On the Parametric Series of Hand-Held Pneumatic Hammers

V. F. Gorbunov, V. I. Baburov

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

The variety of work performed with the use of pneumatic hammers has given rise to a large number of their standard sizes. In different branches of industry and transport, various designs of pneumatic hammers were independently created and improved. The largest categories of hand-held hammers, and those developing practically in isolation from one another, are: a) small-size riveting hammers of the KMP type and chasing hammers; b) chipping-and-riveting hammers of the MR, KE, R, and other types; c) breakers; d) drilling hammers.

Each of these categories of hammers has its own tendencies of development, and their levels of perfection differ substantially. This is a consequence not so much of the departmental subordination of machine-building plants as of the importance of the work performed by the hammers and of their share in the total volume of production. Thus, the most advanced pneumatic hammers—breakers and drilling hammers—are used in carrying out the basic processes in the mining industry: driving workings and stoping extraction of minerals. The influence of these operations on the development of the entire mining industry is obvious. Chipping hammers, however, are used in the performance of secondary production processes, and naturally less attention has been paid to them. Until recently, no one had been engaged in coordinating work in the field of pneumatic hammers.

Comparing hand-held pneumatic hammers by dimensions and energy characteristics, they may be divided into 9 principal groups (Table 1). The technical characteristics of the individual groups of hammers are arranged in a more or less proportional series for almost all the indicators given in Table 1. The exception is the blow frequency, the values of which vary over wide limits for almost every group.

At present, in the field of pneumatic hammers, the preparation and approval of parametric series, standards, and type ranges is under way. Thus, for example, type ranges for pneumatic breakers and drilling hammers have already been approved by the State Committee for Automation and Machine Building under the Council of Ministers of the USSR. The main parameter adopted for breakers and hand-held drilling hammers is their weight [1, 2]. In the type ranges for telescopic and column-mounted hammers [3], the main parameter is impact power. For

Technical characteristics of domestic hammers

Table 1

for riveting hammers, the rivet diameter serves as such a parameter. Work is under way to compile a typage for chipping-and-riveting hammers, where it is planned to take impact energy as the principal parameter.

In our opinion, such a variety of principal parameters for machines of the same type cannot be objectively justified and is explained by the lack of proper coordination in the work of the organizations compiling the typages. It would probably be advisable, from the state point of view, to introduce into machine-building practice a unified typage of pneumatic hammers for various purposes. The advisability of introducing such a typage is confirmed by the following advantages.

In the process of developing the size series and typage of hammers, the most progressive design solutions and data on the economy, manufacturability, and optimum energy characteristics of individual types of hammers will be identified. Comparison of these data will make it possible to identify progressive standards and requirements for hammers of various purposes.

The production of hammers according to a unified series of parameters and typage will reduce the costs of manufacturing spare parts and repairing hammers, owing to greater unification of their parts. At the same time this creates the possibility of specialization of machine-building plants in the manufacture of products of one type.

Unification of hammer designs for various purposes will make it possible to use one and the same machine for the performance of different operations, which will increase the efficiency of the use of hammers in small-batch production. This can be accomplished if factories manufacture sets of working tools for the hammers, to be supplied upon separate orders.

The present work sets forth an attempt to compile a size series of hand-held pneumatic hammers that could form the basis for the development of a typage.

In order to select an index that can serve as the basis for a parametric series of hand-held pneumatic hammers, we shall conduct a brief analysis of the interdependence of the parameters and of their relation to the design configuration and operating modes of the hammers. The requirements for the principal parameter of the series are established in the corresponding instructions [4].

Weight of the hammer. When working with a hand-held mechanized tool, its weight has a substantial influence on the worker’s productivity. From the standpoint of reducing the physical load on the worker, the weight of the hammer should naturally be reduced as much as possible. As is known, weight depends on many factors, among which the main importance belongs to the diameter and length of the barrel, as well as to the design configuration and number of the main devices and mechanisms (air distribution, vibration-damping and starting devices, tool fastening, handles, etc.). The dimensions of the internal cavity of the cylinder are determined as a function of the required energy indicators of the hammer—impact energy and impact frequency—taking into account vibration characteristics. From this standpoint, the weight of the hammer is, as it were, a derived indicator. The design and dimensions of the air-distribution, starting, and other devices of the hammer are selected on the basis of the loads arising, which depend on impact energy and impact frequency, as well as on the convenience of working with the hammer and on allowance for the necessary flow sections of the air ducts. Therefore in the present case as well, weight is a derivative of the energy indicators and the purpose of the hammer. For some groups of hammers it is necessary to provide in the design holders for the tool, swivel devices, etc. In the designs of other hammers these

devices are absent. The dependence of the hammer weight on the pressing force that must be applied to the hammer in order to ensure normal operation is more clearly expressed [9, 11]. In this connection, increasing the weight of the hammer is in some cases (working with the hammer downward) a positive factor, reducing the physical effort of the worker and the vibrational effect on his organism. However, even taking this interrelation into account, we find no basis for assigning hammer weight as the principal parameter of the series.

Impact energy. The influence of impact energy on the productivity of a pneumatic hammer, which is a machine of impact action, is obvious. The effectiveness of all operations, without exception, performed with the use of hand hammers depends on the correct choice of this parameter. In riveting rivets, the impact energy must be assigned depending on their diameter and material [5]. The use of hammers with low impact energy leads to a reduction in work productivity, while an overstatement of the impact energy may cause disruption of the technological process, the appearance of rejects [6], or simply a reduction in the effectiveness of the use of pneumatic energy and increased fatigue of the worker. The performance of chipping operations using hand-held pneumatic hammers likewise requires the selection of a rational value of impact energy. The influence of impact energy in drilling rock [7] and in breaking hard materials [8] has been studied in detail.

In all cases, the choice of impact energy is the determining factor in labor productivity, tool wear resistance, and hammer weight. Obtaining the required impact energy is possible by selecting various ratios of the cylinder diameter and its length (the striker stroke) [11]. Moreover, in order to increase the impact power of the hammer and reduce the required pressing force, it is desirable to obtain a large impact energy by lengthening the striker stroke, rather than by increasing the cylinder diameter. This will have an unfavorable effect on the weight of the hammer, although it is advisable from the energy and sanitary-hygienic points of view. As can be seen from Table 1, arranging hand-held pneumatic hammers by groups evaluated according to impact energy is quite logical also from the standpoint of the work performed by the hammers. Generalizing what has been stated, we consider that impact energy may be adopted as the principal parameter of a series of hand-held pneumatic hammers.

Impact frequency. Modern pneumatic hammers have a very wide range of impact frequencies (Table 1). As follows from experimental studies of hammers of various purposes [5, 7], the productivity of hammers is proportional to the frequency of impacts of the striker on the tool. In this connection, in 1953–1956 many designs of hammers with increased impact frequency (so-called high-frequency hammers) appeared in industry. However, the practice of using these hammers did not confirm the advisability of producing them, owing to an increase in the incidence of vibration disease among workers [10]. In addition, the new hammers were not at that time equipped with the corresponding feeding-and-supporting devices, and therefore their power could not be used sufficiently fully [11]. As a result, the hand-held pneumatic hammers now being produced, as well as those planned for manufacture, rarely have an impact frequency above 2500 impacts/min. The lower limit of the impact frequency of hand hammers—800–900 impacts/min—is due to the assignment of the greatest possible impact energy without increasing the cylinder diameter. Such hammers are necessary, for example, for riveting rivets 15–32 mm in diameter and larger, for breaking up oversized pieces of rock, for destroying

frozen soils, road surfaces (pavement breakers), etc. Obviously, the frequency of blows may be one of the principal, but not the main, indicators of the parametric series of hand-held pneumatic hammers.

Impact power. The combination of the energy and the frequency of blows determines the power of a machine of impact action. The dependence of work productivity on the magnitude of the hammer’s impact power is obvious. It should merely be borne in mind that the use of the power obtained depends on the availability of appropriate means for feeding the tool and the entire hammer in the direction of the object being worked. The minimum necessary pressing forces on the hammer are a function of its design and energy parameters and, consequently, of its power [9]. As can be seen from Table 1, modern hand-held pneumatic hammers have a power of up to 3 hp and higher. The range of power values by groups of hammers in the zone of chipping-and-riveting hammers is nonuniform. This is explained by the necessity and expediency, with the same cylinder diameter, of manufacturing hammers with different impact energy—for example, hammers of the MR and KE series. From the technological point of view, such series of hammers are highly desirable, since the unification of assemblies and parts reaches a very high percentage (up to 95%).

On the basis of the above, it may be concluded that impact power—one of the principal indicators of the size series of hand-held hammers, being a function of impact energy and blow frequency—cannot be recommended as the main parameter of the series.

Air consumption, pressing force, hammer efficiency, and other data of the technical characteristics are derived from the basic energy indicators; therefore it is inexpedient to evaluate them from the point of view of their applicability as the main parameter of the series.

Thus, summing up the brief analysis of the indicators of hand-held pneumatic hammers, we come to the conclusion that the most justified is to assign impact energy as the main parameter of their parametric series.

Selection of the values of the main and principal parameters of the series. When selecting the values of impact energy for hand-held pneumatic hammers, the recommendations of the Committee for Standardization and Normalization of Equipment must be taken into account, as well as the requirements for hammers arising from the specific nature of the work performed and the technology of their manufacture.

The basic requirements for the parametric series may be formulated as follows.

1. The parametric series must have a definite, rationally selected sequence of numerical values of the main parameter of the hammers, corresponding to a series of preferred numbers (GOST 8032-56).

2. The parametric series must consist of an objectively minimal number of values of the main parameter, excluding an excessive variety of hammer type sizes, but satisfying the needs of production (by types of work).

3. In selecting the main and principal parameters of the series, it is necessary to provide for the possibility of maximum unification of parts and assemblies of hand-held pneumatic hammers.

In addition to the indicated basic requirements imposed on the parametric series, it is also necessary to bear in mind its technical and economic progressiveness. The series must not fetter the initiative of designers in the search for the most promising solutions, nor restrict...

possibilities for increasing the efficiency of hammers, reducing their metal consumption, etc.

On the basis of the principal requirements for the parametric series and the results of studies of the working processes and designs of hand-held pneumatic hammers, it appears possible to draw up recommendations on the number and values of the principal parameter (Table 2). In our opinion, the range of variation of impact energy from 0.2 to 6.3 (8.0) kgf·m fully satisfies the needs of the varied operations performed by hand-held pneumatic hammers, and subdivision into 12 (11) intervals does not contradict the basic requirements for the series. The selection of a definite number of hammer standard sizes within each category (Table 2) was made with account taken both of practical need,

Table 2

Parametric series of hand-held pneumatic hammers

identified by us in surveying the conditions of hammer application [12], and also of the recommendations, types, and standards for pneumatic hammers in force in 1961–1963 [1, 2, 3].

The selection and assignment of the magnitudes of the main parameters of the series must, naturally, be carried out with account taken of additional requirements arising from the specific nature of the work performed with hammers, the sanitary-hygienic working conditions of the workers, the possibilities for partial mechanization of individual operations when working with a hammer, etc. Let us briefly consider the prerequisites for selecting the main parameters of the proposed series.

Impact frequency of the hammer. As shown above, a high impact frequency of hand-held pneumatic hammers is desirable from the standpoint of increasing work productivity, but it is limited mainly by two circumstances: vibration hazard (upper limit) and the possibility of ensuring the required impact energy with a limited hammer-cylinder diameter (lower limit). The diameter

the cylinder, in turn, is associated with the pressing force that a worker can maintain for a prolonged period without fatigue. In our opinion, for hand hammers, depending on the nature of the work being performed, it is possible to allow working pressing forces within the limits indicated in Table 3.

Table 3

Distribution of hammers by magnitude of pressing force

On the basis of the data in Tables 2 and 3, and using the method for calculating the energy characteristics of hammers from their design dimensions [1], we determined the limits of blow frequencies for hammers of various categories (Table 4). As can be seen from Table 4, the maximum blow frequency of hand hammers may lie within the range of 2600–2700 blows/min.

On the basis of the investigations we have carried out into the vibration and working processes of pneumatic hammers for various purposes, it is technically possible to create hammers with the characteristics given in Table 4 and with vibration within the limits of the current sanitary standards.

Hammer weight. The weight characteristic of hand hammers is of great importance in the practice of their operation. The hammer weights given in Table 4 were calculated on the basis of an analysis of the weight and energy characteristics of hand pneumatic hammers manufactured by various machine-building plants. The calculation was made taking into account progressive ratios of the metal consumption of the hammers, their impact power, and the design features of individual groups (the presence or absence of auxiliary devices for holding the tool, turning it, removing the products of destruction of the material being worked, etc.).

Air consumption. The pneumatic hammers currently being produced, depending on their design, have very different total air consumption and air consumption per unit of impact power. In selecting the value of the parameter for the proposed series, we shall be guided by the average progressive data derived from analysis of the characteristics of the best domestic hammer models.

The proposed parametric series of hand pneumatic hammers (Table 4), in our opinion, can be recommended for use as the basis for developing their unified standard range. The existing discrepancies in the values of individual parameters of the proposed series and the data of standard ranges for different categories of hammers [1, 2, 3] are small and are explained by the different approaches to solving the problem posed. Assigning the blow energy as the principal parameter of the series naturally led to a departure from the strict requirement for the weight characteristics of hammers that is adopted in the standard ranges for breaking hammers.

The proposed parametric series of hand-held pneumatic hammers is more progressive from the standpoint of unification and standardization of the equipment produced than separate standards for chipping, riveting, breaker, and drilling (hand-held) hammers. Incidentally, we note that this series can easily be extended to the field of telescopic and column-mounted drilling hammers and rotary-impact drilling machines.

Table 4

Values of the principal and basic parameters of the parametric series of hand-held pneumatic hammers

* The numerator gives data for “deep-hole” drilling hammers; the denominator, for hammers with pneumatic supports.

rotary drilling. Such a combination of series of fundamentally similar machines is expedient, but it does not fall within the range of questions addressed in the present work and therefore is not considered by us.

Conclusions

1. The hand-held pneumatic hammers currently being produced—chipping, riveting, pick, and drilling hammers—have, respectively, the weight, rivet diameter, and weight of the machine as the principal parameter of the series of standard sizes.

2. The diversity of the parameters in a series of hammers of the same type increases the costs of manufacturing spare parts and repairs, and makes it more difficult to unify parts and assemblies and to specialize machine-building plants in the production of pneumatic impact machines.

3. The analysis carried out of the conditions of application, the results of investigations of working processes, vibration, and the designs of hand-held hammers, as well as the study of the processes of destruction of the materials being worked, made it possible to establish the feasibility of creating a single parametric series of hand-held pneumatic hammers regardless of their purpose.

4. It has been established that, of all the indices of the technical characteristics of hammers, the most acceptable as the principal parameter of a unified series of these machines is the impact energy. The adopted range of variation of impact energy from 0.2 to 8.0 kgm quite fully satisfies the needs of the manifold operations performed by hammers, and its division into 12 intervals does not contradict the basic requirements for a series.

References

1. Standard sizes of pneumatic pick hammers for 1961–1965. Central Bureau of Technical Information. Moscow, 1962.

2. Yu. O. Kassatsiner, A. M. Kivman. Standard sizes for hand-held pneumatic drills. TsNIITEIugol, Mining Machines and Automation, 10, 1963.

3. Telescopic and column-mounted pneumatic drills. Draft GOST. State Committee for Standardization of Equipment, Moscow, 1963.

4. Instructions for compiling standard-size series. State Committee for Standardization. 1962.

5. S. A. Rychin. Pneumatic Tools. (Design, Operation, and Repair). Sudpromgiz, 1953.

6. G. I. Sudakovich, D. I. Bernadskii. Hand-Held Pneumatic Tools. Mashgiz, 1954.

7. O. D. Alimov. On the mechanism of rock destruction in rotary-percussive drilling with drill hammers. Izvestiya TPI, vol. 75, 1954.

8. L. I. Baron, G. M. Veselov, Yu. G. Koshchin. Experimental Studies of Rock Destruction Processes by Impact. Publishing House of the Academy of Sciences of the USSR, 1962.

9. O. D. Alimov. Interrelation of feed force with the principal parameters of a drill hammer. Izvestiya TPI, vol. 108, Metallurgizdat, 1959.

10. E. Ts. Andreeva-Galanina, E. A. Drogichina, V. G. Artamonova. Vibration Disease. Medgiz, 1961.

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

12. O. D. Alimov, V. F. Gorbunov, V. I. Baburov. Losses that can be avoided. Ekonomicheskaya gazeta, No. 37 (110), September 14, 1963.