the centroid of the mass of the curved segment with the stabilizing fin
It is well known that the integrity of concrete structures is improved by insuring that the wet concrete poured into the form is substantially homogeneous; that is, with the aggregate spread and evenly distributed and all voids or air pockets being eliminated. A typical dynapac concrete vibrator includes an electric or gasoline motor connected through a flexible drive cable within a sheath to the vibrator head. The key to success in assuring the proper spreading of the aggregate and eliminating of the voids in the wet concrete is to provide an intense, reasonably high frequency and amplitude vibration of the head.
The curved segment formed by this machining process provides an imbalance so that upon rotation around the pintle shafts at the ends, the desired vibration is induced. Typically, the attempt to provide a more intense vibration, and thus provide for better aggregate spreading and void elimination, has been concentrated on providing different forms of motors to drive the rotor.
As a point of reference, the centroid of the mass of the curved segment with the stabilizing fin, is positioned appreciably closer to the center of rotation, than in a mass without the fin, as proposed in the prior art ‘222 patent. Thus, while the design of the ‘189 patent may maintain increased rotor stability and strength to resist lateral flexing in the casing, the intensity of the vibration at a given rotating speed is significantly reduced.
This latest approach is simply to increase the size of the driving motor and use a speed enhancer to drive the rotor faster. While this does increase the vibration frequency, and thus to some degree the intensity, the cost of the unit is increased greatly, and of course the added cost and maintenance requirements is a significant negative factor. Typically, the driving speed for this type of concrete vibrator is in the range of 10,000-12,000 rpm. The engine required is typically a four cycle design, which adds additional cost to the unit. This more powerful engine is required in order to maintain sufficient torque to drive through the speed enhancer to reach the required high speed of the rotor.
Therefore, it should be appreciated from reviewing the foregoing description of the known prior art, a need is identified for an improved concrete vibrator, particularly with respect to improving the efficiency of the vibration to provide better aggregate spreading and filling of the voids and air pockets, while at the same time providing such a vibrator that is lightweight and portable.
In accordance with one important aspect of the invention, the rotor includes a curved segment along one of its sides that extends in an arc of less than 180°. By eliminating a portion of the mass below the center line of the rotor, its centroid is positioned in a highly effective relationship with respect to the rotary axis. This positioning or offset of the centroid provides maximum useable vibration to properly distribute the aggregate and to fill or eliminate voids in the wet concrete.
A tubular support assembly is provided on the frame of the motor and surrounds the output shaft. Advantageously, the tubular support assembly serves as a convenient handle for the motor and includes a throttle lever and kill switch for the convenience of operation. A flexible sheath and drive cable is connected between the output shaft of the motor and the drive shaft of the rotor. This support and control arrangement adds to the easy maneuverability of the vibrator.
In addition, the need exists for simplifying the unit to hold down the initial cost and to minimize maintenance requirements over the life of the unit. Overall, the concrete vibrator hose of the present invention should significantly enhance the ease and efficiency of use by the worker, to not only provide an increase in productivity, but to minimize fatigue.
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