Electricity: motive power systems – Reciprocating or oscillating motor – Energizing winding circuit control
Reexamination Certificate
2000-01-06
2001-03-13
Ramirez, Nestor (Department: 2834)
Electricity: motive power systems
Reciprocating or oscillating motor
Energizing winding circuit control
C310S050000, C173S091000
Reexamination Certificate
active
06201362
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an electromagnetic hammer having a ferromagnetic moving mass. Such hammers are used, for example, on sites where civil engineering work is being performed, for the purpose of driving piles (stakes or sheet piles) by percussion, and into a very wide variety of types of ground.
BACKGROUND OF THE INVENTION
Electromagnetic hammers having ferromagnetic masses of conventional type, e.g. as described in document JP-A-56 153018, comprise a tube carrying a coil and, in the vicinity of one of its ends, an anvil. A mass of ferromagnetic material is slidably received inside the tube.
The coil is generally made by winding a copper cable onto an associated former. After the coil has been wound, the former together with its coil is fixed on the tube.
In use, the substantially vertical or inclined tube rests via its anvil on the element to be hammered. The coil is then excited by electrical power supply means, thereby generating an electromagnetic field that raises the mass. Thereafter, excitation of the coil is interrupted and the mass, under the action of its own weight, strikes the anvil which transmits the shock to the element that is to be hammered.
However, it has been found that while the mass is being raised, the coil which is not closely and rigidly supported is itself subjected to a reaction force that tends to compact it. In use, these successive deformations of the coil reduce the performance of the electromagnetic hammer and can lead to the coil being damaged.
Another problem encountered is that since the mass is very heavy and needs to strike the anvil on several occasions in order to drive home the element concerned, the electrical power supply means need to deliver a very high instantaneous level of power repetitively and for a very short duration. Unfortunately, when such means are connected to an electrical power supply mains, the large current peaks drawn suddenly and repeatedly from the mains give rise to voltage drops that are repeated at short intervals, giving rise to a “flicker” effect. The user then has to take out a subscription corresponding to the maximum level of power consumption, even though this level can be several times the mean level of power consumption. When the power supply means comprise an independent generator, then the current peaks drawn from the generator give rise to variations in the speed of the engine of the generator. This gives rise to significant wear on the engine and to an abnormal amount of exhaust fumes being produced.
Documents FR-A-2 015 204 and FR-A-2 581 100 illustrate electromagnetic hammers of the above-described type, in which the means for delivering electrical power to the coil comprise a battery of capacitors. The capacitors accumulate energy in electrostatic form and release it in a very short length of time. The capacitors suffer from the drawback of being expensive and of having a lifetime that is relatively short because of the high rate at which they are charged and discharged. The electrical circuit is also generally complicated.
In certain uses, it is necessary for the electromagnetic hammer to deliver shocks of lower energy and at a high frequency. Unfortunately, the capacitors behave like short circuits at the beginning of charging so they must be associated with a current limiting choke and a resistor so as to limit the current drawn from the mains. In addition, the capacitors and the coil form an oscillating circuit whose resonant frequency determines the maximum frequency of the blows. To obtain a higher frequency, it is necessary to reduce the number of capacitors. That kind of operation is not suitable for being performed on a worksite. In addition, the power of the blows and their frequency are varied by varying the voltage to which the capacitors are charged. Such variation can sometimes be difficult due to the complexity of the circuit.
SUMMARY OF THE INVENTION
An object of the invention is to propose an electromagnetic hammer whose structure enables it to generate high power shocks over a wide range of frequencies, and that provides high performance.
To achieve this object, the invention provides an electromagnetic hammer having a ferromagnetic moving mass, the hammer comprising both a tube designed to rest via an anvil against an element to be hammered, carrying a peripheral coil, and slidably receiving the mass inside itself, and electrical power supply means connected to the coil to excite it so as to generate an electromagnetic field for raising the mass, the mass striking the anvil under the action of its own weight when the coil is no longer excited, in which hammer the coil is made by being wound around the tube, the tube being made of a non-magnetic material and having means for taking up axial forces and for transmitting said forces to the anvil while the mass is being raised.
Thus, the coil is rigidly and closely supported by the tube so that it is subjected to substantially no deformation by the reaction force due to raising the mass. The performance of the hammer is thus not subjected to limitation and remains constant. The coil also presents a long lifetime. Furthermore, the reaction force to lifting is transmitted to the anvil and to the element to be hammered via the means for taking up and transmitting axial forces, such that said reaction force is used for the purpose of driving the element. The element is thus driven not only when the mass falls, but also while it is being raised. As a result the electromagnetic hammer presents a high degree of effectiveness and high efficiency.
In an advantageous embodiment of the invention, the means for taking up axial forces and for transmitting said forces comprise first and second reinforcing rings between which the coil is wound around the tube.
Thus, the reinforcing rings perform two functions. Firstly they make it easier to wind the coil around the tube by forming two cheek plates for the coil, and secondly they serve to take up and transmit to the tube a portion of the reaction force to which the coil is subjected while the moving mass is being raised.
Advantageously, in this embodiment, the means for taking up axial forces and for transmitting said forces further comprise two end rings each located in the vicinity of a respective end of the tube, and reinforcing spacers extending parallel to the longitudinal axis of the tube between each of said reinforcing rings and the adjacent end ring.
The reinforcing spacers serve to take up and transmit axial forces, thereby further reinforcing the tube.
According to another particular characteristic, the tube is covered by a soundproofing cowling extending over the entire length of said tube and preferably beyond its bottom end in such a manner as to cover the anvil and a top portion of the element to be hammered.
In which case, advantageously, the tube has air exhaust orifices in the vicinity of its bottom end, and the cowling has air exhaust orifices close to its top end so as to direct the air that escapes from the tube over the coil while the mass is moving downwards, thereby cooling said coil, an empty gap existing between the coil and the cowling.
Thus, the air displaced by the movements of the mass escapes via the orifices in the tube and is channeled by the cowling to the orifices formed at the top end. The air is thus forced over the coil so that heat is exchanged between the air moved in this way and the coil, thereby providing effective cooling for the coil.
Preferably, the cowling has guide elements at its bottom end for guiding the element to be hammered.
This makes the element easier to drive, and guarantees that the tube is supported by the element to be hammered.
In which case, preferably, the guide elements have respective top ends provided with damping pads associated with the anvil.
Thus, if the element to be hammered has penetrated into the ground too easily under the effect of the mass falling, the blow on the anvil is damped. This can happen, for example, in loose soil.
Also advantageously, the cowling has a top end presenting a central op
Enterprise de Travaux Publics et Prives Georges Durmeyer
Friedman Staurt J.
Jones Judson H.
Nixon & Peabody LLP
Ramirez Nestor
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