AU2021200552A1

AU2021200552A1 - Apparatus for modifying a coating

Info

Publication number: AU2021200552A1
Application number: AU2021200552A
Authority: AU
Inventors: Todd Stewart ANDERSON; Chris Cameron; Rolph Leonard HINTERLEITNER; Anton Wolfgang POSSEGGER; Kirk Angus ROBERTSON; Grant Desmond SEGAR; Hsu-Huei WU
Original assignee: Angus Robertson Mech Ltd
Current assignee: Angus Robertson Mechanical Ltd
Priority date: 2020-01-30
Filing date: 2021-01-29
Publication date: 2021-08-19

Abstract

Apparatus for modifying a coating on sheet material, said apparatus including: a laser capable of producing a laser beam having a wavelength which is readily absorbed by 5 said coating; means for supporting sheet material on which the coating is to be modified at a predetermined position relative to the laser; means for directing the laser beam onto a spreading means which is arranged such that in use the spreading means spreads the laser beam over a predetermined area of said sheet material. 13 1/7 Roll of sheet steel, painted one side, coated with Dridex on other side, Sheet fed through roll former. Sheet fed through burner. Sheet stationary in burner with the line along which sheet to be cut on mid-line of burner. Burner activated to burn Dridex from sheet over preset width. Sheetadvanced toshear which cuts sheet to length. Fig.1

Description

1/7

Roll of sheet steel, painted one side, coated with Dridex on other side,

Sheet fed through roll former.

Sheet fed through burner.

Sheet stationary in burner with the line along which sheet to be cut on mid-line of burner.

Burner activated to burn Dridex from sheet over preset width.

Sheetadvanced toshear which cuts sheet to length.

Fig.1

APPARATUS FOR MODIFYING A COATING

Technical Field The present invention relates to apparatus for accurately modifying all or part of a coating on sheet material. The apparatus has been developed specifically for removing a majority of the anti-condensation coating from a specified area of sheet steel intended for roofing material. However, it will be appreciated that the apparatus of the present invention could be used to modify any of a range of coatings from sheet substrates.

As used herein, the term "modifying" the coating essentially means altering the coating so as to achieve some specified objective. For example, if the coating is an anticondensation coating, the modification will involve modifying the coating so that the coating no longer wicks moisture to any appreciable extent. The modification includes, but is not limited to, melting the coating and burning the coating, partially or completely.

Background Art When corrugated sheet steel is used as a roofing material, warm, moist air rising from the interior of the building tends to condense on the underside of the steel; this condensation can drip, encouraging rot and mould growth. It is therefore advantageous to provide the underside of the steel sheet with a coating which not only provides some heat insulation, but which also is capable of absorbing moisture to prevent dripping.

One suitable coating now in use is sold under the trademark DRIDEX. The DRIDEX coating is formed from polyester fibres bound with an acrylate binder and bonded onto the steel sheet using a hot melt adhesive. The resultant coating can absorb up to 1000 grams per square metre of water at 17 degrees centigrade, and will not readily drip even when carrying a large volume of water:- the time to drip is given as more than six hours. The coating also dries rapidly:- typically, at a temperature of 23 degrees centigrade and 50% relative humidity, the coating has a drying speed of 80 grams of water per square metre per hour.

The DRIDEX coating also has flame retardant properties and has a low thermal conductivity.

The DRIDEX coating normally is applied to roofing steel when the steel is formed as a flat sheet i.e. before the corrugations have been formed into the steel. The coating is continuously brushed or sprayed onto the flat sheet and allowed to dry before the sheet is rolled for supply to the corrugating equipment.

One known drawback of the DRIDEX coating, and other similar coatings, is that because the coatings absorb moisture, if roofing panels are coated right up to the edges of the panel, the presence of the coating can lead to moisture being wicked across the joint between the edge of the panel and any adjacent fittings or panels.

For this reason, the edges of the panel (i.e. along the length of the panel) are not normally coated with DRIDEX:- a margin of about 35mm is width is normally left uncoated along each edge of the panel, so that in use adjacent panels can be overlapped without the risk of wicking. However, the length of each sheet depends upon the shape and size of the roof to which the sheet is to be fitted, and this cannot be predicted when the DRIDEX coating is applied, so the coating is applied along the full length of the sheet. When the required length of each sheet is known, it is advantageous to remove the coating adjacent the ends of each sheet e.g. to about 35 millimetres away from the end.

At present, removing the coating is carried out on site by the roofer fitting the sheet. The most commonly used technique is for the roofer to use a heat gun to burn off the coating adjacent the edge of the sheet. This is time-consuming and awkward on site, and the burning off can be difficult to control:- if the burn off temperature is too high, the sheet and/or the coating on the upper side of the sheet can be damaged.

Disclosure of Invention An object of the present invention is the provision of apparatus capable of modifying a coating on sheet material both accurately and rapidly.

The present invention provides apparatus for modifying a coating on sheet material, said apparatus including: • a laser capable of producing a laser beam having a wavelength which is readily absorbed by said coating; • means for supporting sheet material on which the coating is to be modified at a predetermined position relative to the laser;

• means for directing the laser beam onto a spreading means which is arranged such that in use the spreading means spreads the laser beam over a predetermined area of said sheet material.

In one preferred embodiment of the invention, said spreading means includes: • a burner unit mirror which is arranged such that in use a laser beam reflected from said mirror falls on a predetermined area of said sheet material; • means for rapidly oscillating said mirror over a predetermined arc; • means for reciprocating said mirror such that said mirror travels across the width of the sheet material on which the coating is to be modified, at the same time as said mirror is moved over said predetermined arc.

In a second preferred embodiment of the invention, said spreading means includes: • a lens array arranged such that in use a laser beam impinging on the lens array emerges as a spread beam lying substantially in a single plane and of substantially uniform intensity across the beam; • means for reciprocating the lens array such that the lens array travels across the width of the sheet material on which the coating is to be modified.

Preferably, the lens array includes a Powell lens, most preferably in combination with a cylindrical convex lens; the two lenses are arranged such that in use a laser beam impinges first on said Powell lens and then on said cylindrical convex lens, to produce a substantially parallel laser beam from said convex lens.

In a preferred embodiment of the invention, the coating to be modified by being at least partly removed is a commercially available coating sold under the trademark DRIDEX, and the sheet material is sheet steel. For that application, the most suitable type of laser has been found to be a carbon dioxide laser. However, the apparatus of the present invention may also be used to modify coatings of different types on sheet steel and/or on other materials, and in that case the laser should be selected so that the wavelength of the laser is one which is readily absorbed by that coating.

Preferably, the apparatus also includes means for supporting a roll of sheet material and advancing the roll into a roll former to form corrugations in the sheet material, and then into a burner unit where a predetermined amount of coating is removed from the roll over a selected area. Preferably also, the apparatus includes means for cutting the sheet material into sections of predetermined length.

In one preferred embodiment, the oscillating mirror is a mirror which may be arranged to oscillate using a number of different mechanisms:- for example, the mirror may be pivotably mounted and arranged to oscillate powered by a small electric motor or the mirror may be the mirror of a mirror galvanometer.

Brief Description of Drawings By way of example only, preferred embodiments of the present invention are described in detail, with reference to the accompanying drawings in which:

Figure 1 is a flowchart showing the sequence for using the apparatus of the present invention to remove a coating from sheet material;

Figure 2 is a plan view of the apparatus of the present invention;

Figure 3 is a side view of part of a first embodiment of the apparatus;

Figure 4 is a section on line 4 - 4 of Figure 3, on a larger scale;

Figure 5 is a plan view of a shield panel;

Figure 6 is a side view of part of a second embodiment of the apparatus; and

Figure 7 is a diagrammatic illustration of the operation of the lens array.

Best Modes for Carrying Out the Invention Referring to Figures 1 and 2 of the drawings, sheet steel is supplied as a rolled sheet, painted or colour-coated on one side and coated on the other side with the DRIDEX coating. The paint or colour coating covers the whole of one side of the sheet, but the DRIDEX coating stops a short distance from each of the long edges of the sheet, so that the portion of the sheet which in use will be overlapped with an adjacent sheet is not coated.

The roll 10 is supported at one end of the apparatus 11 in known manner and one end of the roll is led through the apparatus, with the sheet 10a supported on a roller bed (not visible) of known type, mounted on a supporting framework 13. The painted or colour coated side of the sheet is uppermost.

Preferably, the sheet is fed through a set of rolls on a roll former 14 to form the corrugations into the sheet, before modifying the DRIDEX coating by burning off the coating and before the sheet is cut into shorter sections. If this sequence is used, then the sheet is drawn from the roll and pushed through the apparatus by the action of the rolls in the roll former. The movement of the sheet emerging from the roll former then acts to push the sheet through the remainder of the apparatus.

The roll former may be any commercially available type of roll former suitable for forming a desired profile for a roofing sheet; the roll former is of known design and not described in detail.

It would be possible for the sheet to be fed through the roll former either before or after burning off and/or cutting to a length, but for the maximum accuracy in the length of the sheet, it is preferred to feed the sheet through the roll former before burning off the coating and before cutting to length.

The roll former 14 is provided with a first encoder of known type (not shown) to measure the length of sheet passing through the roll former in each operation sequence. This encoder can measure movement in either direction through the roll former, to compensate for any slippage which occurs.

The first encoder is connected to the control equipment and is arranged to halt forward movement of the sheet on the roller bed so that the sheet passing through the apparatus is halted when the cutting line (i.e. the line along which the sheet will need to be cut to give the desired length) is centred on the burner 17. The sheet is guided into the burner 17 by parallel spaced guide rollers 17a, which are freely rotatable and are not driven.

With the sheet stationary, the burner 17 is operated as described below, to burn off the DRIDEX coating for a predetermined distance (typically 35 millimetres) on each side of the cutting line i.e. the total width burned is 70 millimetres.

The coating does not need to be completely burnt away over the predetermined area, but sufficient of the coating must be modified that the remaining coating will no longer significantly wick moisture.

Once burning is complete, the sheet is advanced to the shear 18 which cuts across the width of the sheet along the required cutting line. The remaining portion of the sheet is then advanced and the process repeated until all of the required sheets have been cut from the roll. This results in a number of sheets each of the required length, each with the DRIDEX coating removed from a specified width at each end of each sheet.

Referring to Figures 3 and 4, a first embodiment of the burner 17 is shown in detail. The burner 17 includes a C02 laser unit 20 which is cooled by water cooling (not shown) in known manner. The laser unit 20 is a known typeof C02 laser, which typically produces a beam of infrared light in a wavelength band between 9.4 - 10.6 micro-metres, typically with an energy rating of about 110 watts over an eight millimetres diameter beam.

The laser wavelength is selected such that the laser will burn a plastics material such as DRIDEX, but will not heat the underlying steel or the coating on the other side of the steel. It will be appreciated that the laser selected may be varied depending upon the type of material to be treated.

The laser unit 20 is mounted in a housing 21 with the length of the laser perpendicular to the longitudinal axis of the sheet.

In use, the laser beam is emitted from the end 20a of the laser, and is reflected through 90 degrees by a first angled mirror 22, also located in the housing 21. The reflected beam (indicated by arrows A) is directed vertically up a guide 23, the longitudinal axis of which is perpendicular to the longitudinal axis of the laser unit 20. The guide 23 opens into the lower end of a shielded housing 24 and is reflected through 90 degrees by a second angled mirror 25 to impinge on the mirror 26 of a mirror galvanometer 27. It should be noted that the laser beam is not focused.

The mirror galvanometer 27 is mounted for reciprocating travel along the length of the housing 24; the mirror galvanometer is moved by means of a reciprocating drive belt 28 which in use is operated (e.g. by a stepper electric motor) to reciprocate the mirror galvanometer 27 along the length of the housing 24, and thus across the full width of a sheet in the burner 17. The power supplied to the mirror galvanometer 27 is by means of a supported cable 29. The linear movement of the galvanometer 27 is monitored by a second encoder (not shown) connected to the galvanometer and to the control system of the laser. This is a safety feature:- if the galvanometer is not moving, then the laser must be switched off, to ensure that the laser is not continuously aimed at one spot rather than being moved along the sheet as intended.

A further safety feature is the provision of a third encoder (not shown) which is mounted at the end of the drive belt 28 and set up to detect movement of the drive belt 28:- if no movement of the drive belt is detected over a predetermined minimum threshold, the laser is switched off.

Mirror galvanometers originally were developed to measure current:- a current was passed through the galvanometer coil and the deflection of the coil was measured on a scale by the deflection of a beam of light directed on to a mirror connected to the coil. As the mirror moved with the coil, the position of the reflected beam of light moved across the scale.

In the present invention, a mirror galvanometer essentially is used "in reverse", in combination with a laser, to effectively "distribute" a laser beam over a predetermined distance. In this application, a regularly fluctuating current (typically with a sawtooth profile) is supplied to the galvanometer so that the galvanometer mirror moves in a regular pattern through a predetermined arc about a single axis. Only a single galvanometer mirror is used. Thus, a laser beam impinging on the mirror is in turn deflected over the same arc, and as the mirror galvanometer 27 is moved by the drive belt 28 across the width of the metal sheet 1Oa in the burner 17, the laser beam emitted by the laser unit 20 impinges on the underside of the sheet, and the movement of the mirror moves the laser beam over a band of predetermined width on the sheet, as indicated by arrows B in Figure 4. As noted above, the width of the band typically would be about 70 millimetres, but this could of course be varied as required.

The energy of the laser beam and the length of time which the beam impinges on each part of the sheet are adjusted so that the DRIDEX coating is burnt off the sheet, without damaging either the metal of the sheet or the coating on the opposite side of the sheet. Typically, the laser beam moves across the width of the band B - B to be treated and back about 50 times per second, and the forward movement of the galvanometer 27 across the sheet is about 12 seconds.

Referring to Figures 6 and 7 a second embodiment of the burner 17 is shown in detail. As with the first embodiment, the burner 17 includes a C02 laser unit 20 which is cooled by water cooling (not shown) in known manner. The laser unit 20 is a known type of C02 laser, which typically produces a beam of infrared light in a wavelength band between 9.4 - 10.6 micro-metres, typically with an energy rating of about 110 watts over an eight millimetres diameter beam.

In use, the laser beam is emitted from the end 20a of the laser, and is reflected through 90 degrees by a first angled mirror 22, also located in the housing 21. The reflected beam (indicated by arrows A) is directed vertically up a guide 23, the longitudinal axis of which is perpendicular to the longitudinal axis of the laser unit 20.

The guide 23 opens into the lower end of a shielded housing 24 and is reflected through 900 by a second angled mirror 25 to impinge on a third angled mirror 25a, which reflects the laser beam through 90° to impinge on a Powell lens 40.

A Powell lens is an aspheric cylindrical lens of known type, used for spreading an impinging laser beam evenly in a single plane. A laser beam impinging on one side of the Powell lens produces a fan-shaped "flat" laser beam, which can be further modified into a uniform parallel beam using a cylindrical convex lens as shown in Figure 7.

It will be appreciated that the laser beam can be modified using different types of lens arrays:- any array which produces a spread laser beam of the required width could be used.

The preferred lens array 39 is shown in Figure 7:- a Powell lens 40 receives the laser beam from the third angled mirror 25a to produce a fan shaped beam 41 which then passes through a convex lens 42 to produce a parallel beam 43 of the desired width. The use of a Powell lens gives a more even distribution of intensity across the full width of the beam, ensuring that the coating is burned evenly over the full width of the beam.

The lens array 39 is mounted for reciprocating travel on the links of the housing 24; the lens array 39 is moved by means of a reciprocating drive belt 28 which in use is operated (e.g. by a stepper electric motor) to reciprocate the lens array 39 along the length of the housing 24, and thus across the full width of a sheet in the burner 17. The movement of the lens array is monitored by a second encoder (not shown) connected to the housing of the lens array and to the control system of the laser. This is a safety feature:- if the lens array is not moving, then the laser must be switched off, to ensure that the laser is not continuously aimed at one spot rather than being moved along the sheet is intended.

A further safety feature is the provision of a third encoder (not shown) which is mounted at the end of the drive belt 28 and set up to detect movement of the drive belt 28:- no movement of the drive belt is detected over a predetermined minimum threshold, the laser is switched off.

Once the burn has been completed, the laser is switched off and the mirror galvanometer 27 or lens array 39 is moved back to the starting position while the sheet 10a is advanced into the shear 18, which cuts through the sheet along the centre line of the burn i.e. leaving an equal burnt off portion of coating on each side of the cut.

Any suitable known type of shear 18 may be used:- typically, the shear would be an electrically powered blade which has a cutting profile shaped to correspond to the profile of the sheet to be cut, and is moved vertically downwards onto the sheet, cutting against a stationary edge which also has a profile shaped to correspond to the profile of the sheet to be cut, to avoid deformation of the corrugations during the cutting process.

A further length of sheet is then advanced from the roll, through the roll former, and then positioned in the burner as described above. The process continues until the required number of sheets has been cut.

The laser housing 24 is fitted with safety shields as shown in Figure 5. Each safety shield 30 consists of a rectangular panel 31 of glass fibre reinforced epoxy resin which has two independent continuous copper circuits 32, 33, embedded on one surface; in use, a small current runs continuously through each of the copper circuits via two sets of electrical connections 34, 35. A continuous row of shields is mounted over the top of the burn area, above the upper surface of the sheet, as shown in Figure 4; the shields are connected to each other in series.

In normal operation, no laser light would escape through the sheet being treated, even when the burner is in use. However, there is always a risk of malfunction or that the sheet might be flawed and have a hole in it. The material of which each shield 30 is made readily absorbs energy from the laser beam in the event that the laser impinges on the shield, and this raises the temperature of the shield sufficiently to melt the copper of one or more of the copper circuits 32, 33.

The row of shields is electrically connected to the laser control system, such that any interruption of either of the copper circuits switches the laser off. The thickness of the shield material is such that the laser beam does not penetrate right through the shield before the copper circuit is interrupted and the laser is switched off. This completely avoids the possibility of a malfunction or damage to the steel sheet allowing the laser beam to escape from the apparatus.

Shields made in an identical manner, but differently shaped for the particular application, are used to surround any components in the burn apparatus through which the laser passes in use or on which the laser is reflected in use. All of the shields are connected to the laser control equipment and ensure that if for any reason the laser is misaligned, the laser beam will strike one or more of the shields, interrupt one or more of the copper circuits, and cause the laser to be switched off.

In addition, the laser unit 20 is provided with safety cutouts and shields in known manner, to prevent overheating or misdirection of the laser beam.

The combustion products from burning of the DRIDEX may include toxic or irritating particles and/or toxic gases. These are withdrawn from the housing 24 through a vacuum tube (not shown) and are passed through suitable filters (e.g. carbon filters).

Claims

1. Apparatus for modifying a coating on sheet material, said apparatus including: • a laser capable of producing a laser beam having a wavelength which is readily absorbed by said coating; • means for supporting sheet material on which the coating is to be modified at a predetermined position relative to the laser; • means for directing the laser beam onto a spreading means which is arranged such that in use the spreading means spreads the laser beam over a predetermined area of said sheet material.

2. The apparatus as claimed in Claim 1, wherein the apparatus also includes: • means for supporting a roll of sheet material which has been coated with a coating to be modified by the apparatus; • means for advancing said roll of sheet material into a roll former to form corrugations in the sheet material; • means for advancing the corrugated sheet material to a burner unit for removal of a predetermined amount of coating over a selected area of the sheet material.

3. The apparatus as claimed in Claim 2 wherein said apparatus further includes means for cutting the sheet material into sections of predetermined length.

4. The apparatus as claimed in Claim 2 or Claim 3, further including: a first encoder arranged to measure the length of sheet material passing through the roll former, said encoder being adapted to halt forward movement of the sheet material through the burner unit at a point at which the line along which the sheet will need to be cut is centred on the burner unit.

5. The apparatus as claimed in any one of the preceding claims wherein in use the laser beam produced by the laser is turned through 90 by a first mirror and then turned through a further 90° by a second mirror, before it impinges upon the spreading means.

6. The apparatus as claimed in any one of the preceding claims wherein said spreading means includes:

• a burner unit mirror which is arranged such that in use a laser beam reflected from said mirror falls on a predetermined area of said sheet material; • means for rapidly oscillating said mirror over a predetermined arc; • means for reciprocating said mirror such that said mirror travels across the width of the sheet material on which the coating is to be modified, at the same time as said mirror is moved over said predetermined arc.

7. The apparatus as claimed in any one of Claims 1-5, wherein said spreading means includes: • a lens array arranged such that in use a laser beam impinging on the lens array emerges as a spread beam lying substantially in a single plane and of substantially uniform intensity across the beam; • means for reciprocating the lens array such that the lens array travels across the width of the sheet material on which the coating is to be modified.

8. The apparatus as claimed in Claim 7, wherein the lens array includes a Powell lens.

9. The apparatus as claimed in Claim 8, wherein the lens array also includes a cylindrical convex lens, said Powell lens and said cylindrical convex lens being arranged such that in use a laser beam impinges first on said Powell lens and then on said cylindrical convex lens, to produce a substantially parallel laser beam from said convex lens.

10. The apparatus as claimed in any one of the preceding claims, wherein the coating to be modified is a DRIDEX (Trademark) coating and the sheet material is sheet steel.

11. The apparatus as claimed in Claim 10, wherein the laser is a carbon dioxide laser producing light in the wavelength band 9.4 - 10.6 micro metres.