LIGHTWEIGHT PORTABLE RIG FOR DRILLING SHALLOW BOREHOLES

S. S. Sudakishin, V. P. Krendelev, A. A. Grebenyuk, V. M. Matrosov

(Presented by the scientific seminar of the Department of Exploration Technology)

In connection with the rapid development of construction work and geological investigations in recent years, the volume of drilling of geological-exploratory boreholes to depths of up to 10–15 meters has increased sharply; a considerable part of this work is still carried out with hand sets or drilling rigs that poorly meet working conditions. Drilling of shallow boreholes for the purposes indicated is performed, as a rule, in highly varied rocks: clays, sands, boulder-and-pebble deposits, and partly in hard rocks of the bedrock type. In this case the purpose of drilling boreholes is to obtain rock samples meeting certain requirements: they must be well preserved, possess natural moisture content, and have transverse dimensions within permissible norms. These requirements, as well as the great variety of rocks with different physical and mechanical properties, make it necessary, even when sinking a single borehole, to use various drilling methods (percussive, rotary, combined), various tools, and, finally, different technology. In addition, exploratory work is usually carried out in hard-to-reach taiga, swampy regions, or under conditions of strongly dissected terrain, which complicates the transport of equipment. Taking into account the great need for lightweight drilling rigs, the Department of Exploration Technology of the Tomsk Polytechnic Institute developed a design for the portable drilling rig PBU-15 under an economic contract with the former office Tomzheldorproekt.

The designed drilling rig PBU-15 (certificate of registration with the Committee for Inventions and Discoveries under the Council of Ministers of the USSR No. 25226 of September 25, 1961), according to the technical assignment, is intended for drilling boreholes to depths of up to 15 m in rocks of any category by rotary, percussive, and percussion-rotary methods, with solid and annular sampling and with complete mechanization of the drilling processes. The rig can be successfully used for purposes of geological mapping, emanation surveying, and engineering-geological investigations.

Technical characteristics of the PBU-15 rig

Kinematic Diagram of the PBU-15 Rig

The kinematic diagram of the PBU-15 drilling rig is shown in Fig. 1. From engine 1, through pulley 2, rotation is transmitted by means of V-belt 3 to drive pulley 4, which is freely mounted on main shaft 5 on two ball bearings. Rotation is transmitted to the main shaft through one-way clutch 6 of conical type, which moves along the axis of the shaft, being mounted on splines. The friction clutch is pressed by a spring (the spring is not shown in the diagram). When the friction clutch is disengaged, the spring is compressed.

Mounted on the main shaft are gear \(z_1 = 20\) teeth (on splines) and double-start worm \(z_2\) (on needle bearings). Worm \(z_2\) is immovable in the axial direction; gear \(z_1\) can slide along the splines. The worm is coupled to the shaft by splined clutch 7 and transmits rotation to rotor 8 through worm wheel \(z_1 = 29\) teeth. From gear \(z_1\), rotation is transmitted to the winch through toothed wheel \(z_3 = 60\) teeth, seated on the winch shaft on a key. Engagement of splined clutch 7 and displacement of gear \(z_1\) are independent, which ensures both simultaneous and separate engagement of the rotor and the winch. In the initial position, the winch drum is pressed through clutch 12, freely mounted on the shaft, by spring 13 to the friction clutch with a force of 27 kg, which provides lifting of a load of 69 kg. To lift a larger load, the drum is pressed against the friction clutch by lever 14; for this purpose the end of the latter is moved to the left by hand. To disengage the drum, the lever is moved to the right.

A special mechanism serves to mechanize the process of delivering blows. On the winch shaft, gear \(z_5 = 20\) teeth is mounted on a key; it is in constant mesh with toothed wheel \(z_6 = 60\) teeth, freely seated on an intermediate axle. A cam sector 15 is fastened to the toothed wheel by bolts. When the toothed wheel rotates, the cam sector periodically presses lever 14 away through bearing 16, as a result of which the winch drum is disengaged from the friction clutch. In this case the percussion cartridge, connected with the drum by a cable, falls under the action of its own weight and delivers a blow to the upper end of the driving rod (through the striking sleeve). When the cam sector leaves contact with the bearing, the drum

spring 13 moves to the right, is pressed against friction clutch 9, and receives rotation from it (the percussion chuck rises upward). To disengage the impact mechanism, bearing 16 is shifted by the lever beyond the outline of the cam sector and is fixed in this position with a pin.

Fig. 1. Kinematic diagram of the PBU-15 rig.

Description of the Rig Design

The PBU-15 drilling rig (Figs. 2a, 2b, 2c) consists of two easily detachable parts: the drive and the drill frame.

The drive consists of engine 1 of the ODV-300 type, a frame, V-belt 2, and pulley 3. With the aid of cap nuts 4 and screws 5, this assembly is easily attached to the second assembly.

The drill frame consists of main shaft 6, rotator (rotor) 7, winch 8 with impact mechanism 9, mast 10, frame 11, and a guard (not shown in the figures).

The main shaft serves to transmit rotation to the rotor and the frame winch. It has pulley 12 with a conical friction clutch, engaged by handle 13; a worm drive to the rotor, engaged by handle 14; and sliding gear 15, moved by means of

Fig. 2a. General view of the PBU-15 rig.

Fig. 2b. View of the PBU-15 rig from the winch side.

handle 16, which transmits rotation to the winch. This arrangement of the main shaft makes it possible to engage the mechanisms of the rig separately when the drive is disconnected. The latter is engaged quite smoothly by means of a friction clutch.

The rotator (rotor) of the rig serves to transmit torque to the drilling tool. It consists of a worm wheel and spindle 17, housed in the casing, and an insert of the rotary table 18 for the

Fig. 2c. Side view of the PBU-15 rig.

leading square kelly. Insert 18 is secured by means of two latches 19.

The winch serves for lowering and raising the drilling tool, and also for carrying out percussion drilling and delivering blows to the drilling tool during percussion-rotary drilling. The winch consists of drum 8, brake pulley 20, which has an internal recess for friction cone 21 secured on gear 22, bushing 23, spring 24, and lever 25 for engaging and disengaging the winch drum. All these parts are located on winch shaft 26. Braking of the winch is carried out by means of brake band 27, tightened by lever 28.

The impact mechanism serves for automatically engaging and disengaging the winch drum when carrying out percussion operations. This mechanism consists of a pair of gear wheels 9 and 29, a cam sector 30, and a ball bearing 31 mounted on handle 32. The handle is fixed in the disengaged position by pin 33. Lever 25, on which handle 32 is located, can also be fixed in the position in which the drum is disengaged by means of a latch mounted on casing 34, which covers the gears of the impact mechanism.

The mast of the rig serves for carrying out hoisting and lowering operations. It is a pipe 10 secured in support socket 35 by means of a bolt. At the upper end of the mast a head with roller 36 is fastened; the roller rotates freely on axle 37 and has protective casing 38. In the working position the mast is held by braces, which are fastened by hooks 39. The internal cavity of the pipe (mast) is used for storing gasoline.

The frame of the rig serves for fastening all the assemblies and is the base for the mast. It consists of left and right side members fastened together with angles. The rig frame is connected to drive frame 40 by two screws 5. To impart greater stability, the rig frame and the drive are provided with spikes 41, and for carrying they are provided with handles.

The guard of the V-belt transmission consists of two detachable parts, fastened separately on the rig frame and on the drive frame. The pulleys and the drive belt are covered by the guard.

Operation of the Rig

After the rig has been installed at the point, the engine is started. With the main friction clutch disengaged, the rotor is engaged in order to carry out rotary drilling. Augers, spiral augers, drilling spoons, or core barrels may be used as the bottom-hole tool in this case (in the latter case, water should be poured into the borehole during drilling). To carry out the percussion method of drilling, an impact tool or cartridge is used. In this case the winch and the impact mechanism are engaged. The cable is periodically wound onto the drum, and the tool is raised above the bottom; then it is freely dropped. It is also possible to carry out both drilling methods: in that case the rotor and the impact mechanism are engaged simultaneously. As the borehole is deepened, the cable is paid out from the winch drum. With the aid of the impact mechanism it is possible to carry out pumpless drilling of boreholes with automatic discharge of the tool. Hoisting and lowering operations are performed by means of the winch.

This installation was manufactured according to drawings of the Department of Prospecting Technology in the customer’s workshops and successfully passed shop tests. Drilling of boreholes in frozen rocks was carried out under the specified operating regimes with sufficient effectiveness.