Semicontinuous Casting of Beryllium Copper

a

Semicontinuous Casting of Beryllium Copper By K. G. WIKLE*

Billets in la~ge and small size are cast with high yield of sound, Gne-gramed metal, free from residual beta phase, and at a lower cost per pound than by the conventional Durville process. (C5q; Cu, Be, 4-52)

Up

1954 the Durville technique was utilizedby the American iodustry to cast ingots 01beryllium copper. Their maximum size was about 250 lb. To produce larger ingots, the AlloyDiv. 01 Brush Beryllium Co. turned to TO

continuous casting and within

a year our new

equipmentwas producing rounds and slabs 10 It. long, up to 75 sq.in. in cross section and 1500 lb. in weight. The quality is such that 1200-lb. coils01 0.090-in.strip have been rolled in continuous mills.

Durville Process- Figure 1 sketches the Durville process - essentially

a nonturbulent

Bow

technique in which the casting ladle and the moldare integral. The unit is slowly turned upSIdedown, and the molten metal, at a relatively 10":castingtemperature, is smoothly run into the mold WIth a minimum of turbulence

and oxida-

tion, thus avoiding entrapped oxide, dross and gases. A second advantage is rapid sohdlflcatio» fromthe low pouring temperature, which minim~es gassing, produces a fine-grained

casting,

WIth only a small pipe and cropping loss. A high-qualitycasting, sound, clean and finegrained,is nl great importance especially in the 170and 190grades 01 beryllium copper because this much alloy substantially hardens the copper by solid solution. The metal is hot short above about l5QOO F. and cold short below about 120Q0 F. Thus rolling is somewhat difficult even for the highest quality casting. As in more APRIL 1958

common brasses and bronzes, it is also important that the ingots be free of massive beta structure

for good rolling and forging. The real limitation of the method is in the size of ingots; 40 sq.in. cross section and 3 ft. long appears to be the maximum practicable. Semicontinuous ingots are by no means new in the nonferrous industry. For example, Metal Progress in January 1950 described at length the

casting 01 2000-1b. slabs of brass to feed a new rolling mill of Scovill Mfg. Co., and J. S. Smart, J r., of American Smelting & Refining Co. described his company~s achievements in this line in the October 1955 issue. Schematically, the semicontinuous

casting

process

as used

with

beryllium-copper alloys is illustrated in Fig. 2. Up to 2000 lb. 01 molten metal is poured slowly out of the crucible into a clay-graphite tundish wherein any dross carried over has considerable time to rise to the surface. The metal is then under-poured or teemed into an annular copper

mold through a graphite nozzle which minimizes turbulence. Since there is always a pool of metal at the top of the casting, an opportunity exists for a final dross separation. Also, this pool continually leeds the solidifying metal below, pro*Director of Development, Alloy Div., Brush Beryllium Co., Elmore, Ohio. Three other men are responsible for much of the work leading to the successful process: C. W. Schwenzfeier, vice-president of engineering; J. R. Dejarnett, senior engineer; and J. Kosmo, superintendent in the Alloy Div.

85

Melt Graphite Noule Crucible

---.l.v-~/A

Coppe'Mold

CloY.GraPhit".:=~~~~F;;;;;~ Tundish

c

Water Inlel Water

Jacket

Water Spror Tonk MeltIng Position

Costing Position

Hydraulk Cylinder

Fig. 1 -

Durville

Casting

Techmique

viding a sound. pipeless casting from bottom to top. A solid product results. asting speed is adjustable - about 4 to 6 in. of billet per min., thus a lO-ft. casting can be made in 20 to 30 min. The water level in the tank, and the flow through the jacketed mold and through the spray, can also be readily controlled. 11,e rate of metal Aow is fixed by tbe orifice in the graphite nozzle, chosen before casting beg.ins and appropriate to the billet size and alloy. After the billet is cast, the mold is removed, the casting is lifted up and disengaged hom the tapered dovetail on the false bottom. It is seldom n cessary to crop alI more tban a few inches from the bottom and top to get into sound metal. dvantages - The planned and actually realized. advantages in the semicontinuous casting technique used at Brush are summarized below: 1. Uniformity of Casting Conditions. A large volume of metal IS cast relatively slowly; thus the temperature in the holding furnace can be maintained quite constant and delivered to the mold at a uniform temperature where heat .s ~vithdra\Vn at a steady rate over the entire cas~mg cycle, end to end. resulting in uniform structure from bottom to top. 2. Mini"wm turbulence and oxidati On resu It from careful pouring into a metal reser . f I '. ]voir rom w rich metal lS teemed into the mold below.

6

Fig. 2 - Schematic View of Semicontinuous Casting of Beryllium Copper

Turbulence, are held

entrapped oxide, dross andgases

to a minimum.

3. Rapid Heat Extractioll. Heat is ";tltdra,, at a high rate, first by a water jacket or spray00 tbe mold, second by a water spray directlyon the casting surface just below the mold, and finally by quenching the biJIet in a tank of CircU1,trn/ water just below the lower spray. RapidOlO ing produces a fine-grained structure even m . relatively large cross sections. A lso.jt so, I Preveo~ . gas pockets, gravity segregation, and m' terdeo· dritic shrinkage. The resultant microstructore consists of nne constituents which can be "'~ homogenized prior to rolling or forging... 4. Directional Solidifica.tion. Radial solidifim' tion begins next to the mold, but as the froUD shell is lowered, solidification cbanges to a P "" d d orrunant . Iy Iongitu . diill al diirec ti' on. This pro"~ it optimum conditions for feeding the metal~, shrinks. Piping is prevented. Dangero~ lfr ternal stresses are avoided. The surface" USI' ally scalped

5. Higher or no piping

a depth of 1/16 to '!4 in. d little Yields. Longer castings .an,,,,,,ff '"" aod cropping losses res ul t m

Storog8 6. Lesser Mold Inventory Costs (lIld 'd'

yield - less scrap.

. t pro\'l e Space. Although the eqrnpmeot old · Id large and uniform supply 0f IlqVI met' an

METAL PROGR£~

reliable billet handling may Table I - ~om~nal Composition and Physical Properties of Semicontirnmne Cast Beryllium Cop p e r Alloy' require a larger capital expenditure than for Durville ALLOY 35 ALLOY [0 ALLOY 165 ALLOY 25 castings, the short sleeve Composition meldsare cheaper than large Beryllium 0.25/0.50 0.4·5/0.65 I .60/1.80 1.80/2.15 pemmnent molds, and reCobalt 2.40/2.60 0.25/0.35 025/0.35 quire far less operating and Nickel 1.40/1.60 storagespace for a variety of Copper balance balance balance balance Specific gravi t y R.40 8.75 8.26 8.26 sizes. Density, lb. per r'u. in. 0.304 0.316 0.298 0.298 7. Greater productivity Melting range: OF. 1900/2040 I U8.\/ 1955 1600/1800 1600/1800 per man-hour is possible, Pouring range, OF. 2100/2250 2050/2200 1900/2100 1900/2100 since a larger weight of Shrinkage, in. per flo 3/16 3/16 3/16 3/16 Thermal conductivi tye 0.42 0.4·3 0.25 0.25 metalis melted and poured, Average coefficien l and the mechanized casting 9 X lO-fi 9 X 10. 10 X JO·o of expansion t 9 X 10·' equipment requires only one or two men to operate it. e Cgs. unus at 20° c. 8. No Serio"s Beta Problem. The presence of residdiminishes its tendency to dross during meltual beta structure (a hard and brittle phase, down, holding and pouring. body-centered cubic, containing about 6% Be Beryllium is a strong deoxidizer. No signifiand metastable below 10700 F.) in wrought cant quantity of oxygen gas exists in the molten forms of higb beryllium-copper alloys is most bath to cause gassy or oxidized metal. There undesirable. It interferes with cold working, is no need to use any «deoxidation treatment" reduces die life, and lowers fatigue and impact before pouring. properties as well as ductility in the fabricated Beryllium-copper alloys, such as listed in part. While beta structure is occasionally enTable 1, are melted with a neutral to slightly countered in Durville castings, it is not to be oxidizing flame in a gas-fired Fisher furnace. expected in semicontinuous castings because of After the charge is melted, covered with fine their highly chilled structure. graphite and brought into the pouring temperaMelting Practice ture range, the dross is collected, and gas liberated by gently stirring or churning the metal for Beryllium Significantly lowers the melting about 5 min, with a hot carbon or graphite rod. point of copper and provides a substantial solidAfter a settling period of about 10 to 15 min., a ification range. Thus, fluidity is increased and shrink pig is poured and when this freezes satisfeeding is facilitated. factorily. the casting operation is started. Like aluminum, beryllium provides a someLong holding periods are avoided because the what protective oxide film over the melt which 6

Fig. 3 _ Microstructure of Semicontinuous Cast 25 ~e-Cu Alloy. Slirface is primary beta with alpha Islands and porosity. Transition about 0.050 i11. Surface 175 X

Subsurface

deep Boely dritic

is essent.ially alpha wi.th s~1Jall bet.a., islands. of slab is alpha l1W:I"JX tv/th ?eta mterdenphase. All etched tn am1Jloma perslllphate

750 X

Bady

175 X

m It leuds to become gassy aod the beryllium content will slowly diminish. In pouring, the shortest I die-to-mold distance is used to .. aid turbulence, thus minimizing a ide films, skins and entrapments. llill I lructure In wrought high-strength alloys t' to 2 min. After solution Since 1954 the Brush Beryllium Co. bas been lIIDta1ing at 1450" F. and pickling to remove the furnishing a new form of alloy casting for lbd lCale,thecoil is ready for cold rolUng down lightgages. wrought prodncts - namely, a semiconlinuous F . cast billet. It can be five times heavier than argtng- Billets of the alloy noted in Table I those previously available, and has excellent ","diIy forged into various shapes with higb metallurgical qualities. It can be more economingth and toughness. The high-conductivity cally processed into strip, forgings, bar, rod and '"• .'" o~35 and 10 are forged, after soaking at -tollOO'F " 10 . t 0 sue h iItems as seam welding extrusions in high-production equipment with minimum scrap. ~ nd resistance welding dies and electrodes.

lPRlL 1958

9