US2163753A - Method of making hot molding die plates and other castings and product thereof - Google Patents

Description

Patented June 27, 1 939 METHOD or MAKING nor MOLDING nu: m'ras mm o'maa casrmes nn raonnc'r manor Harry K, Ihrig, Milwaukee, Wis, asslgnor to Globe Steel'Tubes 00., Milwaukee, Wis., a corporation of Delaware No Drawing. Application May 25, 193i, Serial No. 144,639 I -9 Claims. (01. 22-203) which are readily .producible and avoid disad-- 3 This invention pertains to cast metal articles comprising a cast body portion having embedded therein a preformed metallic insert, and ,it is particularly applicable to articles comprising a body portion cast around a metallic tube-to-provide' a tubular passageway in the article.

In various hot molding operations'su'ch as the manufacture of gaskets and the molding of synthetic resinsfthere are used cast die plates which must be heated, say to 200 to 400 F., as by-means of a steam coil passing through the mid-section v of the plate. For the most part the coils for these purposes have been provided by drilling-the solid cast plate from the edgesto provide one or more passageways parallel with the main, or die, surfaces, the holes not-needed but unavoidable in I such production being then plugged. Such opare not wholly satisfactory'because such drilled erations are expensive, and in addition'the plates passageways necessarily provide sharp corners at the ends-,which cause substantial resistance to steam flow and accumulation of scale and corrosion products which may, and frequently do,

ultimately stop up the passageway or so insulate it that efficient heat transferis'not possible.

Attempts to make such articles by casting the body metal around tubes disposed in a mold have likewise not produced satisfactory results. A major reason for this has been inefllcient heat transfer from fluid passed through the tube. For instance, pyrometric measurement of the molding surface of die plates made in this manner has shown that the temperature at'thesurface may be as much as 30 below that of the heated fluid, such as steam, supplied to the tube.

Also, the temperature at different points on the surface of the plate is not uniform. Sectioning of such plates has shown also that-blow holes, or voids, always occur in the casting in the vicinity of the surface of the tube, and apparently the presence of these voids throughout the' structure is responsible for the poor heattransfer and non-uniformity of temperature at the die surface.

It is among the objects of this invention to provide cast articles having 'metallic. inserts ,em-' bedded therein which" are characterized by a sound structure, ease and simplicity of production, and by the possession of satisfactory physical properties.

. A particular object is to'provide cast articles provided with passageways for circulation of fluid,

such as hot molding dies, which are characterized by efllcient heat transfer between the fluid and the surface of thearticle, by acceptable uniformity of temperature over the surface, and

vantages heretofore encountered inthe art.

It is among other objects of the invention to provide a process of making articles of the type referred to which is simple, readily practiced, not i expensive, and produces articles in which the" insertis satisfactorily bonded tothe cast body of the article, and which are structurally sound.'

The invention is predicated upon my discovery that'its stated objects are attained by the'use of l preformed metallic'inserts, which are capable of alloying with silicon, and which, at least in those portions which are to be embedded in the casting, are provided with a silicon-rich surface coat-. ing. '1 have discovered that when such preformed ll inserts'having a silicon-rich surface coating are disposed in a mold and metal is cast about them,

the silicon present at the surface of the insert, is

at least incipiently fused. and eflects satisfactory bonding with the cast metal, and-that it further 20 'acts to produce a sound casting free, or substantially free, from blow holes and the like defects which have been encountered heretofore in attempting to make such articles." In consequence good heat transfer is afforded between a fluid passed through the tubeand the surface of the "article, andat the same time uniformity of surface temperature is achieved.

The silicon coating may be provided in a variety of ways, but I now prefer to provide it by silicon cementation ofthe insert to provide a siliconlzed case, most suitably. one that is rich irrsilicon.- A variety of procedures have been proposed for this purpose but I now prefer toeifect the silicon cementation in accordance with the process disclosed and claimed in my Patent No. 2,109,485, dated March 1, 1938, reissuedMay 10, 1938, aslReissuePatent No. 20,719. Y In accordance with the invention of my aforesaid application the article to be cemented is heated to a temperature above about 1500 F., desirably toflabout 1800 F., in a non-oxidizing atmosphere, and after the article is at heat it is.

contacted with a silicon-impregnating reagent formed by heating a silicon-supplying material, r such as silicon, ferrosilicon or silicon carbide, in

V contact with chlorine gas or a chloride vapor.

In the preferred practice of that invention the article to be cemented is packed in contact with the silicon-supplying. material, in finely divided condition, in .a closed container in which they are heated to the cementing temperature. When the article has reached that temperature chlorine gas is introduced, whereupon uniform impregnation of the article takes place readily and rapidiy.

By controlling the temperature used and the time of exposure, the depth of the silicon impregna tion and the concentration of silicon in the surface may be controlled according toneed.

While the article-is being heated the presence of oxidizing conditions should be avoided. This may be done by passing a current of non-oxidizing gas, such as nitrogen, hydrogen, or mixtures thereof, through the container. The same result may be achieved through the use of the solid residue resulting from a previous cementing operation. I have found also that oxidation does not occur-to a detrimental extent if the article is packed in, for example, silicon carbide in a container closed except for conduits for introducing chlorine gas and for outflow of emuent gases, whereby the use of inert gas may be-dispensed with. I For the purposes of the present invention the depth of impregnation need not be great provided the surface be rich enough in silicon to effect thedesired bonding and absence of blow holes in the cast product; With ferrous metals satisfactory depth may be had by packing-the article in silicon carbide, heating to about 1850 F., and

then passing chlorine through the container for is fused to an extent such as to insure excellent bonding'of the cast body and the insert. Also, blow holes and voids do not form in the cast body near the tubes. This maybe due to deoxidation by the silicon, but I do not limit myself to that assumption.

These cases are likewise highly resistant to conrosion, and by silicon cementing both the insideand the outside of the tube, advantage may be taken of this property to insure high resistance to corrosion by fluid media passed through the tube. In the production of cemented tubes it is desirable to rotate the tubesduring the cementing operation, particularly where both the inside.

and outside surfaces of the tubes are to be cemented. Rotation during cementation insures the production of casesof uniform thickness at both surfaces of the tubes, but the tubes should not be rotated too rapidly if thick cases are desired on the outside surface. Also, where maximum, resistance to corrosion is desired the steel should contain less than about 0.05 per cent of sulfur. v

In another embodiment of the invention of my application aforesaid the insert is heated in a container in a non-oxidizing atmosphere to a temperature as stated above, and there is then introduced into the container a reagent-gas produced by heating the silicon-supplying material in a current of chlorine or chloride vapor in a separate container. For some purposesthis embodiment is less desirable than that just described because where the cementing gas is formed in aseparate container it is necessary that the silicon-supplying material be heated to a temperature of atleast about 2300" F.

' The inserts provided with silicon-rich surfaces iri the foregoing of any other suitable.

manner are disposed in a mold and-the metal, such as iron or steel, is then cast about them. The tubes are, of course, disposed in the relation which they are to bear in the finished casting, and they may be arranged to provide nipples extending outwardly from the casting for connection to a source of fluid which is to be flowed through the tubes. 11? the tubes do not'protrude the connections may be made by toppin and threading the, openings in the casting, or in other manners known in the art.

I As exemplifying the benefits which flow from the present invention, reference may be made to tests of hot molding dies produced in accordance with it. In one test inch iron pipe size seamless steel tubes, threaded on both ends, were treated in accordance with the process disclosed in my aforesaid application by heating them in an electric rotating furnace with silicon carbide ,to a temperature of 1815 F. When the pipes reached that temperature chlorine was passed through the furnace for two and one-half hours,

producing a case about 0.02 inch thick. Two of' these tubes, 12 inches long, were then supported in a mold productive of a plate 2 inches by 4 inches by 9 inches, with.the threaded ends of the tubes disposed to protrude from the casting, and cast iron at'about 2700 Rwaspoured into the molds to produce the castings. Two such castings were connected by couplings threaded to the endsof the tubes, and steam at 360 F. was then introduced into one tube to flow through the tubes of both castings, a steam tray being connected to the eint end. Readings taken with a pyrometer at the plate surfaceshowed a maximum deviation of 3 to 4 F. from the steam temperature, and the temperature over the entire surface was satisfactorily uniform. The castings were then cut open and found to be free from blow holes in the vicinity of the tube surfaces. Microscopic examination of polished sections showed the siliconized case to have been] shape, inserts extending wholly or partially through the casting, andthe like. Also, various modes of forming coils, using tubes, are possible, as by'using a plurality of tubes protruding from the casting and which are connected by suitable fittings, or by forming a coil from tubes and fittings and casting metal entirely around it.

And while the invention has been described with. particular reference to ferrous metals, it will be understood that it is applicable generally to metals capable of cementation or alloying with silicon. V

According to the provisions of the patent statutes l have explained 'the principle and method'of construction of my invention and have 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 thanasspeciflcally described.

I'claimyl 1-. That method ofmaking a ferrous-metal casting provided with a ferrous metal insert,

comprising providing a preformed ferrous metal insert member with an integral silicon-rich cemented case, placing said member in a mold in such position as to have said silicon-rial; case surrounded by metal cast, therein, and casting ferrous meta! into the mold, said silicon-rich case eifecting bonding between said insert member and said cast metal, and the casting being substantially free from blowholes in the vicinity of said insert member.

2. That method of making a ferrous metal casting provided with a ferrous metal insert, comprising providing a preformed ferrous .metal insert member with an integral silicon-rich cemented case at least in those portions which'are to' lie within the casting, placing said member in' a mold in such position as to have said siliconrich case surrounded by'metal cast therein, and casting into the mold to surround said preformed and cased member ferrous metal heated to a temperature above the melting point of said silicon-rich case, said case effecting bonding between said insert member and said cast metal, and the castingbeing substantially free from blowholes in the vicinity of said insert member.

3. That method of making a ferrous metal casting provided with a tubular passageway therethrough, comprisingLproviding a ferrous metal tube with anintegrai silicon-rich cemented case on the portions of the tube which are to lie within the casting, disposing the cased tube in a mold so as to have said silicon-rich case surrounded by'metal cast therein, and casting molten ferrous metal into the mold at a temperature above the melting point of said siliconrich case, said silicon-rich case effecting bonding between said tube and said cast metal, the casting being substantially free from blowholes in the vicinity of said tube, and the tube forming a tubular passageway through the-casting.

4. A method according to claim 3, said case containing about 14, per cent of silicon.

5. A cast ferrous metal article comprising a cast ferrous metal body portion-and a preformed ferrous metal insert embedded in and surrounded by said cast portion and having a silicon-rich surface formed integrally therewith and bonding said cast portion to said insert, and the casting being substantially free from blowholes in the vicinity of said silicon-rich surface.

.6. A cast ferrous metal article according to claim 5, said insert being a wrought. ferrous metal tube. -7. A cast ferrous metal article comprising a cast body portion and a wrought ferrous metal tube embeddedtherein and'surrounded thereby,

said tube having its inner and outer surfaces pro-- vided with an integrally formed silicon-rich cemented case which bonds said cast portion to the outer surface of the tube, and the casting being substantially free from blowholes in the vicinity of said outer surface.

cast ferrous metal body portion having at least one wrought ferrous metal tube embedded therein and surrounded thereby, the outer surface of said tube having an integrally formed siliconrich cemented case bonding the tube to said cast body portion, and the casting being substantially free from blowholes in the vicinity of said miter 1 20 8. A hot molding die or the like comprising it