V. F. GORBUNOV, V. I. BABUROV

ON THE UNIFICATION OF DESIGNS AND STREAMLINING OF PRODUCTION OF PNEUMATIC CHIPPING AND RIVETING HAMMERS

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

In metallurgical and machine-building production, the processing of castings, blanks, and other metal products is carried out by various methods and means, among which the use of pneumatic chipping hammers occupies a large place [3]. They are used to remove burnt-on sand, scale, sand, and molding earth from the surface of castings; with them, blowholes and cracks in castings are cut out, burrs are removed, weld seams are cleaned, etc. As a rule, all work on processing metal products is carried out in cleaning or trimming sections (shops).

In large trimming shops, as many as 150–200 hammers are sometimes operated simultaneously.

In 1962, Tomsk Polytechnic Institute, together with the Tomsk Electromechanical Plant named after Vakhrushev (TEZ), conducted a survey of the operating conditions of more than 5,000 pneumatic hammers at 26 enterprises in the country [1]. At these enterprises, 3,765 hammers were used for trimming, and the remaining hammers for riveting operations. In the course of the survey it became clear that, for trimming metal products and riveting rivets, a large number of different designs of hammers of both serial and non-serial manufacture are used [1].

Serial production of hammers in the USSR is carried out by the TEZ plant and the Izhevsk Mechanical Plant in a quantity of approximately 70,000–80,000 units per year. However, this quantity is clearly insufficient to satisfy the demands of production (Table 1).

As can be seen from Table 1, through serial production of hammers the needs of enterprises are satisfied only by 22–72%. In this connection, many enterprises are forced to organize the manufacture of hammers on their own. The designs adopted as the basis for the hammers they produce are machines developed by their own efforts, hammer designs of foreign firms (the American “Ingersoll-Rand,” the German “Niles”), or serially manufactured designs.

In large quantities (10–12 thousand units per year), chipping and chasing hammers of the RM-75, RM-55, and RM-35 types are manufactured by the Nikolaev Plant named after Nosenko. The Kharkov plants Elektrotyazhmash and Transport Machine Building named after Malyshev, the Moscow Stankolit Plant, the Ural Railcar-Building Plant, and the Chelyabinsk Tractor Plant produce hammers with barrels of identical design, but with different designs of the remaining assemblies. The Dnepropetrovsk Metal Structures Plant

named after Babushkin manufactures hand-held pneumatic hammers of three standard sizes for riveting, chipping, and caulking, but in small quantities—20–40 units per year. The Novo-Kramatorsk Machine-Building Plant, the Dnepropetrovsk Plant of Metallurgical Equipment, and the Elektrostal Heavy Engineering Plant produce type KE chipping hammers of domestic design, sometimes substantially modifying it.

Table 1

Degree to which the requests of certain sovnarkhozes and enterprises for pneumatic hammers were met

The main changes and alterations are, as a rule, made in the designs of starting and stop devices and in the designs of handles. At present, four methods are used for locking handles on hammer barrels, six different end chipping bushings, and seven types of spool-valve devices.

Among all the listed designs of assemblies and parts, naturally, there are successful ones that are simple in arrangement and manufacturable, and, conversely, complicated designs that are clearly obsolete. Thus, for example, the hammer handles of the designs of the Uralvagonzavod and the Chelyabinsk Tractor Plant (ChTZ) are very heavy, angular, and inconvenient in use. At the Dnepropetrovsk Plant of Metal Structures named after Babushkin, hammers are in operation in which no retention of the striker in the barrel cavity is provided. The striker can be freely inserted into the cylinder through the front part of the hammer, that is, through the guide bushing. Such hammers are very dangerous in operation, and their use contradicts safety regulations [4].

Overall, about 250 thousand pneumatic chipping-and-riveting hammers are in operation throughout the country. Approximately the same number of hammers must be manufactured annually by specialized plants (shops), since the average service life of a hammer, taking repairs into account, is 1 year; in fact, it ranges from 2–3 months to 1.5–2 years. The disorderly manufacture of hammers gives rise to a number of undesirable, negative phenomena, among which the following must be noted.

To organize local manufacture of hammers, production floor space, machine tools, and skilled labor are required. And this has a very negative effect on the production of the main types of output of the given enterprise.

Serial production is considerably more economical than local manufacture of hammers. Thus, the cost of an average standard size of chipping hammer—

A hammer at such an industrial enterprise as ChTZ costs, including overhead, approximately 30–45 rubles. At the Kharkov plant “Elektrotyazhmash” it is 28 rubles. The cost of manufacturing the same hammer at the small but specialized TEZ plant is 8–12 rubles, that is, 3–5 times cheaper.

Streamlining the production of chipping and riveting hammers will save the state (according to very incomplete data) no less than 2.5 million rubles per year.

Because of the diversity of hammer designs used, interchangeability of their individual parts and assemblies is impossible. The absence of unification greatly complicates the organization of hammer repair and shortens their service life. For example, at the Chelyabinsk Tractor Plant, 6 standard sizes of pneumatic hammers of both in-house and series production are used, with different designs of individual assemblies. The average service life of one hammer at this plant is 3–6 months, while at the neighboring Ural Heavy Machine-Building Plant, where mainly one standard size of hammer, KE-16, is used, it is 9–12 months.

The absence of unification of the designs of the chipping hammers in operation creates additional difficulties in supplying enterprises with spare parts, as well as in organizing warranty repair of hammers.

Every enterprise, using one design or another, asserts that it is the best and fully satisfies its needs. Such subjective assessments have an adverse effect on the spread in production of more advanced chipping hammers. Often hammers supplied to enterprises in a centralized manner are not used. The Kharkov plant “Elektrotyazhmash,” receiving type R hammers from the Izhevsk Mechanical Plant and type MR hammers from the TEZ plant, does not use them. Chipping is carried out with less advanced hammers of its own production, which have approximately the same parameters.

In the course of our survey it was established that engineers at individual enterprises do not know the rational field of application of the various standard sizes of hammers, and such information is usually not published in the periodical press.

The configuration, dimensions, and weight of the products being worked are important factors on which the productivity of chipping with pneumatic hammers depends.

When removing defects from small and shaped castings, the chipper must frequently turn himself or change the position of the workpiece being processed in order to keep the angle of inclination of the hammer to the workpiece unchanged and to be able to chip the entire surface of the object. In addition, because of the curvilinear surface of the items being processed, the cutting edge of the working tool must be turned about the axis of the hammer. The worker performs this turning by rotating the hammer, if it has a chipping bushing with flats on the inner surface, or by directly rotating the chisel while holding it with his left hand. The latter possibility is provided only if the hammer has a bushing without flats. Thus, the use of heavy hammers and flatted bushings for chipping small shaped castings is inadvisable and has a negative effect on the labor productivity of chippers, since, being constantly in motion, the worker quickly becomes fatigued.

The treatment and cleaning of large castings and of rolling-mill products is less fatiguing. The items being processed are characterized by

relatively even (flat) surfaces and, as a rule, by larger defects. In this case, the use of hammers with faceted bushings helps to increase chipping productivity. And the greater the impact energy of the hammer (up to a rational limit), the higher the productivity. The considerations set forth above are often not taken into account either by consumer plants or by hammer-manufacturing plants.

On the basis of an analysis of operating conditions and areas of application of chipping hammers, we recommend that, for eliminating defects in large castings and other metal products having even, non-shaped surfaces, heavier hammers (weighing 6–8 kg) with an impact energy of 2–3 kgm be used. This conclusion is also confirmed by comparative tests of hammers of various standard sizes, conducted by the Elektro-staltyazhmash plant (TEZ funds).

For machining small, light, and also shaped large castings, the most productive hammers should be considered to be those with an impact energy of 0.9–1.8 kgm and a weight of 3–6 kg (Table 2).

Table 2 gives recommendations for selecting a rational design of the chisel bushing depending on the type of work performed. For riveting, in our opinion, cylindrical end bushings should be used, and for cleaning weld seams—faceted (prismatic) bushings.

In hammers supplied to plants in a centralized manner, the chisel guide bushings, because of the insufficient dimensions of the chisel shanks for these bushings and because their design does not correspond to operating conditions, are as a rule replaced. The total losses of funds in replacing bushings at only the enterprises surveyed amount to about 10–11 thousand rubles. In this connection, manufacturing plants must revise the designs of the bushings of chipping hammers and increase their internal diameter by 3–5 mm.

The need to improve the quality of manufacture of pneumatic hammers and to keep them in serviceable condition throughout their entire service life is dictated by the high cost of the energy consumed. It is known that even slight wear of the hammer barrel, the striker piston, and the chisel shank leads to increased consumption of compressed air [6–7]. In this connection, monitoring the wear of hammers and their energy parameters assumes particular importance. During an investigation of the operating conditions of pneumatic chipping hammers, it was found that plants often use hammers with inadmissible clearances between the piston and the cylinder, and also between the chisel shank and the guide bushing. If it is assumed that only one tenth of the hammers are operated with clearances twice as large as the initial ones, then the monetary losses from increased air consumption amount to about 0.7 million rubles (with the cost of 1 cubic meter of air being 0.2 kopecks). In addition, increased wear of hammer parts inevitably entails a sharp reduction in the worker’s labor productivity, as well as an increase in the vibrational effect of the hammers on his organism.

The absence of strict control over the vibration of chipping hammers and their handicraft manufacture lead to the fact that hammers with vibration characteristics impermissible under sanitary standards are often used [5]. In this connection, the incidence of vibration disease among chipping workers increases. At the Chelyabinsk Tractor Plant, similar illnesses were noted in the steel-casting shop, where locally manufactured hammers are used.

Enterprises that manufacture hammers on their own, as

as a rule, do not have control-and-measuring equipment with which one could carry out high-quality testing and adjustment of hammers. Thus, for example, of 11 enterprises, only three have installations for determining the impact energy of hammers.

Table 2

Recommended areas of application of hand-held pneumatic hammers

The production of chipping-and-riveting hammers should be concentrated at several specialized plants, equipping them with high-performance equipment for mass manufacture. These same plants will be able to supply spare parts as well. The expenses associated with organizing centralized production of chipping-and-riveting hammers ...

—will be recouped by the reduced cost of operation and by the savings from eliminating local manufacture.

The chipping hammers currently produced in series have a maximum impact energy of 1.6 kgm and an impact frequency of 1600 blows/min. Hammers with such parameters clearly do not satisfy production workers. In this connection it is necessary to reconsider the parameters of chipping hammers. At present, in the dressing of castings and forgings, riveting hammers of the KE type have become most widespread; they have an impact energy of up to 2.5–3 kgm and show higher productivity, especially in dressing large castings. In the overall volume of consumption they account for 66%. The field of application of chipping hammers has changed somewhat. This is explained by the fact that the parameters of modern designs of chipping hammers are based on views that took shape among researchers and production workers at a time when pneumatic hammers were the only machines for performing riveting, dressing, chasing, and other operations. Now other means have appeared for mechanizing the cleaning of castings (hydraulic washing, sand- and shot-blasting apparatus, cleaning drums, etc.), which have considerably reduced the field of application of chipping hammers, especially in cleaning small castings. The machining of large castings, however, still does not lend itself to full mechanization.

On the basis of the foregoing, the tasks of research and production organizations in the field of improving the design and production of pneumatic chipping-riveting hammers may be formulated as follows.

1. In the near future it is necessary to solve the problem of unifying the designs and streamlining the production of hand-held pneumatic chipping-riveting hammers, assigning their manufacture in sufficient quantities to several specialized plants.

2. Develop a series of appropriate sizes and parameters of chipping-riveting hammers that ensure highly productive performance of all operations for cleaning castings, eliminating defects in castings and rolled stock, riveting, chasing, etc.

3. Develop a calculation method, acceptable to designers, for the principal parameters and dimensions of chipping-riveting hammers.

4. Continue the development of methods and means for damping hammer vibration; develop methods for calculating vibration-damping devices.

5. Carry out work to increase the efficiency of pneumatic hammers in order to improve the economic effectiveness of their application.

REFERENCES

1. V. F. Gorbunov, V. I. Baburov. On the parameters of hand-held chipping-riveting hammers and their standard sizes. Izvestiya TPI, vol. 123, Publishing House of Tomsk State University, 1963.

2. E. I. Andreeva-Galanina, V. G. Artamonova et al. Vibration Disease. Medgiz, 1961.

3. P. V. Vasilevskii, A. E. Demakov et al. Foundryman’s Handbook. Mashgiz, 1962.

4. Safety rules for work in foundry shops for steel, cast-iron, and bronze casting. Moscow House of Technology, 1962.

5. Collection of the Most Important Official Materials on Questions of Occupational Hygiene and Industrial Sanitation. Issue II, Medgiz, 1962.

6. G. I. Sidorenkov. Theoretical and experimental study of the operation of valve pneumatic hammers and a method for their calculation. Candidate dissertation, Leningrad, 1962.

7. P. S. Khutornoi. Influence of the magnitude of clearances between the main parts of rock drills on their operation. Gornyi zhurnal, No. 5, 1961.