1948-10-14 — Page 8

Page

THE CHINA MAIL, THURSDAY, OCTOBER 14, 1940.

TECALEMIT

THE AUTHORITY ON LUBRICATION

Tecalemit, pioneer's in the field, today hold the position as the largest manufacturers of Automobile Servicing and Industrial Lubrication Equipment In Great Britain:

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LIMITED

HYDRAULIC & MECHANICAL DESIGNING AND MANUFACTURING ENGINEERS.

GREAT WEST Road, BRENTFORD, ENGLAND.

Sole Agents

LEBEL (China) LIMITED.

Union Building, Pedder Street,

HONG KONG

INDUSTRIAL-COMMERCIAL

4

JOHNSON OIDBURNERS

BURNS HEAVY BUNKER OILS

Agents:

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DAVID HOUSE

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ENGINEERING PAGE

Welding Aluminium'| And

By The Electric

The technique of welding aluminium by the electric. arc process differs from that used in the weld-· ing of mild stool, and the following notes have boon propored for the guidance of those`in- tarosted in the wolding of wrought alumimium and aluminium alloy castings. The principal advantages of the metallic arc process for wolding aluminium are greater speed of weld- ing and the reduced distortion.

The heat-affected zone immediately adjacent to the weld is highly susceptible to corrosion, and arc welding has the important advantage over gas .welding of localising this heat-affected zone to

very narrow dimensions.

This electrode in Many of the difficulties en-15% countered in welding alumin- leally suited to the repair of Jum ore due to the inherent broken castings, even though the properties of the metal. Owing costing may not be of the alu-

minium-silicon 'type. to its higher specific and latent (2) "PURE heats, it requires as much heal | ELECTRODE. Input per pound to melt

us

silicon.

ALUMINIUM"

main

The core wire in this electrode mild steel, although its melt-consists of aluminium of 90.5%

C. minimum purity, and its ing-point is about 800" lower. The loss of heat byure is in the welding of pure alu- conduction during welding is minium vessels.

More dare is necessary in the also far greater than pecurs ini

of welds on preparation

alumi- steel, and these considerations nium than for many other metals, explain why it is frequently and it has been found that one necessary to preheat large

welds of the causes of porosity objects of aluminium before is the presence of a film of mols- welding.

nure on the surface of the metal to be welded. This can be re- moved by heating to about 200* C. before welding or by scratch- brushing.

Aluminium and its alluys form on their surfaces on adherent axide lm, which prevents the running together of globules of molten metal unless a

The presence of grease on powerfal dux is used during welding.

the surface to be welded is ob- It has been found that the cor- jectionable, and any dirt or off *L rosion resistance of aluminium, is should be thoroughly removed.{ adversey affected by Impurities, Owing to the Buid character of aluminium and its alloys, it is particularly silicon and iron. For these reasons, pure

to use a sheet frequently necessary aluminium is stili used in the grooved backing strip; to prevent the the manufacture of vessels for

weld metal from running This backing material processing of food and chemicals through. In spite of the development of may be steel, copper or asbestos. Kumerous aluminium alloys. The For the same reason, are welding welding of some of these alloys of aluminium is largely confined presents obstacles due to their to townhand wolding.

dependence for their Anal pro- Wrought Material

perties upon heat-treatment and. in many cases, upon the effect of forging for producing refng- ment of the crystal structure and distribution of the

Arc

EXTRUDED SECTION

Alloys

Process

-CLO

כר?!!

RECOMMENDED.

NOT RECOMMENDED

The rights and wrongs of welding aluminium.

on

fault

the castings. The rate of heat.

casting away and to build up ing must be low add uniform a solld boss which is redrilled. of the interaction Owing to In order to avoid distortion and tracks.

dissimilar alloys, a slight amount Additional preheating ceri be of porosity is sometimes found Castings dispensed with aero engine at the weld junction castings are welded immediately and where sound surface is re after removal from a trichlore-quared after machining the thylene degreasing bath at 80 C in the casting should be chipped On the other hand, localised are out to ensure the junction being welding is frequently successful below the level of the finished without preheating, provided surface. Porosity is also liable to: Details of the preparation of higher currents than those stated occur on superimposed runs if the rolled sheets are given in the in the table are used for the early slag is not completely cleaned off

130, the preceding head. table, from which it will be noted runs. Typical values are

For first runs the are should that fillet welds are particularly 170 and 200 amps. for Nos. 10, 8 omitted. Fillet welds are liable and 6 gauge electrodes respec- be struck about one inch in from would be expected, and returned to the starting point the commencement of the seam On the other hand, many of to cause an entrapment of flux tively. As the non-beat-treatable alloys

before proceeding normally along; used in the form of custings such

the seam. as crankcases, radiators or other parts in the motor-car and acro- plane industries can be welded Gatisfactorily. These cast parts, however. ure rarely fabricated from separate castings, and weld- ing on them is usually under- taken to repair breakages.

even stituents.

Electrodes

соп-

Thickness

of Material

1/18 in.

Table

Gauge

of Electrode

No. 12

No.

Current Ranga in

Plato

Amps.

40-45

3/32 In..

No. 10

80-95

1/8 in.

No. a

TEL: 28001,

To

these applications, cover two electrodes are available:

(1) "ALUMINIUM BILICON" ELECTRODE which deposits an alloy containing approximately

3/10 in.

6

1.4 in.

3/8 in.

No. 4 No. 4

95-105 130-160' 190-210 200-225

PHILCO

Fresh

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Gloucester Arcade

Tel. 33401

Gap Recommended

Close butt Close butt Close butt 1/16 in.

1/8 in.

3/16 In.

or bevelled 70* with 1/16 in. stap

between the edges of the plate., the amount of patter is increased This flux in the presence of a when such high current values humid atmosphere is llable to are used, and normal curren's cause pronounced corrosion of the should be used as soon as the joint and there is no adequate flow of weld metal permits. means of cleaning the joint be- fora service.

Welding

In welding sections of different Direct current should be used, thicknesses, there is a tendency with the electrode connected

ed,

to

Cleaning

Encelive nuxes for welding aluminium are necessarily cor- rosive. Consequently, the slog should be completely removed from the welded article without delay by immersion in boiling water combined with vigorous brushing of the seam. Several washings arranged on a.counter- flow principle are more effective Oc- thun a single immersion. casionally, some alloys are f

in cold i mersed

five per cent nitric acid solution followed by further washing.

The electrode coating la not unduly sensitive to molature. but electrodes should always be stored

In 2 perfectly dry atmosphere, preferably in the original packing, untli required) for use, and, of course, they should not be roughly handled. It la recommended that alumi- nlum alectrodes should be stor. ed at a temperature of not less than 60 degrees Centigrade, Deterioration due

damp

for the thinner material to melt the positive terminal of the away too rapidly unless the edge generator. Tacks should be spac- of the thicker section is gradually ed at not more than 6 in. inter- reduced in thickness, as illustrat- | vals. The electrodes ahould be storage is indicated by fileriness, held vertical with as close an arc splash and porosity of the wold, In repair work on castings, the as possible, and the current and, provided that the damp has crack is usually bevelled to give strength should be adjusted care- not been so severe as to cause an included angle of 80-90, and fully to suit the particular thick-visible conting, deterioration, the It is advisable to drill a holeness of material. The rate of de- electrodes can be restored by dry- about 1 in diameter just beyond position of, the electrode is very ing for about an hour in an oven the end of the fracture to prevent much higher than is usual with maintained at 120 degrees C any further extension

crack. Occasionally it is advan- The sequence of welding should tageous to replace a number of be designed to reduce the risk of smail fractured pieces with a distortion, and in general should

patch of wrought material,

An

be carried out towards the free general rule, heavy and, particularly in such rigid wrought material should be articles us castings. preheated to, 100-200" G.;and castings: from 80.300 G., da pending on the complexity of!

Instead of attempting to weld up cracks in lugs or bosses i Is advisable to cut part of the

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ilgrade and cooling very slowly.

Electronic Eye On The Stars

BY MICHAEL GRANT

The British Telecommunication Research Establishment has de- veloped an electronic, device by which even the largest telescope, otico. focused on a special star, will automatically follow Its movements. Because of the daily. rotation of the Earth a felescope, vlowing a particular star, has to be moved contingiquel to Yollow this rotation; in fact the telescope is, held steady relative to the Earth's movement. So fer clockwork mechanism has been used, to train, the telescope, . the astronomer applying small manual corrections ns necessary to allow for any inaccurity in the clock.

The astronomer has had to be on the alert for another reasons too. The Image of a star formed by

large telencope has small, and

erratic, notions not only because of the rotation of the Earth but Plso: Uncaure of the variations in The refraction of the atmosphere which result in a blurring of the photographic image The new electronic device makes the Tele-. scopo follow automatically all movement, Including the randomh motion due to refraction, of the intar; įrango—since the response of slociranjo dayices is instantane

R

ARNHOLD & CO., LTD.

HOLLAND HOUSE.

HONG KONG

SASSOON HOUSE

SOLE AGENT FOR-

SHANGHAI

BRITISH OIL ENGINES (EXPORT) LTD.

OIL ENGINES

TYPE A.V.

COMPRESSION

IGNITION

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Wanja

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The Vibrator experience bulit.

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Union Building, Hong Kong.,

Tel. 31361

+