Porous metal agglomerates

The invention is concerned with porous metal agglomerates suitable for use in metal fuels and consisting of combustible powders of nodular, flaky, irregular or acicular shape and preferably a mixture of aluminium and silicon although aluminium, aluminium alloy or aluminium mixed with silicon, magnesium or iron or alloys of these metals can be used. The powder is of 0 to 500 microns size range or a cut thereof and is granulated with a synthetic resin binder by build-up to a porous agglomerate having a size range of 100 to 2500 microns and an apparent density of between 0,4 and 1,1.

This invention relates to porous metal agglomerates and more particularly 
to such agglomerates useful as a fuel in blasting agents or explosives. 
As far as possible powder metallurgy terminology used in this specification 
is in accordance with International Organization for Standardization Draft 
1SO/DIS 3252. 
Combustible metal powders have long been used as fuels or sensitisers in 
blasting agents and explosives and in particular aluminium is very widely 
used. In order to obtain optimum and instantaneous use of the energy of 
these fuels it is desirable that the particles thereof have a sufficiently 
large surface to mass ratio to combust at high rate. One convenient method 
of preparing aluminium powder as a fuel is by the atomising process. This, 
however, has the disadvantage of resulting in a high proportion of fines 
of a size less than 80 microns. This fine material is inclined to be 
suspended in air and may result in a spontaneous explosion. It is also 
dense and difficult to handle mechanically. 
It has been proposed in South African Pat. No. 73/6092 to use a carrier for 
this fine material and that product has proved practically and 
commercially successful. 
It is the object of the present invention to provide a fuel for blasting 
agents or explosives which is made from fine particles produced during the 
manufacture of metal powders. 
According to this invention there is provided porous metal fuel 
agglomerates comprising a combustible metal powder of a size range of 0 to 
500 microns, or any cut thereof, granulated with a binder of synthetic 
resin material by build-up to a porous agglomerate with a size range of 
100 to 2500 microns having an apparent density between 0,4 to 1,1. 
Further features of this invention provide for the combustible powder to be 
of nodular, flaky, irregular or acicular shape and to consist of 
aluminium, aluminium alloy, or aluminium mixed with silicon, magnesium, 
iron or alloys thereof. Particularly the powder will comprise a mixture of 
aluminium and silicon or other combustible metals in such proportions as 
to yield optimum and economical use of energy. 
The invention also provides for the binder to be an emulsion or solution of 
vinyl polymers or other resins including thermosetting resins. 
Particularly the binders will be obtained from polyvinyl alcohol and 
polyvinyl acetate. 
An important feature of this invention is a sensitised fuel, comprising 
agglomerates as above defined, having a size range of 100 to 850 microns 
partly filled and coated with a sensitising material such as aluminium 
flake.

In one preferred example of this invention granules were prepared using 
______________________________________ 
80% 200.mu. 85% Al powder 
400g 
16% Coarse Si 60g 
4% Fines Si 40g 
500g 
______________________________________ 
To this was added 16% m/m of SYNTA 1203 (80 g), a polyvinyl alchol based 
adhesive obtained from "Henkel" in South Africa. 
The mixture was subjected to build-up granulation in a Starmix blender for 
5 minutes. Thereafter the resulting granules were air-dried at ambient 
temperature for a period of approximately 24 hours. 
The starting material used had the following size analysis: 
______________________________________ 
85% Al 
-200.mu.m Coarse Si Fine Si 
Density 1,176 1,03 0,767 
(in microns) 
% % % 
______________________________________ 
+425.mu. 0 0 0 
-425.mu. + 315 
0 0,5 0,1 
-315 + 250 10,6 30,8 0,5 
-250 + 150 59,1 41,7 3,8 
-150 + 106 16,8 12,2 51,8 
-106 + 63 8,7 9,2 28,2 
-63 + 45 2,7 3,5 7,2 
-45 2,1 2,1 8,4 
Particle Irregular to 
Angular Angular 
Shape Nodular 
______________________________________ 
The dried product was very free flowing and had the following size 
analysis: 
______________________________________ 
0,946 g cm.sup.-3 
Density = % 
______________________________________ 
&gt;2mm 0 
&lt;2mm &gt;1mm 7,5 
&lt;1mm &gt;850.mu. 4,1 
&lt;850 &gt;500.mu. 32,1 
&lt;500.mu. &gt;425.mu. 26,3 
&lt;425.mu. &gt;250.mu. 23,8 
&lt;250.mu. 6,2 
______________________________________ 
The product may be used as a normal fuel for blasting agents or it may be 
used as a carrier to which a sensitiser or other fine fuel powder may be 
adhered. 
It is very important to note that a change in the shape of the particles, 
for example, nodular, irregular or acicular, or a change in the apparent 
density may result in a failure to granulate with the abovementioned 
concentration of binder. The desired granulation can be effected by 
determining through simple experimentation the necessary concentration of 
binder for particular shapes and density. The effect of the viscosity of 
the binder is also an important variable which must also be determined by 
experimentation. 
The aluminium powder used in the example set out above was atomised 
aluminium powder consisting of nodular and irregular particles. The 
silicon powder used was material including dust which had been collected 
during the manufacture of silicon metal. The apparent density of the 
atomised aluminium powder was about 1,2 g cm.sup.-3 and of the silicon 
powder varied from 0,74 to 1,03 g cm.sup.-3. 
The product forms an efficient and substantially hazard free fuel for 
blasting agents and explosives and it has been found that the silicon 
provides a useful explosive energy content of about 70% of that of 
aluminium. The hazard free material is obtained because substantially no 
dust occurs in the final product from the blender. At ruling costs this 
results in a cheaper fuel than when aluminium alone is used. 
In commercial product granulation may be effected in granulating drums or 
dishes or in mixing pans, augers and high capacity intensive mixers which 
subject the feed to a rolling or mixing motion or both. 
Different purities of feed materials and binders from those indicated in 
the above example can be used and the particular choice will depend on 
costs of materials, end use of the products and quality. As stated above 
particular circumstances may require certain experimentation in order to 
obtain optimum results. 
The invention has further very important advantages. The agglomerates in 
the size range of 100 to 850 microns, or any cut thereof, can be partly 
interstially filled and coated with a sensitising material such as 
aluminium flake to form a sensitised fuel or explosive ingredient for 
pre-packed explosives or blasting agents known as "sausages". This can 
also be done by using the flake in its paste form before it is dried. 
Generally the coating will be effected using a solution which is a mixture 
of an oil soluble basic dyestuff, kerosene diesolene and benzol or other 
suitable solvents. 
As an example of the use of the agglomerates as carriers the following mix 
was prepared: 
400 g of agglomerates sized to -150 .mu.m 
100 g of Al flake made by C. Schlenk AG of Germany and identified as 475 NZ 
with a solution 
1,0 g Fat Blue B DY-SL502 dyestuff supplied by Hoechst S.A. 
30 cm.sup.3 Kerosene SA 1066 supplied by Bush Boake Allen 
2,5 l Diesolene 
2,5 l Benzol 
6 cm.sup.3 of the above solution were used. 
The mixed was blended in Starmix Blender for 2 minutes to promote softening 
of the coating on the aluminium flake and provide adhesion of flake to 
agglomerate. 
The product is a highly effective material for use in explosives giving an 
efficient use of the energy of the material under practical blasting 
conditions. 
Also the porous agglomerates according to this invention provide excellent 
carrier material for use in the process claimed in South African Pat. No. 
73/6092.