Tool driving or impacting – Impacting devices – Spring bodily cyclically moved with hammer head
Patent
1979-09-07
1986-09-02
Reynolds, Wm. Carter
Tool driving or impacting
Impacting devices
Spring bodily cyclically moved with hammer head
173119, 173139, A01B 3300, A01B 500
Patent
active
046090541
DESCRIPTION:
BRIEF SUMMARY
Problems are caused at a variety of workplaces, such as engineering shops etc., by disturbing and harmful noise from tools of impact type such as, on the one hand, pneumatic chipping hammers, scaling hammers and the like, and on the other hand, manually powered tools such as hammers, sledge-hammers and the like. The present invention is concerned with an impact element for tools and devices of impact type which in its mode of action brings about an acoustically damping elongation of the pulse of force.
The collision of two masses (in air) generates a pulse of force the shape of which is a function primarily of the power expended and of the rigidity of the colliding masses. The power expended is dependent primarily on the opposed kinetic energies of the masses and on the duration of the collision. The rigidity depends mainly on the properties of the materials constituting the masses--and the points of the latter involved in the collision--as well as on the area of the colliding faces and the duration of the collision. The usual energy losses are in the form of an air wave, a temperature rise, structure-borne sound vibrations and acoustic wave propagation. Irrespective of the purpose of the collision and of the means by which it is brought about--i.e. irrespective of whether the technical application is chipping, hammering etc., --the pulse of force is the primary factor both with regard to the technical performance and to noise generation.
A pulse of force representing a quantity of kinetic energy given up by an impact element can be illustrated graphically, as shown in FIG. 3 appended hereto, by a graph with a vertical force axis and a horizontal time axis. The curve of the pulse rises, while moving along the time axis, from zero to a peak value and then falls back to zero, at which stage the whole of the energy has been given up. The area enclosed between the curve and the time axis represents the quantity of energy given up. Curves 1 and 2 on the graph enclose approximately the same area, i.e. they represent the same amount of energy. Curve 1 illustrates a rapid pulse, where the area representing the energy has a short extension along the time axis and consequently reaches a higher maximum along the force axis, while Curve 2 shows a pulse having a greater extension in time and a lower maximum level of force. In an operation such as the removal of welding scale from sheet steel by means of a pneumatic scaling hammer fitted with a chisel and of conventional type without a pulse elongating device, the curve of the pulse obtained approximates to Curve 1. The high maximum level is advantageous for the technical performance, i.e. the working efficiency of the tool, but it also gives a steeply rising and falling curve with a short extension along the time axis, resulting in a high noise level. Thus the problem to be solved is to shape the curve so as to obtain, on the one hand, an adequate maximum level of force and, on the other hand, suitable curve gradients with respect to the time axis at all phases of the force cycle so as to achieve both satisfactory technical performance and also acoustic damping.
The pulse of force is composed of numerous sinusoidal vibrations which in combination determine the shape of the pulse. By modification of the pulse some of the component vibrations can be eliminated or reduced. If certain frequencies are absent from the pulses of force delivered, for example, to a metal plate by a scaling hammer or similar tool, this implies that vibrations of these frequencies will not be excited in the plate (the so-called structure-borne sound) and, further, that the radiated air-borne noise will lack these components. Which frequencies it is most desirable to eliminate or reduce depends on the work being performed. In the case of work with a pneumatic scaling hammer the most troublesome frequencies are generally those between 1000 Hz and 4000 Hz. In the case of the impacts of a sledge-hammer on a large metal plate the acoustic spectrum is dominated by lower frequencies.
The above-mentioned
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Edstrom Kjell
Nilsson Goran
Wiklund Henry
Munson Eric Y.
Reynolds Wm. Carter
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