CA1106555A - Dry mold coating for ingot mold - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved ingot mold coating composition comprising 15 - 40%
of Gilsonite with the balance being flour. A method of forming steel ingots using this mold coating composition is also described.

Description

INTRODUCTION
.. -- .
It has been the practice in the processing of molten metals to apply a coatinCJ to the surface of molds prior to pouring metal into the molds. ~his practice has ~een ollowed extensively in the steel industry where ingot molds are normally coated prior to the forming of steel ~ngots. The recognized purpose of all of these coatings has been to improve the sur~ace quaIities of the molded metal. The function that most mold coatings are designed to per~orm is one of repelling splashes of molten metal and preventing th~m from solidifying on the mold walls.
The surface of solidified metal, which results from splashes¦
adhering to the mold walls, normally oxidizes very rapidly. This surface oxidation plus high heat capacity acquired by adhering to the mold prevents the metal, which results from the splashes, from being incorporated into the main body of the ingot after the mold has been completely filled.
The failure of the metal from the splash to be incorporated into the main body of a metal ingot results in surface discontinu-ities which must ~e removed from the ingot by burning, scarfing, grinding or other suitable means prior to fabrication of the ingot into shapes or sheets. If the discontinuities are not removed b~
o~e o~ these types of operations, they will result in defects in the finished metal products~
~ arious organic and inorganic materials have been tested in prior art endeavors to solve the problem of surface defects in metal which are caused by splashes adhering to mold walls. Coal tar, graphite, asphalt and various combinations of these and similar materials have been most widely used. These materials have all been unsatisfactory in that the improvement in metal surface result-ing from their use has been relatively slight in comparison to the expense and dif~iculty involved in applyincJ them to molds.

-2-~ fi~`;~3 Many mold coating compositions are applied to hot ingot molds and stools as aqueous slurries. I:E such formulas are applied and puddled either on the mold or stool and not given adequate drying time, serious explosions will result when molten steel is teemed into the mold. It would, therefore, be beneficial if it were possible to provide a mold coating composition which could be applied in the form of a dry powder and which would have good adher-ence to the mold as well as provide useful and beneficial coatings capable of improving the surface qualities of the metal produced in such molds.
THE INVENTION
The invention provides an improved mold coating composition which contains 15 - ~0% by weight and, preferably, 20 - 30% by weight of Gilsonite with the balance being flour, preferably :in the form of either middlings or shorts.
Gilsonite is an asphalt-like material and is a coal-like ~;
solid. A typical Gilsonite material has a softening point, ring and ball method of 270 - 375F. and contains between 10 - 20% of carbon. ~ `
For more information, see Vol. 10, page 527, et subs, Encyclopedia of Chemical Technologyl Second Edition, John Wiley ~ Sons, 1966.
Any flour can be used but it is preferred to use a wheat flour either in the form of middlings or shorts.
For a further description of middlings and shorts, see Volume 22, page 287, et subs, Encyclopedia of Chemical Technology, Second Edition, John Wiley ~ Sons, 1966.
To prepare the materials~ the Gilsonite should be in -the form of a finely divided powder or dust which is then physically blended with the flour in the proportions previously indicated.
It is possible to substitute for ~he flour 5 - 30% by weight of an alkali metal lignosulfonate.

' .

- 3 -.. .~, 5~i~

l'he invention fincls :its primary util:ity in the treating of ingot molds used to produce steel. Thus, the invention also deals with a method of forming steel ingots which comprises the steps of:
a. coating the mold surface of an ingot mold S w:i-th the compositions previously described;
b. teem:ing molten steel into said mold;
c. allowing said steel to solidify; and then d. removing said ingot from said mold.

To illustrate the invention~ the following ls g-iven by way of example:
Test Method The tester consists of a hot plate with a removable 1/2 inch steel plate top. The temperature o-f the plate is adjustable to over 538C with a control box. Inserted into the side of the plate to a depth of about 5 inches is a temperature probe connected to a recorder which plots the temperature of the plate surface over the length of the test period. A thermometer is also inserted as a double check of the temperature.
To spray the powder, an aspirator is connected to a 35 psi air supply and fed the various powders into the air-stream via a :Funnel on the aspirator. The powder was blown out through a hand held hose directed to the hot plate.
For the test~ the hot plate is positioned vertically. The test products were sprayed onto the hot plate at a surface tempera- ~ -ture of 205C and a photograph was taken. The temperature of the hot plate was immediately turned up until 425C was reached (approx.
15 min.) and another photo was taken. The temperature was held at ;~ 20 425C for 40 min. to see the effect of prolonged exposure to such temperatures and a final photo was taken. The quality of the coating was then judged by these criteria:
1) thickness of coating on hotplate;
2) approximate amount of overspray;
3) adhesion of coating at 425C;

4) final appearance of coating after 40 min. at 425C.
Using the above test method, the following results are presented below in Table I.
,....................................................................... .

' ~ ~, ., r-l a) ~
O H Q) O ~ JJ
C~ )~
(d ~ U~ rl

5-1 7 tl~ Ir-l r l ~t ra Q) ~ ~ O
~ Q~ O ~~I S) O
rl Q~ O Ul (U ~ O U~
C~ W

7 ~ ~ ~
C~ ' O ~ O O
00 O ~ O O
-rl Ul ~r ~ O
r l h S~
~a ~ Q) ~¢ ~

~ (U r~
h ~ r~
~ ~ ~ ~ a 5~1 ~ r I rl I
(U ~ l't:l ~ ~
P~ ~!) a) ~I) Q) l_~ O
a) a~
h ~q c) ~, ~: ~
E-lr ~ > O ~ ~
tdrl 0 ~1 0 0 U ~

o ~ `f o ~1 rl ~rl ~rl ~r7 q~l o ~ o u~ o ta 1 u~
rl ~ ~ U7 ~ Ul r~
1~1 ~ 7 ~:S r~ 1 r-7 ~ Ql ;~
r-l ~rl O rlrl r; ~rl ~ri -rl ~1 .~ '`'~

h d.. G'P d. 0~ dP o~O o\ dP dP I `
O O O O O O O O O
~ rJ cr ~ ~

~'~

i~ ~

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A mold coating composition comprising 15 - 40% by weight of Gilsonite and 60 - 85% by weight of flour.

2. A mold coating composition comprising 20 - 30% by weight of Gilsonite and 70 - 80% by weight of flour.

3. In a method of forming steel ingots which comprises:
a. Coating the mold surface of an ingot mold with the composition of Claim 1;
b. Teeming molten steel into said mold;
c. Allowing said steel to solidify; and then d. Removing said ingot from said mold.

4. In a method of forming steel ingots which comprises:
a. Coating the mold surface of an ingot mold with the composition of Claim 2;
b. Teeming molten steel into said mold;
c. Allowing said steel to solidify; and then d. Removing said ingot from said mold.