CA1151028A

CA1151028A - Valveless pneumatic hammer

Info

Publication number: CA1151028A
Application number: CA000377811A
Authority: CA
Inventors: Abraham Gien; Bernard L. Gien
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-05-16
Filing date: 1981-05-19
Publication date: 1983-08-02
Also published as: AU542882B2; AU7066581A; SE8103065L; DE3119760C2; GB2076719A; DE3119760A1; GB2076719B; SE447666B

Abstract

A B S T R A C T

A valveless pneumatic hammer comprises a hollow casing having a backhead assembly at one end and a bit assembly at the other, and a piston reciprocable in the casing. There is a chamber divider at the backhead end of the casing which co-operates with the piston for conducting fluid under pressure into alternate chambers, one at each piston end, for reciprocation of the piston. The chamber divider is located within the casing by a locating split ring which holds the chamber divider axially against the backhead assembly. The chamber divider also has a recess in the end thereof nearest the piston which together with a bore in this piston end, comprises the fluid chamber at this end of the casing.

Description

TIIIS INV~NTION relates to a ha~nex of the valveless pneumatic type wllich is generally used for "down-the-hole" drilling.

- These hammers normally comprise a hollow casing with an operatively upper and a lower end, and, which has a piston therein which reciprocates betwcen an upper and a lower pressure chamber, and also has a bit asscmbly at the lower casing end and a backhead assem~ly at the uppcr casing end.

The design of such hammers usually provides ~or additional upper chamber space above the piston in order to prevent the prcssure from rising too high when the volume decreases owing to the piston's upward movcmcnt.
This space increases the volume of thc u~per chan~cr and in the conventional design results in an increasc in thc overall hammer length.

The outside diameter o~ typical hammers is usually restricted owing to the size hole that ~hcy arc designed to ~151 , drill, and thus there is di~ficulty in fitting the largcst possible diameter piston inside the bore of the hammcr, which is dcsirable in ordcr to obtain morc effectivc piston impact on the bit assembly. The largcst diamcter piston possible which could fit in the hammer, is of course a piston having a diameter marginally smaller than the inside diameter of the threaded ends of the casing. It is usually not possible to fit that piston of this size however, as a shoulder has to be provided to locate the chamber divider on the inner end thereof in the casing. This same restriction applies to the bit assembly, as a guide is usually located at the other cnd of the casing to secure the bit assembly.

It is an object of this invention to provide a valveless pneumatic hammer which has features which alleviate the above-mentioned problems.

In accordance with this invention there is provided a valveless pneumatic hammer comprising:
a hollow casing;
a backhead assembly at one end of the casing;
a bit assembly at the other end of the casing, having a rod extending into ~he casing and having a passage into the rod end and passing out to atmosphere at tlle other end of the assembly;

/ . . . _ 15~028 ., a chan~cr dividcr in ~he backhead cnd of ~hc casing having a control rod projccting into the casing, the inncrmost cnd of thc divider being adapted to scal against a piston bore during a portion of piston movcmcnt in usc;
a piston having a large bore in onc end and a smaller concentric bore through the othcr end into the lar~ycr bore, the larger bore end being adapted to co-operatc with the chamber divider end for the scaling of the largcr bore, the piston being further adapted to reciprocate between two positions, the first position being with the smaller bore end against the bit assembly where the bit assembly rod within and sealin~ off the smaller bore and the larger piston borc sealed off by the chamber dividcr cnd, ~nd the second position being with thc piston displaced towards the backhead assembly, the lar~er bore unsealed and the chambcr divider control. rod within and sealing off the smaller bore, and with thc bit asscmbly rod removed from the smaller borc;
a first chamber with the piston in the first position, formed around a bit assembly portion cx~ending into thc casing from a steppcd portion of the casin~;

-` 1151028 a second chamber with the piston in thc sccond position, formed by the largcr ~ore of thc piston and tl~e annular reccss in the chambcr divider;
a first fluid supply path ~hrough the backhcad assembly, bctwecn the chamber dividcr walls and the casing wall, into at lcast onc passage in the casing wall opposite thc piston in thc first piston position and into the first chamber;
a sccond fluid supply path through the backhead assem~ly, between the chamber divider walls and casing wall, between thc unsealcd chambcr and piston ends in the second position of the piston and into the second chamber;
a first fluid exhaust path rom the first chamber into the bit assembly passage with the piston in the second position and out into atmosphere;
and, a second fluid exhaust path from the second chamber through the smaller piston bore with the piston in its first position, into the bit assembly passage and out to atmosphere.

Further eaturcs of the invcntion providc for the end portion of thc lar~er bore of t]lC piston to ~c stepped inwardly, and for the inner cnd portion of the " -` llS~28 .

chamber divider to ~e stcpped outwardly, and for thc ~wo stcpped portions to co-operate for sealing off the larger bore by the sliding movemcnt of the chamber dividcr within the larger piston bore.

There is provided for the chamber dividcr to be located within the casing by a split locating ring con-ccntrically fitted within an annular concentric recess in the casing, the depth of the rccess ~eing lcss than or equal to the depth of the internal screw threading in the casing.

The chamber divider preferably has a stepped portion therein which engages with the split locating ring. The backhead end of the chamber divider is adapted to co-operate with the inner end of the back-head assembly for the securing of the chamber divider between the screwed in backhead assembly, and the locating ring.

Further, the depth of the passages in the casing walls making up the fluid supply path, are also prcferably not deeper than the depth of the internal scrcw threadin~
of the casing ends.

~ `here is also provided for the control rod of the chamber dividcr to have a passage thcrethrough -a --`` 1151028 co~lunica~in~3 with a pressul-e valve at the baekhead en~
in order to inerease the air flow through the hammer should the ha~ner ~e used at lower pressures, whieh eause an insuffieient flow of air through the hammer.

One embodiment of the invention is described below by way of example, and with referenee to the aceompanying sketehes in which:-Fig. 1 is a eross-sectional view of a valveless pneumatic hammer with piston in a first position;
Fig. 2 is an enlarged eross-seetional view of a seetion of the hammer of Fig. l; and Fig. 3 is a cross-sectional view of a valveless pneumatie hammer with piston in a seeond position.

A hollow easing 1 has a baekhead assembly 2 at one end thereof, and a bit assembly 3 at the other end.

The baekhead assembly is seeured in the casing end by internal ser~w-threading 4 in the casing.

chamber divider 5 is loeated in the casing between a split locating ring 6 and the inner end 7 of the baek-head assembly. This ehamber divider has an outwardly stepped portion 8 at the end thereof remote from the back-head assembly, and a central control rod 9 projeeting from this end. ~n annular recess 10 is locat~d in this end around the central eontrol rod 9. A central bore 11 extends llS1~28 through the control rod from end to end to a pressure valve assembly 12 ln the backhead assembly.

A piston 13 has a large bore 14 in one end thereof and a smaller bore lS in the other end thereof, which extends through to the larger bore. The large bore end of the piston has an inwardly stepped section 16, which is slidable in airtight manner over the outer surface of the outwardly stepped section 8 of the chamber divider.

..
The bit assembly 3 has a shaft 17 which has a protruding rod 18 extending into the chamber. The assembly 3 is slidable within the casing between pre-determined limits. This degree of slide is achieved, and the assembly is located within the casing, in any suitable manner. A portion of the shaft 17 extends into the casing interior from a stepped section of the casing, and the degree of slide of the bit assembly allows it to move between a raised position in which the said shaft portion is in the casing interior and a lowered position where the bit assembly end is flush with the stepped section of the casing.

- ~ passayeway 19 passes throuyh the end of the projecting rod 18 through to atmosphere out of the bottom of the bit assembly. This passage 19 divides into two separate passages 20 in the outer portion oi the bit`

` ` 115~028 asscmbly and these passages 20 communicate with atmos-phere at the slde of the blt assembly.

Two concentric annular recesses 21 are located in the casing, one near each end of the interior of the casing. The piston has a central stepped annular recess 22, of approximately the same width as the distance between the recesses 21 ~n the casing.

The piston is adapted to reciprocate between two positions. The first position (Fig. 1) is with the piston against the bit assembly in its raised condition, and with the bit assembly rod 18 extending fully into the small bore 15 of the piston. In this position a first chamber 23 is formed around the bit assembly and is defined by the wall of the bit assembly at this position, the casing wall opposite it, the stepped portion 24 of the bit and the overlapping portion 25 of thc piston.

Further in this position the end region of the recess 21 nearest the bit assembly communicates- with the first chamber 23 and the other recess 21 communicates with the casing interior just past the large bore end of the piston. The inwardly stepped portions of the piston and chamber divider are opposite each other and seal off the large bore 14 of the piston, and the /.. .

i~`51028 `, annular recess 10 of ~he chamber, from the intcrior of the casing.

In the second position of piston movement (Fig. 3) the piston is displaced towards the backhead assembly, the small bore end of the piston is removed from the projecting rod 18 of the bit assembly, and the inwardly stepped section 1~ of the piston has now slid past the outwardly stepped portion ~ of the chamber divider, as illustrated. In this position the control rod 9 of the chamber divider is within the small bore 15 of the piston, and the backhead recess 21 is sealed off from the interior of the casing by the piston wail.
At the small bore end the projecting rod 18 is removed from the bore of the piston. A second chamber 26 is formed with the piston in this position and is defined by the large bore 14 of the piston and the recess 10 in the chamber divider.

A first fluid supply path starts through the back-head assembly past the chamber divider and the casing walls into the recess 21 at the backhead end, with the piston in its first position, and then between the casing and the recess 22 in the piston, into the casing recess 21 at the b-it assembly end, and into the first chamber 23.
This first fluid supply path is clearly indicated by the arrows 27 in Yig. 1 of the drawinys.

- ~a , ~15~(~28 , A second ~luid exhaust path from the second cham~er 26 passes from the chamber 26 into the small bore of the piston from thcre into the passage 19 in the bit asscmbly and out to atmospllcre. This exhaust path is indicated by arrows 28 in Fig. 1.

~ second fluid supply path, with the piston in its second position (Fig. 3), passes through the backhead assembly between the chamber divider and casing wall and between the inner wall of the large bore of the piston and the outer wall of the chamber divider into the second chamber 26. This path is clearly indicated by arrows 29 in Fig. 3.

A first fluid exhaust path passes from the first chamber, with the piston in its second position, directly into the passage 19 in the bit assembly and through this passage out to atmosphere. This exhaust path is indicated by arrows 30 in Fig. 3.

A radial opening 31 through the wall of the chamber divider is located at the outwardly stepped portion 8 thereof; The opening is positioned so that it communicates between the second fluid chamber 26 and the passage between the chamber divider and the casing wall when the inwardly stepped section 16 of the piston is on the bit assembly side of the opening 31.

llS1028 `2 In use, air under pressure is admitted to the casing by the backhead assembly and passes along the first fluid path into thc first fluid chamber where the prcssure causes the piston to move towards the backhead assembly and position two. Clearly the ~nd piston surface exposcd to prcssure in chambcr 23 has a laryer arca than the end surface of the piston at the larye bore end.

As the piston moves towards its second position the rod 18 is removed from the second chamber 23 and air from the chamber follows the first fluid exhaust path.

The piston moves towards its second position and the entrance to the grooves at the backhead end is closed off by the piston moving over it and the second fluid supply path is opened by the inwardly stepped section 16 of the piston moving passed the outwardly stepped section 8 of the chamber divider. A second fluid supply path is thus open, and air foll~ws this path into the second chamber 26.

The pressure in this chamber causes the piston to commence moving back towards the bit assembly 3.
Once the piston has moved sufficicntly far for tl-e projecting rod 9 of the chamber divider to be removed /. . .
~ 2 `- ^ 1151()28 from the small bore 15 uf the piston, the sccond ~luid exhaust path is now open, and air from chamber 26 exhausts along this path out to atmosphere.

It will be appreciated that the recess 10 increases the volume of chamber 26 and thus reduces a build up of pressure caused by the piston returning to its second position. This effect is achieved without increasing the overall length of the hammer and represents thus a saving in materials and allows for easier manoeuvrability of the hammer.

Further, air following both of the fluid exhaust paths passes through the bit assembly and thus serves to remove drilling material from the borehole that may have lodged therein.

The location of the chamber divider by means of the locating split ring allows a piston of the maximum diameter to be used and thus the maximum effect of impact of piston against bit assembly is achieved. Preferably the depth of the recesses 21 is also not greater than the depth of the internal screw threading of the backhead end.

If the casing is raised off the surface bcing drilled, the bit assembly drops to its lower position ~3 /

- - -` 1151028 ., ~

with the piston resting thereon. In this positlon, the end of the stepped portion 16 of the pis~on uncovers th~ openlng 31, which communlcatcs between chamber 26 and the passage ~etween the casing wall and the chamber divider. Air thus follows the path between casing wall and chamber divider, through the opening 31 and into chamber 26 and out along the exhaust path 28 to a~nosphere through the bit assembly. This allows for continuous flushing of the borehole and the bit assembly, and since all.the air supply being supplied to the machine is exhausted as described, the machine is inactive in this condition.

It is considered that the invention provides an cffective pneumatic hammer which alleviates difficulties experienced in prior art hanuners of the same type.

Var.iations may be made to the above embodiment without departing from the scope of the invention. For example, the first fluid supply path may pass through a passage or passages whlch are located entirely in the casing wall, and the piston need not have recesses at all in its outer wall.

, ~ .

Claims

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is :-

1. A valveless pneumatic hammer comprising:
a hollow casing;
a backhead assembly at one end of the casing;
a bit assembly at the other end of the casing, having a rod 18 extending into the casing and having a passage into the rod end and passing out to atmosphere at the other end of the assembly;
a chamber divider in the backhead end of the casing having a control rod 9 projecting into the casing, the innermost end of the divider being adapted to seal against a piston bore during a portion of piston movement in use;
a piston having a large bore in one end and a smaller concentric bore through the other end into the larger bore, the larger bore end being adapted to co-operate with the chamber divider end for the sealing of the larger bore, the piston being further adapted to reciprocate between two positions, the first position being with the smaller bore end against the bit assembly where the bit assembly rod within and scaling off the smaller bore and the larger piston bore sealed off by the chamber divider end, and the second position being with the piston displaced towards the backhead assembly, the larger bore unsealed and the chamber divider control rod within and sealing off the smaller bore, and with the bit assembly rod removed from the smaller bore;
a first chamber with the piston in the first position, formed around a bit assembly portion extending into the casing from a stepped portion of the casing;
a second chamber with the piston in the second position, formed by the larger bore of the piston and an annular recess in the chamber divider;
a first fluid supply path through the backhead assembly, between the chamber divider walls and the casing wall, into at least one passage in the casing wall opposite the piston in the first piston position and into the first chamber;

a second fluid supply path through the backhead assembly, between the chamber divider walls and casing wall, between the unsealed chamber and piston ends in the second position of the piston and into the second chamber;
a first fluid exhaust path from the first chamber into the bit assembly passage with the piston in the second position and out into atmosphere; and, a second fluid exhaust path from the second chamber through the smaller piston bore with the piston in its first position, into the bit assembly passage and out to atmosphere.

2. A valveless pneumatic hammer as claimed in claim 1, in which the end portion of the larger piston bore is stepped inwardly, and the innermost end portion of the chamber divider is stepped outwardly,the stepped portions being-co-operable for the selective sealing off of the larger piston bore from the outside thereof by the sliding movement of the chamber divider within the larger piston bore.

3. A valveless pneumatic hammer as claimed in claim 1 in which the chamber divider is located within the casing by a split ring fitted partially within a concentric annular recess in the casing and partially in a concentric annular step-like rebate in an inner edge portion of the chamber adjacent the casing wall, to retain the chamber divider axially against the backhead assembly.

4. A valveless pneumatic hammer as claimed in claim 2 in which the chamber divider is located within the casing by a split ring fitted partially within a concentric annular recess in the casing and partially in a concentric csm/? 17 annular step-like rebate in an inner edge portion of the chamber adjacent the casing wall, to retain the chamber divider axially against the backhead assembly.

5. A valveless pneumatic hammer as claimed in claim 1, 2 or 3 in which the first fluid supply path includes a concentric annular recess in the casing wall in the region thereof opposite the large bore end of the piston, a concentric annular recess in the middle region of the piston, and a concentric annular recess in the casing wall at the region thereof opposite the small bore end of the piston.

6. A valveless pneumatic hammer as claimed in claim 1, 2 or 3 in which the first fluid supply path includes a concentric annular recess in the casing wall in the region thereof opposite the large bore end of the piston, a concentric annular recess in the middle region of the piston, and a concentric annular recess in the casing wall at the region thereof opposite the small bore end of the piston, and in which the recesses in the casing are no deeper than any internal screw threading on the casing.

7. A valveless pneumatic hammer as claimed in claim 1, 2 or 3 in which the bit assembly is moveable between two positions, the first in which the shaft thereof is wholly within the casing and the second in which a portion of the shaft extends from the casing end.

8. A valveless pneumatic hammer as claimed in claim 1, 2 or 3 in which the bit assembly is moveable between two positions, the first in which the shaft thereof is wholly within the casing and the second in which a portion of the shaft csm/? 18 extends from the casing end, and in which the piston is moveable to a third position in which the small bore end of the piston is in contact with the inner end of the bit assembly when the bit assembly is in its second position, and the large bore piston end has sealed off the first fluid supply path as well as the second fluid supply path, there being a fluid path from between the casing wall and chamber wall to the second chamber through an opening in the wall of the end region of the chamber divider.

9. A valveless pneumatic hammer as claimed in claim 1, 2 or 3 in which the bit assembly is moveable between two positions, the first in which the shaft thereof is wholly within the casing and the second in which a portion of the shaft extends from the casing end, and in which the piston is movable to a third position in which the small bore end of the piston is in contact with the inner end of the bit assembly when the bit assembly is in its second position, and the large bore piston end has sealed off the first fluid supply path as well as the second fluid supply path, there being a fluid path from between the casing wall and chamber wall to the second chamber through an opening in the wall of the end region of the chamber divider, and in which the opening is an outwardly stepped portion of the chamber divider.

10. A valveless pneumatic hammer as claimed in any one of claim 1, 2 or 3 in which the control rod of the chamber divider has a passage therethrough communicating with a pressure valve at the backhead end of the divider, the valve being adapted to open when the operating fluid of the hammer is below a predetermined minimum.

csm/? 19