A drill hammer

Abstract

The invention relates to a pneumatic drill hammer (100). An air delivery tube (112) cooperates with an axial bore (B) in a reciprocating piston (106). A check valve (110) is provided in an end of the tube (112). A stop (132) and spring (120) for the check valve (110) are secured in place by a transverse pin (130). First (166) and second (170) flow passages extend from the piston bore (B) to a return chamber (RC) and drive chamber (DC), respectively. The piston (106) has a stem (143) that strikes an anvil (158) inside a cup-shaped bush (160) on a drill bit (108). The bit (108) has exhaust passage (C) that extends from a central position in the anvil (158). The bush (160) seals around the stem (143) to enclose and exhaust a return chamber (RC).

Description

[0001] A DRILL HAMMER

[0002] FIELD OF THE INVENTION

[0003] The invention relates to drill hammer that is pneumatically powered and of the down-the- hole or in-the-hole type. These are well known in the rock drilling industry particularly for drilling into the earth from the surface but also in various underground rock hole boring scenarios.

[0004] BACKGROUND TO THE INVENTION

[0005] The components of these drill hammers vary depending on the design that is chosen to achieve a working mechanism. A switching of supply air between a drive chamber and a return or lifting chamber is required to reciprocate a piston that impacts a drill bit. Both chambers need to be exhausted respectively during the cycle and the exhaust air is channelled through the drill bit to flush the drill hole.

[0006] These hammers also have check valves associated with an inlet through a back-head that supplies the pressurised air to the piston drive mechanism. The check valve is necessary to prevent backflow of water / sludge into the hammer from the bore hole.

[0007] Some of the hammer designs forego important aspects of "in the field" servicing which often requires simple disassembly and assembly. Unnecessary downtime and loss of production are suffered as a result and the drill hammers are more difficult and expensive to manufacture.

[0008] Other drill hammers are made with mechanisms that fail to optimize the space available within the diameter of a hole to be drilled (as determined by the bit diameter). This often also translates to unnecessary weight and / or length of drill hammers with less than optimal efficiency. On the one hand, the components of these hammers are often unnecessarily complicated and, on the other hand, small changes that involve additional parts may be made to improve performance and / or serviceability.

[0009] OBJECT OF THE INVENTION

[0010] It is an object of the invention to provide a pneumatic down-the-hole drill hammer which includes a check valve and / or a drill bit that offer, at least partially, improvements in performance, serviceability and / or simplicity in manufacture / assembly.

[0011] SUMMARY OF THE INVENTION

[0012] In accordance with the invention there is provide a pneumatic drill hammer comprising: a back-head, a wear sleeve, a piston and a drill bit; a check valve with a check valve chamber that includes a seat and a check valve closure; a spring to bias the check valve closure against the seat; the spring located between the check valve closure and a retaining pin that extends transversely through the valve chamber and has its ends secured in oppositely arranged openings provided in a wall of the valve chamber; wherein the check valve chamber is provided in an air delivery tube that is supported from the back-head of the drill hammer and cooperates with an axial bore extending from a back end through the piston; in which the bore of the piston has a first port and a second port that extend outwardly from the piston bore; the first port, located in spaced apart relationship between a rear end of the piston and the second port and the second port located in spaced apart relationship between the first port and a front end of the piston; the first port in communication with a longitudinal supply passage that extends forwardly to a return chamber; and the second port in communication with a longitudinal supply passage that extends rearwardly to a drive chamber; the drill bit having a longitudinal exhaust passage that extends from a central position in an anvil and a cup-shaped bush that extends rearwardly from a circumference of the anvil to cooperate with a stem on a front end of the piston to seal a return chamber when the stem is inside the bush and to exhaust the return chamber when the stem is withdrawn from the bush. The invention further provides for a drill hammer as defined in which a stop is provided in a downstream end of the valve chamber and the retaining pin extends through a passage in the stop, and the stop is provided with a port.

[0013] In accordance with a first aspect of the invention there is provided a check valve for a pneumatic drill hammer comprising: a check valve chamber which includes a seat and a check valve; a spring to bias the check valve against the seat; the spring located between the check valve and a retaining pin that extends transversely through the valve chamber and has its ends secured in oppositely arranged openings provided in a wall of the valve chamber.

[0014] The invention further provides for a check valve as defined in which: the check valve chamber is provided in an air delivery tube that is supported from a back-head of a drill hammer and cooperates with a bore in a back end of a piston; a stop is provided in a downstream end of the valve chamber and the retaining pin extends through a passage in the stop, and the stop is provided with a port (to equalise hydrostatic pressure from within the drill hammer to a space behind the check valve); the stop includes a cylindrical sidewall two opposite holes that align with the openings; the retaining pin has an engaging formation that operatively receives a back end of the spring; the engaging formation is a recess; the recess has curved or inclined side shoulders which displace the back end of the spring when the retaining pin is pressed axially; and the recess the annular.

[0015] The invention further provides for a check valve as defined in which the pin is a press-fit into the opposite openings or the pin includes screw-threaded heads at both ends which are engageable with screw-threads provided inside the opposite openings in the wall of the valve chamber.

[0016] In accordance with a second aspect of the invention there is provided a drill bit for a pneumatic drill hammer comprising: a body with a face at a working end; an exhaust passage that extends from a central position in an anvil and includes at least one vent that opens at the working end; a cup-shaped bush that extends rearwardly from a circumference of the anvil to cooperate with a stem on a front end of a piston to seal a return chamber when the stem is inside the bush and to exhaust the return chamber when the stem is withdrawn from the bush.

[0017] The invention further provides for a drill bit as defined: in which the bush is formed integrally with the drill bit; and which includes an arrangement of longitudinal slots around the bush that are positioned to extend across a reduced diameter guide collar in the wear sleeve at the bottom of the return chamber and a land on the shank around the anvil at the bottom of the slots which is a sealing fit inside the guide collar.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] These and other features of the invention will become more apparent from the following description of one embodiment, made by way of example, with reference to the accompanying drawings, in which:

[0020] Figure 1 shows a cross-sectional side view of a drill hammer that incorporates both the first and second aspects of the invention;

[0021] Figure 2 show a cross-sectional side view of a check valve in accordance with the first aspect of the invention; and

[0022] Figure 3 show a cross-sectional side view of a drill bit in accordance with the second aspect of the invention.

[0023] DETAILED DESCRIPTION OF THE INVENTION

[0024] Referring to the drawings, a pneumatic drill hammer (100) consists of a back-head (102), a housing in the form of a wear sleeve (104), a piston (106) and a drill bit (108). The back- head is secured through screw-threaded engagement into the wear sleeve. In accordance with a first aspect of the invention a check valve (110) is provided in an air delivery tube (112) which is fitted into the back-head (102). A check valve chamber (114) with a valve seat (116) accommodates a check valve closure (118). A compression spring (120) is provided to bias the check valve closure against the seat. The air delivery tube accordingly provides an inlet flow passage (A) which is controlled by the check valve (110).

[0025] The check valve closure (118) is slidably supported for movement along an inside the air delivery tube (112). An outlet from the air delivery tube (112) is provided as radial outlet ports (122) through a sidewall of the air delivery tube. An internal annular rib (124) is located on the sidewall adjacent the outlet ports. A shoulder on the rib provides the valve seat (116). The check valve closure (118) has an opening face (126) providing a working area which is exposed to inlet pressure of the air delivery tube through the seat.

[0026] An annular skirt (128) extends to the opposite side of the check valve closure (118), into the valve chamber (114). The skirt (128) is located over a forward end of the spring (120). The opposite, rearward end of the spring is located against a transverse retaining pin (130). The retaining pin secures a stop (132) in the free end of the air delivery tube (112). The stop is provided with a cup-shape, having an end wall (134) that is located across the end of the air delivery tube and a cylindrical sidewall that extends into the tube. An internal annular rim (136) provided on the cylindrical sidewall of the stop will limit the rearward movement of the check valve closure (118), when the valve (110) is opened. The skirt (128) of the closure (118) abuts the rim (136) in this condition.

[0027] A port (138) provided centrally in the end wall (134) of the stop (132) places the portion of the valve chamber (114) behind the valve closure (118) in communication with an exhaust pressure environment of the hammer (100). The stop will deter against ingress of dirt to the valve chamber while the port still enables an equalisation of pressure across the end wall. The invention provides for the retaining pin (130) to extend transversely through a passage (139) across the stop (132), which in this embodiment is provided by two opposite holes (139) in the sidewall of this cup-shaped component. The retaining pin is sized to protrude through the stop (132) with its ends secured in oppositely arranged openings (140) provided in the adjacent wall of the air delivery tube. The arrangement serves to retain the stop in place and provides the check valve chamber.

[0028] The retaining pin (130) shown in the drawings is provided with a press-fit into the opposite holes (140) of the air delivery tube and may also be a press-fit into the holes (139) of the stop (132). The press-fit dimensions and materials will be selected to provide an engagement between the components that will prevent movement of the pin (130) during operation of the drill hammer (100). In addition to this, a feature of the pin referred to below employs the bias of the spring (120) to resist lateral movement relative to the valve chamber or air delivery tube wall.

[0029] The retaining pin (130) includes an engaging formation (141) that operatively receives a rearward end of the spring (120). In this embodiment, the engaging formation is provided as a recess (141) on the pin. The recess (141) is formed by a reduced diameter middle section between two enlarged pin heads (142) that engage into the openings (140). The heads (142) are provided with a width that substantially corresponds to the combined sidewalls of the tube (112) and the cup-shaped stop (132). The configuration provides that the recess (141) aligns with an interior space in the stop (132) and seats the rearward end of the spring (120).

[0030] The piston (106) which is provided between the back-head (102) and drill bit (108) has a reduced diameter piston stem (143) that extends from a piston head (144) to provide a striking, front end. An axial bore (B) extends from a back end of the head (144) to the front end on the stem. The drill bit (108) is slidably mounted in the end of the wear sleeve (104) opposite to the back-head (102). The axial bore (B) of the piston (106) communicates directly with a longitudinal exhaust passage (C) through the drill bit (108). The arrangement of parts to slidably retain the bit (108) in the front end of the wear sleeve (104) can be of any suitable type. In the embodiment shown, these include a chuck (146) and a two-part retaining ring (148). The chuck has an external thread that screws into the bottom of the wear sleeve to secure the ring (148) against a step. The drill bit and chuck are locked against relative rotation by an arrangement of overlapping, co-operating splines (149) - external on the bit and internal in the chuck.

[0031] The drill bit (108) has a face (150) at a working end provided on a forward head (152) with a rearwardly extending shank (154) which carries the splines (149) below an annular recess (156) that allows travel on the retaining ring (148). The face (150) includes an arrangement of rock breaking buttons. The exhaust passage (C) extends axially from a central position on an anvil (158) that is provided at the back end of the shank (154). There is an arrangement of vents that extend at an incline from the exhaust passage (C) and open through the bit face (150).

[0032] In accordance with a second aspect of the invention, a cup-shaped bush (160) is formed integrally on the back end of the bit (108). The bush is provided by a substantially cylindrical wall that extends rearwardly from a circumference of the anvil (158) and is configured as a cooperating formation to interact with a forward portion of the stem (143) at the front end of the piston (106). A striking surface of the anvil (158) is accordingly provided inside the bush.

[0033] An internal chamfer or taper at the opening of the bush (160) assists in guiding the piston stem (143) onto the anvil (158) when it moves forwardly on an impact stroke. The piston stem is a sealing fit with the bush to seal the return (bottom) chamber when these parts are engaged.

[0034] Figure 1 shows the air delivery tube (112) received within an axial bore (B) at the back end of the reciprocating piston (106) and the bit (108) pushed back into the hammer (100) in a starting condition for down-the hole drilling. Working fluid is supplied to the mechanism when a pressurised air supply in the passage (A) acts on the opening face (126) to move the check valve closure (118) off the valve seat (116) against the bias of the spring (120).

[0035] The outlet ports (122) provide a pressurized air feed respectively into:

[0036] (a) a first annular recess (162) which is spaced along the bore (B) from the back end of the piston (106) and connects to the return chamber (RC); and

[0037] (b) a second annular recess (164) which is spaced further along the bore (B) from the first annular recess (162) and connects to the return chamber (DC).

[0038] It will be understood from Figure 1 that the first annular recess (162) will be in flow communication with the outlet ports (122) when the piston (106) is in a forward condition and the second annular recess (164) will be in flow communication with the outlet ports (122) when the piston (106) is in a rearward condition.

[0039] The first annular recess (162) has radial, forwardly inclined first passage (166) connected to a first longitudinal groove (168) which extends down the side of the piston head (144). The first groove (168) opens into a return chamber (RC). A first supply path is defined with the wear sleeve.

[0040] The second annular recess (164) has radial, rearwardly inclined second passage (170) connected to a second longitudinal groove (172) which extends rearwardly along the side of the piston head (144). The second groove (172) opens into a drive chamber (DC). A second supply path is defined with the wear sleeve.

[0041] The configuration, spacing and sizing of the parts and flow passages will be within the design competence of a person suitably skilled in the art.

[0042] Compressed air from the outlet ports (122) is communicated via the first annular recess (162) along the first supply path to the return chamber (RC). The air in return chamber (22) acts to move the piston (4) upwardly away from the drill bit (5). This results in closing of the first passage (166), which cuts off air supply along the first supply path to return chamber (RC).

[0043] Momentum of the piston (106) causes it to continue moving on a return stroke. The piston stem (143) is withdrawn from the bush (160). Air from the return chamber (RC) will flow into the cup-shaped bush and exhaust through the passage (C) in the drill bit (108) to atmosphere. With further movement of the piston, the second annular recess (164) is thereafter placed in flow communication with the outlet ports (122).

[0044] Compressed air from the outlet ports (122) is communicated via the second annular recess (164) along the second supply path to the drive chamber (DC). The air in drive chamber (22) acts to decelerate the piston (106) which ends the return stroke and then expands as the piston is accelerated back towards the bit (108) on an impact stroke. This drives the piston to strike the drill bit.

[0045] Towards the end of the impact stroke, the drive chamber (DC) exhausts through reverse flow via the second groove (172), second passage (170), second annular recess (164) into the axial bore (B), bit passage (C) and to atmosphere.

[0046] The downward travel of the piston (106) brings the stem (143) into sealing engagement with the bush (160) and the piston delivers a blow to the anvil.

[0047] The first annular recess (162) is again placed in flow communication with the outlet ports (122) to re-establish the first supply path to the return chamber (RC). The cycle is repeated. The assembly of parts thus provides for the operation of the drill hammer (100) to generate return and impact strokes of the reciprocating piston (106). A person skilled in the art will understand the interaction of parts (to seal or permit supply / exhaust flow) in portions of the drill cycle intermediate to those referred to above.

[0048] When the drill hammer (100) is lifted from a bottom of the drill hole, the bit (108) moves downwardly out of the housing and rests against the retaining ring (148). In this condition, an arrangement of longitudinal slots (174) around the bush (160) are positioned extending across a reduced diameter guide collar (176) formed in the wear sleeve (104) at the bottom of the return chamber (RC). A land (178) on the shank (154) around the anvil (158) at the bottom of the slots (174) is usually located in the guide collar (176) this portion of the wear sleeve (104) as the bit (108) slides up and down during operation. The land (178) provides a sealing fit which resists escape of air from the return chamber (RC).

[0049] In the forward, flushing condition of the bit (108), the slots (174) provide a by-pass passage that vents the return chamber (RC) for air to escape past the retaining ring (148) and along the splines (149) between the bit (108) and the chuck (146) to atmosphere. The arrangement avoids trapping of air below the piston. The piston (106) follows the bit (108) moving past the outlet ports (122) of the air distribution tube (112). Air flows into the space behind the piston (106) and along the second groove (172), second passage (170), second annular recess (164) into the axial bore (B), bit passage (C) and to atmosphere.

[0050] The drill hammer (100) assumes a flushing mode which brings the piston (106) to a halt until the bit (108) is again pressed into the housing to open the first supply path to the return chamber (RC).

[0051] During operation of the hammer (100), an area on the inside of the check valve closure (118) opposite to the opening face (126) is exposed to a low pressure environment at a free end of the air delivery tube (112). The pressure is that of the exhaust air, inside the piston bore (B). The opening face (126) is constantly exposed to supply pressure in the inlet passage (A). The arrangement serves to maintain the check valve (110) in an open condition for as long as there is supply pressure in the inlet passage (A). This prevents valve oscillation due to cessation or fluctuation of fluid flow into the assembly.

[0052] Compressed air supply to the back-head to the hammer causes the check valve closure to move in the direction of the flow opening in the check valve. The check valve closure is spring biased in the opposite direction to close onto the valve seat when the compressed air is closed off. If the hammer (100) is in a water / sludge mixture when the airflow is cut off, hydrostatic pressure in the bore hole would usually cause sludge ingress into the hammer. The central port (138) in the stop (132) serves to equalise hydrostatic pressure from within the drill hammer to the space behind the check valve closure (118). The hydrostatic pressure caused by the water pushing up in the bore hole will act on a rear surface area of the valve closure (118) opposite to opening face (126). This facilitates closing of the check valve (110) under spring bias when supply pressure to the hammer ceases. The automatic closure of the check valve serves to trap the compressed air, which is in the hammer. The air that is so contained within the hammer serves to balance the hydrostatic pressure of the water / sludge in the bore hole and deter against said ingress through the ports of the drill bit.

[0053] The bit and bush thus serve to seal the return chamber when the stem is received inside the bush and exhaust the return chamber when the stem is withdrawn from the bush as well as venting past the wear sleeve and bit shank when the return chamber must be vacated in the flushing mode. The bush will preferably be formed as an integral part of the drill bit. This will involve initial casting and subsequent machining of the component.

[0054] The rearward end of the check valve spring locks into the recess of the pin and provides resistance against lateral movement of the pin. A cylindrical front portion of the stop serves as a guide for the rearward back end of the spring. The pin cannot move outside ways and can only come out sideways for disassembly when force is applied to it, but not during normal operation.

[0055] To facilitate manual removal of the pin (130), the recess has curved or inclined side shoulders which displace the rearward end of the spring (120) when the retaining pin is pressed out of the assembly. The recess (141) is machined as an annular formation around the pin and is presented to engage with the spring (120) regardless of the axial orientation of the pin. The rearward end of the spring which is located in the recess provides resistance against lateral movement of the pin. The pin heads (142) are provided with a chamfer at the respective ends to facilitate insertion.

[0056] The spring thus provides a resisting bias into the recess on the check valve retaining pin. Under normal working conditions, the pin will not move sideways, because of the spring force and / or resistance through the press-fit of ends in the openings of the tub. When disassembling the hammer the pin can be removed by applying side pressure, by hand, using a drift, screwdriver or punch.

[0057] It should be appreciated that the pin could have many shapes / configurations to receive the spring in said manner, to use the bias for resistance against axial movement. Instead of a recess cut around the pin, it could have a recess could be formed on only one side of the pin which is positioned to engage with the spring. Also, a pair of spaced apart annular grooves that receive opposite edges of the spring may be provided. Other engaging formations or shapes may also be used. The stop may be omitted in a simplified embodiment of the invention and only the pin used to retain the spring and check valve in the assembly. It is also anticipated that, in a different embodiment, the pin may include screw-threaded heads at both ends which are engageable with screw-threads provided inside the opposite openings of the valve chamber wall.

[0058] The unique locking system of the pin through the wall of the air delivery tube and through the check valve stop, will lock the check valve stop in place. The pin provides a uniquely effective assembly mechanism that is also easy for removal on dis-assembly when this is required for servicing or replacing parts.

[0059] Most hammers available on the market can be either designed to use a drill bit with a foot valve tube or without a foot valve tube - the difference between the two systems lies in the bottom, return chamber of the hammer, which serves to lift or return the piston after it has delivered a blow to an anvil end of the drill bit. In the latter case of the “tubeless” embodiment, a piston stem bush is provided as a separate part that is secured inside the wear sleeve and engages around an end of the piston to form an enclosed return chamber (when it is not being exhausted). The drill bit of the invention makes for a simple hammer with fewer parts for assembly and disassembly.

[0060] The combination of the check valve construction in an air delivery tube and the drill bit construction (with a bush around the anvil) at either end of the piston which provides the first flow path to the return chamber and the second flow path to the drive chamber makes for a unique drill hammer with a relatively simple arrangement of parts that effectively achieve the required impact cycle. Assembly, disassembly and servicing is simplified. A person skilled in the art will appreciate that a number of variations (in addition to those specifically mentioned) may be made to the features of the embodiments described without departing from the scope of the invention.

Claims

CLAIMS1 . A pneumatic drill hammer comprising: a back-head, a wear sleeve, a piston and a drill bit; a check valve with a check valve chamber that includes a seat and a check valve closure; a spring to bias the check valve closure against the seat; the spring located between the check valve closure and a retaining pin that extends transversely through the valve chamber and has its ends secured in oppositely arranged openings provided in a wall of the valve chamber; wherein the check valve chamber is provided in an air delivery tube that is supported from the back-head of the drill hammer and cooperates with an axial bore extending from a back end through the piston; in which the bore of the piston has a first port and a second port that extend outwardly from the piston bore; the first port, located in spaced apart relationship between a rear end of the piston and the second port and the second port located in spaced apart relationship between the first port and a front end of the piston; the first port in communication with a longitudinal supply passage that extends forwardly to a return chamber; and the second port in communication with a longitudinal supply passage that extends rearwardly to a drive chamber; the drill bit having a longitudinal exhaust passage that extends from a central position in an anvil and a cup-shaped bush that extends rearwardly from a circumference of the anvil to cooperate with a stem on a front end of the piston to seal a return chamber when the stem is inside the bush and to exhaust the return chamber when the stem is withdrawn from the bush.

2. A drill hammer as claimed in claim 1 in which a stop is provided in a downstream end of the valve chamber and the retaining pin extends through a passage in the stop, and the stop is provided with a port.

3. A check valve for a pneumatic drill hammer comprising: a check valve chamber which includes a seat and a check valve; a spring to bias the check valve against the seat; the spring located between the check valve and a retaining pin that extends transversely through the valve chamber and has its ends secured in oppositely arranged openings provided in a wall of the valve chamber.

4. A check valve as claimed in claim 3 in which the check valve chamber is provided in an air delivery tube that is supported from a back-head of a drill hammer and cooperates with a bore in a back end of a piston.

5. A check valve as claimed in claim 3 or claim 4 in which a stop is provided in a downstream end of the valve chamber and the retaining pin extends through a passage in the stop, and the stop is provided with a port.

6. A check valve as claimed in claim 5 in which the stop includes a cylindrical sidewall two opposite holes that align with the openings.

7. A check valve as claimed in any one of claims 3 to 6 in which the retaining pin has an engaging formation that operatively receives a back end of the spring.

8. A check valve as claimed in claim 7 in which the engaging formation is a recess.

9. A check valve as claimed in claim 8 in which the recess has curved or inclined side shoulders which displace the back end of the spring when the retaining pin is pressed axially.

10. A check valve as claimed in any one of claims 3 to 9 in which the pin is a press-fit into the opposite openings.

11. A drill bit for a pneumatic drill hammer comprising: a body with a face at a working end;an exhaust passage that extends from a central position in an anvil and includes at least one vent that opens at the working end; and a cup-shaped bush that extends rearwardly from a circumference of the anvil to cooperate with a stem on a front end of a piston to seal a return chamber when the stem is inside the bush and to exhaust the return chamber when the stem is withdrawn from the bush.

12. A drill bit as claimed in claim 11 in which the bush is formed integrally with the drill bit.

13. A drill bit as claimed in claim 11 or claim 12 which includes: an arrangement of longitudinal slots around the bush that are positioned to extend across a reduced diameter guide collar in the wear sleeve at the bottom of the return chamber; and a land on the shank around the anvil at the bottom of the slots which is a sealing fit inside the guide collar.

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