The present invention relates to an improved device
for heat insulation of ladle cover and a method of constructing
the same.
The invention relates more particularly to an improved
heat insulating device for ladle cover, in which strips of
ceramic fibre blanket are wrapped in the form of coils around
the outer peripheral surface of a number of concentric rings
of increasing diameter made of stainless steel strips and held
in position thereon by a number of stainless steel rods
introduced radially into the rings as well as the layers of
ceramic fibre blanket strips wrapped around the rings and the
dish-shaped body thus formed is kept suspended with its plane
Parallel to the horizontal inner surface of the ladle cover by
means of a number of stainless steel hangers and the method
followed for constructing the said device.
In the steel manufacturing process, ladles, used for
transportation/treatment of molten metal, are required to be
preheated by means of burners and maintained at a high
temperature of around 1OOO°C by heat insulation of the ladle
cover before tapping molten metal into the ladles, with a view
to preventing formation of skulls, damage of the refractory
linings and loss of molten metal temperature in the ladles and
extending the working life of the ladle covers.
The existing device for heat insulating the ladle
covers comprises fixing in two layers a ceramic fibre blanket
of thickness 25 mm with the direction of fibres in the two
layers perpendicular to each other, by means of stainless steel
studs and washers of AISI 310 grade which are not kept covered
up by the ceramic fibre blanket, and are therefore corroded by
oxidation by the high temperature environment inside the ladles,
resulting in the failure of the insulation device within a
relatively short period i.e. 6 to 9 months with consequent
increase in the down time of the ladles and cost of maintenance
of the insulation device.
The object of the present invention is to provide an
improved device for heat insulating ladle covers, having an
expected longer working life of around three years.
Thus the invention provides an improved device for heat
insulation of ladle covers, characterised in that the device
comprises multiple layers of strips of ceramic fibre blanket
wrapped tightly around the outer peripheral surface of four
concentric metallic rings of increasing diameter and held in
position with respect to said rings by means of twentyfour
metallic rods inserted into the said rings and the layers of
ceramic fibre strips v/rapped around the rings to form a dish-like
body which is kept suspended with its horizontal plane parallel
to the inner surface of the ladle cover by means of twenty hangers
each having its one end fixed to the inner surface of the lader
cover and other end to the junction of a rod and ring laid in the
said dish-like body formed.
The invention provides also a method of constracting
the improved device comprising the following steps in
sequence :-
(i) 200 mm wide and 50 mm thick strips are cut from ceramic
fibre blanket of type HTZ, density 128 kg/m3 and composition by
weight % : Al2O3 - 33 to 36, SiO2 - 44 to 48, ZrO2 - 16 to 18,
TiO2 - 0.3 and Fe2O3 - 0.1;
(ii) the strips ar*r wrapped manually first round the outer
peripheral surface of innermost ring in multiple layers tightly
upto a radial thickness of 600 mm;
(iii) the next outer ring is then fitted around the outer
peripheral surface of the outermost layer of the ceramic fibre
strips wrapped around ring and pressed by means of a fixture made
from a 50 mm wide metallic strip fitted around the outer peripheral
surface of ring to reduce the radial thickness of ceramic fibre
strips wrapped around ring from 600 mm to 500 mm;
(iv) eight rods are then inserted into matching holes in
ring and next into matching holes of inner rings, and in four
hangers;
(v) the free ends of ring are joined by a screw through
the matching holes therein and the free ends of hangers are fixed
to the inner surface of ladle cover by welding;
(vi) eight rods and ring are removed and ceramic fibre strips
are wrapped manually around the outer peripheral surface of ring
tightly upto a radial thickness of 600 mm;
(vii) ring is again fitted around the outer peripheral surface
of the outermost layer of the ceramic fibre strips wrapped around
ring in the same manner as in steps (iii) to (vi), followed for
fixing ring;
(viii) outer ends of eight rods are fixed at the matching
holes in ring and the rods are fixed next into matching holes
of inner rings, and in four hangers by eight cotter pins
respectively through hole in each rod, and the free ends of
hangers are fixed to the inner surface of the ladle cover by
welding;
(ix) wrapping of ceramic fibre strips, fixing of ring,
sixteen rods, eight hangers and twenty cotter pins are
performed in the same manner as in steps (ii) to (viii).
The invention is described fully and particularly in
an unrestricted manner with reference to the accompanying
drawings, in which -
Figure 1 is a schematic bottom view of the existing
device for heat insulating ladle covers;
Figure 2a is the schematic bottom view of the
improved device for heat insulating ladle covers;
Figure 2b is the vertical section at A-A in Fig. 2a;
Figure 2c is the vertical section of a rod;
Figure 2d is an enlarged view of hanger and ring
at area A in Fig. 2b; and
Figure 2e is an enlarged view of portion B in Fig. 2a
where the two free ends of a ring are joined by a serew.
Referring to Fig. 1 the existing device for heat
insulating the inner surface of a ladle cover comprises two
layers of 25 mm thick ceramic fibre blanket with the fibres in
the two layers being directed perpendicular to each other, and
fixed tightly to the inner surface of the ladle cover by means
of stainless steel studs (1) of AISI 310 grade which are welded
to the ladle cover at their one end at a separation of 150 mm
from the adjacent ones and stainless steel washers of the same
grade. The outer ends of the studs and the washers are left
exposed to the hot environment inside the ladle and so get
corroded in a relatively short period of 6 to 9 months of use
of the ladle causing displacement of the ceramic fibre blanket
layers in the downward direction and making the device
ineffective•
Referring to Fig. 2a, the improved device for heat
insulating ladle covers comprises concentric rings (r1 to r4);
radially introduced rods (R1 to R24); hangers (H1 to H20);
and cotter pins (PI to P24).
Referring to Figs. 2b to 2d, each metallic hanger (H)
having the upper end welded to the inner surface of ladle
cover (2) is typically of length 150 mm, with a hole (3) of
diameter 1A mm at a distance of 100 mm from the upper end
thereof; each ring (r) is made of metallic strip of width 150 mm
with a hole (A) of diameter 14 mm matching with hole (3) of
diameter 14 mm of the hangerj each metallic rod (R) is of length
1050 mm with a pointed end (5), head end (6) and a cotter pin
hole (7) of diameter 6 mm.
Referring to Fig. 2e, the two free ends (8 and 9) of
each ring (r) are joined together by a screw through matching
holes (10 and 11) of diameter 5 mm positioned at a distance of
20 mm from each of the two free ends thereof.
The method of constructing the improved device
comprises the following steps in sequence :-
(i) 200 mm wide and 50 mm thick strips of ceramic fibre
blanket of type HTZ, density 128 kg/m3 and composition by weight
% Al2O3, - 33 to 36, SiO2 - 44 to 48, ZrO2 - 16 to 18, TiO2 -
0.3 and Fe2O3 - 0.1 are PrePared;
(ii) the strips are wrapped round the outer peripheral
surface of ring (r1) in multiple layers tightly upto a radial
thickness of 600 mm;
(iii) ring (r2) is fitted around the outer peripheral
surface of the outermost layer of the ceramic fibre strips
wrapped around ring (r1) and tightened by means of a fixture
made from a 50 mm wide metallic strip fitted around the outer
peripheral surface of ring (r2) to reduce the radial thickness
of ceramic fibre strips wrapped around ring (ri) from 600 mm
to 500 mm;
(iv) rods (R17, R18, R19, R20, R21, R22, R23, R24) are
inserted into matching holes in rings {ri, r2, r3) and hangers
(H1, H2, H3, HA);
(v) the free ends of ring (r2) are joined by a screw
through the matching holes (10, 11) therein and the free ends
of hanger