Quantitative heat-preservation aluminum liquid melting furnace
Technical Field
The invention belongs to the technical field of industrial processing equipment; in particular to a quantitative heat-preservation aluminum liquid melting furnace.
Background
The melting furnace adopts 200-2500Hz medium-frequency power supply for induction heating, the power range is 20-2500KW, and the melting furnace can also be called as a medium-frequency electric furnace according to the characteristics of the melting furnace. The device is mainly used for smelting and temperature raising of other noble metals such as gold, platinum, silver, copper, iron, stainless steel, aluminum alloy, aluminum and the like, and is ideal equipment for processing ornaments and precision castings in college laboratories and research institutes.
At present, most of the existing melting furnaces adopt single-layer shells, so that the temperature inside the melting furnace is easily lost to the external environment through the shells, and the heat preservation effect of the melting furnace is poor; the melting furnace adopts single crucible structure, the crucible both has been used for melting the aluminum product promptly, be used for keeping warm and quantitative aluminium liquid to aluminium liquid again, traditional melting furnace carries out the ration to aluminium liquid, adopt artifical the observation mostly, thereby lead to aluminium liquid content, it is inaccurate to confirm, influence industrial manufacturing, and simultaneously, adopt single crucible, not only make to contain unmelted aluminium sediment in the molten aluminium liquid, and simultaneously, when aluminium liquid content exceeds standard, need close the melting furnace, and with the artifical device of clearing out of unnecessary aluminium liquid, later restart the melting furnace, it is extremely troublesome to operate, and simultaneously, the frequent switch of melting furnace leads to the waste of resource, the steam of melting production, traditional melting furnace does not utilize it, thereby make its energy resource obtain extravagantly.
Disclosure of Invention
The invention aims to provide a quantitative heat-preservation aluminum liquid melting furnace, which solves the technical problems of poor heat-preservation capability, low quantitative precision, complex operation and resource waste of the existing melting furnace.
In order to achieve the purpose, the invention provides a quantitative heat-preservation aluminum liquid melting furnace, which comprises a furnace bottom support frame, an aluminum liquid outlet, a furnace shell, a circuit control center, an aluminum melting crucible, a telescopic support rod, a heat energy recovery device, an exhaust pipe, an upper cover, an aluminum material pushing device, an electromagnetic coil, a feeding transmission device, an aluminum heat-preservation crucible and a material carrying box, wherein the furnace bottom support frame is arranged on the lower end surface of the furnace shell, the upper cover is arranged on the upper end surface of the furnace shell and is connected with the furnace shell through the telescopic support rod, one end of the telescopic support rod is connected to the lower end surface of the upper cover, the other end of the telescopic support rod is arranged on the upper end surface of the furnace shell and extends to the inner side of the furnace shell through the upper end surface of the furnace shell, the aluminum melting crucible is arranged at the upper end of the aluminum heat-preservation, the lower end of the outer side wall of the smelting furnace shell is provided with an aluminum liquid outlet, the aluminum liquid outlet penetrates through the outer shell of the smelting furnace shell to be connected with an aluminum heat-insulating crucible, the upper end of the outer side wall of the smelting furnace shell is provided with an exhaust pipe, the exhaust pipe penetrates through the outer side wall of the smelting furnace shell to be connected with the aluminum melting crucible, the heat energy recovery device is sleeved on the exhaust pipe and is connected with the aluminum heat-insulating crucible, the circuit control center is arranged on the outer side wall of the smelting furnace shell and is connected with an electromagnetic coil, the feeding transmission device is arranged on the outer side wall of the smelting furnace shell, the feeding transmission device and the circuit control center are respectively arranged on two sides;
a control valve is arranged on the aluminum liquid output port and used for controlling the aluminum liquid conveying;
the electromagnetic coil is in a spiral shape with a large upper part and a small lower part, and the electromagnetic coil is sleeved on the outer side wall of the aluminum melting crucible.
Further, the furnace shell comprises a furnace bottom through hole, an inner shell, an outer shell and an inner shell bottom surface, wherein the inner shell is arranged on the inner side of the outer shell, the furnace bottom through hole is formed in the lower end surface of the inner shell, the furnace bottom through hole is connected with the inner shell and the outer shell, the inner shell and the outer shell are connected with each other through the upper end surface, and the inner shell bottom surface is an inwards concave inclined surface;
the vacuum state is between interior casing and the shell body, and flexible bracing piece one end is fixed in between interior casing and the shell body, interior casing adopts high temperature resistant ceramic material, the shell body adopts titanium alloy material.
Further, a shell, a single chip microcomputer, a frequency converter, an external power line, a control switch and a circuit board are arranged in the circuit control center, the single chip microcomputer and the frequency converter are arranged on the circuit board, one end of the control switch is arranged on the shell of the circuit control center, the other end of the control switch is arranged on the circuit board, the circuit board is connected with an external power supply through the external power line, the frequency converter is connected with an electromagnetic coil, the control switch is a PLC touch screen controller, the PLC touch screen controller is in the prior art, a 4.3-inch touch screen PLC all-in-one machine with the model of MHW-6043-.
Further, the aluminum melting crucible comprises an air outlet hole, a material carrying net, a motor, a valve core through hole, a valve core, a rotating shaft and a crucible, the crucible is fixed on the inner side wall of the inner shell, the air outlet hole is formed in the upper side of the inner side wall of the crucible, the air outlet hole is connected with an exhaust pipe, the valve core through hole is formed in the valve core and penetrates through the valve core, the rotating shaft is arranged on two sides of the valve core, the connecting line of the rotating shafts on two sides is 90-degree intersected with the valve core through hole, the valve core is fixed in the lower end face of the crucible through the rotating shaft, the motor is embedded;
the motor is electrically connected with a circuit board in the circuit control center;
and a laser liquid level detector is fixed on the upper end surface of the inner side of the aluminum heat-insulating crucible, the laser liquid level detector is electrically connected with a circuit board of a circuit control center, and the laser liquid level detector adopts an XYM-4 type laser liquid level meter produced in the new direction of Shijiazhuang.
Further, flexible bracing piece is hydraulic telescoping rod, the hydraulic telescoping rod piston rod is connected on the terminal surface under the upper cover, the hydraulic telescoping rod sleeve is located between interior casing and the shell body.
Furthermore, the aluminum material pushing device comprises a first chain gear, a chain, a push plate connecting block, a second chain gear, a pushing motor and push plate blocking rails, the push plate blocking rails are arranged at two ends of the push plate, the push plate baffle rail is fixed on the upper end surface of the melting furnace shell, a groove is arranged on the push plate baffle rail, push plate connecting blocks are arranged at the two ends of the push plate, which are in contact with the push plate baffle rail, the push plate connecting block is arranged in the push plate rail retaining groove, the first chain gear is fixed at one end of the inner side of the push plate rail retaining groove through a rotating shaft, the second chain gear is fixed at the other end of the inner side of the push plate blocking rail through a rotating shaft, the pushing motor is arranged at the inner side of the push plate blocking rail, the output shaft of the pushing motor is connected with the rotating shaft of the second chain gear, the first chain gear and the second chain gear are sleeved with a chain, and the outer side surface of the lower end of the chain is fixed with the push plate connecting block;
the pushing motor is electrically connected with a circuit board of the circuit control center.
Further, the feeding transmission device comprises a transmission rotating shaft, a transmission winding belt, a transmission rail supporting rod, a winding wheel, a transmission belt pulley, a transmission shaft, a driving belt pulley and a transmission belt, the transmission rotating shafts are arranged at two sides of the material loading box and connected with the rolling wheel through the transmission winding belt, the rolling wheel is arranged on the transmission rail supporting rod through the transmission shaft, one of the winding wheels is connected with a transmission belt pulley through a transmission shaft, the transmission rail supporting rod is arranged on the transmission rail, the transmission rail is arranged on the side wall of the smelting furnace shell, an inner groove is arranged on the transmission rail, two sides of the material loading box are connected with the inner groove of the transmission rail, and is connected with the transmission track inner groove in a rotating and sliding way, a motor is embedded in the outer side wall of the transmission track at one side of the material loading box, a driving belt pulley is arranged on an output shaft of the motor and is connected with the transmission shaft through a transmission belt;
and the motor on the side wall of the transmission track is electrically connected with a circuit board of the circuit control center.
Further, the heat energy recovery device comprises a low-temperature steam inlet, steam, a high-temperature steam outlet, a steam heat exchange pipeline, a low-temperature steam conveyor, heat-conducting fins and a recovery device shell, the exhaust pipe is arranged in the shell of the recovery device, the outer side wall of the exhaust pipe in the shell of the recovery device is provided with heat conducting fins, the water vapor is arranged between the recovery device shell and the exhaust pipe, the lower end of the recovery device shell is provided with a low-temperature water vapor inlet, the upper end of the shell of the recovery device is provided with a high-temperature steam outlet which is connected with one end of a steam heat exchange pipeline through a pipeline, the low-temperature steam inlet is connected with the other end of the steam heat exchange pipeline through a pipeline, and the low-temperature steam conveyor is arranged on the pipeline between the low-temperature steam inlet and the other end of the steam heat exchange pipeline;
the water vapor heat exchange pipeline is arranged on the inner side of the aluminum heat-preservation crucible, the water vapor heat exchange pipeline is in a horizontal spiral shape, and heat conduction fins which are uniformly distributed are arranged on the outer surface of the water vapor heat exchange pipeline;
and the low-temperature steam conveyor is electrically connected with a circuit board of the circuit control center.
The invention has the beneficial effects that: the double-layer shell is adopted, so that the contact between the melting furnace and the external environment is effectively blocked, the internal temperature of the melting furnace is prevented from being lost to the external environment, the double-layer shell structure effectively avoids the condition that the traditional melting furnace is poor in heat preservation effect, meanwhile, the inner shell of the double-layer shell is made of high-temperature-resistant ceramic, and the outer shell of the double-layer shell is made of titanium alloy, so that the internal temperature of the melting furnace is effectively prevented from being conducted to the outside through the shell, and the heat preservation capacity of equipment is further improved; the invention adopts a double-crucible structure, the upper crucible of the double-crucible structure is used for melting aluminum materials, the lower crucible of the double-crucible structure is used for preserving heat and quantifying aluminum liquid, the structure is accurate in quantification, when the excess amount of the aluminum liquid is not needed, the redundant aluminum liquid is discharged, meanwhile, the invention can carry out multiple quantification in one melting process, the quantification is accurate, the operation is simple, meanwhile, the invention adopts a material carrying net in the upper crucible, the material carrying net can prevent unmelted aluminum slag from entering the aluminum liquid, the molten aluminum liquid is ensured to be purer, the invention is additionally provided with a heat recovery device, the heat of hot gas generated in the aluminum melting process heats steam, the steam is low-temperature steam and is converted into high-temperature steam, and the high-temperature steam is conveyed to the lower crucible, so as to preserve heat the aluminum liquid, the heat recovery device not only enhances the heat preservation capability of the invention, but also, thereby saving the processing cost and improving the economic benefit; the invention adopts the single chip microcomputer, the PLC touch screen controller and the laser liquid level inspection instrument, thereby effectively and visually knowing the content of the aluminum liquid, and meanwhile, the aluminum liquid can be quantified through the PLC touch screen controller, and the content of the aluminum liquid can be controlled through the single chip microcomputer and the laser liquid level inspection instrument, and when the content of the aluminum liquid can be accurately and automatically kept at the specified content, the manual control is avoided.
Drawings
In order to facilitate understanding for those skilled in the art, the present invention will be further described with reference to the accompanying drawings.
FIG. 1 is a schematic view of the general structure of a quantitative heat-preservation aluminum liquid melting furnace of the present invention;
FIG. 2 is a schematic view of a furnace shell structure of the quantitative heat-preservation molten aluminum melting furnace of the invention;
FIG. 3 is a schematic structural view of an aluminum melting crucible of the quantitative heat-preservation aluminum liquid melting furnace of the present invention;
FIG. 4 is a schematic structural view of an aluminum material pushing device of the quantitative heat-preservation aluminum liquid melting furnace of the invention;
FIG. 5 is a schematic structural diagram of a heat recovery device of a quantitative heat-preservation molten aluminum melting furnace according to the present invention;
FIG. 6 is a schematic structural diagram of a steam heat exchange pipeline of the quantitative heat-preservation aluminum liquid melting furnace of the invention;
FIG. 7 is a schematic view of a feeding transmission device of a quantitative heat-preservation molten aluminum melting furnace according to the present invention.
Detailed Description
Referring to fig. 1-7, a quantitative heat-preservation molten aluminum melting furnace comprises a furnace bottom support frame 1, a molten aluminum outlet 2, a furnace shell 3, a circuit control center 4, an aluminum melting crucible 5, a telescopic support rod 6, a heat energy recovery device 7, an exhaust pipe 8, an upper cover 9, an aluminum material pushing device 10, an electromagnetic coil 11, a feeding transmission device 12, an aluminum heat-preservation crucible 13 and a loading box 14, wherein the furnace bottom support frame 1 is arranged on the lower end surface of the furnace shell 3, the upper cover 9 is arranged on the upper end surface of the furnace shell 3, the upper cover 9 is connected with the furnace shell 3 through the telescopic support rod 6, one end of the telescopic support rod 6 is connected to the lower end surface of the upper cover 9, the other end is arranged on the upper end surface of the furnace shell 3 and extends into the inner side of the furnace shell 3 by penetrating through the upper end surface of the furnace shell 3, the aluminum melting crucible 5 is arranged on the upper end of the aluminum heat-preservation crucible 13, the lower end of the outer side wall of the smelting furnace shell 3 is provided with an aluminum liquid outlet 2, the aluminum liquid outlet 2 penetrates through the smelting furnace shell 3 and is connected with an aluminum heat-insulating crucible 13, the upper end of the outer side wall of the smelting furnace shell 3 is provided with an exhaust pipe 8, the exhaust pipe 8 penetrates through the outer side wall of the smelting furnace shell 3 and is connected with an aluminum melting crucible 5, a heat energy recovery device 7 is sleeved on the exhaust pipe 8 and is connected with the aluminum heat-insulating crucible 13, a circuit control center 4 is arranged on the outer side wall of the smelting furnace shell 3, the circuit control center 4 is connected with an electromagnetic coil 11, a feeding transmission device 12 is arranged on the outer side wall of the smelting furnace shell 3, the feeding transmission device 12 and the circuit control center 4 are respectively.
And a control valve is arranged on the aluminum liquid output port 2 and is used for controlling the aluminum liquid conveying.
The electromagnetic coil 11 is in a spiral shape with a big top and a small bottom, and the electromagnetic coil 11 is sleeved on the outer side wall of the aluminum melting crucible 5.
As shown in fig. 2, the furnace shell 3 includes a hearth through hole 31, an inner shell 32, an outer shell 33, and an inner shell bottom surface 34, the inner shell 32 is provided inside the outer shell 33, the hearth through hole 31 is provided on a lower end surface of the inner shell 32, the hearth through hole 31 connects the inner shell 32 and a lower end surface of the outer shell 33, the inner shell 32 and an upper end surface of the outer shell 33 are connected to each other, and the inner shell bottom surface 34 is a concave inclined surface.
The inner shell 32 and the outer shell 33 are in a vacuum state, one end of the telescopic support rod 6 is fixed between the inner shell 32 and the outer shell 33, the inner shell 32 is made of high-temperature-resistant ceramic materials, and the outer shell is made of titanium alloy materials.
The circuit control center 4 is internally provided with a shell, a singlechip, a frequency converter, an external power line, a control switch and a circuit board, the singlechip and the frequency converter are arranged on the circuit board, one end of the control switch is arranged on the shell of the circuit control center 4, the other end of the control switch is arranged on the circuit board, the circuit board is connected with an external power supply through the external power line, the frequency converter is connected with the electromagnetic coil 11, the control switch is a PLC touch screen controller which is in the prior art, a 4.3-inch touch screen PLC integrated machine with MHW-6043-type MR/MT is adopted, which is produced by Suzhou Meihe science and technology company, a Kuri I57500 k processor is arranged in the singlechip, and the frequency converter is an ATV71HC25N 4Z-type 250KW universal frequency converter produced by the Sch.
As shown in fig. 3, the aluminum melting crucible 5 includes an air outlet 51, a material loading mesh 52, a motor 53, a valve core through hole 54, a valve core 55, a rotating shaft 56 and a crucible 57, the crucible 57 is fixed on the inner side wall of the inner shell 32, the air outlet 51 is arranged on the upper side of the inner side wall of the crucible 57, the air outlet 51 is connected with the exhaust pipe 8, the valve core through hole 54 is arranged on the valve core 55 and penetrates through the valve core 55, the rotating shafts 56 are arranged on two sides of the valve core 55, the connecting line of the rotating shafts 56 on the two sides is 90 ° intersected with the valve core through hole 54, the valve core 55 is fixed in the lower end face of the crucible 57 through the rotating shaft.
The motor 53 is electrically connected to a circuit board in the circuit control center 4.
A laser liquid level detector is fixed on the upper end surface of the inner side of the aluminum heat-preservation crucible 13 and is electrically connected with a circuit board of the circuit control center 4, and the laser liquid level detector adopts a XYM-4 type laser liquid level meter produced in the new direction of Shijiazhu.
The telescopic supporting rod 6 is a hydraulic telescopic rod, a piston rod of the hydraulic telescopic rod is connected to the lower end face of the upper cover 9, and a sleeve of the hydraulic telescopic rod is arranged between the inner shell 32 and the outer shell 33.
As shown in fig. 4, the aluminum material pushing device 10 includes a first chain gear 101, a chain 102, a pushing plate 103, a pushing plate connecting block 104, a second chain gear 105, a pushing motor 106, and pushing plate blocking rails 107, the pushing plate blocking rails 107 are disposed at two ends of the pushing plate 103, and the push plate stop rail 107 is fixed on the upper end surface of the smelting furnace shell 3, a groove is arranged on the push plate stop rail 107, a push plate connecting block 104 is arranged on the two ends of the push plate 103 contacting with the push plate stop rail 107, the push plate connecting block 104 is arranged in the groove of the push plate stop rail 107, the first chain gear 101 is fixed on one end of the inner side of the push plate stop rail 107 through a rotating shaft, the second chain gear 105 is fixed on the other end of the inner side of the push plate stop rail 107 through a rotating shaft, the push motor 106 is arranged on, and the output shaft of the pushing motor 106 is connected with the rotating shaft of the second chain gear 105, the first chain gear 101 and the second chain gear 105 are sleeved with the chain 102, and the outer side surface of the lower end of the chain 102 is fixed with the push plate connecting block 104.
The pushing motor 106 is electrically connected with the circuit board of the circuit control center 4.
As shown in fig. 7, the feeding transmission device 12 includes a transmission rotation shaft 121, a transmission tape 122, a transmission rail 123, a transmission rail support rod 124, a winding wheel 125, a transmission belt pulley 126, transmission shafts 127, a driving belt pulley 128 and a transmission belt 129, the transmission rotation shaft 121 is disposed on both sides of the material loading box 14, the transmission rotation shaft 121 is connected to the winding wheel 125 through the transmission tape 122, the winding wheel 125 is disposed on the transmission rail support rod 124 through the transmission shafts 127, one of the winding wheels 125 is connected to the transmission belt pulley 126 through the transmission shaft 127, the transmission rail support rod 124 is disposed on the transmission rail 123, the transmission rail 123 is disposed on the side wall of the furnace shell 3, the transmission rail 123 is provided with an inner groove, both sides of the material loading box 14 are connected to the transmission rail 123 and are connected to the transmission rail 123 in a sliding manner, a motor is embedded in the outer side wall of the transmission rail 123, the drive pulley 128 is connected to the drive shaft 127 via a drive belt 129.
The motor on the side wall of the transmission rail 123 is electrically connected with the circuit board of the circuit control center 4.
As shown in fig. 5, the thermal energy recovery device 7 includes a low temperature steam inlet 71, steam 72, a high temperature steam outlet 73, a steam heat exchange pipe 74, the low-temperature steam conveyer 75, the heat conduction fins 76 and the recovery device shell 77, the exhaust pipe 8 is arranged in the recovery device shell 77, the heat conduction fins 76 are arranged on the outer side wall of the exhaust pipe 8 in the recovery device shell 77, the steam 72 is arranged between the recovery device shell 77 and the exhaust pipe 8, the low-temperature steam inlet 71 is arranged at the lower end of the recovery device shell 77, the high-temperature steam outlet 73 is arranged at the upper end of the recovery device shell 77, the high-temperature steam outlet 73 is connected with one end of the steam heat exchange pipeline 74 through a pipeline, the low-temperature steam inlet 71 is connected with the other end of the steam heat exchange pipeline 74 through a pipeline, and the low-temperature steam conveyer 75 is arranged on a pipeline between the low-temperature steam inlet 71.
As shown in fig. 6, the water vapor heat exchange pipe 74 is disposed inside the aluminum heat-insulating crucible 13, the water vapor heat exchange pipe 74 is in a horizontal spiral shape, and the outer surface of the water vapor heat exchange pipe 74 is provided with heat conduction fins which are uniformly distributed.
The low-temperature steam conveyer 75 is electrically connected with the circuit board of the circuit control center 4.
The quantitative heat-preservation aluminum liquid melting furnace comprises the following working steps:
1) putting the aluminum material into the material loading box 14, controlling a motor on the side wall of the transmission rail 123 to start through a PLC (programmable logic controller) touch screen controller, driving a driving belt pulley 128 to rotate, driving a transmission belt pulley 126 through a transmission belt 129, driving a rolling wheel 125 to rotate, enabling a transmission rolling belt 122 to be rolled on the rolling wheel 125 through the rotation of the rolling wheel 125, pulling the material loading box 14 to move upwards, and enabling the material loading box 14 to reach the top end of the transmission rail 123, at the moment, continuously shrinking the rolling wheel 125, enabling the material loading box 14 to rotate around the contact position of the material loading box 14 and the transmission rail 123, and enabling the aluminum material in the material loading box 14 to be poured onto the upper end;
2) at this time, the circuit control center 4 controls the push motor 106 to rotate in the forward direction, so as to drive the chain 102 to rotate, further drive the push plate connecting block 104 to move towards one end of the push motor 106, further drive the push plate 103 to move from the outer side of the furnace shell 3 to the inner side of the furnace shell 3, further push the aluminum material placed on the upper end surface of the furnace shell 3 into the aluminum melting crucible 5 on the inner side of the furnace shell 3, and drop onto the material carrying net 52 on the inner side of the aluminum melting crucible 5;
3) at this time, the telescopic support rod 6 is contracted, so that the upper cover 9 moves downwards until the upper cover 9 covers the smelting furnace shell 3;
4) at the moment, the circuit control center 4 introduces sudden change alternating current into the crucible 11 through a frequency converter, so that eddy current is generated inside the aluminum material on the material carrying net 52, the aluminum material is melted, and the melted aluminum material flows into the bottom surface of the inner side of the aluminum melting crucible 5 from gaps on the material carrying net 52;
5) at the moment, the circuit control center 4 controls the motor 53 to rotate, so that the valve core through hole 54 on the valve core 55 is vertical, the bottom surface of the inner side of the aluminum melting crucible 5 is communicated with the aluminum heat-preservation crucible 13, and aluminum liquid on the bottom surface of the inner side of the aluminum melting crucible 5 flows into the aluminum heat-preservation crucible 13 through the valve core through hole 54;
6) hot gas generated during melting of the aluminum material enters the exhaust pipe 8 and then reaches the heat energy recovery device 7, the temperature in the exhaust pipe 8 heats low-temperature steam in the shell 77 of the recovery device through the heat conduction fins 76, so that the low-temperature steam is changed into high-temperature steam, and then the high-temperature steam enters the steam heat exchange pipeline 74 through the high-temperature steam outlet 73;
7) the aluminum liquid flows into the aluminum heat-preservation crucible 13 and contacts with the steam heat exchange pipeline 74 in the aluminum heat-preservation crucible 13, the aluminum liquid is kept warm all the time by heating the steam heat exchange pipeline 74, and after being cooled, the high-temperature steam is continuously conveyed to the steam heat exchange pipeline 74 through the low-temperature steam conveyor 75 and circulates in sequence;
8) meanwhile, a laser liquid level detector at the upper end of the inner side of the aluminum heat-preservation crucible 13 is started to monitor the liquid level of the aluminum liquid and transmit data to a single chip microcomputer and a touch screen of a plc controller, when the liquid level of the aluminum liquid reaches a preset value, the single chip microcomputer controls a motor 53 to rotate, so that a valve core through hole 54 on a valve core 55 is rotated to the side surface, and the aluminum liquid in the aluminum melting crucible 5 is blocked from entering the aluminum heat-preservation crucible 13;
9) when the aluminum liquid needs to be output, the control valve on the aluminum liquid output port 2 is opened, so that the aluminum liquid in the aluminum heat-insulating crucible 13 flows out of the device.
The foregoing is merely exemplary and illustrative of the present invention and various modifications, additions and substitutions may be made by those skilled in the art to the specific embodiments described without departing from the scope of the invention as defined in the following claims.