US3847204A

US3847204A - Method of casting aluminum cylinder

Info

Publication number: US3847204A
Application number: US00020202A
Authority: US
Inventors: R Frederickson
Original assignee: Mcculloch Corp
Current assignee: Mcculloch Corp
Priority date: 1970-03-17
Filing date: 1970-03-17
Publication date: 1974-11-12
Anticipated expiration: 1991-11-12
Also published as: CA955031A

Abstract

A method and an apparatus are provided for forming an article of manufacture comprising a die-cast hollow piece. A core member, consisting of substantially the same composition as that comprising the hollow piece, is at least partially coated with an anti-adhering layer. The core member is located within a mold having a cavity for receiving the molten die casting material and for forming the outer surface of the hollow piece. The molten material is introduced into the cavity and cooled until solidification, at which time, the mold is removed from around the hollow piece. A major portion of the core member is machined out from the cast piece and the coated portions of the core remaining within the piece are knocked out from therein by mechanical impaction.

Description

United States Patent 1 Frederickson 1 1 Nov. 12, 1974 l l METHOD OF CASTING ALUMINUM 22 Filed: Mar. 17, 1970 1211 Appl. No.: 20,202

[52] U.S. Cl. 164/132, 164/345 [51] Int. Cl 822d 29/00 [58] Field of Search 164/72, 75, 131, 132, 267,

3,401,735 9/1968 Pursall 164/1311 X Primary Examiner-Andrew R. Juhasz Assistant Examiner-John S. Brown Attorney, Agent, or FirmBurns, Doane. Swcckcr & Mathis [57] ABSTRACT A method and an apparatus are provided for forming an article of manufacture comprising a die-cast hollow piece. A core member. consisting of substantially the same composition that comprising the hollow piece. is at least partially coated with an anti-adhering layer. The core member is located within a mold having a cavity for receiving the molten die casting material and for forming the outer surface of the hollow piece. The molten material is introduced into the cavity and cooled until solidification. at which time, the mold is removed from around the hollow piece. A major portion of the core member is machined out from the cast piece and the coated portions of the core remaining within the piece are knocked out from therein by me chanical impaction.

14 Claims, 9 Drawing Figures PATENTEDHUV 12 1974 SHEEI 10F 2 INVENTOR ROBERT EUGENE FREDERICKSON 1 METHOD OF CASTING ALUMINUM CYLINDER BACKGROUND OF THE INVENTION This invention relates to the casting of hollow pieces by the use of what are usually characterized as permanent molds and which are hereinafter referred to merely as molds". More specifically, the invention is directed to an improved method and apparatus for die casting articles of manufacture having irregular hollow cavities and holes formed therein.

Manufacturers are currently faced with the problem of providing machinery, such as pumps and internal combustion engines, having higher requirements than have heretofore been called for with respect to cost, weight and tolerance criticality.

Pump bodies and internal combustion engine blocks are presently being manufactured by various die casting processes. A common method for casting lightweight internal combustion engine cylinders is to cast an aluminum body around an iron liner having various ports and blisters formed therein. Upon cooling, the aluminum cylinder having the iron liner cast therein, is machined to provide inlet and exhaust ports which extend entirely through the walls of the cylinder. This machining may be extensive and must be precise so as to constitute a time-consuming and expensive step in the cylinder forming process.

The iron liner about which the cylinder body is cast often has different heat expansion and heat transfer characteristics than the surrounding aluminum. As the result of these property differences, the iron liner and the surrounding body do not expand evenly when operationally incorporated in an internal combustion engine application. This uneven expansion causes distortion of the cylinder at elevated temperatures which distortion, in turn, causes a loss of engine power. Since distortion upsets the critical tolerances of an engine, the seal between piston rings and the inner bore surface of the cylinder becomes less effective and blow-by may result which has the effect of corroding various elements ofthe engine such as the wrist pins. Additionally, the different heat transfer coefficient of the iron liner with respect to the surrounding aluminum cylinder body presents cooling problems in conducting heat from within the cylinder, through the iron liner, through the aluminum body and, thence, to the cooling fins formed on the cylinder. Also, the existing need for lightweight engines militates against the use of a heavy iron liner so that it would be an overall improvement in the art if many lightweight cylinder configurations could be easily formed without including such a liner.

The present invention is therefore directed to the die casting of articles such as aluminum internal combustion engine cylinders which heretofore have been traditionally constructed as composite articles.

In die casting hollow articles having high tolerance requirements, it was found that different heat expansion and heat transfer characteristics of core members with respect to the material being cast resulted in distorted and imperfect tolerances when the cores were used to form internal surfaces such as the bore of an l.C.E. (internal combustion engine) cylinder. Because of this, efforts were made to traverse the teachings of the prior art by discovering a way to form a cylinder of unitary construction by using a core member consisting of the same material as that comprising the die casting material.

Initially, it was discovered that using an aluminum core to form the bore within an aluminum l.C.E. cylinder often resulted in fusion between the cast article and the core which fusion made it necessary to extensively machine the overall core and cast article upon the removal thereof from the molds. This result was especially noticeable when a core was used which had protuberances for forming inlet, outlet and transfer ports within the cylinder.

It was then decided that an attempt should be made to identify a coating which could be applied to the arti- -cle forming surface of the core and which might operate as an anti-adhering film to prevent fusion, brazing or welding of the core to the cast article. Upon anodizing the aluminum core with a refractory substance, it was discovered that fusion often resulted between the core and the cast article. Currently, manufacturers are anodizing cores in order to control the heat conductivity of the mold and not to prevent fusion of the core with the cast article.

A similar result of fusion between the core and cast article occurred when the core member was coated with a high temperature porcelain substance.

After these earlier unsatisfactory results it was unexpectedly found that anti-adhering substances which are resistant to temperatures and pressures in excess of those encountered in die casting processes may successfully prevent fusion between the core and article and may facilitate the removal of the core from the article after cooling. These substances should be substantially impermeable and should volatize only at very high temperatures. It was ultimately discovered that high temperature tetrafluoroethylene, hard chrome, and various solutions of polyimide, when brushed, plated, or sprayed onto an aluminum core and then baked thereon will prevent fusion between the core and a cast article.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a novel means and method for die casting hollow articles.

It is another object of the present invention to provide a novel means and method for preventing the fusion of portions of a core member with a cast article when the two consist of substantially identical material.

It is still another advantage of the present invention to provide a method and apparatus for die casting metallic internal combustion engine cylinders which will have less distortion at elevated temperatures and which will allow closer tolerances so as to produce increased engine power.

It is yet another object of the present invention to provide novel method and means for die casting internal combustion engine cylinders of a new, lightweight, unitary construction which satisfies close tolerance requirements.

It is a further object of the present invention to provide an internal combustion engine cylinder having improved cooling characteristics.

lt is still a further object of the present invention to provide an internal combustion engine cylinder which is uncomplicated and inexpensive to manufacture.

The objects of the present invention are carried out by providing a method and an apparatus for casting hollow articles in which molten die casting material is introduced into a die having a core positioned therein. The die casting material is cooled until it solidifies and is then removed from the mold. A major portion of the core is machined from within the cast article which is then mechanically impacted to knock-out the remaining portions of the core.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is particularly pointed out and distinctly claimed in the concluding portion of the specification and several embodiments are disclosed herein which may best be understood when taken in connection with the accompanying drawings, in which:

FIG. 1 is a sectional view taken along the axis of an internal combustion engine cylinder constructed in accordance with the method and apparatus of the present invention;

FIG. 2 is a sectional view of the internal combustion engine cylinder of FIG. 1 taken along line 22 of FIG.

FIG. 3 is a pictorial view of a core member used to form the bore and various ports within the cast internal combustion engine cylinder shown in FIG. 1;

FIG. 4 is a pictorial view of the core member shown in FIG. 3 properly located within a mold for casting an internal combustion engine cylinder;

FIG. 5 is a schematic view showing blister forming protuberances on a core member which protuberances are formed with bosses extending radially through a cast cylinder wall into a wall of the die;

FIG. 6 shows the blister forming protuberances of FIG. 5 after the bosses have been mechanically impacted so as to knock the protuberances from within the cylindrical wall of the cast article;

FIG. 7 is a partial sectional view of a protuberance having a boss which is tapered to narrow toward the outer end thereof;

FIG. 8 is a partial sectional view of a protuberance being knocked out by a punch inserted within a hole formed in the cylinder wall; and

FIG. 9 is a partialsectional view of the portion of a cylinder shown in FIG. 8 after the protuberance has been knocked out and the hole properly sealed.

DETAILED DESCRIPTION Referring now to the drawings, in which like numerals are used to indicate like parts throughout the various views thereof:

FIG. I shows a sectional view of an internal combustion engine cylinder 10 having an internal bore 12. A charge inlet port 14 is formed within the wall of the cylinder 10 near the lower portion thereof. An exhaust port 16 is formed within the wall of the cylinder 10 above the inlet port 14 so as to facilitate scavenging when the cylinder is used in connection with a two stroke internal combustion engine. By-pass or transfer ports 18 are formed as blisters within the wall of the cylinder 10. The ports 18 are positioned vertically between the inlet port 14 and exhaust port 16 and are spaced angularly therefrom. Each blister I8 may vary in configuration in accordance with the by-pass re quirements of the specific engine design. Referring briefly to FIG. 2, it can be seen that the general extension of the blisters 18 along line e does not coincide with a radial r drawn to the approximate center of the blister. This offsetting angle, which may be approximately 30, is significant in that such angles are difficult to machine using current methods of manufacture.

Returning to FIG. 1, a generally cylindrical recess 20 is formed in the head of the cylinder 10 which recess may be used to retain a spark plug (not shown). The generally spherical portion 22 defining the upper portion of the bore 12 may be used as the combustion chamber of the cylinder and may be of an irregular configuration. Cooling fins 24 are formed on the outer cylindrical surface of the cylinder 10 for effecting heat transfer from the combustion area 22 to the atmosphere surrounding the cylinder 10.

Referring now to FIG. 3, a core member 30 is shown which may be used to form the bore 12, the blisters I8, and the

ports

14 and 16 of the internal combustion engine cylinder 10 shown in FIG. 1. The core member 30 may consist of the same material as the engine cylinder 10 and may be formed with an inner cylindrical surface 32 which defines a recess for receiving a core arbor or positioner 50 of a die described hereinafter in refer ence to FIG. 4. A radially projecting protuberance 38 is provided on the cylindrical surface of the core member 30 to form the exhaust port 16 shown in FIG. I and a second protuberance 40 forms the inlet port 14 shown in the same view. An irregular protuberance 42 is formed on the core member 30 vertically between the

radial projections

38 and 40 but is angularly spaced therefrom to form the irregular blisters 18 shown in FIGS. 1 and 2. It will be noted that surface 44 of the projection 42 subtends an angle of approximately 30 with respect to a plane extending tangent to the cylindrical surface of the core 30 at a line common to the outer surface of the cylindrical core 30 and the surface 44 of the projection 42. The significance of this irregular configuration has been previously discussed with respect to FIGS. 1 and 2.

The core member 30 shown in FIG. 3 may be die cast of a lightweight metal such as aluminum or magnesium by any conventional means. If it is desired to die cast a hollow article such as a pump body of a nonmetallic substance or of any die castable material, it is preferable, although not necessary, that the core member 30 comprise the same material as the die casting material to practice the present invention.

Upon casting the core 30 of the same material as that comprising the hollow cast article, a heat and pressure resistant anti-adhering substance is coated at least on the protuberance surfaces of the core member 30 by a dipping, plating, brushing, or spraying operation.

The coating may comprise a substance such as a liquidized polyimide composition or a silicone oil. A coating of high temperature tetrafluoroethylene or hard chrome was found to be effective for the purposes of the present invention when applied to a core member 30 consisting of an aluminum alloy. The purpose of the coating is to facilitate the removal of the remaining portions of the core from the cylinder casting after machining the bore. Aluminum cores are currently being anodized with refractory materials in order to restrict the rate of heat transfer through the core, the cast article and the outer mold surfaces. It has been discovered. unexpectedly, that such refractory film is not satisfactorily effective to preclude fusion, welding or brazing of a cast aluminum article to an aluminum core member.

In the preferred embodiment of the present invention, a core member 30 consisting of aluminum is cast and the port forming blisters, ports, and combustion chambers are sprayed, brushed or dipped with a liquidized polyimide composition which may be diluted with an appropriate solvent to comprise a solution comprising 50 percent to 90 percent, by volume, of polyimide. N-methylpyrrolidone has been found to be a suitable solvent for this purpose. The liquid mm. of the polyimide solution is then baked on the core 30 at 600 F. for 20 to 30 minutes. For best results, the core member 30 should be cleaned with the solvent and then dry heated before applying the polyimide composition. The cured coating should have a brown color and should not show any bare spots. The uniformity of the coating thickness is not critical.

The core member 30 is then positioned within a mold as shown in FIG. 4 and properly held in place by means of the cylindrical locator portion 50 which projects upward from the bottom of the mold cavity 52 and, itself, provides the spherical surface 53 for forming the combustion chamber 22. Of course, the combustion chamber could alternatively be formed by a surface portion of the core member 30. The surrounding mold 54 may comprise any conventional mold member because the tolerances on the outside surfaces of a hollow article such as an engine cylinder are not generally critical. Therefore, if the material comprising the mold member 54 should expand at a different rate than the cast material, any resulting minor distortion would be acceptable.

After the aluminum core 30 is properly located within the mold 54, molten aluminum is introduced through an inlet duct 56 into the article forming surfaces of the mold member 54. The aluminum is first heated to a temperature within a range of 1200" to l225 F. and enters the cavity 52 under a pressure within a range of 13,000 to 14,000 psi. The overall apparatus may then be cooled for to seconds until the aluminum has solidified at a temperature within a range of 600 to 700 F.

After the aluminum has solidified, the mold 54, which may be of the segmental type, is removed by any conventional means from around the article and the core 30 retained therein. The major portion of the core member 30 is then machined out from the cast article. The

projections

38, 40 and 42 remain within the walls of the hollow cast article. The article is then mechanically impacted by means of a soft hammer, or the like, which impaction causes the remaining portions of the core member to be loosened from within the cast article and to fall out. An access hole may be drilled adjacent a blister forming projection to permit the knocking out of the projection by the insertion of a tool through the hole which tool may directly contact the projection and effect the removal thereof by transmitting mechanical impactions directly thereto.

ALTERNATIVE EMBODIMENTS FIG. 5 shows a core member 30 positioned within a die member 52 which core member 30 is formed with blister forming projections 42. The projections, in turn, are formed with radially extending tapered bosses 60 which extend through the cylinder 10 and into holes 62 formed within the casting mold 52 for retaining the bosses 60.

FIG. 6 shows the cast cylinder after the mold 54 has been removed and after a major portion of the core member 30 has been machined out from therein. It will be appreciated, particularly with reference to FIG. 6, that the step of machining a major portion of the core from the cast article may involve boring out the generally cylindrical portion of the core member and leaving only the protuberances remaining distinctly encapsulated within the wall of the cast hollow article. The blister forming protuberances 42 have been displaced from the blisters within the cylinders by mechanically impacting the radial ends of the bosses 60 formed thereon. Each blister forming protuberance 42 is then broken off from the associated boss 60 at a neck portion 63 of the boss 60. The bosses 60 shown in FIGS. 5 and 6 are tapered to widen toward the radial ends thereof. This configuration permits the boss to plug the hole that was formed within the cylinder 10 thereby. The use of a boss 60 to apply a mechanical impaction directly to a blister forming projection 42 is especially useful when forming off-set transfer ports such as those shown in FIG. 2 which ports may extend at an angle which does not coincide with a radial line drawn from the center of the cylinder 10 to an approximate center of a blister 18. When the boss 60 is left within the cylinder wall to plug up the hole left thereby, it may be desirable to weld the outer portions of the boss 60 to the outer surface of the cylinder to prevent the boss from loosening and being propelled through the hole under the influence of any gas pressure buildup.

As shown in FIG. 7, the protuberance 42 may be formed with a boss 64 having a reverse taper to that of boss 60 shown in FIG. 6. Alternatively, the protuberance 42 may be formed without a boss as shown in FIG.

8 and a hole 65 machined in the cylinder for the insertion of a punch tool 67 for removing the protuberance 42. A steel ball 69 and a sealing material 71 may then be used to fill the hole 65 as shown in FIG. 9.

Also, if the aluminum core member is permitted to form an oxide layer, before casting an aluminum article, it has been found that this layer may function as an anti-adhering layer to prevent fusion between the core and cast article. The formation of an aluminum oxide layer may be encouraged by placing a heated core in an atmosphere with an excess of oxygen.

The removal of core protuberances is facilitated if the protuberance is tapered toward the radial end thereof. It can be seen that the transfer port 18 of the cylinder shown in FIG. 1 has been formed by protuberance 42 of FIG. 3 which does so taper. If it should be that the protuberances left in the cylinder after the rough machining step are falling out too easily, the angle of taper may be reduced so that the cylinder retains a protuberance until mechanically impacted. The angle of protuberance taper is known in the art as the draft.

It can thus be seen that an apparatus and method have been herein described for die casting irregular, hollow articles of manufacture such as internal combustion engine cylinders. Since the core member used to form the hollow portion of the article may comprise the same material as the article, the coefficient of expansion and heat transfer characteristics of the core and of the cast article are also identical which identity reduces distortion of the critical tolerances within the baked onto the core prevents fusion, brazing or welding of the core member with the die cast article. The machining required after the molded material solidifies in the cast article is mainly rough machining of the interior of the cylinder which removes a major portion of the core member. Then, the article only need be impacted to remove the remaining portions of the core as the anti-adhering coating provides for the easy removal thereof. The removed article may then be finely machined, plated and honed.

Through this method and apparatus, it is. no longer necessary to cast a lightweight aluminum cylinder around a heavy iron liner as is the present practice. Since there is no iron liner within the aluminum body of the cylinder, distortion of the critical tolerances of the overall cylinder is reduced when the engine is run at high operating temperatures. Likewise, since the cylinder is not a composite of dissimilar metals, cooling problems caused by having to conduct heat through such composites are avoided. Because the only machining required when practicing the present invention is the boring of a major portion of the core from the cylindrical body, the amount of expensive and timeconsuming machining is reduced. The closer tolerances now made available by the present invention provide a tighter piston fit, which in turn prevents compression loss and blow-by which results in low engine power and the corrosion of engine parts such as wrist pins.

While what has been shown herein are several embodiments of the present invention, it is, of course, understood that the method and apparatus disclosed herein may be modified without departing from the invention. It is therefore intended to cover in the appended claims all such modifications as fall within the true scope and spirit of the present invention.

I claim:

1. A method of molding hollow articles comprising the steps of:

a. providing a mold having a cavity for forming the outer surface of the article;

b. providing a core member having an outer surface for forming the inner surface of the article, the outer surface of said core member including a main body portion and at least one protuberance projecting outwardly therefrom;

c. providing at least a portion of the article forming surface of the core member including said at least one protuberance with an anti-adhering substance layer to prevent fusion between that portion of the core and the article;

d. locating the core member with in the cavity of the mold to define an article forming space between the outer surface of the core and the inner surface 'ofthemo e. introducing molten die casting material into said article forming space and in surrounding relationship with said at least one protuberance;

. cooling the molten material until it solidifies into a cast article with a configuration encapsulating said at least one protuberance;

g. releasing the solidified cast article from the mold;

h. machining the main body portion of core from within the cast article leaving only said at least one protuberance remaining, to form a hollow article encapsulating said at least one protuberance of the core;

i. mechanically impacting the cast article including the encapsulated said at least one protuberance of the core to loosen said encapsulated at least one protuberance free from the hollow article.

2. A method according to claim 1 wherein:

the step of providing a core member having an outer surface for forming the inner surface of the article comprises the step of casting a hollow generally cylindrical metal member forming said main body portion and having a plurality of said protuberances projecting therefrom for forming port holes and blisters within the hollow article;

the step of providing at least a portion of the article forming surface with an anti-adhering substance layer comprises providing each of said protuberances with an anti-adhering substance layer;

the step of machining comprises forming a hollow article with each of said protuberances being distinctly encapsulated by said hollow article; and wherein the step of mechanically impacting is performed so as to loosen each of said distinctly encapsulated protuberances.

3. A process according to claim 1 wherein the step of providing at least a portion of the article forming surface with an anti-adhering substance comprises coating said at least a portion of the core member by the steps of:

a. applying a liquified polyimide composition to said at least a portion of the article forming surface of the core; and

b. baking the composition onto said at least a portion of the core member.

4. A method of molding hollow articles comprising the steps of:

b. providing a core member having an outer surface for forming the inner surface of the article;

c. coating at least a portion of the article forming surface of the core member with an anti-adhering substance to prevent fusion between that portion of the core and the article;

d. locating the core member within the mold;

e. introducing molten die casting material into the space defined by the outer surface of the core and the inner surface of the mold;

f. cooling the molten material until it solidifies;

g. releasing the solidified cast article from the mold;

h. machining a major portion of the core from within the cast article;

i. mechanically impacting the article including the remaining portion of the core to loosen the remaining portion of the core free from the article;

j. the step of coating the article-forming surface of the core member comprising:

1. cleaning the core member with a solvent;

2. heat drying the solvent on the core;

3. applying a liquified polyimide composition to said at least a portion of the article forming surface of the core, with the polyimide composition being thinned to comprise a solution in the range 50 to percent by volume of the polyimide; and

4. baking the solution of polyimide and solvent on the core at approximately 600 F. for approximately 20 to 30 minutes.

5. A method according to claim 4 wherein the solvent consists of N-Methylpyrrolidone.

6. A method of molding hollow articles comprising the steps of:

c. coating at least a portion of the article forming the surface of the core member with an anti-adhering substance to prevent fusion between that portion of the core and the article;

d. locating the core member within the mold;

f. cooling the molten material until it solidifies;

releasing the solidified cast article from the mold;

h. machining a major portion of the core from within the cast article;

j. the step of introducing molten material into the space defined between the core and mold comprising the step of supplying molten aluminum heated within the range of l,200- 1225 F. and subjected to a pressure within the range of 13,000 14,000 psi into the space.

7. A method according to claim 6 wherein the step of cooling the molten material comprises the step of chilling the material 10-15 seconds until the material has a temperature within the range of 600-700 F.

8. A method of molding hollow articles comprising the steps of:

b. providing a metal core member having an outer surface for forming the inner surface of the article, the outer surface of the core member being a generally cylindrical surface having protuberances projecting therefrom for forming port holes and blisters within the hollow article;

c. coating at least the protuberances of the article forming the surface of the core member with an anti-adhering substance to prevent fusion between those portions of the core and the article;

d. locating the core member within the mold;

f. cooling the molten material until it solidifies;

g. releasing the solidified cast article from the mold;

h. machining a major portion of the core from within the cast article by the step of boring out the generally cylindrical portion of the core member and leaving only the protuberances remaining within the wall of the cast article; and

i. mechanically impacting the article including the remaining portion of the core to loosen the remaining portion of the core free from the article.

9. A method according to claim 2 wherein the core member comprises a metal taken from the group consisting of aluminum and magnesium.

10. An article of manufacture made in accordance with the steps of the method recited in claim 1.

11. A method for manufacturing hollow articles comprising the steps:

a. casting an article within a mold having a generally cylindrical core member located therein, the outer surface of the generally cylindrical core member including a main body portion and at least one protuberance projecting outwardly therefrom;

b. providing said at least one protuberance with an anti-adhering substance to prevent fusion to the article;

c. removing the article and core from the mold;

d. removing the entire main body portion of the generally cylindrical core from the article leaving only said at least one protuberance remaining within the wall of the cast article; and

e. mechanically impacting the article to loosen and knock out said at least one protuberance from within the article.

12. The method according to claim 11 wherein the core is cooled before casting the article.

13. A method for manufacturing hollow articles comprising the steps of:

a. casting an article within a mold having a core member located therein;

b. removing the article and core from the mold;

c. removing a major portion of the core from the article; and

d. mechanically impacting the article to loosen and knock out the remaining portion of the core from within the article;

e. the method including the step of forming an oxide coating on the outside surfaces of the core.

14. The method according to claim 1 wherein the step of providing a core member comprises providing a core member with the main body portion of its outer article forming surface being generally cylindrical and having a plurality of said protuberances projecting outwardly therefrom for forming port holes and blisters within the hollow article, and wherein each of said protuberances are provided with an anti-adhering layer and are left remaining after the machining step for loosening by the impacting step.

Claims

1. A method of molding hollow articles comprising the steps of: a. providing a mold having a cavity for forming the outer surface of the article; b. providing a core member having an outer surface for forming the inner surface of the article, the outer surface of said core member including a main body portion and at least one protuberance projecting outwardly therefrom; c. providing at least a portion of the article forming surface of the core member including said at least one protuberance with an anti-adhering substance layer to prevent fusion between that portion of the core and the article; d. locating the core member with in the cavity of the mold to define an article within space between the outer surface of the core and the inner surface of the mold; e. introducing molten die casting material into said article forming space and in surrounding relationship with said at least one protuberance; f. cooling the molten material until it solidifies into a cast article with a configuration encapsulating said at least one protuberance; g. releasing the solidified cast article from the mold; h. machining the main body portion of core from within the cast article leaving only said at least one protuberance remaining, to form a hollow article encapsulating said at least one protuberance of the core; i. mechanically impacting the cast article including the encapsulated said at least one protuberance of the core to loosen said encapsulated at least one protuberance free from the hollow article.

2. heat drying the solvent on the core;

2. A method according to claim 1 wherein: the step of providing a core member having an outer surface for forming the inner surface of the article comprises the step of casting a hollow generally cylindrical metal member forming said main body portion and having a plurality of said protuberances projecting therefrom for forming port holes and blisters within the hollow article; the step of providing at least a portion of the article forming surface with an anti-adhering substance layer comprises providing each of said protuberances with an anti-adhering substance layer; the step of machining comprises forming a hollow article with each of said protuberances being distinctly encapsulated by said hollow article; and wherein the step of mechanically impacting is performed so as to loosen each of said distinctly encapsulated protuberances.

3. applying a liquified polyimide composition to said at least a portion of the article forming surface of the core, with the polyimide composition being thinned to comprise a solution in the range 50 to 90 percent by volume of the polyimide; and

3. A process according to claim 1 wherein the step of providing at least a portion of the article forming surface with an anti-adhering substance comprises coating said at least a portion of the core member by the steps of: a. applying a liquified polyimide composition to said at least a portion of the article forming surface of the core; and b. baking the composition onto said at least a portion of the core member.

4. A method of molding hollow articles comprising the steps of: a. providing a mold having a cavity for forming the outer surface of the article; b. providing a core member having an outer surface for forming the inner surface of the article; c. coating at least a portion of the article forming surface of the core member with an anti-adhering substance to prevent fusion between that portion of the core and the article; d. locating the core member within the mold; e. introducing molten die casting material into the space defined by the outer surface of the core and the inner surface of the mold; f. cooling the molten material until it solidifies; g. releasing the solidified cast article from the mold; h. machining a major portion of the core from within the cast article; i. mechanically impacting the article including the remaining portion of the core to loosen the remaining portion of the core free from the article; j. the step of coating the article-forming surface of the core member comprising:

4. baking the solution of polyimide and solvent on the core at approximately 600* F. for approximately 20 to 30 minutes.

6. A method of molding hollow articles comprising the steps of: a. providing a mold having a cavity for forming the outer surface of the article; b. providing a core member having an outer surface for forming the inner surface of the article; c. coating at least a portion of the article forming the surface of the core member with an anti-adhering substance to prevent fusion between that portion of the core and the article; d. locating the core member within the mold; e. introducing molten die casting material into the space defined by the outer surface of the core and the inner surface of the mold; f. cooling the molten material until it solidifies; g. releasing the solidified cast article from the mold; h. machining a major portion of the core from within the cast article; i. mechanically impacting the article including the remaining portion of the core to loosen the remaining portion of the core free from the article; j. the step of introducing molten material into the space defined between the core and mold comprising the step of supplying molten aluminum heated within the range of 1,200* -1225* F. and subjected to a pressure within the range of 13,000 - 14,000 psi into the space.

7. A method according to claim 6 wherein the step of cooling the molten material comprises the step of chilling the material 10-15 seconds until the material has a temperature within the range of 600*-700* F.

8. A method of molding hollow articles comprising the steps of: a. providing a mold having a cavity for forming the outer surface of the article; b. providing a metal core member having an outer surface for forming the inner surface of the article, the outer surface of the core member being a generally cylindrical surface having protuberances projecting therefrom for forming port holes and blisters within the hollow article; c. coating at least the protuberances of the article forming the surface of the core member with an anti-adhering substance to prevent fusion between those portions of the core and the article; d. locating the core member within the mold; e. introducing molten die casting material into the space defined by the outer surface of the core and the inner surface of the mold; f. cooling the molten material until it solidifies; g. releasing the solidified cast article from the mold; h. machining a major portion of the core from within the cast article by the step of boring out the generally cylindrical portion of the core member and leaving only the protuberances remaining within the wall of the cast article; and i. mechanically impacting the article including the remaining portion of the core to loosen the remaining portion of the core free from the article.

11. A method for manufacturing hollow articles comprising the steps: a. casting an article within a mold having a generally cylindrical core member located therein, the outer surface of the generally cylindrical core member including a main body portion and at least one protuberance projecting outwardly therefrom; b. providing said at least one protuberance with an anti-adhering substance to prevent fusion to the article; c. removing the article and core from the mold; d. removing the entire main body portion of the generally cylindrical core from the article leaving only said at least one protuberance remaining within the wall of the cast article; and e. mechanically impacting the article to loosen and knock out said at least one protuberance from within the article.

13. A method for manufacturing hollow articles comprising the steps of: a. casting an article within a mold having a core member located therein; b. removing the article and core from the mold; c. removing a major portion of the core from the article; and d. mechanically impacting the article to loosen and knock out the remaining portion of the core from within the article; e. the method including the step of forming an oxide coating on the outside surfaces of the core.