US3728102A - Anti-piping composition for the production of metal ingots and castings - Google Patents

Abstract

ANTI-PIPING COMPOSITIONS COMPRISING ALUMINUM AND OXIDISING AGENT ARE IMPROVED BY THE ADDITION OF A FLAME GENERATING MATERIAL SUCH AS PAPER PULP, SAWDUST, WOOD FLOUR OR COB FLOUR.

Description

United States Patent Ofifice U.S. Cl. 75-94 8 Claims ABSTRACT OF THE DISCLOSURE Anti-piping compositions comprising aluminium and oxidising agent are improved by the addition of a flame generating material such as paper pulp, sawdust, Wood flour or cob flour.

This invention relates to the production of metal ingots and castings.

This application is a continuation of my parent application, Ser. No. 783,703, filed Dec. 13, 1968, now abandoned.

In the production of metal ingots and castings by pouring molten metal into a mould, the shrinkage of the metal in the body of the mould as it cools and solidifies requires that molten metal should feed from feeder heads, risers, hot tops, or the head of an ingot mould, to compensate for such shrinkage. If this is allowed to take place undisturbed, there is formed a substantial central cavity in the head metal, a phenomenon known as pipe.

To avoid or minimise this, it is well known practice to apply to the surface of the metal in the mould a socalled anti-piping compound. This is usually a composition of which the ingredients ignite and react exothermical- 1y when fired by the heat of the molten metal. The heat thus generated delays the solidification of the head metal and thus reduces or eliminates the formation of pipe.

The exothermic compositions used as anti-piping compounds are generally of an aluminothermic composition i.e. containing finely divided aluminium and oxidising agent therefore. It is possible to use aluminium in relatively pure elemental form, as powders, turnings, sawings or the like but since it is desirable to keep the cost of the antipiping compound as low as possible it is convenient to use the commercial material known as ball mill dust. This is the ground product from slags obtained in the metallurgy of aluminium and usually contains alumina, flux residues and the like and aproportion of aluminium metal. The proportion of aluminium may vary Widely depending on the source of the ball mill dust but is generally 10 to 30% by weight.

The compositions contain oxidising agents for the aluminium, suitable materials being strong oxidising agents such as alkali metal, and alkaline earth metal nitrates and chlorates, and reducible oxides such as iron oxide and manganese dioxide.

It is also known practice to include a proportion of a fluoride, e.g. an alkali metal or alkaline earth metal fluoride, or aluminium fluoride, or a mixed fluoride salt, e.g. cryolite, or a fluoro complex salt such as a titano, boro or silico fluoride.

When such exothermic compositions are ignited, they 3,728,102 Patented Apr. 17, 1973 tend to generate fumes which are noxious under foundry conditions and this is especially the case where ball mill dust is used as the source, or part of the source, of the aluminium in the composition. An additional disadvantage of the generation of such fumes is the obscuring by clouds of smoke of the metal surface, so that the teeming is made more difiicult.

It is an object of the present invention to provide antipiping compositions of the type generally set forth above, which further contain an additive which reduces their tendency to the generation of fume.

As a result of considerable research and experiment it has been found that the fume emitted from such compositions on burning is itself capable of being ignited (and therefore rendered innocuous) but this ignition does not normally take place spontaneously.

According to the present invention there is provided an anti-piping composition in powder or granular form, which comprises aluminium and oxidising agent therefor together with an organic additive which at the temperature of the molten metal generates flame. In this way, the smoke or fumes produced on application of the composition to the molten metal are consumed in the flame by a socalled after-burner effect.

More specifically according to the invention it has been found that organic materials comprising high proportions of carbon hydrogen and oxygen are very suitable for the purpose and many cellulosic materials are of value, for example, paper pulp, wood pulp and shredded paper. Materials such as wood flour and the like are particularly suitable. The material should preferably have a low bulk densitypreferably 0.2-0.4 gm./cc.-and a low moisture content. Examples of such materials are wood flour and sawdust (preferably from hard wood and of particle size passing a 10 B88 mesh but without a substantial quantity passing a E88 mesh), ground cobs or cob flour, grain hulls and nut shells, with polystyrene and similar plastics chips, cereal flours, and organic gums such as sulphite lye and gum arabic being usable but not preferred. A particularly preferred materials is 20+ 100 E58 mesh cob flour.

The optimum quantity of such additive to the anti-piping composition for the purpose specified will vary with the particular anti-piping composition but will generally be 1- 2.0%, preferably 5-15% by weight. Particularly good results have been obtained by the use of the additives in quantity of the order of 10% by weight.

The improved compositions of the present invention may contain aluminium in any of the forms indicated above and any of the oxidising agents, or fluoride additions mentioned above. They are used in conventional manner by sprinkling the powdered or granular composition onto the surface of the molten metal.

It is further of value to include in the anti-piping composition of this invention a proportion of a humectant such as glycol or glycerol, in a proportion of 1-20%, preferably 5-15% by weight of the composition to aid in reducing dust from the material. Such materials have the additional advantage of supplying plenty of hydrogen and oxygen for burning, while not supplying much carbon, and they thus aid in reducing the smoke and fume from the anti-piping agent.

Further, the anti-piping compositions according to this invention may contain a flame retardant which serves to spread the action of the anti-piping compound over a period of time rather than allowing it to proceed violently for only a short period of time. Suitable materials for this purpose are silica flour and sodium chloride.

3 The following examples of anti-piping compositions according to the invention will serve to illustrate the invention:

EXAMPLE 1 The following anti-piping compositions are formulated (in percentages by weight):

Aluminium foil 4 Washed ball mill dust 52 Alumina 15 Calcined magnesia (minus 150 BSS mesh) 13 Sodium nitrate 9 Haematite 4 Sodium aluminium fluoride 2 Sodium fluoride l Washed ball mill dust (18% aluminium) 83 Sodium nitrate 7 Millscale Sodium aluminium fluoride 3 Sodium silico fluoride 2 To each of the foregoing compositions there was added various proportions of: cob flour, hard-wood flour, plastics chips, ground nut-shells, grain hulls, and the resulting mixtures were tested to observe the extent to which they generated visible fumes. It was found that in each case a proportion of of the wood flour additive, by weight of the composition A or B, was the most suitable. In each case, a marked reduction in fume evolution was observed; the amount of fume generated was visually estimated as about 10% of that generated using anti-piping compounds in which the flame generating additives had not been included.

EXAMPLE 2 An anti-piping composition was made up as follows (proportions by weight):

To samples of this composition was added 10% cob flour of -16+100 BSS mesh and to other samples 10% of cob flour of 20+60 BSS mesh. Such samples, together with control samples, were tested by placing a quantity of material on a flat surface at 1400" C. The flour containing samples each burnt for about 4-5 minutes with vigorous flaming but little visible fume. The control samples generated about 510 times more visible fume than the flour containing samples.

It was found that easier mixing was achieved With the -20+60 mesh flour. If too fine an additive is used, the composition tends to burn undesirably fast; if too coarse, homogeneous mixtures are difficult to obtain. It was also found that the incorporation of the flame generating ingredient did not adversely affect the exothermic properties of the anti-piping compositions.

I claim as my invention:

1. In a granular anti-piping composition for application to the surface of molten metal during casting thereof, the composition consisting essentially of aluminum and an oxidizing agent therefor and wherein the composition generates fumes upon its ignition after application to the surface of the molten metal, the improvement comprising including in the composition 1 -20% by weight of an organic additive, said organic additive being capable of generating a flame at the temperature of the molten metal and being present in an amount sufficient to consume the fumes produced by the composition.

2. An anti-piping composition according to claim 1 wherein the organic additive is cellulosic fibrous material.

3. An anti-piping composition according to claim 1 which includes a humectant in an amount of 1-20 by weight of the composition.

4. An anti-piping composition according to claim 1 which contains a proportion of a flame retardant.

5. In a method of casting molten metal comprising pouring said metal into a mold and applying to the surface of said molten metal during solidification in the mold a granular exothermic anti-piping composition containing aluminum and an oxidizing agent therefor, whereby application of the composition to the molten metal generates fumes, the improvement comprising applying to the surface of said molten metal with said anti-piping composition an organic additive which generates a flame at the temperature of said molten metal the additive being applied in an amount sufiicient to substantially consume the generated fumes.

6. An anti-piping composition according to claim 1 wherein the organic additive is a member selected from the group consisting of paper pulp, shredded paper, wood flour, sawdust and cob flour.

7. A method according to claim 5 wherein the organic additive is a cellulosic fibrous material.

8. A method according to claim 5 wherein the organic additive is a member selected from the group consisting of paper pulp, shredded paper, wood flour, sawdust and cob flour.

References Cited UNITED STATES PATENTS 1,533,892 4/1925 Osborne 164- 42 2,937,425 5/1960 Morgan 27 X 3,123,878 3/1964 Davidson 10638.2 X

FOREIGN PATENTS 969,331 9/ 1964 Great Britain 75--94 1,094,233 12/ 1967 Great Britain 7594 798,710 7/1958 Great Britain l64--53 921,332 3/1963 Great Britain 7594 L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R.