MILL BED

T H E “W a te r Buffalo”, officially desig­

n ated as L V T (L anding V ehicle Tracked), is a dynam ic a n d pow erful am phibious tank th a t can craw l out of the sea and atta c k on land. I t can swim ashore, : through surf, over reefs, a n d surm ount all types of obstacles in jungles, swamps an d rivers. In addition, it can negotiate extrem ely rough terrain.

V ersatility o f th e ‘TVater Buffalo” in negotiating various types of terrain is d u e to th e tracks w hich k eep it moving through w ater, over land, an d u p moun­

tains, achieved by designing them to be p a rt p ad d le an d p a rt tread , called a

“grouser”. D ozens of these grousers are atta c h e d to tw o trucks, one on each side o f th e vehicle in the m an n er of a caterp illar tread.

T he task assigned to U nited States Spring & B um per Co., Los Angeles, w as to m anufacture a large volum e of

(1) Rotating Tacking Fixture (¡21 Welding Conveyor (S) Transportation Conveyor (4) Q uenching F u rn ace (5) Oil Q uenching Tank (6) Tempering Furnace (7) Transporting Conveyor (S) Shot Blast

(0) Painting Conveyor (10) Inspection

(111 Packing

/ ■ T E E L

C onveyor line setup is em ployed by United States Spring & Bumper Co. in assembling , hea t tre ating an d finishing complex p a r t for the N a vy's LVT

these grousers a t a high rate of p roduc­

tion. T h e com plicated shape, th e m ate­

rial from w hich th e grousers are m ade, the necessary m eans of w elding the shape to g eth er, an d o th er steps in the m anufacturing operation w ere p a rt of the production problem s w hich confronted engineers a t U. S. Spring. A ccom pany­

ing photographs a n d draw ings h elp to illustrate some of these problem s.

Figs. 1A a n d IB show the tw o %-in.

plates w eld ed to g eth er a t 90°. T h e length of th e base p late is 13% in. and the w id th of th e curved section is 2% in.

There is approxim ately 36 in. o f fillet weld com pletely around th e curved plate, with only tw o sm all skips to allow bolts to fit into place. T he w eld specified is a 3 /1 6 -in . continuous b ead using T ype 6013 covered electrodes.

T h e grouser is h e a t treated after w eld ­ ing, descaled, an d coated w ith a p ri­

mary coat of zinc chrom ate. T he base plate, a fte r w eldine. h e a t treating

shot blasting, m u st be flat to 1/32-in.

M aterial used fo r this p late is NAX-9130, a h e a t treatab le alloy.

Som e of th e factors w hich h ave been tak en into consideration can thus he readily seen. F irst, w e have the w eld­

ing of th e com plicated shape involving locked u p stresses in the w eld. Secondly, th e re is the m etallurgical problem of arc w elding a 0.30 p e r cen t carbon alloy of self-hardening steel. A h e a t-tre a tin g factor a n d resulting w arpage, plus ad d i­

tional w arpage from a descaling opera­

tion, now e n ter as production problem s.

C hoosing the M ethod of Production:

T h e next step w as to devise a m ethod w h ereby a quality p ro d u c t co u ld be o btained through hig h speed production.

A study of m odern w elding m ethods p roved th a t th e g reatest speed an d effi­

ciency could be achieved th ro u g h m o d ­ ern continuous m ethods of m anufac­

ture. M anpow er shortage w as also an

im portant factor in deciding upon this m ethod of operation. So, a conveyor system of w elding, h e a t treating, d e ­ scaling an d pain tin g w as w orked out w hich p rovided hig h speed production, decreased th e necessary m an-hours, b ro u g h t to a m inim um the tim e elapsed b etw een th e start of the operation and the final finished p roduct, an d resulted in a continual uniform ity of the p ro d ­ uct.

Prelim inary Tests: T h e m ethod of m an u factu re having b e e n decided upon, it w as th en necessary to m ake a thor­

ough study of m etallurgical factors in o rd er to guarantee this uniform ity of product. F irst, it w as vitally im portant to select an electrode w hich w ould give crack-free sound w eld deposits and w ould be acceptable for w elding on a conveyor line. A test w as therefore conducted using various 3 /1 6 -in . T y p e 6013 electrodes, as follow s: Tw o 1-in.

p lates w ere placed to g eth er in the form of a T ee and a fillet w eld w as run along each side arc w elding the tw o p arts together.

A fter w elding, th e various assem ­ blies w ere carefully c u t a p a rt a t in ter­

vals of approxim ately %-in. an d inspected for auto-cracks, fusion zone cracks, por­

osity, d ep th of p en etratio n , an d slag in­

clusions a t th e root of th e w eld, a n d th e form ation of crater cracks a t the finish of th e pass. Tw o electrodes, w hich a p ­ p eared to give the desired results, w ere selected.

T he next factor w as the p ro p e r p re ­ heatin g tem p eratu re. C areful study show ed th a t various tests for p ro p er p re­

h eatin g tem p eratu re w ould give th e d e ­ sired results. T h e “single b e a d ” te st w as decid e d upon. Strips of th e m aterial to b e w eld ed w ere secured an d a single b ead w as laid on th ese strips w hich w ere re h eated to 200, 300, 400, an d 500° F.

Fig. 1— Views, o f grouser tread fo r continuous tracks o f am phibious ta n k L V T ’s

Fig. 2— Floor plan o f grouser conveyor w elding system a t U. S. Spring & B u m p er Co.

Fig. 3— T a cked grousers going into preheat furnace on continuous conveyor prior to finish w elding Fig. 4— T a ckin g th e curved section o f th e grouser to th e

fla t base plate

Fig. 5— S etu p m an assem bling grousers on opposite side o f table fro m operator show n in Fig. 4

I JU[* 18, 1945

!*sbf3s

T he

rate, electrode

d e p th of w eld p enetration, cracks, p o r­

osity, m axim um hardness in h e a t affect­

ed area, and the w eld ductility.

T he m aterials used in this test w ere F leetw eld 7, 3 /1 6 -in . electrode and NAX 9130X 14-in. steel. T h e m achine setting w as 160 am p, 22 v. Accom­

panying tab le gives th e results of this test. T he conclusions d raw n w ere th at th e 500° F p re h e a t w ould b e most satisfactory as it gave a low hardness of th e m etal being w eld ed w idi an in ­ creased ductility. I t also ap p eared th a t a slight saving in electrode w ould be encountered.

An extensive series o f tests w ere m ade to com pare the use of 3 /1 6 and 14-in.

electrodes w ith the conclusion th a t th e 14-in. electrodes w ould increase p ro d u c­

tion b y 2 0 p e r c e n t though m ore w eld m etal w ould be deposited. O n e-q u ar­

te r inch electrode w ould also save over 6000 m an-hours in filling th e original contract. H ow ever, th e larg er electrode

SINGLE W ELD BEAD TEST FOR TH E DETERM IN A TIO N O F PROPER PREHEAT FOR W ELD IN G GROUSERS

---Preheat Tem perature, D cg. F

ahr.---200 300 400 500

Bum-off Rate: Inches per m i n u t e

...

Electrode used per inch of weld ... 1 1 % % %

D epth of w eld penetration m m ...

. ..

Cracks, porosity, etc ... None None None

Max. hardness in heat affected area: RC.

. .

W eld ductility: D egree bend on 1-in. pin

. . .

Fig. 6— A t each w eld in g station a small length of bead is deposited. ’’Stagger"

w eld in g is th u s done on a continuous production basis along entire length of th e 32-ft conveyor line, tw o o f w hich fe e d th e heat-treating furnace as show n

in layout, Fig. 2

Fig. 7— D ischarge end of tem pering furnace, left, drops units on conveyor to shot blast un it adfpining. C leaned grousers are h u n g on chain conveyor fo r paint

dip and hot air dry in tu n n el

/ T E E l T he W eld in g O peration: As this op­

eration was going to be a continuous one, the engineering d e p a rtm e n t designed the layout of tire eq u ip m en t w h ich w ould be necessary, Fig. 2. M aterial is pro c­

essed in th e follow ing m anner: From

steel yard the steel is m oved to a b lanking press. T h ere bo th th e curved u p p e r p a rt an d th e base p la te are blanked. H oles in the base p late are p u n ch ed sim ultaneously w ith th e blank­

ing operation. From the blanking press, the base plates are taken in large quan-

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The uses of