GB2027493A - Pneumatic hammer without separate distributing valve - Google Patents

Abstract

A pneumatic hammer comprises an external cylinder 30 defining an internal cylindrical cavity in which a movable element 40 is mounted for axial sliding, this element being of a lesser axial length than said cylindrical cavity so as to define alternately and/or simultaneously a lower chamber 11 and an upper chamber 10 within the said cylindrical cavity, and means for connecting the movable element to a tool to be actuated by the element, wherein the said movable element 40 has two axially-extending passages, 6, 4, the first of which, 6, communicates with the upper face of the movable element and the second, 4, with the lower face of the movable element, the first passage communicating through a first branch passage 5 of the element with the external surface of the movable element at the lower half of the element and the second passage communicating through second and third branch passages 8, 3 of the element with the external surface of the movable element respectively at the upper half and at about the mid-section of the surface, and wherein the external cylinder 30 has two passages 1, 9 which open on to the internal cylindrical surface thereof and are for communication respectively with a pressurised fluid source and with the atmosphere; the axial distance between the two internal openings of the external cylinder being substantially equal to the axial distance between the first and the second branch passages of the movable element. <IMAGE>

Description

SPECIFICATION Pneumatic hammers The present invention relates to pneumatic hammers.

More specifically, the invention provides a pneumatic hammer in which the components for distributing the compressed fluid which actuates the hammer are, on the one hand, located partially in the body of the piston itself and, on the other hand, in the body of the cylinder in which the hammer moves. This provides increased structural and operational simplicity ensuring lower production costs, and also reduces the risk of breakdown, as the mutually movable parts are reduced to a minimum.

The characteristic features of the hammers of the invention are defined in the claims; the purpose and advantages of these features are explained in the following description relating to embodiments given by way of non-limiting example with particular reference to the attached drawings, in which: Figure 1 shows a vertical section of a first embodiment of a pneumatic hammer of the invention, in the position of which the piston itself, i.e. the movable component which transmits movement to the tool, is in its lowest position; Figure 2 refers to the same structural variant as Fig. 1, but in this figure the movable piston is in its intermediate position, during its upward movement; Figure 3 refers to the same variant as the previous figures, but shows the piston in its highest position; Figure 4 is the same as Fig. 2, but refers to the downward movement of the piston;; Figures 5 and 6 relate to two other structural variants and show the piston in the same relative position as illustrated in Fig. 2.

Referring to Figs. 1 to 4, a pneumatic hammer of the invention is constituted by three elements alone: an external cylinder 30, an upper screw-threaded cap 20 which forms a single body with the cylinder 30 during operation, and a sliding element 40 as piston.

The axial length of the movable element 40 is less than that of the corresponding cylindrical cavity provided within the cylinder 30 by means of which the movable element 40, in accordance with its relative position, defines an upper chamber 10, see Fig. 1, and/or a lower chamber 11, see Fig. 2, in the same way as the piston of a double-acting cylinder.

The upper face of the movable element 40 is provided with a first axial passage 6 which communicates at its lower end with the lateral surface of the said movable element 40, through a passage 5.

The movable element 40 is in addition provided with a second axial passage 4 which communicates on the one hand with the lower face of the movable element 40 and, on the other hand, by means of a second passage 8, with the lateral surface of the movable element, corresponding to the upper lateral area of the movable element. Furthermore, the axial passage 4 communicates with the lateral surface of the movable element 40 through a third passage 3, which is disposed in a substantially intermediate position with respect to the two previously mentioned passages 8 and 5. The upper area of the cylinder 30, chamber 10, communicates with the atmosphere through a first passage 9.A circumferential groove 2 is provided at approximately one third of the height of the cylindrical cavity in which the movable element 40 slides axially, this groove communicating with a compressed air source through an axial conduit 1 provided in the wall of the cylinder 30.

At the height of the passage 9, the internal wall of the cylinder 30 is additionally provided with a circumferential groove 7.

The axial distance between the passages 5 and 8 of the movable element 40 is substantially equal to the axial distance between the circumferential grooves 2 and 7, and the arrangement is such that when the upper chamber 10 is in communication with the pressure source through passages 2, 5 and 6, see Fig. 3, the lower chamber 11 simultaneously communicates with the atmosphere through passages 9, 8, 7 and 4; the movable element 40 is then pushed downwardly by the compressed air.

The axial position of the passage 3 is, in contrast, defined in such a way that when the movable element 40 is in its lowest position (see Fig. 1), this passage is at the height of the circumferential groove 2 of the cylinder 30 so as to be able to supply pressurized fluid to the chamber 11 which has its smallest volume in this position and which is shown equal to zero in Fig. 1 for facility of illustration.

The axial width of the grooves 2 and 7 and the width measured axially of the passages 5, 3 and 8 is however such that when, during upward movement of the piston 40, see Fig.

2, the communication between the passage 3 and the pressurised groove 2 is interrupted, communication between the passage 5 and the pressurised groove 2 begins to be initiated (see Fig. 2).

Simultaneously with communication being established between the passage 5 and the groove 2, communication occurs between the passage 8 and the groove 7, which is always in communication with atmosphere through the conduit or passage 9.

A like situation arises in the downward movement shown in Fig. 4. In this operation the cavity 11 and the cavity 10 are subject to variations in volume only when they communicate either with the pressurised fluid source or with atmosphere.

This moreover avoids losses of load due to fluid compressions in variable-volume chambers which do not communicate externally.

The base of the cylinder 30 is provided with a passage for the holder of the movable element 40, which serves to act on a tool which may be actuated by the pneumatic hammer of the invention.

Operation is as follows: after its working movement, the hammer is as shown in Fig. 1; the chamber 11 is reduced to a minimum volume and communicates with the source of pressurised air through the conduits 4, 3, 2 and 1.

At the same time the upper chamber 10 communicates with the atmosphere through the passage 9. As a resuit of the pressure difference being exerted on the two opposite end faces of the piston 40, it begins to move upwardly to the position shown in Fig. 2 in which, on the one hand, the connection between the lower chamber Ii and the pressurised fluid source begins to be interrupted and, on the other hand, the communication begins to be interrupted between the upper chamber 10 with the passage 9 discharging to atmosphere.

The movable element however continues to move upwardly as a result of the kinetic energy which it has acquired and and a result of the pressure difference which is still acting on its two end faces.

However, after an infinitesimal upward displacement of the movable element, the passage 8 communicates with the groove 7 by means of which the lower chamber 11 is brought to atmospheric pressure through the conduits 4, 8, 7 and 9.

At the same time the passage 5 communicates with the groove 2 and the upper chamber 10 is consequently pressurised through the conduits 1,2, 5 and 6.

Once the inertia force of the movable element 40 has been overcome, it is urged by the pressure acting in the upper chamber 10 to move downwardly to initiate a new stroke.

It is thus evident that the opening or the closing of the passages which supply compressed air to the lower chamber 11 or to the upper chamber 10 is carried out by the same movement of the movable element 40 without requiring additional movable elements actuated by expensive valves.

The pneumatic hammer constructed in accordance with the invention is therefore a great simplification.

It is to be noted that the grooves 2 and 7 may also be omitted; however this woutd require the provision of circumferential positioning means between the movable element and the cylindrical chamber; it would in fact be necessary to prevent any relative rotation between the movable element and the cylindrical chamber, which is avoided in the embodiment illustrated in Figs. 1 to 4.

The embodiment illustrated in Fig. 5 differs from that illustrated in Figs. 1 to 4 in that each of the passages 103, 105, 108 (cf passages 3, 5, 8) is connected to a corresponding circumferential groove of the movable element facilitating inlet and outlet of the compressed air from and to the chambers 10 and 11.

In the embodiment illustrated in Fig. 6 the passage 208 is connected to a circumferential groove of the movable element 40 enabling the circumferential groove 7 shown in the embodiment of Figs. 1-4 to be dispensed with.

Although the present invention has been illustrated by three embodiments by way of example, modifications and variants may be made.

Claims (6)

1. A pneumatic hammer comprising an external cylinder defining an internal cylindrical cavity in which a movable element is mounted for axial sliding, this element being of a lesser axial length than the said cylindrical cavity so as to define alternately and/or simultaneously a lower chamber and an upper chamber within the said cylindrical cavity, and means for connecting the movable element to a tool to be actuated by the element, wherein the said movable element has two axiallyextending passages, the first of which communicates with the upper face of the movable element and the second with the lower face of the movable element, the first passage communicating through a first branch passage of the element with the external surface of the movable element at the lower half of the element and the second passage communicating through second and third branch passages of the element with the external surface of the movable element respectively at the upper half and at about the mid-section of the surface, and wherein the external cylinder has two passages which open on to the internal cylindrical surface thereof and are for communication respectively with a pressurised fluid source and with the atmosphere; the axial distance between the two internal openings of the external cylinder being substantially equal to the axial distance between the first and the third branch passages of the movable element.

2. A pneumatic hammer as claimed in Claim 1, wherein the position and the axial dimensions of the various passages are such that when the second passage of the movable element is no longer communicating with the first passage of the cylindrical cavity, the first and the third branch passages of the movable element do not yet communicate respectively with the first passage and the second passage of the external cylinder.

3. A pneumatic hammer as claimed in Claim 1 or 2, wherein the internal wall of the external cylinder has a circumferential groove at the opening of its first passage.

4. A pneumatic hammer as claimed in Claim 1, 2 or 3, wherein the internal wall of the external cylinder has a circumferential groove at the opening of its second passage.

5. A pneumatic hammer as claimed in any of the preceding claims, wherein the movable element has respective circumferential grooves on its external surface at the points of communication of the three branch passages with the external surface.

6. A pneumatic hammer substantially as described herein and as illustrated in the accompanying drawings.