1. Field of the Invention
The present invention relates to devices for surfacing concrete and, more particularly, to vibrating screeds for concrete surfacing of the type having an elongated blade mounted transversally at the bottom of a pair of hand held handles with a motor being adapted to transmit to the blade a vibratory movement.
2. Description of the Prior Art
Conventional vibrating screeds comprise, for instance, an elongated blade extending horizontally and transversally at lower ends of a pair of handles adapted to be hand held and operated for displacing the screed over a concrete surface. A motor is provided above the blade and between the handles and has its shaft extending vertically downwards from the motor to the blade and is connected thereat such that, with a counterweight or a cam-like arrangement, it imparts oscillatory movement to the blade of high frequency but low amplitude.
The pair of handles permit an easy and constant correction of the level of the concrete with minimum effort. The blade may have different lengths, for example between 4 and 12 feet. A throttle control of the motor is provided at one of the handles such that the speed of the motor may be monitored and adjusted as the blade is displaced over the concrete being surfaced.
For instance, U.S. Pat. No. 4,861,188 issued to Rouillard on Aug. 29, 1989 discloses a method and an apparatus for compacting and smoothing freshly poured concrete during the construction of a floor or other flat surface. The apparatus is a screed divided in two portions. The first portion is used to level, compact and remove excess concrete and the second portion allows the screed to float on the freshly poured and soft concrete.
U.S. Pat. No. 4,848,961 issued to Rouillard on Jul. 18, 1989 discloses a concrete screeding apparatus and, more particularly, an improved portable and lightweight vibrating concrete screed enabling a workman to use same without the need for rigid forms. The screeding apparatus comprises a generally elongated beam having a horizontal surface and a generally vertical surface. A plurality of vibrators are mounted on the beam. The height of the vertical surface diminishes from the centre to the edges so as to increase the amplitude of vibration and, therefore, improve the manoeuvrability of the screed. In addition, the corners formed by the trailing edge and the side edges of the horizontal surface are rounded so as to avoid the penetration of the side edges into the freshly poured concrete.