JP2002128535A - Forming method of glass gob for optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a minute weighted glass gob with a smooth surface and less variation in weight that can be used as a forming material for an optical element. SOLUTION: An optical glass 3 melted in an optical glass crucible 1 continuously outflows from an outlet 5 of melted glass outflow pipe 4. Transfer speed of the melted glass is controlled to keep desired value using a glass flow transfer control devise 7 by contacting the outer part of melted glass outflowing from the outlet and at the same time the cross sectional area of melted glass is controlled by changing the area, and a glass rod 8 with desired cross sectional area against the glass flow is formed. Then the glass rod is cut into desired length with thermal shock by contacting a cutting blade 9 with ultra low temperature, and a glass gob 11 for optical element is produced. The glass gob 11 is globe shaped by a floating/heating devise 12 and pressed/formed to produce a lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a glass lump for an optical element, and more particularly to a method for obtaining a glass lump which is a material for press molding, particularly a minute glass lump, from a molten optical glass. The present invention relates to a method for forming a glass block.

[0002]

2. Description of the Related Art In recent years, a technique for obtaining an optical element by press-molding a glass lump has been proposed. However, the glass lump used here has a smooth surface and a uniform weight. is necessary. In the past, glass preforms as optical element materials were made by polishing optical glass, but recently, in order to reduce the cost, a technique of directly molding from molten optical glass has been used. Is being developed. These cases are described below.

[0003] First, as a first conventional example, a porous receiving mold is disposed below an outlet of molten glass, and a molten glass flow is received in a state where gas is jetted from a glass receiving surface of the receiving mold. A technique is known in which a required amount is separated from a molten glass flow while a molten glass and a receiving mold are kept in a non-contact state via a gas layer, and this is cooled to obtain a desired glass block. The glass lump thus obtained has a free surface on the upper surface and is smooth because it is cooled as it is, and the lower surface is also smooth because it is cooled in the non-contact state described above. As this conventional method, a method described in Japanese Patent Publication No. 54-39846 can be exemplified.

Subsequently, as a second conventional example, gas is blown out from the lower part of a funnel-shaped jig, and molten glass droplets are dropped from above onto the funnel-shaped jig in this state.
A method is known in which the molten glass droplet is rotated in a floating state by a gas jet from below in a funnel-shaped jig, and is turned into a spherical glass lump in a cooling process. The entire surface of the glass block thus obtained is held as a free surface, so that the surface becomes smooth during the cooling process. As a conventional example of this method, there is a method described in Japanese Patent Publication No. 7-5146.

[0005] In addition, as a third conventional example, a glass lump is crushed, and the glass fragments are re-melted in a high-temperature atmosphere while being kept floating in the air by a gas flow from below. A so-called blow-up method is known in which the entire glass block is formed into a spherical shape using the surface tension. This method has been used for a long time to produce fine glass beads used for road signs,
"Glass Handbook" (Asakura Shoten, published in 1975,
This method is described on page 275 of “Sakuhana et al.” And on page 168 of “Glass Encyclopedia” (Asakura Shoten, 1985, edited by Sakuhana).

[0006]

However, the above-mentioned prior art has the following drawbacks. That is, the first
A disadvantage of the second conventional example is that it is not possible to obtain a small mass of glass. That is, since the molten glass flow is received in the porous receiving mold to obtain a glass lump, the minimum weight of the obtained glass lump is the diameter of the molten glass outlet, the molten glass droplet limited by the glass surface tension, and the like. It turns out that it becomes weight (a considerable weight). Similarly, in the second conventional example, similarly, the minimum weight of the obtained glass lump is the weight of the molten glass droplet, so that a small weight of glass lump cannot be obtained.

Here, the following relationship exists between the outer diameter of the outlet of the pipe from which the molten glass flows out and the weight of the molten glass droplet.

2πrγ = mg where r is the radius of the outlet (outer diameter) of the molten glass outflow pipe, γ is the surface tension of the molten glass, and m is the mass of the glass droplet.

For example, if the surface tension is 0.2 N / m (200
When the calculation is performed on the glass of (dyne / cm), a relationship of m (g) = 0.12 × r (mm) is obtained.

That is, pipe inner diameter: 1 mm, pipe wall thickness:
In the case of 0.5 mm, the glass droplet weight is 0.12 g, and when the pipe inner diameter is 2 mm and the pipe wall thickness is 1 mm, the glass droplet weight is 0.24 g, and the pipe inner diameter is 8 mm. When the pipe thickness is 1 mm, the glass droplet weight is 0.6 g.

On the other hand, it is known that the surface tension of molten glass is determined by the composition ratio of the glass.
This is known as the additive law in surface tension,
Among them, the surface tension factor by Dietzel is well known. According to this, among optical glasses, the surface tension of SK-based or SF-based glass is 0.2 N / m (200 d).
yne / cm), but it is as high as 0.6 N / m (600 dyne / cm) for lanthanum-based glass. That is, when a glass droplet of a lanthanum-based optical glass is to be obtained by the above-described method, the weight is almost tripled.

That is, in the above conventional example, the weight of the glass droplets can be changed by the thickness of the glass outflow pipe. However, if the pipe is too thin, it is difficult to actually use the pipe because of its strength. For example, a pipe having an inner diameter of 1 mm and a wall thickness of 0.5 mm is not suitable for practical use. Therefore, in the above-mentioned conventional technology, it is substantially difficult to produce a glass lump having a weight of 0.2 g or less, particularly, a lanthanum-based optical glass having a weight of 0.5 g or less. .

[0013] On the other hand, in the third prior art, a minute weight glass chunk can be obtained by re-melting a minute weight glass shard and forming it into a spherical shape. Therefore, there is a point that the weight variation of the glass block becomes large, and it is necessary to carry out weight selection in advance.

The present invention has been made on the basis of the above circumstances, and a first object of the present invention is to provide a glass body having a very small weight, particularly a smooth glass surface, which has been difficult with the prior art. The purpose is to form a glass lump which can be used as a material for forming an element and has a small variation in weight.

A second object of the present invention is a substantially spherical glass block which is optimal as a material for molding a biconvex lens, a convex meniscus lens, or a concave meniscus lens. An object of the present invention is to provide a molding method capable of molding a minute weight that has been difficult to produce.

A third object of the present invention is to obtain a small-weight optical element, which has been difficult in the prior art, by press-forming a small-weight glass block, which was difficult in the prior art. It is.

It is a fourth object of the present invention to obtain a finer glass lump which is smaller than a conventionally obtained small glass lump.

A fifth object of the present invention is to produce glass blocks of various weights and shapes by using one glass block manufacturing apparatus.

[0019]

In order to achieve the above object, according to the present invention, optical glass melted inside an optical glass melting crucible is continuously discharged from an outlet of a molten glass outflow pipe, and the molten glass is melted. The glass flow moving device is brought into contact with the outer peripheral portion of the molten glass flow flowing out of the glass outlet,
By controlling the movement of the glass flow moving device, the moving speed of the molten glass flow is controlled to a desired value, and at the same time, the cross-sectional area of the molten glass flow flowing out of the molten glass outlet is changed to a desired cross-sectional area. By doing so, a glass rod having a desired cross-sectional area in the moving direction of the molten glass flow is obtained, and the glass rod is cut into a desired length to obtain a glass lump for an optical element.

The diameter of the glass lump thus obtained is controlled by the moving speed of the glass and the length thereof is controlled by the cutting position, so that its weight is controlled and its weight variation is reduced. Few.

In this case, the above-mentioned glass lump is guided into a gas stream, floated, heated while maintaining the floating state, and the surface of the glass lump is softened. Into a spherical shape,
Further, by heating and softening the above-mentioned glass lump and press molding using a predetermined mold, to obtain a molded optical element,
Each is preferable as an embodiment of the present invention.

Further, in the present invention, in the above-mentioned method for forming a glass lump for an optical element, the moving speed of the glass flow controlled by the glass flow moving device may be set such that the molten glass flowing out of the molten glass outlet is discharged. Being faster than the outflow speed of the molten glass, and making the moving speed of the glass flow controlled by the glass flow moving device slower than the outflow speed of the molten glass when flowing out of the molten glass outlet, the size of the formed glass block It is effective in controlling the length.

Here, if the moving speed of the glass flow to be controlled is made higher than the outflow speed of the molten glass flowing out of the molten glass outlet, the molten glass flow is generated between the molten glass outlet and the glass flow moving device. , And its cross-sectional area becomes smaller. Conversely, if the moving speed of the controlled glass flow is made slower than the outflow speed of the molten glass flowing out of the molten glass outlet, the molten glass flow stays between the molten glass outlet and the glass flow moving device. , Its cross-sectional area increases. In particular, by setting the surface temperature of the glass flow to a temperature lower than the yield point temperature of the glass at a position where the glass flow and the glass flow moving device are in contact, a contact mark of the glass flow moving device remains on the surface of the glass flow. Nothing.

In the above-described method for forming a glass lump for an optical element, a step of cutting a glass rod having a desired diameter into desired lengths to obtain a desired glass lump includes the steps of: A thermal shock is applied to the position, and a cutting method is used in which a fracture surface is formed in this portion. Alternatively, a crack (notch) is formed in a desired position of the glass rod in advance, and an external force is applied to this portion. It is effective to use a cutting method in which stress is concentrated on the crack portion and this portion is cut as a fracture surface. In addition, as a method of forming a crack in advance, there is a method of forming a crack shape on a softened glass rod, a method of grinding a solidified glass rod with a diamond blade or the like, and forming a crack shape.

When the thus obtained glass rod is cut to a desired length in the fractured surface to obtain a glass lump, the surface of the cut surface is smooth, and as a result, the entire glass lump is smooth. It is suitable as a material for optical elements.

In the embodiment of the present invention, the glass flow moving device controlled by the glass flow moving device is:
By increasing the speed of the molten glass flowing out from the molten glass outlet, reducing the cross-sectional area of the glass flow, and cutting this glass rod short, compared to the glass block obtained from the conventional molten glass droplet, It is possible to obtain a much smaller glass mass of very small weight. Further, in the embodiment of the present invention, a cylindrical glass block can be applied as a material for forming an optical element for forming a biconcave lens.

As described above, the shape of the roughly spherical glass lump obtained by heating and softening the glass lump while flowing and deforming the glass lump is determined by the surface tension of the glass, the size of the glass lump, the jig and the mold. Varies with configuration. In particular, in the case of a glass lump having a large surface tension and a light weight, a substantially spherical glass lump can be obtained, but in other cases, a material for molding a biconvex, convex meniscus, or concave meniscus lens Thus, a flat, roughly spherical glass block suitable for the above is obtained. Then, in order to deform the glass block into a substantially spherical shape, the temperature of the glass is set to 10 ⁴ to 1 by its viscosity.
^0-7 range, it is desirable to heat. According to this method, it is possible to obtain a glass block having a substantially spherical shape with a small weight, which is difficult to obtain with the conventional technique.

Here, the means for heating the glass lump floating in the gas flow includes a method of heating while floating with a high-temperature gas and a method of bringing a high-temperature heating device close to the floating glass lump. There is a method of focusing infrared rays on a glass lump, and a method of placing a floating glass lump in a high-temperature atmosphere.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, a first embodiment according to the present invention will be described. Here, the molten glass flow is moved by a glass flow moving device at a speed higher than the outflow speed, the glass flow is made thinner, and the thinned glass rod is brought into contact with a thermal shock cutting device kept at a low temperature, This glass rod is cut at the fracture surface, and the obtained cylindrical glass lump is dropped into a floating heating jig installed thereunder, and high-temperature gas is blown out from a lower portion of the floating heating jig. With this high-temperature gas, the cylindrical glass block is kept in a floating state, heated and softened, deformed into a substantially spherical shape, and the obtained roughly spherical glass block is used as a forming material, and a forming optical element is formed. You get.

FIG. 1 is a schematic sectional view for explaining the structure of an apparatus for producing a glass lump in the first embodiment, and FIG. 2 is a schematic view for explaining the structure of a glass flow moving apparatus. FIG. 3 is a plan view schematically illustrating the configuration of the thermal shock cutting device.

Here, reference numeral 1 denotes a glass melting crucible, 2 denotes an electric furnace, 3 denotes molten optical glass, 4 denotes a molten glass outflow pipe, 5 denotes a molten glass outlet, 6 denotes a molten glass flow, and 7 denotes a glass flow moving device. Reference numeral 8 denotes a glass rod having the molten glass flow 6 solidified, 9 denotes a cutting blade of the thermal shock cutting device, 10 denotes a driving device of the thermal shock cutting device, 11 denotes a cylindrical glass block, 12 denotes a floating heating jig, and 13 denotes a heating jig. A high-temperature gas producing apparatus, 14 is a roughly spherical glass block, 15 is a rotary table, and 16 is a rotating device. In FIG. 3, reference numeral 17 denotes a cooling pipe of a cutting blade of the thermal shock cutting device.

A case where the method of forming a glass lump according to the present invention is specifically realized by using the apparatus having such a configuration will be described. First, a glass raw material is put into the glass melting crucible 1, and the glass raw material is heated and melted inside the electric furnace 2. Thus, the molten optical glass 3 melted
Passes through a molten glass outflow pipe 4 installed at the lower part of the glass melting crucible 1 and continuously flows out of a molten glass outlet 5 as a molten glass flow 6.

The glass flow moving device 7 is placed below the molten glass flow 6, that is, at a position where the temperature of the surface is lower than the yield point temperature of the glass.
And the moving speed of the molten glass flow is controlled to be faster than the outflow speed at the outlet of the molten glass flow.

As shown in FIG. 2, the glass flow moving device 7 contacts three driving rollers around the molten glass flow 6 from three places in the outer peripheral direction thereof, and controls the rotation speed of the driving rollers. By doing so, the glass flow moving speed is controlled. Also, the size of the gap formed by the three drive rollers, in other words, the thickness of the molten glass flow passing therebetween is controlled in relation to the rotation speed of the drive rollers.

When the molten glass flow 6 is made faster than the flow rate of the molten glass at the outlet by controlling the rotation of the driving roller of the glass flow moving device 7, as shown in FIG. After exiting the molten glass outlet 5,
In the process of flowing to the position of the drive roller, its thickness becomes thin.

In this way, by moving the molten glass stream 6 at a controlled and desired speed, a glass rod 8 having a desired thickness is continuously formed. , And cut by the thermal shock cutting device 8. As shown in FIG. 3, the cutting blade 9 of the thermal shock cutting device is configured as a pair of blade-shaped thin plates at positions sandwiching the glass rod 8, and the surface of the cutting blade 9 is provided with the cutting blade 9. A cooling pipe 17 through which a refrigerant for cooling the cooling pipe 9 flows is provided. Also,
The cutting blade 9 can be moved forward and backward by the driving device 10 of the thermal shock cutting device so as to come into contact with the glass rod 8.

As described above, when the glass rod 8 exits from the outlet, it is rapidly cooled from a molten state, so that the surface has a large residual thermal stress, and the temperature of the glass rod 8 is relatively high. The cold cutting blade 9 is brought into contact with the glass rod, and thermal strain concentrates on this portion due to a thermal shock, and the glass rod is cut as a fracture surface.

Therefore, as described above, the glass flow moving device 7
Is cut at a desired interval by using a thermal shock cutting device, whereby a cylindrical glass rod 11 having a desired thickness and length is obtained. The cylindrical glass ingot 11 thus obtained has smooth cylindrical side surfaces and a cut surface composed of a fractured surface.

A floating heating jig 12 is provided immediately below the glass rod cutting device including a pair of cutting blades 9, and the cylindrical glass block 11 cut by the thermal shock cutting device is lifted. It falls into the heating jig 12.

As shown in FIG. 1, the floating heating jig 12 has a conical concave portion, and a gas outlet is provided at the apex of the conical portion, that is, at the bottom of the concave portion. A high-temperature gas heated by the high-temperature gas producing device 13 is jetted from the gas jet port.

Thus, the cylindrical glass lump 11 rotates inside the conical concave portion of the floating heating jig 12 while being floated by the high-temperature gas spouted from the gas spout. As described above, the glass lump 11 is heated while being floated and rotated by the high-temperature gas. When the glass lump is heated to a viscosity in the range of 10 ⁴ to 10 ⁷ dPa · s, the glass lump flows and deforms due to its surface tension, and its surface shape is roughly rounded to a spherical shape. After the spherical glass block 14 is thus formed, the temperature of the gas ejected from the gas ejection port is reduced, and the temperature of the spherical glass block 14 is reduced. Take out.

Here, a plurality of floating heating jigs 1 are used.
2 are arranged on the rotary table 15 in the circumferential direction, and the rotating device 16 rotates to receive the cylindrical glass lump 11 into the floating heating jig 12, and the cylindrical glass lump 11 11 is heated in a floating state, and the surface tension is used to substantially deform the glass block into a spherical shape, and thereafter, the step of taking out the obtained spherical glass block 14 is continuously performed.

The optical element is formed by using the thus obtained roughly spherical glass block 14 as a material for forming an optical element. That is, this glass lump 14 is put into a pair of upper and lower molding dies (not shown), and these are heated to a desired temperature, and when they are in a softened state, press-molded to form a molding optical element (not shown). ).

[0044]

Embodiment (Embodiment 1) Hereinafter, embodiments of the present invention will be described more specifically by showing embodiments of the present invention. In this embodiment, an optical glass having optical characteristics equivalent to LaK12 is charged into a glass melting crucible 1 made of platinum as a material of the optical glass, the electric furnace 2 is heated to 1000 ° C., and the glass outflow pipe 4 is Spilled downward through. At the outlet 5 of the outlet pipe, the inner diameter of the outlet pipe is 1 mm and the outer diameter is 2 mm. The glass outflow pipe 4 was kept at 900 ° C. to discharge the glass. Outlet 5
, A molten glass flow at 900 ° C. continuously flowed at a rate of 2.0 g / min.

In this embodiment, the glass flow moving device 7 is installed at a position 400 mm below the molten glass outlet 5. At this position, the surface temperature of the molten glass stream has been cooled to 500 ° C. and has a yield point temperature of 530.
Lower than ° C. As shown in FIG. 2, the glass flow moving device 7 includes three drive rollers, which are made of, for example, carbon, the diameter of the roller is 30 mm, and the cylindrical side surface of the roller is R =
It is processed into the shape of a gentle round groove of 50 mm. The rollers are controlled to a desired rotation speed by a servomotor, and the size of the gap formed by the three rollers is adjusted to a desired size by a roller position adjustment mechanism (not shown).

In this example, the rotation speed of the roller was set at three revolutions per minute, and the gap formed by the roller was set at 1.5 mm. As a result, from the lower part of the glass flow moving device 7 composed of the rollers, a glass rod having a diameter of 1.5 mm
Discharge at a rate of 270 mm per minute. Here,
A molten glass flow having a diameter of 2.0 mm flows out at a rate of 165 mm per minute from the molten glass outlet 5, and as shown in FIG. It becomes thin at the position of 30 mm, and is finally discharged from the lower part of the glass flow moving device 7 as a glass rod having a desired thickness.

100 m below the glass flow moving device 7
At the position of m, a glass flow cutting device by thermal shock is installed. This glass flow cutting device, as shown in FIG.
Two V-shaped cutting blades 9 sandwich the glass rod 8,
It is installed at a position facing left and right, and can be moved in a forward and backward direction by a driving device 10 including an air cylinder. Further, a cooling pipe 17 is provided on the cutting blade 9, and liquid nitrogen flows therein. Therefore, the cutting blade 9 is always kept at an extremely low temperature.

When the cryogenic cutting blade 9 is brought into contact with the glass rod 8, a thermal shock is generated on the glass rod, and a crack is formed from the contact portion of the blade with a broken surface, and the glass is cut at this portion. At this time, the surface temperature of the glass rod 8 is about 400 ° C., the temperature difference with the cutting blade 9 is large, and the surface of the glass rod comes out of the molten state in the air and is rapidly cooled. Large residual thermal stress. For this reason, by bringing such a very low temperature cutting blade 9 into contact, it is possible to reliably cut from this part by thermal shock.

In this embodiment, a cutting blade 9 is cut into the glass rod 8 discharged from the glass flow moving device 7 every 0.5 seconds, and the glass rod 8 is cut to form a cylindrical glass block 11. Obtained. This glass lump 11 has a diameter of 1.5 mm and a length of:
2.0 mm. The cylindrical glass block 11 thus obtained is formed as a smooth surface both on the side surface and on the upper and lower cut surfaces. The temperature of the cylindrical glass block 11 immediately after cutting was 300 ° C.

The average weight of the glass lump 11 thus obtained was 0.014 g, which was very small. On the other hand, the weight variation of this glass lump was small, and the standard deviation was σ, which was 0.0005 g at 3σ.

The glass block 11 thus cut falls into the floating heating jig 12. In this embodiment, the floating heating jig 12 is made of carbon, and a heater for heating (not shown) is installed in the inside thereof, and is constantly heated to 500 ° C. Also, in this embodiment,
The shape of the conical recess in the floating heating jig 12 is as follows:
The diameter of the maximum diameter (upper part) is 10 mm and the inclination angle is 60
Was ゜. At the center of the conical concave portion, a high-temperature gas injection port having a diameter of 0.8 mm for discharging high-temperature gas is opened, and a high-temperature gas supply device 13 including a platinum wire heater is installed here. Where nitrogen gas is 1
Heat to 000 ° C.

Then, the glass lump 11 dropped into the floating heating jig 12 is raised by a nitrogen gas at 1000 ° C., and is heated in that state. 15 minutes after the start of ascent and heating
In seconds, the temperature of the glass mass 11 reached 700 ° C. This temperature was equivalent to 10 ⁷ dPa · s in terms of the viscosity of the glass, and the glass was in a softened state, and the surface was spheroidized by the action of surface tension.

In this state, if the state was further maintained for 10 seconds, the spheroidization was almost completed, and the glass lump was roughly formed into a spherical shape. Here, the heating of the platinum wire heater of the high-temperature gas supply device 13 was stopped. Then, after 10 seconds, the temperature of the spherical glass block 14 dropped to 500 ° C. After that, the spherical glass block 14 thus obtained is
It was taken out of the floating heating jig 12 by an automatic hand (not shown). In the step of floating and heating the glass lump 11 to obtain a roughly spherical glass lump 14,
The glass lump is floated and held by the ejected gas, and at the same time, is kept in a state of being rotated in the recess of the floating heating jig 12.

Thus, the roughly spherical glass block 14
After this was obtained, this was press-molded with a known molding die to obtain a biconvex lens as an optical element. That is, a pair of upper and lower molding dies (not shown) was prepared. These are made of a cemented carbide, and after the formed surface is polished, a platinum-based protective film is formed on the surface. The shape of the molding surface is as follows: diameter: 3 mm, radius of curvature of the upper mold: 20 mm,
The radius of curvature of the lower mold was 50 mm.

Then, in a known molding device (not shown) kept in a nitrogen atmosphere, a pair of upper and lower molding dies is
After setting the glass blocks 14, they were heated to 600 ° C. and press-molded with a force of 500N. Then, while maintaining the above state, cooling was performed, the mold was opened at 400 ° C., and a molded lens (not shown) as an optical element was taken out.

The lens thus obtained has a shape and
The precision was good, there were no scratches on the appearance, no striae inside and on the surface of the glass, and the quality was very suitable as an optical element.

(Comparative Example 1) Here, the size of the glass lump obtained in the present embodiment and the size of the glass lump obtained by the conventional method will be described with reference to a comparative example. In the traditional way,
A molten glass droplet (not shown) was obtained using the apparatus described in FIG. Therefore, the molten glass outflow port 5 of the molten glass outflow pipe 4 has an outer diameter of 2 mm, and when a glass equivalent to LaK12 flows out, its surface tension is large.
The weight of the droplet is 0.35 g, which is much larger than the weight of the roughly spherical glass block 14 of 0.014 g obtained in this example.

Therefore, according to the present embodiment, it is possible to obtain a molding material having a minute shape which cannot be obtained conventionally. That is, the following points are specific to the present embodiment. 1. With the conventional technology, it is possible to form a roughly spherical glass block with high weight accuracy at a small weight, which could not be obtained directly from molten glass, by continuous production from molten glass at low manufacturing cost. Can be. 2. A molded optical element can be obtained by press-molding the roughly spherical glass block of this minute weight as a raw material for molding, thereby making it difficult to manufacture the conventional optical element. Can be obtained. Such a micro optical element is 1/5 inch C
The optical system can be further miniaturized by using it in the optical system of an optical device using a small light receiving element such as a CD. 3. In the present embodiment, since the cylindrical glass block is formed on a smooth surface all around, by floating and heating,
The resulting substantially spherical glass block is also formed with a smooth surface all around. Accordingly, a lens obtained by press-molding the lens is excellent in shape accuracy and appearance accuracy, and is of high quality.

(Embodiment 2) In the second embodiment, the molten glass flow is moved at a speed higher than the outflow speed by a glass flow moving device, and the glass flow is made thinner. After mechanically forming a crack (notch), a bending force is applied to the glass rod by using the cracked portion as a fractured surface, and the glass rod is cut to obtain a cylindrical glass block.

FIG. 4 is a sectional view for schematically explaining the structure of an apparatus for producing a glass lump in the second embodiment. Here, similarly to the above, reference numeral 1 denotes a glass melting crucible, 2 denotes an electric furnace, 3 denotes molten optical glass, 4 denotes a molten glass outflow pipe, 5 denotes a molten glass outlet, 6 denotes a molten glass flow, and 7 denotes a glass flow movement. Apparatus, 8 is a glass rod in which the molten glass stream 6 is solidified, 11 is a cylindrical glass block, 18 is a diamond blade for forming a crack (notch), 1
9 is a guide pipe for guiding the glass rod, and 20 is a cutting pipe for cutting the glass rod. 5 to 11 are cross-sectional views for explaining a process for cutting a glass rod.

Next, the operation of this embodiment will be described. First, the molten glass flows out, and the moving speed of the glass flow is controlled by the glass flow moving device 7 to obtain the glass rod 8 having a desired thickness. This step is the same as in the first embodiment. However,
In this embodiment, the glass flow changes its direction in the horizontal direction on the way, and the glass rod 8 is discharged from the glass flow moving device 7 in the horizontal direction.

The glass rod 8 thus obtained is cut using the cutting pipe 20. That is, as shown in FIG. 5, the rotating diamond blade 18 is cut into the glass rod 8 at a position immediately before entering the guide pipe 19, and a crack (notch) is previously formed at a desired position on the glass rod 8. To form Then, as shown in FIG. 6, after a crack (notch) is formed, the diamond blade 18 is retracted, and the glass rod 8 advances to a state as shown in FIG. Here, as shown in FIG.
The position of the crack (notch) of the glass rod 8 is advanced to the position where the glass pipe 8 is connected to the cutting pipe 20.

At this point, as shown in FIG. 9, the cutting pipe 20 is rotated and bent downward. As a result, a bending force is applied to the glass rod 8, and stress concentrates at the portion of the crack (notch), so that the glass rod 8 is separated and cut with this portion as a fracture surface.

As described above, the glass rod formed into a desired thickness is cut at desired intervals by using a mechanical cutting device, thereby obtaining a cylindrical glass having a desired thickness and length. A lump 11 can be obtained. The cylindrical glass block 11 thus obtained has a smooth cylindrical peripheral surface and a cut surface at the fractured surface.

Hereinafter, embodiments of the present embodiment including more specific numerical values will be further described. The steps of melting the glass, controlling the speed of the molten glass stream 6 with the glass stream moving device 7, and obtaining the glass rod 8 are the same as those in the first embodiment. That is,
An optical glass equivalent to LaK12 is melted, and the inner diameter is 1 mm.
The moving speed of the molten glass flow flowing out of the molten glass outlet 5 having an outer diameter of 2 mm is controlled to a desired speed higher than the outflow speed of the molten glass at the outlet by the molten glass flow moving device 7 made of carbon. Then, a glass rod having a thickness of 1.5 mm is continuously discharged from the glass flow moving device at a speed of 270 mm per minute.

In this embodiment, the glass flow in the softened state is bent in the horizontal direction, and then the glass rod is discharged in the horizontal direction by passing the glass flow through the glass flow moving device 7 installed in the horizontal direction. Subsequently, the glass rod 8 discharged laterally from the glass flow moving device 7 is passed through a sleeve-shaped guide pipe 19 made of cemented carbide. The inner diameter of the guide pipe 19 was 1.6 mm and the length was 5.8 mm.

A cutting pipe 20 is provided adjacent to the guide pipe 19, and the glass rod 8 continuously discharged from the glass flow moving device 7 subsequently enters the cutting pipe 20. go. This cutting pipe 20 is made of cemented carbide, has an inner diameter of 1.6 mm and a length of 4.0 m.
m. The cutting pipe 20 is connected to a rotating device (not shown), and can intermittently rotate its direction by 90 ° according to the feed speed of the glass rod 8.

As shown in FIGS. 4 and 5, a disc-shaped diamond blade 18 on which diamond grains are electrodeposited is provided at the entrance of the guide pipe 19, and the tip of the diamond blade 18 has a diameter of 30 °. Form an angle. The diamond blade 18 was rotated at 5000 revolutions per minute and brought into contact with the glass rod 8 to form a V-shaped groove having a depth of 0.2 mm and an opening angle of 30 ° in the glass rod 8.

Then, in the next step, the glass rod is cut using the position of the V-shaped groove as a fracture surface in the next step (the V-shaped groove was used as a crack for starting the fracture).
It is. In this embodiment, the V-shaped grooves are formed at 2.0 mm intervals in the longitudinal direction of the glass rod 8.

That is, when the V-shaped groove formed in the glass rod 8 has reached the connecting position between the guide pipe 19 and the cutting pipe 20 as shown in FIG. The device (not shown) rotates 90 ° downward. Then, the glass rod 8 is cut using the V-shaped groove as a fracture surface. Note that, as shown in FIG. 9, after the glass rod 8 is cut, the cylindrical glass block 11 falls through the cutting pipe 20, as shown in FIG.

The cylindrical glass ingot 11 thus obtained has a smooth side surface, and the upper and lower surfaces are formed as fractured surfaces except for the V-shaped grooves slightly remaining, so that the glass ingot 11 is smooth. It is. Therefore, the cylindrical glass block 11 obtained in the present embodiment is suitable as a forming material for forming minute, for example, biconcave lenses.

The specific effects of this embodiment are as follows. In other words, the conventional technique makes it possible to produce a columnar glass block having a small weight, which cannot be directly obtained from molten glass, by continuous production from molten glass at a low production cost. The cylindrical glass block is formed with a smooth surface all around. Therefore, when this is press-formed, it is possible to obtain a high-quality, minute-weight, biconcave lens having excellent shape accuracy and appearance accuracy.

(Embodiment 3) In the third embodiment, the molten glass flow is moved by a glass flow moving device at a speed lower than the outflow speed, and the glass flow is thickened. An impact is applied, and the glass rod is cut at the fractured surface to obtain a cylindrical glass block.

FIG. 12 is a sectional view for schematically explaining the structure of an apparatus for producing a glass lump in the third embodiment. Here, 1 is a glass melting crucible, 2 is an electric furnace, 3
Is a molten optical glass, 4 is a molten glass outflow pipe, 5 is a molten glass outlet, 6 is a molten glass flow, 7 is a glass flow moving device, 8 is a glass rod having the molten glass flow 6 solidified, and 9 is a glass rod 8. The cutting blade 10 for cutting by thermal shock is a driving device for driving the cutting blade 9, and the heating device 21 is for heating the cutting blade 9.

The operation of this embodiment is almost the same as that of the first embodiment. However, the moving speed of the glass flow by the glass moving device 7 is lower than the outflow speed of the molten glass flow flowing out of the glass outlet 5. Therefore, the diameter of the obtained glass rod 8 is larger than the diameter of the molten glass flow flowing out of the glass outlet 5.

In this embodiment, the glass flow moving device 7 is used.
The cutting blade 9 is heated to a high temperature by a heating device 21 installed around the cutting blade 9 in order to cut the glass rod 8 discharged from the heater by thermal shock. Then, the cutting blade heated to a high temperature is brought into contact with the glass rod 8, and the contact position is cut as a fracture surface due to thermal shock to obtain a cylindrical glass block.

More specifically, in this embodiment, the SK12
A considerable amount of optical glass is melted and used.
This is almost the same as the case of the first embodiment. This optical glass material was put into a platinum glass melting crucible 1, the electric furnace 2 was heated to 1200 ° C., and flowed out through the glass outflow pipe 4. At the outlet 5 of the outlet pipe, the inner diameter of the outlet pipe is 1 mm and the outer diameter is 2 mm.

The glass outflow pipe 4 was kept at 1000 ° C. to discharge the glass. 1000 ° C from outlet 5
Was continuously discharged at a rate of 2.8 g / min. Further, a glass flow moving device 7 is installed at a position 400 mm below the molten glass outlet 5, and at this position, the surface temperature of the molten glass flow is cooled to 400 ° C., and is lower than the yield point temperature. Temperature.

As shown in FIG. 2, the glass flow moving device 7 is composed of three drive rollers, which are made of carbon and have a diameter of 30 mm.
The cylindrical side surface of the roller is machined into a gentle round groove shape of R50 mm. The rollers are controlled to a desired rotation speed by a servomotor, and the size of the gap formed by the three rollers is adjusted to a desired size by a roller position adjustment mechanism (not shown).

In this example, the rotation speed of the roller was set to 0.5 rotation per minute, and the gap formed by the roller was set to 5.0 mm. As a result, a glass rod having a diameter of 5.0 mm is discharged from the lower portion of the glass flow moving device 7 including the rollers at a speed of 45 mm per minute. A molten glass flow having a diameter of 2.0 mm flows out of the molten glass outlet 5 at a speed of 280 mm / min. As shown in FIG. It becomes thicker at a position about 30 mm below, and is finally discharged from the lower part of the glass flow moving device 7 as a glass rod having a desired thickness.

100 mm below the glass flow moving device 7
Is provided with a glass flow cutting device by thermal shock. This glass flow cutting device has a V-shaped cutting blade 9.
Are installed at positions facing each other with the glass rod 8 interposed therebetween, and the cutting blade 9 can be moved back and forth by a driving device 10 including an air cylinder. Further, a cutting blade heating device 21 by high-frequency heating is installed around the cutting blade 9. Therefore, the cutting blade 9 is always kept at a high temperature.

When this high-temperature cutting blade 9 is brought into contact with the glass rod 8, a thermal shock is generated on the glass rod, and a crack having a fractured surface is formed from the contact portion of the blade, and cut at this part. At this time, the surface temperature of the glass rod 8 is about 300 ° C., the temperature difference from the cutting blade 9 is large, and since this glass rod is rapidly cooled in the atmosphere from a molten state, residual thermal stress is reduced. Since it is large, by contacting such a high-temperature cutting blade 9, it is possible to reliably cut from this portion by thermal shock.

In this embodiment, the glass rod 8 discharged from the glass flow moving device 7 was cut by the cutting blade 9 every 10 seconds, and the glass rod 8 was cut to obtain a cylindrical glass block.
This glass lump has a diameter of 5.0 mm and a length of 8.0 mm.
Met. Then, the thus obtained cylindrical glass ingot has both side surfaces and upper and lower cut surfaces,
It is formed with a smooth surface. The temperature of the cylindrical glass block immediately after cutting was 300 ° C.

The average weight of the thus obtained cylindrical glass lump 11 was 0.5 g. On the other hand, the weight variation of this glass lump was small, and the standard deviation was σ, which was 0.0005 g at 3σ. It is effective for uniformity of product weight and shape.

The cylindrical glass block obtained in this embodiment is formed on a smooth surface, and
It is suitable for use as a material for molding biconcave lenses.
Also, after heating in a floating state and forming it into a roughly spherical shape,
It may be used as a material for molding biconvex lenses, convex meniscus lenses, and concave meniscus lenses.

As a special effect of this embodiment, a thicker glass rod can be obtained from the molten glass flow flowing out of the relatively thin molten glass outflow pipe. That is, even if one type of molten glass outflow pipe is used, cylindrical glass blocks of various thicknesses can be obtained by changing the moving speed of the glass flow moving device.

Fourth Embodiment In a fourth embodiment, a cylindrical glass block obtained by the present invention is heated and softened in a floating state to obtain a roughly spherical glass block. In FIG. 13, reference numeral 11 denotes a cylindrical glass block, 2
Reference numeral 2 denotes a floating holding jig for floating the cylindrical glass block 11, 23 denotes a gas supply chamber provided inside the floating holding jig 22, and 24 denotes a gas supply chamber for supplying gas to the gas supply chamber 23. Gas supply pipe. In FIG. 14, reference numeral 14 denotes a roughly spherical glass block.

In this embodiment, the floating holding jig 22 is formed with a plurality of conical concave portions for floating the cylindrical glass block 11, and the conical concave portion has
That is, a gas outlet is provided at the bottom of the recess, and the gas outlet communicates with the gas supply chamber. That is, the gas supplied from the gas supply pipe 24 to the gas supply chamber 23 is ejected from the gas ejection port.

As shown in FIG. 13, the columnar gas mass 11 is put into a conical concave portion of the floating holding jig 22. In this state, gas is supplied from the gas supply pipe 24, and the columnar glass block 11 is floated and held. Subsequently, the floating holding jig 22 in this state is put in a high-temperature atmosphere such as an electric furnace and held for a while.

Then, the cylindrical glass block 11 is softened, and its surface tension becomes spherical due to its surface tension.
A spherical glass block 14 is obtained. Thereafter, the floating holding jig 22 is taken out of the high-temperature atmosphere and cooled while keeping the spherical glass block 14 floating.
Then, the roughly spherical glass block 14 is taken out from the floating holding jig 22.

More specifically, an optical glass equivalent to SK12 is used as a material of the cylindrical glass block 11 here. In addition, this glass lump 11 is used in Example 1 and Example 3
The method was used for the production. The size of the cylindrical glass block 11 used in the present embodiment is as follows: diameter: 2.0 mm, length:
2.0 mm, weight: 0.02 g.

Carbon was used as the holding material for the floating holding jig 22. The shape of the conical concave portion formed on the floating holding jig 22 has a maximum diameter (upper part).
Had a diameter of 10 mm and an inclination angle of 60 °. In addition,
In this embodiment, one floating heating jig 22 has 10
A total of 100 conical concave portions are formed in 10 lateral portions. At the center of the conical concave portion, a gas ejection port having a diameter of 1 mm for ejecting gas is open.
Nitrogen gas was used as a floating gas.

After the cylindrical glass block 11 at room temperature is put into the conical recess of the floating heating jig 22, nitrogen gas is supplied from the gas supply pipe 24, and the cylindrical glass block 11 is supplied. Was held floating. The floating heating jig 22 in this state
Were placed in an electric furnace maintained at 800 ° C. When held in this state for 20 minutes, the cylindrical glass ingot 11 began to soften, and its surface began to be spherical due to surface tension. In this state, when held for another 5 minutes, a roughly spherical glass ingot 14 was obtained. Then, these floating heating jigs 22 were taken out of the electric furnace and cooled with the nitrogen gas in a state where the spherical glass block 14 was held in a floating state for about 5 minutes. I took it out. The roughly spherical glass block 1 thus obtained
No. 4 has a smooth surface and is suitable as an optical element molding material.

The following effects are specific to this embodiment. That is, according to the present embodiment, similar to the first embodiment,
Although a high-quality, roughly spherical glass block 14 is obtained, the structure of the manufacturing apparatus is simplified and a conventional electric furnace can be used, so that the apparatus cost is reduced, that is, the manufacturing cost is reduced. .

(Embodiment 5) In the fifth embodiment, a function of floating and heating a cylindrical glass block is provided to a conveying means for conveying a material for molding into an optical element molding die. The glass block is floated and heated to form a roughly spherical glass block. Thereafter, the spherical glass block is set in an optical element mold, and press-molded with the mold,
Obtain a molded optical element.

In this embodiment, as shown in FIG.
1 is a cylindrical glass lump, 14 is a substantially spherical glass lump, 25 is a floating heating jig having a split mold structure which can be opened and closed, 26 is a lower mold for molding, and 27 is an upper mold for molding. Reference numeral 28 denotes a body type for slidingly guiding the upper and lower dies.

The floating heating jig 25 has a conical concave portion for floating the cylindrical glass block 11, and a high-temperature gas jet port is formed at the apex of the conical shape, that is, at the bottom of the concave portion. The hot gas outlet is connected to a hot gas supply device (not shown). Then, the high-temperature gas produced by the high-temperature gas supply device is ejected from the gas ejection port. The floating heating jig 25 is shown in FIG.
As shown in FIG. 5, it is configured so that it can be divided and moved from the center to both sides.

In a molding chamber (not shown) of the molding apparatus,
After the cylindrical glass block 11, which is a molding material, is placed in the floating heating jig 25, the high-temperature gas produced by the high-temperature gas supply device is blown out from the gas outlet, and the cylindrical glass block is discharged. 11 is heated and softened in a floating state, and the whole is made spherical by surface tension.

The glass block 14 having a substantially spherical shape as described above is kept in this state with the floating heating jig 2.
5 together with the upper and lower molding dies. The molding die is composed of a lower die 26, an upper die 27, and a body die 28 for slidingly guiding them concentrically.
Is provided with a horizontal hole for carrying a floating heating jig. Floating heating jig 25 carried into this mold
Moves to a position directly above the lower mold 26, where the split mold structure is provided with an opening operation, opened to both sides, and the glass mass 14 held and floated falls onto the lower mold 26. Thereafter, the floating heating jig 25 is withdrawn from the forming die, and the spherical glass block 14 is press-formed by the upper die 27 to obtain a formed optical element.

More specifically, here, optical glass equivalent to SK12 is used as the material of the cylindrical glass lump 11. This cylindrical glass lump 11 is obtained in Example 1
And by the method described in Example 3. In addition, the size of the cylindrical glass block 11 used in the present embodiment is as follows.
6 mm, length: 4.2 mm, and weight: 0.4 g.

As the material of the floating holding jig 25, carbon was employed. The shape of the conical concave portion formed on the floating holding jig 22 has a maximum diameter (upper part).
Had a diameter of 10 mm and an inclination angle of 60 °. At the center of the conical recess, a gas ejection port with a diameter of 1 mm for ejecting gas is open. From here, a 1000 ° C. gas heated by a high-temperature gas generator (not shown) is jetted. Note that nitrogen gas was used as a floating gas.

After the cylindrical glass block 11 at room temperature is put into the conical concave portion of the floating heating jig 25 inside a forming apparatus (not shown) kept in a nitrogen atmosphere, Nitrogen gas was blown out, and the cylindrical glass block 11 was floated and held. In this state, when held for one minute, the cylindrical glass ingot 11 starts to soften, and the surface thereof starts to be spherical due to surface tension. In this state, when held for another one minute, a roughly spherical glass ingot 14 is formed. Obtained. Then, the supply of the high-temperature gas from the high-temperature gas generator is stopped, the roughly spherical glass block 14 is floated and held by the room temperature gas, and the floating heating jig 25 in this state is passed through the lateral hole of the shell mold 28, It moved to just above the lower mold 26.

In this state, an opening operation was given to the split mold structure, and the spherical glass block 14 was dropped on the lower mold 26. At this time, the temperature of the spherical glass block 14 is 600 ° C.
The lower mold 26 and the upper mold 27 were heated to 600 ° C.

The lower mold 26 and the upper mold 27
Is made of cemented carbide, and its forming surface is polished and then provided with a platinum-based protective film. In the present embodiment, the molding surface of the lower mold 26 has a diameter of 6 mm and a radius of curvature of 15 mm. Also, the molding surface of the upper mold 27 is
Diameter: 6 mm, radius of curvature 10 mm.

Then, a pressing force of 1000 N was immediately applied to the upper mold 27 to press-mold this glass lump. Next, after cooling the upper and lower molds to 450 ° C., the molds are opened,
The molded lens was taken out.

As a specific effect of this embodiment, the first embodiment
Similarly to the above, a high-quality molded optical element can be obtained, but can be realized by diverting or modifying a conventional manufacturing apparatus, so that the apparatus cost and the manufacturing cost are reduced.

[0107]

As described above, according to the present invention,
A glass lump suitable as a material for molding an optical element, and particularly a glass lump having a substantially spherical shape, makes it possible to obtain a glass lump having a very small weight, which cannot be obtained by conventional techniques. As a result, it becomes possible to manufacture a molded optical element having a minute weight, which has been difficult in the past.

Further, according to the present invention, it becomes possible to produce a glass block having a very small weight, which is smaller than a conventionally obtained glass block having a small weight. In addition, it is possible to manufacture high-quality glass blocks of various weights and shapes using one glass block manufacturing apparatus, and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a front view schematically illustrating the configuration of an apparatus according to a first embodiment of the present invention.

FIG. 2 is a plan view schematically illustrating a part of the configuration of the device.

FIG. 3 is a plan view schematically illustrating a part of the configuration of the device.

FIG. 4 is a front view schematically illustrating the configuration of an apparatus according to a second embodiment of the present invention.

FIG. 5 is a view for explaining the operation during the process of the second embodiment.

FIG. 6 is a view for explaining the operation during the process of the second embodiment.

FIG. 7 is a view for explaining the operation during the process of the second embodiment.

FIG. 8 is a view for explaining the operation during the process of the second embodiment.

FIG. 9 is a diagram for explaining the operation during the process of the second embodiment.

FIG. 10 is a view for explaining the operation during the process of the second embodiment.

FIG. 11 is a view for explaining the operation during the process of the second embodiment.

FIG. 12 is a front view schematically illustrating the configuration of an apparatus according to a third embodiment of the present invention.

FIG. 13 is a front view schematically illustrating the configuration of an apparatus according to a fourth embodiment of the present invention.

FIG. 14 is a front view schematically illustrating the configuration of an apparatus according to a fourth embodiment.

FIG. 15 is a front view schematically illustrating the configuration of an apparatus according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crucible 6 Molten glass flow 7 Molten glass flow moving device 8 Glass rod 11 Cylindrical glass lump 14 Almost spherical glass lump

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 3/00 G02B 3/00 Z (72) Inventor Hiroyuki Kubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Canon Inc. (72) Inventor Akazu Mizuwa 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term within Canon Inc. (reference) 4G015 FA06 FB03 FC04 FC10

Claims (8)

[Claims] 1. An optical glass melted in an optical glass melting crucible flows out continuously from an outlet of a molten glass outflow pipe, and flows into an outer peripheral portion of the molten glass flow flowing out of the molten glass outflow port. By contacting the moving device, by controlling the movement of the glass flow moving device, by controlling the moving speed of the molten glass flow to a desired value, at the same time, the cross-sectional area of the molten glass flow flowing out from the molten glass outlet, By changing to a desired cross-sectional area, with respect to the moving direction of the molten glass flow, to obtain a glass rod of a desired cross-sectional area,
A method for forming a glass lump for an optical element, comprising cutting the glass rod into a desired length to obtain a glass lump for an optical element. 2. The glass lump obtained by the method according to claim 1 is guided into a gas stream to float, and is heated while maintaining the floating state to soften the surface of the glass lump,
A method for forming a glass block for an optical element, wherein the entire glass block is formed into a spherical shape by surface tension of the glass. 3. A glass optic obtained by heating and softening a glass lump obtained by the method according to claim 1 or 2 and press-molding using a predetermined mold. Device manufacturing method. 4. The method for forming a glass lump for an optical element according to claim 1, wherein the moving speed of the glass flow controlled by the glass flow moving device is controlled by adjusting a moving speed of the molten glass when flowing out of the molten glass outlet. A method for forming a glass lump for an optical element, wherein the method is performed at a speed higher than an outflow speed. 5. The method for forming a glass lump for an optical element according to claim 1, wherein the moving speed of the glass flow controlled by the glass flow moving device is controlled by changing a moving speed of the molten glass when flowing out of the molten glass outlet. A method for forming a glass lump for an optical element, wherein the method is performed at a speed lower than an outflow speed. 6. The method for forming a glass lump for an optical element according to claim 1, wherein the step of cutting a glass rod having a desired diameter into desired lengths to obtain a desired glass lump includes: A method for forming a glass lump for an optical element, characterized by using a cutting method in which a thermal shock is applied to a desired position of a glass rod and a fracture surface is formed in this portion. 7. The method for forming a glass lump for an optical element according to claim 1, wherein a glass rod having a desired diameter is cut into pieces each having a desired length to obtain a desired glass lump. A crack (notch) is formed in a desired position of the rod in advance, an external force is applied to this portion, stress is concentrated on this crack portion, and a cutting method of cutting this portion as a fracture surface is used. A method for forming a glass block for an optical element. 8. The method for molding a glass lump for an optical element according to claim 1, wherein the weight of the desired glass lump is:
A method for forming a glass lump for an optical element, wherein the method is a lightweight glass lump of 0.5 g or less.