US2152528A - Mold - Google Patents

Description

March 28, 1939.

F. C. BIGGERT. JR

MOI-1D Original Filed March 6, 1955 5 Sheets-Sheet l ,2 INVENITOR v WITNESSES March 28, 1939.

F. c, BIGGERT. JR

MOLD

Original Filed March 6, 1953 3 Sheets-Sheet 2 INVENTOR M 6.

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WITNESSES March 28, 1939. F. c. BIGGERT. JR

MOLD

Original Filed March 6, 1933 INVENTOR 3 Sheets-Sheet WITNESSES Patented Mar. 28, 1939 UNITED STATES PATENT OFFICE MOLD Continuation of application Serial No. 659,875,

March 6, 1933. Serial No. 32,762

This application July 23, 1935,

3 Claims. 22-200) This invention relates to the molding of metal castings and particularly to a method and apparatus for making castings for use in the manufacture of rolling mill rolls and is a continuation of the invention disclosed in United States Patent application Serial No. 659,875 for Casting mold filed by the present inventor March 6, 1933, which is in turn a continuation in part of application Serial No. 597,705, filed March 9, 1932.

In the manufacture of castings .for rolling mill rolls as accomplished in the past, various problems have been encountered which have seriously hampered the production of satisfactory castings and have materially added to the manufacturing costs of the rolls. -Among the most difiicult of these has been the problem of preventing the, metal in the riser portion of the casting mold where the upper neck end of the casting is formed from solidifying before that in the body proper of the mold. If this is not prevented the gases formed in the molten metal in the body of the casting have no way of escaping, and as a result gas pockets or fissures are formed which either spoil "or greatly weaken the casting. It also causes shrinkage strains to be set up between the neck and body of the roll which either greatly reduces the strength of the casting at a point where great'strength is needed or results in a fracture at such a point.

To minimize these difficulties it has been the usual practice to make the riser part of the mold relatively large or over-sized. This, however, not only frequently fails to accomplish the end desired, but also greatly adds to the cost of manufacture as it entails the. use of an unnecessarily large amount of metal and results in the production of an over-sized neck on the casting which has to be removed by a machining operation which is the most costly item in the manufacturing cost of the roll.

With this in mind it is the primary object of the invention to provide for making rolling mill roll castings having minimum sized necks which are free of fractures, blow holes and the like especially at the junction of the neck and body of the roll, and for accomplishing such end by regulating the flow of heat from the mold in such a way asto prevent the metal in the mold riser from solidifying until after that in the body of the roll'proper has solidified. I

A particular object is to provide a mold for accomplishing the aforementioned result by heating the riser prior to the pouring of the'casting and continuing the heating thereof until after the body proper of the casting has solidified.

Another object is to provide a mold for the casting of mill rolls in which means are provided for heating the riser or neck of the casting and which are characterized by their effectiveness and convenience, as well as their cheapness.

These and various other objects, as well as the various other novel features and advantages of the invention, will be apparent when the following detailed description is read in conjunction with the accompanying drawings of which Fig. 1 is a vertical section taken through the riser and. upper body portion of a mold designed for use in making mill roll castings, which is constructed in accordance with this invention; Fig. 2 a top plan view of the mold shown in Fig. 1; Fig. 3 a perspective view of a simple form of resistor element devised for use in the neck of the mold; Fig. 4 a view similar to Fig. 1 of another modification of the invention; Fig. 5 a plan view of the mold shown in Fig. 4; Fig. 6 another view similar 20 to Fig. 1 of still another modification of the invention; Fig. 7 a view also similar to Fig. 1 of a further modification of the invention; and Fig. 8 a plan view of the latter.

Referring in detail to the drawings and first to the embodiment of the invention illustrated in Figs. 1, 2 and 3, the numerals l and 2 designate the riser and body sections respectively of a conventional form of mold housing such as is customarily used in the making of mill roll castings. According to the invention a sand mold 3 is formed in this housing in any suitable way but preferably by packing a molding sand or some other suitable non-electric mold-forming material about a removable core having approximately the size of the roll desired. The only departure of any importance from the usual mold-forming practice in this is that the electro-current resisting elements 4 are packed in the sand in the riser of the mold adjacent the inner surface of the mold. This is done as the sand is tamped in place, and their purpose is to heat the riser to sufficiently retard the cooling of the metal in the neck portion of the casting to prevent it from solidifying until after the body of the roll proper has solidified. In this way shrinkage strains between the junction of the neck and body of the roll are eliminated and the gases formed in the body of the casting are allowed to escape, which avoids the formation of blow holes and fissures in the casting and hence insures the provision of a sound union at the junction of the neck and body of the roll which is necessary to preserve the maximum strength of the casting. -To properly accomplish such end and, at the same time, permit the mold riser being made but slightly larger than the finished neck of the roll to thereby minimize the machining of the roll neck as well as minimize the amount of metal required, these heating elements are provided in such numbers and so arranged as to positively maintain the metal in the entire length of the riser in a fluid state until after the body of the roll solidifies which is necessary in order to provide a sound union at the junction of the neck body of the roll.

In their preferred form, the resistors 4 are made of an inexpensive carbonaceous material which is susceptible of being installed with ease and which may be removed from the mold housing with the molding sand and discarded without any appreciable cost. Among the materials which may be used for this purpose are Mexican graphite, a granular form of graphite mined chiefly in Mexico, crushed coke or the like. One method of forming the resistors out of this material is to simply pack the graphite or other material in granular form in cavities made in the sand as the sand mold is built up. A more convenient way, however, is to pack the resistorforming material in inexpensive containers 1 such as shown'in Fig. 3 which are made in the shape of resistor desired. Another method is to mold the resistors to shape by using some suitable binder to hold the material together and then casting or molding the elements.

The shape and size which the resistors take may be varied according to the shape of the mold and the heating condition requirements. However, for the particular purpose shown here and for use with either direct, single-phase or three- -phase current substantially U-shaped resistors are recommended, being curved in the shape of an are about their major axes. In building up the mold they are positioned near the inner surface of the sand in uniform relation with their lower ends disposed adjacent the junction of the neck and body of the casting. One of the re quirements of such resistors is that they be adapted to provide the proper distribution of heat needed, andto accomplish this most economically they are preferably made of lesser cross-section in the vicinity of the junction between the roll neck and roll-body as illustrated in Figs. 1 and 3 in which the resistors are shown as being gradually reduced in thickness from near their centers to their lower ends. This, as will be readily understood, gives them a greater resistance in the reduced portions and provides greater heat in the ,vicinity where it is most needed.

For connecting the resistors to a source of current supply suitable connector terminals 5 are provided. These for convenience are so constructed that they may be connected to the reslstor by merely placing them on the top of the mold in contact with the resistors. To allow them to be connected and disconnected with a minimum amount ofeifort, they are connected to the ends of flexible conductors 6. These are in turn connected to the current supply. With large castings as shown inFigs. 1 and 2 a number of resistors may be connected in series through the use of simple unit connectors 8. This, however, is optional depending upon the current supply and circuit connections used.

In practicing the invention to insure the best results and proper regulation of heat flow from prevent the metal in the neck of the casting from solidifying. This avoids the possibility of the necks chilling regardless of size before the resistors can be brought into operation after the metal is poured. Once in service the heating of the resistors is continued until the body of the roll solidifies.

Referring to Figs. 4 and 5 an embodiment of the invention is illustrated in which gas instead of electricity is used as a heating medium for retarding the solidifying of the metal in the mold riser. According to this embodiment a series of vertical ducts 9, or flue passages, is formed in the sand adjacent the inner surface of the riser portion of the mold, being extended downwardly from the top of the riser to a point adjacent the top of the roll body forming part of the mold. At their lower ends these ducts are connected by passages H which extend to and open into holes I! provided in the side of the mold housing.

For heating the riser a series of burners I3 is provided and adapted to be inserted in the holes I2 in the side of the housing and to produce flames which will travel upwardly through the vertical ducts 9. For supplying the burners with fuel a manifold H to which properly carbureted fuel is supplied, is mounted adjacent the mold, and to it the burners are connected by flexible tubes l5 whereby the burners may be readily removed from the mold as desired. For certain types of castings'it is desirable to heat the riser with the burners before the castings are poured and to remove them during the pouring operation and then return them to themold as soon as the pour is completed, covering the holes I! with suitable plugs l6 while the burners are out. The reason for doing this is to prevent the metal from running out of the burner holes in the event any of the ducts 9 are broken when the casting is poured. For convenience the plugs l6 may be pivotally mounted in the form of gates on the outside of the mold housing, so that they can be easily moved to permit the reinsertion of burners as soon as the metal is poured.

To prevent any sand which may be loosened during the preheating of the riser from dropping into the bottom of the mold and spoiling the casting, a thin metal dam I! may be mounted in the body portion of the mold as shown in Fig. 4 to catch this sand. This dam is preferably made of some light metal such as aluminum which will be readily melted and floated by the molten metal as it rises in the mold carrying the sand to the top of the casting where it will be harmless.

In the embodiment of the invention shown in Fig. 6, which also employs the conventional housing and sand mold, a series of holes I8 is formed in the sand of the riser adjacent its inner surface, being extended from the top of the riser into the roll body portion of the roll. These are adapted to function as a series of auxiliary heating risers, being filled with molten metal when the casting is poured, to retard the chilling of the metal in the main riser. To prevent their injuring the body of the roll, the lower ends IQ of the auxiliary risers III are reduced in size, and offsets 2| are provided at their upper ends so that the metal cast in them will chill and fracture due to shrinkage without harming the upper ends of the roll proper. As in the other embodiment of the invention for heating the riser of this mold before the cast is poured, a burner assembly 22 is provided. This consists of a manifold 23 which is attached to a tube 24 that is protected by ceramic collars 25 and is adapted to be inserted in the riser. At its lower end the tube 24 is provided with a burner 26 which produces a flame that travels upward through the riser. At the upper end of the tube 24 it is equipped with arms 21 which are used to hold the burner in place, it being rested on suitable supports 28 provided for that purpose. In making a casting with this mold the burner assembly is first placed in the mold and operated until the riser is properly heated. It is then removed and the casting poured in the customary way.

In the further modification of the invention shown in Figs. 7 and 8, a series of vertical holes 3| is provided in the riser of the mold adjacent the inner surface of the neck mold and connected together in pairs at their lower ends, being terminated a short distance above the upper end of the roll. At the upper end of one of each pair of these holes a hopperlike cavity 32 is formed in the molding sand. In these cavities a quantity of some suitable thermit material is placedand ignited just before the casting is poured. From the hoppers the molten mass which is formed 'as the thermit burns with exceedingly high temperatures runs down the hole connected thereto and back up the connecting holes. Thus it is collected adjacent the lower end of the roll neck, where the heating of the riser is most effective. An amount is used which is sufflcient to adequately heat the mold so as to prevent the metal in the riser solidifying until after that in the body of the roll has solidified, with the beneficial re sults desired.

Among the chief advantages of the invention is the production of castings of increased perfection through the use of a minimum amount of metal and in sizes requiring a minimum amount of finishing thereby greatly reducing the cost of manufacture.

According to the provisions of the patent statutes, I have explained the principle and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as speciflcally illustrated and described.

I claim:

1. A casting mold for making mill roll castings and the like comprising a mold housing, a mold formed of molding material such as sand packed in said housing and conforming in shape to that of a roll having an enlarged body portion and reduced neck portions, resistor elements formed of loose carbonaceous material packed in said molding material adjacent the inner surface of the roll neck-forming portion of the mold and extended from a point adjacent the body of the roll upward and adapted to be removed from the mold with the mold material, and detachable means for connecting said resistor elements in a current-supplying circuit whereby the neckforming portion of the mold may be heated when the casting is poured to prevent the metal in that portion of the casting from solidifying until after the metal in the body of the roll has solidified.

2. A casting mold for making mill roll castings comprising a mold housing, a mold formed of molding material such as sand packed in said housing and conforming in shape to that of a roll having an enlarged body portion and reduced neck portions, resistor elements formed of Mexiv can graphite packed in said molding material adjacent the inner surface of the roll neck-forming portion of the mold and extended upward from a point adjacent the body of the roll and adapted to be removed from the mold with the mold material, and detachable means for connecting said resistor elements in a current-supplying circuit whereby the neck-forming portion of the mold may be heated when the casting is poured to prevent the metal in that portion of the casting from solidifying until after the metal in the body of the roll has solidified.

3. A casting mold for making mill roll castings and the like comprising a mold housing, a mold formed of molding material such as sand packed in said housing, and conforming in shape to the shape of the casting to be made, resistor elements formed of loose carbonaceous material packed in said molding material adjacent the inner surface of the roll neck-forming portion of the mold and adapted to be removed from the mold with the mold material, said resistor elements being constructed to supply a larger amount of heat to the lower end of the riser than to the top, and means for connecting said resistor elements in a current-supplying circuit to heat the neck-forming portion of the mold and prevent the metal in that portion of the casting from solidifying until after the metal in the body of the roll has solidified.

FLORENCE C. BIGGER'I, JR.

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