GB1599359A

GB1599359A - Sandblasting machine and method for finishing moulded or cast articles

Info

Publication number: GB1599359A
Application number: GB2551578A
Authority: GB
Original assignee: ISPER SpA
Current assignee: ISPER SpA
Priority date: 1977-06-24
Filing date: 1978-05-31
Publication date: 1981-09-30
Also published as: BE868265A; FR2395109A1; JPS5411164A; IT1080956B; FR2395109B1; CA1097080A; NL7806604A; CH630551A5; DE2826156A1

Abstract

Sandblasting process and machine, in particular for cleaning moulded plastic parts, in which the parts to be subjected to sandblasting are conveyed through a jet of sand. In order to avoid the parts colliding with one another, said parts are conveyed separately. In order to achieve thorough treatment, the parts are conveyed with a rolling movement. The machine has a pipeline (14) with a portion which is formed by a grid (25) and through which the parts, subjected to machining, are conveyed with a rolling movement. A jet of sand originating from a centrifugal sandblasting turbine (11) passes transversely into the rotating pipe portion which is formed by a grid (25) and is where the sandblasting takes place. <IMAGE>

Description

(54) SANDBLASTING MACHINE AND METHOD FOR FINISHING MOULDED OR CAST ARTICLES (71) We, ISPER, SPA, INDUSTRIA STAMPI PLASTICHE E RESINE, a Joint Stock Company, organised and existing under the laws of Italy, of Piazza Milano, Zingonia, Provience of Bergamo, Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a sandblasting machine and method for finishing moulded or cast articles, particularly for trimming mouldings of thermo-setting plastics.

The practice of finishing, or more generally surface-treating articles under production by means of sandblasting is very widespread in modern technology. It is used on all metal articles to be painted, enamelled, metallized, etc., on metal articles produced by casting or moulding to remove burrs, on plastics articles to be painted or metallized to improve adhesion, and on moulded plastics parts for trimming and finishing, to cite just some examples related to the field of the invention, which, although having been developed to satisfy specific problems of resin products, is not limited to these and is extended in its application to related sectors such as those stated.

The moulding, die-casting and injection moulding of resin or plastics articles has been developed particularly in the electrotechnical field for economical reasons and for the ease of incorporating metal parts in the mouldings, which would be impossible in the case of the more esteemed and costly ceramic insulant material. Thus objects have been produced by moulding which are increasingly complicated and in their final stages of assembly, or at least in very advanced stages, such as single or multi-stage electrical switches and commutators. The great economy of such production is due to the complete automation and high productivity rate attained, such that the intervention of direct labour has nearly disappeared. The pieces produced in this manner require only surface finishing to remove casting or moulding burrs.Initially, this operation was carried out by an operator using a jet of sand in a box, and wearing a protective mask. However, this manual operation, besides giving rise to some criticism and preoccupation from the health aspect, is out of step with the whole economy of the production process.

Thus completely automatic sandblasting was necessarily brought in.

The method used at the present time consists of disposing a load of articles in a cavity or cradle on to which a wide jet of sand or grit is directed while the load is continuously agitated or turned in such a manner that the entire surface of each piece is exposed to the jet in various positions. This method has proved valid from the point of view of working efficiency and economy in the amount it contributes to the cost of each sandblasted article, but has a serious drawback which is intrinsic to its system and cannot be eliminated unless the system itself is changed, namely that the pieces inevitably collide with each other as they are turned, and if the pieces comprise delicate projections such as is the case with switches and the like, these can become damaged or broken, and this is reflected in an excessive number of production rejects.To obviate this serious drawback, it has been attempted to pass the objects to be sandblasted one by one in front of the sandblasting jet in various positions, either by passing the article several times in different positions in front of the same jet, or by passing the piece in front of different jets disposed in different positions.

To pass the piece again in a different position, the conveyor, belt, chain or wire carrying the objects is returned in front of the jet, but this allows only two passes with two fixed positions.

More simply, the pieces are loaded several times in different positions on the same conveyor belt passing in front of the fixed jet.

This requires an operator for the loading and unloading. An attempt has also been made to load the pieces on to rotatable supports on the conveyor. This can be successful in the case of large costly pieces, but would be too expensive for pieces intended to be sold cheaply. Thus the problem of sandblasting articles having a shape even slightly compli- cated has not yet found a general satisfactory solution.

According to the present invention a sandblasting method for finishing moulded or cast articles is provided wherein the articles to be sandblasted are made to pass in front of a sandblasting jet, individually in a single pass within a reticulated portion of a conduit.

According to another aspect of the invention there is provided a sandblasting machine for finishing moulded or cast articles comprising a conduit arranged so that, in use, the articles to be processed will pass under gravity past a sandblasting jet which is directed into the interior of the conduit transversely.

In order that the invention may be more fully understood, a preferred embodiment in accordance therewith will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a sandblasting machine; Fig. 2 is a side view from the right hand side of the machine as seen in Figure 1; Fig. 3 is an axial section in elevation of the device of Fig. 1 for single pass sandblasting; and Fig. 4 is an axial section through a turbine which generates the sand jet.

Reference will now be made in particular to Figures 1 and 2 which show a machine or installation for carrying out a sandblasting operation, indicated generally by the reference numeral 1. It comprises a housing 2 with an upper support surface 3 from which projects a stepped part 4, which is connected by way of a connector 5 to a suction fan 6 comprising a motor 6'.

The housing 2 is supported on four feet 7, between which there extends a hopper 8 in the form of a lower appendix to the housing 2. A unit formed from an electric motor 10 and a centrifugal sand jet turbine 11 is fixed on to the surface 3 by way of a base 9. A vertical screw conveyor tube 12 is connected to the discharge mouth of the hopper 8 (Fig.

2) to gravity-feed the turbine or turbo-ejector 11 with sand in closed cycle. The screw inside the tube of the conveyor 12 is driven by an electric motor 13. The housing 2 is traversed, in a plane normal to the axis of the turbine 11, by a tubular conduit 14 (Fig. 3) which represents the feeder and single-pass conveyor for the pieces to be sandblasted. The turbine 11 feeds its sand jet towards the interior of the housing, along the axis of the conveyor 14 as described hereinafter. A door 15 enables the interior of the housing 2 to be inspected and maintained.

Figure 3 shows an axial section, in a vertical plane, through the entire portion of the conveyor 14 which traverses the housing 2, together with part of the two conveyor projections thereof. The conveyor tube 14 is disposed with its axis inclined downwards from left to right in Fig. 3, to ensure that the conveyed pieces move forward while rolling, when the tube is rotated. It is mounted in the opposing walls of the housing 2 by way of two rotatable supports 16, each constituted by a flange 17 and backing flange 18 which clamp between them the edges of the perforated wall of the housing 2, and house between them three rolling bearings 19 distributed peripherally 12û apart, on which the tube 14 rolls by way of a sleeve 20 rigid with the tube. A coupling covering 21 is provided to protect the bearing from the sand.

The sleeve 20 of the upstream coupling is also used for transmitting rotary motion to the tube, generated by an electric motor 22 and transmitted to the tube via a reduction gear 23 and belt 24. The conveyor tube 14 is interrupted over at least the entire portion lying within the region of the sandblasting jet, indicated orientatively by the dashed lines running from the turbine 11, of which the impeller is indicated diagrammatically in Fig. 3.

Over this portion, the tube is replaced by a cylindrical basket or cage 25, of the same diameter as the tube 14, and mounted in alignment therewith by means of two end flanges 26. Advantageously, the basket or cage portion 25 has wide meshes compatible with the dimensions of the pieces to be sandblasted, and fairly thin wall wires or bars. To obtain the necessary mechanical connection for maintaining alignment and transmitting motion between the two portions of the tube 14, a stirrup coupling is provided externally and consists of two flanges 27, each disposed at the mouth of a respective portion of tube 14, and facing the corresponding flange 26. The flanges 27 are joined firmly together by two external stirrups 28 disposed 1800 apart. This mechanical coupling enables the basket 25 to be easily replaced without moving the tube 14.

Figure 4 shows the turbine or turbo-ejector 11, which comprises essentially a casing 30 fixed to the base 9. Rigid with the casing 30 there is a sleeve support 31 in which the turbine shaft 32 is supported on two support bearings 33 and a thrust bearing 34, and is driven by a pulley 35 with three races. The impeller carried by the shaft comprises two sets of blades, namely a central set in the form of teeth on a rotating distributor 36, and a set in the form of centrifugal injection blades 37.

The teeth of the rotating distributor 36 rotate within the space defined by the blades of a fixed distributor 38. The fixed blades of the distributor 38 delimit therebetween radially directed slits through which the panel is propelled by the rotating distributor. The turbine 11 is disposed with its axis horizontal and its centrifugal discharge port pointing downwards, as indicated by the arrow. An elbow connector 39 gravity-feeds the sand axially to the tur bine, by receiving it from the screw conveyor 12. A nozzle injector tube 40 feeds water under controlled conditions into the stream of sand to moisten and lubricate it.

The description of operation of the installation will begin with the turbine heretofore described. The sand reaches its central region where the rotating distributor 36 feeds it by way of the fixed distributor 38 uniformly on to the blades of the impeller 37, which project it into a volute delivery path defined by the casing 30, as in the case of a centrifugal pump.

As shown in Fig. 3, the wide jet of sand or grit is directed and centred on the basket 25 of the tubular conveyor 14. The articles to be sandblasted, for example of thermo-setting resin and not shown, are fed continuously into the conveyor 14 one behind the other, the minimum distance apart without touching each other. The speed of rotation of the tube and its slope are chosen such that for a given width and efficiency of the sandblasting jet, each article rotates about itself a number of times and remains exposed for the time necessary for its entire surface to be sufficiently sandblasted. The rotation of the tube helps the article to roll downwards along the tube.

The jet also aids the transverse rolling of the article, which therefore passes through all possible positions. As the pieces follow closely behind each other, the jet is very well utilized, and as it is proportioned uniformly over each piece and over the entire surface of each piece, the exposure thereof can be reduced to the necessary minimum. This is in contrast to the sandblasting of articles which are rotated in a heap, because in this case there is a high statistical influence, which means that a factor even higher than 2 would have to be exceeded in order to obtain a high probability of sand blasting all the pieces, and even then there are always pieces which are sanded to an excessive or insufficient degree. The fan 6 maintains a certain sub atmospheric pressure in the housing 2, to prevent dust leaving through the tube 14. The air is then purified or fed to a stack.It is advisable to make the basket 25 and stirrups 28 of abrasion-resistant material, or better still make them coated, for example enamelled, or covered with special anti-abrasive resins, or coated with rubber specially resistant to sandblasting. The tube 14 is also preferably coated, for example with plastics, so that there is no danger of the pieces suffering damaging impact during rolling. It should be noted that this ideal operation has been obtained by means of a structure and a mechanical system which are extremely simple and of low cost. The entire movement is provided by a small geared motor unit and a direct belt drive.Thus, relative to equivalent previous installations, improved processing with elimination of causes of rejects in this processing stage is obtained, together with greater productivity, completely auto matic continuous operation, and lower installation cost. If desired, even though of less merit, the turbine sander could be replaced by any air jet sander, and in all cases the jet could point in any other sideways direction or from below, and the tube could be made to vibrate instead of rotate.

WHAT WE CLAIM IS: 1. A sandblasting method for finishing moulded or cast articles wherein articles to be sandblasted are made to pass in front of a sandblasting jet, individually in a single pass, within a reticulated portion of a conduit.

2. A sandblasting method according to claim 1, wherein the articles are made to roll through the sandblasting jet.

3. A method according to claim 1, wherein the articles are made to pass through the sandblasting jet by vibrating the conduit.

4. A method as claimed in claim 1, wherein the articles are made to rotate in front of the sandblasting jet within the conduit which is rotated and in which the articles being pro cessed move axially.

5. A method according to any one of the preceding claims, wherein the conduit is kept inclined downwards in the direction in which the articles being processed are fed.

6. A method as claimed in any one of the preceding claims, wherein the sandblasting jet is directed such that it strikes the articles in a direction transversal to the feed direction of the articles.

7. A method as claimed in any one of the preceding claims, wherein the articles to be sandblasted are made to move forward and roll in sequence one at a time.

8. A method according to claim 7, wherein the articles are of thermosetting plastics material.

9. A sandblasting machine comprising a conduit arranged so that, in use, articles to be processed will pass under gravity past a sandblasting jet which is directed into the interior of at least a portion of the conduit transversely.

10. A machine as claimed in claim 9, wherein said conduit comprises a conveyor tube inclined downwards in the feed direction, and having a portion defined by an open-mesh arranged in front of the sandblasting jet.

11. A machine as claimed in claim 9 or 10, wherein said conduit passes through a closed housing, this latter embracing the portion towards which the sandblasting jet is directed in use of the machine.

12. A machine as claimed in claim 11, wherein said conduit is rotatably mounted in the housing walls, and is rotated by an electric motor, a reduction unit and a belt drive which directly engages with the conduit.

13. A machine as claimed in any one of claims 9 to 12, comprising a centrifugal turbine for producing a sandblasting jet, the turbine being such as to directly accelerate sand

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

bine, by receiving it from the screw conveyor 12. A nozzle injector tube 40 feeds water under controlled conditions into the stream of sand to moisten and lubricate it.

The description of operation of the installation will begin with the turbine heretofore described. The sand reaches its central region where the rotating distributor 36 feeds it by way of the fixed distributor 38 uniformly on to the blades of the impeller 37, which project it into a volute delivery path defined by the casing 30, as in the case of a centrifugal pump.

As shown in Fig. 3, the wide jet of sand or grit is directed and centred on the basket 25 of the tubular conveyor 14. The articles to be sandblasted, for example of thermo-setting resin and not shown, are fed continuously into the conveyor 14 one behind the other, the minimum distance apart without touching each other. The speed of rotation of the tube and its slope are chosen such that for a given width and efficiency of the sandblasting jet, each article rotates about itself a number of times and remains exposed for the time necessary for its entire surface to be sufficiently sandblasted. The rotation of the tube helps the article to roll downwards along the tube.

The jet also aids the transverse rolling of the article, which therefore passes through all possible positions. As the pieces follow closely behind each other, the jet is very well utilized, and as it is proportioned uniformly over each piece and over the entire surface of each piece, the exposure thereof can be reduced to the necessary minimum. This is in contrast to the sandblasting of articles which are rotated in a heap, because in this case there is a high statistical influence, which means that a factor even higher than 2 would have to be exceeded in order to obtain a high probability of sand blasting all the pieces, and even then there are always pieces which are sanded to an excessive or insufficient degree. The fan 6 maintains a certain sub atmospheric pressure in the housing 2, to prevent dust leaving through the tube 14. The air is then purified or fed to a stack.It is advisable to make the basket 25 and stirrups 28 of abrasion-resistant material, or better still make them coated, for example enamelled, or covered with special anti-abrasive resins, or coated with rubber specially resistant to sandblasting. The tube

14 is also preferably coated, for example with plastics, so that there is no danger of the pieces suffering damaging impact during rolling. It should be noted that this ideal operation has been obtained by means of a structure and a mechanical system which are extremely simple and of low cost. The entire movement is provided by a small geared motor unit and a direct belt drive.Thus, relative to equivalent previous installations, improved processing with elimination of causes of rejects in this processing stage is obtained, together with greater productivity, completely auto matic continuous operation, and lower installation cost. If desired, even though of less merit, the turbine sander could be replaced by any air jet sander, and in all cases the jet could point in any other sideways direction or from below, and the tube could be made to vibrate instead of rotate.

WHAT WE CLAIM IS: 1. A sandblasting method for finishing moulded or cast articles wherein articles to be sandblasted are made to pass in front of a sandblasting jet, individually in a single pass, within a reticulated portion of a conduit.
2. A sandblasting method according to claim 1, wherein the articles are made to roll through the sandblasting jet.
3. A method according to claim 1, wherein the articles are made to pass through the sandblasting jet by vibrating the conduit.
4. A method as claimed in claim 1, wherein the articles are made to rotate in front of the sandblasting jet within the conduit which is rotated and in which the articles being pro cessed move axially.
5. A method according to any one of the preceding claims, wherein the conduit is kept inclined downwards in the direction in which the articles being processed are fed.
6. A method as claimed in any one of the preceding claims, wherein the sandblasting jet is directed such that it strikes the articles in a direction transversal to the feed direction of the articles.
7. A method as claimed in any one of the preceding claims, wherein the articles to be sandblasted are made to move forward and roll in sequence one at a time.
8. A method according to claim 7, wherein the articles are of thermosetting plastics material.
9. A sandblasting machine comprising a conduit arranged so that, in use, articles to be processed will pass under gravity past a sandblasting jet which is directed into the interior of at least a portion of the conduit transversely.
10. A machine as claimed in claim 9, wherein said conduit comprises a conveyor tube inclined downwards in the feed direction, and having a portion defined by an open-mesh arranged in front of the sandblasting jet.
11. A machine as claimed in claim 9 or 10, wherein said conduit passes through a closed housing, this latter embracing the portion towards which the sandblasting jet is directed in use of the machine.
12. A machine as claimed in claim 11, wherein said conduit is rotatably mounted in the housing walls, and is rotated by an electric motor, a reduction unit and a belt drive which directly engages with the conduit.
13. A machine as claimed in any one of claims 9 to 12, comprising a centrifugal turbine for producing a sandblasting jet, the turbine being such as to directly accelerate sand

in the absence of a carrier fluid.
14. A sandblasting method substantially as herein described with reference to the accompanying drawings.
15. A sandblasting machine substantially as herein described with reference to the accompanying drawings.