EP1076754B1

EP1076754B1 - Pneumatic submersible boring tool

Info

Publication number: EP1076754B1
Application number: EP99917743A
Authority: EP
Inventors: Vladimir Koudelka; Jan Stros
Original assignee: PERMON SRO
Current assignee: PERMON SRO
Priority date: 1998-05-04
Filing date: 1999-05-04
Publication date: 2003-02-05
Anticipated expiration: 2019-05-04
Also published as: WO1999057411A1; CZ136198A3; AU3593999A; EP1076754A1; ATE232264T1; DE69905245D1; DE69905245T2

Abstract

A pneumatic submersible boring tool which is comprised of a front cover (4) with a working tool and with its arrestment, a rear input body (8) with a built in water valve and a working cylinder (1), wherein a striking piston (2) is guided that is provided with axial and side filling and exhaust ducts, whereby, said piston extends into a cavity (14) of said input body (8) by its rear extended part (21) with a filling recess (27) on its surface, which consists in that the front working compartment (17) of the working cylinder (1) is interconnected by a filling groove (16), provided on the surface of said striking piston (2), by a side filling duct (18) connected with it that passes through the wall of said striking piston (2), and by an axial filling duct (19) arranged in the rear extended part (21) of said striking piston (2), connected on said side filling duct (18), with a cavity (14) of said input body (8) whereby a closing pin (15) is built in axially in said cavity (14), and whereby the front face of said pin (15) is placed within the axial longitudinal section that is delimited by the front and the rear dead centres of said rear face (20) of said rear extended part (21) of said striking piston (2) and the external diameter of said closing pin (15) is smaller than the internal diameter of said axial filling duct (19). Pneumatic tool preferably consists of an axial exhaust duct (24) provided in the front part of said striking piston (2), wherein mouths said side exhaust duct (23) that passes through the wall of said striking piston (2) and is a continuation of said exhaust groove (22) formed on the surface of said striking piston (2) and also said side release duct (34) that passes through the wall of said striking piston (2) and is a continuation of the filling groove (16) provided on the surface of said striking piston (2) and interconnected with said bottom working compartment (17) of said working cylinder (1), whereby in said axial exhaust duct (24) an exhaust inertial slide valve (32) of pipe-like shape is placed so that it can slide.

Description

Field of the Invention

The present invention relates to a pneumatic striking tool, preferably to a pneumatic submersible boring hammer.

Background of the Invention

Submersible boring hammers cannot increase their output characteristics by increasing their lateral dimensions, e.g. by increasing the working cylinder diameter, as the dimensions are delimited by the bore diameter and by the annular space necessary to exist between the bore wall and the external diameter of the hammer, whereby, this space is used to raise borings out of the bore by exhaust air.

But it is known to increase the installed output of submersible hammers not only by increasing the air pressure used, but also by a system of compressed air distribution and by the following arrangement of the filling and the exhaust ducts and recesses that supply compressed air into the working compartments of the cylinder and take away exhaust air.

The known and commonly used plate, ring, slide and flap distribution systems usually operate on the principle of an air pressure drop in the cylinder compartment which is being filled after opening of the exhaust duct. From the point of view of the installed output and efficiency it is disadvantageous that the moment of closing one working cylinder compartment at the same time is the moment of opening the filling of the opposite working compartment. This makes impossible to use a controlled air expansion in the cylinder compartment that is being filled without simultaneous backpressure growth in the opposite compartment. Moreover, the so arranged distribution systems are sensitive to the used lubricant, moisture and impurities in the supplied compressed air. They are intricate and, therefore, also cost intensive in production and they incline to be defective and unreliable in service.

A better solution is a system without any independent distribution system, where the compressed air distribution to the working compartments of the cylinder is controlled by the striking piston directly in relationship to its momentary position.

For example, the specification EP 40026 discloses a valveless boring tool having a cylinder and a piston that form the upper and the bottom working compartments together with the cylinder. The piston comprises an axially arranged filling opening, a separate axially arranged exhaust opening and filling and exhaust ducts formed at least partially in the wall of the working cylinder. Subject to the piston position in the cylinder in co-operation with the input pipe they provide for compressed air distribution into the working compartments and for output of exhausted air from the hammer. The input pipe axially passing across the upper working compartment can be fixed in an input body or it can be carried by a piston.

Specification US 5,318,140 discloses a submersible hammer that is comprised of a working cylinder and a piston mounted so that it can move in a cylinder. The input body of the hammer is provided with an extension that comprises a valve part, whereby, the valve part co-operates with the central opening of the piston. A lightening is made in the central opening of the piston that makes possible to interconnect the compartments above and under the valve part in certain piston position.

Document US 4 591 004 A describes a pneumatic percussion machine. However, US 4 591 004 A does not hint at a means of a filling groove, provided on the surface of the striking piston, in order to interconnect the front working compartment of the working cylinder with the rear cavity of the input body.

Generally, the known solutions of this kind differ in detailed design of the filling and the exhaust ducts and the recesses in the piston, the cylinder and in other connected parts of the hammer and the boring bit. Usually, they make possible in one or in both working compartments of the cylinder to close the intensive filling of the respective working cylinder compartment and the subsequent air expansion in it before opening the exhaust independently of circumstances in the opposite cylinder compartment. From the point of view of the output installed and the efficiency, it remains as a disadvantage that the closure of the filling of the given working cylinder compartment in the given piston stroke position means opening of the filling of the same working compartment and, therefore, it brings about rising of back pressure in the same position of the opposite stroke. In the reverse stroke such relations are desirable, as the piston has to be halted in the back dead centre without an impact on the face of the rear working compartment. This can be utilised advantageously by intentionally making a compression compartment that is closed by piston in the rear dead centre, function of which is to act as an accumulator that makes possible to utilise a part of the energy passed on the piston during the reverse stroke for its acceleration in the initial phase of the striking stroke. However, in case of the striking stroke the backpressure produced by premature opening of the filling of the front cylinder working compartment causes undesirable piston breaking. Another disadvantage of this system is that for accelerating the piston it is not possible to utilise the whole length of the striking stroke because in its last phase before a blow, the exhaust duct is opened, what brings about a rapid drop of air pressure in the rear working compartment of the cylinder. Together with the mentioned backpressure rise in the front working compartment in this phase of the piston movement the piston starts to be significantly braked with a consequent decrease in its striking speed and impact energy, i.e. a decrease of the installed output of the tool and of its total effectivity.

A disadvantage of the known designs is also the interconnection between the front working compartment and the cavity in the input body that is always at least partially formed in the wall of the working cylinder. Thereby, the cylinder is made thinner in the front part which is the most stressed one by abrasion caused by the bored off rock exhausted.

Summary of the Invention

The above mentioned disadvantages are eliminated by the embodiment of a pneumatic striking tool, in this,case of a pneumatic submersible hammer according to the present invention, which is comprised of a front cover with a working tool and with its arrestment, a rear input body with a built in water valve and a working cylinder, wherein a striking piston is guided that is provided with axial and side filling and exhaust ducts, whereby, said piston extends into a cavity of said input body by its rear extended part with a filling recess on its surface.

According to the invention, there is provided a pneumatic submersible boring tool as set forth in claim 1.

According to one preferred embodiment of the present invention said closing pin is formed by a front part of a water valve body.

According to another preferred embodiment, in an axial exhaust duct, made in the front part of said striking piston, wherein apart from said side exhaust duct passing through said wall of said striking piston, also said side release duct is mouthed, which passes through said striking piston wall and which follows in said filling groove made on the surface of said striking piston and which is connected with said cylinder bottom working compartment, an exhaust inertial slide valve of pipe-like shape is placed so that it can slide and in said axial filling duct of said striking piston said filling inertial slide valve of pipe-like shape is placed so that it can slide.

It is also advantageous, when on the rear extended part of said striking piston is between said filling recess and said adjacent rear working face of said striking piston a cylindrical part is made which in said rear cylinder working compartment defines length of the compression compartment that is delimited by said input body front face, said adjacent internal diameter of said working cylinder, said striking piston rear working face and by external surface of said cylindrical part of said striking piston rear extended part.

Another advantageous embodiment of the present invention is when said rear extended part of said striking piston is formed as a separate part mounted in the rear part of said striking piston and this separate part is made of a plastic.

By making a pneumatic striking tool according to this invention it is possible to fill the front and the rear cylinder working compartment during the selected sections of the striking and the reversing stroke at full input air pressure directly from the input body cavity, and each of both working cylinder compartments independently of each other, using short and substantially straight and sufficiently dimensioned sections without losses that would otherwise be caused by cross-sectional and directional changes in the compressed air flow route. Also independently of each other, it is possible, from the point of view of tool effectivity, to use in both cylinder working compartments the desired compressed air expansion in an interval between the closing of filling and the opening of exhaust. The full piston working stroke from the rear dead centre up to the blow moment is utilised during the striking stroke to accelerate the piston as a consequence of the exhaust and filling inertial valve and release duct activities, and this without the counter-pressure effect in the cylinder front working compartment, which would otherwise be formed by opening the filling of the front working compartment and by compression caused in it. The so, according to the invention, controlled cycle of filling and exhausting the cylinder working compartments, combined with reverse stroke energy accumulation in the compression compartment of the rear dead centre increases blow rate of the striking piston combined with a growth in its impact velocity and consequently also of its impact energy, what indicates a growth in installed output of the striking tool and in its effectiveness. Creation of a rear extended part of said striking piston by using a separate part mounted in the rear part of said striking piston and the possibility to make this separate part from plastic is practical considering the impact fatigue stress of said piston and inertial forces acting on the rear extended part of said striking piston. This embodiment simplifies production of said tool and increases its operational safety. For design and production simplicity it is preferable if the closing pin controlling, in co-operation with the mouth of said axial filling duct, opening and closing of filling the cylinder front working compartment is formed by the front extended part of the water valve body.

Industrial Use

Design according to the present invention can find use in case of all input air pressures that come into consideration. The design is compact, non-demanding in production and consequently also in price. The design is simple and consequently insensitive to operational conditions, staff and maintenance.

Brief Description of the Drawings

The attached drawing shows an example of an embodiment of a pneumatic striking tool, in this case of a submersible boring hammer, according to this invention, where Fig. 1 shows a section along its longitudinal axis and Fig. 2 shows a partial section through an alternative embodiment of the rear extended part of a striking piston and through the adjacent part of an immersible hammer.

Detailed Description of the Invention

Fig.1 shows a striking piston 2 deposited so that it can move in a working cylinder 1. A front cover 4 with an arresting ring 5, and a boring bit 6 with an exhaust pipe 38 fixed in it, are fastened by means of a front thread 3 in the front part of the working cylinder 1. By means of a rear thread 7 an input body 8 is fixed in the rear part of the working cylinder 1. A water valve body 9 with a spring 10 and a cone 11 and a valve seat 12 are placed in the input body 8. The valve body 9 is provided with openings 13 that interconnect the compartment adjacent to the cone 11 with a cavity 14 of the input body 8. The front part of the valve body 9 is extended and forms a closing pin 15. A filling groove 16 is provided on the surface of the front part of the striking piston 2 that interconnects the front working compartment 17 of the working cylinder 1 with a side filling duct 18 that passes through the wall of the striking piston 2 and is a continuation of an axial filling duct 19. This duct 19 passes through a rear face 20 of a rear extended part 21 of the striking piston 2 and mouths into the cavity 14 of the input body 8. The surface of said striking piston 2 is also provided with an exhaust groove 22 that is interconnected by a side exhaust duct 23 that passes through the wall of the striking piston 2, with an axial exhaust duct 24 that passes through a striking face 25 of the striking piston 2 and is a continuation of a drilling 39 of a drilling bit 6. The rear extended part 21 of the striking piston 2 passes through an opening in the front face 26 of the input body 8. A filling recess 27 is provided on the surface of the rear extended part 21, whereby said recess 27 is delimited by two cylindrical surfaces. The front cylindrical part 28 of the rear extended part 21 of the striking piston 2, adjacent to the rear working face 29 of the striking piston 2, determines the length of the compression compartment that is formed during the reverse stroke of the striking piston 2 in the rear working compartment 30 of the working cylinder 1. The internal wall of the cylinder 1 is provided with an exhaust recess 31 that is adjacent to the rear working compartment 30 of the working cylinder 1. In an axial exhaust duct 24 an exhaust inertial slide valve 32 is placed so that it can slide, whereby its front position is delimited by a front stop 33 and the rear one by the bottom of an axial exhaust duct 24. A release duct 34 is also mouthed into an axial exhaust duct 24, whereby said duct 34 passes through the wall of the striking piston 2 and it is interconnected by a filling groove 16 with the front working compartment 17 of the working cylinder 1. A filling inertial slide valve 35 is placed in the axial filling duct 19 so that it can slide, whereby its rear position is delimited by a rear stop 36 and its front one by the bottom of the axial filling duct 19.

Fig. 2 shows an alternative embodiment of the striking piston 2, where its rear extended part 21 is formed by an independent part 37 with a passing axial filling duct 19, a filling recess 27, a rear face 20 and a front cylindrical part 28. The front part of the separate part 37 forms the rear stop 36 of the filling inertial slide valve 35.

A tool according to the present invention operates in the following way:

When compressed air is brought into the striking tool, the cone 11 opens flow of compressed air through the openings 13 of the valve body 9 into the cavity of the input body 8. From there, compressed air is led through the axial filling duct 19, the side filling duct 18 and the filling groove 16 into the front working compartment 17 of the working cylinder 1. The striking piston 2 is accelerated by the force of compressed air in the front working compartment 17 towards the rear dead centre. From the rear working compartment 30 exhaust air from the previous cycle of the piston 2 escapes through the exhaust recess 31, the exhaust groove 22, the side exhaust duct 23, the axial exhaust duct 24, the exhaust pipe 38 and the boring 39 of the bit 6 to the bottom of the bore and thereby to atmosphere. The striking piston 2 carries away with it the exhaust inertial slide valve 32 and the filling inertial slide valve 35, that are leaned against the respective stops as a consequence of action of inertial forces, so that they are held shifted into their front positions, i.e. flows through the side exhaust duct 23 and the side filling duct 18 are open, flow through the release duct 34 is closed. At certain phase of the reversal stroke, the rear working face 29 closes the exhaust recess 31 and thereby also all exhaust from the rear working compartment 30. The striking piston 2 continues in reverse movement and at the moment when the axial filling duct 19 is closed by the closing pin 15, filling of the front working compartment 17 by compressed air is terminated, and in the next phase of the striking piston 2 reverse movement expansion takes place in it. In the next phase of the striking piston 2 reverse movement, the filling recess 27 interconnects the rear working compartment 30 with the cavity 14 of the input body 8 and the rear working compartment 30 starts to be filled with compressed air that, in relation to the pressure circumstances in the front 17 and the rear 30 working cylinder 1 compartments, gradually slows down movement of the striking piston 2. In the next movement phase of the striking piston 2, the striking face 25 opens flow into the exhaust pipe 38, through which the exhaust air from the bottom working compartment 17 escapes to atmosphere through the boring 39 of the bit 6. After closing of the filling recess 27 by the front face 26 of the input body 8, air in the rear working compartment 30 is compressed, what, together with a pressure drop in the front working compartment 17, causes a rapid breaking of the striking piston 2 up to a halt in the rear dead centre. The exhaust 32 and the filling 35 inertial slide valves continue in their movements because of inertia and so they shift themselves into their rear positions delimited by their rear stops. Thereby, closing of the side filling duct 18 and the side exhaust duct 23 and opening of the release duct 34 take place. By compression the striking piston 2 is accelerated forward towards the striking stroke, together with both

inertial slide valves

32 and 35 that are held by inertia in their rear positions. In the next phase of the striking stroke, the filling recess 27 opens entry of compressed air from the cavity 14 of the input body 8 into the rear working compartment 30. Then, the striking piston 2 closes the exhaust from the front working compartment 17 by its striking face 25. Compression that would otherwise rise in the front working compartment 17 is released through the filling grove 16, the release duct 34, the axial exhaust duct 24 and the boring 39 of the bit 6 to atmosphere during the whole remaining part of the striking stroke of the piston 2. The striking piston 2 continues in its striking stroke up to a position when the compressed air input into the rear working place 30 through the filling recess 27 is closed. In the next phase of the forward movement of the striking piston 2 expansion in the rear working compartment 30 takes place and during further movement of the striking piston 2, the closing pin 15 opens input of compressed air into the axial filling duct 19 at certain moment, but air flow into the front working compartment 17 through the side filling duct 18 and the side filling groove 16 is closed by the filling inertial slide valve 35. Before a blow of the piston 2 on the bit 6 the exhaust recess 31 is opened by the rear working face 29 of the striking piston 2, but an exhaust from the rear working compartment 30 through the exhaust groove 22 and the side exhaust duct 23 does not take place, as the side exhaust duct 23 is closed by exhaust inertial slide valve 32. The striking piston 2 is accelerated by expanding air in the rear working compartment 30 up to the moment of a blow, without any back pressure in the front working compartment 17. Not sooner than when the piston 2 strikes on the boring bit 6, the

inertial slide valves

32 and 35 slide into their front positions by inertia. Thereby, the side filling duct 18 is opened by the filling inertial slide valve 35 and compressed air is brought to the front working compartment 17 through the filling duct 18 and the filling groove 16. Simultaneously, by opening the side exhaust duct 23 by the exhaust inertial slide valve 32 exhaust from the rear working compartment 30 through the recess 31, the exhaust groove 22, the side exhaust duct 23, the axial exhaust duct 24 and the boring 39 of the bit 6 to atmosphere is made possible. After a blow, the striking piston 2 is accelerated into the reverse movement and its working cycle is repeated. By a controlled filling and releasing of the working

compartments

17 and 30 according to this invention the output characteristics and effectiveness of this tool can be increased, whereby its design simplicity and undemanding production and operation are maintained.

Claims

A pneumatic submersible boring tool comprising a front cover (4), a working tool (6), an arrestment (5), a rear input body (8) with a built in water valve (9), and a working cylinder (1) in which a striking piston (2) is guided, the striking piston (2) being provided with an axial filling duct (19), side filling duct (18) and a side exhaust duct (23), wherein a rear extended part (21) of the striking piston (2) extends into a cavity (14) of the input body (8), the rear extended part (21) having a filling recess (27) on its surface, wherein a front working compartment (17) of the working cylinder (1) is connected, by a filling groove (16) provided on the surface of the striking piston (2), with the side filling duct (18), the side filling duct (18) passing through the wall of the striking piston (2), wherein the axial filling duct (19) is arranged in the rear extended part (21) of the striking piston (2) and is connected with the cavity (14) of the input body (8), and wherein the axial filling duct (19) is also connected to the side filling duct (18), wherein a closing pin (15) extends axially in the cavity (14), wherein the front face of the pin (15) is placed within an axial longitudinal section that is delimited by the front and the rear dead centres of the rear face (20) of the rear extended part (21) of the striking piston (2), and wherein the external diameter of the closing pin (15) is smaller than the internal diameter of the axial filling duct (19).
A pneumatic tool according to claim 1, wherein the closing pin (15) is formed by the front part of a water valve body (9).
A pneumatic tool according to claim 1, further comprising an axial exhaust duct (24) provided in the front part of the striking piston (2), opening into the side exhaust duct (23), the side exhaust duct (23) passing through the wall of the striking piston (2) and connected to an exhaust groove (22) formed on the surface of the striking piston (2), and also comprising a side release duct (34) passing through the wall of the striking piston (2), connected to the filling groove (16) and connected with the front working compartment (17) of the working cylinder (1), wherein an exhaust inertial slide valve (32) of pipe-like shape is slidably mounted in the axial exhaust duct (24).
A pneumatic tool according to claim 1, wherein a filling inertial slide valve (35) of pipe-like design is slidably mounted in the axial filling duct (19) of the striking piston (2).
A pneumatic tool according to claim 1, wherein, on the rear extended part (21) of the striking piston (2) between the filling recess (27) and an adjacent rear working face (29) of the striking piston (2), a cylindrical part (28) is made that, in said rear working compartment (30) of said cylinder (1), defines the length of a compression compartment which is delimited by front face (26) of the input body (8), by the adjacent internal diameter of said working cylinder (1), by the rear working face (29) of the striking piston (2) and by the external surface of the cylindrical part (28) of the rear extended part (21) of the striking piston (2).
A pneumatic tool according to claim 1, wherein the rear extended part (21) of the striking piston (2) is formed of an independent part (37) which is fastened to the rear part of the striking piston (2).
A pneumatic tool according to claim 6, wherein the independent part (37) is made of plastic.