V. I. BABUROV, V. F. GORBUNOV, Yu. A. OGARIN

EXPERIMENTAL SETUP FOR STUDYING RIVETING-CHIPPING HAMMERS

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

Despite the large number of works devoted to the study of pneumatic impact machines, at the present time the working processes of chipping and riveting hammers remain little studied, and, what is especially important, the processes of chipping and riveting have not been studied at all.

Usually all pneumatic impact machines—pneumatic drills, breakers, chipping and riveting hammers—regardless of the various operating conditions, are tested under practically identical laboratory conditions, whereas many researchers have shown that one of the most important factors affecting the working characteristics of hammers is the properties of the medium being worked.

Taking account of the specific operating conditions is especially necessary when studying the vibration and efficiency of a machine.

The present work describes a new experimental setup for studying chipping and riveting hammers under conditions close to operating conditions, as well as a number of special devices developed by the authors for recording and oscillographing certain characteristics of hammers.

The method developed by the authors for studying chipping and riveting hammers includes:

1. Investigation of the processes of chipping and riveting in order to determine the requirements that chipping and riveting hammers must satisfy, and also in order to develop recommendations for their rational use.

2. Investigation of the internal working processes and of the influence on them of the pressing force and the air pressure in the hammer network.

3. Investigation of hammer parameters in order to establish their most rational combination for each type size of hammer, taking account of operating conditions.

4. Investigation of designs. Selection of a rational form of the shank of the working tool. Investigation of the operation of air-distribution devices, etc.

5. Investigation of the influence of the medium being worked on the parameters and vibration of hammers. Investigation of the vibration characteristics of hammers in order to develop methods and means for reducing vibration.

In the course of the investigation, the method provides for changing the conditions that affect the internal working processes, parameters, and vibra-

of the hammers. Such conditions include: the pressure of the compressed air in the line, the pressing force applied to the hammer, the position of the hammer relative to the workpiece being processed, the characteristics of the medium being processed (shape, mass, elastic properties), and the characteristics of the working tool. The listed conditions determine the process of operation with the hammer. The air pressure in the line is usually in the range of 4–6 atm and is less often equal to 3 or 7 atm. The pressing force created by the worker during a shift is not constant. If at the beginning of the shift it reaches 30–35 kg, then by the end it decreases to 20–25 kg. Naturally, the magnitude of the pressing force required for normal operation of the hammer depends on the standard size, design, weight, and position of the hammer. Both the chipping process and the riveting process are carried out with the hammers in various positions. However, the chipping of metal articles is performed primarily with the hammer inclined downward at an angle of 30–50°, while riveting is performed mainly vertically downward or horizontally. The dimensions and configuration of the articles being processed are highly varied, but in chipping these are, to a greater extent, large, medium, and small castings of iron and steel, rolled stock, while the material of the rivets is steel and aluminum [2].

A great variety is also observed in the types of working tools used. The length of chisels for chipping ranges from 0.25 m to 2 m, and the diameter from 16 mm to 34 mm.

Fig. 1. Diagram of the test stand for studying riveting-chipping hammers:
1 — pneumatic feeder for moving the carriage; 2 — pneumatic feeder for creating the pressing force; 3 — guide frame; 4 — movable carriage; 5 — steady rest; 6 — table; 7 — workpiece; 8 — posts; 9 — pneumatic hammer.

Taking into account the specific operating conditions of riveting-chipping hammers, the authors developed an experimental setup (Fig. 1). The setup consists of two pneumatic feeders 1, 2; a guide frame 3, along which carriage 4 moves; a steady rest 5; and a table 6, serving to secure the article (workpiece) 7 being processed.

The guide frame 3 is a welded structure made of two channels 4.3 m long. The channels are located on posts 8, embedded in the foundation. Carriage 4 is also a welded triangular structure made of channels and angles. The carriage moves along guide frame 3 by means of pneumatic feeder 1. The possible travel length is 1.3 m. Mounted on the carriage...

a pneumatic feed device 2 is installed, which creates the pressing force on the hammer 9. The dummy set 5 imitates the worker’s hand and serves to give the tool the proper direction. The feed device 2 and the dummy set 5 can be set in the desired position by moving the hinges into the corresponding holes in the base of the carriage and in its uprights. Repositioning the feed device and the dummy set makes it possible to give the hammer under study any fixed position, from vertically downward to horizontal. The height of the movable carriage was selected with allowance for the possibility of placing on the stand any of the known chipping-riveting hammers.

The movement of a chipping hammer fastened at a certain angle to the workpiece is necessary for studying both the chipping process itself and the vibration and internal processes during metal chipping. As the workpiece, a metal blank is fastened on table 6; after one chip has been removed, it can be moved in the transverse direction. To study the operation of riveting hammers, instead of the blank a special holder (rivet set) is installed on the table; through it the impact power is transmitted to a rod (rivet) rigidly fastened on table 6.

In investigating pneumatic chipping-riveting hammers it is necessary to determine the following characteristics and parameters: impact energy, impact frequency, air consumption, pressing force on the hammer, chipping (riveting) speed, vibration amplitude, and rebound of the hammer from the limiting collar of the tool. For describing and studying the dynamics of hammer operation, it is very useful to record the displacement of the striker, of the air-distribution valve, as well as the instants of impact of the striker on the tool and the seating of the hammer body on the collar of the tool. Most of the indicated characteristics can be recorded and determined by widely known methods.

Diagrams of the air pressure in the hammer cavities are recorded on a loop oscillograph using membrane transducers with strain gauges glued to them and an electronic amplifier [1].

The use of capacitive and inductive pressure transducers is also known [4, 5]. Diagrams of the displacement of the striker, the hammer body, and the tool are recorded electrically with the aid of potentiometric or induction transducers [1, 3, 6]. The air pressure in the supply line and in the cavities of the feed devices is registered from the readings of ordinary pressure gauges. Air consumption is determined with a V-1 or RV-4 flowmeter of the Leningrad “Pnevmatika” plant.

In addition to the widely known apparatus listed, we use a number of new devices for recording, for example, such characteristics as the moment of reversal of the valve, the frequency of collision and the duration of contact of the collar of the working tool with the hammer body, the dynamic forces arising between the hammer handle and the rod of the feed device, etc.

The moments of the beginning and end of reversal of, for example, a stepped cylindrical valve are recorded on film according to the circuit shown in Fig. 2. The body of the valve chest 1 (Fig. 2) is insulated by means of gaskets 2 from the hammer barrel 3 and the intermediate ring 4. In order that the length of travel of the valve not change, the ends of the valve chest 1 are undercut on both sides by the thickness of the gaskets 2. One insulated wire 5 is led through the exhaust passages of the hammer to the valve chest and soldered to it. The second wire is connected to the hammer body. When the valve 6 is in contact with the barrel 3 or the intermediate ring 4, the circuit is closed; current passes through it and is recorded by the loop of the oscillograph; the circuit is opened when the valve moves away from the barrel or ring. The dis—

opening and closing of the circuit is recorded on the film in the form of a stepped diagram \(D_{\text{p.z.}}\) (Fig. 3, b). Simultaneous recording of the moments of spool-valve shifting and of other diagrams makes it possible to investigate the operation of the air-distribution device, which is very important in studying the internal working processes, parameters, and designs of hammers.

Fig. 2. Electrical circuit for recording the moments of spool-valve shifting in pneumatic hammers: 1 — body of the spool-valve box; 2 — insulating gaskets; 3 — hammer barrel; 4 — intermediate ring; 5 — conductor; 6 — spool valve; 7 — hammer handle.

The frequency of impacts and the duration of contact of the shoulder of the working tool with the hammer body are recorded on the oscilloscope film by means of the device shown in Fig. 3, a. The electrical recording circuit is the same as in Fig. 2. Here the working contact of circuit 1 is insulated and is brought to tool 2. During operation of the hammer, the contact periodically touches hammer body 3, closing and opening the circuit; on the film a diagram \(D_{\text{s.n.}}\) is recorded (Fig. 3, b), analysis of which makes it possible to reveal regularities in the dynamics of hammer operation and to identify the nature and some of the causes giving rise to vibration.

The forces arising between the hammer handle and the feeder rod (the worker’s hand) are recorded on the oscilloscope film by means of a strain gauge (Fig. 4). Body 1 of the sensor is fixed immovably on piston rod 2 of the feeder (Fig. 1). In body 1 is placed cup 3, to the bottom of which wire strain gauge 4 is bonded. Signals from working strain gauge 4 and compensating gauge 5 are transmitted through a shielded cable to the TU-4M strain amplifier and then to the oscilloscope. During operation of the hammer, the pressing force from the feeder rod is transmitted through cup 3 (Fig. 4) and guide rod 6 to hammer handle 7.

Fig. 3. Electrical circuit for recording the impact of the tool shank against the hammer body (a) and oscillograms of the processes (b): 1 — working conductor; 2 — working tool; 3 — hammer body; 4 — guide bushing; 5 — striker. \(D_{\text{p.z.}}\) — diagram of spool-valve switching; \(D_{\text{s.i.}}\) — diagram of impacts of the body with the tool; \(P_{\text{z}}\) and \(P_{\text{p}}\) — diagrams of air pressures in the rear and front cavities of the hammer.

The deformation of the bottom of the cup, 3–4 mm thick, causes stretching of strain gauge 4 (Fig. 4). As a result of the change in the sensor resistance, an unbalance current of the bridge [1, 5] arises, recorded on the oscillograph film (after appropriate amplification). Such a device is calibrated statically.

Fig. 4. Device for recording oscillograms of forces on the hammer handle:
1—body; 2—feeder rod; 3—cup with bonded strain gauges; 4 and 5—strain gauges; 6—guide rod; 7—grips; 8—hammer handle.

Conclusions

1. The experimental setup described in this work, unlike existing stands of a similar type, makes it possible to conduct studies of chipping and riveting hammers under conditions that practically do not differ from the conditions of their operation.

2. The use of the described setup makes it possible to carry out a comprehensive study of the parameters of working processes, vibration, and operating modes of pneumatic chipping-riveting hammers.

REFERENCES

1. O. D. Alimov, I. G. Basov, V. F. Gorbunov, D. N. Malikov. Drilling Machines, Gostekhizdat, 1960.

2. V. F. Gorbunov, V. I. Baburov. On the unification of designs and the ordering of production of pneumatic chipping-riveting hammers. Article in the present collection.

3. V. F. Gorbunov, V. M. Gusarov, L. S. Berezin. An electrical method for recording vibrograms of pneumatic hammers. IVUZ, Mining Journal, No. 12, 1962.

4. L. F. Osipovsky. Investigation of the efficiency of operation of a drilling hammer with independent rotation of the drill. Abstract of Candidate’s dissertation. Alma-Ata, 1962.

5. N. P. Raevsky. Methods of Experimental Investigations of Mechanical Parameters of Machines. Publishing House of the USSR Academy of Sciences, 1952.

6. N. P. Ryashentsev, E. M. Timoshenko. An induction sensor for studies of the working process of impact-action machines. Proceedings of Higher Educational Institutions, Mining Journal, No. 7, 1960.

7. G. I. Sidorenkov. Theoretical and experimental investigation of the operation of valve-type pneumatic hammers and a method for their calculation. Candidate’s dissertation, Leningrad, 1962.

8. V. V. Yushin. Determination of the parameters of the internal process of mine pneumatic impact machines by the method of electrical measurements. Candidate’s dissertation, Dnepropetrovsk, 1960.