AU1013100A - Tube coating apparatus and method - Google Patents

Description

1 TUBE COATING APPARATUS AND METHOD This invention relates to tube coating apparatus and methods.

This invention has particular but not exclusive application to tube coating apparatus and method associated with continuous roll forming welded tube mills, and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention could be used in other applications, such as coating of drawn tube or the like.

•Hollow section steel tube is generally produced from hot rolled mill edge strip by forming a welded seam steel tube followed by sizing and/or forming the welded steel tube into commercial cross section such as rectangular hollow section (RHS), square hollow section (SHS) or specialised shaped sections. The source hot rolled 0- mill edge strip material by its nature enters the tube mill bearing mill scale, the combination of oxides produced by heat during the production and subsequent hot oo 0 rolling of the steel. Mill scale has the potential to form a reasonably effective barrier against corrosion. However, the scale tends to be relatively weak and variable, and is disrupted unevenly by the roll forming process.

Painting the product tube with a primer has been the general means of providing the tube with corrosion protection. In general, the tube from the mill is cut to lengths after forming, the forming process having disrupted loose mill scale. The lengths generally maintain a variable cover of adherent mill scale, which is painted over.

There are disadvantages of the prior art processes for production of painted welded steel tube. One of the disadvantages is the degree to which the paint is applied over unstable mill scale and sometimes mill fluids.

This invention in one aspect resides broadly in a continuous steel tube coating method including the steps of: subjecting said steel tube to a mechanical cleaning by an aqueous liquid under pressure; airless spaying said optionally dried tube with paint; and curing said paint.

The mechanical cleaning liquid may comprise mill coolant and preferably comprises the same mill coolant used in the rolling and shaping of the tube. Such fluids are known and generally comprise proprietary blends of surface active agents 10 and lubricants in a water base. For steel tube mills the liquids the liquids may include an organic base such as an alkanolamine to suppress the formation of iron oxides on the tube, surface active agents such as polyalkylene polyols to remove greases and oils, stabilisers and the like. Optionally, the tube may be dried after cleaning and before painting.

The steps of the foregoing method may be integrated in paint line apparatus ***including: a cleaning chamber adapted to receive steel tube and including outlets for directing pressurised aqueous cleaning liquid at said tube; and an airless spraying chamber.

If desired, an optional drying chamber may be adapted to continuously receive tube from said cleaning chamber and dry same.

The cleaning chamber preferably includes two or more baffles adapted to conform to the tube profile and providing a pressurisable zone, the pressure differential cooperating with the mechanical cleaning action of the pressurised fluid to enhance 3 scale removal. The cleaning chamber may include a housing having a hinged or otherwise openable portion to provide internal access for placement and/or servicing of the baffles. Typically, the preferred mill fluid cleaning agent is supplied at a pressure of about 40 psi and at flow rates of about 200 litres per minute.

The airless spray enclosure preferably includes baffles to contain the atomised coating fluids. The geometry of the enclosure and baffles is preferably selected to minimise drips on product within the enclosure. The enclosure preferably includes baffles intermediate the ends of the enclosure to provide end zones functioning as buffer voids to substantially eliminate egress of paint particles from the enclosure and 10 thus removing the need for extraction. The spray nozzles are preferably fitted to ports selected as to location to give even coating of product. Preferably, the nozzles are arranged such that collision of paint particles is reduced, thus reducing paint drift, especially axial drift tending to cause particles to pass our of the enclosure. The

**SS*S

enclosure is preferably provided with collection points for recycling overspray, which is preferably maintained in its uncured state by water cooling the enclosure to prevent thermal curing of the overspray prior to collection.

In prior art processes the painting process is generally at the end of the mill line, the tube stacks produced being drained of mill fluids and dried prior to discrete lengths of tube being fed to a paint line. It is envisaged that methods in accordance with the foregoing invention may be incorporated into a conventional paint line.

However, a disadvantage of this arrangement relates to the fact that the painting process is not fully integrated into a continuous mill, resulting in a physically large transfer/accumulator facility for handling the tube through the paint line at the production speed of the mill, to simulate a continuous process. Accordingly, it is 4 preferred that the method be integrated into the mill line under control of control means.

Accordingly, in a further aspect, this invention resides in a welded steel tube mill including a roll forming, welding and shaping portion, a cleaning chamber adapted to continuously receive steel tube from said roll forming, welding and shaping portion and including outlets for directing pressurised cleaning liquid at said tube, an airless spraying chamber for continuously paint coating the tube, and a cutting portion. An optional drying chamber may be adapted to continuously receive tube from said cleaning chamber and dry same.

Preferably, the roll forming, welding and shaping portion comprises a conventional tube mill. For example, the portion may include a strip handling section, a strip accumulator to permit continuous processing of multiple strip rolls with automated butt welding between the respective strips, progressive round tube forming stations, a welding station, a sizing station, and a shaping station, the latter generally including a series of turk's head rolls. The cleaning, drying and painting portions may be located either before or after the cutting portion. However, it is preferred that the cleaning, drying and painting portions be located in the line between the last turk's head and the cutting station. By this means the entry of cleaning fluid into the interior of the tube is prevented, thus preventing drain-out and subsequent effect on the freshly painted tube down the line.

In order to provide for operation of the mill at appropriate line speeds, the cleaning, drying, painting and cutting portions are preferably operated under the control of control means having control over the parameters of the respective portions. For example, there may be provided PLC or other microprocessor control over parameters such as cleaning liquid pressure and volume, drying power, paint mass transfer rate or the like. Preferably the control means utilises as its base data point the line speed of the tube exiting the last turk's head.

The tube on exit from the last turk's head may enter through a baffled end of a cleaning portion including an elongate housing having arranged therein a plurality of medium to high pressure cleaning nozzles adapted to direct cleaning fluid against the whole of the outer surface of the tube. The cleaning station is preferably adapted to receive mill fluid from the mill supply. Depending on the quality of the supply, the mill fluid may be supplied from mill head drainings, or may be fresh. If desired the mill fluid may be recycled at the cleaning station with appropriate filtration and makeup.

ii 10 The tube may pass through an appropriate end baffle on the cleaning housing and into the optional drier. The drier may comprise a heating means as well as drying means to heat the tube prior to painting to encourage fast cure, although the painted tube may be heated after painting to effect curing as described hereinafter.

The painting portion is preferably a controlled environment enclosure. For example, the painting portion may comprise an environmental enclosure in line with the tube line and having appropriate entry and exit baffles. The enclosure is preferably adapted for airless spraying of solvent free coatings. For example, the coatings may comprise water reducible urethanes, alkyds or acrylics.

The enclosure may be temperature controlled to provide for curing control over the coating. For example, in the case where the tube is heated prior to entry into the painting enclosure, the enclosure may be cooled such as by water cooling to prevent thermal curing of the overspray, which may be subsequently recycled as described hereinafter. Preferably, the spraying nozzles operate under the control of the aforementioned control means.

6 The paint process may include means for overspray recovery and recycling with appropriate filtration. The spray nozzles may be of the continuous or pulsed type. In the pulsed type, a combination of the nozzles may be pulsed at a calculated frequency to achieve consistent paint coverage at a given mill line speed. Preferably the nozzles are provided with a second paint flow to clean the nozzles without deposition on the tube such that nozzle cleaning may be achieved while the particular nozzle is on a down cycle in the pulse sequence, thus preventing the need for stopping the line to clean nozzles. Preferably, the geometry of the housing is selected whereby paint drift to the exterior is substantially eliminated and to eliminate 10 drip collection points within the housing.

The curing of the coating will of course depend on the coating system adopted. As foreshadowed above, the tube may be heated in a heating/drying stage prior to painting. Alternatively, the painted tube may pass to a drying station after painting to cure off the coating.

oi The painted tube preferably passes to a flying cut off station whereby the tube is cut to shipping lengths. The flying cut off station is preferably operated under the control of the aforementioned control means such that operation is to line speed, although it is envisaged that operation of the flying cutoff may be controlled with reference to the actual line speed at the cut off. Whilst traditional tube mills use wet cutting, it is preferred in the present mill to use dry cutting and to select the cut off wheels appropriately.

In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawing which illustrates a preferred embodiment of the invention and wherein: 7 FIG. 1 is a schematic view of a tube mill in accordance with the present invention; FIG. 2 is a representation of a cleaning enclosure suitable for use in the present invention; and FIG. 3 is a representation of a painting enclosure suitable for use in the present invention.

In FIG. 1, there is illustrated a tube mill in accordance with the present i invention wherein slit hot rolled strip 10 is loaded onto an uncoiler mandrel 11 with either an overhead crane or fork truck. The strip 10 is fed through a shear and end welder 12 where the front end of a new coil of strip is joined to the back end of the previous coil of strip. The strip is then fed into a spiral accumulator 13 to create a buffer of strip that is consumed by the tubemill while the ends of the coils are being joined by 12 and therefore facilitates the continuous running to the line.

The strip 10 emanates from the spiral accumulator 13 and is fed into the tubemill forming section 14. The forming section 14 roll forms the strip to a round shape 15 and presents it to the welding section 16. At the welding station 16 the longitudinal seam of the formed round section is radio frequency induction welded.

The welded round section 17 is then advanced through a cooling section where the heated zone of the welded area is quenched to be close to the temperature of the bulk of the tube. The tube 17 then advances to the sizing section 21 where the circumferential measurement of the closed welded section 17 is brought to within specified tolerances. The round sized tube 17 is then advanced through 3 turksheads 22 where it is shaped to a rectangle or square.

The forming 14, sizing 21 and turkshead 22 sections are all flooded with a fully synthetic rolling mill fluid (QWERL 531, Quaker Chemical, machining and grinding 8 fluid) which is common to all sections. The tube 17 passes into a wash box 23 through baffles 24 in which a combination of the synthetic mill fluid delivered from manifolds 25 by pump 26, compressed air and rag wiping removes the loose mill scale and any residual oil/grease.

The formed, cleaned tube 17 then advances through a tube heater/drier 27.

The heated tube 17 then passes into a painting enclosure 30, where a coat of paint is applied to the surface of the tube by nozzles delivering an airless spray. Overspray is collected at 32, separated at 33, filtered at 34 and recirculated into airless spray pump 35 to the nozzle manifolds 36.

Immediately after the painting enclosure 30 the coated tube 17 is conveyed through a drying section 37 where it simply air dries. From the drying section 37 the painted tube 17 passes at line speed into a dry flying saw 40 where it is cut to individual lengths 41. The individual lengths are accelerated along a run out rack to *e• **an accumulator for rational packing.

15 Apparatus in accordance with the foregoing embodiment has as a principle advantage the ability to be run from strip to packing at a conventional tube mill line speed. The tube so produced does not have the finish disrupted by run out of mill fluids. The tube does not require drying by handling on knife edges. Since the paint line is integrated into the line, transfer stations between the cut off saw and paint lines of conventional tube mills are avoided. The use of the mill fluid under pressure provides that the coating is made over a stable surface having substantially reduced mill scale, without the need for grit blasting. The use of mill fluid adds value to the process without substantially adding to consumables cost.

In the embodiment of FIG 2, there is provided a washing enclosure having an upper housing portion 51 hinged to a lower housing portion 52. Located in the housing portions 51, 52 are baffles 53 having a profile adapted to conform to the tube stock to provide a pressurisation zone in the housing. Cleaning nozzles 54 are adapted to impinge cleaning fluid on the tube stock in the pressurised zone.

In the embodiment of FIG 3, there is provided a water cooled painting enclosure having baffles 61 therein adapted to contain atomised coating fluids within the enclosure. The baffles 61 are of a geometry selected to prevent dripping onto the tube stock. The enclosure is provided with ports 62 for fitting of spray nozzles which are spaced in relation to each other for event coating of the tube stock and to minimise collision of the atomised particles. This reduces axial drift out of the

*O

*J enclosure, in combination with the provision of buffer voids 63 defined between the baffles 61 and the ends of the enclosure. The lower portion 64 of the enclosure is formed into a collection point for coating overspray which is then recycled. End ports allow the tube stock to pass through the enclosure and baffles.

.el.oi It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as defined in the claims appended hereto.

Claims (7)

1. A continuous steel tube coating method including the steps of: subjecting said steel tube to a mechanical cleaning by an aqueous liquid under pressure; airless spaying said optionally dried tube with paint; and curing said paint.

2. A method according to claim 1, wherein said aqueous liquid includes mill coolant.

3. Paint line apparatus including: *o a cleaning chamber adapted to receive steel tube and including outlets for .OO." directing pressurised aqueous cleaning liquid at said tube; and an airless spraying chamber.

4. Paint line apparatus according to claim 3, wherein there is provided a drying chamber adapted to continuously receive tube from said cleaning chamber and dry same prior to painting. Paint line apparatus according to any one of claims 3 and 4, wherein said cleaning chamber includes two or more baffles adapted to conform to the tube profile and providing a pressurisable zone, the pressure differential cooperating with the mechanical cleaning action of the pressurised fluid to enhance scale removal. 11

6. Paint line apparatus according to any one of claims 3 to 5, wherein said cleaning chamber includes a housing having a hinged or otherwise openable portion to provide internal access for placement and/or servicing of the baffles.

7. Paint line apparatus according to claim 6, wherein said aqueous cleaning liquid comprises mill coolant supplied at a pressure of about 40 psi.

406.. *o oo 6o *e 8. Paint line apparatus according to any one of claims 3 to 7, wherein said airless 4oe@ spray enclosure includes baffles to contain the atomised coating fluids. oo 9. Paint line apparatus according to claim 8, wherein the geometry of said airless *d 0 spray enclosure and baffles are selected to minimise drips on product within o• oZ the enclosure. Paint line apparatus according to claim 9, wherein said airless spray enclosure includes baffles intermediate the ends of the enclosure to provide end zones functioning as buffer voids to substantially eliminate egress of paint particles from the enclosure. 11. Paint line apparatus according to any one of claims 8 to 10, wherein the spray nozzles of said airless spray enclosure are fitted to ports selected as to location to give even coating of product. 12 12. Paint line apparatus according to claim 11, wherein said nozzles are arranged such that collision of paint particles is reduced. 13. Paint line apparatus according to any one of claims 11 and 12, wherein said airless spray enclosure is provided with collection points for recycling overspray, which is maintained in its uncured state by water cooling the enclosure. i 14. A welded steel tube mill including a roll forming, welding and shaping portion, •lilt: a cleaning chamber adapted to continuously receive steel tube from said roll forming, welding and shaping portion and including outlets for directing pressurised cleaning liquid at said tube, an airless spraying chamber for continuously paint coating the tube, and a cutting portion. gil. 15. A welded steel tube mill according to claim 14, wherein there is provided a •log drying chamber adapted to continuously receive tube from said cleaning chamber and dry same before painting in said airless spraying chamber. 16. A welded steel tube mill according to claim 15, wherein said roll forming, welding and shaping portion includes a shaping station including a series of turk's head rolls, and wherein said cleaning, drying and painting portions are located in the line between the last turk's head and the cutting station. 17. A welded steel tube mill according to any one of claims 14 to 16, wherein operation of the mill at appropriate line speeds is effected by operating the 13 cleaning, drying, painting and cutting portions under the control of control means which utilises as its base data point the line speed of the tube exiting said last turk's head. 18. A welded steel tube mill according to any one of claims 14 to 17, wherein said tube on exit from the last turk's head enters through a baffled end of said cleaning portion that comprises an elongate housing having arranged therein a plurality of medium to high pressure cleaning nozzles adapted to direct cleaning fluid against the whole of the outer surface of the tube. oooeo 19. A welded steel tube mill according to claim 18, wherein the cleaning portion is adapted to receive mill fluid from the mill supply. l l A welded steel tube mill according to claim 19, wherein said mill fluid is selected from mill head drainings, or fresh mill fluid. 21. A welded steel tube mill according to claim 20, wherein said mill fluid is recycled at the cleaning station with appropriate filtration and makeup. 22. A welded steel tube mill according to any one of claims 15 to 21, wherein said drier includes heating means to heat the tube prior to painting to encourage fast cure. 14 23. A welded steel tube mill according to any one of claims 14 to 22, wherein said painting portion includes an environmental enclosure in line with the tube line and having appropriate entry and exit baffles. 24. A welded steel tube mill according to claim 23, wherein said enclosure is adapted for airless spraying of solvent free coatings. o*o A welded steel tube mill according to claim 24, wherein said enclosure is temperature controlled to provide for curing control over the coating. 26. A welded steel tube mill according to claim 25, wherein the tube is heated prior to entry into the painting enclosure and the enclosure is cooled to prevent thermal curing of the overspray. 27. A welded steel tube mill according to claim 26, wherein said enclosure includes means for overspray recovery and recycling. 28. A welded steel tube mill according to any one of claims 14 to 27, wherein said enclosure includes spray nozzles of the pulsed type, a combination of the nozzles being pulsed at a calculated frequency to achieve consistent paint coverage at a given mill line speed. 29. A welded steel tube mill according to claim 28, wherein said nozzles are provided with a second paint flow to clean the nozzles without deposition on the tube such that nozzle cleaning may be achieved while the particular nozzle is on a down cycle in the pulse sequence, thus preventing the need for stopping the line to clean nozzles. A welded steel tube mill according to any one of claims 23 to 29, wherein said enclosure is of geometry selected whereby paint drift to the exterior is substantially eliminated and to eliminate drip collection points within the housing. 31. A continuous steel tube coating method substantially as hereinbefore defined with reference to the accompanying example. 32. Paint line apparatus substantially as hereinbefore defined with reference to the accompanying drawings. 33. A welded steel tube mill substantially as hereinbefore defined with reference to the accompanying drawings. DATED THIS SIXTH DAY OF JANUARY, 2000. WELDED TUBE MILLS OF AUSTRALIA PTY LTD ACN 010 853 817 by PIZZEYS PATENT AND TRADE MARK ATTORNEYS