Apparatus for treating a workpiece with a granular media

An apparatus for treating a workpiece with a granular media includes a hopper for storing media and discharging the media into a flow path. A source of compressed air mixes with the media, which is forced through a nozzle for directing media onto the workpiece. A flow sensor includes a beam extending into the flow path and is responsive to flow of media in the flow path to increase and decrease deflection of the beam in response to increasing or decreasing flow of media through said flow path. A proximity sensing device measures deflection of the beam and generates an electrical signal which varies in response to deflection of the beam. The flow path is defined by a conduit having a branch in which the beam is mounted. One end of the beam is mounted on a base in the branch. The base is mounted on a cap closing an open end of the branch, permitting the beam to be easily removed and changed when necessary.

TECHNICAL FIELD

This invention relates to a device for measuring flow of granular media and an apparatus for treating a workpiece with granular media.

BACKGROUND OF THE INVENTION

Treatment of a workpiece with granular media, such as in abrasive blast cleaning and in shot peening, has become relatively common. The flow rate of the granular media in these applications is often set by a fixed orifice or sometimes by a mechanical or electrical valve; however, the actual flow rate is not commonly sensed. The flow rate through the flow path may vary during operation, so it is desirable to have a flow sensor measuring the actual flow rate, which can be processed and displayed to assist in effective control of the process.

Many flow sensors for such applications have been proposed, often using the reaction force of the impact of a falling stream of media onto a slanted surface. However, such flow sensors wear quickly because of the abrasive nature of the impact of the falling media. These devices often have hinges or bearings subject to contamination which affects accuracy and performance. Flow sensing devices incorporating, for example, strain gauges, bearings, or hinges require difficult and delicate procedures for maintenance. Often, delicate wiring connected to the flow sensor is broken or damaged during such maintenance procedures.

SUMMARY OF THE INVENTION

The present invention provides a simple bending beam that deflects as a function of the flow of media, and thus requires no complicated hinges, strain gages or bearings which are subject to damage during maintenance. The bending beam can be easily removed and replaced when necessary. Accordingly, an apparatus for treating a workpiece with a granular media according to the present invention includes a hopper for storing media and discharging the media into a flow path. A source of compressed air mixes with the media, which is forced through a nozzle for directing media onto the workpiece. A flow sensor includes a beam extending into the flow path and is responsive to flow of media in the flow path to increase and decrease deflection of the beam in response to increasing or decreasing flow of media through said flow path. A proximity sensing device measures deflection of the beam and generates an electrical signal which varies in response to deflection of the deflectable member. The flow path is defined by a conduit having a branch in which the beam is mounted. One end of the beam is mounted on a base in the branch. The base is mounted on a cap closing an open end of the branch, permitting the beam to be easily removed and changed when necessary.

DETAILED DESCRIPTION OF INVENTION

Referring now to the drawings, an apparatus for treating a workpiece, such as used in shot peening or blast cleaning operations, is illustrated schematically inFIG. 1. Apparatus10includes a hopper12which stores a granular media, such as shot, sand, or similar material, as indicated at14. Shot14drops from the hopper12into a flow path16defined by a conduit within a housing18. A shot-control device, generally indicated at19(which may be, for example, an orifice or a mechanically or electrically operated valve) controls dispensation of the shot14into the flow path16. The flow path16terminates in a mixing chamber20. A supply of compressed air, generally indicated at22, is communicated with the mixing chamber20via a supply hose24, and a blast hose26communicates the mixing chamber20to a nozzle28, which directs the media onto the workpiece.

As can be seen inFIG. 1, the flow path16is substantially vertical, to permit the media to drop by gravity into the mixing chamber20. Housing18includes a branch30which enters the flow path16at about a 60° angle. The flow sensor of the present invention includes a simple bending beam32which is mounted in the branch30as will hereinafter be described. The beam32is a simple bending beam and requires no bearings or hinges but is simply attached to a rigid member in the branch30. One end34of the beam32extends into the flow path16, where it is impacted by the falling media14. The other end36of the beam32is provided with apertures38(FIGS. 3 and 4) which receive alignment pins40extending outwardly from a base42mounted in the branch30. Screw fasteners43extend through corresponding apertures in a base cap44and through the alignment pins40and are threadedly engaged with base42to thereby secure the beam32through the base42.

The branch30terminates in an open end48. The open end48defines a flange50which is engaged by a cap52. Appropriate fasteners54secure the cap52to the flange50. Alignment pins56receive the fasteners54and orient the cap52relative to the flange50. Alignment pins58extend from transverse surface60of the base42and receive fasteners64which secure the base42to the cap52. An O-ring66provides sealing between the cap52and the flange50. Accordingly, the base42and beam32are removed with the cap52when the latter is removed from the branch30.

A proximity sensor68, of conventional design, is mounted on the branch30and extends through the wall thereof. The end69of proximity sensor68is displaced from the beam32and faces the latter. Sensor68is a non-contact linear displacement sensor and may be, for example, an Omega part number LD701-2-5 displacement sensor. The sensor68responds to changes in the distance between the sensor68and the beam32to generate an electrical signal which varies as a function of the variations in the distance between the beam32and the end of the sensor68.

In operation, media is dropped from the hopper12through the flow path16and into the mixing chamber20, where it is entrained in the air stream from air supply22, which is forced through blast hose26and nozzle28to the workpiece (not shown). The impact of the media on the portion of the beam32exposed to the flow of media in the flow path causes beam32to deflect. The deflection of the beam32varies as a function of the quantity of media impacting upon the beam32. Accordingly, a greater quantity of media impacting on the beam32, which is indicative of a higher flow rate, causes the beam32to deflect toward the sensor68, while a lessening of the flow of media through the flow path16permits the resiliency of the beam32to cause the latter to deflect away from the sensor68. The sensor68generates a signal which, therefore, varies as a function of the distance between the beam32and the sensor68, to thereby generate a signal that is varied as a function of the flow of media through the flow path. This electrical signal can be processed in a normal manner and converted to a display to thereby indicate the actual media flow rates through the flow path16.

Particularly in blast cleaning operations which use abrasive media, impact of the media on the beam32causes wear, thereby requiring service and replacement of the beam32at regular maintenance intervals. This can be easily effected by removing the cap52, replacing the beam32by removal of the screw fasteners43, and then installing a new beam32. The cap52is then replaced on the flange50. The base42and base cap44slidably engage the inner surface defined by the branch30when the base and cap are installed and removed from the branch30, thereby properly orienting the beam32relative to the flow path. Accordingly, proper alignment is assured when the cap52is replaced on the flange50, thereby permitting normal maintenance allowing replacement of the beam32to be completed quickly and easily. Accordingly, flow of media is sensed and displayed using a sensor which is a simple beam and does not require complicated bearings or strain gages requiring wiring which can be damaged during maintenance procedures. Instead, when necessary, the entire beam can be removed and replaced with minimal disruption.

This invention is not limited to the details above, but may be modified within the scope of the following claims.