METHOD AND APPARATUS FOR APPLYING A POWDER COATING TO A MOULD

Abstract: A method and apparatus for forming a powder coated sheet moulded compound part which employs a spaced spraying device for spraying a mould half of the mould with powder coating prior to the moulding process. The spraying device comprises a retractable spray booth (1) to which is removably attached a mould mask (5) for positioning over the mould half to contain spraying to the desired mould area and prevent overspray to surrounding areas. A plurality of individually operable spray guns (3) are mounted within the booth (1), and are connected to a horizontal reciprocator (4). To achieve optimum powder coverage on difficult mould surfaces, the spraying operation and reciprocator may be programmable.

Description: "Method and Apparatus for Applying a Powder Coating to a Mould" FIELD OF THE INVENTION The present invention relates to a method and apparatus for applying a powder coating to a mould particularly to a mould for use in a pressing process for forming powder coated sheet moulded cαnpound (S.M.C.) parts, such as tabletops, construction panels, bathtubs and the like. BACKGROUND ART Heretofore powder coatings have been applied to S.M.C. cσπponents in the mould using hand equipment or robots. The problem arising from this prior method is that the ' surrounding .areas to the mould become contaminated with powder. SUMMARY OF THE INVENTION The present invention overcomes this problem by spraying the mould in a spray booth separate from the press, the booth incorporating a mould mask which is designed to confine spraying to the required mould area thereby eliminating overspray to surrounding areas. According to one aspect of the invention there is provided a method of forming powder coated sheed moulded coπpound parts comprising applying powder coating to the moulding surface of a mould, introducing moulding coπpound to the mould, pressing the charged mould in a press to transfer the powder coating to the cαrpound to form a powder coated moulded part characterised in that one mould half of the mould is retained in the press, there being two other similar mould halves of the mould which are alternatively charged with powder outside the press prior to transference consecutively to the press to mate with said one mould half, for the moulding process, the moulding surface of said other mould half being masked during the coating process to prevent overspray to surrounding areas of the moulded form thereof. g_ E OMPI According to another aspect there is provided apparatus for forming powder coated sheet moulded compound parts comprising a press for forming the parts in a mould, characterised in the provision of spraying means external to the press for spraying one mould half of the mould with powder coating, a mould mask for inserting over a said one mould part in the spraying means for preventing overspray to surrounding areas thereof other than its moulding surface, and means for transferring a said one mould half to and from said press in such a manner that as a said one mould half is being coated with powder in said spraying means, another one said mould half, which has previously been coated in said spraying means, is mated with the other mou_ldhalf.in said press for a pressing cycle. According to a further aspect of the invention there is provided a spraying device for powder coating a mould half in a process for forming powder coated sheet moulded compound parts characterised in the provision of spraying means for spraying the moulded half with a powder coating material, a mo * uld mask for inserting over the mould half to shield surrounding areas of the moulding surface thereof frcm overspray, and a spraying compartment attached to the mask and housing said spraying means. The advantage of this arrangement is that the powder coating is contained in the area to be coated and unnecessary overspraying " to s-urrounding areas is avoided. The spray booth may be provided with an extraction system thereby maintaining the inner surfaces of the mask free frcm powder build p. The mould mask is preferably interchangeable with other mould masks of different design thereby to suit any particular S.M.C. part. Other features and advantages of the present invention will beccme apparent frcm the description that follows. BRIEF DESCRIPTION OF THE DRAWINGS The sole drawing accompanying this specification shows a schematic ^ part cross-sectional view through spraying apparatus according to an embodiment of the invention. BEST MODES OF CARRYING OUT THE INVENTION The spraying apparatus shown in the accompanying drawing comprises a spray booth 1 mounted in position above a male mould half 2 whose upper mould surface is to be powder coated.. A plurality of spray guns 3 are mounted in line across the spray booth 1 and moved over the upper surface of the mould half 1 by a horizontal reciprocator 4. The spray is directed onto the surface of the mould half 2 through a mould mask 5 mounted to the bottom of the spray booth, the mask conforming to the outer contours of the moulding on the upper surface of the mould half 2 thereby to provide the required masking effect. The mask 5 is provi ' ded with -upwardly sloping sides 5' (thus avoiding contact with the mould half) which lead.to an extraction duct 6 surrounding the lower periphery of the spray booth 1. - The upwardly sloping sides 5' of the mask 5 lead from a peripheral lip or skirt 5* * -which in use overlaps the contour edge of the mould surface of the mould half 2 as shown. At least the peripheral lip 5' ' is formed of a heat resistant plastics. An extractor fan (not shown) is connected to the extraction duct 6 for drawing excess powder out of the spray booth 1 which collects around the masking area of the mask 5. The spray booth 1 is retractably mounted by means (not shown) so that it may be withdrawn frcm the mould half 2 after spraying and the mould half (2) shuttled to the press during the press cycle. The mask 5 is interchangeable to enable other masks to be inserted conforming to the shape of the S.M.C. part to be formed in the subsequent pressing process. — ι - A pressing operation may be carried out using a press with a spraying apparatus as above described stationed to either side of the press. The female mould half is positioned in the press and corresponding male mould halves are shuttled between the press and the adjacent spraying apparatus. To form the S.M.C. part moulding compound is charged in the female mould half in the press, and a powder coated mould half is then -transferred frcm one spraying apparatus into the press and the mould is closed to form the S.M.C. part. During pressing the powder coating on one mould half is transferred . to the pressed S.M.C. part and this cαπpletes the press cycle during which the other male mould half is powder coated in the other spraying apparatus for subsequent transferral to the press after withdrawal of the previously formed S.M.C. part, to initiate the next press cycle. I

Claims: CLAIMS 1. A method of forming powder coated sheet moulded compound parts comprising applying powder coating to the moulding surface of a mould, introducing moulding coπpound to the mould, pressing the charged mould in a press to transfer the powder coating to the coπpound to form a powder coated moulded part characterised in that one mould half of the mould is retained in the press, there being two other similar mould halves of the mould -which are alternatively charged with powder outside the press prior to transference consecutively to the press to mate with said one mould half.for the moulding process, the moulding surface of said other mould half being masked during the coating process to prevent overspray to surrounding areas of the moulded form thereof. 2. A method as claimed in claim 1 wherein powder coating is extracted from the working area of the media during powder coating. 3. Apparatus- for forming powder coated sheet moulded compound parts comprising a press for forming the parts in a mould, characterised in the provision of spraying means external to the press for spraying one mould half of the mould with powder coating, a mould mask for inserting over a said one mould part in the spraying means for preventing overspray to surrounding areas thereof other than its moulding surface, and means for transferring a said one mould half to and from said press in such a manner that as a said one mould half is being coated with powder in said spraying means, another one said mould half, -which has previously been coated in said spraying means, is mated with the other mould half in said press for a pressing cycle. 4. Apparatus as claimed in claim 3 characterised in that the peripheral lower surface of the mask has a peripheral edge confo_ * τning to the outer contour of the moulding surface of said one mould half, said lower surface being downwardly sloping to said peripheral edge. 5. Apparatus as claimed in claim 4 characterised in the provision of an extraction duct at the top of said downwardly sloping lower surface of the mask. 6. Apparatus as claimed in claim 5 characterised in a spray booth over the spraying means forming a peripheral gap with the -upper peripoheral edge of said lower surface of the mask, leading to the extraction duct one peripheral wall of which is constituted by the outer wall or walls of said booth. 7. A spraying device for powder coating a mould half in a process for forming powder coated sheet moulded coπpound parts characterised in the provision of spraying means for spraying the moulded half with, a powder coating material, a mould mask for inserting over the mould half to shield surrounding areas of the moulding surface thereof from overspray, and a spraying compartment attached to the mask and housing said spraying means. 8. A -spraying device as claimed in claim 7 characterised in that said mask is removably attached to the spraying coπpartment. 9. A spraying device as claimed in claim 8 characterised in that said spraying means comprises a plurality of in-line spray guns each individually actuable. 10. A spraying device as claimed in claim 9 characterised in that said spray guns are horizontally reciprocable across the spraying area. 11. A spraying device as claimed in 7 characterised in that the peripheral lower surface of the mask has a peripheral edge confoπning to the outer contour of the moulding surface of said one mould half, said lower surface being downwardly sloping to said peripheral edge. « ς_~n MPI 12. A spraying device as claimed in claim 10 characterised in the provision of an extraction duct at the top of said downwardly sloping lower surface of the mould. 13. Apparatus for forming powder coated sheet moulded compound parts substantially as hereinbefore described with reference to the drawings. 14. A method for forming powder coated sheet moulded compound parts substantially as hereinbefore described with reference to the drawings. 15. A spraying device for powder coating a mould half in a process for forming powder coated sheet moulded coπpound parts substantially as hereinbefore described with ' reference to the drawings.

Inventors: LUSH ALAN CHARLES, LUSH, ALAN, CHARLES
Applicants: VOLSTATIC COATINGS, VOLSTATIC COATINGS LIMITED
Application year: 1983
Main classification: B29D7
IPC codes: B05B7, B05B15, B29C37, B29C41, B29C43