CA2055253A1 - Dual bond taphole mix - Google Patents

Abstract

DUAL BOND TAPHOLE MIX

ABSTRACT OF THE INVENTION
A taphole mix which contains a dual bond system including a liquid novolak resin and a powdered pitch.
Such a mix develops a quick initial set and a slow final set. This mix has been found to be highly effective in the soaking bar practice used to seal tapholes in blast furnaces. The preferred mix contains about 72 wt.% calcined fireclay aggregate sized - 3 mesh, 10 wt.% crude kyanite, sized -100 mesh, 3 wt.%
coke breeze, sized -1/4", and plus additions of about 10.5 wt.% powdered pitch, 8.5 wt.% methylnapthalene #2 solvent, and 2 wt.% liquid novolak resin.

Description

20~2~3 DUAL i3OND TAe~QLE MIX

~ACXQR(~ OF TH E I~IY~Q~
The present inventlon relates to taphole mixes rOr use in metal-maklnq ~urnaces and particularly large production blast furnaces. Tapholes (also re~erred to s as iron notches) are notch-shaped ports located ln t~e lower hearth Or metal-~aking ~urnaces.
At the present tim- resin bondet taphole ~ixes are utilized to seal tapholes in such ~urnaces. These mixes typically contain high alumina or calcined fireclay aggrègates, optional SiC or graphite, crude clay, high carbon yielding resins, silicon powder, and a solvent for the resin such as triethylene glycol.
U.S. Patent 4,792,578 describes such materials and the advantages of the resin binder over prior art which dealt with pitch or coal tar as the binder and creosote as the solvent.
In practice, taphole mixes are placed in a device called a mud gun. This "gun" is actually an extruder which is swung up to the taphole. The extruder pushes the taphole mix into the taphole of the furnace against the air pressure within the confines of the furnace.
The "gun" is held against the taphole until the taphole mix hardens. After a given time, the taphole mix has sufficient strength so that the gun can be removed and the taphole is safely sealed. To reopen the taphole for tapping, a drill is usad. Typical tapholes are about 12 n wide with a height of about 18" and a depth of about 6'. Tapholes are plugged after each cast. A
typlcal blast furnace is tapped about 10 times per day.
Recently, many blast furnace operators have begun to use a ~o-called soaking bar practice to seal their tapholes. In the soaking bar practice, after the tapholq mix is extruded into the taphole, the mix is allowed to harden for a ~ufficient time until the gun can be removed without the mix collapsing. Then a solid metal bar i5 insarted through the semi-set taphole mix to allow heat to b~ drawn up the entire lenqth Or the taphole. ~hls procedure provldeq the temperature re~ulred to permanently set the taphols ~ix .
To begin a cast from the furnace, the soakinq bar is si~ply retracted and at tho end of the cast the taphole is again resealed to pr~vent slag and burden rrOm escaplng th- rurnac-.
Although conventional taphole miXes work reasonably well is soaking bar applications, there is a need for an improved taphole mix which sets quickly so as to support a soaking bar readlly and which is easy to work with.

] ~52~3 conventional taphole mixes ~hich utilize coal tar pitch or petroleum pitch are initially so~t but with heat set at relatively steady rates. The present invention utilizes a dual bond consisting o~ llquid novolak resin and e~ther coal tar pitch or petroleum pitch. In this system, the resin ~tarts to s~t at a faster rate than the pitch. This ensures that the taphole mix has sufficient strength so that the "gun"
can be removed from the hole in a relatively short tlme. By controlling the amount of resin in the mix, the taphole mix can have sufficient strength so that the soaking bar can be inserted through the taphole without tearing away the plugged mass. After the soaking bar i~ in the taphole, the pitch then sets and begins to carbonize. A very strong bond is thus created .
The dual bond of liquid novolak resin and either coal tar pitch or petroleum pitch also offers several unique and unexpected features. First and foremost, this dual bond system allows furnace operators to safely seal the taphole using the soaking bar practice within a predictable and acceptable time frame. Such a desirable feature was not possible with conventional mixes. S~cond, a mix containing these two binders has an extrudable consistency at a lower solvent level than a mix which only contains coal tar pitch or petroleum pitch. This lower solvent level provides for easier extrusion and also results in a lower apparent poro~ity. Less extrusion pressure is desirable in term~ of equipment life and maintenance and lower apparent porosity is highly desirable since it can reduce erosion during a cast. A mix containing the dual bond, for example, showed a 23% decrease in coked porosity and a 50% decrease in extrusion pressuxe.
Accordingly, a principal object of the present invention iB to provldo an improved taphole mix which 2~253 ls hlghly Orrectivo ln th- Joakln~ bar practlce used to seAl taphole- ln blagt rurnacos. Another and more speclrlc ob~ect or the lnventlon 19 the provislon Or a dual bond taphole mix ln which the resin starts to set at a faster rate than the pitch so that the gun can be removed in a relatively short time. Yet still another object o the present lnventlon ls to provide a taphole mix which ls easlly extruded and has a lower apparent porosity. Other objects and rurther scope Or applicability o~ the present invention wlll become apparent ~rom the detailed description to follow taken in conjunction with the accompanying drawing.

20~2~3 ~RI~EF DEsc~IpTIoN--F_THE--~BA~
Flg. 1 ig a graph lllUstratlng cold crushlng str~ngth v~rsus tl~ at SOO~F.

2~2~

qE~L~ DESCRIPTI0N OF T~ E~EE~E~ E~Q~IM~T
In Fig. 1 ~r the drawln~s, a rirst curve labelled A repre-cnts the cold crushing strength Or an exemplary ~ix of the present invention including both a pitch and novolak resin binder and a second curve la~elled 8 illustrates the cold cru~hing strength o~ a conventional ~ix containing only a pltch binder. The variation between curves A and B in tho flrst 2 hours shows that the dual bond initlally develop~ strength faster than a mix containing only a pltch binder.
In accordance with the present invention, an exemplary mix contains 65 to 95 wt.t refractory aggreqate, sized -3 mesh either individually or in combination with the following aggregates: silica, lS calcined fireclay, calcined high alumina aggregate, calcined bauxit~, andalusite, fused alumina, tabular alumina, coke breeze, silicon carbide or graphite. The mix also includes O to 20 wt.~ crude kyanite, sized -100 mesh and S to 15 wt.% crude ball clay. The mix may also contain O to 20 wt.% .erro-silicon nitride powder which is effect~ive in providing improved erosion resistance in large furnaces and 0 to 5 wt.~ powder silicon which may be effective in improving hot strength. Plus additions include 1 to 4 wt.% liquid novolaX rosin, such as RL 2304 manufactured by ~orden, Inc., 8 to 14 wt.% powdered pitch either coal tar pitch or potroleu~ pitch, and 6 to 15 wt.% solvent such as methylnapthalene #2 or #5 which is needed to dissolve th6 pitch.
A specific taphole mix of the present invention which provides the improved properties and allows operators to follow the soaking bar practice in a controlled, trouble-free manner includes:
72% calcined fireclay aggregate 10 crudo kyanite 10 ball clay 5 graphite 3 coarse carbon 20S~2~
) Plus addltions 2~ liquld novolak resln 10.5 ~ine coal tar pitch 8.5 solvent While the inventlon has been described in connection with a prer-rred embotiment, it 1~ not intendHd to limit the JCOp- O~ th- inv-ntlon to the particular ~orm set ~orth, but, on the contrary, lt is intended to cover such alternatlves, modi~icatlons, and equivalents as may be included within the spirit and scope o~ the invention a~ derlned by the appended claim~.

Claims (7)

1. In a taphole mix, the improvement comprising a dual bond system including a liquid novolak resin and a powdered pitch.

2. The improved taphole mix according to claim 1 consisting essentially of 65 to 95 wt.%
refractory aggregate sized -3 mesh, 0 to 20 wt.% crude kyanite, sized -100 mesh, 5 to 15 wt.% crude ball clay, and plus additions of 1 to 4 wt.% liquid novolak resin, 8 to 14 wt.% powdered pitch, and 6 to 15 wt.%
methylnapthalene solvent.

3. The improved taphole mix according to claim 2 wherein the refractory aggregate is selected from the group comprising silica, calcined fireclay, calcined high alumina aggregate, calcined bauxite, andalusite, fused alumina, tabular alumina, coke breeze, silicon carbide, graphite and combinations thereof.

4. In a soaking bar method of sealing a taphole in a metal-making furnace, the improvement comprising applying an improved dual bond taphole mix including both a liquid novolak resin and a powdered pitch.

5. The method of claim 4, wherein said improved taphole mix comprises 65 to 95 wt.% refractory aggregate sized -3 mesh, 0 to 20 wt.% crude kyanite, sized -100 mesh, 5 to 15 wt.% crude ball clay, and plus additions of 1 to 4 wt.% liquid novolak resin, 8 to 14 wt.% powdered pitch, and 6 to 15 wt.% methylnapthalene solvent.

6. The method of claim 5, wherein the refractory aggregate is selected from the group comprising silica, calcined fireclay, calcined high alumina aggregate, calcined bauxite andalusite, fused alumina, tabular alumina, coke breeze, silicon carbide, graphite and combinations thereof.

7. The method or claim 4, wherein said furnace is a blast furnace.