METHOD AND A DEVICE OF MANUFACTURING AN OBJECT OF GLASS WITH AT LEAST ONE THREE-DIMENSIONAL FIGURINE ENCLOSED THEREIN

A method of manufacturing an object of glass with at least one three-dimensional figurine enclosed therein, comprises the steps of pouring soft glass into a mold cavity and inserting a heated figurine into the glass. The glass temperature is higher than 1000° C. when inserting the figurine.

BACKGROUND

The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The disclosure relates to a method of manufacturing an object of glass with at least one three-dimensional figurine enclosed therein.

Such a method is known from WO 99/33754. In the prior art method spherical glass articles including figurines are manufactured by successive steps of filling a bottom mold with a droplet of glass, supplying a figurine and pouring another droplet on the figurine and the already present glass. The glass article is then stamped to a spherical shape.

SUMMARY

An aspect of the invention provides a new method for manufacturing an object of glass with a three-dimensional figurine enclosed therein.

This is achieved with the method which comprises the steps of pouring soft glass into a mold cavity and inserting a heated figurine into the glass, wherein the glass temperature is higher than 1000° C. when inserting the figurine.

Due to the relatively high temperature of the glass in the mold cavity its viscosity is still relatively low. As a consequence, the molten glass yields around the figurine rather easily. Furthermore, inserting the figurine into the glass requires relatively little pressure, which provides the opportunity to insert the figurine into the glass at relatively high speed. This results in increased manufacturing speed. In order to prevent the figurine from degradation due to a too high temperature difference, such as cracking, the figurine is pre-heated before being inserted into the glass.

The glass can be poured into a static mold cavity after which the figurine is pressed into the glass. It is noted that after pressing the figurine into the glass an additional amount of glass may be poured into the mold cavity.

The glass in the mold cavity may be heated before inserting the figurine in order to limit or prevent cooling down of the glass after pouring it into the mold cavity. This can be achieved by supplying heat through a filling hole to the mold cavity, for example by means of a burner. Keeping the viscosity relatively facilitates pressing the figurine into the glass.

The figurine may be heated to a temperature below the actual glass temperature in the mold cavity. This requires less heating of the figurines than in prior art manufacturing methods. The temperature to which the figurine is heated may depend on its size and shape.

The glass temperature may be higher than 1100° C. or 1150° C., and preferably higher than 1250° C. when inserting the figurine. This creates a still lower viscosity causing improved yielding characteristics of the glass around the figurine. It is also conceivable that the glass temperature in a glass melting bunker from which the glass is poured into the mold cavity, is higher than 1100° C. or 1150° C., and preferably higher than 1250° C.

In a practical embodiment the glass temperature is in the range of 1000-1300° C. and the figurine temperature is below 1000° C. upon inserting the figurine into the glass. This is possible until the glass is still not fully cured.

In a specific embodiment the glass including the figurine is pressed substantially to a desired shape after the step of inserting the figurine into the glass.

The invention is also related to a method of manufacturing an object of glass with at least one three-dimensional figurine enclosed therein, comprising the steps of pouring soft glass into a mold cavity and inserting a heated figurine into the glass, wherein the viscosity of the glass is lower than 104Pa·s when inserting the figurine, and preferably lower than 103Pa·s. In a practical glass composition, the temperature at these viscosity levels is 1022 and 1183° C., respectively. For the same glass composition the viscosity of the glass is 102Pa·s at 1425° C. and 105Pa·s at 907° C.

The three-dimensional figurine may be composed of metal salts and/or metal oxides and the composition as oxide is a) 20-60 wt. % of Si02, b) 2.5-30 wt. % of Al203, and c) 30-65 wt. % of an oxide of Mg, Ca, and/or Ba, and wherein the sum of a+b+c>95 wt. %, and if there is a difference with 100 wt. %, this difference stands for metal oxides of metals other than Si, Al, Mg, Ca, or Ba, wherein the weight percentage is determined with regard to the total of the oxides. Examples of such metals are iron (II), iron (III), potassium, sodium, lithium, zinc, copper, lead, antimony, zirconium, strontium, arsenic, manganese, titanium, phosphorus (that is also considered as a metal), and the like. In view of this it is remarked that all non-gaseous oxides can be part of the composition in small amounts. Preferably, none of these other metal oxides occur in an amount above 1 wt. %. The total content of these other metal oxides is always smaller than 5 wt. %.

Alternatively, the three-dimensional figurine may be composed of metal salts and/or metal oxides and the composition as oxide is a) 30-40 wt. % of Si02, b) 5-10 wt. % of Al203, and c) 50-60 wt. % of an oxide of Mg, Ca, and/or Ba, and wherein the sum of a+b+c>95 wt. %, and if there is a difference with 100 wt. %, this difference stands for metal oxides of metals other than Si, Al, Mg, Ca, or Ba, wherein the weight percentage is determined with regard to the total of the oxides.

The glass may be any sort of glass. Because of the price and the ease of handling it is preferred to use soda lime glass. Such glass comprises 70-78 wt. % of silicon oxide, 10-18 wt. % of sodium oxide, 4-12 wt. % of calcium oxide, 0.1-5 wt. % of potassium oxide, and small amounts of different oxides. A suitable glass is for instance the sodium lime glass with 76 wt. % of silicon oxide, 16 wt. % of sodium oxide, 6 wt. % of calcium oxide, and 2 wt. % of potassium oxide. A different suitable glass comprises 72.5 wt. % of silicon oxide, 13.6 wt. % of sodium oxide, 8.8 wt. % of calcium oxide, 0.6 wt. % of potassium oxide, 2 wt. % of aluminium oxide, 1.9 wt. % of magnesium oxide, 0.08 wt. % of iron (III) oxide, 0.6 wt. % of antimony (III) oxide, and 0.01 wt. % of titanium oxide. Nevertheless glass having different compositions is conceivable, for example glass comprising 72-77 wt. % of silicon oxide, 11-13 wt. % of sodium oxide, 3-5 wt. % of calcium oxide, 2-3 wt. % of potassium oxide, 2-4 wt % B2O3, 0.5-2 wt % Al2O3, 1-3 wt % BaO, and small amounts of different oxides.

The glass may be a so-called hard glass. For example, a typical hard glass is borosilicate glass with low thermal expansion coefficient, in the order of 3.3×10−6K−1. This glass is hard for melting, it is the Pyrex type. The composition is well known and the typical contents of SiO2 is about 80%. Generally the hardness of the glass depends on the amount of SiO2 in the glass. Preferably, the content of SiO2 in the glass is higher than 50% and more preferably higher than 70%.

The invention is also related to a device for manufacturing an object of glass with a three-dimensional figurine enclosed therein, comprising a mold assembly provided with a mold cavity whose shape corresponds at least substantially to the shape of the intended object and a feeder including a glass discharge for supplying molten glass to the mold assembly, wherein said mold assembly is provided with a filling opening for filling the mold cavity with molten glass and an insertion opening for inserting the figurine into the mold cavity, wherein the glass discharge is located directly above the filling opening.

The device according to the invention prevents the glass from severe cooling between the glass discharge and the mold assembly.

The distance between the glass discharge and the mold assembly may be less than 0.5 m, and preferably less than 0.25 m. In a prior art method the glass that leaves the glass discharge has a temperature of about 1100° C., but has to travel about 3 m through a chute before arriving at a mold. Therefore, the glass will be cooled down below 1000° C. upon entry of the mold.

The device may be arranged such that the temperature of the glass in the mold cavity after filling is higher than 1000° C. This can be achieved, for example, by a short distance between the glass discharge and the mold assembly as mentioned above, and/or by heating the molten glass to a relatively high temperature at the feeder. An elevated glass temperature results in decreased viscosity such that the glass flow between the glass discharge and the mold assembly is relatively narrow. Consequently, the filling opening may be narrow, as well. Alternatively, the device is provided with a heat source, for example a burner, for heating the glass in the mold cavity before inserting the figurine.

The figurine may have any shape, for example a disk shape, and may also carry a message for advertising, for example.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

FIG. 1shows a continuously operating glass furnace1, which contains a mass of molten glass2. The glass2is heated by means of flames3. Under operating conditions the molten glass2flows through a feeder4to a glass discharge5. The glass2may be heated to a temperature of 1100-1700° C., in practice about 1300° C. This means that the glass temperature upon leaving the glass discharge5may have a temperature of about 1300° C. At this temperature the viscosity of the molten glass is rather low such that a flow of molten glass2below the glass discharge5is relatively narrow.

The flow of glass2that leaves the glass discharge5is received by a mold assembly6which is located just below the glass discharge5. The distance between the glass discharge5and the mold assembly6is preferably smaller than0.25m in order to minimize cooling of the glass2before it arrives at the mold assembly6. When an amount of glass2is poured into the mold cavity9the glass flow at the glass discharge5is stopped shortly and a next mold assembly6is positioned below the glass discharge5such that the glass flow may be started again.

FIG. 2shows an embodiment of a mold assembly6for making an object of glass in the form of a marble with a three-dimensional figurine enclosed therein. The mold assembly6includes a lower mold7and an upper mold8, which together form a mold cavity9. The upper mold8is provided with a filling hole10for filling the mold cavity9with soft glass2.FIG. 2illustrates a condition in which the mold cavity9is filled with soft glass2. In this condition the glass temperature is still above 1000° C. It appears that an optimal result is obtained when the glass temperature in the mold is 1000° C. or higher and the temperature of the figurine is about 700° C. In an alternative embodiment the glass in the mold cavity9as shown inFIG. 2is heated before the figurine F is pressed into the glass, as shown inFIG. 3in order to prevent the glass from severe cooling after being poured into the mold cavity. This can be done by a burner (not shown) which is directed into the filling hole10.

In a next step, possibly after filling of the mold cavity9with glass2has stopped, a figurine F is inserted into the soft glass2via the same filling hole10.FIG. 3illustrates how the figurine F is inserted into the glass2. This may be performed at relatively high speed. Since in this case the viscosity of the glass2is still relatively low a relatively low pressure is required for inserting the figuring F into the glass2. The figurine F may have any three-dimensional shape and is made of a material which preferably has a coefficient of expansion in the range of that of the glass2, often a ceramic material. Depending on the size of the figurine F in relation to the size of the mold cavity9the filling hole10may be wider or narrower than shown inFIG. 3.

Before the figurine F is inserted into the glass2it is pre-heated in order to avoid a large temperature difference between the glass2and the figurine F which may cause degradation of the figurine F, for example cracking. Contrary to known prior art manufacturing processes the figurine F is pre-heated to a temperature which is below the actual glass temperature upon inserting it into the glass2. Due to the relatively high glass temperature, above 1000° C. or 1100° C. and preferably above 1200° C., in the mold cavity9the viscosity of the glass2is still low and the glass appears to yield around the figurine F accurately. Furthermore, formation of air inclusions appears to be minimized. In practice, a ceramic figurine F is pre-heated to a temperature above 500° C. and below 1000° C.

FIG. 4illustrates that due to the presence of the figurine F in the mold cavity9the glass level in the upper mold8has increased with respect to the condition as shown inFIG. 3. It is noted that in the embodiment as illustrated in

FIGS. 2-4the glass2and the figurine F are supplied to the mold cavity9via the same filling hole10. In an alternative embodiment separate openings for supplying the glass2and the figurine F, respectively, to the mold cavity9are conceivable.

In the condition as illustrated inFIG. 5the upper mold8has been removed and a new upper mold11has been supplied. The new upper mold11includes a hemispherical mold cavity12and an escape hole13having a smaller diameter than the filling hole10of the upper mold8. The diameter of the escape hole13is selected in dependence on the volume of the figurine F that is to be inserted into the glass2; the larger the volume of the figurine F, the larger the diameter of escape hole13.

When the new upper mold11is pressed onto the lower mold7, as is shown inFIG. 6, the resulting glass marble2, which is too large, is compressed. The glass2is pressed fully against figurine F. The air that may be present is forced out. The glass above figurine F is closed and the excess glass is discharged, likewise at the upper side, via narrow escape hole13. Since the hole is narrow, the pressure within the mold cavity9can nevertheless run up high. Subsequently, the new upper mold11is opened again and a pillar of abundant glass14from the escape hole13is cut off by cutting means15, seeFIG. 7.

It is noted that the discharge5at the feeder4may be controlled accurately, such that an amount of glass2is poured into the mold assembly6, which amount of glass2substantially equals the amount of glass necessary for the final object. With reference toFIG. 7, the amount of glass2is controlled such that the pillar of abundant glass14does not arise in this case. The amount of glass is controlled in dependence of the volume of the figurine F. In case of such an accurate discharge control, it is even conceivable to eliminate the escape hole13, as shown inFIGS. 5 and 6. It is also noted that in case of using an accurate control of glass supply from the discharge5it is not necessary to apply a new upper mold11. On the contrary, the mold assembly may have opposite side parts including vertical contact surfaces, which form a common filling hole in assembled condition, instead of an upper mold8and a lower mold7as shown inFIG. 2.

Due to accurate control of glass supply, the resulting marble can be compressed in the mold cavity by inserting a press tool without an escape hole for releasing excess glass, for example a mandrel, through the filling hole after the steps of filling the mold cavity with glass and pressing the figurine into the glass. A contact surface of the press tool that contacts the glass may be concave such that the resulting product becomes spherical.

The glass marble2is placed on a roller (not shown), which has a length of about 1 to 15 m. At the end of the roller, the marbles move into an annealing furnace. In this furnace, the marbles are annealed for a long period in order to fully eliminate any stresses in the glass2surrounding figurine F. After leaving the annealing furnace the glass marbles2may be placed, as an optional step, on the roller again and be rolled into a perfectly round shape. Preferably, the marbles are partially reheated before being placed again on the roller.

Alternatively, it is conceivable to grind and polish the hardened and cooled marbles by tumbling them in a tumbler to obtain a perfectly round and polished marble. Such tumblers are known per se for shaping and finishing gemstones and the like. In this embodiment a roller is not used.

A further alternative for finishing the marbles is to process them in a bead fine grinding machine and/or a bead calibrating machine (for example model KF and/or model KKM from LUX+CO. KG). Polishing may be done by the above mentioned tumbling process again or by “flame polishing” on a roller.

From the foregoing it will be apparent that the invention provides a method and a device by means of which an object of glass with a figurine enclosed therein can be manufactured. The method can be carried manually or automatically to a smaller or larger extent, but in principle it is also possible to carry out the entire method by hand.

The invention is not restricted to the above-described embodiment as shown in the drawings, which can be varied in several ways without departing from the scope of the invention. Thus it is possible to use an adjustable mold or the like and a vacuum system instead of various upper molds. Furthermore, it is possible to insert several figurines, simultaneously or in succession, into the glass of the object at the same location or at different locations. Pressing a heated figurine into the glass and pressing the amount of glass with the figurine present therein substantially to a desired shape may also be done substantially simultaneously, or in a succession without changing the upper mold part but by movable mold parts.