US2220652A - Manufacture of cartridge cases from aluminum alloys - Google Patents

Description

Patented No. 5, 1940 y PATENT OFFICE FROM ALUMINUM ALLOYS Roland Irmann, Neuhausen, Switzerland, assignf or to Aluminium Industrie Aktien-Gesellschaft,

Neuhausen, Switzerland, a joint-stock com'- pany of Switzerland Application August 21, 1937, serial No. 160,255l In Switzerland September 2, 1936 7 Claims.

This invention relates to the manufacture of cartridge cases from aluminum alloys, and makes use of such alloys as arecapable of being improved, hardened and straightened, by solution yheat treatment. `The use of such alloys'differs essentially from the use of brass in that the aluminum alloys must be subjected to solution heat treatment in order tq afford requisite strength.

The solution heat treatment available for this invention may consist in annealing, quenching and aging the aluminum alloy, either at ordinary or room temperature, as with alloys of the alum'- inum-copper-magnesium type such as -those .known under the trade names .Avional and Duralumin,zor at an elevated temperature, as with alloys of the aluminum-magnesium-silicon type or of the aluminum-copper-silicon type, for strengthening-and hardeningA of the product.

The usual mode of treatment of various articles made of aluminum alloys that are capable of being improved by solution heat treatment, is to subject them to such treatment only after their shaping has been wholly completed; this being for the reason that the material is hardened by the heat treatment so that it can no longer be easily worked by cold deformation, andrfor the further reason that'when intermediate soft-annealing has to be undertaken during the shaping vsteps the effect of a previous hardening or heat y treatment would be substantially neutralized. For these reasons, in previous proposals to make cartridge cases from aluminum alloys which are lcapable, of being improved by heat treatment, the

rsolution heat treatment has been performed onl rby, the selection and trialof various alloys, but

wholly satisfactory results have vnot as yet been achieved; The object of the present invention is to make practical the manufacture of cartridge cases from suitable aluminum alloys.

The accompanying diagrams Figs. l to '7 indicate in central section views some of the successive steps or stages through which the initial blank passes in being shapedinto a cartridge case,

the application thereto of the present invention to be described in connection with said diagrams.

The process may commence with a circular disk A, Fig. 1, of the selected alloy, from which by many operations the cartridge case is shaped. Thev disk is first struck or worked into the form of acup B, Fig. 2. Then, by successive working (Cl. .Z9-1.3)

or drawing steps, with intermediate soft annealing operations, there is obtained' an elongated cy.r

lindrical case C, Fig. 3, having a thick rounded bottom D.

In formerl practice, the recess E forthe recepy tion of the percussion cap is next pressed in fthe bottom and the bottom F is reshaped and the neck H reduced. After the shaping of the case is complete, vent holes are bored in the bottom,

'an ejector groove G is formed, as by milling, and

the reduced neck is cut off at the proper length. The sequence in which some of the operations were performed, was, however, sometimes varied;

as also was the type or design of case.

According 'to the present invention, by improvement in the manufacturing process, cartridge cases can be manufactured, of various designs,

having the necessary mechanical strength. This result is obtained, in accordance with the 4invensolution heat treatment, while the following pressing operations are conducted cool, or at room temperature.

Owing to this special 'order of operations, an increase of strength by thecold Working ofthe metal in its heat-treated condition' is obtained.

The high valuesfor the proof stress and tensile strength obtained equal or exceed those values which the lower parts of the cartridge case and 'in particular the bottom end are required to have.

The procedure of this invention, therefore, is such that the cold working on the lower part of the case, which is carried out after the solution heat treatment, is sufilcient to effect the necessary in crease in strength. This is the importantvfeature, and the invention is not necessarilyco'n- The heat treatment at the latest cerned with the number of operations performed.

in the plastic shaping or pressing' which precedeor. follow'the solution heat treatment.

y Explaining the invention by the diagrams, which show an example, the heat treatment is applied following the attainment as in Fig. 3 of the generalL shape of the case C, by shaping steps as in Figs. 1 and 2 and soft annealings. The entire article C is heat treated, by treatmentappropriate to the 'aluminum alloy used. The ,casek has then the cap recess E struck or pressed into the bottom end (Fig. 4). In some casesit might be preferable to begin to form the recess E before theV heat treatment. After this step the lower. end is plasticaily reshaped, as at F Fig. 5, to its final shape. The corners are squared and the desired sectional Mdesign attained. The pressing of the recess and the nal shaping being cold operations, performed by heavy die pressure, they greatly increase the strength. Now or later may be formed the ejector groove G Fig. 6, as by milling or rolling; but if the bottom reshaping has produced an ejector harige, as sometimes used, the groove is omitted. Next, the neck H is contracted to a form such as Fig. 7 indicates, in the instances of cartridge cases having reduced necks. 'I'his however may be preceded by a heating confined to the upper endsuch as to afford a better plasticity for the cold Working or spinning of the neck metal to the desired shape without impairing the tensile strength as in the ordinary softheat treating. Such top end heating is preferably at relatively low temperature, below the point of recrystallization of the metal, and applied for 3 or more minutes, not above about 30 minutes, avoiding the risk of neutralizing theeffeet of the previous heat-treatment of the case. 'Ihis heat-treatment may be performed after the reducing of the neck instead of before, as later explained, or before and after this reducing operation.

In general, it is preferable to undertake all the cold pressing operations on the bottom, including the beginning of the pressing of the recess E for the reception of the percussion cap, after the solution heat treatment, since in this way the greatest increase in strength is obtained. The simplest method is to shape the bottom at room temperature after the cartridge case has been subjected to solution heat treatment. Obviously, it is also within the invention to press the recess or pocket for the percussion cap or primer, and also to carry out other of the plastic Y shaping operations on the lower part of the case,

either at a lower or at a higher temperature, provided a suicient increase in strength is still obtained. Vent holes in the bottom of the primer recess may be drilled later, after the described operations, as also may be the final trimming or cutting oi of the neck.

The described invention is readily adapted to any particular conditions. 'Ihe necessary strength increase cannot conveniently be expressed numerically because the proof stress and tensile strength of the lower part of the case, particularly of the bottom, cannot be accurately determined by usual methods owing rst to the small dimensions of this part of the case and second to the fact that the increase in strength will tend to be irregularly distributed. Whether the increase in strength afforded by this invention is suilicient or not in any, case can readily be determined by testing by firing the cartridges.

, As is Well known, the lower part of the cartridge case is not supported over its entire area in rifles and machine guns. If the material of the case is not sufliciently strong at the lower part of the case, the bottom of the case may expand under the pressure of the explosion; and this frequently leads to the percussion capbecoming loose or falling out, and if this occurs, jamming is likely to result, and this is more likely to occur in machine guns than in rifles.

By means of the process of this invention. described above, it is possible to avoid the troubles which have arisen with cartridge cases heretofore made of aluminum alloys owing to their being of insufficient mechanical strength. The strengthening by the cold deformation of the lower part of the case after the solution heat treatment may, therefore, be considered suicient if, when the cartridge is fired, no troublesome widening or expansion of the bottom of the case occurs.

The ejector gro'ves, instead of being milled, can be cold pressed or rolled after the solution heat treatment, whereby a still greater increase in strength is obtained by such further cold deformation in the heat-treated condition.

In practice, the upper part of the case, particularly the neck, as above explained, is reduced after the bottom has been pressed. This upper part of the case, and particularly the neck and shoulder, is, therefore, also subjected to cold working in the heat treated condition when the process of the present invention is carried out. The increase in the proof stress and tensile strength which is thereby produced, is, of course, accompanied by a decrease in elongation. The elongation, particularly that at the neck of the cartridgel case, is thereby reduced to such an extent that the plasticity may become insufflcient; which becomes apparent, when the bullet is inserted in the case and afterwards when the cartridge is inserted in the gun and red, by the formation of cracks. The elongation at the neck may be reduced, for example from 16% to less than 2% in the case of a cartridge case made of alloys of the type Al-Cu-Mg, which are known in commerce under the trade names Avional" or Duralumin A further feature of the invention, in relation' to contracted neck cases, is the supplemental heating of the part of the neck which has become insufficiently plasticl namely, in such a manner that a suflicient increase in elongation is obtained. Preferably, care is taken that the proof stress and tensile strength are not reduced too much by this heating. In practice, this can be easily performed by heating the cartridge case during a short time, say from 3 to 30 minutes, at

.a temperature which is below the recrystallization temperature; the temperature must, however, not be too low, as the improvement in the elongation would then take too long. As a modlcation a very short heating, of for instance several seconds, to a temperature somewhat over the recrystallization temperature can give the required results.

Excellent results have been obtained with cartridge cases made of alloys of the Al-Cu-Mg type, for example Avional and Duralumin, as well as with other copper-containing aluminum alloys, by heating the upper part of the case. and especially the neck, which may have become too hard,lfor a short time to a temperature below the recrystallization temperature. For this purpose a heating of 10-20 minutes duration at a temperature of approximately 170 C. has been found to be particularly suitable. When the heating is performed in an air bath, there are difliculties in employing higher temperatures, for example 200 C., owing to the dlillculty of determining correctly the most favorable duration for the treatment. If lower temperatures, for example 120 C., are employed, the duration of the heating may be too long for practical requirements. In cartridge cases made oft, Avional, which have been manufactured in accordance with the present invention, the tensile strength at the neck has been increased by cold working of the upper part of the neck from 46.5 to 51.5 kilograms per square millimeter. The proof stress increased from 34 to 54 kilograms, while the elongation fell from 16.3 to 2 per cent. By heating at a temperature of C. for 15 minutes the elongation again increased to 6 to 8 per y l A vaccurata cent, while the tensile strength was reduced 'only by about 2 tov 4 per cent, and the proof stress by about 5k tof.10,percent.v

'- After these described treatments it was found 5 that the values obtained forrthe proof stress, tensilestrength and elongation at the neck of Y the cartridge cases showed relatively little variation.

For these operations upon the upper ends of 4the cases, an apparatus was used in which the lower ends, which were not required to be heated Y with the upper parts, were placed in a chamber supplied ywith water at a lower temperature than the annealingchamber Vinto which extended the upp'er parts-of the cases tobe heated; and the upper parts were then heated by means of hot air orV gases. This supplemental treatment may f f be performed after the 'neckand shoulderhave y 'jybeen partially formed, the completion ofcou- 2b traction 'following-the treatment.

During the bnefneaung Yfor increasing the elongation of the upper part of the casewhich ,4 y* i has become too hard, care Vshould-be taken that the lower part, whichy should have a particularly high mechanical strength, is protected vfrom be ing heated to too high a temperature. Nevertheless, it is generally advisable to maintain the bottom part at a temperature which is slightly f higher than room temperature, ifi, rder that the not be toogreat. f

The process according to themain feature of the present invention is not nmited'tq Jme pre-z vailing or usual order or sequence of manufac- 35 ture, which has been referred to merely by way AI of example. The important consideration isjthat the increase in strength of the lower part of the case is obtained by interposing the solution'heat treatment before the case has `beenpressed or 40 formed into its nal shape; and as regardsthe aforesaid supplemental feature of the invention,

the improvement is the local heating for improving the elongation of the-upper parts of the case which had become insufliciently plastic owing to .f '45 the cold working.

I claim: f 1. The method of making a. cartridge case from a blank of a light -aluminum alloy that is heat-treatable for hardening, comprising` the pre- VI5() liminary operations of partially shaping such blank by a series of working and annealing steps into a hollow elongated pieceof the general cylindrical form and size of the finished case and having its closed lower end relatively thick 55 walled but of uncompleted rounded form; and

said method being characterized in that its re- Y"main-ing operations comprise the following steps:

' after such working and annealing steps, hardening such incompletely shaped piece by solution- Q heat-treatment thereof Acomprising heating, quenching and aging, at an antecedent stage; and vat a subsequent stage, after vthe completion of such heat-treatment including aging. extensively cold working the lower end of the hardened piece to complete' the plastic shaping thereof,

thereby to increase substantially the strength of the /nished case, while preserving substantially its previously acquired hardness. y

2. The method as in claim 1 and wherein the .Q 'locap' recess in the bottom is' cold-pressedafter the step'of hardening including aging.

3. The method las in claim 1 and herein the ejector groove is cold-'worked in the lower part after the step of hardening including aging.

'derivation of heat by the cooled bot] mpart may y 3 4. The meines-as 'in claim 1 and wherein the cap recess inthe bottom isf cold-pressed aftery the step of-hardening including aging, followed by f the extensive general reshaping of the lower end,

blank by a series oi working and annealing steps into a hollow elongated piece of the general cylindrical form' and with itsclosed lower end relatively thick-Walled.Y

size of the final case and but off uncompleted or rounded bottom contour -vextensively short ofattainingthe 'final contour;

V(2) followed by hardening such incompl'etelyV shaped piece by solution-heat-treatment comprising heating, `quenching and aging thesame;

and (3) thereafter, following the termination'of substantially the strength of the finished VVcase to resist the stresses of explosion within it'while preserving substantially its hardness acquired in` said solution-heat-treatment stage.

6. The method of making a cartridge case with contracted neck from ya blank of a light aluminum alloy that is solution-heat-treatable for hardening, .comprisingltheyfollowing recited stages: (l) partially shaping such blank by customary working and annealing steps into a hollow cylindrical piece of the general cylindrical form and size of the nal case and with its closed bottom end relatively thick-walled but of rounded bottom contour extensively different from the Yfinal contour; (2) followedby hardening such yincompletely Ashaped piece by solution-heattreatment comprising heating, quenching and aging the same; and (3) thereafter, following the completion of such heat-treatment including such aging, extensively cold working the bottomv end of the hardened piece to complete the plastic shapingV thereof, thereby to increase substantially the strength lof the nished case, while preserving above the recrystallization point of thealloy, and l for a brief duration of heating, between a few seconds and about 30 minutes, thereby to improve elongation in connection with the step of shaping the upper end to its contracted form,

and without impairing substantially the previously acquired hardness and strength of the lower end, and applying to the upper end working steps to contract it to the desired shape of neck,y of

f such heat-treatment stage-including such-aging, completing the plastic shaping of the lower-end by extensive cold Working stepsV upon the samef *in` its hardened condition, thereby `to improve which at least the final workingV steps are performed after such supplemental ysoft-annealing thereof. Y

. 7. The method as in claim 6 and wherein the ,upper end softannealing is Vperformed with duration `and temperature so coordinated that the-1VV yield point is reduced under 10% and the tensile l strength under 4% lwhile, elongation is increased by a percentage greater thanthe loss of elongation during the previous recited steps.

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