Abstract:
A method of removing graphite from metal molds used in the glass fabrication industry, the method including placing a metal glass-fabricating mold with graphite bonded thereto in a chamber, providing an oxygen rich mixture of combustible gases in the chamber, said oxygen rich mixture containing from about 10 to about 25% stoichiometric excess of oxygen, and igniting the oxygen rich mixture of combustible gases in the chamber to produce a temperature of at least about 6,000° F. and a pressure wave. A high temperature wave front and the pressure wave thereby produced remove graphite from the metal mold by ablation of the graphite.

Description:
[0001]    This application is a continuation-in-part of U.S. patent application No. 09/188,528 filed Nov. 10, 1998, which claims priority from U.S. Provisional Patent Application No. 60/065,288 filed Nov. 12, 1997. 
     
    
     
       FIELD OF INVENTION  
         [0002]    This invention relates to cleaning molds used in the glass fabrication industry in a cost effective and environmentally safe manner.  
         BACKGROUND OF INVENTION  
         [0003]    The glass industry utilizes glass molding equipment for the fabrication of glass containers and other articles. In the molding process, substantially pure primary graphite powder mixed with various proprietary chemical compounds is applied to the molds in order to facilitate mold separation and glass flow. The various proprietary chemical compounds function to disperse and bond the graphite to the molds. Because glass temperature during molding reaches about 2,000° F., the chemical compounds react to cause a layer of substantially pure primary graphite to become chemically bonded to the molds. After successive applications of the graphite powder/chemical compound mixture as required by the glass process, a closely laminated layer of graphite containing trace amounts of proprietary bonding agent is built up on the mold. This graphite layer must then be cleaned from the mold when its thickness adversely affects the dimensional requirements of the glass container being produced. The characteristics of the bonded layer are that of graphite, in particular with a melting point of about 5,800° F. and a boiling point of about 6,700° F.  
           [0004]    Due to the lubricating nature of the graphite, its removal has in the past been effected 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 layer. 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 layer.  
           [0005]    It is therefore an object of the present invention to provide an improved method for removing a graphite layer from a glass mold, and to provide apparatus for carrying out the method.  
         SUMMARY OF THE INVENTION  
         [0006]    According to the present invention, a method of removing graphite from metal molds used in the glass fabrication industry includes placing a metal glass-fabricating mold with graphite bonded thereto in a chamber, providing an oxygen rich mixture of combustible gases in the chamber, with the oxygen rich mixture containing from about 10 to about 25% stoichiometric excess of oxygen, and igniting the oxygen rich mixture of combustible gases in the chamber to produce a temperature of at least about 6,000° F. and a pressure wave. A high temperature wave front and the pressure wave thereby produced remove graphite from the metal mold by ablation of the graphite.  
           [0007]    The invention also provides apparatus for removing graphite 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, with the oxygen rich mixture containing from about 10 to about 25% stoichiometric excess of oxygen, and an igniter for igniting the oxygen rich mixture combustible gases in the chamber to produce a temperature of at least about 6,000° F. and a pressure wave. A high temperature wave front and the pressure wave thereby produced, remove graphite from a metal mold in the chamber by ablation of the graphite. An exhaust valve is subsequently operable to remove products of combustion from the chamber.  
           [0008]    The apparatus also includes a mold feeder carriage moving horizontally between an open position outside the chamber and an operative position inside the chamber, a chamber closure member moving with the carriage to close an open end of the chamber when the carriage is in the operative position, and 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.  
           [0009]    The ablation step is believed to comprise melting and partial oxidation of the graphite and subsequent removal of brittle oxidic material so formed. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0010]    One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, of which:  
         [0011]    [0011]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.  
         [0012]    [0012]FIG. 2 is a similar view to FIG. 1 showing the feeder carriage and the wedge cams at their operative positions,  
         [0013]    [0013]FIG. 3 is a schematic view showing the fuel system for supplying gaseous fuel to the cleaning and  
         [0014]    [0014]FIG. 4 is a perspective view of a glass half mold used as a test. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENT  
       [0015]    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.  
         [0016]    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.  
         [0017]    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  46 ,  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 .  
         [0018]    [0018]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 .  
         [0019]    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 gas, ignition and vent 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 the valve  112 . The 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.  
         [0020]    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 .  
         [0021]    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 ,  74  and  90 ,  94  open. With the 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 valve  112  reach a steady 150 psi pressure, which is measured by the pressure transducers  108 ,  128 .  
         [0022]    When the cleaning chamber  16  is to be charged with a gaseous fuel mixture, the solenoid valves  74 ,  102  and  94 ,  122  and 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 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 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.  
         [0023]    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.  
         [0024]    The gaseous mixture in the cleaning chamber  16  is then ignited by an igniter in the form of a spark 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 hydraulically actuated 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 valve  158 .  
         [0025]    It will be readily apparent to a person skilled in the art that the above described embodiment of the invention can be fully automated.  
         [0026]    Specific examples of the invention will now be described.  
       EXAMPLE 1  
       [0027]    A glass half mold  172  made of cast iron and with dimensions of 6×8×3 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 graphite had become bonded thereto on external surfaces indicated by X in FIG. 4. The graphite 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 10×6 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.  
         [0028]    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 had 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  
       [0029]    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 graphite had become bonded thereto on the external surfaces as in the previous example. The thickness of the graphite 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, 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  
       [0030]    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 graphite had become bonded thereto on various external areas, with the thickness varying from a minimum of about 0 to about 0.002 inches. 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 detonation were completely devoid of graphite. 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  
       [0031]    This test was a continuation of Example 3 using two small ring shaped portions which had deposits of graphite bonded thereto varying from a minimum of zero to about 0.003 inches. 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 graphite, with the exception of a dust-like material. This residue was removed using a blast of compressed air.  
         [0032]    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.