Abstract:
A cost-effective process for providing a copper-based alloy casting, which has superior wear characteristics, to a cylinder block is described. The process includes heating the copper-based alloy to a molten state for immersing the cylinder block within such, while promoting the entrained gas within the copper-based alloy to migrate in a given direction and terminate in a specified portion of the copper-based alloy to effectively control porosity. In one form, the process further includes cooling the immersed cylinder block in the given direction to effectively reduce microshrinkage of the copper-based alloy.

Description:
This application is a continuation-in-part of application Ser. No. 08/752,362 filed Nov. 19, 1996 now U.S. Pat. No. 5,943,942 entitled “Copper-Based Alloy Casting Process” and naming William T. Dill and William L. Wentland as inventors, the entire disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to hydraulic pumps and motors, and more particularly to processes for providing copper-based alloy castings to cylinder blocks within such pumps and motors. 
     BACKGROUND OF THE INVENTION 
     Axial piston pumps and motors as used in the aerospace industry operate under harsh environmental conditions and often are subject to significant stress concentration levels. That stress arises because pistons reciprocate at high velocities and simultaneously rotate in relation to piston bores formed within a cylinder block. In certain applications, such as an aircraft integrated drive generator (IDG), the relationship of each piston to its respective piston bore within the cylinder block is preferably controlled within a tight diametral clearance range, such as 0.0001″ to 0.0004″. In such an arrangement to produce 400 Hz electric power, for example, oil is pumped into and/or out of the piston bores at up to approximately 6000 psi. 
     Each cylinder block of an IDG typically contains nine pistons; and each IDG typically contains four cylinder blocks per aircraft engine. Thus, to increase service reliability of the aircraft and reduce periodic maintenance, minimal wear of the pistons on associated cylinder block bores is desirable. In order to protect the piston bores from the harsh, aircraft operating environments, a bushing may be inserted into each of the piston bores to reduce sliding friction and wear caused by piston movement. An example of a preferable piston embodiment for movement within a cylinder block is disclosed in U.S. Pat. No. 3,319,575 to Havens. 
     One previous method of manufacturing the cylinder block with bushings includes diffusion bonding each of the nine bushings to a respective piston bore surface. This process requires separate machining of each of the piston bores within a tightly controlled tolerance measurement to match outer diametral bushing dimensions. In addition, separate manufacture of each of the nine bushings within correspondingly tight inner and outer diametral dimensions is required. Such a process further requires interference fitting each of the bushings into the piston bores, before applying pressure to diffusion bond the material of the bushing, usually bronze, and the material of the cylinder block which defines the surface of the piston bore, usually steel, together. 
     In addition, each cylinder block may include a valve plate, sometimes referred to in the art as a “port plate”, which is secured to an end of the cylinder block. The valve plate rotates with the cylinder block in operation to regulate the amount of propulsive oil entering and exiting each piston bore. Such a plate is preferably constructed from the same wear resistant material as the bushings. The aforementioned diffusion bonding process has also been utilized to secure the valve plate to the end of the cylinder block. However, this requires an additional piece of hardware to be manufactured and separately bonded to the cylinder block. 
     Thus, the prior diffusion bonding process poses significant manufacturing obstacles, as each machining operation and processing step requires additional labor and production cost; and the tightly toleranced dimensions often result in an increased amount of scrap material. These obstacles address the downfalls associated with the construction process. However, more serious performance-driven problems can be encountered by using a diffusion bond to secure the bronze bushings and the valve plate to the cylinder block. During a diffusion bonding process, the bronze material of the bushings and the valve plate never reach a molten state. Because of this, gas and other impurities can become entrapped within the bronze material. Once the pressure applied during the process is relieved, the bushing may be left with significant amounts of porosity. In addition, diffusion bonding can result in microshrinkage, as volumetric changes in the bronze material occur during cooling. Microshrinkage results in microscopic voids near the surface of the bushing and the valve plate surfaces. These entrapped gases and voids in the bushing surfaces create stress risers. Since bronze material which has been diffusion bonded tends to be soft (i.e. 18-45 HR B ), the voids and/or entrapped gases greatly decrease the bushings&#39; ability to reduce friction and wear caused by piston movement. Thus, the piston in operation creates a wear path in the bushing. The extra clearance in the piston bore caused by this piston wear can trigger fluid leakage in the cylinder block and piston assembly. Excess leakage can result in low charge pressure, and electrical performance frequency ratings of the IDG from being reached. Eventually, the wear can cause the hydraulic unit to completely malfunction. 
     Accordingly, objects of the present invention include providing an improved process of forming a copper-based alloy casting substantially free of voids or entrained gas on a cylinder block, and providing an advanced cylinder block design, which has advantageous wear reduction characteristics. Other objects of the invention include the following: 
     (i) to provide a cost-effective method for manufacturing a cylinder block with a copper-based alloy casting; 
     (ii) to eliminate separate construction operations for each bushing and the valve plate; 
     (iii) to eliminate separate assembly operations for each bushing within the cylinder block; 
     (iv) to eliminate separate assembly of the valve plate to the cylinder block; 
     (v) to create a copper-based alloy casting with superior wear characteristics including ductility, strength, hardness, and cavitation resistance; 
     (vi) to effectively reduce microshrinkage of the bushing and valve plate surfaces during processing; 
     (vii) to effectively control porosity to a specified location of the copper-based alloy during the manufacturing process; 
     (viii) to effectively isolate impurities of the casting material to a specified location of the copper-based alloy during the manufacturing process; 
     (ix) to increase service reliability of the cylinder block; and 
     (x) to provide a plurality of wear-resistant annular members which are functionally equivalent to the bushings and valve plate, but integrally cast as part of the cylinder block. 
     SUMMARY OF THE INVENTION 
     In one form, this invention relates to a method of providing a copper-based alloy casting, which is substantially free of voids or entrained gas, to a cylinder block by controlling the direction and conditions under which the cylinder block is immersed and cooled. Each cylinder block includes a first end, a second end opposite to the first end, and at least one piston bore extending through the cylinder block. 
     In one form, the inventive process includes an initial step of providing a negative pressure around the cylinder block and a copper-based alloy. The negative pressure creates a vacuum which promotes entrained gas contained within the copper-based alloy to migrate in a given direction as the copper-based alloy is heated. The process further includes a step of heating the copper-based alloy to a molten state. The heating step causes the cylinder block to immerse in the molten copper-based alloy in a gravitational direction. The heating further promotes the entrained gas to migrate in the given direction which is opposite to the gravitational direction. The migration of entrained gas terminates in an extreme portion of the copper-based alloy which is adjacent to the second end of the cylinder block. 
     Preferably, the process includes a step of cooling the copper-based alloy and the immersed cylinder block in the given direction beginning from the first end of the cylinder block. The cooling step further promotes the entrained gas contained within the copper-based alloy to migrate to the extreme portion which is adjacent to the second end of the cylinder block. Additionally, the method preferably includes a step of providing a weighted thermally insulative housing which promotes the cylinder block to immerse in the molten copper-based alloy. The weighted housing further acts to insulate the second end of the cylinder block and promote cooling of the copper-based alloy from the first end of the cylinder block. In one aspect of the invention, it is preferred that the weighted housing include carbon material that will react with oxygen to reduce oxidizing of the cylinder block. 
     In one aspect of the invention, to create production hardware, the method includes removing the extreme portion of the cooled copper-based alloy. This extreme portion contains the voids and entrained gas located adjacent to the second end of the cylinder block. Finally, a copper-based alloy annulus may be formed within the piston bore by removing a portion of the cooled copper-based alloy from the piston bore. 
     The invention further contemplates a cylinder block which includes a copper-based alloy casting formed by the aforementioned process. The cylinder block production process may include the preferable steps of cooling the copper-based alloy and immersed cylinder block in the given direction; providing a weighted thermally insulative housing; removing the extreme portion of the cooled copper-based alloy; and forming a copper-based annulus within the piston bore. 
     The invention further contemplates an advanced design of a cylinder block which has advantageous wear characteristics. The cylinder block includes a housing having a substantially cylindrical bore extending therethrough. The substantially cylindrical bore terminates at an end of the housing, which defines a bearing surface. The cylinder block further includes a substantially voidless annular member which is cast from a copper-based alloy and integrally coupled to the housing within the bore. 
     Preferably, the cylinder block also includes a substantially voidless annular plate member which is cast from the copper-based alloy and integrally coupled to the bearing surface of the housing. The annular member may integrally include the annular plate member as a projection which extends radially outwardly from an extreme portion of the annular member adjacent to the end of the housing. Preferably, the substantially voidless annular copper-based alloy member is moltenly bonded to the housing within the bore. 
     As another aspect of the invention, a method provides a copper based alloy casting in a cylinder block having a first end, a second end opposite the first end, and at least one cavity. The method includes the steps of placing the first end of the cylinder block adjacent a mass of copper-based alloy, heating the mass of copper-based alloy to a molten state where at least the first end of the cylinder block is immersed into the mass of copper-based alloy by a force applied to the cylinder block in the mass of copper-based alloy. 
     According to a further aspect of the invention, the heating step includes induction heating the mass of copper-based alloy to a molten state where at least the first end of the cylinder block is immersed into the mass of copper-based alloy by said force. 
     According to another aspect of the invention, a method provides a cast copper-based alloy bushing in a bore of a machine component. The method includes the steps of placing the machine component adjacent a mass of copper-based alloy, heating the mass of copper-based alloy to a molten state where a force applied to the machine component and the mass of copper-based alloy immerses at least a portion of the machine component into the mass of copper-based alloy with at least some of the copper-based alloy flowing into at least a portion of the bore; cooling the mass of copper-based alloy and the machine component to solidify the mass of copper-based alloy; and removing a portion of the copper-based alloy in said bore to form a cast copper-based alloy bushing in said bore. 
     In accordance with one aspect of the invention, the heating step includes induction heating the mass of copper-based alloy to a molten state where the force immerses at least a portion of the machine component into the mass of copper-based alloy with at least some of the copper-based alloy flowing into at least a portion of the bore. 
     Other objects, aspects, and advantages of the invention will become readily apparent upon consideration of the following drawings and detailed descriptions of preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For drawing FIGS. 2-4 and  6 - 7  included herewith, gravitational force acts in a generally downward direction, as specifically illustrated by vector  100 , when each figure is viewed with the reference numerals in their normally upright position. In all figures, like reference numerals indicate like elements or features. 
     FIG. 1 is a flow diagram for a casting process according to the present invention; 
     FIG. 2 is a schematic cross-sectional view of a cylinder block during an initial stage of the casting process; 
     FIG. 3 is a schematic cross-sectional view of a cylinder block during the casting process, in which the cylinder block is partially immersed in the molten copper-based alloy; 
     FIG. 4 is a schematic cross-sectional view of a cylinder during a further embodiment of the casting process, in which the immersed cylindrical block is cooled in a given direction; 
     FIG. 5 is a schematic cross-sectional view of a preferred embodiment of a cylinder block according to the present invention; 
     FIG. 6 is a schematic cross-sectional view of a cylinder block during an initial stage of an alternate embodiment of the casting process according to the invention; and 
     FIG. 7 is a schematic cross-section view of a cylinder block during the casting process of FIG. 6 in which the cylinder block is completely immersed in molten copper-based alloy. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a flow diagram for an exemplary embodiment of a process, generally depicted  10 , for providing a copper-based alloy casting which is substantially free of voids and/or entrained gas to a machine component, such as a cylinder block  14 . FIGS. 2-4, when viewed in conjunction with FIG. 1, depict various stages of the casting process  10 . 
     As shown in FIG. 2, a sealed assembly  16  includes the cylinder block  14  which has a first end  18  defined by an end surface  20 , and a second end  22  defined by a bearing surface  24 . Bearing surface  24  is opposite to the end surface  20  of the first end  18 . While the external shape of the block  14  need not be cylindrical in shape, it is typically referred to in the art as a “cylinder”. The cylinder block  14  includes a spline  26  which can engage a respective splined portion on a shaft (not shown). When the spline  26  of the cylinder block  14  is engaged with the shaft, the block  14  can rotate for use in a conventional hydraulic pump or motor. Preferably, the cylinder block  14  of an aircraft integrated drive generator (IDG) is constructed from ASTM A681, CL A6 electroslag remelted (ESR), spheroidized annealed steel. 
     The cylinder block  14  includes a plurality of axially disposed piston bores  28 . The piston bores  28  are typically arranged in an annular array about an axis of rotation  27  (FIG. 5) concentric with the shaft. Preferably, an aircraft IDG unit contains nine piston bores  28 ; although only two such bores are illustrated in the cross-section of FIG.  2 . Each of the piston bores  28  communicates with a corresponding piston bore passage  30  formed in the bearing surface  24  of the second end  22  of the cylinder block  14 . The piston bores  28  extend from the piston bore passages  30  of the second end  22  to the first end  18  of the cylinder block  14 . Preferably, each piston bore  28  is substantially cylindrical in nature and defines a piston bore surface  34 . To suitably prepare the piston bores  28  for treatment by the inventive process, each can be machined with rough diametral tolerances of ±0.001″. 
     The sealed assembly  16  further includes a freeze or expansion plug  36  which protects the integrity of the spline  26  during the casting process. Preferably, the freeze plug  36  is constructed of 300 series stainless steel. While FIG. 2 depicts a plug which caps the first end  18  on an outer diameter of the cylinder block  14 , FIG. 4 illustrates an alternative embodiment of the plug  36  which is interference fit within an inner diameter of the cylinder block  14  at the first end  18 . In the FIG. 4 plug embodiment, the inner diameter should preferably have a 64 maximum surface finish to obtain an adequate interference fit for preventing leakage and contamination of the spline  26  during the casting process  10 . 
     A generally cylindrical container  38  is provided to hold a copper-based alloy  40 , such as bronze. Preferably, the copper-based alloy  40  is constructed from cylindrical bar stock in accordance with ASTM B505, UNS. No. C93700, except the phosphorus content should be 0.05% maximum by weight. The copper-based alloy  40  can be slip fit into the container  38  in preparation for the casting process  10 . 
     As depicted in FIG. 2, a generally cylindrical cover or housing  42  is provided over the cylinder block  14  via step  59 . Preferably, the housing  42  is constructed from a thermally insulative material such as carbon. An example of a suitable material which may be utilized to form the housing is known and sold in the industry under the trademark Purebon® P-4107 and manufactured by Pure Carbon Company, Inc. A further example of a carbon housing material which may be utilized is sold under the tradename “UCAR” Grade CVN by Union Carbide Corporation. 
     As shown in FIG. 2, the thermally insulative housing  42  includes an annulus portion  44  of which an inner diameter is substantially the same dimension as an outer diameter of the container  38 . This sizing arrangement allows the annulus portion  44  of the housing  42  to translate along a length of the container  38  in the gravitational direction, as shown by the vector  100 , while substantially sealing and insulating the sealed assembly  16  and the copper-based alloy  40  within the container  38 . Additionally, the graphite material of the housing  42  tends to more readily attract oxygen than the steel surfaces of the cylinder block  14 , thereby reducing oxidation on the surface of the cylinder block  14 . 
     The insulative housing  42  is connected to a threaded bolt  46  which extends coaxially in relation with the housing  42  and substantially concentric with respect to the annulus portion  44 . Preferably, the threaded bolt  46  is secured to an additional freeze plug  48  which protects the spline  26  from the second end  22  of the cylinder block  14 . The plug  48  can be constructed and inserted in a similar fashion to that of plug  36 . An alternate embodiment contemplated by the inventive process  10  includes utilizing a push rod and weight (not shown) or other rigid member which provides axial displacement between the insulative housing  42  and the second end  22  of the cylinder block  14 . 
     In preparation for the cylinder block  14  to be cast by the inventive process  10 , preliminary steps can be undertaken to further ensure a desirably processed block. First, the cylinder block  14  can be demagnetized to remove any steel dust which is partially magnetized to the block  14  because of machining. Next, the sealed assembly  16  and the copper-based alloy  40  can be degreased in a degreasing solvent to remove excess oil and grease which accumulates during handling of the steel and bronze materials. Additionally, the sealed assembly  16  can be rinsed in a suitable isopropyl alcohol solution or acetone, and force air dried to remove any remaining impurities. 
     As shown in FIGS. 1 and 2, the casting process  10  begins with an initial step  12  of providing a negative pressure around the cylinder block  14  and the copper-based alloy  40  via a vacuum furnace  50 . The vacuum furnace  50  preferably should be of a type which can control cooling direction from the first end  18  of the cylinder block  14 , when the cylinder block  14  is positioned in the vacuum furnace  50  with the thermally insulative housing  42  above the sealed assembly  16 . By positioning the cylinder block  14  in this manner surrounded by a negative pressure, this arrangement promotes any entrained or entrapped gas within the copper-based alloy  40  to migrate upward in a given direction, generally depicted by vector  102 , as the sealed assembly  16  is immersed within the copper-based alloy  40 . As appreciated in FIGS. 2 and 3, the given direction of vector  102  is substantially opposite in direction to the gravitational direction, depicted by vector  100 . 
     The furnace  50  can be preheated to 950° F.±50° F. until the complete load within the furnace  50 , including the sealed assembly  16 , the thermally insulative housing  42  and the copper-based alloy  40 , reaches the preheat temperature. Preferably, if this preheating step is employed, the vacuum level of the furnace  50  should be held between 10-1,000 microns, once the furnace temperature reaches 600° F. Preheating is advantageous to the casting process  10  because it allows the cylinder block  14  to approach the casting temperature in a graduated manner, rather than by shocking a room temperature steel block with extremely hot bronze material. An alternative preheat to that described above, includes convection heating at one atmosphere of N 2  to a preheat temperature of 1200° F. 
     As illustrated in FIG. 1, the casting process  10  continues with a step  52  of heating the copper-based alloy  40  to a molten state along with the sealed assembly  16 . Preferably, step  52  includes heating to a temperature above 1000° F. and backfilling the furnace  50  with N 2  to a partial vacuum of 10-380 Torr, while increasing the temperature to 1850° F.±25° F. Referring to FIG. 3, as the copper-based alloy  40  reaches a molten state, the weight of the carbon cover  42  promotes the cylinder block  14  to move in the gravitational direction of vector  100  and immerse in the molten copper-based alloy  40 . 
     As the first end  18  of the cylinder block  14  immerses to the bottom of the container  38 , as illustrated in FIG. 4, it is preferable to hold the sealed assembly  16  at a temperature of 1850° F.±25° F. for a period of 30-60 minutes. This time frame allows the molten bronze and steel materials to react sufficiently to form a molten bond. However, at temperatures above this preferable range, adverse metallurgical conditions can result with the steel. The extended period additionally promotes any entrained gas and impurities of the bronze stock to migrate through the piston bores  28  and the piston bore passages  30  in the given direction of vector  102 . As the entrapped gas migrates through the piston bores  28  in the given direction, it moves to an extreme portion  54  of the copper-based alloy  40 . This extreme portion  54 , as shown in FIG. 4 is adjacent to the second end  22  of the cylinder block  14 . Thus, one can appreciate in light of this description, this “bottom casting” arrangement enables control of the direction of immersion of the cylinder block  14  in conjunction with the direction of movement of entrained gas. 
     After the heating step  52 , the process  10  includes a step  56  of cooling the immersed assembly  16  by inert gas beginning from the first end  18  of the cylinder block  14 . Cooling occurs in the given direction as illustrated by vectors  104  in FIG.  4 . Preferably, step  56  is accomplished by quenching the first end  18  with N 2  gas to cool the sealed assembly  16  and migrated copper-based alloy  40  to less than 150° F. 
     As the copper-based alloy  40  is cooled from the first end  18 , entrained gas within the bronze is further promoted to migrate to the extreme portion  54 . This “bottom cooling” effect is enhanced because the carbon housing  42  is thermally insulative of the second end  22  of the copper-based alloy  14 . In such an arrangement, the copper-based alloy  40  does not instantaneously cool from liquid to solid, but rather gradually cools and changes state beginning from the first end  18 . 
     During this liquid to solid change of state, the copper-based alloy  40  volumetrically decreases. Since the housing  42  is insulating the second end  22  of the cylinder block  14  as the first end  18  cools, molten bronze from the second end  22  flows down in the gravitational direction  100  to make up any difference in volume. As the copper-based alloy  40  flows downward, the extreme portion  54  is left with voids where the bronze unevenly flows. Thus, the resulting microshrinkage, generally depicted by  58 , is controlled and isolated in the extreme portion  54  of the hardened copper-based alloy  40  adjacent to the second end  22  of the cylinder block  14 . 
     Once 150° F. is reached, the hardened assembly  16  can be removed from the vacuum furnace  50  and allowed to cool to room temperature. Next, the insulative cover  42  can be removed from the hardened assembly  16  by detaching the housing  42  from the threaded bolt  46 . This allows the carbon cover  42  to be reused while utilizing a fairly inexpensive bolt as a consumable item. The assembly  16  can then be set into a deep freeze at −110° F.±10° F. for at least one hour before warming to room temperature. This freezing step improves the steel properties of the cylinder block  14  after having been subjected to the casting process  10 . Preferably, the resulting steel hardness of the cylinder block  14  should be between 50-55 HR B . 
     In order to create a finished cylinder block  14  as illustrated in FIG. 5, the process  10  can include a machining step  60 . Step  60  includes removing the extreme portion  54  of the cooled copper-based alloy  40  which contains the entrained gas and microshrinkage  58 . By removing this extreme portion  54  adjacent to the second end  22 , an annular plate member  32  cast from the copper-based alloy  40  is created as being integrally coupled to the bearing surface  24  of the cylinder block  14 . This annular plate member  32  is typically referred to as a valve or port plate. The valve plate  32  may be further machined to include a plurality of fluid inlet and outlet passages  62 . The fluid passages  62  serially communicate with each piston bore passage  30  during operation of the cylinder block  14 . The fluid passages  62  allow oil to flow through the piston bore passage  30  and into the piston bore  28  as the cylinder block  14  rotates to provide hydraulic power and lubrication of the piston bore surface  34 . 
     Each piston bore surface  34  may be formed in a step  64  of the process  10  by removing a portion of the cooled copper-based alloy  40  from the piston bore  28 . This processing step  64  creates an annular member  66  which is preferably cast from bronze, substantially free of voids, and integrally coupled to the cylinder block  14  within the piston bore  28 . Such an arrangement provides a molten bond between the bronze and steel materials which has superior wear characteristics of hardness, ductility, strength and cavitation resistance. 
     FIGS. 6-7 illustrate another exemplary embodiment of the process  10 . This embodiment is similar to the embodiment described in connection with FIGS. 1-5, but uses induction heating to heat the copper-based alloy, rather than using the vacuum furnace  50 . 
     More specifically, the preparation and arrangement of the sealed assembly  16 , the cylindrical container  38 , the insulative housing  42 , the threaded bolt  46 , and the freeze plug  48  are the same as for the embodiment described in connection with FIGS. 1-5. Rather than using the vacuum furnace  50 , one or more induction coils  70  surround the container  38  in the areas adjacent the mass of copper-based alloy  40 . Preferably, an upper induction coil  70 A and a lower induction coil  70 B are provided and can be individually controlled to provide differential heating of the corresponding upper and lower portions of the mass of copper-based alloy  40 . It should be noted that the annulus portion  44  of the insulative housing  42  has been reduced in length to allow clearance for the coil(s)  70 . However, the annulus portion  44  still extends and translates along the length of the container  38  while substantially sealing and insulating the seal assembly  16  in the copper-based alloy  40  within the container  38 . 
     After the components  16 ,  38 ,  42 ,  46  and  48  are arranged as shown in FIG. 6, the induction coil(s)  70  are used to heat the copper-based alloy  40  to a temperature of 1850° F.±50° F., which should be a molten state for the copper-based alloy  40 . As the copper-based alloy  40  reaches the molten state, gravitational force acting via the weight of the carbon cover  42  and the sealed assembly  16  immerses the cylinder block  14  into the copper-based alloy  40 . During heating, the graphite material of the housing  42  tends to more readily attract oxygen than the steel surfaces of the cylinder block  14 , thereby reducing oxidation on the surfaces of the cylinder block  14  even though no vacuum has been applied around the cylinder block  14 . 
     Optionally, if two induction coils  70 A and  70 B are provided, the heating of the copper-based alloy  40  can be controlled so that the cooper-based alloy heats generally from top to bottom. More specifically, the upper induction coil  70 A can be controlled to induce eddy currents in the upper portion of the mass of copper-based alloy  40  before the lower coil  70 B induces eddy currents in the lower portion of the mass of copper based alloy  40 . In connection with this time sequenced control of the coils  70 A and  70 B, or as an alternative thereto, the upper induction coil  70 A can be controlled to induce eddy currents at a first intensity in the upper portion of the mass of copper-based alloy  40  and the lower induction coil  70 B can be controlled to induce eddy currents at a second intensity in the lower portion of the mass of copper-based alloy  40 , with the first intensity being greater than the second intensity to ensure that the heating occurs in the desired direction. 
     Optionally, the casting process may begin by using the induction coil(s)  70  to pre-heat the mass of copper-based alloy  40  and the sealed assembly  16  to 950° F.±50° F. prior to heating to the copper-based alloy  40  to 1850° F.±50° F. 
     As illustrated in FIG. 7, after the first end  18  of the cylinder block  14  immerses to the bottom of the container  38 , it is preferable to hold the sealed assembly  16  and the copper-based alloy  40  at a temperature of 1850° F.±50° F. for a period of 30 seconds to 5 minutes. This time frame allows the copper-based alloy  40  and the steel materials of the cylinder block  14  to react sufficiently to form a molten bond. Additionally, even though a vacuum has not been applied, it is believed that this time frame and/or the directionality of heating will allow a significant amount of any entrained gas and impurities in the copper-based alloy to migrate through the piston bores  28  and the piston bore passage  30  in the direction of vector  102 . Thus, as with the embodiment described in connection with FIGS. 1 and 5, this “bottom casting” arrangement enables control of the direction of immersion of the cylinder block  14  in conjunction with the direction of movement of entrained gas. 
     After the heating described above, the mass of copper-based alloy  40  and the sealed assembly  16  are cooled. Preferably, the cooling is controlled so that the copper-based alloy  40  and the sealed assembly cool in a direction  102 . This can be accomplished by quenching the container  38  adjacent the first end  18  with N 2  gas, as illustrated by vectors  104  in FIG. 4, to cool the sealed assembly  16  and copper based alloy  40  to less than 150° F. Either with or without the quenching, if two induction coils are provided, the induction coil  70 A can be used to induce eddy currents in the upper portion of the mass of copper-based alloy  40  to further ensure that the cooling occurs in the desired direction  102 . As another option, again either with or without the quenching, the induction coil  70 A can be controlled to induce eddy currents at a first intensity in the upper portion of the mass of copper-based alloy  40  and the induction coil  70 B can be controlled to induce eddy currents at a second intensity in the lower portion of the mass of copper-based alloy  40 , with the first intensity being greater than the second intensity to ensure that the cooling occurs in the desired direction. 
     As with the embodiment described in connection with FIGS. 1-5, the above-described cooling of the copper-based alloy  40  from adjacent the first end  18  of the cylinder block  14  further promotes migration of entrained gas within the alloy  40  to the extreme portion  54 . This “bottom cooling” effect is enhanced because of the carbon housing  42  thermally insulates the second end  22  of the copper-based alloy  14 . In such an arrangement, the copper-based alloy  40  does not instantaneously cool from liquid to solid, but rather gradually cools and changes state beginning from adjacent the first end  18  and ending at the extreme portion  54 . 
     After the copper-based alloy  40  and the sealed assembly  16  have been cooled to below 150°, the copper-based alloy  40  and the sealed assembly  16  are preferably allowed to air cool to room temperature. The remainder of the induction heating embodiment preferably is performed exactly the same as for the vacuum furnace embodiment described in connection with FIGS. 1-5. Accordingly, this embodiment of the process produces a finished cylinder block  14  as illustrated in FIG.  5 . 
     Thus it can be seen that the induction heating embodiment described in connection with FIGS. 6 and 7 differs from the vacuum furnace embodiment only in that the heating is accomplished with the induction coil(s)  70 , rather than the vacuum furnace  50 , and the cooling of the copper-based alloy  40  and the cylinder block  14  can be controlled using the induction coils  70 A and  70 B, with or without quenching. 
     Numerous modifications in the alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. For example, the copper-based alloy annular member  66  may integrally include the annular plate member  32  as a projection extending radially outward from a portion of the annular member  66  which is adjacent to the bearing surface  24  of the cylinder block  14 . 
     Accordingly, this description is to be construed as illustrative only and is for the purpose of enabling those skilled in the art to make and use the invention and teaching the best mode of carrying out the invention. The exclusive rights of all modifications which fall within the scope of the appended claims is reserved.