As is known, for example, from U.S. Pat. No. 5,746,800 (Ambrogio) or U.S. Pat. No. 5,679,409 (Seeman), it is desirable to lubricate a molten glass contacting surface of a glass manufacturing machine, for example, an internal surface of a forming mold of such a machine, with a thin layer of carbon soot as a substitute for periodically brushing such a surface with a conventional oil and graphite-based mold dopant. Such a soot coating is obtained by the partial oxidation of a carbonaceous gas, such as acetylene or a mixture of an acetylene-based gas, such as methacetylene and propadiene (occasionally referred to as mapp gas or as MAPD gas) by way of a burner whose flame is directed towards the mold surface to be coated.
The aforesaid Seeman '409 patent describes a mold surface soot-coating system in which a mixture of MAPD gas and oxygen, after igniting by a natural gas-derived pilot flame, is directed toward a surface to be coated. As noted in Seaman '409, because of the inherently intermittent nature of the operation of a soot burner in a glass manufacturing machine, a mixture of MAPD gas and oxygen must be carefully controlled so as to prevent backfiring of the flame from the burner into the burner nozzle (column 3, lines 9-20), and it is understood that the system of the Seeman '409 patent has proven to be capable of operating in a successful manner in sooting glass-making molds of a Hartford 28 rotary tableware glass forming machine, where a single sooting burner can service all molds on a rotating table. In that regard, the pulse rate of a sooting burner for a Hartford 28 tableware machine occurs at a fairly high frequency, and any tendency for backfiring to occur by the backflow of oxygen into the fuel line through an air-fuel mixer can be avoided by careful control of the operating conditions of the sooting apparatus.
The Hartford 28 glass making machine does not lend itself to the manufacture of hollow glass containers with restricted openings, however, such as the containers used in packaging various food and beverage products, because such products must be manufactured on a machine with split molds. An individual section (I.S.) machine, for example, as described in commonly-assigned U.S. Pat. No. 6,098,427 (Kirkman), or U.S. Pat. No. 3,617,233 (Mumford), the disclosure of each of which of is incorporated herein by reference, is a two-step forming machine type that operates with split glass-forming molds, and such a machine type is widely used in the manufacture of such containers. In view of the need to provide a separate sooting burner for each of the various machine sections of an I.S. machine, a sooting burner for an I.S. machine will operate much less frequently than one for a Hartford 28 machine. For that reason, heretofore it has not been possible to adapt a premix type burner of the type taught by the Seeman '409 patent to I.S. machine operation because of backfiring occurring as a result of backflow of oxygen from the fuel oxygen mixer into the fuel line during the relatively long durations between burner firing pulses.
The glass forming machine described in the aforesaid Ambrogio '800 patent, the disclosure of which is incorporated by references herein, corresponds to an individual section (I.S.) glass container forming machine. However, this reference teaches the use of a spark energization device, element 23, that is positioned away from the sooting head, and such positioning requires the use of well-shielded cables from the spark enegization device to the spark electrodes, elements 22, to prevent electromagnetic interference (EMI) in the cables from interfering with the operation of electronic control systems or other electrical elements of the glass forming machine.
Commonly-assigned Published U.S. Patent Application No. 2003-0221455A1 (Scott et al.), the disclosure of which is also incorporated by reference herein, teaches a sooting system for sooting molds of an I.S. glass forming machine. The aforesaid Scott et al. application specifically teaches the use of a surface mixing burner to intermittently separately emit streams of an oxidant and a carbonaceous fuel to be ignited by an electrical spark between spaced elements of an igniter at a location downstream of the surface mixing burner, to thereby inhibit backfiring resulting from mixing of oxidant and fuel in the oxidant or fuel lines during dwell periods between firing pulses. As previously mentioned, the potential problem of backfiring is more severe in the case of an I.S. machine than it is in the case of a Hartford 28 tableware glass forming machine, such as that to which the teachings of U.S. Pat. No. 6,068,889 (Seeman) is applicable, because the dwell periods between successive firing pulses are longer for an I.S. machine than for a Hartford 28 machine.
Whatever sooting system that is used in connection with an I.S. glass container forming machine, it is important that a very high voltage, for example, 12,000-15,000 volts, depending on the spacing between igniter electrodes, be used to fire the spaced igniter electrodes of an intermittently operated sparking device to properly ignite mixing oxidant and fuel streams, or a previously-mixed mixture thereof, to produce soot therefrom. Such a voltage is produced from a conventional power supply, for example, 12-24 volts d.c., by an electronic element that converts the lower voltage power supply to the higher voltage that is needed to intermittently operate the sparking device. This may be done by a capacitive discharge method, in which a spark is produced by shorting a capacitor with a predetermined level of stored energy. It may also be done by the inductive generation method, in which a high voltage inductive spike is generated when current flow through the primary of a transformer is interrupted; this will cause the secondary side to multiply the voltage into a pulse that will be between 20 k and 35 k volts, based on the turns ratio. For purposes of a glass-forming machine sooting system, an inductive discharge sparking system is advantageous in that it results in somewhat lower peak amperage pulses, for example, approximately 6 amps versus as high as 100 amps for a capacitive discharge igniter, and this presents a lower safety risk to nearby workers.
Because the physical environment around the molds of an I.S. glass container forming machine is crowded, heretofore it was not known to install a high voltage source for a sparking device close to the machine molds to be lubricated. When the high voltage source is positioned remotely from the machine molds, unduly long electrical cables are needed to conduct a high voltage sparking pulse from the low voltage source. This tends to be operationally troublesome in that the high voltage cables, when unduly long, produce excessive levels of electromagnetic interference (EMI), which can not be adequately shielded because such shielding, over a long cable, adds excessive capacitance to the spark, thereby reducing the voltage across the sparking gap to a level that may be too low. This problem is compounded in a sooting system for an I.S. machine when such machine is operated on a multiple cavity basis, that is, on a basis where multiple molds are provided to simultaneously produce 2, 3 or 4 containers at each machine section, because it is necessary to provide a sooting head for each of the molds at each of the machine sections, and EMI from the cable to each sooting head can interfere with the operation of the forming machine's electronic control system, especially if the sparking devices for the sooting heads are fired in overlapping pulses.
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USPTO Backgrounds