GB2334053A

GB2334053A - Percussion boring machine with hard contacting surfaces

Info

Publication number: GB2334053A
Application number: GB9902760A
Authority: GB
Inventors: Alfons Hesse
Original assignee: Tracto Technik GmbH and Co KG
Current assignee: Tracto Technik GmbH and Co KG
Priority date: 1998-02-07
Filing date: 1999-02-08
Publication date: 1999-08-11
Anticipated expiration: 2019-02-08
Also published as: AU1546099A; GB9902760D0; DE19804919A1; DE19804919C2; GB2334053B; AU749893B2

Abstract

A percussion boring machine comprises a striking piston (3) pneumatically or hydraulically reciprocated in a housing (1) having a front (13) and rear (18, figure 1) striking face wherein at least the front striking face (13) has a higher hardness than the housing. The face itself may be hardened, or it may be provided with an insert. The piston (3) may also have hardened striking faces (16). The front striking face (13) may be provided with a through passage for the rear end of a tool (10) movably guided on the tip of the machine. The piston (3) may be move along a control pipe (6, figure 1) and then contact and impart its energy to internal collar (7). There is a stop ring (8, figure 1) at the rear of the housing with a compressed air hose. The housing may comprise front and rear parts welded together.

Description

Percussion boring machine The invention relates to a percussion boring machine for the production and widening of boreholes in the ground, the destructive replacement of underground pipelines or ramming pipes or the like into the ground. on boring machines of this kind have proved extraordinarily useful; they are used in particular for trenchless laying of pipelines and comprise, like the machine known from German patent specification 21 57 259, a housing having an impact tip which can be fitted in the housing to move against the force of a spring. However, in place of the movable impact tip a tool mounted to move in the impact tip can be used. In the machine housing there is a reciprocating striking piston, which is moved periodically to and fro pneumatically or hydraulically between a forward and a rear end position or reversing position under the influence of a pressure medium supplied through a pipeline. Such percussion boring machines usually have a control sleeve adjustable mechanically, electrically or by means of a pressure medium to change the machine over from forward to reverse travel.

In the case of forward travel the impact piston imparts its kinetic energy to a front striking face of the housing, or in the case of reverse travel to a rear striking face of the housing. The front striking face may comprise an internal collar of the housing and have a central passage through it in which the rear end of a longitudinally movable tool is guided.

When this is the case, the striking piston imparts its energy first to the tool and then the balance of it to the internal collar or to the housing.

In each case the striking faces of the housing, of the tool and also of the striking piston are subjected to extraordinarily high mechanical stresses. Thus in the case of large machines the impact energy may be as much as 10 000 joules. With a striking rate of 180 to 600 blows/minute this leads eventually to deformation of the striking faces and ~ consequently to a correspondingly limited working life of the machine.

Accordingly it is desirable to increase the life at least of the particularly stressed front striking face and hence of the percussion boring machine.

According to an embodiment of a first aspect of the present invention there is provided a percussion boring machine, particularly for the production of boreholes in the ground, comprising a striking piston, pneumatically or hydraulically reciprocated in a housing having a front and a rear striking face, wherein at least the front striking face has a higher hardness than the housing.

Thus, in an embodiment of the first aspect of the present invention at least the more stressed, front striking face has a higher hardness than the housing. This can be achieved by plating, by hardening or by the use of an insert having a higher hardness, while the housing and also the striking piston normally consist of a steel having a lower hardness but greater toughness.

Although the striking piston can be replaced at less expense in the case of wear on its striking faces, at least its front striking face should have a higher hardness than the body of the piston.

According to an embodiment of a second aspect of the present invention there is provided a percussion boring machine, wherein the housing comprises a front and a rear part and the parts of the housing are welded together.

Such a machine preferably also embodies the first aspect of the present invention.

Thus, irrespective of the nature of the striking faces, the machine housing may comprise a front and a rear part which are connected together by a butt weld. This offers advantages in the manufacture of the housing, since the rear part of the housing can be made from a simple tube, while the front part with the striking face must be made from solid material. A further advantage comes from the fact that the front part or its striking face can be hardened before joining the parts of the housing, while the other part is left untreated or is given some other heat treatment.

The invention will now be described in more detail, by way of example, with reference to an embodiment shown in the accompanying drawings, in which: Fig. 1 shows schematically a percussion boring machine, partly in section, and Fig. 2 shows the front part thereof, formed in accordance with an embodiment of the present invention.

The construction and operation of the percussion boring machine correspond in principle to those of the machine described in German patent specification 21 57 295. It has a housing 1 with a front part 2 into which an impact tip is screwed, and a striking piston 3. The striking piston 3 has in its rear part a compressed air chamber 4 with radial control openings 5 and is guided in the machine housing 1 to move longitudinally along a control pipe 6. When it meets an internal collar 7 of the machine housing 1 it imparts its impact energy thereto. In the rear part of the machine housing there is a stop ring 8 through which the control pipe 6 projects and is connected on the far side of the stop ring with a compressed air hose.

In place of the screwed-in impact tip with the tool 10, a head which is axially movable or is fixed to the housing part 2 may be used. However, a screwed-in impact tip has the advantage that in case of wear it can be quickly replaced.

When the machine is advancing the striking piston 3 moves to and fro under the influence of the compressed air supplied to the striking piston chamber 4 through the compressed air hose 9 and the control pipe 6: it imparts its impact energy substantially exclusively to the internal collar 7. Only in the relatively rare event of a reversal of the direction of movement (reverse travel) becoming necessary is the striking piston 3 controlled so as to strike the stop ring 8 with its rear end. This is described in more detail in German specification 21 57 295.

In the front part 2 of the housing with the impact tip a tool 10 is axially movably guided with its rear end 12 projecting through the internal collar 7 having the striking face 13. The tool 10 is supported on the impact tip or on the machine housing 1 as the case may be by means of a collar 14 and a prestressed spring 15.

The internal collar 7 has a hardened surface 13 and accordingly a higher resistance to wear and deformation than the material from which the front part 2 of the housing is made. In the same way the striking piston 3 also has a hardened surface 16, although this is not essential, since it is possible to exchange the striking piston in the event of its front face becoming worn. To do this it is only necessary to unscrew the stop ring 8 with the control pipe 6 from the housing.

Furthermore, the rear, annular striking face 17 of the piston 3 and the opposed striking face 18 of the stop ring 8 are hardened, although this is not essential, since the machine is only exceptionally operated so as to travel backwards. Consequently the faces 17, 18 are subjected to far less mechanical stress than the striking faces 13, 16.

The housing consists - independently of the nature of the striking faces - of two parts which are joined together by a weld 19, though it may be formed in one piece.

Claims

Claims 1. A percussion boring machine, particularly for the production of boreholes in the ground, comprising: - a striking piston - pneumatically or hydraulically reciprocated in a housing having a front and a rear striking face - wherein at least the front striking face has a higher hardness than the housing.
2. A percussion boring machine according to claim 1, wherein said striking face is hardened.
3. A percussion boring machine according to claim 1 or claim 2, wherein said striking face is provided with an insert.
4. A percussion boring machine according to any preceding claim, wherein the front striking face has a through passage for the rear end of a tool movably guided in the tip of the machine.
5. A percussion boring machine according to any preceding claim, wherein the front and/or the rear striking face of the piston has a higher hardness than the body of the piston.
6. A percussion boring machine, particularly one according to any preceding claim, wherein the housing comprises a front and a rear part and the parts of the housing are welded together.
7. A percussion boring machine substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.