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A Chromium-cobalt Steel
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Cutting-off Steel From Bar
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The Effect Of Tempering On Water-quenched Gages
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The Forging Of Steel
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Temperature For Annealing
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Restoring Overheated Steel
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Annealing Of High-speed Steel
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Shrinking And Enlarging Work
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Plant For Forging Rifle Barrels
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Judging The Heat Of Steel
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Composition And Properties Of Steel
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Heat Treatment Of Lathe Planer And Similar Tools
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Hardening Carbon Steel For Tools
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Hints For Tool Steel Users
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Nickel
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Cyanide Bath For Tool Steels
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Corrosion
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Classifications Of Steel
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Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
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Heavy Forging Practice






Category: FURNACES

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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Previous: Protective Screens For Furnaces



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