US2636849A - Method of electroforming gun barrels and liners - Google Patents

Description

April 28, 1953 A. BRENNER 2,636,349

METHOD OF ELECTROF'ORMING GUN BARREL-S AND LINERS Filed Dec. 13, 1946 Patented Apr. 28, 1953 UNITED STATES ATENT OFFICE METHOD OF IELECTROFORMENG GUN BARRELS ANU LINERS Abner Brenner, Ghevy Chase, Mela, assignor to the United States of rimerica as represented by the Secretary of. War.-

d Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes. without the payment. of any royalty thereon.

' My invention. relates to. methods of making. gun barrels, barrel liners and the like; and it has particular reference to techniques -for manufacturing rifled gun barrels and liners from certain relatively hardmetals.

Broadly stated, a. principal. object. of my inv'ention is to provide a. method for making rifledbore. gun barrels and liners out of metals, such as, cobalt, tungsten, molybdenum and alloys thereci, winch are. too hard. to machine or cast by the usual. commercial processes.

A more specific object: of my invention is to provide a method, for making rifled gun bores without having to storm. the ri-fiings by conventional machining, swaging or breaching operations.

' Another object isto simplify the manufacture. of. gun barrels and liners whose walls have variously designed tapers and whose bores have coniplexrifiings.

A further object is. to reduce the time and effort needed to. make such gunv barrels and liners.

A still. further object is to improve the economy of gun manufacture.

The exact manner in which I accomplish these objects will become evident as this disclosure proceeds. Briefly stated, however, the process. consists of electrol'orming. gun barrels or liners by plating a. suital'ole metal. or alloy upon a master. This master is. a precision-made negative of the lands and grooves comprising the desired bore. rifiings of a gun barrel or liner.

" The plating upon the master carried on until a sheath-tn positive is. built up therearound to a suitable thickness. This positive, which is actually an electroiormed gun barrel or barrel-liner consists, oi a tube whose bore faithfully reproduces the lands. and grooves of the negative or master. When completely formed. the newly formed. barrel or liner is then removed from the master and machined on its outer surface. to its required outside diameter. The master is used over and over again in repeating the process just outlined.

A preferred form of the master used in practicing my invention and the product which can obtained thereby may be seen by reference to the drawings: wherein:

1 illustrates in longitudinal section a typical master or steel negative of the required rifled gun bore, upon which a gun barrel comsec. 266) 2 prised of two different metallic layers has been electrotormed, together with various fittings used in the plating process;

. Fig. 2- is a cross sectional view taken from line 2'2. of the Fig. l rifled master without showing, the electroplated metal coatings included in the Fig. 1 illustration;

3 shows the Fig. 2 master after it has been. electroplated first with a thin layer of cop per, then a thicker layer of lead. and finally a flash coating of copper;

Fig. 4 depicts the. result of electroplating a layer of hardenable gun-metal. upon the previously copper and lead plated master shown in. Fig. 3;.

Fig. 5 repeats the View of. Fig. l except that the exterior of the hardenable. gun-metal layer has been ground to provide a smooth surface which is necessary in cases where a gun barrel liner is being. made. The thus ground,v plated master is also a prerequisite in cases where a. complete gun barrel is produced by this invention as, will be evident from the next drawing;

Fig. 6 shows the Fig. 5 product upon whose hardenable metal layer has. been electroplated a layer of softer and less. expensive metal to. iorm a complete, rifled gun barrel;

Fig. l shows the complete electroiormed gun barrel of Fig; 6 from whose bore the master has been extracted; and

Fig. 3 shows a master similar to that of Fig. 2, etc, but made of metal other than steel, the external surface thereof being coated. with an electroplated layer of lead.

The art of gun barrel. and gun. liner manufac ture has undergone successive improvements designed to speed up and reduce the costs of their manufacture. Thus, for example, delicate machining of gun bore riflings ilands and grooves) has given way to swaging or broaehing operations in making the barrels of many small arms weapons and barrel-liners for larger caliber guns. At the same. time, the concomitant metallurgical improvcrnents which have been made for the purpose oi" increasing the resistance of the gun barrels or liners to erosion and corrosion, have likewise increased the hardness. of the gun metals to the point where machining or breaching, operations are no longer feasible. In fact, these metals are so hard that they are not. capable of being put to practical use by employing conven tional. casting methods.

Thus, the problem has been to develop a method whereby gun barrels and liners can be ecohomically and satisfactorily mass-produced from the very hard, corrosion and erosion resisting metals now known to be most useful in gun manufacture. Examples of such metals are cobalt, tungsten, chromium, molybdenum and various alloyed combinations thereof.

[is earlier mentioned, I have invented a method whereby rifled gun barrels and liners can be made from the aforementioned hard or hardenable metals without resorting to any difdcult machining, broaching or casting operations. This method is fast, very economical and capable of producing barrels and liners with excellent gun bore rifiings (such as are represented by I4 in Fig. 7), as the following description of my method will make clear.

To begin with, I make a master II or negative mold of the bore of the sun which is to be manufactured. This master II may take the form of a cylinder or rod whose outer wall is shaped exactly like the interior bore of the gun being made, thus forming an exact negative counterpart having negative riflings to (see Figs. 1-2) of the desired guns bore rii'iings I 4 (see Fig. 7).

In making master II, I preferably utilize a steel rod, machining the necessary negative rifiings I5 (see Figs. 1-2) on the rods outer wall. However, other methods and metals may be used. For example, the master can be made by casting a low melting alloy, such as babbit metal, into a mold. Still another technique is to cast or plate a soft metal such as lead or babbit metal around a steel rod, and then provide the necessary negative lands and grooves thereon by drawing the thus coated rod through an appropriate die. Regardless which method is used for making this master, and notwithstanding the complexity of the required gun bores rifiings and wall taper, the job of making one such master by external machining, etc., is obviously much simpler than the job of making numerous gun barrels or liners whose bores require individual internal machining or other operations.

Having thus obtained the master I I (see Figs. 1 to 7), the actual process of electroforming rifled gun barrels or layers is now capable of being carried out. The first step is to attach an extractor I! (see Fig. 1) to the master. This attachment may be made by threaded connection (not shown) or by any other convenient means. In fact, it is possible and may even be preferable to make the extractor a continuous unit of the s master.

The next step is to carefully polish the master to remove burrs or other surface imperfections. This is important because those imperfections would cause nodules in the gun barrel or liner that is subsequently plated upon the master, or even prevent the masters easy removal from the resultant electroformed product.

The master is then prepared for the electroforming operations to follow by attaching at its free end (i. e., not the end to which the extractor I1 is attached) a plastic cap 26 (see Fig. 1). This cap 26 may be designed so that it can be pressfitted onto the master and act as a mask" to prevent metallic electrodeposition beyond a certain desired area on the master. Obviously, however, any other means of attaching this plastic cap or in fact any other conventional type of masking device may be used for this purpose.

On the other end of the master, namely, that to which the extractor I1 is connected, another masking device such as the plastic cap 21 shown in Fig. 1 should be attached. One convenient way of installing cap 21 is to slidably remove the handle bar 28 from the opening 29 which extends Lil transversely through extractor I1, slip the plastic cap over the extractor into the illustrated snug fitting or press-fitted relationship therewith, after which the handle 28 may be returned to the position in the extractor which Fig. 1 shows.

The master to be electroplated having thus been properly protected so that the actual plating operations will produce the rifled barrel or liner of desired dimensions, and also so that the extractor I! will not become plated with the metallic coatings, the actual electroforming steps can be begun.

When the master II is made of steel, a preferable procedure is then to apply thereon a copper coating 23 about 0.0005 inch thick (see Figs. 3-4-56), from a cyanide bath. Note: Use of such a copper coating, while optional, is desirable as an added precaution against corrosion. Whether or not this copper coating is applied, the next step is to electroplate an approximately 0.0003 inch coating of lead 24 (see Figs. 1-3-45-6) or other low melting point metal. If a non-corrosive metal such as stainless steel or non-ferrous metal is used for the master there is no need for a first coating 23 of copper and, instead, the lead coating 24 is applied directly thereon as shown in Fig. 8.

As will later become apparent, the product being electroformed by my process is removable without damage from the master because this lead envelope 24 (which coats the master I I Figs. 34-5-6) can be melted at a temperature considerably lower than that which would have any effeet on the master or the product electroformed therearound. The reason for using lead, in addition to its having a relatively low melting point, is that lead does not readily diffuse into the steel or copper of the master. If this should happen, it would prevent the electroformed product (barrel I3) from being slipped off the master.

Other metals, for example cadmium, could be used in place of lead. Care must be taken, however, to employ a metal which will not alloy (as does tin) with the metals it comes into contact with, as this would cause a bond between master I I and the electroformed product that would make their later separation difficult.

At this point, the lead coated master II is polished by any desired means to provide a smooth, bright surface. A preferred technique is electropolishing, and a suitable material for use in that process is a mixture of acetic anhydride and perchloric acid. After polishing the leaded surface, a flash or thin coating 25 of copper from a cyanide bath may be utilized to assure that the outside wall surface of the master II is perfectly clear and smooth preparatory to plating the desired gun barrel or liner thereon. At this stage, the master II appears as illustrated in Figs. 3-4-5-6.

The thus polished master II, optionally provided with a copper coating 25, is then placed in an electrolytic bath containing in solution the salts of the metals from which the gun barrels or liners are to be electroformed. The choice of metals from which to make the gun barrels or liners may vary depending on the requirements of the user. Examples, as earlier mentioned, of the more desirable hardenable metals which may be used include cobalt, cobalt-tungsten alloy, cobalt-molybdenum alloy, etc. The temperature of the electrolytic bath should always be somewhat below the melting point asses-4e The entire. gun: barrel: or." liner; may then; be:

plated with the; chosen metal about the master ll untilv the necessary wall thickness: of the finished product is attained. Or, preferred, the plating, with the special hardenable metal may be stopped after a wall thickness is attained (such as that of the layer represented. by 28 in Figs, -i--5-6-7 which is suliicicnt to house the lands and grooves of. the final. productis bore. (This particular thickness will, of course, vary with the riiiing requirements. of the individual weapon part being made; eg., it would be about 9.0; inch in the military type caliber .50 gun.) The master, with its partially formed barrel or liner plated therearouncl, may then be trans-- ferred to another bath containing a cheaper, more abundant metal, such. as iron, and the plating process resumed until. the barrel or liner acquires a further layer such as is represented. by M in Figs- 6-7, and the barrel is thus built to its required total cross-sectional diameter.

In making gun barrels or liners of such composite electroplated coatings, caution must. be observedin the selection of metals. because of a. possibility that cracking will occur when the product is later annealed, due to the differences in the various coefiici'ents or expansion- For example, I have found that a layer of nickel, plated from a strong nickel chloride bath, could.

not be used over a cobalt or a cobalt-tungsten.

all-oy'fo'r this reason. On the other hand, I have found that a good combination for such com-- posits coatings consists of a cobaltdungsten inner lining with the balance of. the electroformed product made up of either cobalt or iron.

as an extra added precaution in. a strain-free final product, it has been found prelerable to grind the outside wall surface of the barrel orliner'being' electrof'ormed after a coating several hundredths of an inch thick been de-' posited on the master H (compare unground product of Fig. l with ground product shown in Fig. 5). This procedure is helpful because the metal which plates on the master has a tendency to form a pattern duplicating the masters lands and grooves (see- Fig. i). Were the contours of those lands and grooves permitted to be thus "transmittcd throughout. the entire electroformed product, lines of weaknes between the lands and grooves would result; Grinding to eliminate the contours or pattern of the rifiings (see Fig. 5) prevents this occurrence.

When the: electroformed sheath or envelope (barrel. It in the drawings) has been plated to a. suificient thickness to meet the requirements of the desired gun barrel or barrel liner (as in Fig. 6), master H is removed therefrom (resulting in the product shown by Fig. 7). This. is done by heating the assembly to about 401') C. to melt and eliminate the lead coating it, the master M then being easily extracted from the electroformed barrel [3 with the aid of the earlier described extractor IL Preferably}. prior to so heating the assembly, the handle 28 should be slidably removed from extractor ii, and plastic cap 21 should be slipped oif the assembly. The other plastic cap 26 should likewise be removed, the purpose being to avoid the possibility of high temperatures damaging these masking aids. Of course, if the plastic or other masks used have a sufficiently high melting point they need not be removed prior to this heating step.

A further caution, which experience has shown to be valuable in practicing my invention, should be observed in the: actual. proness. of extracting the master. In this extraction, the. end. of the electroformed. barrel; I31 that bears against the extractor l1 should. be: perpendicular to the axis of that barrel [3; otherwise the hot master llmaybe bent. during. its extraction.

After the electroformed' barrel [3 has been. freed from. master H, it may be heat treated to anneal. the alloy from which. the: barrel 13; was

made... The last. step in my novel. process: is: to

machine. or grindv this electroiormed barrel. It to: itsv final form in. accordance. with. the: various requirements. for its overall diametral dimensions: (which variance depends, among. other things, on whetherthe product is to. be used as a gun barrel or a. separate reliner to be inserted into a barrel). This. machining: or grinding step can. be done. with standard. macl'iin'ery and, for purposes of: mass production, can be readily processed with conventional cienterless. grinders.

The time-required for my entire. unique process as above described will. of course vary with the thickness. of: the l ner. or barrel desired to be thus electrofbrmed, and. the. metals. from which those. products. are to be: made. For example, the time required to plate a 0.02 inch thick coating, of cobalt tungsten alloy (like the metal layer 20 shown in Figs, l-4-5-6-7) for use as a gun liner inv one typical instance was found to be about. at hours when. av currentdensity of 2. aniperes: per square decimeter was used. The. remainder' of the electroformed liner envelope (similar to the metal layer 2-! shown. in. Figs; 1-6- 7) was made of cobalt which. was plated. on top. of the: cobalt-tungsten. alloy at: a. minimum rate or 0.005 inch per. hour.

In this specific example, an. entire liner inch.

thick, plus a. margin. for machining the outside wall surface, was plated in. approximately three days. However, the actual time per unit product required of an operator during this operation was very low because a large number of liners were accommodated. in. the single plating bath, and they required no attention during the plating process.

It should be understood that the: composition of the. various alloys mentioned. above is not critical in the practice of. the. present invention. That is to say, practically any alloy of cobalt. and tungsten or cobalt and molybdenum may be utilized in the. process hereinabove described, the sole determining criterion. being the particu-- lar properties in the finished liner or barrel which is desired by those who practice my in- I vention. However, for the purposes of illustration, suitable alloys now will be described by reference to one manner in which they may be made. These alloys, and more particularly a method and bath for electrodepositing them, are disclosed in co-pending patent applications of which I am a co-applicant.

In co-pending application Serial No. 708,566 which. I. filedon November 8,. i946, jointly with Polly Burkhead and Clara A. Sentel for Method of and Bath for Electrodepositing Tungsten Alloys, there is described a bath which consists of '70 grams per liter sodium tungstate, 28 grams per liter cobalt chloride, 100 grams per liter Rochelle salt, 50 grams per liter ammonium chloride, and the remainder is made up of water plus sufficient ammonium hydroxide required to adjust the alkalinity of the bath. This bath is operated at a temperature of about C., at a current density of 1 to 3 amperes per square decimeter, and the pH is maintained between 8 and 9.

In co-pending application Serial No. 708,565

which I filed on November 8, 1946, jointly with Polly S. Burkhead for Carbonate Electrolytic Bath and Methods for Electrodepositing Cobalt or Cobalt-Molybdenum Alloys Therefrom, there is described a bath which consists of 1000 grams per liter of potassium carbonate, 15 grams per liter of cobalt chloride or cobalt sulphate, 100 grams per liter of sodium molybdate, and the remainder is made up of water. This bath is operated at a, temperature of between 90 and 135 C., at a current density of 1 to 5 amperes per square decimeter and a pH of 11.

All the aforementioned objects of my invention have been attained by means of the methods and alternative techniques earlier outlined. However, it will be obvious to anyone generally skilled in the art that my invention can be practiced in numerous other ways without departing from the spirit or scope of my discoveries.

My invention is therefore extensive in its adaptation and is not to be restricted to the specific form here shown by way of illustration.

I claim:

4 l. The method of manufacturing a gun barrel having a rifled bore out of metals that are highly resistant to erosion and corrosion but are too hard to machine or cast conveniently, which COlllprises making a steel negative form whose external dimensions substantially correspond to required internal dimensions for the desired gun barrels rifled bore, polishing said negative form to a smooth finish, plating a thin layer of lead upon the outer surface of said negative form, thereafter electropolishing the lead-coated negative form to a bright and smooth finish, thereafter electroplating the metal from which said gun barrel is to be made to a desired part of the desired total thickness upon the outer surface of said lead-coated negative form at a temperature below the melting point of said lead coating, thereafter grinding smooth the outer surface of the metal which has been thus electroplated upon the lead-coated negative form in order to eliminate the contour of the underlying lands and grooves from the subsequent plating, thereafter resuming electroplating the metal from which said gun barrel is to be made as aforesaid until the desired total gun barrel thick ness plus a margin for final machining has been reached, thereafter heating the thus electroplated negative form to a temperature high enough to melt and eliminate said lead coating from said negative form, thereafter extracting said negative form from the resultant gun barrel that has been electroformed therearound, and then grinding the outside Wall surface of the resultant gun barrel to the desired overall crosssectional dimensions.

2. The method of manufacturing a gun barrel having a rifled bore out of metals that are highly resistant to erosion and corrosion but are too hard to machine or cast conveniently, which comprises making a metallic negative form whose external dimensions substantially correspond to required internal dimensions for the desired gun barrels rifled bore, polishing said negative form to a smooth finish, plating upon the outer surface of said negative form a thin layer of a fusible metal which does not readily alloy with the metal of the negative form, thereafter electropolishing the fusible metalcoated negative form to a bright and smooth finish, thereafter electroplating the metal from which said gun barrel is to be made to a desired part of the desired total thickness upon the outer surface of said fusible metal-coated negative form at a temperature below the melting point of said fusible metal coating, thereafter machining smooth the outer surface of the metal which has been thus electroplated upon the fusible metal-coated negative form in order to eliminate the contour of the underlying lands and grooves from the subsequent plating, thereafter resuming electroplating the metal from which said gun barrel is to be made as aforesaid until the desired total gun barrel thickness plus a margin for final machining has been reached, thereafter heating the thus electroplated negative form to a temperature high enough to' melt and eliminate said fusible metal coating from said negative form, thereafter extracting said negative form from the resultant gun barrel that has been electroformed therearound, and then machining the outside wall surface of the resultant gun barrel to the desired overall cross-sectional dimensions.

3. The method of claim 2 in which the electroplated metal from which the gun barrel is to be made is selected from the group consisting of cobalt, cobalt-tungsten alloy, and cobalt-molybdenum alloy.

4. The method of claim 2 in which cobalt is the metal from which the gun barrel is to be made.

5. The method of claim 2 in which an alloy of cobalt-tungsten is employed as the metal from which the gun barrel is to be made.

6. The method of claim 2 in which an alloy of cobalt-molybdenum is employed as the metal from which the gun barrel is to be made.

ABNER BRENNER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 602,212 Desolle Apr. 12, 1898 850,912 Edison Apr. 23, 1907 1,151,318 Wood Aug. 24, 1915 1,412,174 Eustis et al Apr. 11, 1922 FOREIGN PATENTS Number Country Date 12,264 Great Britain of 1888 239,977 Great Britain Sept. 24, 1925

Claims (1)

1. 2. THE METHOD OF MANUFACTURING A GUN BARREL HAVING A RIFLED BORE OUT OF METALS THAT ARE HIGHLY RESISTANT TO EROSION AND CORROSION BUT ARE TOO HARD TO MACHINE OR CAST CONVENIENTLY WHICH COMPRISES MAKING A METALLIC "NEGATIVE" FORM WHOSE EXTERNAL DIMENSIONS SUBSTANTIALLY CORRESPOND TO REQUIRED INTERNAL DIMENSIONS FOR THE DESIRED GUN BARREL''S RIFLED BORE, POLISHING SAID "NEGATIVE FORM TO A SMOOTH FINISH, PLATING UPON THE OUTER SURFACE OF SAID "NEGATIVE" FORM A THINN LAYER OF A FUSIBLE METAL WHICH DOES NOT READILY THEREAFTER ELECTROPOLISHING THE FUSIBLE METALCOATED "NEGATIVE" FORM TO A BRIGHT AND SMOOTH FINISH, THEREAFTER ELECTROPLATING THE METAL FROM WHICH SAID GUN BARREL IS TO BE MADE TO A DESIRED PART OF THE DESIRED TOTAL THICKNESS UPON THE OUTER SURFCE OF SAID FUSIBLE METAL-COATED "NEGATIVE" FORM AT A TEMPERATURE BELOWTHE MELTING POINT OF SAID FUSIBLE METAL COATING, THEREAFTER MACHINING SMOOTH THE OUTER SURFACE OF THE METAL WHICH HAS BEEN THUS ELECTROPLATED UPON THE FUSIBLE METAL-COATED "NEGATIVE" FORM IN ORDER TO ELIMINATE THE CONTOUR OF THE UNDERLYING LANDS AND GROOVES FROM THE SUBSEQUENT PLATING, THEREAFTER RESUMING ELECTROPLATING THE METAL FROM WHICH SAID GUN METAL IS TO BE MADE AS AFORESAID UNTIL THEDESIRED TOTAL GUN BARREL THICKNESS PLUS A MARGIN FOR FINAL MACHINING HAS BEEN REACHED, THEREAFTER HEATING THE THUS ELECTROLATED "NEGATIVE" FORM TO A TEMPERATURE HIGH ENOUGH TO MELT AND ELIMINATE SAID FUSIBLE METAL COATING FROM SAID "NEGATIVE" FORM, THEREAFTER EXTRACTING SAID "NEGATIVE" FORM FROM THE RESULTANT GUN BARREL THAT HAS BEEN ELECTROFORMED THEREAROUND, AND THEN MACHINING THE OUTSIDE WALL SURFACE OF THE RESULTANT GUN BARREL TO THE DESIRED OVERALL CROSS-SECTIONAL DIMENSIONS.

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