US3612154A

US3612154A - Centrifugal pipe casting method

Info

Publication number: US3612154A
Application number: US881719A
Authority: US
Inventors: Jean Denyszyn
Original assignee: Glamorgan Pipe and Foundry Co
Current assignee: Glamorgan Pipe and Foundry Co
Priority date: 1969-12-03
Filing date: 1969-12-03
Publication date: 1971-10-12
Anticipated expiration: 1988-10-12

Abstract

Centrifugal pipe-casting method utilizing a rotatable mold and a permanent-type reusable core for partially closing the mold at its pipe withdrawal end. The portion of the core-facing casting material within the mold presents a surface with indentions for receiving and solidifying casting material so as to hold the end of the pipe and prevent distortion and end-cracking prior to removal of the pipe from the mold.

Description

United States Patent [72] Inventor Jean Denyszyn Lynchburg, Va.

[21] Appl. No. 881,719

[22] Filed Dec. 3, 1969 [23] Division of Ser. No. 639,535, May 18, 1967,

Pat. No. 3,499,479

[45] Patented Oct. 12, 1971 [73] Assignee Glamorgan Pipe & Foundry Co.

[54] CENTRIFUGAL PIPE CASTING METHOD 2 Claims, 4 Drawing Figs.

[52] U.S.Cl 164/114 [51] Int. Cl B22d 13/02 [50] Field of Search 164/66,

[56] References Cited UNITED STATES PATENTS 3,197,827 8/1965 Haughtori 164/299 3,327,769 6/1967 Latour 164/286 2,486,870 11/1949 Nolan 164/302 X 3,074,130 l/l963 Wittmoser... 164/302 X 3,168,765 2/1965 Bernhardt 164/302 Primary Examiner-l Spencer Overholser Assistant Examiner.lohn S, Brown Attorney-Shanley and O'Neil ABSTRACT: Centrifugal pipe-casting method utilizing a rotatable mold and a permanent-type reusable core for partially closing the mold at its pipe withdrawal end. The portion of the core-facing casting material within the mold presents a surface with indentions for receiving and solidifying casting material so as to hold the end of the pipe and prevent distortion and end-cracking prior to removal of the pipe from the mold.

PATENTEU 0211 21am FIG] CORE

I IIIIIIII T N E M F. V 0 M L AW W W3 TM 66 m L w" 6 2 CENTRIFUGAL LO SUPPORT CENTRIFUGAL L COVER PLATE FIG. 2

INVENTOR JEAN DENYSZYN CQ ATTO CENTRIFUGAL PIPE CASTING METHOD This application is a division of application Ser. No. 639,535, now US. Pat. No. 3,499,479 entitled Centrifugal Pipe-Casting Apparatus", filed May 18, 1967 by Jean Denyszyn.

This invention is concerned with centrifugal casting of pipe. In its more specific aspects, the invention is concerned with a permanent-type core which can be used repeatedly with centrifugal casting apparatus in the formation of no-hub pipe.

In the centrifugal casting of iron pipe, a controlled amount of molten iron is fed into a rotating elongated mold which moves longitudinally during casting to form a pipe. The rotating mold is a pennanent or semipermanent structure which must be open at one end for withdrawal of the cast pipe. During casting, that end of the rotating mold must be partially closed with a core to form what is commonly referred to as the bell end of the pipe and retain metal in the mold for the entire casting. Such cores must be readily removable upon completion of each cast.

To a large extent, the art has relied on use of expendabletype sand cores which are friable and can be removed from the mold and the pipe upon completion of each cast. The manufacture of such sand cores, the careful handling required with cores, the removal of sand from the cast pipe, and other such problems increase the cost of manufacturing cast pipe using sand cores. It is also difficult to manufacture uniform, symmetrical sand cores which will consistently fit the pipe withdrawal end of a rotating mold and provide crack and distortion-free pipe ends. In practice cracks are ordinarily formed in the pipe ends by metal which runs between the mold and the sand core. This metal forms fins on the pipe which,

due to rapid cooling, generate cracks which are propagated into the pipe.

An object of the present invention is to provide casting apparatus able to withstand continuous rugged use and semiautomated functioning with a minimum of attention by working personnel. Also to provide casting methods which will consistently produce uniform product which does not need trimming, cleaning, or machining to be within required specifications. To meet these requirements a permanent-type metallic core which can be accurately and quickly fitted to a rotatable mold is provided. Further, a metallic core is provided which is adaptable for use with self-locking mechanisms for rotatable molds.

However, it has been found that merely substituting metallic cores for sand cores does not provide the yield and economies required for commercial production. Many of the difficulties encountered are believed to stem, at least in part, from toorapid chilling of molten metal contacting a metallic core. This rapid chilling of the metal at the bell end of the pipe is believed to be the cause of the distortion produced, for example an elliptical shape occurs at the pipe withdrawal end of the pipe rather than the desired circular configuration. Cracking of the pipe at the pipe withdrawal end as a result of this distortion or because of fin formation also decreases the yield. Distortion and end cracking caused by metallic cores have been found to decrease yield in excess of twenty percent so that it has not been economically possible, prior to the present invention, to replace sand cores with permanenttype cores.

It is the primary objective of the present invention to provide a permanent-type core, which circumvents the abovedescribed pipe-casting problems, which uniformly produces crack-free and distortion-free pipe, and which can be used repeatedly, notwithstanding rough handling and extreme thermal stresses.

Referring to the accompanying drawings:

FIG. 1 is a schematic view of centrifugal casting apparatus,

FIG. 2 is a cross-sectional view of portion of a rotatable mold casting apparatus and a permanent-type core embodying the present invention,

FIG. 3 is an end view of a portion of permanent-type core embodying the present invention, and

FIG. 4 is a sectional view of a portion of the core of FIG. 3.

In operation of the apparatus shown in FIG. 1, molten metal is controllably fed for each casting operation from pouring box 12 to the interior of rotatable mold 141 through spout 16. At the beginning of the cast spout 16 extends about half the length of the mold toward its bell end. Rotatable mold 14 is spun about longitudinal axis 18 during each casting operation.

Prior 'to casting, core 20 is fitted to the rotatable mold 14. At the start of casting, metal from spout 16 contacts facing 22 of core 20. The metal is fed at such a rate, and the rotatable mold moves longitudinally (as indicated by arrow 26) at such a rate that a substantially uniform thickness pipe 24 is formed. Casting machines using a rotatable longitudinally moving mold, e.g. Delavaud centrifugal pipe-ca5ting machines, are well known in the art and no further explanation of the general principle of operation is required for an understanding of the invention. The removable core problems discussed above are also well known in the art and have constrained these semiautomatic machines to use of sand cores for many years.

FIG. 2 shows the permanent-type core of the present invention and portions of a rotatable mold along with self-locking structure. Core 28 is substantially symmetrical about longitudinal axis 30 and has an elongated hollow tubular configuration. The hollow portion of core 28 is in communication with the hollow tubular internal cavity of mold 34. The interior surface of core 28 is generally smooth and curvilinear defining a portion of a conical surface. The exterior surface of core body 32, which includes shoulder 33, has a configuration adapted for functioning of centrifugally operated self-locking fingers such as that shown at 36. Rotation of the mold provides the force for functioning of the self-locking mechanism. Other suitable locking mechanisms may be used in practice of the invention.

Core 28 is removably secured to rotatable pipe mold 34 and presents a patterned surface to a portion of the hollow tubular internal cavity defined by rotatable pipe mold 34. The patterned surface of one end of mold 28 closes a portion of the hollow internal cavity of rotatable mold 34 contiguous to the internal periphery of the mold determining the minimum internal diameter of the pipe. The patterned surface presented by core 28 contact molten metal poured into the mold and establishing the mold surface for the pipe end wall.

Contact of molten metal with a metallic core is believed to have been responsible for the problems experienced before the present invention. Rapid chilling of the casting metal where contact was made with the core, and the differential chilling of metal contacting the core and metal contacting the mold, caused distortion of the pipe at its withdrawal end. An elliptical configuration at the withdrawal end of the cast pipe resulted rather than the desired circular configuration. Normally the ellipticalness extended several inches along the length of the pipe. As a result, either the entire pipe was scrapped or some portion of the pipe had to be cut off in order to salvage a pipe with limited uses, so that commercially acceptable yield could not be obtained.

The present invention solved these difficulties be devising means for holding metal at the withdrawal end of the pipe during the casting and pipe-forming stages to prevent shrinkage, distortion, and cracking at the pipe end.

In practice, the core body configuration of the present invention can vary widely to suit the type of lock design employed. However, a core-facing insert 40 is positioned at the end of core 28 contacting the rotatable mold 34. Diametral dimensions of core-facing insert 40 are selected to maintain the pipe ends within thickness requirements. The facing insert 40 fits firmly into the mold to keep molten metal from between the core and the mold. That ortion of core-facing insert 40 which comes into direct contact with the molten metal is manufactured with recesses for receiving and solidifying casting metal so as to hold the end of the pipe at the pipe withdrawal end of the rotatable mold against radial shrinkage forces during casting of the remainder of the pipe and until the pipe is removed from the mold.

Recesses in the core-facing insert 40 can vary in shape, depth and number depending on the type of metal being cast and the size pipc being cast. They can be formed in core-facing insert 40 by various means including drilling and knurling.

In the embodiment shown in FIGS. 3 and 4 a plurality of indentations, such as 44, are used. These indentations can be distributed uniformly about core-facing insert 46 in order to provide uniform gripping of the metal. Preferably the outer configuration of the indentations is curvilinear in order to avoid opportunity for forming minor cracks at the end surface of the pipe.

The depth of the indentations can vary depending on the diameter of the pipe being cast and the type of metal being cast. A depth of about one thirty-second inch has been found satisfactory for standard cast iron pipe. The depth of the indentations should be sufficient to hold the pipe against radial shrinkage forces. However, the depth of the indentations should not cause difficulty in removing the core or require removal of protrusions formed in the end surface of the pipe by the metal which is cast in the indentations.

The number of indentations can also vary with the size of the pipe. In a representative embodiment of the invention for casting 4-inch diameter pipe, 30 indentations of outer diameter, one thirty-second inch depth, and a conical configuration as shown in FIG. 4 have been found to be satisfactory. With a 3-inch diameter pipe, 24 such indentations have been found to be satisfactory.

Considering useful life of a core, unexpected results are obtained by using brass for the core facing means. This longer life is believed to stem from the better thermal conductivity of the brass than that available with other suitable metals such as stainless steel. in practice a brass facing means about A in thickness, with recess means as above described, is welded to the core body. Suitable core body metal is ductile iron. This combination has resulted in long useful life, in excess of 5,000 casts per core, notwithstanding the thermal shock encountered when the core is immersed in water after each casting.

Suitable metals for the core-facing means include stainless steel, steel, iron, etc. Also satisfactory operation can be obtained by casting the entire core from a metal such as ductile iron and preparing the abovc-described pattern in the face which contacts the molten metal. However, a brass core-facing means and ductile iron core body combines features which make the core perform satisfactorily during each cast and rugged enough to withstand thousands of casts.

Alternate heating of the core during casting and cooling by quenching in water immediately after casting cause thermal fatigue which eventually determines the life of the core. This can be circumvented by eliminating the quenching step, but advantages, such as ease of handling of the core by the operator after quenching, making the quenching practice more suitable economically.

The present invention eliminates the problem of ellipticalness and end cracking in centrifugal pipe casting and provides permanent-type apparatus able to withstand the rugged use and thermal stresses encountered. As a result, the yield and quality of the product, and production rate of centrifugal casting apparatus, are increased. Specific structure and materials have been set forth in disclosing the invention. However, the scope of the invention is not limited to such disclosure but rather is to be determined from the appended claims.

What is claimed is:

ll. Method for centrifugal casting of no-hub pipe using a reusable-type metallic core removably secured to a rotatable mold having an internal surface for molding molten metallic casting material and having a pipe withdrawal end, comprising the steps of controllably feeding molten metallic casting material into the mold with the reusable-type metallic core positioned at the pipe withdrawal end of the mold presenting a patterned surface sealing a portion of the mold contiguous to its internal surface to determine the minimum internal diameter of the pipe being cast and establish a mold surface for the end wall of such pipe rotating the mold during controlled feeding of molten metallic casting material to the mold, and

solidifying molten metallic casting material at the pipe withdrawal end of the mold prior to solidification of the remainder of the pipe while avoiding pumping of such material with the patterned surface of the metallic core establishing a pattern in the pipe end wall and holding the pipe at the pipe withdrawal end of the mold so as to prevent shrinkage distortion at that end of the pipe during casting and solidification of the remainder of the pipe.

2. In the centrifugal casting of no-hub pipe, a method for preventing radial shrinkage of the pipe at the pipe withdrawal end of the mold when using a reusable-type metallic core for partially closing that end of the mold along its inner periphery, comprising the steps of controllably feeding casting metal to the rotatable mold,

rotating the mold about its longitudinal axis and moving the mold longitudinally to distribute the metal being controllably fed into the mold, and

presenting a patterned surface of the metallic core for establishing the minimum internal diameter for the pipe being cast and defining a mold surface for the end wall of such pipe, such patterned surface being in transverse relationship to the longitudinal axis of the mold and positioned along the inner periphery of the rotatable mold to receive and solidify molten casting material prior to solidification of the remainder of the pipe so as to hold the pipe at the pipe withdrawal end of the mold during casting and solidification of the remainder of the pipe while avoiding pumping of such molten casting material.

Claims

1. Method for centrifugal casting of no-hub pipe using a reusable-type metallic core removably secured to a rotatable mold having an internal surface for molding molten metallic casting material and having a pipe withdrawal end, comprising the steps of controllably feeding molten metallic casting material into the mold with the reusable-type metallic core positioned at the pipe withdrawal end of the mold presenting a patterned surface sealing a portion of the mold contiguous to its internal surface to determine the minimum internal diameter of the pipe being cast and establish a mold surface for the end wall of such pipe, rotating the mold during controlled feeding of molten metallic casting material to the mold, and solidifying molten metallic casting material at the pipe withdrawal end of the mold prior to solidification of the remainder of the pipe while avoiding pumping of such material with the patterned surface of the metallic core establishing a pattern in the pipe end wall and holding the pipe at the pipe withdrawal end of the mold so as to prevent shrinkage distortion at that end of the pipe during casting and solidification of the remainder of the pipe.

2. In the centrifugal casting of no-hub pipe, a method for preventing radial shrinkage of the pipe at the pipe withdrawal end of the mold when using a reusable-type metallic core for partially closing that end of the mold along its inner periphery, comprising the steps of controllably feeding casting metal to the rotatable mold, rotating the mold about its longitudinal axis and moving the mold longitudinally to distribute the metal being controllably fed into the mold, and presenting a patterned surface of the metallic core for establishing the minimum internal diameter for the pipe being cast and defining a mold surface for the end wall of such pipe, such patterned surface being in transverse relationship to the longitudinal axis of the mold and positioned along the inner periphery of the rotatable mold to receive and solidify molten casting material prior to solidification of the remainder of the pipe so as to hold the pipe at the pipe withdrawal end of the mold during casting and solidification of the remainder of the pipe while avoiding pumping of such molten casting material.