COOLING OF SCISSORS FOR CUTTING OF GLASS GOBS

Abstract: The invention relates to a method of cooling a cutting element of shears used to cut a string of liquid glass into glass gobs for the manufacture of glass objects, for instance glass bottles, in which method a string of liquid glass mass is taken from a glass melting furnace and cut into suitable gob-forming lengths with the aid of the shears, and in which the cutting element of the shears is liquid cooled. The cutting element of the shears is cooled with a cryogenic liquid which is applied to those surfaces of the cutting element which come into contact with the liquid glass mass. The invention also relates to an arrangement for cutting a glass gob from a string (3) of liquid glass in the manufacture of glass object, for instance glass bottles, the arrangement comprising two mutually co-acting cutting elements (2; 41, 42), coolant conducting conduits (23, 13, 11, 11') provided with a nozzle (51; 45, 46) effective in bringing a coolant into contact with the cutting elements (2, 41, 42). The inventive arrangement is characterized by a pressure vessel (14) which includes a phase separator (16) in the conduit line (23, 13, 11, 11') at a location between a source (21) for cryogenic liquid and the nozzle (51; 45, 46).

Description: COOLING OF SCISSORS FOR CUTTING OF GLASS GOBS The present invention relates to a method for cooling a cutting element of shears used to sever a glass gob from a continuous string of liquid glass in the manufacture of glass objects, for instance glass bottles, the method com¬ prising discharging a string of liqυid glass mass from a glass melting furnace and cυtting the liqυid glass string into appropriate lengths with the aid of shears to form gobs or drops and cooling the cutting elements of the shears with a cooling liqυid. The invention also relates to apparatus for carrying out the method. When making glass, and particularly when manufacturing glass objects, such as bottles for instance, there is first prepared a mass of liquid glass of predetermined co posi- tion and of suitable temperature and viscosity. The glass mass is normally taken from the furnace in the form of one or two glass strings which are cut into lengths, i.e. sizes, suitable for the application or purpose intended. In this respect, the liqυid glass string is passed vertically through a ring at a constant speed. The string is severed immediately beneath the ring with the aid of shears, which clip from the string pieces or gobs of glass of predeter¬ mined size at predetermined time intervals, normally of constant frequency. When two mutually parallel strings of liqυid glass are taken from the furnace and passed to mutu¬ ally the same machine, the shears will be provided with two cυtting elements on each leg or arm of the shears, so that the two strings can be clipped simultaneously. When a glass gob is formed by cυtting the string with the aid of said shears, the gob will continue downwards in a chute and enters a mould for producing the object, e.g. a glass bottle. Since the liquid glass string has a very high temperature when it passes through the ring, e.g. a temperature of 1100'C, it is necessary to cool the cυtting elements of the shears. At present this is effected with an aqueous coo- lant, which is sprayed onto the shears. The coolant inclu¬ des a lubricant which will ensure that the glass gob is cut cleanly and smoothly from the string. The lubricant is normally a solubilized cutting oil or a biologically degra- deable substance which has lubricating properties. However, it is very difficult to prevent the lubricant-con¬ taining water from coming into contact with the glass mass. Such contact will result in the presence of larger or smaller defects in the glass object produced. It is also highly essential that lubricant-containing water will not fall into the chute used to convey the glass blob into the mould, since otherwise additional defects may occur. Subsequent to cooling the shears the coolant falls to the floor and also on parts of the machine used to produce the glass objects, therewith dirtying the floor and the machi- ne. Furthermore, it is necessary to collect and cleanse the coolant, before discharging it to a recipient. One object of the present invention is to provide a method and apparatus which avoid the occurrence of defects in glass objects due to contact of the glass with the water coolant during the manufacture of said objects. Another object is one of creating a cleaner environment in the vicinity of machines used for the manufacture of glass objects, by avoiding dirtying floor space and machines with water coolant that contains a lubricant. A further object is to obviate the need to thoroughly cleanse water coolant collected from the surroundings. In accordance with the invention these objects are achieved by means of a method for cooling a cutting element of shears used to cut a glass gob from a string of liquid glass in the manufacture of glass objects, e.g. glass bottles, said method comprising taking a string of liquid glass mass from a glass melting furnace, cυtting the string into appropriate lengths with the aid of shears to produce glass gobs and cooling the cutting elements of the shears with a liquid. The method is characterised by cooling the cutting elements of the shears with a cryogenic liqυid, which iε applied to the surfaces of the cutting element which comes into contact with the liquid glass mass. The invention also relates to apparatus for carrying out the method, said apparatus comprising two mutually co-acting cutting elements and a coolant conduit having a nozzle for bringing the coolant into contact with the cυtting ele¬ ments, and being characterized in that a pressure vessel which incorporates a phase separator is arranged in the conduit at a location between a source of cryogenic liquid and the nozzle. Preferred embodiments of the invention are set forth in the subsidiary claims dependent on the independent claims. The present invention will now be described in more detail with reference to non-limiting exemplifying embodiments thereof illustrated in the accompanying drawings. Figure 1 illustrates schematically an arrangement of appa¬ ratus for carrying out the inventive method, and Figure 2 illustrates schematically and from above a holder device intended for the attachment of two cutting elements to the legs of the shears, and also illustrates a coolant connection, this embodiment enabling gobs to be cut simul¬ taneously from two molten glass strings. The arrangement illustrated in Figure 1 includes shears 1 having two legs 4 which can be swung towards and away from one another about a pivot axis 5, which extends perpendi¬ cular to the plane of the drawing. At the ends distal from the axis 5, each leg has mounted thereon a cutting element 2 for cutting a glass gob or drop from a string of liquid glass mass 3. The liquid glass string is taken from a glass melting fur¬ nace located above the shears. The glass mass leaves the furnace in the form of a horizontal string which travels at a constant speed and which passes through a ring (not shown) located at a short distance above the shears 1. The glass gob separated from the string is transported gravi- tationally along a chute, to a mould located in a machine (not shown). The Figure 1 arrangement also includes a storage tank 21 for a cryogenic liquid, e.g. liquid nitrogen or liquid car¬ bon dioxide. The tank 21 rests on a stand or base 22. Extending from the tank 21 is a conduit 23 which leads to a pressure tank 14. Mounted in the conduit 23, adjacent the storage tank 21, is a main closure valve 24, while an elec¬ tromagnetic valve 25 is mounted in the conduit at a loca¬ tion adjacent the pressure tank 14. The valve 25 is con¬ trolled from a control unit 26. Extending from the bottom of the pressure tank 14 is a con¬ duit 13 which incorporates a manually operated closure valve 15. The conduit 13 branches out into two branch con¬ duits 11 and 11' at a point downstream of the valve 15. The branch point is referenced 12. The end of each branch con- dυit 11, 11' distal from the branch point 12 is connected with a nozzle 51 which is firmly attached to a respective cutting element 2. The nozzle 51 is directed towards its associated cutting element, and particularly towards the cυtting surface thereof. The conduits 13, 11 and 11' are preferably as short as possible, so as to avoid or at least minimize vaporization of the liquid in the conduits to an undesirable gas phase. The conduits are preferably vacuum conduits which include two mutually concentrical steel pipes with a highly effective insulator spaced from the inner surface of the outer steel pipe and with a region of high vacuum located between the insulator and outer pipe. When the branch conduits 11, 11' are of rigid construction, they may incorporate joints which will enable them to be bent. The pressure vessel 14 includes a phase separator 16, which may have the form of an upwardly open vessel to which the conduit 23 extends, a sintered body or some other known kind of phase separator. Conencted to the top of the pres¬ sure tank 14 is a gas pipe 17. The gas pipe 17 incorporates a safety valve 36 which opens automatically when the pres¬ sure in the tank 14 exceeds a pre-determined highest pres¬ sure, e.g. 4.5 bars. The gas pipe also incorporates an electromagnetic valve 30, which is opened and closed by a pressure sensor 34. The valve 30 is intended to maintain the pressure in the tank 14 constant at a pre-determined level, e.g. 3.5 bars. The pressure tank has mounted therein a level sensor 32, which is intended to indicate four dif- ferent liquid levels. The lowest liquid level _a is a warn¬ ing level, at which the liquid level is excessively low, whereas the highest level is a warning level, at which the liquid level is excessively high. Of the intermediate liαuid levels, between the aforementioned levels, the lower level c_ is the lowest level for the liqυid phase and the level of liqυid in the vessel at which the valve 25 must be opened for the delivery of cryogenic liquid. The fourth level e_ indicates the liqυid level at which the electromag¬ netic valve must be closed. The level sensor 32 is connected by a line 29 to the con¬ trol unit 26 which controls opening and closing of the electromagnetic valve 25. Figure 2 illustrates schematically a holder device 40 on which two cutting elements 41, 42 are arranged for attach¬ ment to the legs 4 of the shears illustrated in Figure 1. This will ena ' ble two strings of liquid glass to be cut into gobs simultaneously. The cutting elements 41, 42 are atta¬ ched to the holder device, by means, for instance, of bolts 43, therewith enabling the cutting elements to be replaced. The end of the gas pipe 13 (not shown in Figure 2) distal from the pressure tank 14 is fitted with a T-piece 44, the two free ends of which are each connected to a respective conduit 11. The conduit 11 is attached to the cutting ele- ment and optionally also the holder device 40 with the aid of means not shown. Each of the conduits 11 is provided with a respective nozzle 45 and 46, which are spaced from the cutting surface of respective cutting elements 41, 42. The nozzles 45, 46 are directed towards the cutting sur- faces of respective cυtting elements 41 and 42, for optimal cooling of said surfaces. It will be understood that the respective conduits carrying nozzles 51, 45, 46 may be connected directly to a pressure tank 14 or to individual pressure tanks 14. When initiating cooling of the shears 1 (Figure 1) with cryogenic liαuid, the valve 24 and the valve 25 incorpora¬ ted in the conduit 23 are opened. When these valves are open, cryogenic liquid, for instance nitrogen, carbon di¬ oxide, argon, is forced by the pressure in the tank 21 through the conduit 23 and into the pressure tank 14. The liquid flows into the container of the phase separator 16, where gas present in the liquid will rise upwards. When the phase separator container is full, the liquid will flow over the upper defining surface of the container and enter the pressure tank 14 itself. When the pressure in the tank 14 has reached a pre-determined value, e.g. 3.5 bars, as a result of gas present in the tank 14, the valve 30 is ope- ned. The pressure in the tank 14 is measured with the aid of a pressure gauge 34, which causes the valve 30 to open when the pressure has reached said pre-determined value, and will cause the valve 30 to close when said pressure falls from a high value to the pre-determined value. When the liquid level 33 in the pressure tank 14 has risen to the upper liquid level e_, which is indicated by the level sensor 32, the valve 25 is closed by the control unit 26, which receives control signals from the level sensor or gauge. The valve 15 is then opened and liquid begins to flow from the tank 14 through the branch conduits 11, 11' and the nozzles 51, these nozzles themselves being cooled from ambient temperature to working temperature and also cooling the cutting surfaces of the cutting elements 2. When the level of liqυid in the tank 14 has fallen to the lower, pre-determined level c_, the valve 25 is again opened. Subsequent to commencing cooling of the shears 1, a string of liqυid glass can be taken from the furnace and passed vertically through the ring located above the shears 1, so as to initiate the cutting of glass gobs from the string. The cutting elements 2 mutually co-act in cutting gobs from the string, in a manner similar to the blades of con¬ ventional scissors. It is preferred, in accordance with the present invention, to cool the shears 1 continuously, since if a valve or like device is closed there is generated a gas phase which further reduces the cooling effect. It is also highly advantageous to cool the cutting element 2 with a cryogenic liquid, since such liαuid will obtain a given residence or stay time and therewith exert a better cooling effect on the undersurface of the cutting elements, where it has not earlier been possible to exercise such a persistant cooling effect. It will be understood, however, that both the upper surface and the lower surface of respective shear cutting elements can be cooled. Notwithstanding this it has been found sufficient, however, to cool solely the upper surface of the shears 1. It has also been found advantageous to direct the cryogenic liquid onto the cutting surfaces of the cutting elements 2 with the greatest possible precision, and then preferably against those cutting surfaces which come into contact with the liquid glass. It has also been found that the pressure of the liquid leaving the nozzle 51 should lie within the range of 0.2-2 bars, preferably 0.5-1 bar. In accordance with the present invention, it is also highly advantageous to separate the gas phase present in the cryo¬ genic liquid at the shortest possible distance from the nozzles 51, so as to thereby enhance the cooling effect of the cryogenic liqυid. Another advantage afforded by the inventive method is that the chutes used for conveying the glass gobs to the machi¬ ne moulds can be made of a carbon fibre material. When the chutes are made of carbon fibre material, the glass gobs • will move at a greater speed and therefore reach the machi¬ ne mould more quickly.

Claims: CLAIMS 1. A method of cooling a cutting element of shears used to cut a string of liquid glass into gobs for the manufacture of glass objects, for instance glass bottles, in which a string of liquid glass mass is taken from a glass melting furnace and cut by said shears into appropriate lengths to form said glass gobs . while cooling said cutting element with a liquid, characterized by cooling the cutting element of said shears with a cryogenic liquid and applying said cryogenic liquid to cυtting element surfaces which come into contact with the liquid glass mass. 2. A method according to Claim 1, characterized in that the liquid used is liquid nitrogen or liqυid carbon dioxide. 3. A method according to Claim 1 or Claim 2, characterized by directing the cryogenic liqυid onto the horizontal, up¬ wardly facing surface of said cutting element. 4. A method according to one or more of Claims 1-3, charac¬ terized by isolating a gas phase from the cryogenic liquid immediately prior to applying said liquid to said cutting elements. 5. A method according to one or more of Claims 1-4, charac¬ terized by spraying cryogenic liqυid onto said cυtting elements at a pressure of 0.2-2 bars, preferably 0.5-1 bar. 6. A method according to Claim 5, characterized by spraying cryogenic liαuid continuously onto the cutting element of said shears. 7. An arrangement for cutting a glass gob from a string (3) of liαuid glass in the manufacture of glass objects, for instance the manufacture of glass bottles, said arrange¬ ment including two mutually co-acting cutting elements (2; 41, 42), coolant conduits (23, 13, 11, 11') provided with nozzles (51; 45, 46) for bringing a coolant into contact with the cutting elements (2; 41, 42), characterized by a pressure vessel (14) which includes a phase separator (16) in the conduit (23, 13, 11, 11') between a source (21) of cryogenic liquid and the nozzle (51; 45, 46). 8. An arrangement according to Claim 7, characterized in that the pressure vessel (14) is provided with a gas valve (30) which is effective in holding the pressure in the vessel (14) constant. 9. An arrangement according to Claim 7 or Claim 8, charac¬ terized in that the pressure vessel (14) is provided with a level sensor (32) for maintaining the liquid level (33) in the pressure vessel (14) within a pre-determined highest level (e) and a pre-determined lowest level (c). 10. An arrangement according to Claims 7, 8 or 9, charac¬ terized in that the nozzle (51; 45, 46) on the conduit (11, 11') is arranged to direct a stream of cryogenic liαuid onto that part of the cutting element (2; 41, 42) which comes into contact with the liquid glass.

Inventors: MENZEL PAUL, MENZEL, PAUL
Applicants: AGA AB, AGA AKTIEBOLAG
Application year: 1988
Main classification: C04B7
IPC codes: C03B7