AIR PLASMA INDUCED LOW METAL LOSS

Abstract

Even a very small amount of air plasma can reduce the dross during melting. A method and device is shown, whereby substantial saving in the cost of melting aluminum and the energy to melt aluminum is possible by the technique of introducing a small amount of air plasma in the melting environment. In this manner even though the air contains oxygen, and the common practice is presently directed at air being eliminated from the melting environment, an air plasma is able to very effectively be utilized.

Description

PATENTS CITED IN TEXT

U.S. Pat. No. 5,963,709 and pending patent application Ser. No. 10/725,6161

Other US Patents

U.S. Pat. No. 3,648,015.

U.S. Pat. No. 5,403,453.

U.S. Pat. No. 5,387,842.

U.S. Pat. No. 5,414,324.

U.S. Pat. No. 5,456,972.

U.S. Pat. No. 5,669,583.

U.S. Pat. No. 5,938,854.

U.S. Pat. No. 6,146,724.

U.S. Pat. No. 6,245,132.

Application:

The general physical and chemical characteristics of molten aluminum include: Aluminum melts combine with oxygen, moisture, or other oxidizing materials to form dross, and the tendency and ease with which this dross can be entrained in the melt affects the casting made from the melt. Other factors which affect the casting made from aluminum and its alloys are, the readiness with which the melt will absorb nascent hydrogen, and the evolution of hydrogen during solidification of the casting to form porosity (the principal source of hydrogen is moisture from the products of gas/oil combustion); the 3.5 to 8.5% contraction in volume which occurs when the melt solidifies and the low density of molten aluminum which results in low hydrostatic pressure in the mold. Good founding practice begins with good melting practice which is almost always dependent on the type of melt casting furnace used. As will be noted in the sections below the use of any electrically operated system for the melting of aluminum impacts favorably on dross formation as electrically heated systems minimize convection. When the aluminum melts react with the atmosphere or moisture, a dross of aluminum oxide and nitride is formed, which contains some mechanically entrained gas and metal. Since the dross is wetted by the aluminum melt and has about the same density, it often becomes entrained in the melt during melting, handling, or casting, and does not readily separate at the surface of the melt. It is commonly believed that the quantity of dross formed during melting increases with 1) the use of fine or badly weathered or corroded scrap; 2) the presence of magnesium in the alloys in the charge; 3) the increase in turbulence (such as from induction melting) which breaks the protective oxide surface of the melt in the furnace; and 4) the increase in the temperature of gases specially air and oxygen in contact with the surface. The oxide on the melt surface contains a considerable amount of liquid metal, causing the dross layer to be “wet.” Common experience has it therefore that high temperatures cause more dross and that wet dross is increased also by a higher temperature of melting. The melting/casting furnaces presently used in the aluminum industry can typically be classified into three types depending on the source to power the same. These are resistance-heated furnaces, induction-heated furnaces, and gas- or oil-fired furnaces. The common types and their advantages are tested in Table 1. Although each type of the existing melt furnaces have some advantages, they all suffer from several general drawbacks, namely high energy cost, high dross, harmful gas generation, low quality aluminum, and high operational noise, as individually discussed below:

• • Resistance-heated furnace—The resistor elements are inserted in protection tubes or otherwise suspended and installed in the furnace lining with heat transfer to the metal by radiation. The general temperature of operation of these furnaces is between 700 and 1000 C. The heating elements used are generally made of metallic wires (max temperature that these can normally reach is about 1050 C) or silicon carbide (maximum temperature they can reach is about 1500 C). Nevertheless the normal use of electric furnace to melt or contain aluminum is about 700 to 800 C. The costs for investment, maintenance, and operation of this type of furnace are high because of the cost of electricity and when silicon carbide elements are used which frequently are imbalanced because of aging.
  • Induction-heated furnaces—In addition to energy inefficiency, induction furnace are generally characterized by high maintenance and labor costs and therefore, the use of this kind of furnace is usually limited only to some very special applications. Induction furnaces also cause churning of the liquid leading to oxide (dross) inclusions. There is also a growing concern about electromagnetic fields (EMF) in the workplace. However, this issue remains controversial. Again when using induction furnaces the melt is kept at about 700 to 800 C.
  • Gas- or oil-fired furnaces—This type of furnace is more energy inefficient than the other two types of furnaces because of uncontrolled combustion flames inside the furnace. All gas- or oil-fired furnaces suffer from high noise due to the burning explosive process and serious environmental problem due to the release of harmful combustion product gases such as PAH, soot, sulfur dioxide, NOx, and CO. In addition, this type of furnace usually has low recovery rated because air is allowed into the furnace for the operation of the gas/oil burners which results in severe melt loss due to oxidation. Moisture in the gas often leads to hydrogen pick up in the melt.

TABLE 1
Typical operating parameters of common aluminum furnaces.
	Dross	Energy Efficiency	Capital Cost
Indirect Fixed Crucible	5-15%	7-17%	low
Electric Induction	5-10%	low	Very high
Direct Flame	5-15%	Very low	Very low
Electric radiant	2-6%	70%	Medium
Sloping Dry Hearth	5-15%	18%	Medium

It is clearly noted from the chart above that conventional radiant electric heating is the most efficient and clean method of heating. The total metal melt loss in dross could be as high as 80% of the dross weight. In radiant rod furnaces, electric currents of up to 4000 to 5000 amperes are commonly used to heat silicon carbide resistance elements which radiate to the furnace load and walls (note however as described above such elements are not the most optimal). These furnaces are made to oscillate, thereby facilitating conduction to the melt from the furnace walls. Radiant rod furnaces require relatively low investment cost, but are primarily being used as holding furnace. Operating costs are impacted by dross formation and energy usage. Typical dross loss

The result of reduced dross is significant from our experiments. We find that even a small amount of air plasma in an aluminum heating furnace can substantially reduce dross.

It is common knowledge that nitrogen gas is used as a cover to reduce the oxidation (dross formation). There are several technologies which are also used to recover aluminum from dross by re-melting and cleaning means. Our invention will make possible substantial savings in melting costs because Nitrogen a gas often used during melting or holding aluminum to melt aluminum can be eliminated. The dross is often reclaimed by re-melting thus incurring energy and productivity penalties. Thus by using our invention the energy costs are reduced for aluminum processing and the productivity of aluminum melting can be enhanced. We anticipate that the product of the invention can be used to separate debris from aluminum where the debris can be sprues or dross or other contaminants.

EXPERIMENT # 1

Equipment:                       (H23) Total 23 kW
Heating Elements:                Molybdenum disilicide
Plsama Airtorch ™ #:             BR
Power Rating:                    10.0 KW
Inlet input to Plasma Airtorch ™: Compressed air, ~3-4 CFM.
Exit dia of Plasma Airtorch ™:   ¾″ diameter × 0.5″ length
                                 exit nozzle
Target:                          Furnace pouring spout/launder
Material of the Charge:          356 Aluminum alloy ingot
                                 {Tliquidus = 615 C., Tsolidus = 555 C.}
Weight of Charge:                33 + 6 + 12.5 = 51.5 pounds

	Furnace temperature,
	° C.	Furnace current,		Observations: Time
	(B-type sensors)	Amps	Airtorch, ° C.	of start and finish
Time	Process	Over temp.	Primary	Secondary	(K-sensor)	pouring.
3:08	RT	RT	0	0	RT
3:09	RT	RT	15.5	48.9	RT
3:45	RT	RT	23	75	RT	Start-up door opened
3:50	37		33	73	RT
3:55	94		37	84	RT	13.3 V, 71 A;
						Increased from 45 to
						50% power
4:00	198		36	84	RT
4:05	203		21	62
4:10	199		20	54	RT
4:15	201		18	51	RT
4:20	228		19	63	RT	60% power
4:25	254		22.9	76	RT
4:30	324		30	94	RT	Red glow started;
						65% power
4:35	370		31	96	RT
4:40	400		31	97	RT
4:45	400		39	93	120
4:50	400		37	86	342
4:55	430		37	117	527	80% power;
						SV = 1500 C., door
						closed
5:00	541		49	151	682	100% power,
						Pri = 188 V, Output
						dropped to 95%
5:05	642		47	46	728
5:10	696		47	148	700
5:15	753		48	151	679
5:20	794	781	49	153	674
5:25	836	823	50	155	672
5:30	875	864	50	157	659	Soft metal
5:35	902	892	51	159	661	Soft; Gap bottom
						closing
5:40	918	990	51	160	1019	Little quantity
						dripped into
						crucible. Shiny
						liquid
5:42	923	918	52	161	1081	Metal started
						pouring semi-
						continuously
						(shiny).
5:45	930	926	52	162	1123	Metal pouring
						droplets;
5:47	940	935	50	155	1157	More close to
						continuous pouring;
						92% power
5:48	944	941	50	154	1173	Continuous pouring
5:50	954	951	50	156	1181	Continuous pouring
5:52	980	977	51	159	1188	Continuous pouring
5:54	1079	1080	50	156	1201	Stopped pouring
5:57	1142	1139	50	155	802	Door opened
5:59	1006	993				New ingot of 12.5
						pounds charged
6:00	994	987	51	156	650	One more ingot of 6
						pounds charged
6:00:30						Door closed
6:02	952	962	50	155	820	Heating
6:05	952	967	50	155	996	Heating; Click noise
						twice inside furnace
6:10	980	993	51	158	1075	Tr. Hot; Two
						droplets fell.
6:12	996	1010	52	161	1097	Metal pouring semi-
						continuously
6:15	1013	1027	52	160	1106	Metal pouring more
						continuously
6:17	1029	1039	51	160	1114	Metal pouring more
						continuously
6:18	1040	1047	51	159	1117	Continuous almost
6:20	1052	1059	51	158	1119	Continuous almost
6:25	1091	1111	50	156	1125	Continuous almost
6:27	1101	1099				Door opened;
						Furnace shutdown
Results:
Weight of dross = 200 grams.
Metal is shiny.
% Dross = 0.855

EXPERIMENT # 2

Equipment:                       (H23) Total 23 kW
Heating Elements:                Molybdenum disilicide
Plasma Airtorch ™ #:             BR Power rating: 10.0 KW
Inlet Input to Plasma Airtorch ™: Compressed air, ~3-4 CFM.
Exit:                            ¾″ diameter × 0.5″
Target:                          Furnace pouring spout/launder
Material of the Charge:          Aluminum alloy ingot
Weight of Charge:                35 pounds

	Furnace temperature,
	° C.	Furnace current,		Observations: Time
	(B-type sensors)	Amps	Airtorch, ° C.	of start and finish
Time	Process	Over temp.	Primary	Secondary	(K-sensor)	pouring.
1:24	1500					Ingot charged into
						furnace; ~1 minute
						for loading
1:25	1200
1:30	1034
1:35	1007					Beginning to sag
1:40	1026					Began to flow; Slow
						dripping
						Furnace opened
						brifely
1:45	1016				−900	Steady flow just
						starting
1:48	1022					Good flow rate;
						Steady stream
1:50	1059					Flow slowing -
						ready to stop
						flowing
Weight of dross = 134 grams. Metal is shiny.
% Dross = 0.84
Cumulative weight of dross of 2 melts (33 + 6 + 12.5 + 35 pounds) = 334 grams.
Cumulative % dross = 0.850

EXPERIMENT # 3

Equipment:                       (H23) Total 23 kW
Heating Elements                 Molybdenum diSilicide
Plasma Airtorch ™ #:             BR Power rating: 10.0 KW
Inlet Input to Plasma Airtorch ™: Compressed air, ~3-4 CFM.
Exit:                            ¾″ diameter × 0.5″
Target:                          Furnace pouring spout/launder
Material of the Charge:          Aluminum alloy ingot
Weight of Charge:                17 + 17.5 = 34.5 pounds

	Furnace temperature,
	° C.	Furnace current,		Observations: Time
	(B-type sensors)	Amps	Airtorch, ° C.	of start and finish
Time	Process	Over temp.	Primary	Secondary	(K-sensor)	pouring.
3:15		590				Furnace started &
		flashing				slowly taken to
						1500 C.
3:30	1500	766	46.5		415	Ingot charged
3:32	1400	709	52		475	Some smoking
3:45	750	674	51.9		650	Controller confg
						changed from K to B
						type
3:50	808	729	53.3			Smoking door area
3:55	893	803	54.6
4:00	935	841	56.4		669	Melting
4:04	955	857	56.6		658	Dripping to flow
4:10	996	900	57			Starting to pour;
						Good flow.
4:15	1074	981	55.3			Flow stopped
						Aim: Take melter to
						1500 C. and charge
						new ingot;
4:58	1500	1411	47.8		772	17.5 pound Ingot
						charged
5:00	1320	1187	51.8		775
5:08	1234	1085	53.1			First drip
5:10	1228	1079	52.9			Flowing steady
5:13	1279	1129	52.0			Flow slowing
5:14	1330	1200	50.9			Flow stopped
Weight of dross = 180 grams.
Metal is shiny.
% Dross = 1.149%

EXPERIMENT #4

Equipment:                       (H23) Total 23 kW
Plasma Airtorch ™ #:             BR Power rating: 10.0 KW
Inlet Input to Plasma Airtorch ™: Compressed air, ~3-4 CFM.
Exit:                            ¾″ diameter × 0.5″
Target:                          Furnace pouring spout/launder
Material of the Charge:          356 Aluminum alloy ingot
                                 {Tliquidus = 615 C., Tsolidus = 555 C.}
Weight of Charge:                33.5 Pounds

	Furnace temperature,
	° C.	Furnace current,		Observations: Time
	(B-type sensors)	Amps	Airtorch, ° C.	of start and finish
Time	Process	Over temp.	Primary	Secondary	(K-sensor)	pouring.
10:25	274					Start up
10:35	444		31.0	131	784
10:48	743	749	421	123	799
10:55	920	924	45.8	122	814
11:10	1100	1103	39.7	115	821	Hold
11:25	1103	1103	33.1	90.7	822
11:55	1150	1150	31.2	146	822
12:05	1280	1254	44	111	822
12:10	1331			150
1:03	1065	1081				Ingot charged
1:14	1088	1100				Steady flow
1:20	1077	1093				Steady flow
1:25	1079					Stopped flow
Weight of dross = 400 grams (for expt # 4 & 5: 34 + 17.5 + 35.5 = 87 pounds total charge)
% Dross = 1.013.
Metal is shiny.

EXPERIMENT # 5

Equipment:                       H23) Total 23 kW
Plasma Airtorch ™ #:             BR Power rating: 10.0 KW
Inlet Input to Plasma Airtorch ™: Compressed air, ~3-4 CFM.
Exit:                            ¾″ diameter × 0.5″
Target:                          Furnace pouring spout/launder
Material of the Charge:          380 Aluminum alloy ingot.
Weight of Charge:                27.5 pounds

	Furnace temperature,
	° C.	Furnace current,		Observations: Time
	(B-type sensors)	Amps	Airtorch, ° C.	of start and finish
Time	Process	Over temp.	Primary	Secondary	(K-sensor)	pouring.
11:25	690		40	118	669
11:30	830		40	124
11:36	915		53	152	719
11:40	1000		55	159	719
11:45	1020		42	125	719
11:50	1045		42	121	722
11:55	1085		43	123	722
12:15	1125		35	102	722
12:30	1200		38	105	725
12:35	1265		46	133	724
12:40	1331		47	133	728
1:05	1480		47	134	645
1:10	1500		47	130	742
1:20	1550
1:25	1060		44	124	796	27.5 pounds ingot
						charged
1:30	1053		43	125		First drips
1:35	1061		43	125		Steady drips
1:37	1065		43	125	787	Steady stream
1:39	1070		43	125	787	Stopped; Shutdown
Weight of dross = 125 grams.
Metal is shiny.
% Dross = 1.001%

EXPERIMENT # 6

Equipment:                       (H23) Total 23 kW
Plasma Airtorch ™ #:             BR Power rating: 10.0 KW
Inlet Input to Plasma Airtorch ™: Compressed air, ~3-4 CFM.
Exit:                            ¾″ diameter × 0.5″
Target:                          Furnace pouring spout/launder
Material of the Charge:          Copper
Weight of Charge:                1.35 pounds

	Furnace temperature,
	° C.	Furnace current,		Observations: Time
	(B-type sensors)	Amps	Airtorch, ° C.	of start and finish
Time	Process	Over temp.	Primary	Secondary	(K-sensor)	pouring.
9:22	RT		41			1600 C./1.5 h
9:25	70		36
9:30	164		38
9:35	265		32
9:40	339		28
9:46	464		39			1600 C./1 hr
9:50	600		46
9:55	741		48
9:57	822					Shutdown
10:15						Re-started
10:20	432		26
10:25	504		27
10:30	563	608	35
10:36	650	698	33
10:40	701	750	39
10:45	768	821	34
10:50	836	893	39
10:55	897	959	39
11:00	971	1034	38
11:09	1092	1157	40
11:15	1176	1243	50
11:20	1237	1307	49.5
11:25	1286	1356	49
11:27						Furnace shutdown
						due to OVT SP was
						at 1350; reset to
						1720 C.
11:31	1099	1172	23
11:35	1158	1229	32
11:45	1297	1365	41
11:50	1361	1432	47
11:56	1419	1487	46
12:01	1452	525	46
12:05	1474	1548	45.1
12:10	1501	1577	45.1
12:29	1571	1656	44
12:35	1581	1673	44
12:40	1594	1684	44
12:43	1600	1689	40
12:47:00	1600	1690	40			1.35 pound ingot
						charged
12:48:22						Started
						pouring/leaking
12:48	1507	1611
12:49:00						Completed pouring
12:52	1569	1661				Shutdown
1:53	1395	1475	47			Re-started for next
						melt
2:02	1453	1538	46
2:15	1507	1600	45
2:28	1542	1635	44
2:40	1565	1667	44
2:45	1577	1677	44
3:01:00 to 3:01:30	1600	1701	43			5.0 pounds Cu ingot
						charged in 30
						seconds
3;04:00	1459
3:03:30						Pouring began
						(Molten metal
						leaked from bottom
						hearth)

Summary of Rapid Copper Melting:

			Time for			Furnace temp,
			melting	Time for	Furnace temp.	after charging
		Time for	(beginning of	complete	at the time of	& closing
Run #	Charge, lbs	charging, M:S	pouring), M:S	pouring, M:S	charging, C.	door, C.
1	1:35	0:20	1:22	0.38	1600	1507
2	5:00	0:30	2:00*	—	1600	1459
*Molten metal leaked through the hearth. Dross Very Low. Shiny.

From the results and the table 2 we note that in addition to dross reduction the energy and time required to melt aluminum is also low when even a small amount of air plasma is present. The heat transfer coefficient may have been increased because of the presence of even small amounts of plasma. In our experiments we estimate that that at least 5% of the total heat came from the plasma generator.

Most importantly the dross content is reduced substantially which is an unusual result and totally unexpected from common wisdom which is that as the temperature is higher then the dross increases especially in the presence of hot air. The reason for the low dross, we suspect possibly comes from the air nitrogen becoming partially ionized. However, this reasoning is only a speculation at this stage. Normally it would be expected that an Airtorch™ enhanced melting which uses hot air (i.e. hot oxygen) would show high dross but the experiments all appear to indicate that the dross in reality reduced substantially. As discussed below this is thought to occur because of the plasma content in the air, albeit small.

The surface of a metallic part especially if the surface is electrically conducting, i.e. where electrons are available in abundance, may give up electrons to the air plasma and also produce heat according to the reaction:

2N⁺+2e⁻=2N+E (approximately 1480 kJ/mole)

2N=N₂+E

This is a manner in which nitrogen and heat automatically could be thought to deposit on the surface of aluminum thus increasing the energy transfer rate substantially as well as providing a cover of nitrogen gas which prevents oxidation. Typically ˜1 CFM of air plasma contains in excess of 10²³ atoms and one percent ionization leads to nearly 10²² ions which can easily produce a layers of inert (non oxygen containing) atoms after absorbing electrons from the solid or liquid metal surface. The air plasma is expected to be mostly nitrogen plasma although the presence of oxygen plasma may not be ruled out because the first ionization energies of nitrogen and oxygen are very similar.

EXPERIMENT #7

A Plasma Airtorch™ with a ¾″ diameter nozzle system was used for melting small pieces of aluminum with the sample in proximity with the hot air plasma atmosphere generated by the Airtorch. During solidification and cooling the plasma Airtorch was powered down slowly. The melted and solidified product looked clean. The clean melt and resultant clean surface solid is presumably because of the ionized plasma which protected the aluminum from large oxidation even though the atmosphere contained mostly air. This is an example which shows that a air plasma can be used by itself providing all the heat required to melt aluminum.

The melting or holding environment comprises of the total atmosphere in the melting or holding device. When the plasma generator is a device of the type displayed in FIG. 2 (products of U.S. Pat. No. 5,963,709 and pending patent application Ser. No. 10/725,6161) the device can be retrofitted to any metal processing system such as a launder or flowing metal channels or molten metal pumps.

The typical devices which may used with the element to melt or contain liquid metal are furnaces (batch, continuous, holding, melting), crucibles, laddles, launder systems (channels for moving liquid metals), holding furnaces, melting furnaces, casting furnaces, transportation vessels for molten metals and other similar equipment.

EXPERIMENT #8

Several small batches about 50 gms of Aluminum alloy 356 were melted in different configurations for a comparative study of the melting surface on resolidification. One batch was heated with a Plasma Airtorch™. The result is shown as (A) in FIG. 1 (a composite photograph). A similar melt was made by heating a small quantity of aluminum in a regular metallic wire furnace with an air environment. Yet another sample was heated in a propane torch gas heating environment atmosphere. All the melts were made in a crucible and after the melts solidified, the aluminum was removed from the crucible by tilting the crucible and allowing the solid to fall out. Notice how much more shiny (A) is compared to the other two clearly indicating that the molybdenum disilicide melted material had low dross and was clean. The metal in (A) slid out much more easily from the crucible. The data conclusively indicates that the use of an Air Plasma in the heater configuration reduces the dross content and the metal loss in the dross. Air contains both nitrogen and oxygen as the predominant gasses. An air plasma is one that contains a nitrogen ions and electrons. Our experiments indicate that even a very small amount of air plasma in the air can substantially reduce the dross.

A typical device in which the method of air plasma melting can be done is shown in FIG. 2. In this device aluminum charge is introduced from one end into a chamber which has heating elements and a plasma Airtorch is placed on top. The chamber now has the environment of an air plasma. Clean liquid metal is discharged from the other end (i.e. a liquid with low dross content).

An air plasma can be created by the products of U.S. Pat. No. 5,963,709 and pending patent application Ser. No. 10/725,6161 (herein incorporated fully). Small amounts of thermal plasma may also be created in very high temperature environments. Very small amounts of thermal ionization are possible by high temperature heating elements such as molybdenum, tungsten and molybdenum disilicide materials. The type of useful plasma for the invention is one which can be employed at normal or high pressure as opposed to very low pressure plasma. Plasma can also created by RF means U.S. Pat. Nos. 3,648,015, 5,403,453, 5,387,842, 5,414,324, 5,456,972, 5,669,583, 5,938,854, 6,146,724, 6,245,132 all incorporated herein. Not all techniques can produce Air Plasma at normal pressures and not all techniques except for U.S. Pat. No. 5,963,709 and Ser. No. 10/725,6161 can be considered to produce substantial heat. Unless an air plasma is used, the cost benefits to melting aluminum from using air instead of a gas like nitrogen, helium or argon are difficult to realize. Of course gas plasmas may also be employed and their use is anticipated.

The best mode appears to be the use of even a small amount even as low as 0.5-1% (of the total environment) of air plasma in any existing or specially constructed device which holds or melts molten aluminum. In this manner even though the air contains oxygen and common practice would involve hot oxygen being removed from the environment, an air plasma is able to very effectively utilize hot air and yet provide beneficial melting. The environment also protects against oxidation in the solid cool down or solid heat up stage.

DETAILED DESCRIPTION OF DRAWINGS

FIG. 1. This is a color photograph (composite photograph). Samples A, B and C represent solidified melts of aluminum alloy 356 after melting and solidification. Note sample A is much more shiny than sample B or sample C. Sample A was melted using a Plasma Airtorch placed above a crucible containing the initial solid sample. Sample B was melted by placing in crucible and melting carried out conventionally with a wire wound electric heater furnace (max temperature 1000 C) and sample C was melted with a gas torch heater. Note, the shiny surface of sample A indicates less of an oxidized surface i.e. the clear difference in the oxide/dross levels. The samples B and C have clear wrinkled and non-shiny oxidized surfaces.

FIG. 2 shows a aluminum melting device consisting of a furnace box with stand 1.1, for melting and collecting liquid metal 1.2 in a crucible 1.3, through a pouring spout 1.4. The furnace environment is contained in the refractories (insulation) 1.5. Molybdenum disilicide heating elements 1.6 and the plasma Airtorches (plasma generator) 1.7 provide heat to the charge introduced from the port 1.10. The plasma and hot air from the plasma generator 1.7 arrive at the charge through a port 1.9. The Plasma generators 1.7 are held to the main furnace body by clamps 1.8. The metal charge 1.11 is introduced through the port 1.10 which can rotate (with the help of a motor 1.12). The molten metal 1.2 and any separated impurity (for example a entrained sprue filter) 1.13 are collected as shown. In this embodiment of the invention three plasma generators 1.7 are shown.

GLOSSARY

Charge: The ingot, or other parts made of metal which are melted or heated. The charge can include ingots, cut pieces of metal, metal chips, or metal waste, or mixed debris and metal.

Melting: All processes involving partial or fully molten metal whether in containment, direct melting or transfer configurations.

Dross: Oxide and complex oxide scale(s) formed on molten aluminum or other metals which can additionally contain trapped metal as well as fluxes.

Air-Plasma: The plasma obtained from the ionization of air. The air plasma may contain substantially hot air and a percentage of ionized air gases.

Claims

1-10. (canceled)

11. An apparatus for processing a metal comprising:

a receptacle for containing the metal; and

at least one plasma arrangement configured to provide a combination of a heated gas and an ionized gas over a free surface of the metal,

wherein, when the plasma arrangement provides the combination over the free surface, a dross that is formed when an entire charge of the metal is melted comprises less than about 3% by weight of the entire charge.

12. The apparatus of claim 11, wherein the combination provides at least about five percent of the total heat used for melting of the entire charge.

13. The apparatus of claim 11, wherein the receptacle comprises a heating arrangement configured to provide heat to the entire charge.

14. The apparatus of claim 13, wherein the heating arrangement comprises a plurality of resistance heating elements.

15. The apparatus of claim 14, wherein the resistance heating elements comprise molybdenum disilicide.

16. The apparatus of claim 11, wherein the heated gas is air.

17. The apparatus of claim 11, wherein the heated gas comprises oxygen.

18. The apparatus of claim 11, wherein the combination comprises a small amount of the ionized gases.

19. The apparatus of claim 11, wherein the combination comprises less than about 1% of the ionized gases.

20. The apparatus of claim 11, wherein the combination comprises between about 0.5% and about 1% of the ionized gases.

21. The apparatus of claim 11, wherein the metal comprises aluminum.

22. The apparatus of claim 11, wherein the receptacle comprises at least one of a launder system or a molten metal transportation vessel.

23. The apparatus of claim 11, wherein the at least one plasma arrangement comprises a plurality of plasma arrangements.

24. The apparatus of claim 11, further comprising an enclosure configured to provide an enclosed region above the receptacle, wherein the combination is provided into the enclosed region.

25. The apparatus of claim 11, wherein the receptacle comprises at least one of a furnace, a crucible, a holding furnace, a melting furnace, or a casting furnace.