This invention relates generally to electric arc furnace steel making and specifically to such systems having a ladle metallurgical furnace therein, which systems require decreased energy input per unit of steel produced compared to similar systems. It is particularly directed to making alloy steel at a rate limited only by the maximum melting capacity of the arc furnace. In addition the invention, without modification, is adaptable to nearly every end use found in the steel industry today from continuous casting to unique, one of a kind melts of widely varying compositions in a randomized production sequence.
For example, the invention enables the production of up to four different types of steel (as distinct from grades of steel) in a single electric arc furnace system without slowdown or delay in the processing sequence of heats regardless of the number or randomized order of the different types of steel to be made in a campaign. Thus the system will produce at least non-vacuum arc remelt steel, vacuum arc remelt steel, vacuum oxygen decarburized non-vacuum arc remelt steel and vacuum oxygen decarburized vacuum arc remelt steel.
For some years extending up to about the last decade and a half the vacuum arc degassing system was practiced throughout the world for the production of steel having alloy, gas, grain size and inclusion contents within narrowly defined ranges. In this system steel tapped from an electric arc furnace was thereafter subjected to the combined effects of a low vacuum, a purging gas, and alternating current heating arcs struck between graphite electrodes and the wildly boiling surface of the molten steel while it was subjected to the combined effects of a low vacuum and the purging gas. This system is usually referred to as the vacuum arc degassing system. Millions of tons of steel have been produced by this method and significant tonnage continues to be produced at this date. This method has advantages unachievable by the prior competitive systems including the ability to teem at plus or minus 10° F. at any desired time extending for as long as at least eight hours from furnace tap. Thus a 100 ton ingot could be produced from a system having only one 50 ton arc furnace, and ample time was always available to compensate for planned, or unexpected, downstream delays, thereby avoiding return of a melt to the arc furnace.
However, during normal operations in such systems the throughput of the system is governed by the processing time in the arc furnace and, in most installations, the processing time for a single heat can be upwards of four to four and one half hours due to the extensive steel making which takes place in the arc furnace; in other words, the steel resides in the arc furnace long after the scrap charge has melted and reached tapping temperature.
With increasing pressures on the steel maker to lower costs and increase throughput using conventional arc furnace technology the lengthy, by comparison, arc furnace steel making technology has had to be abandoned in favor of shorter cycles which achieve the same end result.
For approximately the past 15 years the ladle metallurgical furnace system has begun supplanting traditional arc furnace and vacuum arc degassing steel making technology. In the ladle metallurgical furnace system the arc furnace has been confined to being almost solely a melting unit, with most steel making deferred to downstream operations. For the arc furnace in such a system this has resulted in a much shorter dwell time of the scrap charge in the furnace since raw scrap (and early lime and carbon additions) can be brought to tapping temperature in about two hours, or less, compared to the four to four and one half hours required in conventional arc furnace steel making in the same size furnace. The use of larger electrodes has also contributed to decreased furnace dwell time. In a specific example which will be described in greater detail hereafter, the furnace dwell time from the beginning of charging to the end of tapping will be decreased from four to four and one half hours to two hours or less.
In this invention, the increased throughput will be achieved by reducing heat sink in the molten steel contacting components of the system, the use of carryover heat from melt to melt and the prompt placement of a stripped ingot, while it is still hot, into a heating furnace to heat the initially partially heated ingot to deformation temperature for the subsequent forging operation.
The decrease of heat loss due to heat sink will be achieved by preheating a selected component or components of the metal contacting units. For example, by preheating the tapping ladle until the refractory lining will be in the vicinity of about 2000° F., and then slowing the cooling rate of the tapping ladle by use of a refractory cover which is applied to the upper open end of the ladle until moments before tapping, the tapped metal will be minimally cooled during the tapping step.
Heat input to the system will be further decreased by carryover of a minor, but effective, quantity of molten steel from one tap to the next. Thus, for example, assuming start up from an empty arc furnace, and with an aim of teeming 75 tons of molten metal, approximately 80-85 tons of solid scrap will be charged into the arc furnace. After melting, a melt consisting of seventy-five tons of molten metal will be tapped into a tapping ladle.
Upon completion of tap, and return of the arc furnace to an upright position, the furnace cover will be moved away from the furnace bowl and approximately seventy-five tons of solid scrap will be charged into the approximately ten tons of molten steel carried over from the immediately preceding melt. The carryover melt plus the turnings from the scrap charge bucket in the succeeding heat will form a reservoir of hot metal which will engulf and thereby melt the scrap hot tops and other large pieces in the arc furnace charge at a much faster rate than if the furnace bowl was totally empty before the first scrap charge bucket was emptied into the arc furnace; the carryover metal will surround and transfer conductive heat to the large pieces of scrap much sooner than would occur if the bushelings and other small pieces of scrap had to change from solid to liquid state before conduction heating of the large pieces could begin.
The invention ensures that at least four different steel making processes may be practiced in any day and in any sequence, the specific process performed depending only on the sequence in which the different types of steel are ordered to be made. This hitherto unattainable flexibility in end use will be attainable in a single plant which will be adaptable to carry out steel making processes which are currently recognized as separate and distinct but which are seldom, if ever, found in existing plants.
Thus, for example, the steel maker may have a sufficient number of orders for low alloy steel that one or more successive heats of steel need only be subjected to the basic processing steps of melting, refining in the ladle metallurgical furnace, degassing at the vacuum degassing station, teeming and solidification.
However if the steel maker's next customer desires a vacuum arc remelt (VAR) product, the steel maker, after melting, ladle metallurgical refining, vacuum degassing and teeming a succeeding melt to form an ingot, may divert the solidified vacuum degassed ingot to a vacuum arc remelt unit in which the solidified vacuum degassed ingot will be converted into a VAR electrode, the VAR electrode remelted in the VAR unit to form a VAR ingot, and the resultant VAR ingot thereafter processed as required, such as forging and heat treatment.
And should a third customer order a vacuum degassed and vacuum oxygen decarburized steel, that third customer's order may be started without delay in the arc furnace without alteration of the first two stages—the melting and ladle metallurgical refining stages—and then subjected to vacuum oxygen decarburization in the vacuum degassing unit, to be followed by teeming and solidification.
And, further should the steel maker's fourth customer order specify a vacuum oxygen decarburized vacuum arc remelted steel, the processing of such a special steel may be incorporated into the production sequence without delay and without alteration of either of the first two processing stages—arc furnace melting and ladle metallurgical furnace refining—which steps require the longest blocks of time as will be seen hereafter.
It is accordingly an object of the invention to provide, in a system having a single arc furnace, a single ladle metallurgical furnace and a single vacuum treatment station, the ability to carry out at least four dissimilar steel making processes in randomized order, namely high volumes of standard grades of vacuum degassed steel, vacuum arc remelted steel, vacuum oxygen decarburized extra low carbon steel, and vacuum oxygen decarburized vacuum arc remelted extra low carbon steel.
Another object of the invention is to carry out the above described steel making processes in which the vacuum treatment common to all four processes cannot be compromised by unintended degradation of the vacuum integrity of the system attributable to utilizing the metal containing vessel as a component of the vacuum system.
A further object of the invention is to decrease the heat energy required per unit, such as a ton, of steel produced as contrasted to conventional ladle metallurgical furnace refining systems.
The invention is illustrated more or less diagrammatically in the accompanying drawing in which
Like parts will be used to refer to like or similar parts from Figure to Figure of the drawing.
The system of this invention, which system enables at least four separate and distinct inventive steel processes to be carried out, is indicated generally at 10 in
A scrap house is indicated generally at 11 and scrap suitable for making any desired type of steel from extra low carbon stainless to low alloy is indicated at 12. Scrap stocking means, here a rail system, is indicated at 13. The rail system will be constructed so as to be able to transfer system scrap, such as hot tops and pyramid ingots, from downstream collection points in the system and, also, fresh scrap received from outside the system. Scrap may arrive by non-rail transport such as truck. Scrap charging cars are indicated at 14, 15, each scrap car traveling on an associated set of rails 16, 17 each of which extends from the scrap house to a terminus 18, 19 adjacent an arc furnace indicated generally at 30. Scrap cars 14, 15 carry charging buckets 20, 21 respectively which receive scrap from the scrap house by any suitable means, such as a mechanized crane, not shown for purposes of clarity. Each of scrap buckets 20, 21 includes a bail 22, 23 respectively mounted on trunnions located on each side of the scrap buckets, and U-shaped lifting brackets 24, 25 respectively.
A spare charging bracket is indicated at 26 having a bail 27 and lifting bracket 28.
The arc furnace includes a bowl indicated generally at 31, best seen in
A chute system for adding charge materials such as carbon and lime to the furnace is indicated at 49. A sampling device is indicated at 50, the sampling device accessing the heat in the furnace through flapper 51. A slag off door is indicated at 52. An oxygen and carbon injection lance system is indicated at 53. When the arc furnace cover 35 is in operating position on top of the arc furnace bowl, the bottom surface of the rim 37 of the cover 35 makes contact about its entire periphery with the top surface of the rim of the bowl 31 as best seen in
The arc furnace ducting system is indicated generally at 55 in
From
The three electrodes 45, 46 and 47 are moveable by a gantry type lifting assembly 66, see
A tapping ladle car is indicated at 70 which runs on track 71 which track extends, in this instance, from just beneath the arc furnace 30 at its upstream end to a position just short of the next treatment station shown in
Although only one tapping car 70 and tapping ladle 72 are used, a second tapping car and ladle has been shown in
While a melt is being made in the arc furnace 30, a tapping ladle 72 will undergo preheating to at least about 2000° F. by a preheat lance 76. Immediately upon preheating the tapping ladle to a desired temperature, the preheat lance is turned off and removed, and a shield, indicated generally at 77 in
A slide gate for the arc furnace is indicated at 84. In
Referring now to
The LMF station includes a roof, indicated generally at 90, through which three electrodes 91, 92 and 93 project downwardly in its center region. The electrodes receive power from a power source 94 and power leads 95, 96 and 97 shown in
An alloy wire addition system is indicated generally at 108 in
From
Following extinguishment of the arcs the LMF roof and electrodes 95, 96 and 97 are raised to a position in which they clear the upper rim 117 of the LMF ladle. The LMF car 87 is then moved to its downstream terminus 123 of the LMF track 88, shown best in
Vacuum treatment station 126 includes a stationary vacuum tight tank base 127, here shown as embedded in the ground in
The vacuum tank base 127 includes a pair of ladle saddles, one of which is indicated generally at 138. Each ladle has a pair of projections indicated at 139, see
Vacuum tank cover assembly 128 carries a sight port 140, a bulk alloy and charge material dispenser 141, a wire feed assembly indicated generally at 142, and a temperature and sampling port 143. Again, although the illustrated structure indicates the flexibility of adding up to four wire alloys, aluminum will be the most often added since it will have its maximum grain refinement effect at this time in the cycle. A central port, which is covered by a vacuum tight cover plate 144 during non-vacuum decarburization cycles, is illustrated best in
The vacuum system, which functions during straight vacuum degassing and vacuum oxygen decarburization cycles, and also the gas purging system, are illustrated best in
In
The ambient atmosphere in the present invention is removed through an offtake duct 149 which is part of a multistage steam jet ejector system, preferably a four or five stage system.
It will be noted from
In vacuum oxygen decarburization cycles, including both vacuum arc remelt and non-vacuum arc remelt cycles, the vacuum treatment station is, in effect, modified to include oxygen lance blowing. Referring to
The melt is subjected to the action of a purging gas during treatment, preferably at all times the tank is sealed, though the purging gas may be interrupted if, at any time, an operator observing the boil through the sight port 140 decides the boil is momentarily too heavy. The purging gas system is indicated best in
Following vacuum treatment at the vacuum treatment station 126 as shown in
The base frame is raised and lowered by jack means, only two of which, 180, 181, are labeled. The jack means are secured to vertical posts 182, 183, 184 and 185. A rigid wheeled frame formed by the longitudinal sides 178 and 179, and cross members 186, 187 receive the ladle in the position shown at the right side of
From the foregoing it will be seen that the teeming car, and a teem ready ladle 86 carried by it, can be moved in six directions to precisely align ladle teeming nozzle 166 with the flared end 195 of pouring trumpet 199. Thus the ladle teeming nozzle 166 on the bottom of the ladle can be positioned exactly above the upper flared end 195 of the pouring trumpet as seen in
Teeming car 170 moves downstream to the teeming station, which includes a teeming pit area indicated generally in abbreviated form at 192 in
First ingot bottom pouring means includes a primary receptacle or mold, here ingot mold 196, which rests on mold stool 197. Stool 197 in turn rests on runner base 198. The central bore of pouring trumpet 199 connects with an aligned vertical hole in the mold stool 197, which hole connects to horizontal runner 202 which in turn communicates with an ingot entry hole 200 in mold stool 197 to thereby enable the interior of ingot mold 196 to be filled from the bottom up. It will be understood that the pouring trumpet 199, the mold stool 197, and the runner base 198 are formed of strong pressure resistant ceramic material, and are discarded after each use. Ingot mold 196 may have flux material placed in its bottom prior to pouring for the purpose of lubricating the mold walls to facilitate mold stripping. A removable and reinstallable hot top is indicated at 201.
A solidified vacuum degassed ingot 205 is shown in
A crane carrying a ladle with several tons of carryover steel and slag is shown poised above the mold stripping area where, after having teemed the heat into ingot mold 196, it is preparing to teem the few remaining tons of steel in the ladle into the small pyramid mold 207, and the slag into the slag dumping area 206, either by using the ladle slide gate or tipping the ladle while resting on its side on the ground using hook eye 208 of
In like manner, the still hot ingot 205 will be placed on the transfer car 209 and conveyed to a heating furnace to heat the hot ingot to deformation temperature in the forge department preparatory to going to the forge press.
Referring now to
The use and operation of the invention is as follows.
It will be assumed that a first heat of steel is to be made at the start of a campaign. (It will be understood that the word campaign is used in the sense it is generally understood in the steel industry, that is, the number of heats which can be made in an arc furnace before relining of the furnace is required.) It will also be assumed that a vacuum oxygen decarburized vacuum arc remelt product has been ordered by a customer. Further, it will be assumed that a vacuum oxygen decarburized vacuum arc remelted ingot of about 75 tons is the required end product of the melt shop portion of a full production sequence; that is, melting followed by subsequent processing which concludes in an ingot ready for the next phase of the steel making process, usually forging.
The invention will be applicable to virtually any size commercial steel making process. For purposes of description, and solely by way of example, it will be assumed that the capacity of the arc furnace will be about 75 to 115 tons. For specific descriptive purposes a heat size of on the order of about 75 tons will adequately describe the invention.
Referring first to
It will be understood that in the first charge of the arc furnace in a heat the scrap 12 will include small pieces such as flashings and bushelings so that the bottom refractories in the furnace bowl 31 will not be damaged from heavy piece such as hot tops in the dropped scrap charge. There will be a heel of molten steel in the furnace left over from the preceding heat, said heel comprising sufficient tons of hot metal to, firstly envelop the scrap charge including large pieces and, secondly, to cushion the impact of large pieces of solid scrap on the refractory bottom of the furnace. The large pieces will have been transported back to the scrap house by the scrap rail system 13, which rail system includes transfer car 209, from completed downstream steps of the process. The solid pieces will include large cut off hot tops following solidification of the ingots in both VAR and non-VAR heats and small ingots from pyramid molds 207.
After the first charge of scrap 12 from first charging bucket 21 is charged into the open bowl 31 of the furnace the scrap crane will move from its elevated
Immediately after the second charging bucket 20 is emptied into the furnace the arc furnace cover 35 will move to the arc-operative position shown by the solid lines of
As soon as the scrap from first charging bucket 21 is melted, the arcs are terminated, and then the electrodes are elevated to the clearance position shown in phantom in
Both before and after charging from second charging bucket 20 occurs, samples will be taken from sampling device 50, and also temperature. In this phase of processing, carbon and slag forming materials, particularly lime, will be added along with desired alloys depending on the values reported from samples. Further, oxygen and carbon will be added to the melt in the furnace by the carbon and oxygen injection system 53.
During all the above described operations a spare scrap charge bucket 26 will be loaded and waiting for transference to an open scrap car and thence to the furnace should the need arise.
Referring now to
Tapping ladle 72, prior to tapping, is heated by a preheat lance 76 so that the tapped metal from the furnace melt will not be unduly cooled when it contacts the tapping ladle. The increased wall temperature of the tapping ladle 72 is prolonged by a preheat shield indicated generally at 77 on the top of the ladle. The preheat shield is formed from a backing plate 78 to which a high heat resistant refractory insulation layer 79 is attached. The preheat shield 77 is raised and lowered as required by the hook 80 of a crane, hook 80 engaging shield bracket 81. The preheat shield 77 is placed over a tapping ladle 72 for the maximum of time that the tapping ladle is required to wait for tap to begin. As a consequence the tapping ladle 72 will cool only minimally during its wait time before tapping begins. In a tapped heat size of about 75 tons approximately 1½ tons of lime, and sufficient pounds of alloys to bring the alloy content up to about 60% of the final required alloy content in many heats, will be made from the alloy feed assembly 82 directly into the tapping ladle 72.
After the heat in arc furnace 30 has been tapped into tapping ladle 82, tapping ladle car 70 with the tapped melt is moved downstream to its terminus shown at the right side of
The LMF car 87 will be preheated by a preheat lance 89 shown in the upstream position of LMF car 87 in
While necessary conditioning will be taking place at the LMF upstream position of
LMF roof 90 is shown best in
Chemical additions, temperature and sampling systems are shown best in
In
In
In
Solid alloy materials in particulate form will be made by the bulk alloy chute system indicated generally at 101 in
The cover 90 has a roof water cooling system indicated at 119. A wire feed slide plate system is indicated generally at 120, the slide plate system having a flap plate 121 under the control of a flap plate control system 122 which, when opened, permits the wire feed take 113 to enter the cover 90 so that the exit end of the wire feed tube 113 can be brought close to the surface of the melt to ensure contact of the alloy wire, which may be aluminum for example, with the melt.
After alloy additions have been made to the LMF and the temperature of the melt brought to a desired level, which will, for example, be on the order of about 3000° F., the cover 90 and electrodes 91, 92 and 93 will be elevated so that LMF car 87 and ladle 86 carried by it will be moved to the downstream terminus position represented by stop 123 in
Ladle 137 is completely contained within the vacuum tank 125, as seen in
Should the steel maker wish to make a vacuum oxygen decarburized heat of steel, either VAR or non-VAR quality, the tank top 129 is modified to receive an oxygen lance 153. The lance 153 enters the tank 125 through a port which is opened when cover plate 144 is removed. The lance passes through a slide structure 154 with a tight fit so that the steam jet ejector system will be able to maintain a sub-atmospheric pressure in the system, thus presenting entry of ambient air into the tank enclosure in an amount sufficient to counteract to any appreciable degree contact of the melt with ambient atmosphere.
An auxiliary heat shield is indicated at 156 for use particularly during processing which will require vacuum oxygen decarburization. A refractory cover plate 157 having a central opening 158 will contain the vigorous bail during vacuum oxidation decarburization cycles. It will be understood that cover plate 157 will usually not be needed in heats which do not call for vacuum oxygen decarburization. It will be noted that the metal shell of the ladle will contain weep holes 155 so that any moisture in the refractory will be pulled out of the refractory by the very low vacuum. The combination of the very smooth cover and tank flanges 145, 146 and the O-ring seal 147 and the exposure of the weep holes to the very low vacuum will ensure that no significant moisture which would contain deleterious hydrogen will be present in the system, thus making possible final hydrogen gas contents of less that 2.2 ppm, and often less than 1.0 ppm so that ultra clean steel suitable for airplanes and space application will always result. This is in contrast to systems in which the vacuum station includes only a cover which is placed on the upper rim of a ladle, thus making the ladle a portion of the vacuum tank enclosure. In such systems an absolute vacuum seal cannot be guaranteed between the cover and upper rim of the ladle due to the presence, often unnoticed, of particles on these surfaces which prevent a high vacuum seal from being formed. And, in addition, the possibility of moisture containing air remaining in the refractory due to the absence of weep holes which permit such moisture to enter the refractory is always present.
Referring now to
The duration of the vacuum treatment will depend on the temperature of the metal at the start of treatment, the intensity of the boil and, during vacuum oxygen decarburization cycles, the quantity of oxygen added by lance 53 to the melt.
Following treatment at the vacuum treatment station 126 and removal of vacuum tank cover assembly 128 to the tank open position of
With the ladle 137 on the ladle positioning frame structure 171, the ladle is capable of movement in six directions in order to precisely position the ladle teeming nozzle 166 over the upper open flared end 195 of pouring trumpet 199 which projects upwardly above the level of track 190 as follows.
Teeming car 170 consists of a rigid base frame composed of two longitudinal side frames 178, 179 and two transverse cross members 186, 187. Vertical jack posts 182, 183, 184 and 185 extend upwardly from the four junctions of the longitudinal side frames 178, 179 and the transverse cross members 186 and 187.
The ladle positioning frame structure 171 consists of two longitudinal cradle base members 174, 175 and two transverse base cradle members 176, 177. The four sided ladle base so formed is moved upwardly and downwardly by jack means, two of which are indicated at 180, 181, the jack means being mounted on the vertical jack posts 182, 183, 184 and 185. Two slightly V-shaped transverse cradle members 172, 173 extend between longitudinal cradle base members 174, 175. The slightly V-shaped transverse cradle members 172, 173 are contoured to matingly receive the ladle projections 139 (not shown in
Thus, by actuation of vertical jack means 180, 181 and transverse jack means 188 and 189, together with the movement of the teeming car 170 via the wheels 191 along track 190, the ladle pouring nozzle can be moved in six directions to precisely position the nozzle 166 over the pouring trumpet 199.
The teeming pit is shown best in
Ingot mold 196 rests on mold stool 197 which in turn rests on runner base 198. The channel in pouring trumpet 199 connects with runner base entry hole 203, which in turn connects with runner 202 in runner base 198, which in turn connects with ingot entry hole 200 in the mold base 197. A hot top is indicated at 201. A suitable mold coating material may be present in the ingot mold prior to teeming for the purpose of coating the inside surface of the ingot mold.
Following teeming, the ladle 137, which may have three to five tons of hot metal and about three tons of slag, will be crane lifted to the mold stripping area 204, see
When the pigs in pyramid mold 207 solidify they will be crane lifted to transfer car 209 where they will be returned via scrap rail system 13 to the scrap house 12.
After ingot 205 has solidified in ingot mold 196, the ingot and its mold are transferred by crane to mold stripping area 204 where the mold and ingot are separated as seen best in
If the ingot in the mold stripping station 204 is intended for vacuum arc remelt treatment, it is processed as follows.
From the stripping station 204 the ingot is crane lifted as seen in
An attachment stub 210 is welded to the smooth cutoff end of the VAR electrode 211. A copper crucible 212 will be then placed into the water jacket tank portion 218 of the VAR unit. The exposed end of stub shaft 210 is clamped to the lower end of the VAR ram 213 by a conductive coupling. The VAR ram is connected to a DC power source 214. The ram slides in a vacuum tight opening in the cover 215 of the VAR unit. After the cover 215 seals via seal 216 to tank portion 218 of the VAR unit, DC current will be conducted through the ram 213 and stub shaft 210 to strike an arc 217 to the bottom of the VAR crucible 212. The DC arc will melt the end of the VAR electrode 211 and the resultant molten metal forms a pool 219 in the copper crucible 212. The molten pool 219 is rapidly solidified from the bottom up as cooling water 220 surrounding the copper crucible 218 conveys away heat from the molten pool of steel 219 in crucible 218. The melting process will continue until the VAR electrode 211 is completely consumed and a new VAR ingot has been created.
After the VAR electrode 211 had been fully melted, the DC current is terminated, the vacuum is terminated, and the cover 215 removed to expose a finished VAR ingot 223, shown partially completed in
A typical cycle time for a heat size of approximately 75 tons commencing with swinging the arc furnace cover 35 to a first charge position through completion of remelt of the recharge scrap, completion of tapping and return of the arc furnace to level position ready for swinging the furnace to a first charge position, will be about 1 hour and 45 minutes as follows.
It will be assumed that the tapping ladle has been preheated to approximately 2000° F. by preheat lance 76 prior to tapping and each charging bucket 20, 21 will be loaded with approximately 41½ tons of solid scrap.
Down stream processing of the melt from level, covered condition through crane lift from the vacuum treatment station will require less than about 1 hour and 45 minutes so there will be no possibility of back up due to slowness of downstream operations. For example, the time in the LMF will be only about 35 minutes, or less, and the time at the vacuum treatment station will be only about 30 minutes.
The cycle time may approach or even slightly exceed two hours if 90 tons are to be teemed. The cycle time will however be less than directly proportional to the size of the heat due to arc furnace electrodes of up to 16 inches diameter and 75 to 90 MVA current. It will also be understood that the composition of the steel to be produced—from low alloy to high chromium stainless—will have insignificant impact on the cycle time.
Although a preferred embodiment of the invention has been disclosed, it will be apparent that the scope of the invention is not confined to the foregoing description, but rather only to the scope of the hereafter appended claims when interpreted in light of the relevant prior art.