Study of a Gear-Type Rotary Attachment for an Impact Machine

N. P. Ryashentsev, A. P. Tronov

(Presented by the Department of Mining Machines and Mine Transport)

In construction and installation work, manually operated mechanized impact tools are finding ever wider application. A drawback inherent in most types of electric and pneumatic hammers produced by domestic industry is the absence of a device for rotating the tool.

In 1950 A. I. Moskvitin wrote that “...if it were possible to make a sufficiently light, simple, and reliable device for the self-rotation of the working tool in a not very long hammer, such a hammer would provide higher productivity” [1].

However, over the past decade the solution to the problem of self-rotation of the working tool has undergone no fundamental changes.

To become acquainted with the operating principle of the gear-type rotary attachment, let us turn to Fig. 1 (a, b). If a plate 3 is placed on the inclined elastic teeth 1, fixed on the base 2, and loaded with a static force \(P\), then plate 3 will move downward and to the right. This displacement consists of a vertical displacement \(h\) and a horizontal displacement \(l\). After removal of the load \(P\), the teeth 1, straightening, will return plate 3 to its former position. However, under certain additional conditions that provide, for example, limitation of the displacement of plate 3 to the left, the teeth 1, slipping, will raise plate 3 by the height \(h\), but will not be able to move it to the left by the amount \(l\).

With repeated application of the load \(P\) and with the condition limiting the travel of the plate to the left observed, the latter can be moved to the right by the amount \(h = nl\), where \(l\) is the number of compression cycles.

Obviously, inclined elastic teeth fixed on an annular base, under the same conditions, make it possible, in \(n\) compression cycles, to turn an annular washer about the axis of the ring through an angle \(\alpha = n\alpha'\), where \(\alpha'\) is the angle of rotation of the washer in one loading cycle.

This principle forms the basis of the working process of the gear-type rotary device made by the firm “Sintron.”

The elastic teeth may be made of various materials—steel, vulcolan, or rubber.

Figure 1 (v, g) shows the diagram of one variant of the rotary devices of the firm “Sintron” (v) with gear-type rotary washers of the annular type (g) [2].

The rotary attachment consists of flanges 1, 7, connected to the body by rods 5, a chuck 2 with a flange, and rotary washers 3, 6. During operation of the hammer, striker 8 delivers blows to the shank of chuck 2, which, while performing reciprocating motion, successively deforms the teeth of rotary washers 3 and 6. In this process the tool is rotated, despite the absence of a device limiting rotation of the tool in the direction opposite to the inclination of the teeth. This fact can be explained only by the difference between the working processes of the rotary washers under dynamic and static loads.

Fig. 1. Rotary device of the “Sintron” firm:
a, b—diagram of the toothed rotary element;
c—longitudinal section; d—general view of the washer.

The toothed rotary attachment, operating with the MS-15 solenoid hammer, provides rotation of the tool at a speed of 40–80 rpm in cases where the tool does not bear against the face. But even with slight pressure on the hammer, the rotational speed of the tool decreases considerably. The reason is that, when the tool is constrained by the object being worked, the axial displacements of the chuck necessary for intensive rotation of the tool are possible only when the hammer body moves away from the face. Experiments show that the amplitude of oscillation of the body should be within 3–4 mm. When pressure is applied to the hammer, the withdrawal of the body from the face decreases, and the rotary device becomes inoperative. For this reason the simple and economically advantageous rotary device of the “Sintron” firm cannot find wide application.

Experimental studies of the rubber toothed rotary device, carried out by the Laboratory of Electric Machines of Impact Action, made it possible to reveal the mechanism of the working process of toothed washers and to outline ways of creating and improving an operational rotary attachment.

The purpose of the experimental study of the toothed rotary device is:

1. To reveal the mechanism of the working process of the rotary device under dynamic and static loads.
2. To determine the optimal parameters of the rotary washers: the angle of inclination of the tooth to the base, and the duration of the rotary cycle.
3. To obtain recommendations for improving toothed-type rotary devices.

As was stated above, in order to rotate the tool it is necessary to ensure an axial displacement of the chuck by 3–4 mm. This means that, when the rotary attachment operates together with an impact machine, the tool, while oscillating, inevitably separates from the face, and that the main rotation of the tool occurs at the time when it is not in contact with the face.

Thus, the resisting moment is determined only by friction forces, and the torque cannot be the principal criterion of the quality of rotary washers.

The evaluation of rotary washers should be carried out according to the magnitude of the tool rotation angle and the duration of the rotary cycle per single blow, as well as according to the magnitude of the axial displacement of the chuck and the energy expended on rotating the tool.

The desire to create a gear-type rotary device that ensures rotation of the tool under axial pressure on the hammer, excluding oscillations of the housing, is in contradiction with the nature of a gear-type rotary device of the given design and means converting an impact-rotary machine into an impact-rotational machine.

The dynamics of the working process of the rotary device must be studied by recording the axial and angular displacements of the chuck over time at specified values of the impact energy.

The working cycle of the rotary device was recorded on a test stand, the general view of which is shown in Fig. 2, a.

Fig. 2, a. General view of the test stand for studying the working process of rotary washers.

The stand consists of the following principal units: the drive, the rotary device, the sensor unit, and the object being machined.

The purpose of the drive unit is to impart the required impact energy to the hammer striker. This unit is assembled from guide tube 1, fastened by screws 2 to bed 3, striker 4, spring 5, stop 6, and screw 7.

The rotary device consists of base 8, flange 9, nut 10, chuck 11, and rotary washers 12 and 13.

Figure 2, b shows the sensor unit. Its main parts are: hexagonal tool 14, on which chuck-travel sensor 15 is mounted; bushing 16 with fixed contact of the chuck-travel sensor 17 and movable contact 18; and rotation-angle sensor 19, fastened to post 20.

The procedure for conducting the experiments is as follows:

The striker 4 is locked by the catch 6, and the spring 5 is compressed by the screw 7. The magnitude of the energy imparted by the spring to the striker is calculated by the formula \(A=\dfrac{cx^2}{2}\), where \(c\) is the stiffness of the spring and \(x\) is the amount of compression.

Fig. 2, b. Sensor unit of the stand for studying the working process of rotary washers.

After the catch 6 is released, the striker 4 delivers an impact to the shank of the chuck 11, which, moving to the left, deforms by means of the flange 9 the teeth of the rotary washer 12. At the same time the chuck, and with it the tool, while moving in the axial direction, simultaneously rotate in the direction of the tooth inclination. During rotation the tool turns the sleeve 16 and the movable contact 18, which, moving along the rotation-angle sensor 19, changes its resistance, connected into the circuit of the oscillograph loop.

Thus the angle of rotation of the tool for a single impact is recorded.

At the same time the tool 14 moves relative to the sleeve 16 in the axial direction. In doing so, the tool 14 carries the chuck-stroke sensor 15 relative to the contact 17, fixed on the sleeve 16. The sensor 15 thus makes it possible to record the chuck stroke.

The circuits of sensors 15 and 19 are powered from separate batteries.

Sensors 15 and 19 are made in the form of potentiometers wound on an insulating base with constantan wire of diameter \(0.2\) mm.

Recording of the chuck stroke and the angle of rotation is carried out by an MPO-2 oscillograph.

On the described stand, the working processes of rotary washers made of rubber rings with the parameters given in Table 1 were investigated.

Recording was carried out at impact energies of \(0.2;\ 0.4;\ 0.6;\ 0.8;\ 1.0;\ 1.2;\ 1.4\) kgm. At each value of impact energy, the experiment was repeated three times.

After oscillographing the working process of rotary washers under “idle” impact modes of the striker on the chuck, with rotary washer No. 60 (angle of inclination of the teeth to the base \(60^\circ\)), the following two series of experiments were conducted:

1. To determine the difference in the course of the working processes under static and dynamic loading of the rotary washers, oscillographic recording was made of the rotary cycle when the striker hit the chuck through a spring of stiffness \(1\ \text{kg/mm}\).

Table 1

1. The second series of experiments made it possible to determine the working process of the rotary cycle in the case when, at the moment the striker hits the chuck, the tool is in contact with the face.

Oscillographic recording was carried out as follows. At tool 14 the object being worked (building brick) was installed in such a way that tool 14 touched the face without pressure. Then, at a specified impact energy, without resetting the object being worked, the working process of the rotary device was recorded three times.

The procedure for processing the oscillograms was as follows:

1. We determine the scales of oscillation of the chuck, \(m_s\), and of the rotation angle \(m_\alpha\):

\[ m_s=\frac{S}{h}; \qquad m_\alpha=\frac{a}{b}, \]

where

\(S\) — displacement of the chuck, mm;
\(h\) — deflection of the beam of the loop on the oscillogram of chuck oscillation, mm;
\(a\) — angle of rotation of the chuck, degrees;
\(b\) — deflection of the beam of the loop on the oscillogram of the angle of rotation, mm.

1. From the oscillogram of the working process of the gear-type rotary device we determine:

a) the maximum axial displacement of the chuck toward the face;
b) the maximum angle of rotation;
c) the reset angle;
d) the magnitude of deformation of the rear rotary washer;
e) the working angle of rotation;
f) the energy of translational and rotational displacement of the chuck;
g) the time required to reach the maxima of the axial and angular displacements of the chuck;
h) the total time of the rotary cycle.

1. The results of the experiments and of the experimental processing are entered in a table.

2. We plot the dependences of the axial and angular displacements of the chuck on the impact energy.

3. We draw conclusions and recommendations.

Let us proceed to consider the results of the experimental investigation of the rubber gear-type rotary device.

In Fig. 3, a, oscillograms are given of the axial displacement of the chuck and of the angle of rotation for a washer with a tooth inclination angle to the base of 80° at a striker impact energy of \(1.2\ \text{kgm}\).

Point \(a\) corresponds to the moment when the striker impacts the shank of the cartridge. After the impact, the cartridge, deforming the front washer, moves until it stops at point \(b\). Under the action of the elastic forces of the front washer, the cartridge moves in the opposite direction, passes point \(v\), and deforms the rear washer up to point \(g\). Then the cartridge again passes through the initial position (point \(d\)) and secondarily deforms the front washer along the curve \(d—e—u\). Thus, the axial displacement of the cartridge follows the law of an oscillatory process with damping.

Fig. 3. Oscillograms of the working processes of the rotary device:
1—curve of axial displacement of the cartridge; 2—curve of the angle of rotation;
\(a\)—with impact loading and idle travel of the cartridge; \(b\)—with static loading and idle travel of the cartridge; \(v\)—with impact loading and limitation of the tool travel by the object being worked.

The rotation of the tool begins \(1—2\) msec after the impact (point \(k\)). The maximum value of the angle of rotation is reached at the time when the teeth of the rotary washer, relaxing, return the cartridge to its initial position. Consequently, rotation of the tool under dynamic loading of the washers is possible owing to slipping of the cartridge flange over the teeth of the rotary washer.

In the segment \(l—m\), the initial angle of rotation is released, and in the segment \(m—n—o\) it is partially restored owing to deformation of the rear washer and secondary deformation of the front washer.

The working processes of rotary washers with tooth inclination angles to the base of \(60^\circ\), \(45^\circ\), and \(30^\circ\) proceed similarly. Figure 3, \(b\) shows oscillograms of the working process of the rotary device under a load close in character to static (impact through a spring) for a washer with a tooth inclination angle to the base of \(60^\circ\) and with an impact energy of \(0.8\) kgm.

In the axial direction, the cartridge moves along the curve \(a—b—u\), where in the segment \(a—b\) compression of the washer occurs, and in the segment \(b—u\) the cartridge returns to its initial position.

The curve of angular displacement of the cartridge consists of the segments \(k—l\)—rotation of the tool, and \(l—p\)—release. The maximum angle of rotation is reached somewhat earlier than the maximum axial displacement.

The oscillograms shown in Fig. 3, \(v\), characterize the course of the working process of a rotary washer with a tooth inclination angle to the base of \(60^\circ\) at a striker impact energy of \(0.8\) kgm, in the case when the tool before impact bears against the working face (building brick). It is seen that the amount of penetration of the tool into the working face is insignificant; therefore, the amount of angular displacement of the cartridge is small.

The plots in Fig. 4 illustrate the dependence of the principal parameters of the working process of the rotary washers on the impact energy under dynamic loading (curves No. 80, No. 60, No. 45, No. 30), under impact through a spring (curve No. 60P), and when the tool is constrained by the object being worked (curve No. 60 K).

The number of a curve corresponds to the value of the inclination angle of the teeth to the base. On the basis of the oscillograms in Fig. 3 and the plots in Fig. 4, the following conclusions are drawn:

1. To ensure effective rotation of the tool at a constant energy transmitted to the chuck, it is necessary to reduce the release angle.

2. In view of the fact that the maximum angle of rotation under dynamic loading of the rotary washer is reached at the moment when the tool is moving in the direction away from the face, it is expedient to carry out rotation of the tool during idle impact modes of the striker against the chuck. However, this condition reduces the productivity of the machine. Therefore, we consider that a more rational design of the rotary device is a design with one rotary washer located between the chuck flange and the hammer housing.

Fig. 4. Plots of the dependence of the maximum angle of rotation, the release angle, and the chuck travel on impact energy: — maximum angle of rotation, – – – release angle, –×–×– axial displacement of the chuck.

1. When the tool is constrained by the object being worked, the front rotary washer is practically inoperative. Rotation of the tool is possible only with a considerable rebound. In this case, rotation occurs through the interaction of the chuck flange with the rear washer.

2. The rotary washer with a tooth inclination angle to the base of 60° has the most favorable ratio of the parameters of the working process.

3. The working-cycle time of the washers studied under impact loading does not exceed 24 msec.

4. Under static loading of the rotary washer, the maximum angle of rotation and the release angle do not depend on the impact energy. The cycle time is determined by the half-period time of oscillation of the striker on the spring.

On the basis of the foregoing, two ways may be outlined for improving the design of the toothed rotary attachment.

1. In order for the rotary attachment to remain operable when axial pressure is applied to the hammer, the angular displacement of the chuck must be made independent of its axial displacement. A rotary device of this type (Fig. 5) consists of a cylindrical flange

Fig. 5. Toothed rotary device with extraction of striker energy for rotation before impact on the tool.

6 with a hexagonal opening, through which chuck 2 moves freely, rotary washers 5 and 7, a shaped nut 8, and a flange 9. The tool is prevented from falling out by collar 3 and retaining spring 4. During operation of the hammer, striker 10 first displaces flange 6, which deforms washer 5, rotating together with chuck 2 and tool 1, and then delivers an impact to the chuck.

1. The hammer is equipped with an elastic handle that isolates the operator from the oscillating body. When working with an elastic handle, the amplitude of oscillations of the body is considerably greater than when working without it; therefore axial displacements of the chuck are possible that are necessary for effective rotation of the tool. Impact interaction of the hammer body with the object being worked takes place through an intermediate element—the rotary washer. It is therefore natural to assume that the energy of the oscillatory motions of the body is expended in performing useful work—the rotation of the tool.

References

1. Moskvitin A. I., Electric Reciprocating Machines. Publishing House of the Academy of Sciences of the USSR, Moscow–Leningrad, 1956.

2. Patentschrift No. 934579, Insbesondere für Schlagwerkzeuge bestimmte Vorrichtung zum Umsetzen einer hin-und hergehenden Bewegung in eine kreisende Bewegung.