METHOD AND APPARATUS FOR CLEANING MOLDS USED IN THE GLASS FABRICATION INDUSTRY

Abstract: Graphite-like material is removed from metal molds used in the glass fabrication industry by placing a metal glass-fabricating mold with graphite-like material deposited thereon in a chamber, providing an oxygen rich mixture of combustible gases in the chamber, and igniting the oxygen rich mixture of combustible gases in the chamber to produce a high temperature and a pressure wave. A high temperature wave front and a pressure wave impinge on and remove graphite-like material from the metal mold by ablation of the graphite-like material.

Description: METHOD AND APPARATUS FOR CLEANING MOLDS USED IN THE GLASS FABRICATION INDUSTRY This invention relates to cleaning molds used in the glass fabrication industry in a cost effective and environmentally safe manner. BACKGROUND OF INVENTION The glass industry utilizes glass molding equipment for the fabrication of glass containers and other articles. In the molding process, various chemical compounds are applied to the molds in order to facilitate mold separation and glass flow. Due to the high temperatures involved, these compounds as well as the glass produce a reaction in which a layer of material is deposited on the mold. This material consists primarily of a series of strata which have carbon interspersed within as well as a variety of trace elements. The characteristics of the material are primarily that of graphite, in particular with a high melting point which is much higher than that of the mold substrate from which the material deposited is to be removed. Glass molds may be made from a variety of materials, but can be categorized as being constructed of various metals, a block of metal having been machined to create a mold which provides the contours of the article to be molded. The mold design may be further enhanced to increase its working life by the use of liner materials which have higher abrasion resistance as well as improved resistance to oxidation or formation of carbides. The present invention does not depend upon the metal from which the mold is fabricated because there is a large differential between the thermal absorption and conduction characteristics of the graphite-like material and the mold metal. Flow guides and other objects designed to fit within the glass making machinery may also receive graphite-like deposits in the same manner as the mold. Throughout this application therefore, the term "molds" is also intended to include such components used in the glass making industry, primarily but not limited to those used by or within mechanized glass making equipment. The sequential deposition of layer upon layer of the graphite-like compound is sufficient to produce large dimensional changes in the mold surface, such that the mold cannot be closed properly and/or the surface of the molded article is deformed to an unacceptable amount. The net result is that the mold must be removed from operation and the graphite-like compound removed. Due to the lubricating nature of the graphite-like compound, its removal can be facilitated by abrasion using relatively high energy particles in a so-called blasting operation. This is effective but results in damage to the mold due to the inability to limit the particle trajectory solely within the boundary of the graphite-like compound. The result is damage to the mold which limits the mold life. The blasting operation can be moderated to minimize damage to the mold, but a proportionately longer time is then required to totally remove the graphite-like compound. In either case, such techniques have been found to be undesirable for cost, practical or technical reasons. It is therefore an object of the present invention to provide an improved method for removing graphite-like material from a glass mold, and to provide apparatus for carrying out the method. SUMMARY OF THE INVENTION According to the present invention, a high energy thermal impulse is used to impart sufficient energy transfer to remove the thermally insulating graphite-like compound while not affecting the high thermally conductive metal mold substrate on which the graphite-like compound is deposited. The invention utilizes the ignition of an oxygen rich mixture of combustible gases to produce a high temperature and a pressure wave. Due to the highly combustible nature of the oxygen rich mixture, very high peak temperatures are produced during the burning process. Despite this high temperature, the total energy produced during the ignition process is low compared to the thermal mass of the mold substrate and only raises the substrate temperature by a few 10's of degrees Centigrade. When the temperature wave front contacts the thermally insulating graphite-like compound the temperature thereof is raised sufficiently to cause it to oxidize at a fast rate until it is totally vaporized. As the compound is ablated, energy is consumed. " When the ablation is completed and the mold substrate is encountered, the substrate (being of highly thermally conductive material) reflects and absorbs the thermal energy and reflects the mechanical wave without damage. The cleaning method in accordance with the present invention is based on using a combination of high instantaneous temperatures and a pressure wave. The peak temperatures which are encountered vary with materials and are primarily dependent on both the thermal radiation absorption characteristics of the material and its thermal conductivity. The higher the absorption, the higher the peak temperature, and the lower the thermal conductivity the higher the peak temperature. In this method, the graphite-like compound is high in absorption and low in thermal conductivity, thereby producing an optimal situation for energy transfer. In contrast to the optimum ability of the graphite-like compound to reach peak temperatures, the metal mold is poorly suited to reach high temperatures even when exposed to similar thermal and pressure wave conditions. This reduced ability is due to the nature of metal to reflect the thermal radiation to a varying degree, which in any case is larger than that of the graphite-like compound. The peak temperature of the mold is further moderated by the high thermal conductivity thereof. The result is the production of a somewhat lower peak temperature in the mold compared to that of the graphite-like compound, even when both materials are exposed to the same thermal conditions. The removal of the graphite-like compound is facilitated by the high peak temperatures and the effect of the pressure wave. The method of the invention is dependent on the peak temperature of the graphite-like compound being high enough to cause, in all or in part, the graphite-like compound to vaporize and/or oxidize and/or break into smaller pieces. The pressure wave portion of the method of the invention dislodges, by impulse action, portions of the graphite-like compound which have oxidized or broken into smaller pieces, thereby cleaning the molds by ablation to a higher degree than would be possible by thermal methods alone. The method of the invention is made practicable by the use of a combustible mixture of gases which are confined within a pressure vessel. Consideration such as maximum mixture pressure and/or the ability of the vessel to withstand the dynamic pressures involved may dictate the vessel design. In order to optimize the production of peak temperatures within the graphite-like compound, the oxygen concentration of the mixture should be optimized for complete oxidation of the combustible gas. The mold to be cleaned is placed within the pressure vessel, after which the vessel is sealed and filled with a mixture of oxygen and combustible fuel. The fuel may take the form of combustible vapour or any combustible gas. Any combustible mixture may be used in the method of the invention, provided that the energy release which results from ignition is large enough to produce peak temperatures in the graphite-like layer which are high enough to facilitate oxidation of the graphite-like compound. Once the filling process is completed, the mixture is ignited. The result inside of the vessel is an advancing wave front which is created as the mixture burns. This advancing wave emits large amounts of thermal radiation and exerts high dynamic pressures on any object which it encounters. The thermal radiation is readily absorbed by the graphite-like compound and consequently raises the temperature thereof prior to the pressure wave reaching the outer surface of the graphite-like compound. During the time in which the graphite-like compound is being heated, the compound may (although not necessarily) be vaporized or oxidized. Also, the graphite-like compound serves as a thermal insulating blanket, absorbing thermal energy rather than transferring it to adjacent objects. The result is a somewhat reduced thermal flux reaching the mold surface during the vaporization and oxidation process. Following the thermal wave which impinges on the graphite-like compound is the pressure wave. The differences in arrival time of these two effects is due to the finite propagation velocity of the pressure wave compared to the speed of light at which the thermal flux wave travels. As the pressure wave advances, the thermal flux emissions increase due to the ever expanding sphere of combustion. The result is a peak thermal flux which is sufficient to oxidise and/or vaporize and/or crack all or part of the graphite-like layer. When the pressure wave arrives, ablation of the graphite occurs and a certain degree of thermal and mechanical energy is expended in the process. If the total energy is insufficient, the entire amount of graphite-like compound will not be removed. In such cases, the method is repeated until a satisfactory amount of removal is achieved. If on the other hand, sufficiently large thermal and mechanical energy is available to entirely remove the graphite-like compound, the added energy will be absorbed and partially reflected by the mold itself. The heating effect is further diminished by the reflectance of the flux from the metal mold surface. Because of the relatively large thermal mass of the mold, such reflection and absorption is harmless to the mold and no damage occurs. The pressure wave is reflected back by the mold surface with little effect on the mold owing to the strength of the metal. Once the pressure wave reaches the mold, further combustion is not possible due to the total consumption of the combustible gases between the mold and the pressure vessel. The result of the combined effect of the pressure wave and thermal energy deposition in the graphite-like compound is the production of both ash and carbon dioxide. The ash may or may not be attached to the surface of the mold. To complete the operation, such ash can be removed by a blast of air which is applied after the mold has been removed from the pressure vessel. Alternatively, a liquid can be used to remove the residue. The present invention also provides apparatus for cleaning molds used in the glass fabrication industry and which includes a cleaning chamber which can be securely closed after loading and a system for supplying gaseous fuel thereto. Accordingly, the present invention also provides an apparatus for removing graphite-like material from metal molds used in the glass fabrication industry, the apparatus including a housing having a mold-receiving chamber, a gas supply for supplying an oxygen rich mixture of combustible gases to the mold-receiving chamber, and an igniter for igniting the oxygen rich mixture of combustible gases in the chamber to produce a high temperature and a pressure wave, whereby a high temperature wave front and a pressure wave impinge on and remove graphite-like material from a metal mold in the chamber by ablation of the graphite-like material. The gas supply for supplying an oxygen rich mixture of combustible gases to the mold-receiving chamber may include an oxygen gas supply line and a combustible gas supply line, each supply line including an intermediate tank and a charge cylinder, and a valve assembly to enable an initial supply of gas to be supplied to the mold-receiving chamber from the intermediate tank and a further supply of gas to be supplied to the bolt-receiving chamber from the charge cylinder. Each gas supply line may also include means for supplying pressure to the gas in the charge cylinder during supply of gas therefrom to the mold-receiving chamber. The housing may have a mold feeder carriage movable between an open position outside the chamber and an operative position inside the chamber, and a chamber closure member moving with the carriage to close an opened end of the chamber when the carriage is in the operative position. The apparatus may also have a pair of wedge members movable between retracted and operative positions and which, in the operable positions, engage the closure member to retain it in the chamber-closing position. DESCRIPTION OF THE DRAWINGS One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, of which: Fig. 1 is a diagrammatic side view of mold cleaning apparatus, with the feeder carriage and the wedge cams at their fully retracted open positions away from the cleaning chamber. Fig. 2 is a similar view to Fig. 1 showing the feeder carriage and the wedge cams at their operative positions, Fig. 3 is a schematic view showing the fuel system for supplying gaseous fuel to the cleaning chamber, and Fig. 4 is a perspective view of a glass half mold used as a test. DESCRIPTION OF PREFERRED EMBODIMENT Referring to the accompanying drawings, Figs. 1 and 2 show mold cleaning apparatus having a base 12 which carried a housing 14 with a mold cleaning chamber 16 which is open at one end 18 and also carried a feeder carriage 20 (seen in its retracted position in Fig. 1) which is slidably mounted thereon for movement towards and away from the mold cleaning chamber 16. The feeder carriage 20 has a mold carrying basket member 21 projecting forwardly therefrom and a chamber closing member 22 at the rear end thereof. When the feeder carriage 20 is in its operative position, the closure member 22 closes the open end 18 of the chamber 16 as shown in Fig. 2. For clarity, the basket member 21 has not been shown in Fig. 2. The chamber housing 14 carries upper and lower vertically moveable wedge members 24, 26, shown in their retracted positions in Fig. 1. When the feeder carriage 20 is in its operative position (shown in Fig. 2) the upper wedge member 24 is moved vertically downwardly and the lower wedge member 26 is moved vertically upwardly to engage the rear of the closure member 22. The upper and lower wedge members 24, 26 have angled faces 28, 30 respectively which engage complementarily inclined faces 32, 34 respectively on the rear of the closure member 22 to force the closure member 22 into firm closing engagement with the open end 18 of the chamber 16 and retain the closure member 22 in such firm closing engagement. Movement of the upper and lower wedge members 24, 26 is effected by hydraulic cylinders 36, 38, and movement of the feeder carriage 20 is effected by means of a hydraulic cylinder 40. The feeder carriage 20 has forward and rear wheels 42, 44 which run on tracks 44, 48 respectively. When the feeder carriage 20 is in the fully retracted position, as shown in Fig. 1, a vertically movable support bearing 50 supports the bolt carrying basket member 21. When the feeder carriage 20 advances to the operative position, the support bearing 50 is retracted as shown in Fig. 2 to permit the closing member 22 to pass. Movement of the support bearing 50 is effected by a hydraulic cylinder 52. Fig. 3 shows the fuel system for feeding the required mixture of oxygen and required gas to the mold cleaning chamber 16. Oxygen from a 150 psi supply is fed along line 60 through a manually-operable ball valve 62, a filter 64, a pressure gauge 66, a pressure regulator 68, a solenoid valve 70, a check valve 72 and a solenoid valve 74 to an intermediate tank 76. Similarly, natural gas from a 150 psi supply is fed along line 80 through a manually- operable valve 72, a filter 84, a pressure gauge 86, a pressure regulator 88, a solenoid valve 90, a check valve 92 and a solenoid valve 84 to an intermediate tank 96. Beyond check valve 72, oxygen fuel line 60 is also connected to a fuel line 100 and feeds oxygen through a solenoid valve 102, check valve 104, pressure gauge 106, pressure transducer to 108 and check valve 110 to a mixing valve 112. Similarly, beyond check valve 92, natural gas line 80 is also connected to a fuel line 120 which feeds natural gas through a solenoid valve 122, check valve 124, pressure gauge 126, pressure transducer 128 and check valve 130 to a mixing valve 112. Mixing valve 112 is opened and closed by a hydraulic cylinder 132 and, when opened, feeds an oxygen-natural gas fuel mixture along passages 134, 136 into the cleaning chamber 16 at longitudinally spaced positions therein. Oxygen line 100 is also connected by line 140 and solenoid valve 142 to a hydraulically-operated gas charge cylinder system 144. Similarly, natural gas line 120 is also connected by line 146 and solenoid valve 148 to the gas charge cylinder system 144. In the gas charge cylinder system 144, oxygen is supplied through line 140 and solenoid valve 142 to two charge cylinders 150, 152, and natural gas is supplied through line 144 and solenoid valve 148 to a charge cylinder 156. The volume of charge cylinders 150, 152 and 156 is controlled by a hydraulic cylinder 154. In use, intermediate tanks 76, 96 are filled with oxygen and natural gas respectively at 150 psi with solenoid valves 102, 122 shut and solenoid valves 70, 90 open. With the mixing valve 112 closed and the cleaning chamber 16 closed as shown in Fig. 2, with molds to be cleaned (not shown) in the basket member 21 therein, solenoid valves 74, 94 are closed and solenoid valves 70, 102, 142 and 90, 122, 148 opened so that natural gas flows from line 60 through solenoid valve 102, check valve 104 and solenoid valve 142 into charge cylinders 150, 152, with hydraulic cylinder 154 being contracted to cause charge cylinders 150, 152 to be filled to maximum capacity. Similarly, oxygen flows from line 80 through solenoid valve 122, check valve 124 and solenoid valve 148 into charge cylinder 156. The charging cylinders 150, 152 and 156 and lines 100, 120 to mixing valve 112 reach a steady 150 psi pressure, which is measured by the pressure transducers 108, 128. When the cleaning chamber 16 is to be charged with a gaseous fuel mixture, the solenoid valves 74, 102 and 94, 122 and mixing valve 112 are opened, with solenoid valve 70, 142 and 90, 148 closed, to cause gas at 150 psi in the intermediate tanks 76, 96 to flow through lines 100, 120 and through the mixing valve 112 into the cleaning chamber 16 to pressurize the chamber 16 to approximately 75 psi, which is measured by pressure transducers 108, 128. When this pressure has stabilized, solenoid valves 102, 122 are closed and solenoid valves 142, 148 are opened, and charged cylinders 150, 152 and 156 are contracted by means of hydraulic cylinder 154 to pressurize lines 100, 120 and chamber 16 to 150 psi, again measured by the pressure transducers 108, 128. The mixing valve 112 is then closed, so that the charge of oxygen and natural gas is sealed in the chamber 16 and is ready for ignition. At this time, solenoid valve 70, 74 and 90, 94 are opened (with solenoid valves 102, 122 being closed) to cause the intermediate tanks 76, 96 to again be pressurized to 150 psi. The gaseous mixture in the cleaning chamber 16 is then ignited by an igniter in the form of a glow plug 160 located immediately downstream of the mixing valve 112. Ignition then travels along passages 134, 136 into the cleaning chamber 16 at longitudinally spaced positions therein. The resultant explosion causes the molds on the basket member 21 to be cleaned in the manner previously described. The cleaning chamber 16 is then exhausted through an exhaust line 156 provided at the rear end of chamber 16 and controlled by a solenoid valve 158. The explosion is suitably monitored, for example by a vibration sensor 162 adjacent the wedge member 26, an acoustic sensor 164 adjacent the housing 14, and a thermocouple 166 in the exhaust line 156 downstream of the solenoid valve 158. During the ignition and exhaust sequences, the intermediate tanks 76, 96 are opened to re-pressurize lines 100, 120 to 75 psi, and the gas charge cylinder system 144 is then actuated to pressurize the lines 100, 120 to 150 psi as previously described. It will be readily apparent to a person skilled in the art that the above described embodiment of the invention can be fully automated. Specific examples of the invention will now be described. Example 1 A glass half mold 162 made of cast iron and with dimensions of 6 x 8 x 3 inches as shown in Fig. 4 was utilized for this test. The half mold was used in production and had been removed for cleaning. Observation of the mold showed that a graphite-like compound had been deposited on internal surfaces indicated by X in Fig. 4. The compound thickness varied from place to place, from a minimum of about 0.002 to more than about 0.012 inches, following the contour of the mold. The mold was allowed to cool to a temperature of about 24°C and was then placed inside a pressure vessel with dimensions of 10 x 6 inches. The pressure vessel was sealed and filled with oxygen and natural gas. Both gases were injected from a 150 psi source using pressure regulator valves. The gases were allowed to freely fill the container and reach a dynamic equilibrium on their own accord. Once filled, the charging valves were closed. The mixture was then ignited using a high voltage discharge in the pressure vessel. A sharp impact noise was heard and the vessel became hot to the touch. The measured temperature was about 60°C. The pressure vessel was then opened and examined. The mold was observed not to have moved appreciably. The mold was also noticeably warm, so much so as to be too hot to be held by bare hands. The measured temperature was 65°C. After observation, the mold was removed by hand with the assistance of leather faced gloves. Once removed, detailed observation of the mold showed that the majority of the graphite-like compound have been removed, but that a small amount still remained. The mold was again placed in the pressure vessel and the method repeated. The result after the repeated method was complete cleaning of the mold, with the exception of a small amount of powder residue which could be easily wiped from the surface of the mold using a cloth. Example 2 A glass half mold made of brass alloy and with the same dimensions as before was utilized for this test. Again, the mold had been used in production and had been removed for cleaning. Observation showed that a graphite-like compound had been deposited on the internal areas as in the previous example. The thickness of the graphite-like compound varied from place to place from a minimum of about 0.001 to over about 0.004 inches, following the contour of the mold. The mold was cleaned in a similar manner to that described in Example 1, with similar results. After removal from the pressure vessel, detailed observation of the mold showed that it was completed devoid of the graphite-like compound, again with the exception of a small amount of powder residue which could easily be wiped from the mold surface using a cloth. Example 3 Three small ring-shaped proportions of a glass mold made of a steel alloy and with dimensions of approximately 4 3 inches were utilized for this test. The ring-shaped portions had been used in production and had been removed for cleaning. Observation showed that a graphite-like compound had been deposited on various internal areas, with the thickness varying from a minimum of about 0 to about 0.002 inches, primarily on the internal surfaces of the ring. The ring-shaped portions were treated as in the previous examples, with similar results. After removal from the pressure vessel, detailed observation showed that the surfaces of the ring-shaped portions which were exposed to the gas were completed devoid of the graphite-like deposit. Surfaces which were shielded from direct exposure, such as the surface which the ring-shaped portions were resting on, had little if any of the deposit removed. Example 4 This test was a continuation of Example 3 using two small ring shaped portions which had deposits of graphite-like compound varying from a minimum of 0 to about 0.003 inches, primarily on the internal surfaces of the ring shaped portions. In this example, a tree-shaped frame was used to support the ring-shaped portions in the pressure vessel such that there was minimal shielded surface area of the ring-shaped portions. The same procedure was followed as before. After removal from the pressure vessel, detailed observation of the ring-shaped portions showed that their surfaces were devoid of the graphite-like compound with the exception of a dust-like material. This residue was removed using a blast of compressed air. Other embodiments and examples of the invention will be readily apparent to a person skilled in the art, the scope of the invention being defined in the appended claims.

Claims: WE CLAIM 1. A method of removing graphite-like material from metal molds used in the glass fabrication industry, the method including: placing a metal glass-fabricating mold with graphite-like material deposited thereon in a chamber, providing an oxygen rich mixture of combustible gases in the chamber, and igniting the oxygen rich mixture of combustible gases in the chamber to produce a high temperature and a pressure wave, whereby a high temperature wave front and a pressure wave impinge on and remove graphite-like material from the metal mold by ablation of the graphite-like material. 2. A method according to claim 1 wherein the oxygen rich mixture of combustible gases includes oxygen and natural gas. 3. Apparatus for removing graphite-like material from metal molds used in the glass fabrication industry, said apparatus including: a housing having a mold-receiving chamber, a gas supply for supplying an oxygen rich mixture of combustible gases to the mold-receiving chamber, and an igniter for igniting the oxygen rich mixture of combustible gases in the chamber to produce a high temperature and a pressure wave, whereby a high temperature wave front and a pressure wave impinge on and remove graphite-like material from a metal mold in the chamber by ablation of the graphite-like material. 4. Apparatus according to claim 3 wherein the gas supply for supplying an oxygen rich mixture of combustible gases to the mold- receiving chamber includes an oxygen gas supply line and a combustible gas supply line, each supply line including an intermediate tank and a charge cylinder, and a valve assembly to enable an initial supply of gas to be supplied to the mold-receiving chamber from the intermediate tank and a further supply of gas to be supplied to the mold-receiving chamber from the charge cylinder. 5. Apparatus according to claim 4 wherein each gas supply line also includes means for supplying pressure to the gas in the charge cylinder during supply of gas therefrom to the mold-receiving chamber. 6. Apparatus according to claim 3 wherein the housing has a mold feeder carriage movable between an open position outside the chamber and an operative position inside the chamber, and a chamber closure member moving with the carriage to close an open end of the chamber when the carriage is in the operative position. 7. Apparatus according to claim 6 also including a pair of wedge members movable between retracted and operative positions and which, in the operable positions, engage the closure member to retain it in the chamber-closing position.

Inventors: MARTIN TERRY W, MAULE ALEX, MARTIN, TERRY, W., MAULE, ALEX
Applicants: ABLATION TECHNOLOGIES INC, ABLATION TECHNOLOGIES INC.
Application year: 1998
Main classification: B08B7
IPC codes: B08B7