Title:
EXOTHERMIC HOT TOPS
United States Patent 3622536


Abstract:
A composition for lining the inner surface of a casting mould for casting metal or of a hot top for such a mould which comprises ballmill dust, a fluoride, a binder resin and a specific combination of inorganic fibers.



Inventors:
Ruddle, Ronald W. (Rocky River, OH)
Yendrek, Michael (Cleveland, OH)
Application Number:
04/768554
Publication Date:
11/23/1971
Filing Date:
10/17/1968
Assignee:
FOSECO INTERNATIONAL LTD.
Primary Class:
Other Classes:
164/53, 249/197, 249/199, 523/220, 524/34, 524/437
International Classes:
B22C3/00; (IPC1-7): C08G51/10; C08K1/14
Field of Search:
249/197,199 164
View Patent Images:
US Patent References:
3326273Exothermic hot top1967-06-20Jago et al.
3297296Hot top composition for casting molds1967-01-10Edstrom et al.



Other References:

Rose, The Condensed Chemical Dictionary (1966), pages 62, 86, 87, & 632..
Primary Examiner:
Liebman, Morris
Assistant Examiner:
Person S. M.
Claims:
we claim as our invention

1. A composition suitable for lining the inner surface of a casting mould for casting metal or a hot top for such a mould, which comprises 1.5 to 10 percent of an amosite asbestos I of average fiber length not exceeding 2 inches, 1.5 to 10 percent of a fibrous material selected from the class consisting of a chrysotile asbestos II slag wool and mixtures thereof, of average fiber length equal to or greater than amosite asbestos I, 0 to 5 percent of a chrysotile asbestos III which is of average fiber length less than that of the amosite asbestos I, a binder resin in a proportion not exceeding 10 percent, 0 to 10 percent of a metal fluoride and the balance, being more than 50 percent, of ballmill dust, the total inorganic fiber content of the composition being at most 20 percent by weight, said composition being essentially free from organic fibrous material.

2. A composition according to claim 1 having substantially the following composition

3. A composition according to claim 1 having substantially the following composition

4. A composition according to claim 1 having substantially the following composition

Description:
This invention relates to the provision of linings for moulds used to make ingots or castings from molten metal, and for hot tops, risers and the like used with such moulds. It further relates to the new compositions which are employed in the production of such linings.

In the production of ingots and castings from molten metal it is necessary to provide that molten metal may feed to the body of the ingot or casting to compensate for the shrinkage which occurs on cooling since otherwise the ingot or casting may be formed with internal cavities or fissures. The usual method is to provide that the solidification of the head metal in an ingot mould or in a hot top provided thereon, or in the risers and feeder heads of a casting mould is delayed, so providing a reservoir of molten metal which may feed to the ingot or casting proper. This delay may be achieved by setting up a barrier to the loss of heat from the head metal by lining the head of the ingot mould or the hot top, risers, feeder heads and the like with a refractory heat-insulating composition, or by using a composition of which the ingredients are ignited by the heat of the molten metal to react exothermically.

In recent years there have come into use, for the production of linings for the inner molten-metal-contacting surfaces of metal casting moulds, or of a hot top for such a mould, shaped bodies or linings made of compositions which contain predominantly a refractory filler material, usually with minor amounts of an organic fibrous material and of a binding medium. The organic fibrous material is usually a paper pulp, e.g. repulped old newsprint. The binding medium may be based on any of a wide variety of materials, e.g. a natural or synthetic resin or glue, e.g. a silicone resin, urea- or phenyl-formaldehyde resin, a cellulose glue, sulfite lye, or sodium-silicate.

The refractory material used in the said compositions is generally a siliceous material such as sand, quartz, quartzite, inorganic silicate, or may be a material such as dolomite. The refractory material may also include a fibrous refractory, e.g. asbestos, glass fiber, or rock wool.

It has also been proposed to modify such compositions by the inclusion of "ball mill dust."

Ballmill dust is obtained from the skimming and drosses formed during the melting of aluminum and aluminum alloys in an oxygen-containing atmosphere. Usually the skimmings and drosses pass to the secondary melters for pulverizing by ballmilling or grinding. In some cases the dross may need to be reduced in size in a jawcrusher but generally it is sufficiently fine for ballmilling without any pretreatment. After ballmilling it is usual to screen the residue. The coarse material (normally +10 or +16 mesh) contains most of the metallic aluminum and is removed for remelting. The fine material, which is called ballmill dust, may be washed by the producer in order to remove water-soluble salts.

The dross usually is composed mainly of aluminum oxide (resulting from the oxidation of the molten metal) and particles of aluminum or aluminum alloy, together with a few percent each of metallic contaminants such as copper, silicon, iron, zinc, magnesium, and/or their compounds. Some silica is generally present as are fluorides and chlorides of sodium, potassium, and/or other metals (from fluxing ingredients and their various reaction products). Aluminum nitride is also usually present, resulting from the reaction between aluminum and atmospheric nitrogen.

Generally the fluxes used with aluminum or mixtures contain one or more of the following components: sodium fluoride, sodium chloride, sodium sulfate, potassium chloride and cryolite.

The ballmill dust may contain up to 50 percent sodium chloride and values of 10 to 15 percent total fluorides (water-soluble and water-insoluble) have been noted.

Sodium aluminate, sodium carbonate and the oxides of the alloying elements are also often found.

Generally speaking the less developed the aluminum industry in a particular country, the higher quality the ballmill dust available in it, e.g. there is a considerable quantity of ballmill dust containing up to 40 percent aluminum available in Spain. This is due to both the limited use of fluxes, leading to higher aluminum contents and low chloride and fluoride content of the dusts, and to restricted refining capacity. In the United Kingdom any ballmill dust is refined to extract aluminum metal if its metal content exceeds 30 percent. By comparison, ballmill dusts containing over 60 percent metallic aluminum are by no means uncommon in other European countries.

The residual aluminum content of ballmilling dust depends therefore on the source and on the type of processing it receives but normally is between 10 and 30 percent. It may however contain as little as 5 or as much as 60 or 70 percent metallic aluminum. For optimal exothermic performance when pouring ferrous metals, it is preferred that the ballmill dust contain from about 5 to about 45 weight percent aluminum metal (e.g. about 10 to 25 percent), and accordingly it may in some instances be desirable to fortify aluminum-lean dust with blown or ground aluminum metal. With nonferrous metal casting, a higher aluminum content may be desirable.

It is to be understood that the term "ballmill dust" used herein means a product as thus defined.

Thus, a composition which has been proposed for lining the inner surface of a casting mould for casting metal or of a hot top for such a mould comprises a predominant amount (i.e., at least about 50 percent) of ballmill dust, advantageously together with about 2 to 30 percent by weight of organic fibrous material, about 1 to 10 percent by weight of a binding medium and optionally from about 1 percent up to 10 percent fibrous refractory material. Preferred compositions are those containing 78 to 94 percent ballmill dust, 3 to 9 percent of organic fibrous material and 1 to 8 percent of binding agent. The organic material and the binding agent may be any of those referred to above or mixtures thereof.

A suitable product of the type may be formulated as follows:

Ballmill dust 85.00% Urea/formaldehyde resin 1.25% Phenolformaldehyde resin 2.50% Amosite asbestos 1.75% Paper pulp 6.50% Calcium fluoride 3.00%

(Amosite asbestos used in this composition is of average fiber length now exceeding 2 inches).

It is found however that a composition so formulated does however suffer from occasional deficiencies in the form of "boiling" when contacted by molten metal. In extreme cases, this may cause porosity in the riser and even in the casting and result in the scrapping of the casting.

The "boiling" appears to be caused by the combination in the product of moderate permeability (12 to 20 AFS units) and a moderately high-volatile content of the order of 10 percent.

In addition the aforesaid product also suffers from another drawback. If sleeves made from the composition set out above are rammed up in a sand mould which is later subjected to drying for up to 24 hours at temperatures ranging up to 700° F., the paper in the product tends to char, thus weakening the sleeve to the point where virtually all strength is lost and the sleeve rendered unusable.

It has now been found that the foregoing disadvantages can be overcome by the use of a composition in which the paper pulp is omitted but the inorganic fiber content is increased and is made up of both short and long fiber materials. Since different types of asbestos fiber may be used in this invention the various forms are hereinafter referred to as Asbestos I, Asbestos II and Asbestos III and the characteristics of these are hereinafter set forth.

According to the present invention therefore there is provided a composition suitable for lining the inner surface of a casting mould for casting metal or of a hot top for such a mould, which comprises, by weight, 1.5 to 10 percent of an amosite asbestos I of average fiber length not exceeding 2 inches, 1.5 to 10 percent of a chrysotile asbestos II or slag wool, or both, of average fiber length equal to or greater than asbestos I, 0-5 percent a chrysotile asbestos III which is of average fiber length less than that of the Asbestos I, a binder resin in a proportion not exceeding 10 percent, 0 to 10 percent of a fluoride and the balance, being more than 50 percent, of ballmill dust, the total inorganic fiber content of this composition being at most 20 percent by weight.

An essential characteristic of the present invention is the combination of inorganic fibers as set forth. It will be observed that the inorganic fiber content essentially includes Amosite asbestos I and either slag wool or a Chrysotile Asbestos II. It is to be observed that satisfactory results are not obtained by using for the second (longer fiber) ingredient, a long fiber amosite asbestos. These may be as follows:

ASBESTOS I

Amosite Asbestos: Composition: 5.5 FeO, 1.5 MgO, 8 SiO2, H2 O

Fiber length-- not greater than 2 inches. Open enough to eliminate clumps. Grades AW, A10 or S33 of North American Asbestos Corporation are satisfactory. Grade S-33 has the following grading:

+4 mesh 10 oz./lb.

+10 mesh 3 oz./lb.

-10 mesh 3 oz./lb.

Fiber lengths may vary from one-eighth to 11/2 inches.

ASBESTOS II

Chrysotile Asbestos: Composition: 3MgO, 2 SiO2, 2H2 O

Grade 4T of Carey-Canadian Mining Ltd. is very satisfactory. It has an average fiber length greater than 2 inches. It has a grading of:

+4 mesh 2 oz./lb.

+10 mesh 10 oz./lb.

-10 mesh 4 oz./lb.

ASBESTOS III

Chrysotile Asbestos: The variety known as chrysotile asbestos shorts e.g. that sold as Grade 7D of Carey Canadian Mining Ltd., is very suitable. It has an average fiber length less than 2 inches and is graded:

+10 mesh 5 oz./lb.

-10 mesh 11 oz./lb.

Slag Wool: (optional ingredient)

Most grades of pelletized wool satisfactory.

"Thermofiber" packing wool of U.S. Gypsum Corporation, Federal Specification: HH-I-521C, Type 3 is very satisfactory.

The fluoride used is preferably calcium fluoride but any other fluoride may alternatively be employed.

The following is an example of a specific composition according to the invention:

Ballmill dust 78.0 % Urea-formaldehyde resin 2.0% Phenol-formaldehyde resin 3.0% Amosite asbestos I 4.9% Slag wool 4.9% Chrysotile Asbestos II 4.2% Calcium fluoride 3.0%

The composition of the ballmill dust preferably used in the practice of the invention may vary widely, e.g. within the ranges shown below:

Percent Aluminum 5 to 70 Aluminum oxide 15 to 60 Zinc 0 to 5 Chloride 0 to 30 Lead 0 to 1

Most preferably, however, the composition contains approximately 15-45 percent aluminum, about 1 percent chloride and not much more than 0.1 percent each of zinc and lead. A minimum aluminum content of 15 percent seems to provide a sufficiently intensive reaction to make feeding of steel castings efficient in riser sizes down to about a 3 -inch diameter. However, improved efficiency can be obtained by using higher aluminum contents in the feeding of both ferrous and nonferrous alloy castings. Generally speaking, the advantage of higher aluminum contents is most marked with the smaller diameter risers, but advantage is to be expected with all sizes.

Impurities such as zinc, chloride, and lead are detrimental in that they cause the evolution of excessive or toxic fumes during combustion of the product. They do not effect the resultant castings however. The presence of some fluoride is beneficial since it increases the sensitivity of the mixture; for example, the addition of 2 percent sodium fluoride (one-half percent in the finished product) results in improved burning especially on small diameter risers.

The ballmill dust should preferably not contain large particles of dross since, if included, these tend to increase the density of the final product, and reduce the efficiency of the aluminum combustion.

The slabs or sleeves may conveniently be formed by a slurry technique as follows: The ingredients of the composition are made up to an aqueous slurry. Advantageously, a small quantity of a surfactant known per se is included in the composition to facilitate this. The slurry is charged into a vessel having a perforate wall or walls and pressure or vacuum is applied to cause the slurry to be urged against the perforate walls. The liquid medium of the slurry passes through the perforate walls as effluent and the solid constituents are compacted against the perforate walls as layers of desired thickness.

One of the most convenient methods of effecting this process when making sleeves is to spin a porous mould containing the slurry at high speed, thereby to drive the water from the slurry; the mode of action is that of a normal domestic spin-dryer. By this method, the internal diameter of the sleeve formed may only be controlled by the amount of slurry added to the mould, and the solids content thereof. In this connection the solids content of the slurry is preferably 10 to 50 percent, most preferably 30 to 35 percent. Typical spinning times and speeds are 1,200 to 1,400 r.p.m. for 1.5 to 3 minutes. The compacted sleeves may be withdrawn from the mould, and are fairly easily handleable.

In another method the porous former connected to a suction tube is introduced into a tank of the slurry, and liquid medium sucked through the former, and out through the tube, the solids of the slurry thus depositing on the outside of the former. However, economic considerations usually limit the use of this method to small slabs or sleeves. Water extraction times tend to be longer than with spin-forming. It is preferred to use a slurry of 15 to 20 percent solids content, lower concentrations of solids requiring longer water extraction times. This method is of great value where, for example, the internal diameter of a sleeve must be formed to close dimensional tolerances.

Before use the slabs or sleeves must be dried. This is generally effected by drying on vented core plates in normal ovens through which air is passed.

It must be appreciated that where the foregoing technique is employed any binder which is soluble in the liquid medium will be largely lost in the effluent (from which if desired it may be recovered) and it is therefore necessary to employ sufficient binder to ensure that enough is present in the liquid, which is retained by the compacted solid constituents to provide the necessary composition as earlier described. However, a water-insoluble, thermoscreening binder may be employed in solid binder form (e.g. phenolic resins in a suitable state of polymerization). In such case losses with the effluent will be negligible. A mixture of insoluble and soluble binders may be employed.

Further, it is desirable that the ballmill dust used contain not more than 50 to 60 percent of material of particle size -200 mesh (Tyler) since slurries made using dust with these or even higher fine dust contents tend to be nonporous and tend to require longer spinning or compacting to extract the water. Where long water extraction times are acceptable, however, materials containing up to 85 percent, or over, of -200 mesh particles may be used.

The following are examples of suitable recipes especially suitable for use in forming lining slabs according to the rotary vacuum-forming technique described above:

EXAMPLE I

Ballmill Dust 81% Phenol-formaldehyde Resin 3% Urea-formaldehyde Resin 2% Fluorspar 3% Amosite asbestos I 6% Slag wool 5%

EXAMPLE II

Ballmill Dust 78% Phenol-formaldehyde Resin 3% Urea-formaldehyde Resin 2% Amosite asbestos I 6% Fluorspar 3% Slag wool 5% Chrysotile short fiber asbestos III 3%