METHOD AND MEANS FOR COOLING HOT EXPLOSIVE CHARGES

Method and means for cooling hot explosive charges

The present invention relates to a method for cooling hot emulsion or slurry explosive charges, packaged in paper or plastic, to ambient temperature by means of air and/or also water. The invention also comprises equipment for carrying out said cooling method. The equipment comprising transport means for cartridges, cooling means and transport means for cooled cartridges to final packaging of the product.

The term "explosive" shall mean a detonable composition which can be either cap-sensitive or noncap-sensitive. The explosive shall have a cylindrical form of any desired length and a diameter of generally 50 mm or less.

Well known emulsion explosives as described in US patents No. 4,356,044 and No. 4,322,258 are genenerally formed at elevated temperatures which are necessary to form the oxidizer salt(s) in water. Typical production temperatures are from 70°C to 120°C. It has been found, however, that once the emulsion has been formed at elevated temperature, it should be cooled rapidly to ambient temperature in order to preserve its long-term storage stability. Moreover, when such emulsion explosives are chemically gassed for sensitivity purposes, the formulated emulsion should be cooled quickly to minimize coalescence of the chemically generated gas bubbles within the emulsion. Usually hot emulsion explosives have been packaged in plastic cartridges. Slurry explosives in general can be packaged in a sausage-like form as described in US patent No. 3,783,735. Further, the EP-patent application No. 0340980 describes explosives having no other packaging than a polymerized skin of one of the explosive components. Finally, hot explosives can be packaged in paper cartridges as described in Norwegian patent No. 160770. Whatever packaging material is used, rapid cooling is desired and especially for paper cartridges where the cooling should be by means of air, this has proved to be difficult by known methods and means.

US patent No. 4,867,920 describes a method of cooling hot emulsion explosives which subsequent to cooling are packaged in paper cartridges having crimped ends. After formation the gassed emulsion explosive is formed into a continuous strip of generally constant width and length. The strip is then passed through a cooling bath to cool the explosive to a predetermined tempera¬ ture. Then the desired length of the cooled emulsion explosive is cut and wrapped in paper to form a cartridge. The cooling liquid is preferably water or an aqueous salt solution. Though this method allows packaging of the emulsion explosive in paper cartridges, the cooling and gassing process must be finished before cartridging. In order to maintain a high production capacity, this method also requires a rather long cooling bath, approximately 100 m or more.

The object of the present invention was to develop a method and equipment to obtain rapid, efficient cooling by low energy consumption for various types of explosive charges whether they are packaged in paper or plastic. It shall be possible to obtain said cooling by using air at ambient temperature. Another object was to obtain a safe, compact equipment which is flexible for switching from one type of charges to another and that the whole cooling process should be possible to inspect easily.

Rapid cooling of explosives packaged in paper was considered to be the main problem and it was believed to be best performed by using air. The three most important factors for obtaining good air-cooling were found to be:

1) cooling time

2) cooling air temperature

3) cooling air velocity at the surface of the cart¬ ridges

Regarding factor 1) , the cooling time will depend on the produc¬ tion rate, the charge diameter and the physical size of the cooler. With a production rate of for instance 100 cartridges per minute and a cooler being 5 m long and 2.5 m high one should be able to cool cartridges having a diameter of 35 mm within 15 minutes.

Regarding factors 2) and 3) , the cooling will be more efficient the lower the temperature of the cooling air is. However, the inventors found that air of ambient temperature could be used without pre-cooling provided the air was efficiently used. In order to obtain optimal heat transfer from the hot cartridges to the cooling air, it was found that a combination of high air speed at the surface of the cartridges and high degree of exposure of these to the cooling air with minimal shielding would result in desired heat transfer.

Increased cooling could also be obtained by installing water spray nozzles in the^' air cooler unit. This would be particularly advantageous for cooling of plastic cartridges, but it can also be used for paper cartridges when the paper allows some moisture without losing too much quality.

A new method and equipment were then designed in view of the above stated pre-requisite. Cartridges filled with explosive were supplied to a tooth belt with cartridge carriers mounted thereon.

The tooth belt could be twisted from horizontal to vertical position without causing problems with the cartridges. Such a belt could be utilized in a cooler to obtain maximum exposure of the cartridges to the cooling air and possible water spray therein. A further advantage with such twistable belts was the possibility for easy input and output of the cartridges to and from the cooler. A substantial length of the tooth belt was placed in a compact cooler to which cooling air was sucked or blown. A combination of blowing and sucking of the air will also be possible. Nozzles for spraying water onto the cartridges could also be installed inside and/or outside the cooler. At least one side panel of the cooler should be made of transparent material to allow inspection. The width of the cooler can be adjusted according to the length of the cartridges. To allow cleaning of the cooler at least one panel should be removable and the bottom of the cooler should be open.

The special features of the invention are as defined by the attached claims.

The invention will be further explained with reference to the drawings.

Fig. 1 shows a flow-sheet of the process according to the invention from cartridging to packaging of the cooled cartridges.

Fig. 2 shows a side view of the cooling equipment according to the invention. Fig. 3 shows the cooling equipment of Fig. 2 viewed from above. ϊ.

Fig. 4 shows cartridge carriers on a tooth belt.

In Fig. 1 is shown preparation of empty cartridges 2 from a roll of paper 1. An explosive charge 3, for instance an emulsion matrix, and a gassing agent 4 are charged into the cartridge 2. The thereby produced explosive cartridge 5 is then transferred to a double tooth belt 6 having cartridge carriers 13 mounted thereon. During this operation the belt 6 is in vertical position and is then twisted to horizontal position 7 before the belt 6 goes into the cooler 8. Cooled cartridges 5 are transferred to a conveyor 11 from which the cartridges 5 are delivered to packing boxes 12.

In Figs. 2 and 3 the cooling equipment is shown more in detail. The cartridges 5 are placed between cartridge carriers 13 on the vertical tooth belt 6 which then is twisted to horizontal position 7 before it enters the cooler 8. The belt 6 with all the cartridges 5 is guided through the cooler 8 in such a way that maximum exposure of the cartridges 5 to the cooling air is obtained. This can of course be obtained in several ways and one arrangement of the belt 6 to the cooler 8 is shown in Fig. 2. Subsequent to the cooling operation the belt is again twisted to vertical position 9 from which the cartridges 5 are released from the belt 6 by means 14 onto a conveyor 11.

In Fig. 4 a double tooth belt 6 i shown in horizontal position with cartridge carriers 13 mounted thereon. The cartridges 5 are each placed inside two carriers 13 and will be kept in position even when the belt 6 is twisted to vertical position. Air is sucked through cooler 8 by fans 10. Only two such fans are shown, but transport of air through the cooler 8 can be obtained in several ways using various arrangements of fans and blowers. For additional cooling the air cooling can be supplied by water sprays onto the cartridges 5 through nozzles (not shown) arranged inside and/or outside the cooler 8.

Example

An emulsion matrix and gassing agent were fed into the paper cartridges having a diameter of 35 mm and a length of 200 mm. These cartridges were transferred to a double tooth belt in vertical position. The tooth belt was twisted to horizontal position before it entered a cooler according to the invention. The cooler had the following size: length: 5000 mm, height: 2500 mm and depth: 400 mm. The total length of the tooth belt inside the cooler was 90 meters.

200 ³ air/min at an ambient temperature of 25°C was sucked through the cooler. Inlet temperature of the explosive charges was 80°C and they left the cooler with a temperature of 32°C at the centre core of the cartridges.

With production rate of 100 cartridges per min and a physical size of the cooler as stated above, the cooling time of the cartridges was 15 minutes.

By the present invention it became possible to cool explosive charges, even when they are wrapped in paper, in a rapid and economical way by primarily utilizing air at ambient temperature. The method and equipment are highly flexible and can be used for various types of explosive charges whether they are packaged in paper or in plastic. The cooling efficiency can easily be adjusted to required production rate, for example by regulating the flow and temperature of cooling air through the cooler. The cooler itself is compact and needs little space. It can easily be placed in a standard 20 feet container and its energy consumption is low.

High degree of safety is attained because all moving parts are plastic against metal, and by using transparent plastic walls around the cooler visual inspection is easy. The cooler is easy to clean, because one side of the transparent plastic walls can be removed and its bottom is completely open.

The cooler handles the product very gently, which allows open cartridges to go through the cooler. After cooling the cartridges can be closed with a star crimp or a finger fold.

The main advantages by using a tooth belt is that it can be twisted from a horizontal position in the cooler to a vertical position outside the cooler to ease the input and output of the cartridges to and from the cooler.