EARTHMOVING MACHINE FOR CABLE TRENCHES

S. I. Shubovich, A. I. Khalyavin, V. T. Gorbenko

(Presented by the scientific seminar of the Department of Applied Mechanics)

When laying underground cable for urban electric-power networks, the earthwork for preparing trenches constitutes the most labor-intensive part of the work associated with the use of manual labor. The use of an excavator to mechanize these operations is not always possible and is economically disadvantageous, since the trench has to be dug with a width of 600–800 mm instead of 150–300 mm; this entails additional work for backfilling and compacting the soil and additional costs, in some cases for restoring street pavement. Industry does not yet produce special machines for these purposes; therefore, some organizations are attempting to create such machines on their own [1].

Below is a description of an earthmoving machine for cable trenches developed by the Department of Applied Mechanics of the Tomsk Polytechnic Institute named after S. M. Kirov.

In developing the design of an earthmoving machine for cable trenches, the task was set of creating a machine that would be convenient and reliable for work in urban conditions, i.e., compact, maneuverable, and capable of cutting a trench in soils heavily contaminated with construction debris (fragments of brick, pieces of metal, etc.). These requirements determined the basic layout of the machine. The running gear was adopted as a crawler type, and the cutting part as an auger equipped with cutters with hard-alloy tips. The drive of the mechanisms in the experimental machine was adopted as electric.

The structural layout of the machine is shown in Fig. 1, and its external appearance in Fig. 2. The machine contains two main mechanisms: the soil-cutting mechanism and the machine travel mechanism, which serves both for maneuvering operations and for providing feed during soil cutting.

As the cutting element, as noted above, an auger 12 (Fig. 1) was used, equipped with cutters 13 with brazed hard-alloy plates. Such an auger-milling cutter combines the functions of a cutting tool and an excavating device for removing loosened soil from the trench. The choice of an auger-milling cutter as the cutting and excavating device was based on the desire to eliminate the main drawback of the cutting chain widely used for these purposes—abrasive wear of the moving joints, i.e., hinges, sprockets, and other parts.

In order that the loosened soil extracted by the auger to the surface be thrown off to both sides of the trench, two rectangular openings are made in the housing of the auger cutter 9, and three radial blades are fastened to the auger shaft; their purpose is to forcibly discharge the soil from the beveled casing (Fig. 1) through the above-mentioned openings.

The shaft of the auger cutter has two supports. The lower support is a self-aligning plain bearing with corresponding seals, while the upper support is made in the form of a cam compensating coupling with a centering spherical element. Such an arrangement of the auger supports ensured operation of the bearings without jamming under the unavoidable and fairly considerable deformations both of the auger itself and of its housing during operation under load.

Fig. 1

Fig. 2

The auger cutter is driven by a 28 kW alternating-current electric motor through a V-belt drive and a cylindri-

...a closed-type cylindrical-conical reducer 8. The reducer housing and the auger housing are joined together and form a single unit. The electric motor and reducer are mounted on plate 15, which can rotate in a vertical plane on hinges 16. When the plate is turned clockwise, housing 9, together with the auger-cutter, is sunk into the ground; when turned counterclockwise, the auger is raised and can be set in the transport position. The turning of the plate and, consequently, of the entire cutting mechanism is carried out by means of screw device 5. Using this mechanism, it is possible to set the auger-cutter in the required position depending on the desired trench depth.

The travel mechanism of the earthmoving machine consists of a 4.2 kW electric motor, an automotive-type gearbox 2, a V-belt transmission 3, a main drive with side clutches (not shown in Fig. 1), frame 14, and crawler tracks. The main drive and crawler tracks in the experimental machine were taken from the OM-5 coal loader. Since the OM-5 main drive is made with a hydraulic control system for the side clutches, the feed mechanism is controlled by a single handle of the spool-type distributing device, which has four positions: “forward motion,” “right turn,” “left turn,” and “stop.” The presence of the gearbox made it possible to vary the travel speed (the feed speed of the auger-cutter) from 0.3 m/min to 3 m/min, depending on the hardness of the soil. Changing the direction of travel was considered possible by means of the gearbox and by reversing the electric motor.

All controls for the machine mechanisms are brought out to a control panel located in the immediate vicinity of the operator’s workplace, which is near the gearbox (Fig. 1).

The principal parameters and characteristics of the described machine are given below.

The experimental earthmoving machine was tested on a site that had formerly been a construction area; therefore, its soil was heavily contaminated with fragments of brick, concrete, pieces of metal, etc. Tests carried out under these conditions showed that the cutting part, made in the form of an auger-cutter, successfully cuts a trench; moreover, brick, metal, and other inclusions are cut and crushed by the cutt—

The only exceptions were pieces of concrete products; when they fell in, the auger, as a rule, became jammed. This made it necessary to stop digging, raise the cutting organ, go around the obstacle, and then deepen it again.

On heavily contaminated soils, the digging speed, with a trench width of approximately 400 mm and a depth of 800 mm, reached 20 meters per hour; on “clean” sections (i.e., without especially large solid inclusions), it reached 30 meters per hour. The power consumption in this case was 20–25 kW for the cutting mechanism.

The tests showed that the milling cutter copes well with clearing the trench of loosened soil, and the small amount that remains on the trench bottom proves useful, since it can be used as a soft bedding layer during the subsequent laying of the cable.

A known shortcoming of the auger-cutter used was that the soil extracted from the trench was thrown onto the surface near the trench edge, which sometimes led to sloughing of the edges.

During the tests it was established that the wear resistance of the cutters was quite sufficient; however, their strength, especially when working in heavily contaminated soils, proved low. There were cases in which, when the cutters encountered solid inclusions, the carbide plates broke.

Summing up the work carried out, it may be concluded that an earthmoving machine for cable trenches using an auger-cutter as the cutting and excavating organ is fully serviceable, but requires design refinement.

REFERENCES

E. B. Pergament. Experience in mechanizing work at the Magnitogorsk Electrical Installation Administration. Journal Promyshlennaya energetika [Industrial Power Engineering], Gosenergoizdat, No. 10, 1960.