On methods of supplying water into the blasthole during drilling with flushing
Abstract Generated abstract
This paper compares central and side methods of supplying flushing water during blasthole drilling as measures for suppressing mine dust and reducing silicosis risk. Based on 1956 tests at the Tashtagol mine using gravimetric dust sampling, flow and pressure measurements, and PA-23 rock drills, the authors evaluate how water consumption affects airborne dust under both supply arrangements. The results indicate that side flushing produced substantially lower dust levels, allowed wider regulation of water flow, and could achieve sanitary dust standards at about 35 to 40 liters per meter of hole, while central flushing was limited by pressure conditions and entrained unwetted fine dust. The paper also discusses hydraulic coupling design, operating practice, and tool preparation, arguing that side water supply can reduce repair and maintenance costs despite higher shank manufacturing costs.
Full Text
ON METHODS OF SUPPLYING WATER INTO THE DRILL HOLE DURING DRILLING WITH FLUSHING
B. V. ZAKHVATKIN, K. A. KRISTIN
(Presented by the scientific seminar of the Department of Mining Machines and Mine Transport)
At present, the most reliable method of combating silicosis is dust suppression by means of wet drilling (with flushing of the drill hole with water) or by dry dust collection.
Two methods are known for supplying water for flushing a drill hole: 1) the central method, in which water is supplied into the drill opening through the needle passing inside the rock drill; 2) the side method, in which water is supplied into the central opening of the drill through a water coupling located on the drill shank, bypassing the rock drill.
At the Tashtagol mine, beginning in 1950, the side method of supplying water has been used; it did not permit drilling holes without flushing, since the central opening on the shank side becomes wedged shut. This made it possible to introduce drilling with flushing quickly. However, at other mines the central method of supplying water for flushing drill holes is also used.
In 1956, the research group of the Tashtagol mine conducted comparative tests of the central and side methods of supplying water into the drill hole. For these experiments a blind heading was selected, equipped with a local-ventilation fan installation. Before each experiment the heading was thoroughly ventilated and samples were taken to determine the dust content of the air before drilling. Then the dust content of the air was determined throughout the entire drilling period.
To determine the dust content of the air, the gravimetric sampling method was used. Water consumption was determined with a flowmeter, and the air and water pressure with manometers. Drilling was carried out with a PA-23 rock drill. For the different methods of water supply the machine was reequipped accordingly. The holes drilled were horizontal, from 1.5 to 2.0 meters long. The water supply was regulated by a main-line valve. In all, 13 experiments were conducted: six with central flushing of the hole and seven with side flushing. The observation results are given in Fig. 1.
With side flushing and a water consumption of 78 liters per 1 m of drilled hole, complete dust suppression was achieved. Reduction of dust formation to sanitary standards was achieved with a water consumption of 30–40 liters per 1 m of hole.
With central water supply, achieving complete dust suppression or even a reduction of dust formation to the limits of sanitary standards
it was not possible. In addition, with the central flushing method it is impossible to supply more than 30.0 liters of water per 1 m of blasthole, since the water pressure becomes higher than the compressed-air pressure and the perforator stops working.
The increased dustiness of the air with central flushing is explained by the fact that a water-air mixture is fed into the blasthole and part of the dust leaves the blasthole with air bubbles. This dust is not wetted by the water and remains suspended in the air. The particles of such dust are very fine and present the greatest danger to the organism.
Fig. 1. Dependence of air dustiness on water consumption. I—when water is supplied laterally into the blasthole; II—when supplied centrally.
When the water consumption is more than 35–45 liters per 1 m of drilled blasthole, the dustiness decreases only slightly. Thus, the investigations carried out showed that the dustiness of the air at the face, under equal conditions and with lateral water supply, is approximately 1.8–2 times less than with central supply. In this case the difference is greater, the greater the water consumption. The water consumption through the hydraulic coupling is proportional to the pressure in the supply line. This dependence for the hydraulic coupling of the Tashtagol mine design is shown in Fig. 2. Knowing the de—
Fig. 2. Dependence of water consumption by the hydraulic coupling on pressure in the line.
airborne dust content; from the curve in Fig. 2 one can determine the water pressure in the main line required to meet sanitary standards when drilling holes in rocks of different hardness (Table 1).
Table 1
Water pressure and flow rate for flushing holes, ensuring dust suppression to sanitary standards when drilling rocks of different hardness
| Rock hardness according to the hardness scale of the USSR Academy of Sciences | Net drilling time, minutes per 1 linear m of hole | Water consumption, l/min | Water pressure in the main line, atm |
|---|---|---|---|
| IV | 16.0—13.3 | 3.0 | 1.45 |
| V | 13.2—11.0 | 3.6 | 1.9 |
| VI—VII | 10.9—7.3 | 5.5 | 3.3 |
| VIII—IX | 7.2—5.0 | 8.0 | 6.75 |
| X | 4.9—4.0 | 10.0 | 8 |
At the Tanganrog mine in 1950, several types of hydraulic couplings were tested. As the tests showed, the most perfected was the coupling designed by the Dust Laboratory of the Academy of Sciences of the Kazakh SSR. In the course of operation, some changes were made to its design in order to simplify it and increase the strength of the fitting. At present, two standard sizes of hydraulic couplings are used at the mine. The normal service life of the rubber seal of these hydraulic couplings is 30–40 hours.
The production of rubber seals for the hydraulic couplings has been organized at the mine’s drill-sharpening shop. The monthly consumption of seals is 300–400 units. The seals are made from raw rubber by vulcanizing it in special molds designed by P. N. Gorsky and V. P. Bibenko. The vulcanization process is carried out at a temperature of 150° for 40 minutes.
The shanks of drills for drilling with side flushing differ from ordinary shanks by having a cylindrical section onto which the hydraulic coupling is fitted. The shanks are upset on a drill-sharpening machine with the aid of special dies. The holes in the face of the shank are plugged.
The cylindrical part of the shank is turned on a lathe and ground. The hole in the shank for supplying water into the drill channel is drilled at an angle of 45°; this prevents breakage of the shanks. After machining, the end of the shank is hardened over a length of 20–25 mm.
Conclusions
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Drilling holes with flushing is at present one of the most effective measures for combating dust in the mine atmosphere.
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Compared with central water supply, side water supply for flushing holes has the following advantages: a) the drills are strengthened almost twofold—
the dust content of the air is reduced for the same water consumption; b) it becomes possible to regulate the water supply over wide limits, which makes it possible to achieve complete dust suppression; c) the lubrication conditions of the drill hammer are improved and wear of parts is reduced.
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To ensure sanitary standards for airborne dust content at the working face, the water consumption for flushing should be 35–40 l per 1 m of blasthole.
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Despite a certain increase in the cost of manufacturing drill shanks, the total costs of maintenance and repair of drilling hammers and tools with lateral water supply are lower than with central supply.
ERRATA NOTED
| Page | Line or formula | Printed | Should be |
|---|---|---|---|
| 5 | formula (8) | $d$ solid |
$S$ hot |
| 80 | 13th line from bottom | solid | hot |
| 85 | formula (1) | $\dfrac{100}{\gamma_m}(f_m - h_k)$ | $\dfrac{100}{\gamma_m}(f_m - t_k)$ |