 at the downstream of the space between the mold 
members as shown in FIG. 1A is detected by a sensor, not shown. 
Subsequently, on the basis of the detection signal, the right mold set is 
advanced in the direction B until it bears against the stopper. With a 
very slight delay relative to this advancement, the left mold set is 
advanced in the direction A. Thereby, as shown in FIG. 1B, the molten 
glass is pressed correspondingly to a cavity formed by the pair of mold 
members 12, 12' and the pair of groove forming rings 18, 18'. At this 
time, as shown in FIG. 1B, the ends of the groove forming rings 18 and 18' 
are not in contact with each other but are spaced apart from each other by 
a spacing D and accordingly, on the left and right surfaces of the pressed 
molten glass, there are formed grooves around the portions thereof 
corresponding to the shaping surfaces 12a and 12a' of the mold members. 
Thus, a glass optical part body portion 30 is formed inside the grooves. 
Subsequently, as shown in FIG. 1C, the shearing machine 6 is closed and the 
molten glass 4 is cut. Thereby, an ear 32 protruding outwardly of the 
grooves is formed around the glass optical part body portion 30. 
The glass continues to be pressed until the glass temperature becomes lower 
than the strain point. In the meantime, the left mold set is not stopped 
by the stopper or the like, but continues to apply pressing pressure to 
the glass. 
Thereafter, as shown in FIG. 1D, the left and right mold sets are opened 
and further the shearing machine 6 is opened, and the molded article is 
removed. For this removal, a take-out robot, not shown, is utilized. 
As previously described, the right mold set is brought into contact with 
the stopper, whereafter the left mold set is advanced, whereby the cutting 
position of the glass flow flowing down from the nozzle can always be kept 
at a predetermined position. 
FIG. 2 is a front view showing the molded article obtained through the 
above-described steps, and FIG. 3 is a fragmentary schematic 
cross-sectional view thereof. 
In these figures, the reference numeral 30 designates the optical part body 
portion, the reference numeral 32 denotes the ear protruding outwardly 
thereof, and the reference numerals 34 and 36 designate grooves formed on 
the opposite surfaces of the body portion 30 between the body portion 30 
and the ear 32. The cross-sectional shape of the grooves is a wedge shape 
as shown in FIG. 3, and with respect to the direction parallel to the 
optic axis of the lens, the inner side and the outer side form angles 
.theta..sub.1 and .theta..sub.2, respectively, on the left surface side, 
and the inner side and the outer side form angles .theta..sub.1 ' and 
.theta..sub.2 ', respectively, on the right surface side. These angles 
are, for example, .theta..sub.1 =30.degree., .theta..sub.2 =15.degree., 
.theta..sub.1 '=45.degree. and .theta..sub.2 '=15.degree.. 
In the above-described process, the mold members 12 and 12' are 
PID-controlled to a fixed point temperature on the basis of the result of 
the temperature measurement by the thermocouples 24 and 24'. This fixed 
point temperature can be suitably set and changed. 
The molded article formed in the manner described above can be intactly 
incorporated into a lens barrel for use, or can be used with the ear 32 
removed thereafter. 
This removal can be mechanically accomplished with ease by producing a 
tensile stress at a desired location because the grooves 34 and 36 are 
formed. That is, the ear can be removed, for example, by applying a force 
thereto by fingers to thereby break the ear, or by a fall shock from a 
slight height, or by applying a force to the ear while supporting the body 
portion 30 by the use of a jig for exclusive use therefor. 
FIG. 4 is a fragmentary schematic cross-sectional view showing the optical 
part body portion 30 having its ear 32 removed. 
As shown, the optical part body portion 30 has on the outer peripheral 
portion thereof inclined surfaces 35 and 37 which are parts of the grooves 
34 and 36 and a broken-away surface 40 formed during the removal of the 
ear. The broken-away surface is formed at a desired location because 
during the removal of the ear, break occurs stably from the bottom of the 
groove 34 to the bottom of the groove 36. 
The inclined surfaces 35 and 37 just perform the function as the chamfered 
portions of the both surfaces of the optical part body portion 30. 
In the press described above, the left mold set is not stopped by the 
stopper or the like and therefore can apply pressing pressure uniformly to 
the glass until the glass is cured and the final shape of the molded 
article is determined, whereby without any drop being created on at least 
one surface, the accuracy of the shaping surfaces of the mold members can 
be transferred to the molded article sufficiently well. The right mold set 
can be supported at its stopped position by a sufficiently great force so 
that it may not retract relative to the pressing of the left mold set. 
The thickness of the molded article is determined by the viscosity of the 
molten glass supplied, the temperature of the mold members, the pressing 
pressure and other molding conditions, and a molded article of a desired 
thickness can be provided by suitably adjusting these. The viscosity of 
the molten glass supplied can be adjusted, for example, within the range 
of 10.sup.6 -10.sup.2 poise. The temperature of the mold members can be 
initially set, for example, to the range of the transition point to the 
strain point of the glass and thereafter be varied as required. The 
pressing pressure can be adjusted, for example, within the range of 1-500 
kg/cm.sup.2. 
The thickness of the molded article can also be adjusted by varying the 
projection amounts of the groove forming rings 18 and 18' from the shaping 
surfaces 12a and 12a' of the mold members, and the greater are the 
projection amounts, the greater becomes the thickness of the molded 
article. 
FIG. 5 is a cross-sectional view showing a modification of the 
above-described embodiment of the method of manufacturing a glass optical 
part according to the present invention. This figure corresponds to FIG. 
1B, and in this figure, members similar to those in FIG. 1B are given 
identical reference numerals. 
This modification differs from the embodiment of FIG. 1 only in that the 
groove forming ring is not provided around the right mold member 12' and 
the outer diameter of the mold member 12' is great. 
Also, in FIG. 5, there is shown a stopper 50 for setting the foremost stop 
position of the right mold set in the direction B. 
The result of the manufacture of a specific glass optical part carried out 
by the use of the method as described above will be shown below. 
EXAMPLE 1 
By the use of the apparatus shown in FIG. 1, but with the groove forming 
rings 18 and 18' removed therefrom, a concave meniscus lens of both 
spherical surfaces having an outer diameter of 16.0 mm.phi., a maximum 
light ray effective aperture of 14.8 mm.phi., a marginal thickness of 1.33 
mm and a thickness difference of 0.55 mm was manufactured as follows. 
The diameters of the mold members 12 and 12' were 16.0 mm.phi.. 
Dense flint glass having a transition point temperature of 455.degree. C. 
and a strain point temperature of 378.degree. C. was stabilized as a 
viscosity of 10.sup.5.1 poise and caused to flow down from the nozzle 2 of 
plantinum having an inner diameter of 15 mm.phi.. 
The press conditions were: the initial temperature of the mold members was 
360.degree. C., heating was stopped in 2 seconds after the start of press, 
the pressing pressure was 50 kg/cm.sup.2, the pressing time was 9 seconds 
and thereafter, the molded article was parted from the mold, and this 
press cycle was continuously effected. 
Thus, 600 molded articles were obtained. The opposite surfaces of the body 
portions of these molded optical parts are optical surfaces having no 
surface flaw and good in their external appearance, and the irregularity 
of the surface accuracy thereof was 3 newtons or less on the convex 
surface and was 1.5 newtons on the concave surface. Also, the irregularity 
of the thickness was .+-.0.09 mm. This is sufficiently practically usable 
as an optical lens. 
The molded articles obtained in this example can be made into optical 
lenses of an ordinary shape by effecting core removing work as desired. 
EXAMPLE 2 
By the use of the apparatus as shown in FIG. 5, a convex meniscus lens of 
both spherical surfaces having an outer diameter of 21.0 mm.phi., a 
maximum light ray effective aperture of 20.0 mm.phi., a marginal thickness 
of 1.78 mm and a thickness difference of 1.42 mm was manufactured as 
follows. 
The diameter of the mold member 12 was 21.0 mm.phi., the diameter of the 
mold member 12' was 26.0 mm.phi., and the projection amount of the end of 
the groove forming ring 18 was 1.20 mm. 
Dense flint glass having a transition point temperature of 430.degree. C. 
and a strain point temperature of 373.degree. C. was stabilized as a 
viscosity of 10.sup.4.7 poise and caused to flow down from the nozzle 2 of 
platinum having an inner diameter of 15 mm.phi.. 
The press conditions were: the initial temperature of the mold members was 
380.degree. C., the glass was at 330.degree. C. in 3.5 seconds after the 
start of press, the pressing pressure was 40 kg/cm.sup.2, the pressing 
time was 14 seconds and thereafter, the molded article was parted from the 
mold. 
The concave surface of the body portion 30 of the molded optical part thus 
obtained is an optical surface having no surface flaw and good in its 
external appearance, and the surface accuracy thereof was sufficiently as 
high as 1 newton or so. Also, the convex surface was of such a degree that 
some drops were seen in the central portion thereof. Accordingly, this 
optical part can be used well as a surface reflecting mirror with 
reflecting film formed on the concave surface thereof. Also, the optical 
part can be used as an optical lens with the convex surface thereof worked 
into better surface accuracy. 
Subsequently, the variation in the thickness of the molded article was 
measured with the projection amount of the end of the groove forming ring 
18 being varied. 100 times of molding were effected per the same 
projection amount. The result is shown in FIG. 8. 
As can be seen from FIG. 8, the thickness of the molded glass optical part 
can be adjusted by varying the projection amount of the groove forming 
ring 18 from the shaping surface 12a of the mold member. 
EXAMPLE 3 
By the use of the apparatus as shown in FIG. 1, a convex meniscus lens of 
both spherical surfaces having an outer diameter of 28.8 mm.phi., a 
maximum light ray effective aperture of 27.0 mm.phi., a marginal thickness 
of 2.18 mm and a thickness difference of 0.89 mm was manufactured as 
follows. 
The diameters of the mold members 12 and 12' were 28.8 mm.phi., and the 
projection amounts of the ends of the groove forming rings 18 and 18' were 
0.45 mm. 
Dense crown glass having a transition point temperature of 659.degree. C. 
and a strain point temperature of 602.degree. C. was stabilized as a 
viscosity of 10.sup.3.7 poise and caused to flow down from the nozzle 2 of 
platinum having an opening of 25 mm.times.5 mm. 
The press conditions were: the temperature of the mold members was 
550.degree. C., the pressing pressure was 18 kg/cm.sup.2, the pressing 
time was 8 seconds and thereafter, the molded article was parted from the 
mold. 
The opposite surfaces of the body portion 30 of the molded optical part 
thus obtained are optical surfaces having no surface flaw and good in its 
external appearance, and the surface accuracy thereof was 3 newtons or 
less. Also, the marginal thickness of the molded optical part was within 
.+-.0.05 mm relative to the target value 2.18 mm. 
In the above-described three examples, the setting of the pressing time was 
effected after it was measured and confirmed that the glass temperature 
becomes lower than the strain point during the lapse of the pressing time. 
As described above, the pressing operation was continued until the glass 
reaches a temperature below the strain point, whereby the transfer of the 
shape of the molded glass lens surface by the mold members was 
accomplished well. 
In the above-described examples, both the surfaces of the molded optical 
part are shown as being spherical, but of course, one or both of the 
surfaces can be made aspherical. 
As described above, according to the present invention, the glass continues 
to be pressed without the space between the pair of shaping mold members 
being closed until a temperature below the strain point of the glass is 
reached, to thereby obtain a glass molded article having an ear protruding 
outwardly relative to the optical part body portion formed between the 
shaping mold members, whereby it does not happen that during the press, 
dust is created and adheres to the shaping surfaces of the mold members to 
deteriorate the surface accuracy and thus, there is provided an optical 
part of good optical characteristic. Also, pressing pressure can be 
uniformly applied to the glass until the glass is cured and the final 
shape of the molded article is determined, whereby the accuracy of the 
shaping surfaces of the mold members can be sufficiently well transferred 
to the molded article without any drop being created on at least one 
surface and thus, an optical part of a desired shape and accuracy is 
easily obtained. 
A third form in which the present invention is carried out will hereinafter 
be described. 
FIG. 9 is a cross-sectional view schematically showing the process of a 
third embodiment of the method of manufacturing a glass optical part 
according to the present invention and the construction of mold members. 
In FIG. 9, the reference numeral 102 designates a molten glass outflow 
nozzle connected to a glass melting apparatus, not shown, and the 
reference numeral 104 denotes molten glass caused to flow down 
continuously from the nozzle 102. The reference numeral 106 designates a 
shearing machine (cutting edge) disposed just beneath the nozzle 102 for 
cutting the flowing-down molten glass 104 at suitable timing. 
The reference numerals 112 and 112' denote a pair of shaping mold members 
disposed on the opposite sides of the flowing-down molten glass, and in 
the present embodiment, it is for shaping a convex meniscus lens whose 
concave surface is aspherical. The reference characters 112a and 112a' 
designate the shaping surfaces of the mold members 112 and 112' for 
forming the both surfaces of the lens. The shaping surface 112a is 
finished as a mirror surface, and the shaping surface 112a' is finished as 
a ground surface. These mold members of a rotation-symmetrical shape and 
are disposed coaxially with each other with their shaping surfaces opposed 
to each other. A pair of mold sets are constructed including the 
above-described mold members 112 and 112'. 
The mold member 112 is of such structure that an outer piece 112-2 is 
slidably mounted on the outer periphery of an inner piece 112-1. The outer 
piece 112-2 is biased forwardly relative to the inner piece 112-1 by a 
compression spring 113. The outer piece 112-2 is formed with a 
crank-shaped guide groove 114 with which a guide pin 115 projectedly 
provided on the inner piece 112-1 is engaged and restrained. 
As the mold members 112 (the inner piece 112-1 and the outer piece 112-2) 
and 112', use can be made of a shaping surface of Ni group heat resisting 
alloy base material grounded and finished into surface roughness Rmax 0.01 
.mu.m and a desired shape and accuracy, and coated with a nitride ceramics 
coating layer having a thickness of about 0.8 .mu.m. As the mold base 
material, use can also be made of Mo group heat resisting alloy, Fe group 
heat resisting alloy, stainless heat resisting alloy, No, Ta, carbon, a 
carbon composite material or the like. The coating layer is used to make 
up for the hot strength of the base material, and besides nitrides such as 
BN, TiN and AlN, carbides such as TiC, SiC and TaC or C (diamond) or 
others can be used for the coating layer. These can be attached by the use 
of various film forming techniques. This coating layer need not be a 
single layer, but may be provided with an intermediate layer to improve 
the contact strength and the heat resisting property. In the case of a 
coating layer formed by the CVD method, treatment such as super-precision 
grinding or polishing can be applied to make the surface of the coating 
layer itself into good surface accuracy. Further, where the hot strength 
of the base material is great and the shape accuracy can be maintained 
even though press shaping is effected a sufficient number of times, 
platinum, platinum alloy, Ni or an alloy thereof which is a soft material 
can be used for the coating layer. 
In the left mold set, the inner piece 112-1 of the shaping mold member 112 
is mounted on a mounting member 116. 
A heater 122 and a thermocouple 124 for temperature measurement are 
contained in the inner piece 112-1 of the mold member 112. 
Although not shown, the mounting member 116 is supported for reciprocal 
movement in the directions of arrows A and B by a base stand, not shown. 
This reciprocal movement is effected by driving means, not shown. 
On the other hand, in the right mold set, the shaping mold member 112' is 
mounted on a mounting member 116'. A groove forming ring 118' is mounted 
around the mold member 112' by a bolt. The end of the ring 118' is formed 
into the shape of a cutting edge and protrudes from the shaping surface 
112a' of the mold member 112' by a suitable amount. In some cases, the 
groove forming ring is not mounted. 
A heater 122' and a thermocouple 124' for temperature measurement are 
contained in the mold member 112'. 
Although not shown, the mounting member 116" is supported for reciprocal 
movement in the directions of arrows A and B by a base stand, not shown. 
This reciprocal movement is effected by driving means, not shown. However, 
in the right mold set, the foremost stop position in the direction B is 
set by a stopper, not shown. The above-mentioned stop position can be 
suitably set by making the position of the stopper variable and adjusting 
the position thereof. 
The manufacturing process will hereinafter be described with reference to 
the drawings. 
First, as shown in FIG. 9A, the left and right mold sets are opened at a 
predetermined interval and the molten glass 104 is caused to flow down 
from the nozzle 102 into the space between the mold members 112 and 112' 
while the shearing machine 106 is maintained open. At this time, as shown 
in FIG. 9B, the crank-shaped groove 114 formed in the outer piece 112-2 of 
the mold member 112 is engaged by the guide pin 115 projectedly provided 
on the inner piece 112-1, and the outer piece 112-2 is in the foremost 
position in the direction A relative to the inner piece 112-1. The arrival 
of the lower end of the molten glass 104 at the location below the space 
between the mold members as shown in FIG. 9A is detected by a sensor, not 
shown. 
Subsequently, on the basis of the detection signal, the right mold set is 
advanced in the direction B until it bears against the stopper. With a 
very slight delay with respect to this advancement, the left mold set is 
advanced in the direction A. Thereby, as shown in FIG. 9C, the molten 
glass is pressed correspondingly to a cavity formed by the pair of mold 
members 112, 112' and the groove forming ring 118'. At this time, as shown 
in FIG. 9C, the end of the groove forming ring 118' is not in contact with 
the mold member 112, but is spaced apart from the latter by a suitable 
spacing. Also, at the initial stage of press, the viscosity of the glass 
is relatively low and therefore, the compression spring 113 is not 
compressed any further and the outer piece 112-2 is at the foremost 
position in the direction A relative to the inner piece 112-1. 
Subsequently, as shown in FIG. 9D, the shearing machine 106 is closed and 
the molten glass 104 is cut. Further, with the progress of press, between 
the mold members, the glass is cured in succession from its thinner outer 
peripheral portion to its central portion and therefore, the foremost 
position of the outer piece 112-2 is first determined, and then the inner 
piece 112-1 is further advanced against the force of the compression 
spring 113 to thereby press the uncured central portion of the glass. 
Thereby, sufficiently good surface accuracy is obtained without any drop 
being created on the surface (the spherical surface) of the molded article 
corresponding to the shaping surface 112a' of the mold member 112'. The 
pressing pressure can be initially set to a relatively low value and be 
gradually or stepwisely varied to relatively high values. 
Thereby, there is provided a molded article of such a shape that an ear 132 
formed by the groove forming ring 118' protrudes outwardly of the glass 
optical part body portion 130. 
Press is continued until the temperature of the glass becomes lower than 
the strain point. In the meantime, the left mold set continues to apply 
pressing pressure to the glass without being stopped by the stopper or the 
like. 
Thereafter, as shown in FIG. 9E, the left and right mold sets are opened 
and further the shearing machine 106 is opened, and the molded article is 
removed. For this removal, a take-out robot, not shown, is utilized. At 
this time, the outer piece 112-2 is brought back to the foremost position 
in the direction A relative to the inner piece 112-1 by the compression 
spring 113. 
FIG. 10 is a front view showing the molded article obtained through the 
above-described steps. 
In the above-described process, the mold members 112 and 112' are 
PID-controlled to a fixed point temperature on the basis of the result of 
the temperature measurement by the thermocouples 124 and 124'. The fixed 
point temperature can be suitably set and changed. 
The molded article formed in the manner described above can be incorporated 
into a lens barrel for use without the ear 132 being removed, or can be 
used with the ear 132 removed. 
This removal can be mechanically accomplished with ease by producing a 
tensile stress at a desired location because the groove 134 is formed. 
That is, the ear can be removed, for example, by applying a force thereto 
by fingers to thereby break the ear, or can be removed by a fall shock 
from a slight height, or can be removed by applying a force to the ear 132 
while supporting the body portion 130 by the use of a jig for exclusive 
use therefor. 
Also, the molded article formed in the manner described above can be used 
as a surface reflecting mirror with reflecting film being formed on the 
aspherical surface side thereof and without the other surface side being 
worked, and can be used as an aspherical lens by the other surface side 
being worked into a desired shape and accuracy and made into a desired 
thickness. 
In the above-described press, the left mold set is not stopped by the 
stopper or the like and the inner piece 112-1 of one mold member 112 is 
moved at a greater stroke than the outer piece 112-2 and therefore, 
pressing pressure can be well applied to the glass until the glass is 
cured and the final shape of the molded article is determined, whereby the 
accuracy of the shaping surface of one mold member can be sufficiently 
well transferred to the molded article without any drop being created. The 
inner piece 112-1 and the outer piece 112-2 can be driven by discrete 
hydraulic cylinders, and the right mold set can be supported in its 
stopped position with a sufficiently great force so that it may not be 
retracted relative to the pressing of the left mold set. 
The thickness of the molded article is determined by the viscosity of the 
molten glass supplied, the temperature and pressing pressure of the mold 
members and other molding conditions, and by suitably adjusting these, 
there can be provided a molded article of a desired thickness. The 
viscosity of the molten glass supplied can be adjusted, for example, 
within the range of 10.sup.6 -10.sup.2 poise. The temperature of the mold 
members can be initially set to the range of the transition point to the 
strain point of the glass and thereafter can be varied as required. The 
pressing pressure can be adjusted, for example, within the range of 1-500 
kg/cm.sup.2. 
The thickness of the molded article can also be adjusted by varying the 
projection amount of the groove forming ring 118' from the shaping surface 
112a' of the mold member 112', and the greater is the projection amount, 
the greater becomes the thickness of the molded article. 
The result of the manufacture of a specific glass optical part carried out 
by the use of the method as described above will be shown below. 
EXAMPLE 
By the use of the apparatus as shown in FIG. 9, a convex meniscus lens 
whose concave surface is a rotation-symmetrical aspherical surface and 
having an outer diameter of 25.6 mm.phi., a maximum light ray effective 
aperture of 23.4 mm.phi., a marginal thickness of 1.02 mm and a thickness 
difference of 1.29 mm was manufactured as follows. 
Dense flint glass having a transition point temperature 430.degree. C. and 
a strain point temperature 373.degree. C. was stabilized as a viscosity of 
10.sup.4.0 poise and caused to flow down from the nozzle 102 of platinum 
having an inner diameter of 15 mm.phi.. 
The pressing conditions were: the temperature of the mold members was 
330.degree. C., the pressing pressure was initially 10 kg/cm.sup.2 and 40 
kg/cm.sup.2 in 7 seconds after the start of press, the pressing time was 
18 seconds, and when this time elapsed, the temperature of the mold 
members reached 360.degree. C. and the molded article was parted from the 
mold. 
The ear of the molded article obtained in the manner described above was 
removed and the shape of the convex surface side thereof was measured with 
a result that the accuracy of the spherical surface corresponding to the 
shaping surfaces of the outer piece and inner piece was as good as 2 to 3 
newtons relative to the mold, and the level difference of the boundary 
between the inner piece and the outer piece was 2.2 .mu.m. However, since 
such level difference existed in the light ray effective aperture, the 
grinding, lapping and polishing of the convex surface side were further 
effected and the core-removing work was carried out. 
When the surface accuracy of the aspherical surface of the thus obtained 
aspherical lens was measured, it was found that the shape accuracy of the 
shaping surfaces of the mold members was sufficiently well transferred to 
said aspherical surface. Also, when the evaluation of the imaging of the 
aspherical lens was done, it was found that a sufficiently practical 
performance was obtained, and the uniformity of the refractive index of 
the lens was also good. 
In the present embodiment, use is made of the mold member 112 whose shaping 
surface 112a is mirror-surface-worked to predetermined accuracy, but where 
the lens surface corresponding to this shaping surface is further worked 
after the termination of press, the shaping surface of one or both of the 
inner piece 112-1 and the outer piece 112-2 can be made into a rough 
surface. 
In the above-described embodiment, there is shown a case where the molded 
optical part is aspherical on one surface thereof, but of course, both 
surfaces can be made aspherical or spherical. 
As described above, according to the present invention, the molten glass 
continues to be pressed without the space between the pair of shaping mold 
members being closed until a temperature below the strain point of the 
glass is reached, and a glass molded article having an ear protruding 
outwardly of the optical part body portion formed between the shaping mold 
members is obtained, whereby during press, no dust is created and 
therefore it does not happen that any dust adheres to the shaping surfaces 
of the mold members to deteriorate the surface accuracy, and thus, there 
is obtained an optical part of good optical characteristic. Also, the 
pressing pressure can be uniformly applied to the glass until the glass is 
cured and the final shape of the molded article is determined, and 
particularly the plurality of constituent members of one mold member are 
moved at different strokes and in the course of molding, the glass in that 
portion thereof wherein drops may be created can be partially additionally 
pressed and thus, without any drop being created, the accuracy of the 
shaping surface of one mold member can be sufficiently well transferred to 
the molded article, and there can be easily obtained an optical part of a 
desired shape and accuracy.