SOME RESULTS OF AN EXPERIMENTAL STUDY OF THE PROCESS OF SCOOPING ROCK AND WAYS TO IMPROVE ROCK-LOADING MACHINES

G. V. RODIONOV and A. D. KOSTYLEV

(Presented by the scientific and technical conference of the Mining-Mechanical Faculty of the Tomsk Polytechnic Institute)

Periodic-action loading machines have in recent years come into widespread use in many branches of the national economy of the USSR. Thus, for example, in the mining industry, for loading blasted rock during underground workings, loading machines of the UMP-1, PPM-2, EPM-1, PML-5 types and others are used. In construction, in transport, and also in agriculture, various types of loaders are employed, often using standard crawler tractors as their base, but, along with this, sometimes having a special design as well. Such means of mechanization include T-107 loaders based on the S-80 tractor, TL-2—TsNIS based on the SKhTZ-NATI tractor, T-63 auto-loaders, and many others.

Despite the external diversity of the designs of these loading machines and the different conditions of their application, from the standpoint of the arrangement of the working members and the principle of operation they have much in common. Thus, all such machines have single-bucket-type working members with a nonautomatic controlled scooping cycle, and the bucket is introduced into the material being loaded, as a rule, by moving the entire machine toward the face. The thrust force in most loading machines is determined by the force of adhesion of the running gear to the soil or to the rails, depending on the type of travelling mechanism. It is precisely by this feature that these machines are often called thrust-action loaders.

The technical capacity of any periodic-action loader is determined by the following generally known formula:

\[ Q_{cp}=\frac{3600}{T}\cdot W_m\left(\frac{m^3}{\text{hour}}\right), \tag{1} \]

where \(W_m\) is the useful capacity of the transport mechanism, \(m^3\);
\(T\) is the duration of loading of this mechanism, in sec.

The quantity \(T\) can be expressed by the equation:

\[ T=\frac{W_m}{q\cdot K_n}\cdot t_c+t_o+t_n, \tag{2} \]

where \(q\) is the useful capacity of the bucket in \(m^3\); \(K_n\) is the bucket filling coefficient; \(t_c\) is the duration of one scooping cycle in sec; \(t_o\) is the time for exchanging a loaded transport vessel for an empty one, in sec, and \(t_n\) is the total downtime in sec, referred to one transport vessel.

The time \(t_c\) entering into equation (2) combines the duration of all operations connected with scooping and unloading the bucket, including delivery of the material to a transport vessel, if such occurs. The time \(t_c\) is determined mainly by the kinematic parameters of the machine itself, but to a certain extent also by organizational factors and the degree of training of the operator. As for \(t_o\) and \(t_p\), these time expenditures depend exclusively on the organization of the work both of the machine itself and of the transport serving it. Given a sufficient number of transport mechanisms and their timely arrival, \(t_o\) may be equal to zero.

If we look at the practice of using loading machines, it can be established that most of them operate with a low bucket filling and a technical capacity considerably below the calculated value.

Thus, observations of the operation of UMP-1 rock-loading machines in the mines of the Kuzbass have shown that the actual bucket filling in these machines ranges from 0.30 to 0.55, and the technical capacity from 7.8 to 15.7 m³/h.

According to the data of Candidate of Technical Sciences V. V. Shumilov, who carried out observations of the operation of rock-loading machines in the mines of the Donbass, the capacity per machine time and the filling of buckets are presented in Table 1.

Table 1

It should be borne in mind that the calculated capacity of the PML-5 machine is 20 m³/h, of the EPM-1 machine—30–45 m³/h, and of the UMP-1—30–40 m³/h.

The degree of filling of the bucket of an intermittent-action loading machine is determined mainly, on the one hand, by the physicomechanical properties of the material being loaded, its lump size and the height of the pile, and, on the other hand, by the dimensions and geometric shape of the bucket and by the magnitude of the thrust force developed by the machine’s running gear. The totality of these factors, together with the bucket kinematics during the period of scooping the material, thus determines the depth of penetration of the bucket into the pile and, consequently, the degree of filling of the bucket with one material or another. In view of this, the practical performance figures cited above for the use of various types of loading machines prove to be far from accidental if certain technical and design parameters of the machines are compared. Thus, for example, if one compares the activity of the working members of loading machines in terms of the ratio of the developed thrust force to the bucket width, the following picture is obtained: for the PML-5 machine this ratio is 8.2 kg/cm, for the EPM-1—10.4 kg/cm, for the PPM-2—27.2 kg/cm, and for the UMP-1—29.4 kg/cm.

All these machines are intended for identical conditions of application, but, as is evident from the foregoing, the values of the specific index chosen for comparison prove to differ greatly among the various types of machines.

Great diversity is also observed in the design of the working members and in the geometric form of the buckets themselves (Fig. 1), which may

cause a change in resistance when the bucket penetrates into the pile of material and, consequently, a greater or lesser filling of the bucket.

The loading of various kinds of useful minerals, hard rocks, and ballast materials is a very labor-intensive and large-scale process for a number of leading branches of the national economy. The Laboratory—

Fig. 1. Buckets of various loading machines.

of Mining Mechanization of the Mining-Geological Institute of the West Siberian Branch of the Academy of Sciences of the USSR was assigned the task of studying the working process of periodic-action loading machines with the aim of improving their working members and developing scientific and technical foundations for their calculation and design. It should be noted here that until recently such questions attracted little attention from research organizations, as well as from individual scientists. Only in the most recent period have some theoretical and experimental studies been carried out in this direction.

After carrying out certain preliminary investigations, the mechanization laboratory, in the period from 1950 to 1955, conducted experimental studies—considerable in scale—of the process of scooping rocky minerals by the buckets of loading machines; a brief presentation of the results of these studies is the main purpose of the present article.

To obtain the most accurate and comparable data, the investigation was carried out in the laboratory, but under conditions close to production conditions, with buckets of full-scale size and with rocks having a lump size characteristic specifically of practical conditions.

The principal tasks of the investigation were:

1. To establish the dependence of the magnitude of the forces of penetration and scooping on the geometric shape and dimensions of the bucket, and also on the bulk density, lump size, and height of the rock layer.

2. To study the process of filling the bucket under various methods of scooping the material.

3. To make a preliminary study of certain special technical methods for reducing the forces of bucket penetration.

4. To substantiate a rational bucket geometry and scooping kinematics with the aim of improving the working members of cyclic-action loading machines.

As the test stand for conducting the experiments, a UMP-1 rock-loading machine was used, on whose boom experimental bucket samples were mounted. The machine was moved by means of a winch. The penetration and scooping forces were recorded by self-recording instruments with hydraulic sensors.

As a result of carrying out the planned experimental program, very extensive experimental material was obtained, making it possible to draw a number of generalizing theoretical and practical conclusions. But since in a short article it is very difficult to cover the results obtained fully, only some general conclusions of greatest interest will be presented below.

The basic interrelations that occur when loose or lumpy materials are scooped by a bucket are shown in Fig. 2. Presented here is the dependence of the penetration force on the depth of penetration of the bottom into the layer of material and the dependence of the scooping force on the angle of rotation of the bucket.

The experiments conducted showed that the geometry and structural elements of the bucket substantially affect the magnitude of the force required for its penetration into the mass of material. The experiments showed that a convex front edge of the bucket bottom, other conditions being equal, gives penetration forces 12–16% lower than a straight edge. Reinforcing the front edge of the bottom with teeth reduced the penetration force by approximately 18–20%; moreover, for ordinary lump sizes of rock the optimum spacing between teeth proved to be 160–180 mm. The best results were given by teeth having a trapezoidal shape in cross section. As it turned out, the shape of the bucket side walls has a large influence on the magnitude of the penetration force. Thus, for example, if the penetration force of the bucket bottom without walls is taken as 100%, then certain walls caused these resistances to increase by 42–55%. The best results were obtained with side walls having a cutout in their lower part, as shown in Fig. 3. Such walls increased the resistance to penetration by only 10–15% compared with the resistance of the bottom alone. It was also established that, during bucket penetration, the front edge of its bottom must move directly along the ground. If, however, the edge is at some distance from the ground, even by 75–100 mm, then, owing to the formation in front of the edge

Fig. 2. Basic relationships during bucket operation.

Test conditions:

Material: iron ore, ordinary. Angle of inclination of the bucket bottom \(\chi = 10^\circ\). Layer height \(800\ \text{mm}\).
The bucket moves along the ground.

of a large drag prism, the penetration forces increase by approximately 30–50%, especially in coarse-lump rock.

When the bucket dimensions were changed, it was established that the forces increase approximately in proportion to the bucket width. The most optimal angle of inclination of the bucket bottom to the horizontal proved to be 5–10°. As for the scooping force, the bucket geometry did not have any noticeable influence on it.

On the basis of the experiments carried out, an experimental bucket was designed and manufactured, shown schematically in Fig. 3. The distinguishing features of this bucket were the convex shape of the front edge, the trapezoidal cross section of the teeth, the presence of a deep cutout in the side walls A, and smooth transitions on the front edge in the gaps between the teeth B, eliminating the possibility of pieces of rock becoming wedged between the edge and the soil.

Fig. 3. Schematic diagram of the bucket of the UMP-1 machine with improved geometry.

In the laboratory, comparative tests were carried out on the experimental bucket and the standard buckets of the UMP-1 and PML-5 machines, the dimensions of all three buckets being identical.

Figure 4 shows the dependence of the penetration force on the depth of penetration of the bottom into the rock for these buckets.

From this figure it is evident that, at one and the same penetration depth, the buckets of the UMP-1 and PML-5 machines gave rise to forces 100–120% greater in magnitude than did the experimental bucket.

In order to verify the results of the laboratory investigations, testing of the bucket with improved geometry was organized in comparison with the standard bucket of the UMP-1 machine. These tests were carried out under production conditions in one of the mines of Kuzbass, while driving a development drift through sandstones of medium hardness, with the size of pieces after blasting averaging 100–250 mm and reaching a maximum of up to 500 mm in cross section. The buckets were compared with strict constancy maintained in all mining-technical conditions and other factors. With the standard bucket, the average net loading time for one 2.0 m³ car ranged from 8 min 0.2 sec to 10 min 56 sec; the bucket fill factor was 0.45–0.60, and the technical productivity of the machine was at the level of 14.0–15.7 m³/hr. With the use of the experimental bucket, these indicators improved sharply: the loading time for one car was 4 min 27 sec–5 min 07 sec, bucket filling was 0.85–1.1, and average productivity was 25.0–26.5 m³/hr. In all, during the testing of the buckets, about 40 linear meters of the development drift were driven. The technical productivity of the UMP-1 machine with the improved bucket during this period increased on average by 75%, and the practical productivity, taking into account all auxiliary operations and downtime, by 30%. Thus, the production tests fully confirmed the correctness of the results of the laboratory investigations and the high effectiveness of such a measure as improving the geometry of the buckets of loading machines.

A substantial influence on the filling of the bucket of a loading machine is exerted by its kinematics during the scooping process.

Sometimes the operation of the machine proceeds as follows: the bucket is forced to a certain depth into the pile of material, then the machine is stopped and the bucket is turned with the chassis already motionless. This is how many operators of loading machines work. But, from the standpoint of bucket filling, a much more effective process is one in which, after the bucket has reached a certain initial depth, the thrusting motion of the machine is combined in time with scooping up the material, i.e., with turning the bucket in the vertical plane. At one of the Kuzbass mines, observations were made of the work of two operators of a UMP-1 rock-loading machine who had approximately the same production experience but operated the machine differently: one of them had mastered separate scooping well and strove to reduce the time of each cycle to a minimum, while the other combined penetration of the bucket with its turning. The observations were carried out in one rock heading and on the same loading machine. With separate scooping, the net loading time for one mine car averaged 10 min 54 sec, and filling it required from 21 to 32 cycles. With combined scooping, under the same conditions, the car was loaded in 8 min 08 sec with 12–18 scoopings. Similar observations were made of the operation of a T-107 loader and led to analogous conclusions: the most effective method is the time-combination of the processes of bucket penetration and scooping up the material.

Fig. 4. Dependence of the bucket penetration force on penetration depth for different scooping methods.

Experimental conditions:

Material—iron ore, ordinary.
Height of the material layer, 0.8 m.
Angle of inclination of the bucket bottom, $\alpha_0 = 10^\circ$.

○ — bucket of the UMP-1 machine,
● — bucket of the PML-5 machine,
◉ — experimental bucket.

• • • • penetration and tearing-away of the bucket—simultaneous,
        — penetration and tearing-away of the bucket—separate.

Experiments showed that the kinematics of the working members of some types of loading machines (this applies, in particular, to the PPM-2 and UMP-1 machines) for carrying out a combined scooping cycle is irrational and hinders good filling of the bucket, especially when the height of the material layer is small.

For this reason, it is advisable to design the hoisting mechanisms of loading machines with drums having a variable winding radius for the traction chains or ropes. This is found in some existing designs of loading machines, in particular in the PML-5 machine, the T-107 loader, and others. Along with ensuring greater bucket filling, such a measure will also make the load on the machine drive more uniform. It should be especially noted that combined scooping sharply reduces the forces both during pene-

...as well as turning of the bucket. The reduction in penetration forces is shown in Fig. 4 by dashed lines, as established by special experiments.

The adhesive weight of any cyclic-action loading machines must be selected in strict accordance with their purpose, the dimensions of the working member, and the specific conditions of use.

With a combined scooping cycle, when use of the reserve of kinetic energy of the machine itself during bucket penetration practically does not occur, the adhesive weight of the machine may be determined by the following simplified formula:

\[ g_M=\frac{p_{\mathrm{vn}}+g_m\left(G_M\pm i\right)}{\mu-\left(G_m\pm i\right)}. \tag{3} \]

In this formula the following notation is adopted:
\(g_M\) — adhesive weight of the machine, in kg;
\(g_m\) — weight of the transport mechanism with load, in kg;
\(p_{\mathrm{vn}}\) — resistance of the bucket to penetration into a pile of material to the selected depth, in kg;
\(G_M\) — rolling resistance of the loading machine;
\(G_m\) — rolling resistance of the transport mechanism;
\(\mu\) — coefficient of adhesion of the running gear;
\(i\) — track gradient in thousandths.

This formula assumes that the transport mechanism is connected with the machine chassis and moves together with it. If, however, the machine and the transport mechanism are separated from each other, then this formula takes the following form:

\[ g_M=\frac{p_{\mathrm{vn}}}{\mu-\left(G_M\pm i\right)}. \tag{4} \]

On the basis of the experimental investigations carried out, the following approximate empirical relationship has been established between the penetration force and the principal factors affecting it:

\[ p_{\mathrm{vn}}=c\cdot k_h\cdot k_\phi\cdot p_0\cdot B, \tag{5} \]

where
\(c\) — coefficient taking into account the size composition of the rock, the degree of its compaction in the layer, etc.;
\(k_h\) — coefficient taking into account the effect of layer height;
\(k_\phi\) — coefficient taking into account the geometric shape of the bucket;
\(p_0\) — specific force of bucket penetration to the selected penetration depth, in kg/cm;
\(B\) — bucket width, in cm.

As the experimental data obtained show, the relationship between the principal factors affecting the forces of bucket penetration is complex and is far from being reflected by the formula given above. Nevertheless, within the studied range of variation of the values of the variable factors, this formula gives results quite satisfactory for engineering calculations, agreeing with data from the practical operation of loading machines.

The investigation carried out made it possible to establish the values of the specific penetration forces for iron ore, granite, limestone, and sandy shale of various sizes, as well as the values of all coefficients included in formula 5. The values of the specific resistances to bucket penetration \(p_0\) are given in Fig. 5.

Analysis of the experimental data and the technical parameters of various types of loading machines made it possible to conclude that the adhesive weight of a number of loading machines often does not correspond to the actual resistance

to bucket penetration, which is determined by the dimensions and geometry of the latter and by the specific conditions of application. This applies, in particular, to underground rock-loading machines of the PML-5 and UMP-1 types, T-107 tractor loaders, etc. Therefore the actual performance indices of their operation that were given above become understandable.

Fig. 5. Dependence of the specific bucket-penetration forces on penetration depth for various rocks.

Test conditions:

Bucket of improved geometric shape.
Angle of inclination of the bucket bottom \(\alpha_0 = 10^\circ\).
Height of the material layer: 800 mm.
The front edge of the bottom moves along the ground.

○ — ordinary iron ore.
⊙ — ordinary granite.
● — sandy shale.
◉ — ordinary limestone.

In order to find certain new technical means for reducing the penetration forces of the buckets of loading machines, experiments were conducted to study the influence of vibration of the bucket bottom on the process of scooping rocky ores. These experiments were preliminary in character, but nevertheless they are of certain practical interest. It is known that vibration as a mechanical process, often a highly undesirable and harmful phenomenon, is finding ever-wider application in some fields of engineering.

In carrying out these experiments, as the first stage of the study, the task was not set of making an in-depth investigation of all the changes that occur in a loose body under the influence of vibration, which is a topic of great independent significance. The aim was only to determine to what extent, and under approximately what regimes, vibration can cause one or another reduction in the forces of bucket penetration into a layer of coarse-lump rocky material. For conducting the experiments, a special bucket was designed and manufactured, shown schematically in Fig. 6. In the upper part of the bucket an electric motor 1 was installed, which, by means of a V-belt transmission, drove crankshaft 2 in rotation with a variable eccentricity that could be set at will. From this crankshaft, oscillatory motion was transmitted by connecting rod 3 to bucket bottom 4, hinged to the bucket body. The experimental bucket was installed on the existing stand, and, with the aid of self-recording apparatus, the forces arising when the bucket penetrated into the rock layer were recorded.

As a result of the experiments performed, a number of interesting interrelations were established, undoubtedly indicating that vibration of the active elements of the working members of loading machines can bring about a sharp reduction in penetration forces. It turned out that, under the influence of vibration, the mechanism of the scooping process undergoes a substantial change. A highly interesting fact is that, under the influence of the bottom, a considerable mass of rock was brought into oscillatory motion, the particles of which

stood away from the bucket at a distance of up to 2–2.5 m. The observed decrease in the bucket penetration forces was due to a reduction in the coefficient of friction and the appearance of a certain mobility of the rock particles under the influence of vibration. These phenomena were also noted by some other investigators. The process of bucket penetration in the presence of vibration proceeded more smoothly than usual.

Figure 7 shows, as an example, the dependence of the magnitude of the bucket penetration force on the depth of penetration and the frequency of oscillations, at constant penetration velocity and amplitude. As can be seen from this graph, with increasing frequency the penetration forces decreased considerably. Thus, at a frequency of 2000 oscillations/min, the penetration forces during vibration amounted to only 30–40% of the forces occurring in the ordinary digging process. The amplitude of oscillations had an even more substantial influence on the digging process. With an increase in amplitude from 2.5 to 15 mm, the penetration forces dropped sharply in magnitude and, at a low bucket penetration velocity of about 0.075 m/sec, amounted to only 6–19% of the usual penetration forces of a bucket with a fixed bottom. This dependence is shown in Fig. 8.

Fig. 6. Diagram of an experimental bucket with a vibrating bottom.

Thus, at large amplitudes, the penetration force decreased as a result of vibration by a factor of 5–12. As the experiments showed, the essential factor for the digging process with the use of vibration is the bucket penetration velocity, that is, in essence, the time factor.

Fig. 7. Dependence of the magnitude of the penetration force on penetration depth and oscillation frequency.

Test conditions:

Bucket penetration velocity—0.15 m/sec.
Oscillation amplitude—15 mm.

● — Oscillation frequency 2000 oscillations/min
◐ — ” ” 1500 ”
○ — ” ” 1000 ”
⊙ — ” ” 650 ”
○ — Bucket penetration without vibration.

With an increase in the penetration velocity, the influence of vibration on the forces proved to be less substantial. The specific energy consumption of the digging process with the use of vibration decreased somewhat.

Applications of vibration in the field under consideration may be new working members of periodic-action loading machines; moreover, oscillatory motion may be imparted both to the entire bucket and to its individual elements. A practical solution to this problem requires appropriate investigations. It should be noted, however, that a sharp reduction in penetration forces as a result of using vibration may create technical prerequisites for a transition to working members of continuous action for those conditions which until now have been exclusively the sphere of application of loading machines with working members of periodic action.

Fig. 8. Dependence of the magnitude of the penetration force on the penetration depth and the oscillation amplitude.

Test conditions:

Bucket penetration speed—0.07 m/sec.
Oscillation frequency—1500 osc./min.

— Oscillation amplitude 15 mm
○ — ” ” 10 mm
◐ — ” ” 5 mm
◑ — ” ” 2.5 mm
● — Bucket penetration without vibration.

Brief Conclusions

1. As a result of the creative efforts of designers of Soviet machine building in recent times, a great variety of periodic-action loading machines, differing in their purpose, has been created and has found mass application in many branches of the national economy. Experience shows that mechanization of the loading process brings about a significant increase in labor productivity. At the same time, however, the designs of many loading machines have a number of substantial shortcomings; their productivity under operating conditions proves to be considerably lower than the calculated value, and this reduces the overall effectiveness of mechanized loading. For this reason, an important immediate task is the further improvement of the designs of loading machines, and first of all of their working members, which have not undergone substantial changes in recent times.

2. Investigations carried out by the mechanization laboratory of the Mining-Geological Institute of the West Siberian Branch of the Academy of Sciences showed that the buckets of most types of loading machines, owing to the imperfection of their geometry, cause the occurrence of large resistances when they penetrate into a layer of one material or another. This hinders penetration of the buckets to the required depth, reduces their filling, and leads to a decrease in machine productivity.

The kinematics of the working members of loading machines also proves to be imperfect, preventing the working cycle from being carried out with combined-

the processes of bucket penetration and its rotation in the vertical plane. Very often there is a discrepancy between the adhesive weight of the loading machine and the dimensions of the bucket, which under severe operating conditions leads to a sharp reduction in its productivity.

1. As a result of the experimental studies carried out, specific ways have been outlined for improving the geometry of the buckets of loading machines; the kinematics of the working members has been substantiated, ensuring the greatest filling of the buckets; and the actual forces arising during the scooping of rock have been identified. Taken together, all this makes it possible to formulate a number of practical recommendations for improving the designs of loading machines and their principal technical parameters. Certain new technical methods for reducing scooping forces have also been studied, in particular vibration, which is already planned for use in the design of new types of loading machines.