US2039397A - Method of forming tappets - Google Patents

Description

y 1935- J. DOSTAL 1 2,039,397

METHOD OF FORMING TAPPETS Original Filed Sept. 28, 1929 2 Sheets-Sheet 1 INVENTOR Josey A. flosial.

ORNEYS.

M y 1936. J. DOSTAL 2,039,397

I METHOD OF FORMING TAPPETS Original Filed Sept. 28, 1929 2 Sheets-Sheet 2 INVENTORI Josey?! A. flasial.

' ATTORNEYS.

Patented May 5, 1936 METHOD OF FORMING TAPPETS Joseph-L. Dostal, Flint, Micln, assignor to EatoniErb Foundry Company, a corporation of Mich- Original application September 28, 1929, Serial No. 395,949. Divided and this application July 17, 1933, Serial No. 680,774

6 Claims.

This invention relates to a method of forming tappets and particularly to an improved method of forming cast iron tappets for'use in connection with internal combustion engines, the principal object being the provision of a new and novel method by means of which an improved tappet may be produced economically in quantities, and is a division of my application for Letters Patent of the United States for improvements in Means for producing hardened cast iron valve tappets, filed September 28, 1929, and serially numbered 395,949.

Objects of theinvention include the provision of a method of forming cast iron valve tappets including casting the face of the tappet against a chill and controlling the temperature of tie mold and/or chill so as to obtain the desi; gd hardness of the tappet face and/or softness of the tappet body; a method of casting a cast iron tappet in a metallic mold in such a manner as to obtain a chilled face for the tappet and a relatively soft body therefor; a. method of producing quantities of cast tappets by the use of a metallic mold having a movable chill plate by the use of which the temperature of the chill plate may be controlled so as not to exceed a predetermined maximum necessary to obtain the desired hardness of the chilled face of the tappet; a method of producing a plurality of cast iron tappets by the use of a metallic mold having a removable chill plate forming that face of the mold adapted to produce the face of the tappet, and replacing the chill plate by a cooler chill plate when the temperature of the chill plate being employed in the casting operation approaches a predetermined high temperature; and the continuous production of cast iron valve tappets by the employment of a cast iron of predetermined composition in a metallic mold, having certain walls of the mold depressions insulated against the transfer of heat thereto, and certain other walls of the depressions formed by a chill plate so constructed as to permit control of the temperature thereof.

The above being among the objects of the present invention, the same consists of certain novel steps of operation in the manufacture of cast iron valve tappets to be hereinafter described with reference to the accompanying drawings, and then claimed, having the above and other objects in view.

In the accompanying drawings which illustrate apparatus suitable for the satisfactory carrying out of the present invention, and in which like numerals refer to like parts throughout the several different views,

Figure 1 is a side elevational view of a conventional form of valve tappet which may be cast according to the present invention, showing a part of the gate formed in the casting operation attached thereto.

Fig. 2 is a vertical sectional view taken centrally through a mold suitable for use in connection with the present invention, as on the line 2-2 of Fig. 3, and giving an elevational view of the inner face of one 'of the mold halves, together with the chill plate employed in connection therewith.

Fig. 3 is a vertical sectional view taken transversely to the length of the mold shown in Fig. 2 as on the line 3-3 of Fig. 2, and illustrating one of the mold cavities as being filled with metal.

Fig. 4 is a plan view of the mold shown in Figs. 2 and 3, without the chill plate, and with the mold halves slightly separated.

Fig. 5 is a fragmentary perspective view of one end of the chill plate used in connection with the mold indicated in Figs. 2 to 4, inclusive.

It is, of course, well understood in the art that valve tappets for internal combustion engines formed from white cast iron and including a chilled face and relatively soft body are desirable both from the standpoint of economy in production and efficiency and long life in use.

The prior practice in the production of such valve tappets has been to provide a sand mold having a chill plate inserted for forming the face of the tappet, and in such method of production it is possible to obtain a satisfactory uniformity of product in quantity production. In such case, however, due to the fact that the sand cores or molds are destroyed after eachcasting operation, the production cost of the tappets is higher than desired, and one of the main objects of the present invention is to eliminate the heretofore relatively high expense in connection with the use of sand cores or molds. This saving, in accordance with the present invention, is primarily accomplished by the use of permanent metallic molds which may be used over and over again and which thus result in a very slight charge per tappet for molding costs.

In employing a permanent metallic mold for this purpose, however, it will be apparent that the molds themselves tend to absorb a very material amount of heat from the metal being cast, and while this is of advantage in certain respects,

- it is also a decided disadvantage in other respects. The advantages are that the body of the mold in absorbing heat from the molten metal being cast tends to reduce the transfer of heat tively .termediate section 29.

I a -s The disadvantage of the absorption of heat by 1 the mold from the metal being cast is that in order to provide the desired chilling of the face of the tappet, the surface of the mold forming the face of the tappet must be maintained at a relatively low temperature or otherwise the desired degree of hardness of the face of the tappet will not be obtained. Accordingly, the adaptation of permanent molds to the art of casting valve tappets having chilled faces creates several dimculties which are overcome in accordance with the present invention. Briefly stated, in accordance with the present invention the metal which is to form the body portion of the tappet is insulated against excessive transfer of heat to the body of the mold by providing the corresponding-surfaces of the mold depression with a relathin coatingof heat insulating material capable of satisfactorily withstanding the high temperatures of the metal being poured, and. providing a separate member adapted to form the face of the tappet and so cooling this member as to limit its maximum temperature or, if necessary, removing such member after its temperature has attained a predetermined high value and replacing it with another like and cooler member. The above method, particularly where the temperature of the mold itself is controlled, results in a product of uniform quality in quantity production.

Referring now to the accompanying drawings, as a matter of illustration only, in Fig. 1 is shown one conventional form of tappet which may be formed in accordance with the present invention. This tappet, generally known as the mushroom type, comprises a cylindrical body portion In having an enlarged head l2 connected thereto through an undercut portion l4, and a reduced end I 6 opposite the head 12 provided' with flats l3 on diametrically opposite sides thereof for the purpose of allowing ready engagement with a wrench or other tool. In casting these tappets they are gated at the end l6 and in Fig. 1 a gate is shown attached thereto as in the manner in which the tappet is removed from the mold.

Referring to the drawings, it will be noted that the mold shown comprises two main halves 22 and 24 having matching planular faces and, for ease in manufacture, each half is made up of a plurality of superposed sections each including a bottom section 26, a top section 28 and an in- These sections of each half are maintained in alignment by dowel pins 30 and secured together as a unit by screws 3|.

Dowel pins 32 secured to the half 24 and fitting, within openings 33 in the half 22 serve to maintain alignment of the halves 22 and 24 during operation. Cooperating cavities 34 are formed in the opposed faces of the intermediate members 29 of the halves 22 and 24 simulating the shape of the desired tappet, but preferably of slightly larger diameter than the desired tappet due to the preferred use of a heat insulating coating to be more fully disclosed. The depressions 34 open upon the lowerface of the sections 29 at which point the head l2 of the tappet is adapted to be formed. Matching depressions 35 forming gates for the cavities 34 are formed in the opposed faces of the sections 23. A channel 36 is formed at the top of the sections 28 between the opposed faces thereof and is connected by means of a triangularly shaped trough 38 with the gate depressions 35, thetrough 38.thus serving as a sprue. It will be noted from an inspection of Fig. 2 that the trough 38 tapers from a minimum depth at one end of mold to a maximum depth at the opposite end thereof so that when metal is poured into one end of the trough 36 it .will successively flllsuccessive gates 35 and corresponding cavities 34. It is to be understood, of course, that the channel 36 and trough 38 stop short of opposite ends of the mold halves 22 and 24.

A channel 40 is formed between the upper ends of the opposed faces of the sections and extends completely through the mold halves 22 and 24 from end to end. Relatively loosely received in the channel 40 is a chill member, plate or block 42 which substantially completely fills the channel 40 and the upper surface of which substantially abuts the lower faces of the sections 29 thereby to serve as a closure for the bottom of the depressions or cavities 34 and acts to serve as face of the cavities 34 defining the face of the head I2 of the tappet although, 'due to the necessary looseness of fit of the chill plate 42 in the channel 40 a slight amount of clearance may be present between the top of the chill plate 42 and the sections 29 which may act to-permit the escape of gas from the mold cavities. Dowels 44 are threaded into the half 22 and project through suitable openings 46 in the half 24. These dowels project through the lower portion of the channel 40 and the chill plate 42 is provided with transverse grooves 48 in its lower surface of reception of the dowel pins 44 which thereby maintains the chill plate 42 against inadvertent longitudinal shifting movement and serve as guides therefor when the mold halves are separated.

The walls of the depressions 34, gates 35, channel 36 and trough 38 are preferably provided with a relatively thin adherent coating 50 of heat insulating refractory material of the type disclosed in United States Patents No. 1,453,593; 1,492,694; 1,506,130; 1,560,838 or 1,568,234. None of this coating however is applied to the chill plate 42 for it is this plate which is adapted toform the chilled face for the tappet and consequently which is designed to chill the metal cast against it as rapidly as possible. Before each pouring operation, however, all of these surfaces including the surface of the chill plate 42 are preferably provided with a coating of lampblack in the manner referred to in United States Patent No. 1,492,694.

. A thermo-couple 52 embedded in an end of the chill plate 42 and extending to a point directly below one of the depressions 34 is connected by leads 54 to a device 56 adapted to indicate the temperature at the point of the thermo-couple.

In operationt the mold halves 22 and 24.

are mounted in a suitable molding machine (not shown) so that the cavities in the mold halves are movable into alignment with each other so as to bring the dowel pins 32 into registration with the openings 33, and provided with suitable means for holding the halves 22 and 24 together.

The thin adherent refractory coating 50 1s of more or less permanent nature and need be renewed only at relatively long intervals, for instance, not more than once a day when the molds are used for continuous production. It may be noted that this coating 50, besides forming a heat insulating coating reducing the rate of heat trans-. fer between the metal being poured and the metal of the mold halves 22 and 24,- also serves as a means for preventing the molten metal from wearing away any sharp edges of the metal defining the mold depressions. The halves 22 and 24 having been clamped together, the various surfaces of the depressions are then coated with the lampblack previously referred to and molten metal is introduced into one end of the channel 36 where it flows down the trough 38 and successively fills the mold depressions. Preferably, only enough of such metal is introduced into the channel 36 as to fill only the depressions 34 and a portion of the depressions 35, thus effecting a saving in the amount of scrap resulting from the molding operation;

Per cent Silicon 2 Carbon 3 Manganese .06

Sulphur less than 1 Phosphorus lessthan .25

Remainder iron.

It will be apparent when the molten cast iron is poured into the mold such ironv will be insulated from direct contact with thesurfaces of the depressions 34 by the heat insulating coating 50 but will come into direct contact with the upper sur-- face of the chill plate 42 except for the relatively thin coating of lampblack previously referred to and which offers very little resistance to the transfer of heat through it. Accordingly, with the composition of iron referred to or an equivalent composition as far as the chilling characteristic thereof is concerned, that portion of the molten cast iron coming into contact with the chill plate 42 will be solidified so quickly as to prevent segregation of the carbon in the iron and the face of the'tappet will, accordingly, be formed from what is generally known as white cast iron which is of extreme hardness, while the body of the tappet is being insulated from the rapid absorption of heat therefrom, will permit a greater or lesser degree of segregation of the carbon in the metal and, accordingly, the body of the tappet will remain relatively soft. In actual operation castings are repeatedly made in the molds until the temperature of the halves 22 and 24 reaches a temperature of 400 degrees F. to 500 degrees F. or higher and until the temperature of the chill plate 42 reaches the neighborhood of about 300 degrees F. and thereafter the temperature of the chill plate-42 is maintained as near to 350 degrees F. as possible and not to exceed 400 degrees F. If the temperature raises above this value, suitable means for cooling the chill plate and/or mold may be employed, as for instance cold air directed against'the face of the mold and chill plate until the temperature falls to the'desired point. The chill plate 42 being greatly ex-.

cooling air upon separation of the halves and consequently may be normally maintained at the desired temperature by thus directing air against it when the halves are separated between casting operations. The mold halves themselves being of greater bulk than the chill plate, are not cooled to the same extent as the chill plate and consequently the temperature remains higher. Should, for any reason or another, the temperature of the chill plate 42 exceed the desired maximum temperature, it may be simply lifted out of place andreplaced by another and cooler chill plate and the operation continued uninterrupted. I have found that when the temperature of the chill plate 42 as determined by the thermo-couple 52 is maintained between 300 degrees and 400 degrees F. and preferably as closely as possible to 350 degrees E, the'surface of the tappet when formed from the composition of iron given has a Brinell hardness reading between 300and 400 or higher, corresponding to. a Rockwell reading in excess of 37, which is a satisfactory degree of hardnessto insure a long life and little wear of the face of the tappet. Also that if the, mean temperature of the mold halves 22 and 24 is kept above 400 degrees F. and upto 500' degrees F. or over, the main body portion of the tappet will be suificiently easily machinable to permit turning of its outer surface and drilling and tapping its end surface l6 for the reception of the usual adjusting screw (not shown).

It will, of course, be apparent thatwhen the molds are separated, the individual tappet castings are removed, the gates 20 are broken oil or otherwise removed, the body andend portion l6 of the tappet is machined and the face of the head l2 ground where necessary to bring its surface into the desired final condition.

In the following claims the phrase continued production-by repeatedly casting-in a mold or equivalent phrase is to be interpreted to mean such continued use of a mold in casting opera- .tions' that it does not have the' opportunity to cool to room temperature between each pouring of metal thereinto.

'1. In -the continued production of cast iron.

members having a chilled face by repeatedly casting molten cast iron of a type adapted to form white cast iron when chilled into a metallic mold having a separate chill plate, the step of artificially cooling the chill plate to maintain its average temperature' between 300 F. and 400 1". during the casting operations.

2. In the continued production of cast-- iron members-having a chilled face by repeatedly casting molten cast iron of a type adapted to form white cast iro'n'when chilled into a metallic mold having a separate chill plate, the step of maintaining the temperature of the chill plate between 300 F. and 400 F. and the temperature of the mold in excess of 400 F. during the casting operations.

3. In the continued production of cast iron members having a chilled face by repeatedly casting molten cast iron of a type adapted to. form white cast iron when chilled into a metallic mold having a separate chill plate, the steps of heating the mold to above 400 F. and the chill plate to above 300 F., and then limiting the max- 75 casting operations and replacing it with a cooler chill plate when its temperature exceeds approximately 400 F.

5. In the continued production of cast iron valve tappets from molten cast iron of' a type adapted to form white cast iron-when chilled by the use of a metallic mold having a removable uninsulated chill plate, the steps of heating the chill plate to above 300" F. by repeated casting operations and-replacing it with a cooler chill plate when its temperature exceeds approximately 400 F., and insulating the surfaces of the mold cavities other than the chill plate against the transfer of heat to the mold.

6. In the continued production of cast iron articles having a relatively soft machinable portion and a chilled portion by repeatedly casting molten cast iron, of a type adapted to form white cast iron when chilled, in a metallic mold having a separate chill plate for said chilled portion, the steps of maintaining the temperature of the mold at a sufliciently high value to prevent chilling of the surfaces of the article formed thereby, and artificially cooling said chill plate to maintain the temperature thereof sufiiciently low to insure chilling of the surface of the article formed thereby.

JOSEPH L. DOSTAL.

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