PNEUMATIC HAMMER WITH VIBRATION-DAMPING DEVICES BSZ-135V

V. I. BABUROV, A. I. PASHNIN

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

The BSZ-135V pneumatic chipping hammer with vibration damping (Fig. 1) was created on the basis of the BSZ-135 hammer of the Bezhetsk Steel Foundry [1]. In its principle of design, the BSZ-135V hammer is similar to the MRV-16 and MRV-12 hammers previously developed at TPI [3] and consists of two assemblies moving relative to one another in the axial direction.

The first assembly of the hammer, comprising handle 2 with the starting device, false barrel 9, and rubber coupling 13, is separated from the second, which is the impact assembly of the machine, by means of conical spring 18.

Handle 2 of the hammer has a conventional starting device with a ball shutoff mechanism. From the handle, compressed air enters the hammer cavities through flexible hose 4. The hose is connected to the barrel and to the handle by means of fittings 7 and clamps 5.

In the body of the handle there is a longitudinal cutout for accommodating retainer 6 of intermediate link 15. Fitting 7 with flexible hose 4 is screwed into the retainer.

False barrel 9 is screwed onto the cylindrical part of the handle; in the larger base of the false barrel there is also a longitudinal cutout for retainer 6. Thus, the retainer prevents self-unscrewing of the false barrel and handle during hammer operation. Rubber vibration-damping coupling 13 is fastened to the lower part of the false barrel; its inside diameter corresponds to the outside diameter of working tool 14. Longitudinal cutouts are made on the outer surface of the coupling to facilitate turning the tool by hand. With a chisel diameter of 22 mm, the outside diameter of the rubber coupling is 36 mm. Thus, convenient control of the working tool by the chipper’s gloved hand is ensured.

The working tool can be freely inserted into the hammer cavity through coupling 13. This is one of the principal advantages of the proposed coupling design.

The impact assembly of the hammer consists of intermediate link 15, the air-distribution device, barrel 11, striker 10, and bushing 12.

The intermediate link is screwed onto the barrel and fixed by stopper 8. It is intended to create a pre-valve air--

chamber and fastening on the barrel of the distribution device, consisting of an annular valve 16 and cover 17. The hammer barrel, in order to reduce weight and improve the exhaust conditions of the spent air, is profiled on two sides. In the lower part of the barrel there is an annular projection along which the false barrel moves.

Fig. 1. Design of the BSZ-135V pneumatic hammer. 1 — trigger; 2 — handle; 3 — ball; 4 — hose; 5 — clamp; 6 — retainer; 7 — nipple; 8 — stop; 9 — false barrel; 10 — striker; 11 — barrel; 12 — bushing; 13 — rubber coupling; 14 — working tool; 15 — intermediate link; 16 — valve; 17 — valve cover; 18 — conical spring

In the nonworking position, the impact unit, under the action of the conical spring, rests on the rubber coupling. When the operator presses on the handle, spring 18 is compressed, the false barrel moves downward and moves away from the coupling. The magnitude of the displacement under the working pressing force is

of 10–15 kg is 7–10 mm. Approximately in this position the barrel oscillations occur during operation of the hammer.

The weight of the hammer is 6.2 kg, including the handle with the starting device, false barrel, and coupling—2.9 kg, and the impact unit—3.1 kg.

The results of tests of the hammer showed that the use of an elastic handle as a means of vibration isolation makes it possible to reduce the vibration displacement of the handle, at a pressing force of 18–20 kg, by a factor of 5–6. At the same time, the vibration acceleration decreases by a factor of 4–5 (see the table). It should be noted that reducing the stiffness of the conical spring will make it possible to reduce the vibration displacement of the handle still further [2]. Structurally this is entirely feasible.

Table

Results of tests of the BSZ-135 and BSZ-135V hammers

The vibration of the worker’s left hand is reduced especially noticeably. Thus, for example, the vibration acceleration in the transverse direction, at a pressing force on the handle of 20 kg (taking into account the weight of the hammer), is 130 g on the chisel, 10 g on the rubber coupling, and 0.6 g on the back side of the hand. Thus, the inertial force of transverse vibration is reduced by a factor of 13.

Conclusions

The design of the BSZ-135V hammer makes it possible to substantially reduce the vibration acting on the worker’s hand. The proposed design of the vibration-protective coupling reduces the inertial force of transverse vibration by a factor of 13.

The use of the BSZ-135V hammer in trimming operations will greatly improve workers’ labor conditions.

REFERENCES

1. V. I. Baburov, A. I. Pashnin, A. N. Shchipunov. Results of tests of the BSZ-135 chipping hammer. Article in the present collection.

2. V. I. Baburov, A. I. Pashnin, L. N. Fedorov, V. O. Vekhter. Influence of the stiffness of shock absorbers on the vibration characteristics of the handle of a pneumatic hammer. Article in the present collection.

3. V. F. Gorbunov, Yu. A. Oparin, V. I. Baburov. Design of a hand pneumatic hammer with vibration-damping devices. Izvestiya TPI, vol. 139, 1965.