Abstract:
A suspension device for workpieces in electrostatic painting thereof comprises a carrier, a suspension member (2) in which the workpieces are suspended and which, by the intermediary of a connector (4) is suspended in the carrier. The suspension member (2) has an aperture (14) through which the connector (4) extends. In order to protect the suspension member (2) and the connector (4) from the build-up of layers of paint, an elastic protector device (15) is disposed to cover the suspension member (2) within an area (11) which encompasses the aperture (14), the connector (4) extending through the protector device (15).

Description:
TECHNICAL FIELD 
     The present invention relates to a suspension device for suspending workpieces in electrostatic painting thereof, and comprises a carrier, possibly movably disposed in the form of a conveyor, at least one elongate, preferably approximately horizontal suspension member in which the workpieces are suspended and which in its turn is suspended in the carrier by the intermediary of at least one connector, the suspension member having, in an upper portion, a through-going aperture through which extends a portion of the connector. 
     1. Background Art 
     In the surface treatment of workpieces by electrostatic coating, both wet spraying and powder coating, the workpieces are as a rule suspended free from one another in a suspension device. The suspension is such that the workpieces may be got at for spraying from different directions. The suspension device includes some form of carrier which, in practice, may consist of a conveyor which carries the workpieces along a line, or a carriage which may be driven on a substrate. 
     In electrostatic spraying, the sprayed paint material (in the form of a powder or liquid) supplies an electric charge to the workpieces and so this charge must be conducted off to earth or to the voltage unit which is used for the charging operation, if the sprayed paint material is to adhere sufficiently to the workpiece. It follows from this that it is of cardinal importance to have good electric contact up to the workpiece. This electric contact must thus pass via the suspension device, for which reason the components included in the device must possess good conductivity and completely adequate electric contact with one another. 
     Given that both the workpieces and the suspension device are electrically connected to earth or to the voltage unit, it will readily be perceived that the paint material will be just as capable of adhering to the workpieces as to the metal components included in the suspension device. When the suspension device with suspended workpieces is then transported into an oven for curing the paint material, the paint material will naturally also cure onto the components included in the suspension device. As the suspension is used, the coating layer will be gradually built-up so that extremely large layer thicknesses occur. 
     Such paint material as has fastened to metal components included in the suspension device has involved problems in that the electric connection between these metal components cannot be maintained when the paint layer grows in thickness. 
     2. Problem Structure 
     The present invention has for its object to design the suspension device intimated by way of introduction such that it obviates the drawbacks inherent in prior art designs and constructions. In particular, the present invention has for its object to realise a suspension device which, despite the build-up of thick layers of paint material, affords good electric contact between included components. The present invention yet further has for its object to realise a suspension device which is both simple and economical in use and in which used components may readily be replaced at low cost. 
     3. Solution 
     The objects forming the basis of the present invention will be attained if the suspension device intimated by way of introduction is characterized in that a protector device of yieldable, preferably elastic material is disposed to cover the suspension member within an area which encompasses the aperture, the connector also extending through the protector device. 
     Further advantages will be attained if the subject matter of the present invention is also given one or more of the characterizing features as set forth below. 
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
     The present invention will now be described in greater detail hereinbelow, with particular reference to the accompanying Drawings. In the accompanying Drawings: 
     FIG. 1 schematically shows in perspective obliquely from above a suspension device according to the present invention; 
     FIG. 2 is a perspective view of an end portion of a suspension member included in the device according to the present invention; and 
     FIG. 3 is a vertical section through a part of the suspension member according to FIG. 2. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     The present invention will be described and exemplified below with reference to powder spraying, but the invention may of course equally advantageously be applied in electrostatic spraying of liquid paint material, so-called wet spraying. 
     FIG. 1 schematically illustrates a highly simplified embodiment of the present invention. In the Figure, reference numeral 1 relates to a carrier which, in the illustrated embodiment, is designed as a conveyor for conveying workpieces, but which may just as well be a conveyor with a single rail. Suspension members 2 are suspended in the carrier 1 and are conveyed in the direction of the arrow 3. The suspension members are connected to the carrier 1 by the intermediary of connectors 4 which will be described in greater detail below. The suspension members 2 serve for suspending the workpieces 5 which are to be powder coated. The workpieces 5 are connected to the suspension members by means of suspension hooks 6. 
     While the carrier in the embodiment intimated in FIG. 1 is designed as a conveyor, it may, in an alternative embodiment, also be provided in the form of a carriage drivable on a substrate or some suitably designed rack or stand. 
     FIG. 2 shows in perspective an end portion of one suspension member 2. The suspension member 2 is elongate and is designed as a plate profile with two substantially vertical and parallel main portions 7 and 8, respectively. Along their length, the main portions 7 and 8 have a number of anchorages 9 for suspension hooks 6 in which the workpieces are subsequently intended to be suspended. 
     The suspension member 2 has an upper, upwardly directed portion 10 which, in the illustrated embodiment, is elongate so that it extends along substantially the entire length of the suspension member. The upwardly directed portion is strip- or band-shaped and, in the embodiment shown on the Drawing, is realized in that two sheet strips 11 and 12 laid against one another have been joined together. The sheet strips 11 and 12 are of one piece manufacture with the main portions 8 and 7, respectively, of the suspension member 2. 
     The suspension members 2 are suspended in the carrier 1 by the intermediary of the connectors 4 where at least the lower portions are made of metal wire. Preferably, the entire connector is produced from this material. 
     When the subject matter of the present invention is put into use, it is vital that there is good electric contact, first between the workpieces 5 and the suspension hooks 6, second between the suspension hooks 6 and the suspension members 2, third between the suspension members 2 and the connectors 4 and fourth and last between the connectors 4 and the carrier 1. It is possible by such means to realize good electric connection up to the workpieces 5. 
     On spraying with electrostatically charged powder, the suspension device according to the invention will have the same electric potential as the workpieces 5. This implies that the suspension device has the same ability to attract electrically charged powder floating in the air as the workpieces themselves. Consequently, the device according to the present invention will also receive a considerable coating of powder, since this is employed time and again and is covered with one layer after another. For this reason, the anchorages 9 are disposed interiorly between the two main portions 7 and 8 so that they will be electrically discrete from the ambient surroundings, and as a result powder can hardly penetrate in to the anchorages. It is considerably more difficult to prevent powder coating from depositing on the upwardly directed portion 10 of the suspension members serving for securement of the connectors 4. 
     According to the present invention, the connectors 4 have lower, hook-shaped end portions 13 which have been passed through apertures 14 in the upwardly directed portion 10 of the suspension member. A protector device 15 is produced from a resiliently yieldable, preferably elastic material and is disposed to cover that part of the upwardly directed portion 10 which encompasses any of the apertures 14. The lower, hook-shaped end portion 13 of the connector 4 extends, in this instance, through the material of the protector device 15 and through the most suitable of the apertures 14. 
     The protector device 15 is suitably made of a silicon rubber with good heat resistance. The protector device is elongate and has a cross section of the shape of an inverted U. In this instance, the protector device has a shank 16 and 17, respectively, on each side of the upwardly directed portion 10. The protector device is dimensioned in such a manner as to display a good fit against the upwardly directed portion, so that a seal is thereby obtained between the protector device and the upwardly directed portion. Despite the sought-for seal between the protector device and the upwardly directed portion, it may be important that the protector device is capable of carrying out minor displacement movements in relation to the upwardly directed portion so that a good electric contact is thereby guaranteed between the connector 4 and the upwardly directed portion 10. 
     On suspension of a suspension member 2, this is moved with the protector device over the relevant aperture 14. Thereafter, the hook-shaped end portion 13 of the connector 4 is quite simply pressed straight through the material in the protector device 15 at the same time as the end portion 13 is passed through the relevant aperture 14. There will hereby also be attained a seal fit between the protector device and the connector. 
     FIG. 3 is a vertical cross section through the upper portion 10 of the suspension member 2 in the region of the connector 4. It will be apparent from this Figure that both shanks 16 and 17 of the protector device 15 sealingly abut against the upwardly directed portion 10. It will also be apparent from this Figure that the edges 18 and 19 of the aperture 14 abut against the end portion 13 of the connector 4 and there realize electric contact between both of these parts. 
     Since the protector device 15 is made from elastic, heat resistant material, the powder which may possibly adhere therein will readily be removed even after the powder has set and cured. This implies that the region around the aperture through which the connector 4 extends may be kept free of adhering powder so that the aperture is thereby kept free at the same time as good electric conductive capacity is guaranteed. 
     It is advantageous if the material selected for the protector device 15 has as good dielectric properties as possible, so that the electric field force on the outside of the protector device may thereby be reduced, with the result that powder deposition on the protector device is also reduced. 
     In the foregoing, the upwardly directed portion 10 of the suspension member has been described as an elongate band-shaped strip on the upper side of the protector device. This design is not necessary, but instead the upwardly directed, elongate portion may be replaced by a number of upwardly directed anchorage lugs which in themselves house the above considered apertures 14. If, in such a design, the anchorage lugs have an upper, arched edge, the protector device 15 is given corresponding configuration so that, like a cap, it can be moved down over the anchorage lug. 
     The present invention may be modified without departing from the spirit and scope of the appended claims.