Blasting machines have been and are presently in use for cleaning various surfaces such as those on stationary tanks, ships, road surfaces, etc. by directing abrasive material at high velocity against the surface being cleaned. The apparatus for this purpose typically includes a centrifugal wheel or other propelling means for generating the energy necessary to direct the abrasive with sufficient force to remove debris and other material from the surface to be cleaned. A recovery apparatus is employed to recover both the spent abrasive and any debris generated as a result of the impact of the abrasive with the surface under the high velocity. The debris and abrasive are then typically passed to a collection hopper for delivery to the propelling or blasting device. During delivery of abrasive to the hopper air is often passed in contact with the abrasive to remove the debris before the abrasive is directed to the hopper for reuse in the blasting device. The nature of the blasting process often requires only a relatively simple abrasive-cleaning operation to place the abrasive in form for reuse.
The recovery apparatus for this purpose may include a broom apparatus for sweeping the spent abrasive and debris into a hopper located in the lower part of the machine more or less in the vicinity of the opening exposing to the blast a portion of the surface being cleaned. From this lower hopper or bin an elevator can be employed to move the abrasive to a position where it can be delivered to the hopper for gravity delivery to the centrifugal wheel or other blasting device. An alternative to this system is one in which the kinetic energy of the abrasive is employed to direct the rebounded abrasive directly into the upper hopper for reuse in blasting. In this latter situation the abrasive is energized sufficiently to rebound through ductwork to the elevated hopper or other collecting device.
It is between the apparatus for recovering the abrasive and the blasting device where a cleaning operation may be employed to remove debris from the abrasive before it is reused in the blasting device. Typically, the debris is of such a nature that simply passing air across the abrasive as it is being directed toward the hopper or the centrifugal wheel will be sufficient to place the abrasive in the proper form. However, in some cleaning operations this approach to cleaning or removing the debris is not satisfactory. Particularly when cleaning a concrete or asphalt surface such as those represented by streets and highways, in order to remove the stripes or other marking that are along the center or other parts of the surface, the debris generated is so great that the abrasive cleaning systems may not remove sufficient amounts of the debris before the abrasive is recirculated through the centrifugal wheel or other propelling means. The resulting building-up of debris in the system makes the blasting operation less efficient. Moreover, satisfactory abrasive cleaning operations have not been available in compact, mobile blasting machines which are otherwise suitable for cleaning road surfaces.
In the present invention these deficiencies in the abrasive recovering and cleaning operation are overcome. In particular, in compact, mobile blasting machines that must operate in restricted areas, the size and maneuverability of the machine, as well as its adequacy in accomplishing its work efficiently, are important considerations. Problems are, therefore, presented in reaching these goals, and thus providing for efficient and effective recycling of the abrasive while performing adequate cleaning of the abrasive, even when the machine is employed to clean surfaces such as concrete and asphalt that results in the production of greater amounts of debris in the shot compared with a treatment of a metal surface such as steel.
The present invention meets this challenge by relying on the rebound energy of the abrasive to carry the particles from the surface being treated to the upper part of the device where the particles enter and pass through an elongated, multiple cleaning zone chamber for removing substantial amounts of debris from the abrasive. The cleaned abrasive collects in a lower part of the machine and is conveyed to an elevated hopper located in the upper part of the machine and from which abrasive passes to the blasting device such as a centrifugal wheel. These functions are provided in a compact, maneuverable, mobile machine that is convenient and efficient to use, even in cleaning abrading surfaces such as concrete and asphalt.
In the preferred embodiment the abrasive cleaning portion of the machine contains a vertically-positioned chamber in which a series of showers of debris and abrasive are formed and through which air is drawn to remove the debris. The abrasive after having been showered for debris removal is collected in the lower portion of the cleaning apparatus for delivery to the elevated hopper for recycle to the blasting device. To form the series of showers, the chamber can have an array of baffles including a plurality of spaced-apart sets of baffles along the length or height of the chamber. Between the sets of baffles there ae a series of air inlets, and the baffles direct showers of debris and abrasive along a wall having the inlets therethrough. On an opposing wall there are air outlets connected to an exhause fan for drawing the air containing separated debris away from the chamber. In this manner each shower of abrasive and debris is subjected to an air current from the side inlets, through the respective separation zones of the chamber toward the side outlets and ultimately to an exhaust fan for entraining, collecting and removing the debris from the abrasive material. The bottom of the chamber is constructed to return the abrasive to an elevator or other means for recirculation of abrasive to the elevated collection hopper for feeding to the blasting device.
The recovery conduit used to direct the spent abrasive and debris to the abrasive cleaning chamber is configured to direct rebounding abrasive sufficiently inwardly to enter the cleaning apparatus. The recovery conduit receives the removed debris and rebounded abrasive usually in a diffuse pattern, concentrates this stream, while reducing the remaining energy to an acceptable level, and delivers the stream to the abrasive cleaning apparatus. This system thus provides a recovery apparatus which employs the kinetic energy of the abrasive to move the debris and abrasive through a substantial height of the machine in order to accomplish adequate cleaning of the abrasive.
The above discussion is a rather general description of features of the invention in conjunction with some problems which have existed in prior surface-cleaning machines. Other features and advantages of the invention will become apparent in the detailed discussion of the preferred embodiment of the invention which follows.