Abstract:
The invention relates to a method of manufacturing successive spherical glass articles, in each of which is accommodated a three-dimensional object of figuring, which method comprises the following steps, to be performed in a suitable sequence, of: (a) providing a container with a mass of molten glass, which container comprises a discharge opening through which liquid glass can be delivered; (b) providing thermally resistant figurines; (c) wholly enclosing successively at least one figurine by molten glass by feeding molten glass thereto from at least two sides; (d) portioning the molten glass before or after step (c) such that molten glass masses are formed, in each of which a figurine is embedded; and (e) modelling these masses to a spherical form by substantially omnidirectional rolling for a time with simultaneous cooling so that the glass solidifies.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to the manufacture of spherical glass objects, in each of which a three-dimensional object is accommodated. A method of this type is known in many embodiments. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to design a method such that a very large production speed on industrial scale can be realized wherein the obtained spherical glass articles nevertheless comply with very high technical standards. 
     It is a further object of the invention to provide a method with which the mass production can take place at very low cost. 
     The invention generally provides a method of manufacturing successive spherical glass articles, in each of which is accommodated a three-dimensional object or figurine, which method comprises the following steps, to be performed in a suitable sequence, of: 
     (a) providing a container with a mass of molten glass, which container comprises a discharge opening through which liquid glass can be delivered; 
     (b) providing thermally resistant figurines; 
     (c) wholly enclosing successively at least one figurine by molten glass by feeding molten glass thereto from at least two sides; (d) portioning the molten glass before or after step (c) such that molten glass masses are formed, in each of which a figurine is embedded; and 
     (e) modelling these masses to a spherical form by substantially omnidirectional rolling for a time with simultaneous cooling so that the glass solidifies. 
     In such a method the problem may occur that air is enclosed in the zone in which the glass masses fed from at least two sides make mutually contact. As a result of the great viscosity of the glass, air or other gas inclusion is no longer able to escape. Air bubbles or other gas inclusions affect to a considerable degree the aesthetic quality of the product for manufacture. It is therefore desirable to perform the method according to the invention such that there is no or only negligible danger of air inclusions. In this respect the method according to the invention can preferably comprise step 
     (f) performing step (c) substantially in the absence of a gas which cannot dissolve in molten glass, such that gas inclusions, for instance air bubbles, are prevented. 
     A specific embodiment comprises step 
     (g) performing step (f) in a gaseous environment under substantial underpressure. 
     An alternative embodiment of the method comprises step 
     (h) performing step (f) in the presence of a gas which can dissolve in molten glass, for instance hydrogen, helium, neon, argon. 
     In order to prevent thermal stresses, the embodiment of the method is recommended which comprises step 
     (i) performing step (c) after pre-heating the successive figurines, for instance to a temperature in the order of 850° C. 
     A specific embodiment has the special feature that step (e) is performed by means of a first roller in which is recessed a helical groove with a smooth round form, which roller is driven rotatably at a first peripheral speed and co-acts with a second roller driven at a second peripheral speed differing from the first peripheral speed, which second roller is smooth or likewise provided with a helical groove. 
     A specific embodiment has the special feature that the glass substantially consists of the following constituents: 
     c. 76% SiO 2    
     c. 16% Na 2 O 
     c. 6% CaO 
     c. 2% K 2 O. 
     A preferred embodiment has the special feature that each figurine is provided beforehand with a glaze coating comprising at least one oxide from the group of which Si, Al, Na, Mg, Zr form part, with colouring pigments on the basis of elements from the group of which Fe, Pb, Cr form part. 
     A specific embodiment has the special feature that the glazing of the figurines consists substantially of the following constituents: 
     61.5% SiO 2    
     14.7% AL 2 O 3    
     4.7% Na 2 O 
     6.6% K 2 O 
     11.2% CaO 
     1.3% rest 
     A specific embodiment of the method according to the invention is herein characterized in that the material of the figurines contains the following constituents: 
     c. 65% SiO 2    
     c. 19% AL 2 O 3    
     c. 1.9% Na 2 O 
     c. 4.2% MgO 
     c. 6.4% CaO 
     A specific embodiment has the special feature that the material of the figurines consists substantially of a ceramic mass, for instance kaolin (china clay), pipe clay or the like. 
     It should be understood that the material must be modelled beforehand until it has obtained the desired three-dimensional form. The material can for instance be wetted in powder form, thus resulting in a certain cohesion. A first cohesion is then obtained by a pre-heating, which can take place in a manner to be described below. Only after embedding in the still red-hot plastic glass mass does a definitive hardening of the figurines takes place. 
     A specific embodiment has the special feature that the material of the figurines contains at least approximately the following constituents: 
     61.0% SiO 2    
     21.0% AL 2 O 3    
     1.0% FE 2 O 3    
     1.2% CaO 
     0.5% MgO 
     0.2% Na 2 O 
     2.0% K 2 O 
     A variant has the special feature that the material of the figurines contains at least approximately the following constituents: 
     62.0% SiO 2    
     2.0% AL 2 O 3    
     1.1% FE 2 O 3    
     0.5% CaO 
     32.0% MgO 
     0.7% Na 2 O 
     1.0% K 2 O 
     In order to avoid thermal stresses, the method according to the invention is preferably performed such that cooling of the spherical articles takes place by progressing through the temperature path from the annealing temperature to the strain temperature at a chosen speed such that cooling takes place in substantially stress-free manner. 
     The invention further relates to a method which comprises step 
     (j) annealing after step (e) by again fully heating the spherical glass articles to remove internal stresses and subsequently cooling slowly to for instance about 50° C. 
     A further variant of the method according to the invention comprises the following steps or: 
     (k) dividing the molten glass delivered via the discharge opening into successive portions; 
     (l) providing a mould with at least roughly hemispherical bottom and an at least roughly hemispherical cover for placing thereon and removing therefrom; 
     (m) pouring a first portion of glass onto the bottom; 
     (n) placing at least one figurine on and optionally partially in this first portion of glass; 
     (o) pouring a second portion of glass onto the first portion of glass and the figurine; 
     (p) placing the cover while pressing the thus enclosed mass; 
     (q) removing the cover; 
     (r) removing the formed, at least more or less spherical glass mass with figurine enclosed therein; and 
     (s) performing step (e). 
     In yet another embodiment the invention provides a method of manufacturing successive spherical glass articles, in each of which is accommodated a figurine, which method comprises the following steps of: 
     (t) providing a container with a mass of molten glass, which container comprises a discharge opening which can be closed by a valve and into which a vertical tubular central mandrel extends such that a tubular flow of liquid glass can be delivered via the discharge opening; 
     (u) opening the valve for delivering said flow of liquid glass while simultaneously supplying successive figurines intermittently via the mandrel such that these objects are received in the hollow space of the glass flow; 
     (v) causing the glass flow to contract and thus embedding the successive objects in the glass mass; 
     (w) successively separating the lower part of the glass flow in which a figurine is situated such that still molten glass masses are formed, in each of which a figurine is embedded; and 
     (e) modelling these masses to a spherical form by substantially omnidirectional rolling with simultaneous cooling so that the glass solidifies. 
     A preferred embodiment has the special feature that the mandrel has a widened lower part which can co-act as valve body with the mouth edge of the discharge opening serving as valve seat. 
     Yet another embodiment is characterized in that step (c) takes place using a number of concave rollers together bounding a round passage opening. 
     In some conditions this latter embodiment can advantageously have the special feature that the rollers are driven at an increased peripheral speed reinforcing the contraction of the glass flow. It is noted herein that the rollers in this case have a “pulling” function. An effective stretching of the glass flow hereby occurs. In the case where the rollers are driven at a relatively low speed or are slowed down relative to the driving glass flow, a certain expansion occurs upstream relative to the rollers, followed by a contraction as a result of the relatively narrow passage opening defined by the co-acting rollers. 
     A specific embodiment has the special feature that the rollers have partly spherical cavities co-acting in register positions during rotation. 
     A practical embodiment has the special feature that step (v) is performed by cutting through the glass flow between the figurines. 
     This latter embodiment can advantageously be performed such that use is made of two plates with co-acting, generally concave, substantially V-shaped cutting edges. 
     As already described above, the figurines are preferably pre-heated prior to embedding. The possibility is also described of making use of a mandrel extending through the discharge opening of the glass container. In this embodiment the figurines can be pre-heated simply by making use of a chosen residence time of each figurine in the tubular cavity defined by the mandrel. 
     Said compositions of glass, figurines and glazing have a number of advantages, particularly in combination with each other. It may for instance be important for the figurines and the glass to have substantially the same thermal coefficient of expansion. This is realized with sufficient precision with the described compositions so that thermal stresses are prevented. The colour-fastness of the glazing must further comply with high standards. These are also fulfilled with the described composition of the glazing. 
     Finally, the invention relates to a spherical glass article in which a three-dimensional object is embedded, which spherical article with the three-dimensional object embedded therein is manufactured by applying one of the above described methods. 
     It should be understood that more than one figurine can be embedded in a glass mass. The figurine can be thermally resistant in a manner such that form and colour are wholly retained despite the very high temperature of the glass. Ceramic materials for instance are very suitable in this respect. A glass figurine or a combination of a number of glass figurines can also be envisaged which fuse together to a greater or lesser degree with the encapsulating glass during embedding In this embodiment the contours of the figurine(s) in the finished product are less sharp than in the first described embodiment with for instance a ceramic figurine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be elucidated with reference to the annexed drawings. Herein: 
     FIG. 1 shows a highly schematic cut-away perspective view of a continuously operating glass furnace; 
     FIG. 2 shows a schematic cross-section through a glass discharge in which a central mandrel is received; 
     FIG. 3 shows a schematic cross-section through an alternative embodiment of a glass discharge, to which heating means and contraction rollers are added; 
     FIG. 3 a  shows a schematic cross-section through the contraction and modelling rollers; 
     FIG. 3 b  shows a top view of alternative rollers which are provided with hemispherical recesses; 
     FIG. 4 is a schematic side view of the discharge arrangement according to FIG. 3 with a device connecting thereto for rolling the glass masses into spherical articles; 
     FIG. 5 shows a partly broken-away perspective view or a variant of the device according to FIG. 4; 
     FIG. 6 shows a partly broken-away perspective schematic view of a complete installation adapted to manufacture glass marbles with a figurine accommodated therein; 
     FIGS. 7,  8 ,  9 ,  10 ,  11 ,  12  show cross-sections through the processing station of the device according to FIG. 6 where successive figurines are embedded in a glass mass; 
     FIG. 13 shows a cross-section through a mould adapted to perform the embedding process in for instance a helium environment; and 
     FIG. 14 shows a schematic view of a embodiment in which transporting of the glass articles from the embedding station to the modelling rollers does not take place by ejection but solely by making use of the force of gravity. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a continuously operating glass furnace  1 . The basin  2  contains a mass of molten glass  3  which is fed in a manner to be described hereinbelow via a so-called feeder  4  to a glass discharge  5  to which a cutting device  6  is added in a manner to be described hereinbelow. 
     A raw material silo  7  connects onto basin  2 . Heating takes place via fuel supply pipes  8  which heat glass mass  4  from above, as symbolically designated with flames  9 . Connecting onto basin  3  in per se known manner are regenerators  10 ,  11  which in successive alternation store heat and supply combustion air  11  to burners  8 . Owing to the alternation of the flow direction and the alternating direction of flames  9 , respectively in the shown direction from regenerator  10  to regenerator  11  and from regenerator  11  to regenerator  12 , an effective heat storage in the receiving generator takes place, which stored heat can be used to pre-heat the combustion air used for the burners. A very high efficiency is hereby obtained. A chimney  13  serves for discharge of the combustion gases. 
     The invention relates in particular to the structure in the vicinity of glass discharge  5 . 
     FIG. 2 shows that the glass mass  3  can be delivered via a discharge channel  14 . Owing to the presence of a central tubular mandrel  15  the glass is delivered in a tubular flow  16  which is subjected in natural manner to a certain contraction as a result of the force of gravity. It should be understood, that at the moment it leaves discharge channel  14  the glass has a temperature in the order of 1100° C. and is therefore red-hot to orange-hot and completely plastic. 
     Central mandrel  15  has a widened lower part  17 . Mandrel  15  can also be driven rotatingly in per se known manner as is designated symbolically with arrow  18 . Since the discharge channel is provided on its underside with an internal flange  19 , the shape of which is adapted to the shape of the widened part  17  of mandrel  15 , the widened part  17  of mandrel  15  can, by moving the mandrel up and down as according to arrow  20 , co-act as a valve body with the flange part  19  serving as valve seat. Glass flow  16  can hereby be controlled as desired. 
     FIG. 3 shows an embodiment in which a relatively wide mandrel  21  is used. Into this hollow mandrel the three-dimensional objects or figurines for embedding and preferably embodied in ceramic material can be lowered from the top such that they come to lie in pinch  23  of the tubular glass flow  16 . With suitable timing in combination with the contraction process to be described hereinbelow the figurines  22  acquire a determined regular mutual spacing. It is noted that the generally still untreated figurines  22  can be pre-heated during the stay in the cavity  24  inside mandrel  21  such that they are as it were pre-baked and acquire a certain cohesion. Owing to this heating the temperature difference between objects  22  and glass flow  16  is limited at the moment of contact, whereby thermal stresses remain within certain limits. 
     Downstream of pinch  23  an additional forced contraction of the glass flow takes place by using for instance three modelling rollers  25  which have in cross-section for instance the form shown in FIG. 3 a . By moving the structure of FIG. 3 a  to the centre a limited, wholly round passage is realized which is bounded by the rotatably driven rollers. Alternatively, the rollers can also be provided as according to FIG. 3 b  with shallow, half-round cavities  26 . 
     Downstream of rollers  25  the glass flow  29  is severed between the embedded objects  22  by means of two knives  27 ,  28  for moving towards each other. 
     Depending on the speed at which rollers  25  rotate, an effective contraction of glass flow  16  can occur or a certain expansion can first occur as designated with  16 ′. 
     A heating element  29  is situated in the area of the opening of through-feed channel  14 . 
     FIG. 4 shows that after leaving cutting device  6  consisting of knives  27 ,  28 , the still plastic masses  30  are received by a roller  31  which is driven rotatably by means which are not drawn and which is provided with a half-round helical groove  32 . As a result of the rotating drive of roller  31  the articles  30  roll downward as according to arrow  33  while being guided by guide means (not drawn) and leave roller  31  in still hot but at least solidified state. 
     Three parameters are important for stress-free cooling or “annealing” of the glass. 
     The annealing temperature T a : below this temperature the thermal stresses present equalize within about 15 minutes through viscous relaxation. In order to make the glass stress-free, the product must therefore be heated to just above T a  and then cooled slowly. 
     The strain temperature T s : below this temperature internal stresses virtually no longer equalize (at T s  the equalization period is about 15 hours). 
     The cooling speed (v): during cooling of products it is necessary to progress through the path T a  to T s  slowly in order to avoid stress build-up due to temperature gradients. 
     Both said temperatures are dependent on the composition of the glass, while (v) depends on the form and geometry of the product. For the composition of the glass as according to the appended claim 10, in which the values are shown in percentages by weight, the following temperatures can be calculated: 
     T a =505° C. 
     T s =187° C. 
     For this type of glass an annealing progression of about 40° C. was used, i.e. 520° C.-480° C. 
     The cooling speeds for the glass articles to be manufactured with the method according to the invention are dependent on the diameters: 
     diameter=22 mm: v=6° C./m 
     diameter=35 mm: v=2.4° C./m 
     Permanent stresses in the glass can be prevented by cooling according to these speeds between 520 and 480° C. 
     It should be taken into consideration here that below T s  temporary stress can still develop in the glass due to rapid cooling. These stresses can be prevented, again depending on the diameter of the spherical article, by a controlled cooling to room temperature. Indicative cooling speeds for this purpose are: 
     diameter=22 mm: v=10° C./m 
     diameter=35 mm: v=5° C./m 
     It should therefore be understood that heating must first take place if necessary to T a , whereafter a period of 15 minutes is reserved in order to arrive at a stress-free state. An annealing treatment then takes place in accordance with the specification given above, whereafter a controlled cooling to room temperature finally takes place in accordance with the cooling speeds given above. 
     The cooling progression immediately after forming of the glass at temperatures above 1000° C. to said temperature of about 520° C. is not of great significance in the occurrence of stresses in the end products. It is the final cooling progression below 520° C. which is the main concern in practice, wherein a separate heat  15  treatment, annealing between 520° C. and 480° C., is also necessary. 
     The influence of the inserted figurine generally consisting of ceramic material is not wholly predictable. It may however be anticipated that, particularly when there is substantial pre-heating, no problems will occur, assuming that said cooling speeds are observed. 
     Attention is drawn to the fact that for the sake of clarity in the drawing the second roller which co-acts with roller  31  is not drawn in FIG.  4 . Reference is made in this respect to FIGS. 5 and 6 in which two different possibilities are shown in more detail. 
     FIG. 5 shows a container  101  for liquid gas onto which connects a discharge  102 . A glass flow  103  flows downwards herethrough. Glass flow  103  is guided round a hollow mandrel  104  onto which connects a feed  105  for figurines  106 . The figurines are discharged into the pinch of rollers  107 ,  108  such that the figurines  106  are wholly embedded by liquid gas at that position owing to the contraction of glass flow  103 . As is shown, rollers  107 ,  108  are provided with substantially hemispherical cavities  109 ,  110  respectively, wherein rollers  107 ,  108  are driven such that the respective cavities, positioned in register in each case, together define a sphere. The supply of figurines  106  is further synchronized with the successive forming in each case of said spherical shape by cavities  109 ,  110 . Thus is ensured that a figurine  106  is always accommodated in the centre of a glass sphere  111 . After leaving the pinch between rollers  107 ,  108  the still plastic glass articles  111  each with a figurine  106  therein drop onto two profiled rollers  112 ,  113 , which are each provided with a more or less semi-cylindrical, helically extending recess. In this embodiment the rollers  112 ,  113  are rotated in opposite direction relative to one another, whereby articles  111  are transported as according to arrow  114  to then be subjected to a final processing, as will be elucidated hereinbelow with reference to FIG.  6 . The rollers can also rotate in the same direction. The pitch of the groove must then be in opposite direction. 
     FIG. 6 shows a container  115  with liquid glass  116 . The container has two discharges  117 ,  118  and two plungers  119 ,  120  which are movable up and downward under the control of a central control unit and which can deliver in pulsating manner one droplet of glass respectively  121 ,  122  at a time via discharges  117 ,  118 . For the sake of clarity FIG. 6 also shows as alternative that the glass flow can be portioned by making use of cutting knives  27 ,  28  (compare FIG.  3 ). The droplets or portions of glass  121 ,  122  are carried at points in time to be described hereinafter to a turntable or carrousel  125  via conduits  123 ,  124 . The carrousel rotates intermittently through angles of 60°. Six bottoms of moulds are placed angularly equidistant on the carrousel. The relevant bottoms are designated with  126  in FIGS. 7,  8 ,  9 ,  10 ,  11 ,  12 . Carrousel  125  is drivable for intermittent rotation in the direction of an arrow  127 . In the drawn position a bottom  126  is filled via conduit  124  with a plastic glass droplet  122 . A step of 60° then takes place whereby a position is reached at which a figurine is discharged onto and partly into the plastic glass mass via a chute  128 . The figurine is delivered by a heating device  129 , where a heating to for instance 850° C. takes place. The infeed tube  130  of heating device  129  connects onto a discharge device  31  with a spiral-shaped vibrating chute  132 . 
     A subsequent step of 60° then takes place to a following position. In this position a droplet  121  is poured via conduit  123  onto the figurine and the already present glass filling on the bottom. 
     Carrousel  125  is then again rotated through a distance of 60° to a position where a cover or stamp  133  closes the bottom in the manner of a mould and the glass article acquires a general spherical shape. The stamp is raised again and carrousel  125  further rotated through 60° to the position of an ejecting mechanism  134  which carries the formed, generally spherical article to a discharge tube  135  by ejection from below. Not shown is that additional directional provisions can for instance be applied for this purpose, for instance an airflow, a pusher or the like (see FIG.  11  and  12 ). 
     Situated at the end of discharge conduit  135  are roller  31  and a non-profiled, generally cylindrical roller  136  which co-acts therewith and which is driven at a different speed. 
     Above roller  31  is situated a burner  137  which serves for so-called “fire-polishing” of the formed glass articles. A temporary heating hereby takes place which facilitates the precise modelling of the spherical glass articles to a spherical shape. Downstream of burner  137  a cooling takes place such that the glass articles with the figurines enclosed therein solidify completely and can be tipped at the end onto an endless conveyor belt  138  to be carried through a thermal treatment device  139 . A reheating to the core of the articles herein takes place first, followed by a very gradual cooling. Thus is ensured that the obtained articles are essentially free of thermal stresses. 
     FIGS. 7-12 show in more detail the structure in the region of carrousel  125 . 
     The figures show the respective stations corresponding with the described six positions. 
     FIG. 7 shows the situation in which a droplet  122  is poured via conduit  124  onto the bottom  126 . The bottom consists of two parts, i.e. a hemispherical lower part  140  and an upper correspondingly formed part  141  with an opening  142 . 
     FIG. 8 shows the situation in which a figurine  106  is placed by means of a pick and place unit  143 . 
     FIG. 9 shows the situation in which a glass mass  121  is poured onto the figurine via conduit  123 . 
     FIG. 10 shows the situation in which press  133  completes the spherical shape under pressure to form a spherical plastic glass mass with a figurine enclosed therein. 
     FIG. 11 shows the manner in which the formed round articles  111  can be fed via conduit  135  to rollers  31 ,  136 . 
     FIG. 12 shows that the still plastic glass articles  111  can also be placed on the interface of rollers  31 ,  136  without interposing of tube  135  but by making use of a chute  144 . Attention is drawn to the presence of an ejector  161  in the embodiment of FIGS. 11 and 12. This serves to remove a formed article  111  from ejector  134  and to push it to chute  144 . 
     FIG. 13 shows a mould  150  comprising a bottom  151 , a cylindrical part  152  and stamp  133  which together with bottom  151  can bound a spherical cavity  153 . Important in this embodiment is the possibility of extracting air from the cavity  153  via a gas passage opening  154 , a cylinder jacket-shaped cavity  155  and apertures  156 ,  157  in order to form an underpressure or to admit a gas soluble in glass, for instance hydrogen, helium, neon, argon or the like. It is important that this provision is operative prior to pouring of the following drop  121  onto the first drop  122 . The forming of air bubbles is prevented in this manner. 
     FIG. 14 shows an alternative to carrousel  125 . Use is made herein of an endless conveyor  161  which carries mould bottoms  126 . The treatment stages which are designated respectively with a, b, c, d and e correspond with the production stages on carrousel  125  as according to FIG.  6  and FIGS. 7-12. 
     As will be apparent, in stage (e) a formed article  111  is deposited on roller  31  under the influence of the force of gravity without interposing of an ejector.