Page
ALUMINIUM AND ITS
ALLOYS
Their Mechanical Working Explained
Aluminium, from the machin- ing point of view, ranks as a soft metal but in certala" directions this complicates its mechanical working, owing to the fact that It tends to clog such tools as twist urills. for example, and so pre- vent the heat generated at the cutting point from being carried
ay with sufficient rapidity, In- general. the technique required approximates to that of working brass. Cutting tools for alumin- tum need a greater side and top rake than do those, for cutting steel, and the edges must be kept ut maximum sharpness. This can be attained by using a very fime abrasive wheel. The tools should have a front clearance of approximately 7 to 8 degrees, and a top rake from 40 - 50 degrees. though slighter smaller angles than these may sometimes be de- sirable. The total angle of the tool-cutting edge will range from
# 40 to 55 degrees.
It is important that the cutting cool edges should be completely regular and snarp, with no not- ches, fash, or grinding wl:cel marks. Lathe tools should have a side rake of 10-20 degrees. a clearance of 6 degrees, and a top rake of 30-50 degrees, the entire 'angle of the tool-cutting edge being from 35 to 55 degrees. 11 it is found that the chips of cer- tajn alumiinium alloys do not break, up readily enough, quicker curling and thus quicker breaking can be produced by reducing both top and side rake angles. Too, great a reduction may impair the finish of the job, however, and regard should be had to this.
"Perting tools need a top ̋rake of 12-20 degrees, with a front cleu-. ance angle of not more than 4 circular-forming degrées. When operations have to be performed, it is best take a roughing cut and a preliminary, and complete the operation with a very light finish- ing cut with a former tool.
SPECIAL DRILLS
In drilling aluminium and s alloys, the trouble usually encoun- tered is that the metal piles up at the cutting edges, with the re- sult that the drill ceases to func- tion, and if compelled, breaks. The proper type of drill for this work is one of special design with a quick, spiral and an included point angle of 140 degrees. A speed of 100-200 feet a minute may be employed, or even more, according to the conditions.
are
Milling cutters for aluminium should be, for preference, of the type with coarse tooth spiral, and should have a good deal of top rake on the cutting, edges. Nick- e'd teeth in milling. cutters often useful in breaking up the chips. Inserted tooth milling cut- ters, given a gorid deal of side and top zake in the teeth, will be.. found quite satisfactory. Helical „milling cutters will also do well en aluminium f proper top rake is given to the cutting edges. This applies also to those cutters whose teeth are staggered.
in
Sawing aluminium is another operation demanding care tool design. The front of the saw teeth calls for adequate top rake and a certain amount of side rake In many instances, according to the form of tooth employed: The hook angle should be 10-25 de- grees. Care should be taken to avoid too rapid a feed of the saw, and for this purpose it will be found an advantage if the me chanism is furnished with a posi- tive feed. No hook should be given to the teeth of saws for- hand feed, but it is important to avoid giving them a negative rake.
SAW TEETH
used, or alternatively a soluble ofl-cu ting compound.
Either the widia ungspai car- bide), or the fuse-welded super- high-speed steel tools can be em- ployed with success for machining alum nium. Where the alumin. ium material to be dealt with is high in silicon, the widia tools are, In fact, more suitable than steel. But care must be taken, neverthe- less, to see that the proper shapes
are given to the tools.
GENERAL RULE
It is difficult to lay down any hard and fast rule for the speeds and feeds to be employed in the working of aluminium and its alloys. It can be said that, on the whole, fine to medium feeds combined with high speeds are best. The feed may range from as much as in: to as little as 3 1,000 in, depending on whether or not the cut is a roughing or finishing one. Actual speeds and feeds vary according to the type of material being worked, the na- ture of the work, the form and kind of tool, the coolant employ- ed, and the design and type of machine driving the tool. A good general rule is that as the feed decreases, the speed should rise, and that the greater the curl on the chip, the less should be the speed. Speeds an feeds can ul- so be affected by the thinness or heaviness of the cutting com. pound; the ligh or the "uting cum- pound, the quicker the speed and he lighter the feed. If it is de- sired primarily to remove a large quantity of metal in a given time, this is best attained by raising the speed rather than using a heavier feed. Special care should be devoted to the prevention of all chatter, which ruins the cut-
ing edges of the tools,
In working alumtulum me- chanically, a coarse feed is always lable to cause the metal to ex- pand. and this may. If not wat- ched, cause the work to finish wrongly to size. Before taking the final finishing cuts, therefore, the plece or part should be given a chance to cool down. It can then be measured and finished to ae- curate dimensions.
While aluminium alloys can sometimes be machined dry, as- suming that properly designed tools have been employed, it is almost always preferable to use a cutting compound. A sluble cn- ting oil, or a mixture of lard oll and kerosene oil, the proportions of each varying according to the type of work and the speed and feed, will be found quite suitable.. Pure lard oil is excellent for the heavier, work.
".
In grinding tools for work on aluminium, care should be taken to see that the correct kind of ab- rasive wheel, grain size, and bord.: are used, while the wheel speed should also be accurate. On all these points the abrasive wheel. makers will give expert and sound advice, and should be consulted.
ELECTRICALLY "CONSOLI. DATED CONCRETE
me-
A novel method of consolidat- -- ing concrete by electrical thods has been developed 12 which the concrete is bonded to the structural steel by means of an electrical vibrátor. Prior to its use ten to twelve workmen were
employed in running 500 to 600 yards of concrete per day, The same amount of work" was done by a skilled mechanic and four labourers with the vib rátor. The vibrator consists of a motor and and vibrating head carried on "a welded frame fitted with clamps so that the machine can be clamped to the steel structure. The 3-h.p. driving motor gives sufficient power to set into vibration" an 18-in. steel girder. The motor is spring sus- pended and drives, an eccentric weight at 3,600 r.p.m. about an axis parallel with the structural member to which it à clamped. The rapid rotation of the eccent ric-weight produces the required vibration. An adjustable eccen- tric is fitted to regulate the de- gree of vibration to suit the size and weight of any beam from 8 large chips, suitable coolant: 10. large chips. A suitable coolant in, to 18 in. wide. In consolidat-
The saw teeth must be given proper clearance" on the sides to avoid sticking or retardation in the cut, which generates exces- sive heat. Coarse teeth, are de- sirable, with rounded gullets and clean edges, so as to facilitate chip removal. Speeds employed, in the case of circular saws, should be from 12 to 16.000 feet a minute. In band-Bawing, high speeds can also be obtained, and are desir- able, if they can be given by the machine without excessive vibra- tion, leading to toch breakdrown. The feed should be fine as com- pared with the peripheral speed.
should always be employed for heavy sawing of aluminium and alloys of aluminium Mineral all let down with kerosene, can be
sre
ing the concrete no special pre- cautions of preparations made. Without any preliminary spreading the concrete is dumped
HONG KONG DAILY PRESS, SATURDAY, JULY 27, 1935.
ENGINEERING AND BUILDING
·SEPARATION OF BLAST - FURNACE SOFTENING OF
DUST
By Electrostatic Methods
For the removal of dust, as well aq water, tar and other liquid parties from air or gas, the most efficient method is un- doubtedly the electrostatic, or- iginated, by Sir Oliver Lodge. Extensive
has experience
also been obtained with this, prin- iple, especially in the case of the "Lodge-Cottrell" equipment, now represented by over 3,000 electroflters, and 95-98 per cent of the total dust is removed from
#
gaseous medium, irrespective of the size of the particles. This is an important practical point since the temoval of particles below 10 microns (1 micron equals one thousandth part of a millimetre), practically in the "cloud" stage, is extremely diff- cult by ordinary methods, and especially when huge volumes are concerned, such as blast- furnace gas and the waste com- bustion gases from power stät- lons amounting to about 500,000 cubic feet at about 250-350 F. per ton of coal burnt,
to
Fra the past there seems have been a general impression that électrostatic methods of. dust separation. In spite of their admitted efficiency, are costly in power consumption. This, how- Lever, is not correct, the total net power consumption being in many cases considerably less. for example, than either centrifugal or water-washing methods.
and
Because of the effective co- operation of the five main com. panies operating the "Lodge. 'Cottrell process in Great Bri tain. the United States Germany, with pooling of al patents and experience, the elec trical power required now aver- ages only 1-2 kw.h.. per 1,000,- 000 cubic feet of air, combustion gas, or other medium.
PRACTICAL FIONEER The practical pioneer in this field is Sir Oliver Lodge, whose work on the subject dates back to 1883. and the modern "Lodge- Cottrell" service represents an association of the patents, re- searches and experience of Sir Oliver Lodge and his "associates. in Great Britain. Dr. F. G. Cot. trell in the United States, and Dr. Erwin Moller in Germany, the British company being Lodge-Cottrell. Ltd., of. Birming ham (George Street Parade) and London, which developed '» from the original Lodge Fume Deposit Company.
Essentially the basic principle consists in the use of chambers ortowers made of. say. concrete, through which passes the dust or tume-ladened air' or gas. In the tower is a series of vertical metal plates or pipes, known as collector electrodes, which are connected to the earth. In the narrow spaces
these between
plates, or in the" pipes, hang
wires or rods with numerous points, forming discharge elec- trodes. The latter are coupled to а high-tension direct current supply, so that a brush discharge takes place. "giving a glow of light, or corona, and creating a powerful electrostatic field. Ag the gases pass through this field all the sold or liquid particles are electrified.....and repelled against the earthed collector electrodes, "that is, the pipes or plates. Here they give up their charge and fall down to the bot- tom of the tower into a hopper." or partly adhere to the plates while the dust-free gas passes on. For this reason the collector electrodes are equipped with motor-driven
rapping hammer
to shake off the dust, while the high-tension current is produced by stepping up the ordinary low- tension supply in a special trans- former and then converting it to direct current by a motor-drives rectifer...
As a result, well over 90 per cent, and often more than 95. Der cent, or the total dust in the gases is separated to the dry state, as already indicated, irre- gpective of the size of the dust particles or the number per unit volume.
fairly evenly on the floor and operating the vibrator for 15 seconds is sufficient to spread the concrete,
GAS CLEANING
Plant In South Africa
The efficiency of gas cleaning. and dust elimization' generally. by electrostatic means is well - ustrated by a plant at the new steel work now in operation at Pretoria, of the South African Iron and Steel Industrial Cor- paration, which has involved a capital outlay of over £5,000,000, mostly provided by the Union .Government. The normal pro- duction is 150.000 tons of steel per annum, and included is a blast furnace of 500" tons of pig iron per 24 hours capacity, along with # by-product coke oven
plant
of 57 ovens, for the production of 450 tons of coke per 24 hours, using a blend of 25 per cent. Natal coal, and 75 per cent. Transvaal coal Also there are two steel melting fur- naces, one steel mixer. and heavy and light rolling mills, in addi- tion to sheet mills, the 'tron ore used being a local Pretoria pro- duct 48 per cent. Fe), which is blended with high-grade Ruston- berg hematite (88 per cent. Fe) from the Transvaal, the rated performance being 17 cwt. of coke, per ton of pig iron.
lower
For the cleaning of the blast- furnace gas an electrostatic plant on the latest 2-stage prin- ciple is installed, supplied by Lodge-Cottrell, Ltd., of Birming- ham and London (Bush House), cleaning down to much than the ordinary gas engine standard of 0.0088. grain's of dust per cubic foot, In general the plant comprises a pre-cooler, three main dry electrostatic treaters. three slat cooling to- wers." and three wet electrostatic treaters, along with the neces- sary fans, valves, pipes, sludge pumps for the settling ponds, transformer house, and other ac- cessories, This is generally on the same lines as the "Lodge- Cottrell" electrostatic cleaning plant just recently put into operation in India at the Tata works. Jamshedpur, and the in- stallation that has been com pleted in England at the Corby Works" (Northants) for Stewarts and Lloyds, Ltd. In this latter connection also it may be stated a unit has now been ordered to bring up the total capacity to 8,0001000 cubic feet of gas per hour.
· NO TRACES OF DUST The results already obtained as regards cleaning of the blast- furnace gas at Fretoria have surpassed expectations and re- peated analysis of large samples of the gas (360 cubic feet and upwards) show no traces of ore dust. Thus the amount of sol-. nble material caught by the fl- ter of the testing apparatus averages 0.0004 grains per cuble foot, or less than one-tenth of the. guarantee (0,004 grains per cubic foot)
•
at
It may be stated also that on the 2-stage principle of cleaning the hot blast-furnace gas, about 450 deg. Fah, Is treated in the first stage of the electrostatic plant, when about 97-98 per cent. of the total dust is removed in the dry state, On the usual lines the "gas, passes through cham- bers containing vertical earthed collector plates and" discharge electrodes connected to high. tension current supply at 60,- 000-70,000 volts, stepped up from ordinary low-tension supply in a special transformer and con- verted to direct current by mo- tor-driven rectifiers. The dust particles are ionized and repeiled to the collector chambers, which are provided with rapping ham- to discharge the "ac- mers cumulated material. In "the" second stage all the Buspended molature and the remaining 2-3 per cent. of the total dust is re- moved, "and the final cleaned blast-furnace gas is dry, cold) (about 75 deg. Fah.) and dust- free, generally, containing as low as 0.002-grains of dust per "cubic " foot, or even below this figure, as at Pretoria, well below the usual guarantee of 0.004 grains. Gas with this extreme degree of cleanliness is, of course, suitable for any purpose, including mo- dern close packing for the stoves, and general combustion using the latest designs of completely automatic burner "control gear.
WATER
On Base Exchange Principle
One of the main advantages of water softening on the base ex- change principal is simplicity, the water merely running through a granular product contained in closed cylinders and emerging with complete sero hardness.
If the water contains much temporary hardness, however. (calefum bicarbonates), the zero hardness water" is alkaline be- cause a corresponding amount of sodium bicarbonate is formed by the reaction with the base ex- change material Th's is not suit- able for towns supply, and when not much temporary hardness is present the remedy, is to by-pass part of the hard, water so that the final blended water. as supplied to the consumer. contains any de- sired degree of hardness, with, of course, less alkall.
Base exchange softening lends itself easily to such control, since it is carried out with entirely clos- ed pipe circuits. The latest scientific principles for the special conditions of owns water supply are well illustrated by two-base exchange installations that have been completed in England at Harpsden (Shiplake and Greys Read) for the Henley-on-Thames Water Company, and the same prin- ciples, can, of course, be used for boller feeding and other industriäl applications. It was necessary to find an auxiliary supply of water In the above district, and an arte- stan bore, 19 in, diameter has bṛen sunk to a depth of over 200 feet. which at Shiplake is being pwop- ed by means of two plunger pumps, each of 5,000 Kal- lons per hour capacity, repre- senting a total head of 250 feet. driven by automatically-controll- ed Diesel engines, each of which is 15 bhp. These pumps discharge" the water through & base ex- change softening plant into four horizontal closed steel cylinders, ⚫each, containing compressed, air, which, in turn, discharges the wa- ter to the mous.
VERTICAL CYLINDERS
The air pressure within the cylinders varies according to the amount of water drawn off by the consumers, and when it falls or rises one or other, or both, of the Diesel engines automatically start up or close down us required, su as to maintain a constant supply 'of water.
The base exchange plani nas been supplied by the Paterson En- gineering Co. Ltd.,. of London (Windsor House, Kingsway, W:C,2), and consista of two verti- cal closed cylladers, 5 i5 44 in. diameter,. filled with the firm's "Basex" softening material." The water from the borehole is 21 degs total hardness, and it is necessary to deliver the softened water to the consumers at 7 degs. total hardness. Accordingly, the main supply zero hardness water from the two softeners is mixed con- tinuously in the pipe circuits be- fore reaching the compressed-air tanks by means of suitable automa- tic valve gear, adjusted as requir- ed, with a portion of by-passed hard water, so that the final wa- ter is always 7 degs, each of the softeners also being fitted with a water meter.
The duty of the softening plant is 24 hours continuous pumping by one pump, or 12 hours by two pumps, and the total capacity of the plant, as already fhdicated Is 10,000 gallons of softened water per hour, with 80,000 gallons be- tween regenerations. Included also are the necessary brine tanks for reviving the base exchange mater- Jai,
The Greys Road plant is on the same lines, consisting of three unite, each ft. diameter, having a duty of 30,000 gallons of water per hour reduced from 21 degs.
hardness to zero hardness and blending to give a 7 degs water, the duty between, regenerations being 188,000 gallons,
Important "Lodge-Cottrell" plants also are now in course of erec- tion in England at the Hams Hall and the Nechells power stations (Birmingham) for the removal of dust from chimney. gas in connection with pulveris- ed fuel firing.
PORTL
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MERALCAE
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RAPID HARDENING
PORTLAND CEMENT
IN PAPER BAGS OF 94LBS NETT
PRODUCT
OF"
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