Heavy Forging Practice





In heavy forging practice where the metal

is being worked at a welding heat, the amount of flame that will

issue from an open-front furnace is so great that a plain, sheet-steel

front will neither afford sufficient protection nor stand up in

service. For such a place a water-cooled front is often used. The

general type of this front is illustrated in Fig. 103, and appears to

have found considerable favor, for numbers of its kind are scattered

throughout the country.



In this case the shield is placed at a slight angle from the vertical,

and along the top edge is a water pipe with a row of small holes

through which sprays of water are thrown against it. This water runs

down in a thin sheet over the shield, cooling it, and is collected

in a trough connected with a run-off pipe at the bottom. The lower

blast-pipe arrangement is similar to the one first described.



There are several serious objections to this form of shield that

should lead to its replacement by a better type; the first is that

with a very hot fire, portions in the center may become so rapidly

heated that the steam generated will part the sheet of water and

cause it to flow from that point in an inverted V, and that section

will then quickly become red hot. Another feature is that after

the water and fire are shut down for the night the heat of the

furnace can be great enough to cause serious warping of the surface

of the shield so that the water will no longer cover it in a thin,

uniform sheet.



After rigging up a big furnace with a shield of this type several

years ago, its most serious object was found in the increase of

the water bill of the plant. This was already of large proportions,

but it had suddenly jumped to the extent of several hundred dollars.

Investigation soon disclosed the fact that this water shield was one

of the main causes of the added cost of water. A little estimating

of the amount of water that can flow through a 1/2-in. pipe under

30-lb. pressure, in the course of a day, will show that this amount

at 10 cts. per 1,000 gal., can count up rather rapidly.



Figure 103 is a section through a portion of the furnace front and

shield showing all of the principal parts. This shield consists

essentially of a very thin tank, about 2-1/2 in. between walls,

and filled with water. Like other shields it is fitted with an

adjustment, that it may be raised and lowered as the work demands.

The tank having an open top, the water as it absorbs heat from

the flame will simply boil away in steam; and only a small amount

will have to be added to make up for that which has evaporated. The

water-feed pipe shown at F ends a short distance above the top

of the tank so that just how much water is running in may readily

be seen.



An overflow pipe is provided at O which aids in maintaining the

water at the proper height, as a sufficient quantity can always be

permitted to run in, to avoid any possibility of the shield ever

boiling dry; at the same time the small excess can run off without

danger of an overflow. The shield illustrated in Fig. 104 has been

in constant use for over two years, giving greater satisfaction

than any other of which the writer has known. It might also be

noted that this shield was made with riveted joints, the shop not

having a gas-welding outfit. To flange over the edges and then

weld them with an acetylene torch would be a far more economical

procedure, and would also insure a tight and permanent joint.



The water-cooled front shown in Fig. 105 is an absurd effort to

accomplish the design of a furnace that will provide cool working

conditions. This front was on a bolt-heating furnace using hard

coal for fuel; and it may be seen that it takes the place of all

of the brickwork that should be on that side. Had this been nothing

more than a very narrow water-cooled frame, with brickwork below

and supporting bricks above, put in like the tuyeres in a foundry

cupola, the case would have been somewhat different, for then it

would have absorbed a smaller proportion of the heat.



A blacksmith who knows how a piece of cold iron laid in a small

welding furnace momentarily lowers the temperature, will appreciate

the enormous amount of extra heat that must be maintained in the

central portion of this furnace to make up for the constant chilling

effect of the cold wall. Moreover, since there would have been

serious trouble had steam generated in this front, a steady stream

of water had to be run through it constantly to insure against

an approach to the boiling point. This is illustrated because of

its absurdity, and as a warning of something to avoid.



Water-cooled, tuyere openings, as mentioned above, which support

brick side-walls of the furnace, have proved successful for coal

furnaces used for forging machine and drop-hammer heating, since

they permit a great amount of work to be handled through their

openings without wearing away as would a brick arch. Great care

should be exercised properly to design them so that a minimum amount

of the cold tuyere will be in contact with the interior of the

furnace, and all interior portions possible should be covered by

the bricks. However, a discussion of these points will hardly come

in the flame-shield class, although they can be made to do a great

deal toward relieving the excessive heat to be borne by the furnace

worker.





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