Sand Blasting Apparatus

Abstract

A sand blasting apparatus with a cylindrically shaped, suction bell with a hollow interior, a workpiece holding disc which receives a workpiece and seals the open end of the bell, a slotted disc within the bell and above the workpiece holding disc in the abradent path for creating cyclonic downward flow and a vacuum system applying a vacuum to an opening near the open bell end to remove the abradent.

Description

The invention relates to a sand blasting apparatus, especially for eroding or balancing electronic components, such as thick-film circuits supported by a holding means. Apparatuses of this type normally have protective walls positioned about the sand blasting nozzle, which walls are intended to prevent excessive spreading of the sand beyond that portion of the surface which actually is being processed. Moreover, in most cases there is further provided a suction means at the level of the structural component to be processed.

Known sand blasting apparatuses of this type primarily are disadvantageous in that reliable sealing of the sand blasting area cannot be obtained, this resulting in continual contamination of the processing facilities which contamination particularly also causes frequent troubles in operation. These disadvantages are the more apparent especially in automatic and semi-automatic processing machines wherein, on the one hand, a reliable sealing would be of particular importance in the interest of the mechanical parts provided for performing the automatic sequence of operations, and wherein, on the other hand, a satisfactory sealing heretofore could not be obtained in the first line because of the automatical supply and discharge (e.g. by means of special conveyor belts) of the components to be processed.

Accordingly, the invention is based primarily upon the object of providing a sand blasting apparatus which prevents in optimum simple manner the egress of sand beyond the actual processing area. According to the invention, this object in the first line is solved in that the sand blasting nozzle and said holding means are each disposed on one of a pair of complementary components which in their engaged condition enclose said nozzle and said holding means within a hollow space being substantially sealed relative to the exterior of said space, whereby it is of particular advantage when the nozzle is positioned within a suction bell or jacket having an opening which is adapted to be closed by means of a disc. According to the invention, permits positive enclosing of the processing space with a simple configuration of the disc for the holding means and of the suction bell or jacket, without any additional cover means, whereby it is expedient that the suction bell or jacket opens downwardly and is provided with a rubber sealing ring with said disc being adapted to be pressed against said sealing ring with engagement.

The invention is particularly suited for use in apparatuses for the successive erosion or balancing of components mounted on at least two holding means. If the holding means are each positioned on an associated one of a plurality of discs, and said individual discs are adapted to be moved sequentially beneath the bell or jacket, a positive sealing or isolation can be obtained with automatic operation, whereby either the disc holding means may be loaded manually for every cycle of operation, or whereby sequential, automatical charging of the holding means with automatic discharge after the processing operations is rendered possible. Precise positioning of the disc, being prior condition for the aspired positive sealing can be obtained in particularly good manner if according to the invention the discs are each arranged on a turntable so as to be adapted to be positioned beneath the bell or jacket, or if there is provided means for separately lifting said discs beneath the bell or jacket, whereby it may be advantageous if the turntable is lifted as a unit so that the respectively positioned disc is thereby brought into sealing engagement with the opening of the bell or jacket.

According to the invention, the egress of sand can be substantially completely prevented if a suction conduit or vacuum line is connected with the hollow space formed by the components, and if the cross-sectional area of an air inlet and the degree of sealing between the components is selected such that there exists a vacuum within the hollow space during the sand blasting operation when the components are engaged with each other, whereby it is advantageous if the direction of suction is aligned with the direction of the flow of sand by positioning the air inlet in the upper portion of the bell or jacket and the suction conduit in the lower region of the bell or jacket. In this case, the air inlet may be provided either in the bell or jacket itself, or adjacent the holding means on the disc.

If the air inlet is provided with guide vanes such that the entering air is placed under turbulence to flow in the manner of a cyclon downwardly within the bell or jacket towards the outlet, as an important feature of the invention there may be provided thorough cleaning of the disc and of the components per se from sand particles so that no sand residues are allowed to enter the remainder of the apparatus after the separation between the bell or jacket and the disc.

Hereby, the aspired cyclon-type turbulence or swirling may be realized in particularly effective and simple manner if the guide vanes are formed by a disc or plate being provided with obliquely extending slots having point or radial symmetry. On the whole, the subject matter of the invention has to be seen in the novel individual features and in combinations of the features employed in the invention.

In the following, preferred embodiments of the invention are explained in greater detail by referring to the drawings, wherein:

FIG. 1 is a partial sectional view of a suction bell or jacket having a disc-shaped support plate for the holding means of a thick-film structural component and structure for supplying a sand blasting stream for application to the workpiece and removing the stream from the bell or jacket;

FIG. 2 is a plan view of the disc or plate according to FIG. 1;

FIG. 3 is a perspective view of a sand blasting apparatus comprising four discs or plates positioned on a turntable;

FIG. 4 is a sectional view of a modified suction bell or jacket having guide vanes; and

FIG. 5 is a plan view of the guide vanes according to FIG. 4.

According to FIGS. 1 and 2, a suction bell or jacket 1 comprises a sealing ring 2 with the edge 4 of a disc 3 being adapted to be pressed against such sealing ring 2 with sealing engagement. A circuit substrate 6 of a thick-film circuit is fixedly positioned within a recess 5 of the disc 3 and is correspondingly blasted by the sand blasting nozzle 7 after the disc 3 has been placed into the suction bell or jacket 1.

Sand blasting nozzle 7 is fed an air stream enriched with an abrasive powder such as aluminium oxide. This air stream comes from a mixing chamber 8 of known state of the art, which is supplied by a common air pressure pump system 9.

The disc 3 is mounted to a slide 10 of vertical movement to be moved up and down for change of substrate on the disc after abrading by the jet stream abradant and reloading the disc for the next abrading cycle.

For further explanation of a practically constructed arrangement, FIG. 3 illustrates a turntable 8 that can be turned by a definite angle, in the case shown of 90 degrees, positioned beneath the suction bell or jacket 1, which turntable has attached thereto four discs 3 each adapted to receive circuit substrates. The turntable 8' is adapted to be positioned beneath the suction bell or jacket in such manner that each of said discs 3 may be placed into the bell or jacket 1 when the turntable 8' is raised or lifted. Since the discs 3 are lifted jointly with the turntable 8', one single lifting mechanism only is required for the turntable instead of requiring one mechanism for each of the discs, this providing economical savings especially in the case of a greater number of discs.

FIG. 4 illustrates the suction bell or jacket 1 in combination with a vacuum line 13 and an air inlet 14. As shown at 15, the inflowing air is subdivided into separate air flows by slots 12 provided in a plate 11 and acting as guide vanes, which flows, after their egress from the slots 12, propagate in spiral fashion through the suction bell or jacket and flow out through vacuum line 13 after having reliably cleaned the circuit substrate 6 and the disc 3 from sand residues.

FIG. 5 shows the symmetrical arrangement of the slots 12 formed in plate 11, which arrangement with a minimum amount of constructional expenditure ensures optimum cleaning by means of a plurality of individual air flows.

The air flown through the vanes, which may be performed by slots in a disc of same diameter as the bell as well as by small stripes of metal sheets or any other material arranged in such a manner that a guide is formed to direct the air stream to a helical stream. This helical downward stream leaves the suction bell via the tangentially connected vacuum line 13 without changing its streaming direction. By this, the abradant particles which are re-propelled by the surface of the substrate being abraded, are accelerated to follow the helical air stream through the exit pipe 13.

The separate air flows mentioned above really exist only between the slots or the guide vanes. They recombine again when leaving these vanes, although different stream velocities in the helical air movement may still exist, which is of negligible effect to the function of the suction bell system. It may, however, support the cleaning effect of the air stream at the level of the bottom disc and the substrate especially when the substrate is not a plane plate but has some height and forms of more complexity where the abradant tends to deposite in corners or edges. In these cases, the vanes are formed in such a way to direct parts of the air stream towards these corners to perform better cleaning process.

Claims

We claim:

1. Apparatus for sand blasting a workpiece comprising:

a roughly cylindrically shaped suction bell having a hollow interior, a roughly circular bottom opening, a top opening and an opening adjacent said bottom opening,

a workpiece holding disc adapted for closing said bottom opening in a sealing relation with said workpiece within said hollow interior of said suction bell,

means mounted within said hollow interior and in communication with said top opening for receiving and applying a sand blasting stream to a workpiece in said hollow interior, including disc means mounted within said hollow interior adjacent said top opening and having a plurality of slots extending through said disc at an angle to the axis of said bell for creating cyclonic downward flow of the stream onto said workpiece, and

means connected to said bottom opening for applying a vacuum to said opening adjacent said bottom opening to remove said stream.

2. The apparatus as in claim 1 wherein said slots are symmetrically disposed about said axis.

3. The apparatus as in claim 1 wherein said holding disc includes a sealing ring for engaging the periphery of said bottom opening and means for mounting said workpiece.

4. The apparatus as in claim 1 wherein said holding disc includes means for holding a plurality of workpieces.

5. The apparatus as in claim 1 wherein said removing means includes means for providing a vacuum within said hollow interior.