阅读说明：本技术 铸造金属的方法 (Method for casting metal ) 是由 F-J·沃斯特曼 C·皮尔 M·巴斯 于 2020-05-14 设计创作，主要内容包括：描述了金属或盐的铸造以及通过铸造金属或盐制成的产品。例如,铸造金属或盐的方法包括排空铸模,使用惰性气体对铸模加压并将铸模耦合到熔融金属或盐的加压源,其中,对该源的加压程度足够高以驱使熔融金属或盐响应排空进入铸模。(Casting of metals or salts and products made by casting metals or salts are described. For example, a method of casting metal or salt includes evacuating a mold, pressurizing the mold with an inert gas, and coupling the mold to a pressurized source of molten metal or salt, wherein the source is pressurized to a degree sufficiently high to drive the molten metal or salt into the mold in response to the evacuating.)

1. A method of casting a metal or salt, the method comprising:

evacuating a casting mold (115), pressurizing the casting mold with an inert gas and coupling the casting mold to a pressurized source (105) of molten metal (135) or salt, wherein the source (105) is pressurized to a degree sufficiently high to drive the molten metal (135) or salt into the casting mold in response to the evacuating.

2. The method of claim 1, wherein evacuating the casting mold (115) comprises:

coupling the casting mold to a vacuum chamber (130), for example, wherein the volume of the vacuum chamber is 10 to 100 times, or 30 to 50 times, the volume of the casting mold (115).

3. A method according to any preceding claim, wherein the source of molten metal or salt is pressurised to below 0.2MPa gauge or less, for example to about 0.1MPa gauge.

4. A method according to any preceding claim, wherein the source of molten metal or salt is pressurised using the inert gas, for example dry inert gas.

5. The method of any one of the preceding claims, wherein the molten metal or salt is one of copper, steel, aluminum, a metal alloy, a salt, or a salt mixture.

6. A method according to any preceding claim, wherein the mould is for casting a coil, for example a coil according to any of claims 13 to 24.

7. A method according to any preceding claim, wherein the mould is evacuated, for example in 0.1 seconds or less.

8. The method of any preceding claim, wherein:

prior to said evacuating, pressurizing the interior of said casting mould similar to the pressurizing of said source, said molten metal or salt being exposed to said inert gas pressurizing said casting mould.

9. The method of any preceding claim, further comprising:

increasing the pressurization of the source (105) of the molten metal (135) or salt during the emptying, after the emptying, or both.

10. The method of any preceding claim, wherein the casting mold comprises a core, a plurality of slides, or a core and a plurality of slides.

11. The method of claim 10, wherein the casting mold includes a gas permeable core, and wherein evacuating the casting mold includes evacuating at least a portion of the casting mold by pumping gas through the gas permeable core.

12. The method according to any of the preceding claims, wherein the pressurized source (105) comprises a crucible comprising resistive or inductive heating elements integrated therein or arranged along a surface thereof.

13. A coil (300) comprising:

a cast monolithic metal strip (310) covered by an insulator and layered to form a plurality of turns about an axis (307), the metal strip having a width (320) substantially perpendicular to the axis (307) and a height (315) substantially parallel to the axis (307), wherein the width is greater than the height.

14. The coil as recited in claim 13, wherein the cast monolithic metal strip (310) has a substantially rounded rectangular cross-section parallel to the axis.

15. Coil according to any one of claims 13 to 14, wherein the insulators of adjacent turns of the metal strip are in contact with each other over substantially the entire width (320) of the metal strip.

16. The coil of any of claims 13 to 15, wherein the coil exhibits physical properties of being cast in a casting process in which the pressure differential is relatively low, for example wherein the physical properties are the size of microbubbles in the coil.

17. The coil of any of claims 13 to 16, wherein the coil exhibits physical characteristics that are directly cast into a shape that is nearly suitable for use, e.g., the metal strip is free of micro-defects caused by stresses that result from molding the metal strip with a force applied perpendicular to the axis.

18. The coil of any of claims 13 to 17, wherein the metal strip comprises aluminum and the insulator comprises alumina.

19. The coil of any of claims 13 to 17, wherein the metal strip comprises copper.

20. A coil according to any one of claims 13 to 19, wherein the cast monolithic metal strip coil has a substantially trapezoidal cross-section parallel to the axis, wherein the direction of the cross-section intersects similar cross-sections of other coils of a motor or generator, the coils being arranged substantially concentrically about a centre.

21. The coil of claim 20, wherein the generally trapezoidal cross-section is formed by a single winding of the cast unitary metal strip.

22. Coil according to any one of claims 13 to 19, wherein in at least one cross section parallel to the axis, the regions of the cast monolithic metal strip have a non-uniform width, for example wherein the width of the regions gradually increases or decreases along the axis.

23. The coil of claim 22, wherein in the at least one cross-section parallel to the axis, regions of the cast monolithic metal strip have a non-uniform height, e.g., wherein the height of the regions gradually increases or decreases along the axis.

24. Coil according to any one of claims 13 to 23, wherein the coil is cast in an extended shape, forming a plurality of turns around an axis with a spacing between adjacent turns, e.g. wherein the spacing between adjacent turns is 5 to 10 times wider than the thickness of the metal strip along the axis.

Technical Field

The present invention relates to a method of casting metal and the resulting product.

Background

In the field of metal working, casting is a process of adding molten metal to a mold (also referred to as a tool or a die) having a cavity. The molten metal is then allowed to cool and solidify, and the solid casting is then removed from the mold. If the casting has a relatively complex geometry (such as with holes, undercuts and/or integrated channels), core and/or multi-slide techniques may be used. The castings can be used to make a variety of products.

Disclosure of Invention

The casting of metals and products made by casting metals is described. For example, a method of casting a metal or salt includes evacuating a mold, pressurizing the mold with an inert gas, and coupling the mold to a pressurized source of molten metal or salt, wherein the source is pressurized to a degree sufficiently high to drive the molten metal or salt into the mold in response to the evacuating.

The above and other methods may include one or more of the following features. Evacuating the mold may include coupling the mold to a vacuum chamber, for example, having a volume 30 or 50 times greater than a volume of the mold. The source of molten metal or salt may be pressurised to less than 0.2MPa gauge or less, for example to about 0.1MPa gauge. The source of molten metal or salt may be pressurized using an inert gas. The molten metal or salt is one of copper, steel, aluminum, an alloy, a salt, or a salt mixture. The mold may be used to cast coils, such as the coils in the present application. The mold may be evacuated in a time period such as 0.1 seconds or less. In some implementations, the mold is pressurized prior to evacuation similar to the source, and the molten metal or salt is exposed to an inert gas that pressurizes the mold. The mold may include a core, a plurality of slides, or a core and a plurality of slides. The casting mold may include a gas permeable core. Evacuating the mold includes evacuating at least a portion of the mold by drawing gas through the gas permeable core. The pressurized source may comprise a crucible comprising resistive or inductive heating elements integrated therein or arranged along a surface thereof.

In another example, a coil includes a cast unitary metal strip covered by an insulator and layered to form a plurality of turns about an axis, the metal strip having a width generally perpendicular to the axis and a height generally parallel to the axis, wherein the width is greater than the height.

The above and other coils may include one or more of the following features. The cast monolithic metal strip may have a substantially rounded rectangular cross-section parallel to the axis. The insulators of adjacent turns of the metal strip are in contact with each other over substantially the entire width of the metal strip. The coil may exhibit physical characteristics of being cast in a casting process where the pressure differential is relatively low, for example, the physical characteristics being the size of microbubbles in the coil. The coil may exhibit physical characteristics that are directly cast into a shape that is nearly suitable for use. For example, the metal strip may be free of micro-defects caused by stress resulting from shaping the metal strip by applying a force perpendicular to the axis. The metal strip may comprise aluminum and the insulator may comprise alumina. The metal strip may comprise copper. The cast monolithic metal wire coil may have a generally trapezoidal cross-section parallel to the axis, wherein the direction of the cross-section intersects similar cross-sections of other coils of the motor or generator, the coils being arranged generally concentrically about a center. The generally trapezoidal cross-section may be formed by a single winding of cast unitary metal strip. In at least one cross-section parallel to the axis, regions of the cast unitary metal strip may have a non-uniform width. For example, the width of the region gradually increases or decreases along the axis. The regions of the cast unitary metal strip may have a non-uniform height in at least one cross-section parallel to the axis, e.g., the height of the regions may gradually increase or decrease along the axis. The coil may be cast in an extended shape, forming a plurality of turns around the axis with spaces between adjacent turns. For example, the spacing between adjacent turns is 5 to 10 times wider than the thickness of the metal strip along the axis. In some cases, the spacing between adjacent turns may be, for example, 1 to 20 mm.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

Drawings

FIG. 1 is a schematic view of a casting system.

FIG. 2 is a schematic view of a casting system during a casting campaign.

Fig. 3 is a schematic view of a conductive coil that may be cast using a casting system such as that of fig. 1 and 2.

Figure 4 is a schematic cross-sectional view of one possible conductive coil of figure 3.

Like reference symbols in the various drawings indicate like elements.

Detailed Description

Fig. 1 is a schematic view of a casting system 100. The casting system 100 includes a crucible 105, a crucible pressure vessel 110, a casting mold 115, a feed tube 120, a pressurized inert gas source 125, and a vacuum chamber 130. The feed tube 120 extends into the crucible 105 and forms a fluid flow path adapted to pressure drive molten metal 135 from the crucible 105 into the interior 117 of the mold 115. The molten metal 135 may be, for example, aluminum, magnesium, zinc, copper, iron, or alloys thereof, including steel. The casting mold 115 may be selected based on the metal 135 to be cast, and may be, for example, a steel or sand mold. In some implementations, a ceramic mold may be used. In some implementations, a core and a slider may be used. For example, the core may be permanent or temporary. The casting system 100 may be operated to drive metal 135 from the crucible 105 through the feed tube 120 into the interior volume 117 of the mold 115 using a relatively low pressure differential.

The gas source 125 may include a relatively high pressure inert gas, such as nitrogen or a noble gas. In some implementations, the inert gas can be dried. The gas source 125 may be, for example, a pressurized gas tank or line. The gas source 125 is connected to one or both of the internal volume 117 of the mold 115 and the internal volume 112 of the crucible pressure vessel 110 by one or more lines 140, 145. One or more valves 150, 151 may be used to open and close the lines 140, 145. As discussed further below, the gas source 125, lines 140, 145, and valves 150, 151 are configured to pressurize the internal volume 117 of the mold 115 and the internal volume 112 of the crucible pressure vessel 110 at substantially the same rate.

As discussed further below, the line 145 is sized and the gas source 125 is capable of providing a flow of inert gas of sufficient volume to rapidly fill the interior volume 112 of the crucible pressure vessel 110. For example, in some implementations, the line 145 and the gas source 125 can fill the interior volume 112 of the crucible pressure vessel 110 in less than 1 second. Generally, the interior volume 112 can be filled without creating associated turbulence in the metal bath. To facilitate rapid filling, the valve 151 is typically located proximate to the interior volume 112 of the crucible pressure vessel 110. With this arrangement, the volume of the line 145 between the valve 151 and the internal volume 112 is relatively small and the rate of change of pressure in the internal volume 112 increases.

In some implementations, the interior of the crucible pressure vessel 110 can be customized to conform to the exterior of the crucible 105. For example, in some cases, the exterior of the crucible 105 may be generally cylindrical or conical, while the interior of the crucible pressure vessel 110 may define a generally cylindrical or conical volume that conforms to the exterior of the crucible 105 with a small tolerance. Such customization may reduce the size of the internal volume 112 and the speed variation under pressure.

In some implementations, resistive or inductive heating elements may be integrated into the crucible 105, integrated into the crucible pressure vessel 110, and/or disposed along the surfaces of both. Such a heating element may help to reduce the size of the internal volume 112.

The vacuum chamber 130 is connected to the interior 117 of the casting mold 115 by a line 155. Line 155 is opened and closed using one or more valves 160. The vacuum chamber 130 has a volume that is significantly greater than the volume of the interior 117 of the mold 115. For example, the volume of the vacuum chamber 130 may be 50 or more times the volume of the interior 117 of the mold 115. The valve 160 may be a snap-acting valve, such as a valve that can complete a transition from a closed state to an open state in less than 100 milliseconds.

As discussed further below, the line 155 is sized and the chamber 130 is capable of drawing a sufficient volume of inert gas flow to rapidly empty the interior 117 of the mold 115. For example, in some implementations, the line 155 and the chamber 130 can empty the interior 117 of the mold 115 within 0.1 seconds. To assist in evacuation, a valve 150 is typically disposed proximate the interior 117 of the mold 115. With this arrangement, the dead volume of line 140 between valve 150 and interior 117 is relatively small, and little or no additional air needs to be drawn through line 155. In addition, the valve 160 is generally disposed proximate to the interior 117 of the mold 115.

In implementations where the mold 115 includes a sand core or other gas permeable core, the line 155 may be connected to draw gas through the solid (gas permeable) portion of the core. This allows gas to be drawn from the entire casting volume of the casting mold 115 and avoids gas venting from the core.

In some implementations, the interior 117 of the casting mold 115 is connected to the atmosphere, such as by one or more lines 165. In the illustrated implementation, the line 165 includes a one-way valve 170 that allows only one-way flow out of the interior of the mold 115. In other implementations, when one or more valves 150, 160 are open, one or more lines 165 may be an unobstructed, valveless channel that allows for a smaller flow rate than the flow rate through lines 140, 155.

In preparation for casting, the mold 115 and crucible pressure vessel 110 are filled with an inert gas from a gas source 125, and the pressure in the mold 115 and crucible pressure vessel 110 eventually rises above atmospheric pressure. For example, the mold 115 and crucible pressure vessel 110 may be pressurized to 1MPa gauge, but typically the mold 115 and crucible pressure vessel 1102 will be pressurized to 0.2MPa gauge or less. For example, the mold 115 and crucible pressure vessel 110 may be ultimately pressurized to 0.02-0.08MPa gauge. The pressurization process ensures that reactive gases, such as atmospheric oxygen, do not remain in the mold 115 and crucible pressure vessel 110 during casting. For example, relatively pure inert gas may be flowed from the gas source 125 into the mold 115 and the crucible pressure vessel 110, while a mixture of inert gas and reactant gas exits the mold 115 and the crucible pressure vessel 110 through one or more of the escape lines 165. Depending on the respective flow rates and volumes, the reaction gases in the mold 115 and the crucible pressure vessel 110 will eventually be depleted, and the gases in the mold 115 and the crucible pressure vessel 110 will have a gas composition similar to the gas source 125.

Before, during, and/or after filling the mold 115 and crucible pressure vessel 110 with inert gas, the crucible 105 may be heated to melt the metal 135. The feed tube 120 extends into the molten metal 135 in the crucible 105. As or after the metal 135 melts, the pressure of the interior 117 of the mold 115 and the interior 112 of the crucible pressure vessel 110 may be adjusted to form a head 175 of molten metal 135 that fills the gating system of the mold 115. In the illustrated implementation, the molten metal 135 rises to a level 180 that is slightly below the portion of the casting mold 115, and the product is ultimately cast. In some implementations, the feed pipe 120 includes a heating system to control the temperature of the molten metal 135 in the feed pipe 120 (not shown).

The particular method of adjusting the pressure in the mold 115 and the crucible pressure vessel 110 may depend on the particular configuration of the casting system 100. For example, in some implementations, the pressures in the mold 115 and crucible pressure vessel 110 may inherently result from the respective flow rates through lines 140, 145, and 165. For example, the dimensions of lines 140, 145, and 165 may be selected to allow gas to escape from casting mold 115 through line 165, resulting in a mold 115 pressure that is lower than the desired pressure in crucible pressure vessel 110. Other implementations are possible including implementations with pressure sensors and active feedback control.

Generally, the casting mold 115 will be heated to a temperature suitable for good shape filling behavior and minimal fatigue wear of the mold. For example, when casting copper, the permanent mold 115 will be heated to a temperature between 100-350 ℃. In contrast, when casting aluminum, the permanent mold 115 will be heated to a temperature between 250-350 ℃.

Fig. 2 is a schematic view of the casting system 100 during a casting process. In the case of pressurizing both the mold 115 and the crucible pressure vessel 110, the valve 150 is closed and the valve 160 is opened. Since the volume of the vacuum chamber 130 is significantly greater than the volume of the interior 117 of the mold 115, the pressure in the interior 117 of the mold 115 drops very quickly to almost zero. For example, the pressure in the interior 117 of the mold 115 may drop to almost zero in 0.1 seconds. Instead, the crucible pressure vessel 110 remains pressurized and fills the mold 115 as the head 175 of the molten metal 135 rises to the level 185.

As described above, in some implementations, the pressure in the mold 115 and crucible pressure vessel 110 can be about 0.1MPa above atmospheric pressure. In cast metal, this is a relatively low pressure differential, i.e., about 2 atmospheres. In contrast, high pressure die casting may be performed at pressures up to, for example, around 120MPa, i.e., a pressure differential of about 120 atmospheres. At such high pressures, the velocity of the molten metal in the mould reaches very high velocities, such as 200 m/s.

By operating at such a relatively low pressure, the casting process is both safe and fast. In fact, relatively low pressure casting processes may not be subject to strict regulatory requirements. Furthermore, the melt never needs to be exposed to an oxidizing atmosphere, but only to an inert atmosphere and a (substantially) vacuum.

In some cases, products cast using such relatively low differential pressure processes may exhibit physical characteristics characteristic of the casting process. For example, in some cases, the likelihood of the product containing microbubbles is greatly reduced as compared to products cast using high pressure. In high pressure casting, any gas trapped in the molten metal expands significantly upon release of the high casting pressure. In contrast, in casting processes where the pressure differential is relatively low, the volumetric expansion of the gas in the molten metal is much less.

In another example, in some cases, the use of such products cast with relatively low differential pressures may reveal surface texture features of the casting process.

In some implementations, the pressure applied to the molten metal 135 may be increased during or after evacuation of the interior 117 of the mold 115. For example, in some implementations, an additional source of pressurized inert gas may be connected to the interior 112 of the crucible pressure vessel 110 through a valve/line system (not shown). Such a valve may open in response to the opening of the valve 160 to increase the pressurization of the interior 112 of the interior volume 112 of the crucible pressure vessel 110. In another example, in some implementations, the interior volume 112 of the crucible pressure vessel 110 can be pressurized by a valve 151. In either case, pressurization of the interior volume 112 in combination with evacuation of the interior 117 of the casting mold 115 may increase the filling rate and mass inertia, resulting in a thinner wall thickness of the casting.

The casting process schematically illustrated in fig. 1 and 2 may be used to cast a variety of different products, including products that are difficult to cast using other casting techniques.

Fig. 3 is a schematic view of a conductive coil 300 that may be cast using, for example, the casting system 100. The conductive coil 300 is a unitary casting that may be used, for example, in an electric motor or generator. The surface of the metal strip 310 is covered with a relatively thin insulator so that the metal strip 310 forms a coiled electrical conduction path.

The conductive coil 300 defines a gap 305 about an axis 307 and a metal strip 310 is "wound" in a series of layers 312, each forming one turn of the coil 300. Metal strip 310 has a height 315 that is less than width 320, where width 320 is substantially perpendicular to axis 307 and height 315 is substantially parallel to axis 307. As discussed in further detail below, the dimensions of metal strip 310 are generally non-uniform-whether within a single layer 312 or from one layer 312 to another layer 312. In the illustrated implementation, metal strip 310 is generally rectangular in cross-section, contacting the generally flat insulating surface of adjacent layer 312. This need not be the case. For example, in some implementations, for example, the surface of metal strip 310 may be intentionally textured, such as with adjacent layers 312 engaging each other to increase the contact area.

Although the layer 312 in the conductive coil 300 is shown in the schematic view as having a generally sharp edge 325, the gap 305 is shown as having a rectangular parallelepiped shape, typically the edges 325 and the edges of the gap 305 are at least somewhat rounded. Further, while the cross-sectional area of metal strip 310 is shown as being generally rectangular with sharp edges, this is not typically the case.

The conductive coil 300 may be cast from one or more metals, including aluminum, copper, manganese, or steel. A conductive coil cast from aluminum is lighter than a comparable sized conductive coil cast or otherwise formed from copper. The insulator may be formed from one or more layers of different materials and may include a metal oxide such as alumina or the like.

In some implementations, the conductive coil 300 may be cast directly into a shape that is nearly suitable for use in, for example, an electric motor or generator. In other implementations, the conductive coil 300 may be cast in an extended shape, forming multiple turns about the axis 307, but must be compressed in the direction of the axis 307 prior to use. For example, the spacing between adjacent turns is 5 to 10 times wider than the thickness of the metal strip along the axis. In some cases, the spacing between adjacent turns may be, for example, 1 to 20 mm.

Whether coil 300 is cast in an extended shape or in a shape that is nearly suitable for use, it is not necessary to bend, or otherwise shape, metal strip 310 by applying a force perpendicular to axis 307, for example, by winding metal strip 310 around a bobbin. The physical structure of metal strip 310 may be a characteristic of such a casting. For example, when the conductive coil 300 is directly cast into a nearly suitable shape for use, the metal strip 310 may maintain this nearly suitable shape without applying external forces. In another example, the surface of metal strip 310 may be free of micro-defects caused by such shape-related stresses formed by the application of a force perpendicular to axis 307.

Fig. 4 is a schematic cross-sectional view of one possible conductive coil 300. The cross-section, generally parallel to axis 307, is arranged to cut through the concentrically arranged coils, traversing the metal strips 310 of the coil 300 in different regions 405, 410, 415, 420, 425, 430, 435, 440.

In the illustrated implementation, the coil 300 is sized to fill a majority of the design space of the motor or generator within the illustrated cross-section with a single metal strip. In more detail, the motor or generator may comprise a plurality of concentrically arranged coils, such as mounted on a stator arranged around the rotor. As shown in fig. 4, the coils will be arranged concentrically around the center located below the coil 300. The additional coils will thus be arranged, such as below, to the left and to the right of the coil 300, and oriented such that their respective axes point to the center of the concentric arrangement. With this arrangement, less space is available for each coil towards the centre of the concentric arrangement than towards the outside of the concentric arrangement.

The motor and generator coils typically have a trapezoidal cross-section that is narrower on the side aligned towards the center of the concentric arrangement and wider on the side aligned towards the outside of the concentric arrangement. In a coil formed by winding a wire around a bobbin or other member, such a trapezoidal cross section is generally achieved by winding several times more to the outside than to the center of the concentric arrangement.

In contrast, the profile of coil 300 may be designed to have a trapezoidal cross-section with a single metal strip wound about axis 307. This profile reflects the non-uniform size of the regions 405, 410, 415, 420, 425, 430, 435, 440. For example, width 445 of region 420 is less than width 450 of region 405. The width of regions 410, 415 is between widths 445, 450. Similarly, the width of region 440 is less than the width of region 425, and regions 430, 435 have intermediate widths.

In some implementations, the height of the regions 405, 410, 415, 420, 425, 430, 435, 440 may also be non-uniform. For example, height 455 of region 425 may be less than height 470 of region 440. The regions 430, 435 may have heights 460, 465 that are between heights 455, 470. Similarly, the height of region 405 may be lower than the height of region 420, with regions 410, 415 having an intermediate height.

The different regions 405, 410, 415, 420, 425, 430, 435, 440 each have a greater proportion of height and width that can be filled in the design space of the motor or generator than can be filled using wires having a circular or other cross-section. Thus, cast conductive coils may be advantageous in many respects. For example, casting may provide relatively precise control over the size and arrangement of metal strip 310. This allows a relatively large portion of the cross-sectional area (as shown in fig. 4) to be filled with the conductive metal. By contrast, a coil formed from a wire having a circular cross-section necessarily includes relatively large voids in which no current is conducted. Thus, the maximum current density per cross-sectional area is reduced, and for example, the magnetic field strength that can be generated and the power density of the motor are also reduced.

Furthermore, since metal strip 310 is in contact with itself in adjacent layer 312 over a relatively large area, heat may be transferred relatively efficiently across coil 300. This may be beneficial, for example, in some applications where the current density is relatively high, the heat of resistive heating is directed away from the coil 300.

Various embodiments of the invention have been described herein. Nevertheless, it will be understood that various modifications may be made. For example, other products may be cast, including, for example, vehicle suspension systems, tire rims, structural components, and the like. In another example, instead of casting the molten metal 135, a salt or a mixture of salts may be cast. Casting salts may be used as cores, such as in high pressure die casting.

Accordingly, other embodiments are within the scope of the following claims. The present application further relates to the following aspects:

1. a method of casting a metal or salt, the method comprising: evacuating the casting mold, pressurizing the casting mold with an inert gas and coupling the casting mold to a pressurized source of molten metal or salt, wherein the source is pressurized to a degree sufficiently high to drive the molten metal or salt into the casting mold in response to the evacuating.

2. The method of aspect 1, wherein evacuating the mold comprises: coupling the casting mold to a vacuum chamber, for example, wherein the volume of the vacuum chamber is 10 to 100 times the volume of the casting mold.

3. The method of aspect 1, wherein the source of molten metal or salt is pressurized to less than 0.2MPa gauge or less.

4. The method of aspect 1, wherein the source of molten metal or salt is pressurized using the inert gas.

5. The method of aspect 1, wherein the mold is used to cast a coil.

6. The method of aspect 1, wherein the mold is evacuated in 0.1 seconds or less.

7. The method of aspect 1, wherein prior to the evacuating, pressurizing the interior of the casting mold is similar to pressurizing the source, the molten metal or salt being exposed to the inert gas pressurizing the casting mold.

8. The method of aspect 1, further comprising: increasing the pressurization of the source of the molten metal or salt during, after, or both during and after the emptying.

9. The method of aspect 1, wherein the mold comprises a core, a plurality of slides, or a core and a plurality of slides.

10. The method of aspect 9, wherein the casting mold includes a gas permeable core, and wherein evacuating the casting mold includes evacuating at least a portion of the casting mold via the gas permeable core pumping gas.

11. The method of aspect 1, wherein the pressurized source comprises a crucible comprising resistive or inductive heating elements integrated therein or disposed along a surface thereof.

12. A coil, comprising: casting a unitary metal strip covered by an insulator and layered to form a plurality of turns about an axis, the metal strip having a width generally perpendicular to the axis and a height generally parallel to the axis, wherein the width is greater than the height.

13. The coil of aspect 12, wherein the cast monolithic metal strip has a substantially rounded rectangular cross-section parallel to the axis.

14. The coil of aspect 12, wherein the insulators of adjacent turns of the metal strip contact each other substantially across the width of the metal strip.

15. The coil of aspect 12, wherein the coil exhibits physical properties cast in a relatively low differential pressure casting process.

16. The coil of aspect 15, wherein the physical characteristic is a size of a microbubble in the coil.

17. The coil of aspect 12, wherein the coil exhibits physical characteristics that are directly cast into a shape that is nearly suitable for use, e.g., the metal strip is free of micro-defects caused by stresses that result from molding the metal strip with a force applied perpendicular to the axis.

18. The coil of aspect 12, wherein the metal strip comprises aluminum and the insulator comprises alumina.

19. The coil of aspect 12, wherein the cast monolithic metal bar coil has a generally trapezoidal cross-section parallel to the axis, wherein the direction of the cross-section intersects similar cross-sections of other coils of a motor or generator, the coils being arranged generally concentrically about a center.

20. The coil of aspect 20, wherein the substantially trapezoidal cross-section is formed by a single winding of the cast unitary metal strip.

21. The coil of aspect 12, wherein in at least one cross-section parallel to the axis, the regions of the cast monolithic metal strip have a non-uniform width.

22. The coil of aspect 21, wherein the width of the region gradually increases or decreases along the axis.

23. The coil of aspect 21, wherein, in the at least one cross-section parallel to the axis, regions of the cast monolithic metal strip have a non-uniform height, e.g., wherein the height of the regions gradually increases or decreases along the axis.

24. The coil of aspect 12, wherein the coil is cast in an extended shape, forming a plurality of turns about an axis with a spacing between adjacent turns, e.g., wherein the spacing between adjacent turns is 5 to 10 times wider than the thickness of the metal strip along the axis.