GB2346572A - Powder coating of large structures - Google Patents

Abstract

A powder coating process for structures such as structural steelwork and non-ferrous fabrications, which is not dependent upon fixed powder application booths or ovens, comprises powder applicators and heaters which are mobile in relation to the workpiece and are able to traverse one or more workpieces sequentially or concurrently by means of their location on mobile gantry systems. The workpiece may be sensed.

Description

Powder Coating Process for Structures.

This invention relates to the powder coating of large fabricated structures.

Conventional powder coating processes of relatively small components and assemblies in batch or mass production environments are well known using electrostatic application of the powder and heating ovens, or fluidised bed.

Powder coating of larger components such as pipelines using induction heating coils is also known.

Large and irregular stuctures such as structural steelwork or non ferrous fabrications and the like are usually wet paint coated due to their size and irregular shapes being unsuitable for the above or any other known powder coating processes. Wet paint coating of such structures is wasteful in terms of material overspray, time in terms of the number of coats required and the drying time, and damaging to the environment in terms of VOC emissions.

It is the objective of the present invention to provide a powder coating system which is independent of the restrictions on size and varying shape of the workpiece normally imposed by spray booths, fluidised bed or heating ovens and the like. The present invention replaces the need for booths, ovens and the like. The new process is able to coat structures ranging from simple beams to truss type structures and the like. fig 1.

The new process utilises mobile and integrated sensing, heating, application and curing heads fig 3 and fig 4, which are mounted such that they can traverse one or more workpieces, 1, and carry out the sequence of operations, sequentially or concurrently, fig 2.

The traversing of the heads which may be in one or more planes over or under or to the side of the workpiece, 1, is achieved using one or more gantry systems, H1, C, H2, running on one or more tracks, 6. The gantry system may be floor, side or overhead positioned. In order to achieve passage of the gantry or heads under the workpiece for example, the workpiece may be supported on a plurality of supports, 3, which may be of a retractable nature.

However this does not exclude the option of moving the workpiece in relation to the gantry or heads.

The sensing of the workpiece may be achieved through several known methods such as machine vision, 3D data on the workpiece, or photo cells or the like. Temperature sensing may also be achieved by any known means such as infra red or digital heat detectors for example.

The heating system may be one or more infra red heaters, 4, suitable in heat output capacity for the application or any other known heating system, controlled by photo cells, infra red, or digital detectors or the like. One or more heaters may be varied in their output, or switched on or off to compensate for variations in distance of the heaters from the workpiece, or the temperature of the workpiece, or moved in or out from the workpiece, both to cater for different sizes of workpiece or variations in process perameters. The heaters may be located either in a box structure or on an open frame so movement is not as restricted, fig 5.

There may be one or more powder application gantries, C, with the ability to apply undercoat or secondary coats of different material, fig 4., using one or more application heads, A or B, with one or more application guns, 7. The traversing application head may be large enough to accommodate the desired size range of workpieces, with the application guns, 7, able to traverse in a reciprocating motion.

The excess powder may be collected in one or more recovery recepticles, 5.

Process parameters of position, motion, heat input, application of powder, temperature and surface finish may be controlled and integrated using any known means such as PLCs.

Claims (12)

1. CLAIMS : 1. To provide a method of coating metallic structures without the need for fixed geometry equipment such as pre heat ovens, coating application booths, or curing ovens, which are large in relation to the workpiece, by the provision of heating, coating and curing devices, which are mobile to and small in relation to the workpiece.
2. 2. A method as claimed in claim 1, where one or more of the heating, coating and curing devices are controlled such that they traverse the workpiece in one ore more planes of movement to gain coverage of the workpiece.
3. 3. A method as claimed in claim 1, where the heating and or curing devices are short wave infra red.
4. 4. A method as claimed in claim 1, where the heating, coating and curing devices are mobile within one ore more gantry systems.
5. 5. A method as claimed in claim 3, where the gantry system is mobile in relation to the fixed workpiece.
6. 6. A method as claimed in claim 3, where the workpiece is alternatively able to move in relation to the gantry system.
7. 7. A method as claimed in claim 3, where a combination of both gantry and workpiece movement is possible.
8. 8. A method as claimed in claims 4,5,6,7, where one or more gantry systems may be floor or overhead mounted.
9. 9. A method as claimed in any preceding claim, where on ore more of the heating, coating and curing devices are able to sense the position of the workpiece and are programmed to move to optimum positions and settings and avoid collisions as the workpiece or gantry system moves.
10. 10. A method as claimed in claims 2,5,6,7, where the workpiece supports are retractable in turn in phase with the position of the workpiece to the heating, coating and curing devices.
11. 1 I. A method substantially as hereinbefore described with reference to the accompanying drawings.
12. 12. An assembly substantially as hereinbefore described with reference to the accompanying drawings.