GB2024194A - A melting apparatus for explosives - Google Patents

Abstract

A melting apparatus for explosives comprising a feed hopper (1) for unmolten explosive and a collecting vessel (2) for molten explosive beneath the hopper. The bottom of the hopper is a melting grate (20) constituted by an array of generally parallel spaced apart hollow radiator ribs (21) for receiving a flowing heat transfer medium. The ribs are of wedge-shaped cross-section with their apices directed upwardly and the mutual spacing therebetween is made adjustable to allow the heat of the melt to be controlled by controlling the amounts of unmolten material progressively let through the grate from the hopper to the collecting vessel. <IMAGE>

Description

SPECIFICATION A melting apparatus for explosives The invention relates to an apparatus for quick, continuous melting of explosives, comprising a feed hopper for the unmolten explosive, a collecting vessel for the molten explosive below the feed hopper, and a melting grate constituting the bottom of the feed hopper and comprising a plurality of parallel, mutually spaced radiator ribs adapted to be heated by a heating medium flowing in their interior, and having a wedge-shaped cross section the apex of which is directed upwardly.

Such an apparatus serves for the first fusing of a solid explosive available, for instance, in the form of granules, flakes or pieces, in particular of trinitroto luene (TNT) or mixtures of TNT and trimethylene triammine, TNT and nitrate of ammonium or TNT/ I trimethylene-triammine/aluminium. The unmolten explosive sinks from the feed hopper down to the melting grate where it is transformed into a melt through contact with the radiator ribs which are heated from the inside, and then drops through the gaps between the spaced apart radiator ribs into the collecting vessel which is heated indirectly from the outside.From the collecting vessel, the explosive may either be processed directly, such as by being poured into projectile bodies, or be subjected to further treatment, e.g. in a melting or tempering vessel in which the fusing process is continued by the addition of further solid components and the melt is brought to the exact casting temperature.

Any kind of melting orfusing apparatus for explosives must meet the strictest safety require ments. For instance, the difference between the temperature of the heating medium and the melting temperature of the explosive is limited to a relatively low maximum value of a few degrees Celsius. For this reason, the melting capacity of the apparatus mentioned cannot be improved simply by raising the temperature of the heating medium in the radiator ribs. Often the melting capacity is limited by the fact that the resulting melt should or may have a certain maximum temperature only. With explosive mix tures having a relatively low heat of fusion, this cannot be achieved unless the heating medium is used only at a temperature below the safety limit.

Then, of course, the apparatus is not workfing at its theoretically possible maximum melting efficiency.

It is an object of the invention to develop the above-mentioned melting apparatus so that, with the most varied explosives being treated, a certain temperature of the explosive melt can be obtained without any loss of the maximum melting perform ance obtainable in consideration of the safety re quirements.

This object is met, in accordance with the inven tion, in that the mutual spacing between the radiator ribs rib of the melting grate and thus the inner width of the gaps between the radiator ribs is made adjust able.

The apparatus according to the invention makes it possible to give up a mode of operation with which all the explosive supplied to the melting grate is always transformed into a melt at the radiator rods so that the temperature of the resulting explosive melt necessarily lies close to the temperature of the heating medium. With the apparatus according to the invention, on the other hand, the temperature of the melt can be lowered by simply widening the spacing between the radiator ribs. If the spacing is greater, a certain proportion of unmolten explosive will pass through the gaps between the radiator ribs.

This proportion is fused only in the previously formed explosive melt and cools the melt by withdrawing from it the required heat for fusion. The greater the spacing between the radiator ribs, the greater is the proportion of unmolten explosive which passes between them and the lower the temperature of the explosive melt becomes. The adjustability of the spacing is thus a simple means of obtaining an accurate adjustment of a certain temperature of the explosive melt. As this requires no alteration of the temperature of the heating medium, the apparatus according to the invention always maintains its maximum melting capacity.

The magnitude ofthe spacing to be adjusted for a certain temperature of the melt mainly depends on the specific heat of fusion of the respective explosive and on the shape and size of the solid explosive material. Coarser explosive, of course, requires a greater spacing in order that a certain proportion may pass between the radiator ribs without melting at the ribs. A relatively low heat of fusion likewise requires a relatively large spacing so as to compensate for the low heat of fusion by increasing the unmolten proportion. In general, these considerations as well as the observance of the customary safety regulations provide a mutual spacing of the radiator ribs in the range of millimeters for the explosives and explosive mixtures mentioned above. The maximum adjustable spacing is conveniently about 4 mm.Of course, with the apparatus according to the invention it should also be possible to make the spacing so small that the mode of operation with which all the explosive is transformed into the molten condition atthe radiator rods is not necessarily given up in each individual case.

On the whole, this guarantees the universal applicability of the apparatus according to the invention for any kind of explosives and for a wide range of desired or admissible temperatures of the explosive melt.

In a preferred embodiment of the novel apparatus, the adjustability of the inner width of the gaps between the radiator ribs is obtained by making adjacent radiator ribs adjustable in height with respect to each other. This adjustability in height involves a change of the width of the gap because the radiator ribs have a wedge-shaped crosssectional configuration. Conveniently, the radiator ribs are provided with pins at their front ends to permit this adjustment in height. The pins engage in oblique cam slots or openings of a common adjustment rod which is for instance displaceable horizontally by hand. It is sufficient if only every second radiator rib is adjustable in height.However, in the interests of a particularly low structural height of the melting grate, it is preferred to provide for all the radiator ribs to be adjustable in height, and to design this adjustability in such a way that adjacent radiator ribs will each be adjustable in opposite directions.

In another embodiment, the change- of the gap width is obtained by displacing the radiator ribs with respect to each other in the horizontal direction. This is best effected by means of a telescopic latticework to which the radiator ribs are coupled.

We have discovered that, to obtain a high degree of melting efficiency, the pressure under which the solid explosive rests on the inclined lateral surfaces of the radiator ribs should be as high as possible.

This is obtained in the most simple manner by the weight of the unmolten explosive itself. To this end, the feed hopper is filled up to a correspondingly high level. If the structural height of the feed hopper should not be sufficient, it may merge directly at its top end into a storage bin for the explosive. It is also possible to connect the feed hopper to a remote storage bin by means of a feed pipe.

As an alternative or in addition, the increase in pressure at the radiator ribs may also be achieved by exposing the underside of the melting grate to low pressure, preferably by ensuring that the collecting vessel is open only at the melting grate and is provided with a socket for connection to a low pressure source. This may also serve to suck oft any resulting vapours and the like although, of course, the low pressure will be adjusted so as to be higher than would be the case if only vapours had to be withdrawn.

Finally, the pressure may conveniently be increased by providing a plunger in the feed hopper to produce an additional load on the unmolten explosive.

The radiator ribs tend to cool down below the melting temperature of the explosive most easily at their tips or apices which are directed into the unmolten explosive. This has the undesired consequence that the explosive forms crusts or scales at those locations. This phenomenon is most effectively avoided by rounding off the radiator ribs at their tips. Moreover, the radiator ribs may be contoured at least at their lateral wedge surfaces so as to enlarge their effective areas and thus to improve the heat transfer. For this purpose, conveniently, a profile is chosen which will not present any flow resistance against the explosive which flows down.

The invention is now further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a part-sectional elevation of an apparatus for melting explosives, as seen in the direction ofthe arrow 1 in Figure 2; Figure 2 is a vertical elevation of the apparatus accordingly to Figure 1, as seen in the direction of the arrow 2 in Figure 1; Figure 3 an elevation on an enlarged scale of the part marked X in Figure 1.

The whole apparatus shown in the drawings for quick continuous melting of explosives is made of stainless steel. It comprises a feed hopper 1 for unmolten explosive of square cross-section and below the latter, a collecting vessel 2 for the molten explosive, likewise of square-cross section. Approximately one-half of the height of the feed hopper 1 extends down into the collecting vessel which is in sealing contact with the outside of the feed hopper 1 along an inclined upper edge 3. The feed hopper is closed by a lid 4. The collecting vessel 2 has an - inclined bottom 5 with a connecting flange 6 at its lowest part. A heatable outlet stud 7 together with a discharge valve 8 (shown only in Figure 2) for the molten explosive are connected to the flange 6.The collecting vessel 2 is surrounded by a heating coil 9 with an inlet pipe 10 and an outlet pipe 11 (see Figure 1) through which a heating medium, e.g. water, is circulated for indirect heating of the molten explosive.

A melting grate 20 constitutes the bottom of the feed hopper 1 and comprises an array of parallel, spaced, horizontal radiator ribs 21. Each one of the identical radiator ribs 21 is formed as an endless tube which has a wedge-shaped cross-section the rounded tip 22 of which is oriented upwardly. The wedge angle at the tip 22 is an acute angle of, for instance, 300. All the radiator ribs are sealed at both ends by a rectangular fron plate 23 each.Two vertically aligned pins 24 and 25 are each welded into the front plates 23. The pints 24 and 25 project to the outside in the longitudinal direction of the radiator ribs 21 and extend into vertical guide slots (not shown) in the feed hopper 1. The dimensions of the front plates 23 are so chosen that the plates abut each other laterally in the transverse direction of the radiator ribs so as to form a continuous front end limitation of the melting grate 20. However, each radiator rib has a certain freedom of adjustment in height, i.e. in the vertical direction, because of the guidance provided by the pins 24 and 25.

When all the radiator ribs are disposed at the same level, they abut against each other laterally at the widest portion of their cross-section which corresponds to the width of the front plates 23. Therefore, partically not clearance or gap remains free between the radiator ribs 21. However, the wedge-shaped cross-section of the ribs permits the formation of gaps between them, and the width of these gaps may be increased by adjusting the heights of two adjacent radiator ribs with respect to each other, cf.

Figure 3. Starting from a medium height which all the radiator ribs 21 have in common, this adjustment is effected in the illustrated embodiment by raising every second radiator rib 21' and, at the same-time, lowering the adjacent radiator ribs 21" each in the opposite direction to the movement of the rib 21'.

This is effected by means of a horizontally displaceable adjustment bar 26 which is disposed between the front plates 23 and the guide means not shown for the pins 25 in the feed hopper. The bar 26 is formed with cam openings 27' and 27", respectively, which are inclined in opposite directions and through which the pins 25 extend. Figure 3-shows the entire arrangement in a position in which the radiator rib 21' are lifted to their highest position by means of the cam openings 27', and the radiator ribs 21" are lowered to their lowest position by means of the cam openings 27". The resulting gaps 28 between the radiator ribs have their greatest width of approximately 4 mm corresponding to their disposi tion of the ribs 21' and 21".

Another adjustment bar (not shown) is disposed at the other end of the radiator ribs (not shown in the drawings). A lever mechanism 29 associated with a ratchet means 30 having several positions of adjustment serves for joint horizontal displacement of both adjustment bars.

The radiator ribs 21 are internally heated by means of a heating medium such as water which is supplied through an outer manifold 31 extending transversely of the radiator ribs, and which leaves the apparatus at the other side through a similar manifold 32. Both the manifolds 31 and 32 include branch pipes 33 which extend into the interior of the apparatus, and with which front end connectors 34 of the radiator ribs 21 are connected by means of short flexible hose sections (not shown) so that the heating medium flows through the heating elements or ribs 21 in the longitudinal direction.

In operation unmolten explosive is filled into the feed hopper 1, falls down on to the melting grate 20 and is immediately converted into liquid melt at the radiator ribs 21. The melt flows through the gaps 28 into the heated collecting vessel 2. When the spacing between the radiator ribs or the width of the gaps 28 is enlarged by actuation of the lever mechanism 29, part of the explosive will pass in the unmolten state through the gaps 28 into the explosive melt in order to be heated therein. This lead to a lower temperature of the explosive melt. The desired temperature can be controlled by adjustment of the gap width without any alteration of the temperature of the heat transfer medium for the radiator ribs 21.

The more unmolten explosive rests on the melting grate, the grater the melting capacity becomes because the solid explosive is pressed into the liquid film on the melting grate under the pressure of this mass, thus improving the heat transfer. This effect can be enhanced still further by producing a low pressure below the melting grate 20. For this purpose, the collecting vessel which is open only towards the melting grate may be provided along its edge 3 with a socket 15 for connection to a low pressure source. As an alternative, the unmolten explosive may also be loaded into the feed hopper by means of a plunger 16 (shown in discontinuous lines). This produces the desired additional pressure.

Claims (11)

1. An apparatus for quick, continuous melting of explosives, comprising a feed hopper for the unmolten exlosive, a collecting vessel for the molten explosive beneath the feed hopper, and a melting grate constituting the bottom of the feed hopper and comprising an array of generally parallel mutually spaced radiator ribs adapted to be heated by a heating medium flowing in their interior and having a wedge-shaped cross-section the apex of which is directed upwardly, the mutual spacing between the radiator ribs being adjustable.

2. An apparatus as claimed in claim 1, wherein the maximum adjustable spacing between the radiator ribs is approximately 4 millimeters.

3. An apparatus as claimed in claim 1 or 2, wherein adjacent radiator ribs are adjustable in height relative to each other.

4. An apparatus as claimed in claim 3, wherein the radiator ribs of adjustable height are each provided with a pin which engages in an oblique cam opening formed in a common horizontally displaceable adjustment bar.

5. An apparatus as claimed in claim 1 to 2, wherein the radiator ribs are displaceable in a horizontal direction with respect to one another.

6. An apparatus as claimed in claim 5 wherein the radiator ribs are coupled to a telescopic latticework.

7. An apparatus as claimed in any one of claims 1 to 6, wherein, in cross-section, the radiator ribs are rounded off at their tips.

8. An apparatus as claimed in one of claims 1 to 7, wherein the radiator ribs are contoured.

9. An apparatus as claimed in one of claims 1 to 8, wherein the collecting vessel is open at the melting grate only and is provided with a socket for connection to a low pressure source.

10. An apparatus as claimed in one of claims 1 to 9, wherein the feed hopper comprises a plunger for loading the unmolten explosive.

11. An apparatus as claimed in claim 1, substantially as herein described with reference to the accompanying drawings.