POWER OPERATED PISTON TOOL WITH PISTON AUTOMATIC RETURN

Abstract: The present invention provides a defect-less and easy to operate power actuated piston tool with automatic piston return, designated for driving fasteners into a base like masonry, concrete, wood or the like. The tool according to the invention is characterized by that on piston shank (11) of piston (1), there is an elastic returning bush (7), situated between piston head (12) and fastener guide (5), said returning bush (7) is a one-piece in shape of bellow, made of elastomeric material, of regularly variable diameter.

Description: Power operated piston tool with piston automatic return The object of th is invention is a power operated piston tool with piston automatic return . I n power operated piston tools, of ind irect action , designed for driving fastening elements into a base like masonry, concrete, wood or the like, a piston element, d riven by firing gases , coming from firing cartridge, is used as an intermediary element, acting upon the fastener, as opposite to tools of d irect action , where firing gases act directly upon fasteni ng element. I n tools of ind irect action , the piston after fastening is in its forward position , that is piston shank tip is at the fastener g uide muzzle end . I n order to return the piston to its firing position , in conventional , semiautomatic tools, manual reloading is required . This reloading consists of pulling backward the barrel means, having a returning tooth , engaging the respective cavity on piston means , which causes the piston to return . This operation is also used to shift the firing cartridge belt about one position , thus making the tool ready for next firing . In other kind of power piston tools, described in patent EP 0223740, the piston return is actuated by the firing gases which , after pushing the piston to its forward position , while still expanding , cause the piston to retract. However, after retracting , the piston strikes against its rear abutment, thus causing the reflection effect, which may displace the piston of some distance from its firing position , creating a dead space, decreasing the firing power of a subsequent fire . As a result, fasteners are driven into the base at uneven depth and the firing chamber becomes spoiled with firing remains, due to incomplete burning of blowing charge. Besides, problems can occu r when the piston itself is driven into the base after fastening operation . I n that case, to return the piston to its firing position , an additional manual push-rod is needed . I n any case, after transporting or other periods of prolonged disuse of the tool, it is always useful to check with manual push-rod , whether the piston is well in its firing position , the only one initial position ensuring tool correct functioning . I n another kind of power piston tool , illustrated i n US patent No 3 , 331 , 546 , to return the piston member, a plurality of stacked washers constructed from polyurethane elastomer, are applied . The washers are positioned within the barrel , on the piston shank. After firing the washers are rapidly collapsed , thus absorbing part of firing energy and functioning as a buffer. At the end of power stoke, and after d issipation of the firing gases, escaping throug h vent holes in the barrel , the washers will return to their original shape, due to elastic memory, and thus they return piston to its firing position . The venting holes, situated in washers' side portions cause stress concentration and thus damage to spring elements. The other problem arises when exchanging worn-out washer elements, as they require strictly defined positions and quantity, otherwise malfunction may occur, if not a serious tool damage. It is an object of this invention to provide a power operated piston tool , free from above mentioned imperfections, in which the piston return is carried-out mechanically, by use of one-piece elastic returning bush . The returning bush is situated on piston shank between piston head and fastener guide, is made of elastomeric material and has a shape of bellow, whose diameters both external and internal are regularly varied . The walls of so formed returni ng bush are approximate in shape to a sinusoid , or to a stack of frusto-spherical seg ments, or frusto- conical segments, or stack of barrel-shape segments or/and other surface of revolution segments, creating uniformly spaced swellings and narrowings of wave like structure. The returning bush according to this invention advantageously has the maximal internal diameter of at least one segment at its both ends of slightly smaller size than the respective diameter of remaining segments, so the end seg ment walls are thicker than others seg ment walls. The internal end surface of external segments is markedly curved outside in such a way, that the position of curvature points of bush ends is clearly distanced from bush face. The length of returning bush is selected in such a way that after initial blocking , the piston shank end face does not reach its extreme forward position and remains at a distance from the base, the distance slightly g reater than the head height of fastening element. The maximal external diameter of returning bush according to present invention is smaller enough than the internal diameter of guid ing barrel , that after initial blocking of the bush , its external d iameter sti l l remains smaller than internal diameter of guiding bush , thus preserving the slight clearance. After driving fully the fastening element into the base, and subsequent stopping the piston movement, the energy accumulated in the returning bush is being relieved and rejects the piston to the rear, due to shape memory of elastomeric material. It is the first and the g reatest returning force acting upon the piston . After returning the piston to its rear position , there remains some slight force due to not fully recovering the bush free shape, which force retains the piston in its rear position that is firing position . The object of this invention is illustrated in a preferable 95 embodiment in the accompanying drawings in which fig .1 is a longitud inal cross sectional view of the power piston tool , showing the piston in its firing position , at the moment of firing the cartridge, fig .2 is the same view showing the piston at the end of normal power stroke, at the moment of d riving the 100 fastening element into a base, after initial blocking of returning bush , fig .3 is the same view after driving the fastening element fully into the base, fig .4 is the cross sectional view of middle part of the returning bush and fig .5 is somewhat enlarged view of one of returning bush end in cross section . 105 In power tool shown in fig .1 a piston 1_, mounted for reciprocation within the g uiding barrel 2., is in its firing position at the rear end of the barrel 2. where the piston head 2. is, as near, as possible, to the firing chamber 4 .On piston shank 1_i, between the piston head 2. and fastener guide 5. an elastic 110 returning bush 7_ is situated , being in the shape of one piece bellow, constructed from an elastomer, whose diameters both external and internal are reg ularly varied . The walls of so formed returning bush 7. are approximate in shape to a stack of frusto-spherical segments, creating uniformly spaced swellings 115 and narrowings of wave like structure. I n another embodiment of the invention the returning bush is of shape of stack of frusto- conical segments. I n yet another embodiment of the invention, the returning bush is of shape of the stack of barrel shape segments or/and another surface of revolution segments. The 120 returning bush 7_ has the maximal internal diameter D4 , of its extreme two segments at its both ends, of slightly smaller size than the respective diameter D_2. of remaining segments , so that the bush end segment walls are a little thicker than other segments walls. The internal end surface of external segments 125 is markedly curved outside in such a way, that the position 71 of curvature points of bush ends is clearly distanced from the bush faces 72.. The length of the returning bush 7. is selected in such a way that after initial blocking of the returning bush 7. , the piston shank end face does not reach its extreme forward 130 position and remains at a distance from the base 30. the distance slightly greater than the head height of fastening element 6.. The maxima l external diameter D_l of the returning bush 7. is smaller enoug h than the internal diameter of the g uiding barrel 2., that, after initial blocking of the returning bush 135 Z . its external diameter sti ll remains smaller than i nternal diameter of the g uiding bush 2. ,thus preserving a slight clearance. When the piston 1 is in its firing position , an initial stress within the returning bush 7. remains, enough to ensure that the piston head 12. abuts the bottom of the barrel 2., near 140 the firing chamber 4. . On the piston head 1_2_ there is a plurality of groves 121 , acting as sealing means for firing gases and providing some space to gather impurities. Ports A in the guiding barrel 2. and ports B. and C_ in external barrel 8. are provided to enable the firing gases evacuation after firing . 145 After firing the cartridge upon striking the firing pin 20., the firing gases set the piston 1 into motion , with rapidly accelerating velocity, towards the fastener 6.. Piston head V2,, after passing the port A, opens gas flow connection toward the space between the guid ing barrel 2. and external barrel 8. and 150 from there, through port B_, toward silencer 1_1 and from there, via port C_, into the atmosphere , thus reducing the firing noise and gas pressure in firing chamber, to value close to atmospheric pressure. Accelerated piston 1 strikes against fastener 6. , driving it into base 30., and at the same time, 155 compressing the returning bush 7.. At a distance of several millimeters before fully setting the fastener 6. into the base 30. in itial blocking of the returning bush 7. takes place. In this position the piston shank 1_ end face does not reach its extreme forward position and remains at some d istance from the base 30. 160 slig htly greater than the head height of the fastener 6. and a clearance exists between the guiding barrel 2. and returning bush 7.. The returning bush 7^ at the final stage of the piston 1 motion , forms a shut tubular column ,thus absorbing little firing energy which ensures driving the fastening element 6. to the full 165 depth . I n the event of free flight shot or overd rive of the piston , this shut tubular column will function as a buffer, to absorb the high energy of the piston . After thrusting the fastener 6. into the base 3jD, the piston 1 stops and d ue to elastic memory, inherent in elastomeric 170 material , the returning bush 7. will return the piston to its firing position , where it is ready for the next firing operation , the more easier that the counter-pressure acting upon the piston from the firing chamber 4 , has fallen to atmospheric pressure. To reload the power piston tool , it shou ld be removed from 175 the contact with the base 30., then the springs of firing-pin assembly move the subassembly of piston 1_ and its guiding barrel 2. forward , about a stroke, enabling : first to remove the used firing cartridge 9. from the firing chamber 4 and , secondly, after the tool is pressed anew against base 30. for the 180 subsequent firing , to shift the cartridge belt 40. about one position . By virtue of particular configuration of the elastic returning bush 7_, during the normal power stroke, substantially little energy will be absorbed by the returning bush 7. being pressed , 185 and thus there will be little interference with the velocity of the piston 1, so the bulk of firing energy is used for driving the fastener 7. into base 30., while only small portion of this energy will be used for returning the piston 1_ to its firing position , thus reducing the tool reflection effect and ensuring that the piston J_ 190 will always return to its firing position , after venting the space behind its head 12.. The particular wave like shape of returning bush 7., as well as, thickening the bush 7. end segments and particular position of cu rvature points of bush 7. ends ensures correct functioning of the tool and eliminates the elastomeric 195 bush tendency to curl , which tendency could d rive to a situation when the piston 1_ could be blocked within the guid ing barrel 2.* Besides, the returning bush 7. does not oppose a great resistance to the piston 1_ movement , so it does not brake its velocity and it does not impair the effectiveness of fastening the 200 fasteners and does not provoke any tool reflection effect.

Claims: Claims 1 .A power actuated piston tool with piston automatic return , comprising an external barrel with a guiding barrel situated there within , a piston means mounted for reciprocation within said guiding barrel , between firing position and fastening position , a firing-pi n assembly, situated at the rear end of external barrel , operatively connected therewith , and means for automatic return of piston means from its fastening position to its firing position , situated on piston shank between piston head and fastener g uide, said means for automatic piston return is a one-piece elastic returning bush (7.) made of elastomeric material in the shape of bellow, whose diameters both external and internal are regularly varied , creating uniformly spaced swellings and narrowings of wave like structure. 2. A power actuated piston tool , according to claim 1 , wherein the walls of returning bush (7.) are approximate in shape to a sinusoid , or to a stack of frusto-spherical segments, or to a stack of frusto-conical segments, or to a stack of barrel shape segments and/or other su rface of revolution segments. 3. A power actuated piston tool , according to claim 1 or 2 , wherein the maximal internal diameter (D4.) of at least one segment of the returning bush (7.) at its both ends , is of smaller size than respective diameter (D2 of the remaining segments. 4. A power actuated piston tool , according to claim 1 or 2, wherein the end segment walls of returning bush (7.) are thicker than other segment walls. 5. A power actuated piston tool , according to claim 1 or 2, wherein the internal end surface of external segments of returning bush (7.) is markedly curved outside in such a way, that the position of curvature points (7J_) is clearly distanced from the returning bush (7.) face (72.). 6. A power actuated piston tool , according to claim 1 or 2 , wherein the length of the returning bush (7.) is selected in such a way, that after initial blocking , the piston shank ( V) end face does not reach its extreme forward position and remains at a distance from the base (30.), the distance greater than the head height of fastening element (<3). 7. A power actuated piston tool, according to claim 1 or 2, wherein the maximal external d iameter (D J of the returning bush (7.) is smaller enough than the internal d iameter of the guiding barrel (2Z), that after initial blocking of the returning bush (7_), its external diameter still remains smaller than the internal diameter of the guiding bush (2.), thus preserving the small clearance.

Inventors: CAGODZINSKA BOGUSDAWA, CAGODZINSKI MAREK, ROGOWSKI ZBIGNIEW, CAGODZINSKA, BOGUSDAWA, CAGODZINSKI, MAREK, ROGOWSKI, ZBIGNIEW
Applicants: CAGODZINSKA BOGUSDAWA, CAGODZINSKI MAREK, ROGOWSKI ZBIGNIEW, CAGODZINSKA, BOGUSDAWA, CAGODZINSKI, MAREK, ROGOWSKI, ZBIGNIEW
Application year: 1998
Main classification: B25C1
IPC codes: B25C1