EP3213870B1

EP3213870B1 - Rotary impact tool and uses of same

Info

Publication number: EP3213870B1
Application number: EP17158516.9A
Authority: EP
Inventors: Filip VANELSTRAETE
Original assignee: Fve Consulting bvba
Current assignee: Fve Consulting bvba
Priority date: 2016-03-02
Filing date: 2017-02-28
Publication date: 2018-12-26
Anticipated expiration: 2037-02-28
Also published as: PL3213870T3; BE1023584B1; ES2717540T3; EP3213870A1

Description

Field of the Invention

The present invention relates to the field of tools used to loosen or fasten nuts or bolts, and in particular to rotary impact tools and the use thereof.

Background

In the fields of construction and mechanical construction, one is often confronted with fasteners (in particular nuts and bolts) that are so tightly engaged with their counterpart that it becomes difficult or impossible to impart the torque required to loosen them by muscle strength alone. Conversely, there are situations where a fastener needs to be tightened to a level that cannot reasonably be achieved by muscle strength alone. It is known in such cases to use an impact-based method to loosen or tighten the fastener, i.e. to repeatedly hit it (or a tool engaged with it) with an impact tool such as a hammer. In order to reduce the amount of effort required to handle the fastener in that way, and to reduce the risk of injury associated with the process of repeatedly hitting the fastener, impact tools have been proposed that use a motor driven mechanism.
An impact wrench may consist of an assembly in which an output shaft or anvil is struck by a rotating mass or hammer. The output shaft is coupled to a fastener to be tightened or loosened, and each strike of the hammer on the anvil applies torque to the fastener. An impact wrench can thus deliver a high torque to the fastener without having to secure the tool to a fixed structure in order to absorb a corresponding reaction torque (as would be the case with a conventional non-impact fastener driver).
It is a disadvantage of the known impact wrenches that the front surface of the fastener must be accessible to the fastener engaging element (hereinafter also referred to as "socket") in the axial direction. The socket of the impact wrench that engages with the fastener typically presents a shallow recess for receiving the fastener. Hence, it is impossible to use a traditional impact wrench as such on a nut that is screwed onto a bolt or threaded rod at some distance from its free end, i.e. leaving a substantial length of the bolt or the threaded rod sticking out from the nut at the free end.
While this general problem has been recognized in literature for conventional non-impact nut drivers, as can be seen for example in US patent application publication no. US 2004/0069096 A1 and in Canadian patent application publication no. CA 2510234 A1 , the solutions proposed in that context depend on a transmission assembly that changes the position of the rotation axis by translation or angular rotation provided by the non-impact nut driver. If such non-impact nut drivers were to be used in applications where high torques must be applied to fasteners, correspondingly high reaction torques would have to be absorbed, which would lead to the highly impractical requirement of securing the tool by attaching it to some fixed structure, which essentially precludes handheld operation of the tool.
WO 2012/138721 A2 discloses a generally hollow rotary impact device for use with an impact wrench, the rotary impact device having an annular exterior surface and including an input member (for receiving the shaft of the impact wrench), an output member (for engaging with the nut or bolt to be acted upon), and an inertia member (for increasing the torque of the rotary impact device). The hollow rotary impact device disclosed in WO 2012/138721 A2 could be used in cases where part of the bolt or threaded rod protrudes from the nut to be fastened or loosened, provided that it has a sufficient length to receive the protruding end of the bolt or the threaded rod. The rotary impact device would need to have a sufficiently heavy inertia member to compensate the spring effect associated with the increased length of the rotary impact device. It is a disadvantage of this approach that the rotary impact device becomes increasingly heavy and cumbersome to handle with increasing operating length.
Further tools are know from US 3,273,428 ; US 5,392,671 ; US 2011/0048175A1 ; US 2013/0239755 A1 ; and US 5,615,587 .
It is an object of embodiments of the present invention to overcome at least some of the stated disadvantages of the prior art.

Summary of the Invention

According to an aspect of the present invention, there is provided a rotary impact tool, comprising: a fastener engaging element mounted on a rotatable shaft; and a drive mechanism arranged to strike a hammer element onto an anvil; wherein said drive mechanism, said hammer element, and said anvil are arranged in a housing; wherein said hammer element, said anvil, and said rotatable shaft are configured to be rotatable around a common axis; wherein said anvil is connected to said rotatable shaft so as to impart a torque pulse onto said rotatable shaft upon being struck by said hammer element; wherein said hammer element and said anvil have a hollow core extending around said common axis; wherein said housing, said rotatable shaft and said fastener engaging element comprise a through hole communicating with said hollow core; and wherein said hollow core and said through hole are arranged to receive an end of a threaded rod bearing a fastener that is meant to receive said torque pulse.
It is an advantage of the present invention that it allows the fastener engaging element to reach the fastener notwithstanding the presence of the protruding end and regardless of its length and without having to lengthen the socket-shaft combination. An increase of energy build-up in the socket-shaft combination by elastic deformation of the latter can thus be avoided. The aforementioned energy build-up is further reduced by the increased area moment of inertia to mass ratio of the hammer-anvil combination, which results from shaping them with a hollow core.
It is a further advantage of the present invention that due to the hollow core of the hammer-anvil combination, the striking surfaces of the anvil are more remote from the common axis of rotation than is the case in prior-art rotary impact tools. This allows the tool according to the invention to operate with lower impact forces, which reduces the wear of the components. This avoids the need to use materials with a high yield point, which are more expensive and more difficult to shape.
The present invention is inter alia based on the insight of the inventor that generating high torque using a light inexpensive handheld power tool requires the socket-shaft combination to be as short as possible, as any energy absorbed by elastic deformation of the socket-shaft combination must be considered as "lost" from the point of view of energy transmission to the fastener. The present invention is also based on the insight of the inventor that the efficiency of the tool can be improved by increasing the area moment of inertia of the anvil/hammer combination, which is achieved herein by shaping them so as to have a hollow core. The present invention is further based on the insight of the inventor that by providing a through hole in the rotatable shaft and the fastener engaging element, a protruding end of a bolt or threaded rod can pass through them.
In an embodiment, the rotary impact tool according to the present invention further comprises means for receiving mains electric power, and said drive mechanism comprises an electrical motor powered by said mains electric power.
It is an advantage of this embodiment that the tool can can be used wherever mains electric power is available, which includes typical indoor settings and professionally equipped outdoor building sites. The means for receiving mains electric power may comprise a power cord with a suitable plug or a socket for receiving such a power cord. The electrical motor may operate on mains power that has been transformed by a suitable transformer. In an embodiment, the rotary impact tool according to the present invention further comprises a battery, and said drive mechanism comprises an electrical motor powered by said battery.
It is an advantage of this embodiment that it provides a lightweight handheld alternative to existing pressure-driven wrenches with similar/comparable torque output.
In a particular embodiment, the electrical motor operates on a rotor axis that is oriented at an angle relative to the common axis or the electrical motor operates on a rotor axis that is at a distance from the common axis, and a gearing mechanism transmits power from the electrical motor to the rotatable shaft.
It is an advantage of this embodiment that the rotation can be generated by a standard electrical motor, which is arranged inside the tool's housing in such a way that it does not impede the passing through of the free rod end on which the fastener to be acted on is mounted.
In a particular embodiment, the electrical motor has a hollow rotor, and the rotor axis coincides with the common axis.
It is an advantage of this embodiment that the general lay-out of the components of the tool is straightforward, and that no complicated transmission is necessary between the motor and the hammer element.
In an embodiment of the rotary impact tool according to the present invention, the rotatable shaft and the hammer element are arranged such that axial travel of the hammer element relative to the rotatable shaft allows the hammer element to disengage from the anvil after impact, and to start a new impact cycle.
This embodiment may be implemented by configuring the hammer element and the anvil in a "Schodeberg"-arrangement. It is an advantage of this arrangement that it allows the rotary impact tool to continue to operate without interruption of manual intervention after each impact.
In an embodiment of the rotary impact tool according to the present invention, the hammer element is equipped with a clutch arranged to move an impact surface of the hammer element in and out of the path of the anvil.
This embodiment may be implemented by configuring the hammer element and the anvil in a "Maurer"-arrangement. It is an advantage of this arrangement that it allows the rotary impact tool to continue to operate without interruption of manual intervention after each impact.
In an embodiment of the rotary impact tool according to the present invention, the fastener engaging element is a snap-on mechanism adapted to receive a removable socket.
It is an advantage of this embodiment that the socket is easily applicable and removable from the anvil member, and allows the use of the tool with different sockets for different sizes and shapes of bolts or nuts.
According to an aspect of the present invention, there is provided a use of the rotary impact tool as described above to loosen or fasten a nut on a threaded rod, wherein an end of said threaded rod is passed through said through hole.
It is an advantage of this use that it provides a method of loosening or fastening nuts to a very high torque with a handheld tool, without requiring the tool to be attached to a fixed structure to absorb a corresponding reaction torque.
In an embodiment of the use of the rotary impact tool as described above, the rotary impact tool is used to loosen a nut from a threaded rod that is arranged to hold formwork in place, after curing or partial curing of concrete poured inside a space defined by said formwork, wherein an end of said threaded rod is passed through said through hole.
It is an advantage of this use that it provides a method of tearing down modular formwork for the pouring of concrete that is much faster, less cumbersome, and less prone to causing injuries than the traditional methods based on manual hammering. The method can be applied with a handheld tool, without requiring the tool to be attached to a fixed structure to absorb a corresponding reaction torque.

Brief Description of the Figures

These and other technical effects and advantages of embodiments of the present invention will now be described in more detail with reference to the accompanying drawings, in which:

Figure 1 illustrates a rotary impact tool according to the prior art;
Figure 2 illustrates typical sockets as are used in rotary impact tools according to the prior art;
Figure 3 illustrates a known anvil of the "Schodeberg" type;
Figure 4 illustrates a known anvil of the "Maurer" type;
Figure 5 presents a perspective view of a rotary impact tool according to the present invention as implemented in an exemplary housing design, shown in a typical use situation;
Figure 6-9 illustrate a rotary impact tool according to a first embodiment of the present invention, using an arrangement of the "Schodeberg" type;
Figure 10-12 illustrate a rotary impact tool according to a second embodiment of the present invention, using an arrangement of the "Maurer" type; and
Figure 13 is a photograph of a formwork wing nut on which the rotary impact tool of the present invention can advantageously be used.

Throughout the Figures, like reference numerals have been used to designate like components.

Description of Embodiments

Throughout the following description, terms such as "horizontal", "vertical", "top", and "bottom" are used with reference to the normal orientation of the tool when in use, as illustrated in the perspective views of Figures 1 and 5.
The operation of known rotary impact tools will be explained with reference to Figures 1-4.
Figure 1 illustrates a rotary impact tool according to the prior art. Its socket 4 has a recess or indentation corresponding to the shape of the nut 1 on which it is designed to act, allowing the socket 4 to interact with the nut 1 and apply intermittent fastening or loosening torque on the nut 1.
As shown in Figure 2b, the socket 4 fits onto the anvil member 6 through a square indentation. The anvil member 6 is hammered upon repeatedly using a cylindrical hammer (not shown), driven by a motor through a drive shaft. A hammer shifting mechanism allows axial travel of the hammer relative to the drive shaft between two successive blows of the hammer on the anvil member 6. Various hammer/anvil mechanisms are known to the skilled person. Figure 3 illustrates an anvil of the "Schodeberg" type, known from US patent no. 2,712,254 to Carl T. Schodeberg . Figure 4 illustrates an anvil of the "Maurer" type, known from US patent no. 3,361,217 to Spencer B. Maurer .
It is immediately clear that the rotary impact tool illustrated in Figure 1 is unsuitable for use on a nut 1 that has a rod end 2 of a substantial length L protruding from it, as it is impossible for the socket 4 to reach the nut 1.
The rotary impact tool according to the present invention comprises: a fastener engaging element, such as a socket mounted on a rotatable shaft; and a drive mechanism arranged to strike a hammer element onto an anvil; wherein said drive mechanism, said hammer element, and said anvil are arranged in a housing; wherein said anvil is connected to said rotatable shaft so as to impart a torque pulse onto said rotatable shaft upon being struck by said hammer element; and wherein said housing, said rotatable shaft and said fastener engaging element comprise a through hole arranged to receive an end of a threaded rod bearing a fastener that is meant to receive said torque pulse. The "hammer element" as referred to herein comprises a hammer, i.e. an element with a surface designed and arranged to strike the anvil. The hammer element may further comprise additional components, such as a hammer cage that guides the movement of the hammer (see in particular the "Maurer" mechanism as described in more detail below).
The high torque output is obtained by accelerating a rotating mass (the hammer) so as to store kinetic energy in it, and then delivering that energy to an anvil by impacting it. The anvil is connected to the rotatable shaft so as to impart a torque pulse onto the rotatable shaft upon being struck by the hammer element. It should be noted that upon being impacted by the hammer element, the fraction of the received kinetic energy that is absorbed as elastic deformation of the anvil-shaft combination is kept to a minimum by designing them to be short and rigid. To this end, the anvil and shaft are preferably designed to have a cross section with a large area moment of inertia; this is achieved at least in part in the present invention by providing the anvil with a hollow core.
Figure 5 presents a perspective view of a rotary impact tool 3 according to the present invention, as implemented in an exemplary housing design, shown in a typical use situation. The tool 3 may be used for loosening or fastening of a nut, bolt or similar fasteners on a bolt or threaded rod 2, a substantial part of which protrudes from the nut. To this end, the rotary impact tool 3 of the present invention has a hollow fastener engagement element (or socket) 4, hammer 5 and anvil member 6; i.e., a through hole (a bore or a generally tunnel-shaped orifice) is arranged so as to allow the rod 2 to pass through it and the socket 6 to reach the nut 1.
As shown in Figure 5, a nut 1 is present on a threaded tie rod or bolt 2, protruding over a substantial length L beyond the nut 1. The rotary impact tool 3 has an integrated or snap-on socket 4. The socket 4 has an indentation corresponding to the shape of the nut 1 on which it is designed to act, allowing the socket 4 to interact with the nut 1 and apply intermittent fastening or loosening torque on the nut 1. If it is a snap-on type socket, it is easily applicable and removable from the anvil member 6, for instance by means of a ball/spring locking mechanism as known to persons skilled in the art, and allows the use of the tool with different sockets for different sizes and shapes of bolts or nuts.
The hollow hammer and anvil member (not shown in Figure 5) allow the tie rod or bolt 2 to protrude significantly beyond the nut 1, while the very short and hollow socket/anvil combination ensures high torque transmission of the rotary impact tool 3 to the nut 1. The nut 1 can have various shapes such as hexagonal, square, rectangular, polygonal, winged with one or more wings, etc. Without loss of generality, Figure 5 and the subsequent figures only illustrate a nut 1 having a hexagonal 3-winged shape and corresponding sockets, but the skilled person will appreciate that the same principle applies to all shapes of nuts, bolts or similar fasteners, and their corresponding sockets.
Thanks to the properties of the rotary impact tool according to the present invention, it can be operated in a hand-held manner in situations where correspondingly powerful non-impact tools would have to be attached to a fixed structure in order to absorb the reaction torques. In practical embodiments, the rotary impact tool is integrated in a hand-held housing. The housing may comprise a substantially cylindrical main body, whose axis is oriented along the axis of rotation of the shaft of the fastener engagement element. A grip portion may be attached to the main body, e.g. a grip of the pistol grip type, allowing a person to hold the tool and to operate an activation switch with the same hand. The activation switch activates the drive mechanism. A further switch may be provided to alternate between clockwise and counterclockwise operation of the tool.
As mentioned above, the rotatable shaft and the fastener engaging element comprise a through hole arranged to receive an end of a threaded rod bearing a fastener that is meant to receive the torque pulses. If any part of the housing of the rotary impact tool is aligned with the rotatable shaft, the through hole must run through the relevant portion of the housing and other components must be arranged to stay clear of the through hole, to allow the protruding end of the bolt or rod to pass through the entire tool. In other words, the through hole becomes a tunnel through the entire tool, allowing the fastener to be accessed by the fastener engaging element. Preferably, the components of the rotary impact tool according to the present invention are arranged in such a way that only the shaft, and the socket lie in the path of the threaded rod, and only these elements (and the walls of the enclosure lying along the same axis) must be provided with suitable bores.
The hammer is driven by a motor, hydraulic, pneumatic or electrical (connected to mains or battery-powered), through a gearing mechanism. The alignment of the motor can be sideways or angled (removed from the axis of the rotating shaft) or alternatively a motor with a hollow rotor can be used (the hollow core surrounding the axis of the rotating shaft). A battery-operated unit with a light electrical motor is preferred, as it allows the tool to be used autonomously.
Thanks to the design of the rotary impact tool, the reaction torque, i.e. the torque to be absorbed by the person operating and holding the tool, is kept to a minimum.
Although numerous hammer/anvil mechanisms have been described in literature, the most commonly used are the so called "Schodeberg" mechanism and the "Maurer" swing mechanism, both having various variants and improvements that are known to the skilled person.
For clarity purposes, the "Schodeberg" mechanism may be briefly described as follows. The driving mechanism drives a cylindrical hammer that has one or more impact surfaces. These impact surfaces impact the anvil, which is arranged to transmit the impact torque via the shaft and the socket. The shaft has a first helical groove and the hammer has a second helical groove. A ball is received in the first and second helical grooves to rotationally couple the hammer to the shaft and permit axial travel of the hammer relative to the shaft. The axial travel of the hammer relative to the shaft allows the hammer to disengage from the anvil after impact, and to start a new impact cycle. Further details may be found in the literature on this topic.
For clarity purposes, the "Maurer" mechanism may be briefly described as follows. The driving mechanism drives a cage member within which is pivotally mounted a swinging hollow hammer member. An output shaft extends through the cage member and through the hollow hammer member and includes forward and reverse impact anvil surfaces. The pivoting point of the hammer element does not coincide with the rotation axis of the output shaft, such that the hammer will swing in respect to the cage as it rotates with the cage. As a clutch is driven in the forward direction, the forward impact jaw on the hammer's internal surface is moved in and out of the path of the anvil jaw on the output shaft by cam action and during an impact blow the inertia of the rotating hammer member acts as automatic means to hold the impact jaw in engagement with the anvil jaw. Further details may be found in the literature on this topic.
It will be clear to the skilled person that these and other known hammer/anvil mechanisms may be used in embodiments of the present invention, provided that the anvil, hammer, and relevant parts of the housing can be made hollow, so as to enable the bolt or threaded rod to protrude (indefinitely) beyond the nut.
Figures 6-9 illustrate an embodiment of the rotary impact tool according to the present invention, based on a "Schodeberg" type arrangement of hammer and anvil. The hollow hammer 5 has a helical groove and is driven by a hydraulic, electrical or pneumatic motor 7 through a cylindrical drive shaft 8 with similar helical groove and a gearing mechanism 9. The position and alignment of the motor 7 is indicative only and can be positioned and aligned differently than shown in the drawings, without affecting the principles as set forth above. Alternatively, a motor with a hollow rotor can be applied. The improved rotary impact tool according to this embodiment furthermore comprises a housing 10, and a hammer shifting mechanism of the "Schodeberg" type, wherein the cylindrical drive shaft 8, the anvil member 6, and the hammer 5 are made hollow. The hammer shifting mechanism allows axial travel of the hammer relative to the hollow drive shaft between two successive blows of the hammer on the anvil member. Further details about the hammer shifting mechanism can be found in the relevant literature, including the aforementioned patent US 2,712,254 , which is incorporated by this reference for this purpose.
Figure 8 presents two views of the anvil-shaft combination for use in an embodiment of the present invention using the "Schodeberg" mechanism.
Figure 8a shows the side of the impact surfaces upon which the hammer element acts. In the illustrated embodiment, the impact surfaces are formed as two protrusions emerging from a disc-shaped body. While the use of two impact protrusions is preferred for symmetry reasons, the skilled person will appreciate that the arrangement can also operate with a single impact protrusion, or a larger number of impact protrusions.
In a traditional impact wrench, the impact surfaces are arranged on a beam-shaped body, as shown in Figure 3. The disc-shaped body as shown in Figure 8 has the specific advantage that it provides a higher area moment of inertia, and thus more rigidity against elastic deformation. This design further promotes the rapid distribution of force gradients over a larger area, such that the maximum material tensions are reduced, which improves the durability of the tool.
Figure 8b illustrates an exemplary shape of a socket. The illustrated configuration can be used with a wingnut having three wings.
Figure 9 illustrates another exemplary shape of a socket, to be used with a hexagonal nut. A socket of the illustrated type could be used as a snap-on accessory for use with hexagonal nuts such as those used in the automotive industry (e.g., for removing the wheels of a car or truck from their axles).
Figures 10-12 illustrate an embodiment of the rotary impact tool according to the present invention, based on a "Maurer" type arrangement of hammer and anvil. Figure 10 provides a cross-section of the rotary impact tool, as seen in a vertical plane containing the common rotation axis. Figure 11 schematically illustrates the modified "Maurer" arrangement, including a hammer 5 and anvil member 6, wherein the anvil member 6 is made hollow. Further details about the "Maurer" arrangement can be found in the relevant literature, including the aforementioned patent US 3,361,217 , which is incorporated by this reference for this purpose.
Figure 11 presents a cross-section of an embodiment of the rotary impact tool according to the present invention using the "Maurer" arrangement. At the periphery, there is a cylindrical housing comprising the hammer element consisting of a rotating hammer cage, which contains the pivoting hammer. The shape of the hammer presents two lobs that impact the anvil. The anvil is shaped as a hollow shaft with a protruding surface. It is typical of this arrangement that the hammer disengages from the anvil after having hit it, by pivoting around its upper hinge. In this way, the hammer element can immediately continue rotating and start a new impact cycle.
Figure 12a illustrates the hollow-core anvil with an exemplary socket 4, as seen from the side of the socket. A socket of the illustrated type could be used as a snap-on accessory for use with hexagonal nuts such as those used in the automotive industry (e.g., for removing the wheels of a car or truck from their axles).
Figure 12b illustrates the hollow-core anvil with another exemplary socket, as seen from the side of the socket. The illustrated configuration can be used with a wingnut having three wings.
A particular use case concerns the loosening of nuts on threaded rods that hold together panels of formwork used for pouring concrete. Modular formwork panels typically consist of a metal structure (e.g., a steel frame) and surfaces of wood, wood derivatives, or plastics. They typically have a width of 1.20 m, and are erected side by side to define the surfaces of the concrete structure that is to be formed. In structures that have parallel or nearly parallel surfaces, such as walls and beams, the formwork elements are erected so as to face each other and (usually horizontally) interconnected by steel threaded rods known as formwork tie rods, having a length of e.g. 1 m. To allow their removal after the curing of the concrete, the formwork tie rods are sheathed by a plastic tube that extends from one formwork element to the opposing formwork element, and the ends of the rod that protrude from the formwork are secured by nuts. A typical nut used for this purpose is the formwork wingnut shown in Figure 13. It has a traditional polygonal (e.g. hexagonal) prism-shaped body with a threaded bore, an optional large disc-shaped flange that contacts the outer surface of the formwork, and additionally a pair of wide-spaced wings suitable for being hit with a hammer.
As concrete is poured into the formwork as a dense liquid, the formwork elements must withstand a considerable hydrostatic pressure, which is directed outwards and pushes the outer surface of the formwork elements against the nuts. As a result, the nuts will become extremely tight by the time they can be removed to tear down the formwork, when the concrete has undergone a sufficient degree of curing. Especially in areas undergoing the largest hydrostatic pressure, it is not practically feasible to loosen the nuts in this situation by manually turning a wrench, as a person cannot exert sufficient force to deliver the necessary torque. Thus, traditionally, the nuts are removed by hitting them (in particular the wings) with a hammer. Using this method, it may take an experienced builder up to one minute to loosen a nut to the point where it can be screwed off of the rod by hand. It is immediately clear that for larger concrete structures, involving large numbers of formwork panels, a lot of time and effort is spent loosening all the nuts, and that the operation is ergonomically inappropriate.
Traditional impact wrenches cannot be used in this situation, because the protruding ends of the threaded rods prevent the impact wrench's socket from accessing the main body of the nuts.
The rotary impact tool according to the present invention may advantageously be used to loosen a nut from a threaded rod that is arranged to hold formwork in place. As the rotary impact tool according to the present invention has a through hole, the protruding end of the threaded rod may be passed through the through hole, allowing the fastener engaging means (i.e., the socket that engages with the main body of the nut) to reach the nut. The rotary impact tool may then be operated to loosen the nut in a convenient and ergonomically safe manner, requiring little strength, and taking significantly less time than the traditional method.
The through hole in the rotary impact tool must have a suitable size to accommodate the protruding end of the threaded rod. For formwork tie rods having exemplary diameters of 10/12 mm (cylinder diameter / thread diameter), 15/17 mm, or 20/24 mm, the through hole diameter must be at least 12 mm, 17 mm, and 24 mm, respectively, to be increased with a sufficient margin to allow the rod to easily pass through the through hole (e.g. 2 mm extra in diameter).
In-the-field measurements of the torque required to loosen a nut from a rod used to hold formwork panels together, near the bottom of the poured concrete volume, indicate that a torque of at least 1350 Nm tends to be required. Accordingly, the rotary impact tool according to the invention preferably delivers a torque of at least 1350 Nm. More preferably, the rotary impact tool according to the invention delivers a torque of at least 2500 Nm, which would allow the tool to be used in situations where concrete volumes of greater height (resulting in higher hydrostatic pressure levels) are poured.
The rotary impact tool according to the present invention may advantageously be used to fasten a nut on a threaded rod or bolt. As the rotary impact tool according to the present invention has a through hole, the protruding end of the threaded rod or bolt may be passed through the through hole, allowing the fastener engaging means (i.e., the socket that engages with the main body of the nut) to reach the nut. The rotary impact tool may then be operated to fasten the nut in a convenient manner, requiring little strength, and taking significantly less time than the traditional method. As the torque that can be imparted by the rotary impact tool according to the present invention may be very high, embodiments of the rotary impact tool of the present invention may be equipped with a torque limiting mechanism to provide the fasteners from being damaged.
While the invention has been described hereinabove with reference to specific embodiments, this has been done to illustrate and not to limit the invention, the scope of which is determined by the accompanying claims. Features that have been described only in the context of any particular embodiment, may be applied to other embodiments to achieve the same technical effect.

Claims

A rotary impact tool (3), comprising:
- a fastener engaging element (4) mounted on a rotatable shaft (8); and

- a drive mechanism arranged to strike a hammer element (5) onto an anvil (6);
wherein said drive mechanism, said hammer element, and said anvil are arranged in a housing (10);
wherein said hammer element, said anvil, and said rotatable shaft are configured to be rotatable around a common axis;
wherein said anvil is connected to said rotatable shaft so as to impart a torque pulse onto said rotatable shaft upon being struck by said hammer element;
characterized in that said hammer element and said anvil have a hollow core extending around said common axis;
in that said housing, said rotatable shaft and said fastener engaging element comprise a through hole communicating with said hollow core;
and in that said hollow core and said through hole are arranged to receive an end of a threaded rod (2) bearing a fastener that is meant to receive said torque pulse.
The rotary impact tool according to claim 1, further comprising means for receiving mains electric power, wherein said drive mechanism comprises an electrical motor (7) powered by said mains electric power.
The rotary impact tool according to claim 1 or claim 2, further comprising a battery, wherein said drive mechanism comprises an electrical motor powered by said battery.
The rotary impact tool according to claim 2 or claim 3, wherein said electrical motor operates on a rotor axis that is oriented at an angle relative to said common axis or said electrical motor operates on a rotor axis that is at a distance from said common axis, and wherein a gearing mechanism (9) transmits power from said electrical motor to said rotatable shaft.
The rotary impact tool according to claim 2 or claim 3, wherein said electrical motor has a hollow rotor, and wherein said rotor axis coincides with said common axis.
The rotary impact tool according to any of the preceding claims, wherein said rotatable shaft and said hammer element are arranged such that axial travel of said hammer element relative to said rotatable shaft allows said hammer element to disengage from the anvil after impact, and to start a new impact cycle.
The rotary impact tool according to any of the preceding claims, wherein said hammer element is equipped with a clutch arranged to move an impact surface of said hammer element in and out of the path of said anvil.
The rotary impact tool according to any of the preceding claims, wherein said fastener engaging element is a snap-on mechanism adapted to receive a removable socket.
Use of the rotary impact tool according to any of the preceding claims to loosen or fasten a nut on a threaded rod, wherein an end of said threaded rod is passed through said through hole.
Use according to claim 9, wherein the rotary impact tool is used to loosen a nut from a threaded rod that is arranged to hold formwork in place, after curing or partial curing of concrete poured inside a space defined by said formwork, wherein an end of said threaded rod is passed through said through hole.