Method and apparatus for manufacturing glass containers

Abstract: A method for manufacturing a glass container includes the steps of (a) providing a plunger (1) coated with a ceramic coating (3) or a sprayed metal coating (2) of self-fluxing alloy or both coatings on at least one portion of a surface of the plunger and (b) forming a lubrication carbon layer on surfaces of molds including a blank mold and a neck ring by periodically injecting (14) flames of at least one kind of gaseous hydrocarbon having a carbon to hydrogen ratio more than 0.75. The coating of the plunger (1) prevents the plunger from being oxidized so that flaking of an oxidized layer which will be accompanied by generation of defects at an inside surface of a glass container does not occur. Due to the carbon layer formed through flame injection of hydrocarbons, oiling of the molds is unnecessary and generation of bubbles in the oil film does not occur. This method not only increases the impact strength of a glass container but also increases the uniformity of impact strength.

Description: The present invention relates to methods for manufacturing glass containers, directed to increasing the impact strength of the containers, and also to apparatus for carrying out the methods. In a conventional method for manufacturing glass containers using an individual section machine, for the purpose of easily separating a formed glass container from molds including a blank mold, a neck ring, and a baffle, the molds are oiled at intervals, for example at a rate of once per twenty to sixty minutes. However, there are the following drawbacks in the conventional glass container manufacturing method. More particularly, graphite included in the lubrication oil adheres to a plunger for forming parisons and the adhering graphite in turn shifts from the plunger to a parison during the press process thereby causing defects in the inside surface of the glass container. Further, when heated, the lubrication oil tends to generate bubbles which will cause defects in the inside surface of the glass container. These defects caused at the inside surface of the glass container not only decrease the impact strength of the glass container but also cause the impact strength of the glass container to fluctuate. EP-A-377452 describes a way of forming a coating on a glass mould plunger, in which self-fluxing alloy particles are fed into a chamber and a supersonic spray stream containing the particles is formed by igniting a combustible mixture. The spray stream is directed onto a plunger substrate to form a coating which is then ground and polished. US-A-4648893 (FR-A-2570364) describes lubrication of a split mould in the manufacturing of glass bottles. The mould is opened, and a jet of gas directed into the opened mould. The jet of gas is heat-treated, e.g. by injection through a flame, to form a powdery carbon material to lubricate the mould. The heat-treated gas may be acetylene. EP-A-368267 describes a two-stage process in which the inner surfaces of a hollow mould are coated with a carbon layer by the combustion of hydrocarbon gas. The first stage uses an oxygen-rich gas mixture, the second stage introduces the carbon-producing hydrocarbon gas. Acetylene is suggested. AT-E-50 973 describes lubricating the surface of a mould by injecting gaseous hydrocarbon into the mould. The gaseous hydrocarbon has a carbon to hydrogen ratio higher than 0.75. JP-A-1-239 029 describes coating a plunger with a ceramic material to form glass bottles with good impact strength. The problem addressed herein is to provide new methods and apparatus for making glass containers, whereby impact strength of the resulting glass containers is increased and stabilised. In one aspect, we provide a method of making a glass container by press-blow forming, comprising putting a glass gob into a blank mould having a neck ring and pressing a plunger into the mould through the neck ring to form a parison, and blow-forming the parison to a final configuration of the glass container; flames of gaseous hydrocarbon having a carbon to hydrogen ratio over 0.75 being injected into the mould to form a lubricating carbon coating on its inner surface before the parison is formed therein, wherein the plunger includes a first portion for forming a mouth portion of the parison and a remaining second portion, the first portion of the plunger having a sprayed metal coating of self-fluxing alloy, having a hardness less than Vickers hardness 800, and the second portion having a ceramic coating. In another aspect, we provide apparatus suitable for carrying out the above method, comprising a blank mould, a neck ring and a plunger movable through the neck ring to press-form a parison in the blank mould, and a flame injector adapted to inject flames of gaseous hydrocarbon having a carbon to hydrogen ratio over 0.75 into the mould, the plunger having a first portion for forming a mouth portion of the parison and a remaining second portion, wherein the first portion of the plunger has a sprayed metal coating of self-fluxing alloy, having a hardness less than Vickers hardness 800, and the second portion has a ceramic coating. This enables a lubrication oil film which is formed on molds in the conventional method to be replaced by the carbon layer formed through flame injection of at least one kind of gaseous hydrocarbon. Because of this carbon layer, bubbles from an oil film are not generated and graphite shifting from oil to the plunger and in turn from the plunger to the parson does not occur. As a result, the impact strength of a glass container may be greatly improved. Further, when the plunger is coated with a coating of ceramics and self-fluxing alloy, the oxidation of the surface portion of the plunger is prevented so that faking of an oxidized layer and the subsequent mixing into the parison will not occur. This also increases the impact strength of the glass container. Importantly, with application of both the carbon layer formation and the plunger coating, a greater impact strength stabilizing effect (a synergism) can be obtained than with a summation of the stabilizing effect due to the carbon layer formation only and the stabilizing effect due to the plunger coating only. Preferred aspects are set out in the dependent claims. Specific embodiments of the invention are now described with reference to the accompanying drawings, in which: FIG. 1 is a cross-sectional view of one section of an individual section machine illustrating that molds are being formed with a carbon layer using a glass container manufacturing method useful in understanding the present invention; FIG. 2 is a partial, cross-sectional view of the machine of FIG. 1 illustrating a parison being manufactured; FIG. 3 is a front elevational view of a plunger coated with a ceramic coating; FIG. 4 is a front elevational view of a plunger coated with a sprayed metal coating of self-fluxing alloy; FIG. 5 is a front elevational view of a plunger coated with both a ceramic coating and a self-fluxing alloy coating, which can be used in the method in accordance with a first embodiment of the invention; FIG. 6 is a graph illustrating a relationship between an accumulated fracture rate and impact strengths of glass containers; FIG. 7 is a cross-sectional view of one section of an individual section machine illustrating air being blown out from vertically extending holes to form an air curtain in a glass container manufacturing method in accordance with a second embodiment of the invention; FIG. 8 is a cross-sectional view of one section of an individual section machine illustrating air being blown out from horizontally extending holes to form an air curtain in the method in accordance with the second embodiment of the invention; FIG. 9 is a cross-sectional view of an apparatus for executing a glass container production method in accordance with a third embodiment of the invention; and FIG. 10 is a graph illustrating impact strengths of glass containers manufactured in accordance with all the methods of the first through third embodiments of the invention compaired to impact strengths of glass containers manufactured in accordance with conventional methods. COMPARATIVE EXAMPLE FIGS. 1 to 4 illustrate an apparatus and portions thereof used in a glass container manufacturing method useful in understanding the present invention. In FIG. 1 which illustrates one section of an individual section machine, a plunger 1 is provided which is movable relative to a blank mold 12, a neck ring 10, and a guide ring 11 so that the plunger 1 can form an inside configuration of a parison when the plunger 1 pushes a gobbet of glass inserted in the blank mold 12. When the blank mold 12 is opened, that is, when a baffle 13 (see FIG. 2) is dismounted from the blank mold 12, a nozzle 14 located above the blank mold 12 injects flames of at least one kind of gaseous hydrocarbon thereby forming a film-like lubrication carbon layer on surfaces of the blank mold 12, the neck ring 10, and the guide ring 11. The hydrocarbon or hydrocarbons supplied to the nozzle 14 include a hydrocarbon with a carbon to hydrogen ratio of more than 0.75, for example acetylene. A pilot firing device continuously operates and the gaseous hydrocarbon is injected to the pilot firing device to be thermally cracked quickly and to form a carbon layer on the inside surfaces of the molds including the blank mold 12 and the neck ring 10. A portion of the plunger 1 which will be brought into contact with a gobbet of glass is coated beforehand with a ceramic coating 3 constructed of at least one kind of ceramics selected from the group of TiN, TiC, TiCN, TiB 2 , SiC, and Al 2 O 3 , or a sprayed metal coating 2 constructed of at least one kind of self-fluxing alloy selected from cobalt series alloys including cobalt series Cr 3 C 2 . These coatings 2 and 3 are oxidation-proof coatings. Then, as illustrated in FIG. 2, a parison 15 is manufactured using the plunger coated with the ceramic coating 3 (FIG. 3) or the sprayed metal coating 2 (FIG. 4) of self-fluxing alloy. The molds are formed with the carbon layer through flame injection of at least one kind of gaseous hydrocarbon. Then, the parison 15 is blow-formed to a glass container with a final configuration. In the above-described glass container manufacturing method, both formation of the oxidation-proof coating on the surface of the plunger 1 and formation of the carbon layer on the surfaces of the molds are used. Due to the formation of the ceramic coating 3 or the self-fluxing alloy coating 2 on the surface of the plunger 1, oxidation of a surface portion of the plunger 1 is prevented so that flaking of any oxidized layer from the plunger 1 and mixing of oxidized metal powders into a parison does not occur and therefore, reduction of impact strength of the glass container due to mixing of the metal powders does not occur. Further, since the carbon layer is formed not through oiling but through flame injection of the gaseous hydrocarbon or hydrocarbons, reduction of the impact strength of the glass container due to bubbles which are generated in the case of oil can be prevented. Impact strength tests were executed using vial glass containers having a volume of 200 cc and a thickness of 2.2 mm. The test results are shown in TABLE 1. In TABLE 1, method A corresponds to the conventional method including an oiling, method B (a comparison, and not included in the present claims) corresponds to a case where only a carbon layer formation was executed, method C (a comparison, and not included in the present clams) corresponds to a case where only a plunger coating formation was executed, and method D is a case where both the carbon layer formation and the plunger coating formation were executed. Average (in-lbs) Fluctuation (in-lbs) Method A (Conventional) 7 1 - 16 Method B (Comparison) 12 5 - 20 Method C (Comparison) 10 5 - 15 Method D 20 9 - 22 Herein 1 in-lbs = 0.113 Nm. As will be understood from TABLE 1, by executing both the plunger coating and the carbon layer formation, the average impact strength was doubled and the fluctuation of the impact strength was greatly reduced. In addition, the lower limit of the impact strength distribution was raised. FIG. 6 illustrates a relationship between an accumulated fracture rate and impact strengths of glass containers, wherein references A, B, C, and D correspond to the references of TABLE 1. As can be understood from D in FIG. 6, the fluctuation or dispersion range of the impact strengths of the glass containers manufactured was very small and the lower limit of the dispersion rangewas raised. TABLE 1 and FIG. 6 together show that there is a synergism in the increase in the impact strength and in the reduction of the dispersion range of the impact strengths in accordance with method D as compared with methods B and C. EMBODIMENTS OF THE INVENTION In the invention the oxidation-proof coating to be formed on the plunger has a coating structure such as shown in FIG. 5. Since other structures are the same as those of the comparative example like members are denoted with like reference numerals. As illustrated in FIG. 5, the plunger 1 includes a first portion for forming a mouth portion (an opening portion) of a parison and a remaining, second portion. The first portion of the plunger 1 is coated with a sprayed metal coating 2 of self-fluxing alloy having a hardness less than Vickers hardness 800, and the second portion is coated with a ceramic coating 3. The self-fluxing alloy and the ceramics were discussed in the useful in the comparative example. Using a plunger the entire surface of which is coated with Ni series self-fluxing alloy (see FIG. 4) may cause an oxidized layer to form, though very small, on the surface of the plunger when the plunger contacts a gobbet of glass at high temperatures. The oxidized layer may be flaked from the plunger and adheres to a parson so that a defect is caused at an inside surface of the parison. When the glass container is cooled after blow forming of the glass container, cracks will initiate at the foreign substances due to a thermal expansion difference between metal and glass. In contrast, in a case where the entire surface of the plunger is coated with a ceramic coating 3, the above-described flaking of an oxidized layer does not occur because a ceramic coating is a highly oxidation-resistant material. However, since the ceramic coating has a very high hardness, for example, a hardness greater than Vickers hardness 1000, the inside surface of the mouth portion of the glass container is often scratched by the plunger when the plunger is lowered, so that defects having lengths of several hundred microns are caused at the inside surface of the glass container. Since the mouth portion of the glass container usually has a thick wall, the defects caused in the mouth portion will not decrease the impact strength of the glass container. However, the defects caused at the mouth portion of the glass container reflect light and degrade the economic value of the glass container. In the invention, since the first portion of the plunger is coated with a self-fluxing alloy coating and the second portion is coated with a ceramic coating, defects which may be caused at a mouth portion of a glass container in the manufacturing method according to the comparative example will be prevented. More particularly, though the second portion or tip portion of the plunger is brought into contact with a gobbet of glass at high temperatures more than 1,000 °C, the ceramic coating can endure the high temperature and the surface of the second portion of the plunger is not oxidized. Since the first portion of the plunger is heated to a relatively low temperature, for example 500 °C, the self-fluxing alloy can endure the temperature. Since a self-fluxing alloy having a hardness lower than Vickers hardness 800 is selected for the material of the coating of the first portion of the plunger, the mouth portion of the glass container will not be scratched by the first portion of the plunger. For the purpose of confirming the effects due to the second embodiment, tests were executed. Plunger A, Plunger B and Plunger C (comparison) were prepared. With respect to plunger A, the first portion was coated with a coating of Cr-Ni-B series self-fluxing alloy and the second, tip portion was coated with a coating of TiN. With respect to plunger B, the first portion was coated with a coating of Cr-Ni-B series self-fluxing alloy and the second portion was coated with Al 2 O 3 . With respect to plunger C, the entire surface of the plunger was coated with a coating of self-fluxing alloy. Plungers A, B and C were mounted to different sections of the same individual section machine, and press and blow forming of juice glass containers having a volume of 300 ml were continuously executed. The test results are shown in TABLE 2. Impact Strength Plunger A (in-lbs) Plunger B (in-lbs) Plunger C (in-lbs) Minimum 9 10 2 Maximum 21 22 12 Average 14.3 17.5 8.3 Durability 120 hr 120 hr 48 hr Herein 1 in-lbs = 0.113 Nm. Further, plunger D (comparison), the entire surface of which was coated with a coating of TIN, was prepared. Plunger A and plunger D were mounted to different sections of the individual section machine, and press and blow forming of glass juice containers (X) with a mouth portion of a small diameter and glass juice containers (Y) with a mouth portion for a one touch cap were executed using the plungers A and D. The rate of generation of inferior goods was observed over two days. The test results are shown in TABLE 3. Plunger A (Second Embodiment) Plunger D (Comparison) Glass container X 0 % 10 - 15 % Glass container Y 0 % 7 - 9 % As will be understood from TABLE 2 and TABLE 3, in accordance with the invention defects generated at the inside surface of the mouth portion of the glass container can be greatly suppressed, while the impact strength of the glass container is maintained at the same level as the strength obtained by the comparative example, method D. FIGS. 7 and 8 illustrate other plunger arrangements embodying the invention. Since the structures other than the plunger are the same as those of the first embodiment, like members are denoted with like reference numerals. In these embodiments the plunger 1 is held below a position located by 20 mm above the top of a positioner 20 for guiding the upward and downward movements of the plunger 1. Further, air is blown out from a base portion of the plunger 1 to thereby form an air curtain which covers the plunger 1. The air curtain is formed in order to prevent foreign substances from attaching to the outside surface of the plunger 1. Since the air is blown out from the base portion of the plunger 1, the air can protect almost all portions of the plunger 1. If the air were blown out from a portion near the top of the plunger, the lower portion of the plunger could not be covered by the air curtain. The reason why the plunger 1 is held below the position located 20 mm above the positioner is that, below this limit, the air curtain is well maintained up to the top of the plunger and can cover the entire portion of the plunger. With reference to FIG. 7, structures of an apparatus will be explained in more detail. The plunger 1 is coupled to a head 17 of a drive mechanism (a drive mechanism for driving the plunger in a vertical direction) via a split ring 19 so that the plunger 1 and a cooling pipe 18 installed within the plunger 1 can be driven inside positioner 20 into a space defined by the blank mold and the neck ring to press and form the parison. Holes 21 are formed in the split ring 19. Compressed air supplied from a lower portion of the positioner 20 flows from the cooling pipe 18 into a space defined in the plunger 1 to cool the plunger 1 from the inside thereof and then is exhausted through the holes 21. A plurality of vertically extending holes 22 are formed in the base portion of the plunger 1. One portion of the cooling compressed air is blown out through the vertical holes 22 to form the aforementioned air curtain. The vertically extending holes 22 may be replaced by a plurality of horizontally extending holes 23 (which may be horizontally and upwardly extending holes) as illustrated in FIG. 8. The air blown out from the holes 23 collides with an inside surface of the positioner 20 and turns in an upward direction. Due to the collision, the air curtain is formed more evenly around the plunger 1 than in the case of the vertically extending holes. For the purpose of keeping the air clean, a filter may be installed in the plunger mechanism. Further, to cover the entire outside surface of the plunger 1, the speed of a current of the air curtain is selected at a speed larger than 0.5 m/sec and preferably at a speed within the range of 1 to 3 m/sec. To confirm its effects, tests were executed using an individual section machine having the plunger mechanism shown in FIG. 7 to execute pressing and blow forming of glass containers with a thin thickness having a weight of 170 g and a volume of 300 cc. The speed of a current of the air curtain was 2.5 m/sec at the top of the positioner. The top of the plunger is adjusted in position to be located above the top of the positioner by 20 mm. Measuring the impact strengths of ten glass containers, it was found that the average impact strength was 19.0 in-lbs and the range of fluctuation of the impact strengths was 15.0 in-lbs to 20.3 in-lbs. In a case where no air curtain was formed, it was found that the average impact strength was 7.7 in-lbs and the range of fluctuation of the impact strengths was 4.0 in-lbs to 9.0 in-lbs. From these test results, it can be understood that the impact strength of a glass container can be increased by 2.5 times as compared with a case where no air curtain is formed. FIG. 9 illustrates an apparatus for executing a method in accordance with a further embodiment of the invention. In this embodiment, the positioner 20 includes a bushing 24 and a spring guide 25. An abrasion-proof layer 30 is formed on the sliding surfaces between the bushing 24 and the spring guide 25 so that dusts are prevented from being generated by abrasion of the sliding surfaces. Metal dusts would decrease the impact strength of a glass container. More particularly, the abrasion-proof layer 30 is constructed of ceramics, for example, TiN, TiC, SiC, or Al 2 O 3 . This layer 30 has a Vickers hardness greater than 1000 at a room temperature. Though the positioner 20 itself is constructed of iron, the abrasion-proof layer 30 greatly increases the abrasion-proof characteristics of the positioner 20. Even if glass powders (with a Vickers hardness of Hv 500) and iron powders (with a Vickers hardness of Hv 200 to 800) invade into the sliding surfaces, the sliding surfaces are not scratched, because the hardness of the abrasion-proof layer 30 is greater than that of these powders Further, the sliding surfaces constructed of ceramics will prevent the sliding surfaces from sticking to each other, which would occur if the sliding surfaces were constructed of metal. The sliding surfaces between the split ring 19 and the bushing 24 are preferably formed with similar abrasion-proof layers 31, and also the sliding surfaces between a washer 29 and the bushing 24 are preferably formed with abrasion-proof layers 32. For the purpose of confirming the effects of this embodiment, the above-described positioner was mounted to one of the eight sections of the individual section machine, and press and blow forming of glass juice containers having the volume of 180 cc was executed. The metal powder generation rate of the one section and that of a section mounted with a conventional positioner were examined. The results of this test showed that the metal powder generation rate at the other section mounted with the conventional positioner was 4.7 % per 72 hours, while the metal powder generation rate at the one section mounted with the positioner in accordance with Fig. 9 was 0.09 % per 0.5 months. The glass container production was continued using the one section mounted with the positioner in accordance with Fig. 9, and when one month elapsed, no increase in the metal powder generation rate was seen. The main features of the invention are in the combination of the means of forming a carbon layer through flame injection of gaseous hydrocarbons and the means of forming an oxidation-proof layer on the plunger which were discussed in the embodiments. The tests wherein the means of all the above embodiments were applied in combination to glass container production were executed using vial glass containers having a volume of 200 cc and a thickness of 2.2 mm, and the test results are shown in FIG. 10. The test results according to the conventional method are shown also in FIG. 10 for comparison. As is apparent from FIG. 10, the impact strength of the glass containers made by this preferred embodiment of the invention was twice that of the glass containers manufactured according to the conventional method and the fluctuation of the impact strength was reduced so that reliability of the strength of glass containers was greatly improved. Using the above teachings, the following effects may be obtained. First, the fluctuation of the impact strength of glass containers is reduced so that the reliability of the glass container strength is greatly improved. Second, the impact strength of the glass containers can be increased by about twice.

Claims: A method of making a glass container by press-blow forming, comprising putting a glass gob into a blank mould (12) having a neck ring (10) and pressing a plunger (1) into the mould through the neck ring (10) to form a parison (15), and blow-forming the parison (15) to a final configuration of the glass container; flames of gaseous hydrocarbon having a carbon to hydrogen ratio over 0.75 being injected into the mould (12) to form a lubricating carbon coating on its inner surface before the parison (15) is formed therein; wherein the plunger (1) includes a first portion for forming a mouth portion of the parison (15) and a remaining second portion, characterised by the use of a said plunger (1) wherein the first portion has a sprayed metal coating (2) of self-fluxing alloy, having a hardness less than Vickers hardness 800, and the second portion has a ceramic coating (3). A method according to claim 1, wherein the ceramic coating (3) is of material selected from TiN, TiC, TiCN, TiB 2 , SiC, and Al 2 O 3 . A method according to claim 1 or claim 2, wherein the self-fluxing alloy is of cobalt series Cr 3 C 2 . A method according to any one of the preceding claims wherein the hydrocarbon is acetylene. A method according to any one of claims 1, 2 or 4, wherein the self-fluxing alloy coated on the first portion of the plunger (1) is Cr-Ni-B series self-fluxing alloy and the ceramics coated on the second portion of the plunger is TiN or Al 2 O 3 . A method according to any one of the preceding claims in which, when not pressed into the mould (12), the plunger (1) lies inside a positioning guide (20) and air is blown from around a base portion of the plunger (1) to form an air curtain around the plunger (1) and thereby prevent substances from attaching to its outer surface; and wherein the top of the plunger (1) does not then project more than 20mm above the positioning guide. A method according to claim 6, wherein an air current speed of the air curtain is at least 0.5 m/sec. A method according to claim 7, wherein the air current speed of the air curtain is in the range of 1 to 3 m/sec. A method according to any one of claims 6 to 8, wherein a plurality of vertically extending holes (22) are formed in the base portion of the plunger (1) and the air is blown out through the vertically extending holes (22). A method according to any one of claims 6 to 8, wherein a plurality of horizontally extending holes (23) are formed in the base portion of the plunger and the air is blown out through the horizontally extending holes (23). A method according to any one of the preceding claims, wherein a positioning guide which guides the plunger (1) includes a bushing (24) and a spring guide (25) slidingly contacting each other at sliding surfaces thereof, at least one of the sliding surfaces being coated with an abrasion-proof layer (30). A method for manufacturing a glass container according to claim 11, wherein the abrasion-proof layer (3) is constructed of material selected from the group of TiN, TiC, SiC, and Al 2 O 3 . Apparatus suitable for carrying out a method according to any one of claims 1 to 12, comprising a blank mould (12), a neck ring (10) and a plunger (1) movable through the neck ring to press-form a parison (15) in the blank mould (12), and a flame injector (14) adapted to inject flames of gaseous hydrocarbon having a carbon to hydrogen ratio over 0.75 into the mould (12), the plunger having a first portion for forming a mouth portion of the parison (15) and a remaining second portion, characterised in that the first portion of the plunger (1) has a sprayed metal coating (2) of self-fluxing alloy, having a hardness less than Vickers hardness 800, and the second portion has a ceramic coating (3).

Inventors: HAYASHI MASATO, NOMURA MAKIO, NOZAWA MITSURU, TAKABA AKIHIKO, HAYASHI, MASATO, NOMURA, MAKIO, NOZAWA, MITSURU, TAKABA, AKIHIKO, HAYASHI, MASATO, C/O ISHIZUKA GARASU K.K., NOMURA, MAKIO, C/O ISHIZUKA GARASU K.K., NOZAWA, MITSURU, C/O ISHIZUKA GARASU K.K., TAKABA, AKIHIKO, C/O ISHIZUKA GARASU K.K.
Applicants: ISHIZUKA GLASS, ISHIZUKA GARASU KABUSHIKI KAISHA
Application year: 1991
Main classification: C03B40
IPC codes: C03B9, C03B40