US3044164A - Process for making metal plates provided with drillings - Google Patents

Description

July 17, 1962 H. BAUER 3,044,164

PROCESS FOR MAKING METAL PLATES PROVIDED WITH DRILLINGS Filed March 11, 1958 F/g. J. Con/7210005 (Era/[17 i I000 mm Rows-WM G'IUp/li/E Cora;

jm/eflton' HEINRICH BAUER BYPLM/L AT TOR NEYS United States Patent 3,044,164 PRGCESS FOR MAKING METAL PLATES PROVIDED WITH DRILLINGS Heinrich Bauer, Hannover, Germany, assignor to Vereinigte Leichtmetall-Werke, Gesellschaft mlt beschriinkter Haftung, Bonn, Germany Filed Mar. 11, 1958, Ser. No. 720,584 6 Claims. (Cl. 29-528) This invention relates to a method of making metal sheet articles having passageways.

In many industries such as, for instance, the plastics industry, there is a need for metal sheets which have a great number of passageways or channels through which a heating medium or .a coolant can be caused to flow. If such metal articles can be cast without subsequently rolling them out, the channels may be provided by casting a plurality of tubes into the sheet, the tubes being preferably ofthe same metal as the sheet proper. Difliculties arise where the cast perforated block must be rolled subsequently, for instance by hot rolling, to obtain thinner.

sheets. In this latter case there is always the danger that the passageways will become partially or entirely closed during the rolling step.

The known method of casting a plurality of tubes into a cast metal block also suffers from another drawback even though no subsequent rolling is involved. When a great number of channels have to be provided in the cast block, the tubes providing for these channels may have to be placed very close to each other in the casting mold, and it may either occur that the tubes touch each other at certain points, or that the interspaces between them become so narrow, that the strength of the wall portions separating adjacent channels becomes much decreased, or that failures occur due to lack of the cast metal to fill the interstices completely, so that hollow spaces and cross linking openings between channels are formed.

In view of these drawbacks, another known method was devised, the so-called tube-in-strip process which is described for instance in Metal Industry of March 30, 1956, pages 253-254. This known method is suitable for manufacturing channeled articles of a thickness up to 2 millimeters and comprises the casting of rods or bars of a brittle, friable material inert relative to the cast metal, into the billets destined for subsequent rolling.

These bars or rods of friable material are usually of elongated rectangular cross section and are embedded in the billet in such a manner that the broader sides of the rectangle forming the cross section are parallel to the fiat top and bottom surfaces of the billet, which are to be contacted by the rolls of a rolling mill in the subsequent rolling treatment. During the rolling step, the ingot is rolled down to the desired reduced diameter, which is usually in the order of 0.5 to l millimeter (mm.) and at the most about 2 millimeters. By this treatment,,the rods or bars of friable material are rolled out to form very thin separating layers in the interior of the resulting sheet. When a billet of 200 millimeters thickness is rolled down to a thickness of 2 millimeters, the deformation of a castin graphite bar is very considerable and leads to a cross section of the latter taken at right angle to the direction of rolling, which shows a considerable width parallel to the rolling plane, but is very thin in the direction perpenducular to that plane. The bar is pulverized and can be easily blown out of the sheet, during the subsequent blowing step.

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order to blow the channels in a sheet having a thickness of 1.5 mm., or 0.75 mm. thickness of the walls of the channels to be formed, a blowing pressure of from 150 to 200 atmospheres above normal is required. The shape of the cross sectional area of the channels depends on the ductility of the sheet metal and while some permit the formation of tubes of circular cross sections, others only permit to form tubes of elliptic cross section. As a further drawback, the distance between adjacent tubes in the blown sheet must be at least about 5 mm. in order to provide sufiicient welding surface for absorbing the high expanding pressures.

Yet another drawback of this known method must be seen in the fact that the resulting finished or semifinished article cannot have two smooth surfaces on opposite sides, since one of these surfaces will always be corrugated due to that side having been blown up in the region of the channels.

It is, therefore, an object of my invention to provide a method for making metal sheet articles having passageways, and in particular a number of passageways located close to each other in a metal sheet of relative thickness compared with the distance between adjacent passageways and/or their diameter, which thickness should be of at least above 2 mm. .and preferably above 4 mm.

It is a further object of my-invention to provide a method for making metal sheet articles having'passageways of the above-described nature, and which metal articles have two even, flat main sheetsurfaces opposite each other, which surfaces are free from corrugations.

It is yet another object of my invention to provide a method for the aforesaid purposes, in which the resulting separating walls between adjacent channels in the perforated metal sheet possess uniform texture .and are free i It is a drawback of this known method that the maxi- I from holes or failures in the mechanical properties of the cast material.

These objects are attained and the drawbacks of the known art avoided by the method according to my invention which comprises, in combination, the basic steps of (a) embedding, in a known manner, a number of cores, or at least one core, in a cast ingot, which core or cores need not be of a friable material, in contrast to the cores used in the blowing process, but must not be of greater, and should be preferably of less mechanical resistance than the cast material itself, and (b) drilling holes through the cast article in such a manner than the drill having a suitable diameter follows the softer core material through the cast article, and is .thus guided through the same. a

In a preferred mode of operation, where the thickness of the cast ingot is thicker than the desired thickness of the final finished or semi-finished article, a step of hot rolling the ingot containing the cores, by passing it through a rolling mill in the same direction as the cores in the ingot extend, and thereby reduce its diameter to the desired thickness, can be interposed between the casting and the drilling step.

In this manner, perforated sheet metal articles in which the channels extend parallel to the broad surfaces of the sheet, can be produced of any desired thickness, beyond that permissible if the passageways are to be formed in the sheet by the known blowing methods. Thus, billets for rolling having a thickness of 350 mm. and rounds of a diameter of 800 mm. can be produced without difficulty, and be rolled down to any desired reduced diameter, down to a limit of 2 nun. and preferably 4 mm., which thickness will permit drilling of reasonably long channels. Such channels could not be bored except with great difiiculty andloss of working time from the full material of the metal plate, since due to lack of cooling in the interior of the long borehole, the danger of overheating and breaking of the drill head is excessive. Furcore material guiding the drill head through the metal plate is completely removed from the latter during the drilling step.

It is important that the cores cast into the metal ingot are not of a material harder than the sheet metal itself, since then the drill will attempt to deviate from the course prescribed by the core, and try to pass through the softer sheet metal. As, on the contrary, the core material to be used according to my invention is softer than the surrounding metal, it forces the drill to follow the path prescribed by the core, through the sheet metal block, regardless of how closely adjacent the nearest core or cores are located. It will also be understood that the diameter of the drill head will preferably be larger than the diameter of the core. This permits to provide for somewhat smaller core diameters, and correspondingly larger distances between adjacent cores than it is later intendd to leave for the thickness of the walls intermediate two adjacent bore holes. 7 in the casting mold as closely together as 2 mm., without the danger of incomplete filling of the interspaces by the molten metal. In this manner the bond tubes can ultimately be close to each other and relatively thin interposed separating walls of uniformly cast texture can be left standing between adjacent relatively large drilled The cores may be placed holes, while avoiding 'all the difficulties encountered in the present art of rupturing such thin walls during the drilling of channels through the sheet.

As materials for the core or'cores to be cast into the ingot, mold sand, graphite, glass fiber material-s, asbestos,

slag-wool and the like haverbeen found to give very satisfactory results. It will be easily understood that metals or alloys could also be used under certain circumstances, as long as they remain inert during the casting of the sheet metal around such metallic cores, i.e., as long as they do not melt or form an alloyed layer around the core centers, which alloyed layer would be harder than the sheet metal itself.

The bars or rods of core material are preferably of a cross sectional shape which will lead, in the rolled plate or sheet, to a regular, for instance a circular or square cross section so as to facilitate the guidance of the drill head. It will, of course, be understood that this is no critical requirement. The core bars are preferably of rectangular cross section, having a Wider and a narrower dimension, and are so placed in the ingot mold that the narrower side of their rectangular cross section is parallel to the rolling plane, and the wider side extends perpendicularly thereto, i.e., these bars are embedded in the billet turned about an angle of 90 compared with corresponding core bars in the tube-in-st-rip process. Conse quently,the deformation of the bars by the rolling step is not to a thin and wide strip of material, but an approximately square cross sectional shape of the bars after rolling is obtained, due also to the fact that the billet according to the invention does not have to be rolled down to the narrow dimension of above 2 As has been stated before, it is immaterial whether the core itself is broken up, or preserves a more coherent nature. Where graphite cores are used, the graphite itself has a very desirable lubricating effect on the drill head during the drilling of the channels along the path determined by the graphite cores.

Oneadvantageous method of casting; the sheet metal about the cores is the continuous casting process described, for instance, in the patent application of Roth et a1. Serial No. 704,103, filed December 20, 1957, and assigned to the same assignee as the present application.

Considerable advantages are obtained when the metho according to my invention is applied to making metal sheets having a plurality of passageways, where the thickness of the metal sheet is such that it can be directly produced from the cast block, for instance by scrubbing the which it is guided by the softer core material.

surface of the latter, and without a subsequent rolling. In this case, passageways may be drilled into the block following the cores embedded therein, which passageways are of particularly large diameter and have separating walls of particular thinness, which far exceeds anything that can be produced by the known methods. in particular, the completely uniform texture of the regions of metal sheet constituting the separating walls between adjacent passageways leads to outstanding mechanical resis-tance of the final article.

instead of being used for the production of sheet metal, the method according to my invention may, of course, be equally applied to the manufacture of long bars or rods, having longitudinally extending channels therethrough, and is generally applicable to advantage, wherever a long drill hole has to be drilled through a thin-walled material, and where an even slight deviation of the drill head from its course through the mother metal may lead to tearing of the wall of the drill hole.

On the other hand, a slight deformation of the cores embedded in the sheet or bar of mother metal, caused, for instance, when a rolling step is required to attain the desired sheet thickness, is not as critical as it would be, for instance, in the known passage-blowing methods, since the passageway cross section ultimately provided in the sheet, depends in the first order on the diameter of the drill head used, and if the latter is chosen sutliciently larger than the core diameter, slight deformations in the core throughout the sheet, will be automatically straightened out by the drill cutting more to one side of the metal surrounding the core, and at another instance a little more to anoher side, thus providing a perfectly straight drill hole, while always following the general path along Prior or following the drilling step, the articles of manufacture produced according to the invention may be subjected to a heat treatment, such as, for instance an annealing step at 500 C. in the case of aluminum, and a subsequent quenching as Well as a hot or cold storage in order to age the resulting articles.

Core-containing ingots can be produced and drillholes applied thereto according to this invention from each of the metals selected from the group consisting of those metals which are stable in air, have atomic weights between 9 and 66 and pertain to groups (column) I to IV of the periodic table of Mendeleyev, as well as alloys the major portion of which consists of at least one of these metals. The metals belonging to this category are copper (in group I of the periodic table), beryllium, magnesium and zinc (in group II), aluminum and scandium (in group III), and titanium (in group IV).

The process according to the invention is suited particularly with aluminum metal, aluminum alloys, magnesium metal, magnesium alloys, copper and copper alloys, which are particularly desirable in certain cases in view of good thermal conductivity, and also other related non-iron metals. The most suitable material is selected in each case depending upon the desired thermal conductivity as well as the resistance to corrosion of the same, which may vary with the purposes for which the article is to be used. Thus copper will be preferred in many instances where heat exchanger or refrigerator elements are to be produced. It is particularly when working copper that the new process reveals its decisive advantages over those known in the art.

The method according to the invention is limited to metal sheets of a minimum thickness of above 2 mm. and preferably 4 mm., which still permits the use of a drill entering its marginal end surface, where the drill will have to be introduced with its point being led against the end surface of a core.

The drills used are conventional special long-hole drills for non-ferrous metals.

A particular advantage of the method according to my invention resides in the fact that, contrary to the known method of blowing passageways through blocks or sheets, both large, opposite side surfaces of the sheet remain even and flat, i.e., they are not corrugated by the outer walls of channels therethrough being raised during the blowing step. Longitudinally perforated plates produced according to the invention are, therefore, particularly suited as walls in heated molds for the transfer of a heating agent flowing through the channels of the perforated sheet.

If, .on the other hand, the body to be heated has an uneven surface, the fiat side surface or surfaces of the perforated sheet can be easily adapted to the shape of the body to be heated, by correspondingly shaping the side surface to be brought into contact therewith, through milling, planing or similar working.

, The ratio D/L of the diameter D of a drill hole to the length L of the article in which the passageway is to be drilled, had to be larger than one to forty in the known processes, if the article was made of aluminum, or an aluminum alloy, and not smaller than one to forty, if the article was made of copper.

Only thanks to the process according to the invention is it now possible to reduce articles in which the ratio D/L is smaller than one to forty if the article is made of aluminum and its alloys and smaller than one to forty if the article is made of copper.

The invention will be still better understood from a number of examples explaining the same, without being intended to limit the scope of the invention, which examples will be described hereinafter in connection with the accompanying drawing in which the steps of the method according to my invention are illustrated in the following manner:

FIGURE 1 shows in perspective View a continuously cast ingot containing cores cast therein according to the first step of my invention, described in Example I given hereinafter, which step is known per se;

"FIGURE 2a shows a metal sheet obtained by hot rolling the ingot shown in FIGURE 1;

FIGURE 2b shows in perspective, a portion of the same rolled down sheet and a few of the cores contained therein, on a ten times larger scale;

'FIGURE 3 shows the same portion of a metal sheet as FIGURE 2b, after passageways have been drilled therethrough according to a subsequent step of my invention.

Example I Longitudinally perforated rectangular plates to be used as heat transfer plates in heated plastics molds are to be manufactured with the following dimensions: 2000 millimeters (mm.) long, 800 mm. wide, and 20 mm. thick. Twenty-five passageways for the heating medium, each having a diameter of mm. are to be provided in the plates extending in parallel with the 2000 mm. long edges.

Step I (FIGURE 1 ).A continuous cast ingot is produced from aluminum metal, for instance according to the method described by Roth et al., supra, in such a manner that the ingot has a length of 1000 mm., a width of 850 mm. and a thickness of 220 mm., while 25 graphite rods having rectangular cross-sectional dimensions of 9 x 42 mm. are embedded therein during the casting step.

The opposed large side surfaces S of the cast ingot are then milled down with milling cutters M by about 10 mm. and the resulting milled ingot is rolled down in the direction indicated by arrows R in a hot rolling mill, according to step II (FIGURES 2a and 2b).

The resulting hot rolled plates shows the graphite cores now having dimensions of 9 X 4 mm. in its end surface E, and has, after cutting, a length of 2000 mm., a width, after trimming the marginal edges, of 800 mm., and the desired thickness of 20 mm.

Step III (FIGURE 3).The desired passageways of 10 mm. diameter are now drilled through the sheet in the direction of the graphite cores extending therethrough, with the latter guiding the drill heads. After 6 the mold is 'built from a plurality of such plates, the passageways are used for alternately heating and cooling the mold walls, by passing heating or cooling agents therethrough.

Example II A rectangular plastic body is to be produced in a heatable pressure mold, which article is to have a flat, even top surface, while its bottom surface is to be provided with a network pattern of longitudinal and transverse ribs. Consequently, a top and bottom mold wall plate having passageways therein for the flow of heating fluid therethrough, are to be produced, each having the following dimensions: 700 mm. long, 500 mm. wide, mm. thick. The passageways are to extend therethrough in longitudinal direction (parallel to the 700 mm. extension) at a distance of 25 mm. from each other, each passageway having a diameter of 22 mm.

According to step I (FIGURE 1, but with difierent dimensions from those indicated in the drawing) of the method according to the invention, two blocks having dimensions of 710 x 510 x mm. are cast from duralumin, with cylindrical rods pressed of form sand material poor in silica, and having a diameter 20 mm. being embedded inthe cast blocks as drill-guiding cores. The

embedded form sand cores.

Example III Longitudinally perforated rectangular plates which are to be used as internally heatable wall portions of a plastics casting mold are to be produced from the aluminum alloy AlMgSi in a size of 2000 by 800 by 20 mm. A total of 32 passageways of circular cross section extend through the plate parallel to the'2000 mm. edges thereof, and will serve for the flow of a hot fluid therethrough. The internal diameter of each passage is to be 10* mm. and the distance between adjacent passageways 20 mm.

It would be extremely difficult and time consuming to attempt drilling such passageways into a full metal block of the above dimensions. Due to the unsatisfactory cooling in the drill hole mentioned hereinbefore, the drill head would tend to become blunt rapidly and might deviate and break easily. Frequent resharpening of the drill head would also be required.

Therefore, the above described semi-finished article is produced in the following manner:

(1) 32 graphite bars having a length of 1300 mm. and a rectangular cross section of 10 x 60 mm. are placed in a mold aligned in a row with their 60 mm. transverse axes in parallel, and molten AlMgSi alloy is cast about the bars so as to form a rectangular billet having the di mensions of 1500 x 1020 x 225 mm., in which the graphite bars extend parallel to the 1500 mm. edges. The large 1500 x1020 rnrn. side surfaces are then milled oif with a milling cutter by about 10 mm.

(2) The billet is then hot rolled by passing it in the direction in which the graphite bars extend, through a rolling mill, until the resulting light metal plate has a thickness of 20 mm. The graphite bars in the plate have been broken up, due to their having less ductility than the aluminum alloy, but remain entirely in the plate and have assumed a cross section of 10 x 6 mm., similar to that shown in FIGURE 2b of the drawings.

It is of great importance for the subsequent drilling step that the graphite bars remain in the plate, and are not finely pulverized so as to fall out of the plate, as would be the case in the tube-in-strip process.

(3) The plate is trimmed to the desired size, and the graphite bars are then drilled out of the plate by using a drill of mm. diameter, whereby passageways of the same diameter are provided through the plate. 7 Drilling is a very easy operation, since the major portion of the material to be removed from the drill hole consists of graphite which guidesand simultaneously lubricates the drill. 7

No drill water or coolant is therefore required, and the. .Wear of the drill itself is negligible.

The drilled plate is then annealed above500 and subsequently quenched. p The finished plates can be used in the construction of the plastics mold. V V Example IV Heatable pressure plates of copper metal having a rectan-gular shape of 1500 x 800' X 40 mm. and being provided with 40 passageways therethrough which extend parallel to the 1500 mm. edges and each having a diameter of mm. are to be manufactured in order to construct a device for pressing plastic plates.

It is impossible to drill holes having a length of 1500 mm. and a diameter of 15 mm. through a solid copper plate, since a drill of such length would break oil in .the drill hole.

Therefore, 40 graphite rods, each having a length of 1000 mm. and an elliptic cross section with a longer elliptic axis of 35 and a shorter one of 15 mm., are incorporated, for instance according to' the process de- Cit stantially half as long as to as long as the other diameter in the direction normal to said one diameter, (b) drilling passageways through said body following the path of said core, thereby simultaneously removing the material of said core and removing by said drilling also metal from the walls of said passageways, thereby forming passageways being circular in cross-section with a diameter larger than the largest diameter of said core.

2. A process for making a metal article, as described in claim 1, further comprising the step of hot rolling the cast body of the article diameter by passing the same through a rolling mill in the direction in which said core scribed in the patent application of Roth et a1. supra, in a V '2 continuously cast copper ingot having a dimension of 7 1 000 x 850 x 100m. in such a manner that they extend in parallel with the 1000 mm. axis of the ingot and are aligned parallel to the 850 mm. axis with their longer elliptic axis parallel to each other and to the 100 min.

' edges of'the ingot.

The ingotblock is then milled down on all sides by about 5 preparatory to rolling it in the same manner 1 as in the preceding example down to a final thickness of 40, which corresponds to a reduction of thicknessof The elliptic graphite bars are thereby deformed to assume a circular cross section of 15 mm. diameter. The bars can be drilled out easily with a 15 mm. drill head, after the plates have been trimmed to accurate size.

It will be understood that while there have been given herein certain specific'examples of the practice of this invention, it is not intended thereby to have this invention limited toor circumscribed by the specific details of materials, proportions or conditions herein specified, in View of the fact that this invention may be modified according to individual preference or conditions without necessarily departing from the spirit of this disclosure and the scope V of the appended claims.

What is claimed is:

1. A process for making a metal article having passageways therethrough which extend in the lengthwise plane in which the'article extends, comprising the steps of (a) casting the body of the article about at least one core of a material of a resistance to drilling of less than that of the metal forming the article so as to embody the core.

in said body with at least one end of each core accessible from the outside, and, said core having one diameter subextends and thereby reducing the thickness of the body. 3. A process according to claim 1, wherein the core material, is a known core-forming material selected from the group'consisting of form sand, graphite, glass fiber material, slag wool or asbestos.

4. A process as described in claim 1, wherein the drilling step is preceded by an annealing and subsequent quenching step.

5. A process as described in claim 1, 'wherein the drill- I ing step is followed by an annealing and subsequent quenching step.

6. A process for making a metalplate having a plurality of parallel passageways through the plate in a direction perpendicular to the dimension of the plate, comprising the steps of (a) casting metal about a plurality of graphite bars each having an elongated cross section and placed in alignment with each other with the longer axes of said bar cross sections parallel with each other so as to obtain a metal billet embedding said bars therein, said bars having one diameter being substantially half as long as to as long as the other diameter in the directionnormal to said onediameter; (b) hot rolling said billet by passing the same through a rolling mill in the direction in which said bars extend and in a plane transverse to the direction in which said longer axes of said bar cross sections extend, so as to obtain a plate of determined thickness above 2 mm, and containing the bars deformed to an approximately regular cross sect-ion, and (c) drilling passageways through said plate along the paths provided therein by said bars thereby simultaneously removing said graphite and removing by said drilling also metal from the walls of said v passageways, whereby passageways circular in cross-section with a diameter larger than the largest diameter of said core are being formed.

References Cited in the file of this patent UNITED STATES PATENTS

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