Monday, August 9, 2010

Chromadek




                    Availability and properties
                   Chromadek® for Exterior Applications
                   Pre-painted hot-dip galvanised steel sheet
Introduction
CHROMADEK® is ArcelorMittal South Africa’s trade name for a range of colour coated sheet products. It is produced by coating sheet on a sophisticated coil coating line, where steel substrate surfaces are thoroughly chemically cleaned before a primer coat is applied to either one or both sides of the sheet.  After elevated temperature curing, the top coat is applied, to either one or both sides and again cured in the gas fired furnaces.
This coil coating process allows accurate control, in a controlled factory environment, of the important parameters for application of paint coatings, such as cleaning, pre-treatment, paint application and curing conditions.
The CHROMADEK® range of products has been developed for a range of different end uses:
Ø Exterior applications such as roofing, cladding, signboards and garage doors, for less corrosive as well as marine environments (covered in this Data Sheet)
Ø Interior applications such as cool room panels, ceiling strips and light fittings (Data Sheet C1.6)
Ø Domestic appliances, such as fridges, freezers, geyser wrappers and air conditioning units. 
(Data Sheet C1.7),
Other coated products processed on ArcelorMittal South Africa’s colour coating unit includes CHROMAPREP® (See Data Sheet C1.8) and TEXTRADEK® (See Data Sheet C1.6)
General description of CHROMADEK® for Exterior Applications                                                 
Over and above its aesthetic attributes, CHROMADEK® paint coatings are designed to provide superior corrosion protection under conditions where the performance of unpainted galvanised sheeting may prove inadequate. Furthermore, the coatings exhibit excellent formability and elasticity to facilitate roll profiling and bending operations without damage to the paint coating.
Chromadek is applied onto a galvanised coated substrate, which has been produced by the addition of Antimony and Aluminium to the molten zinc in the bath, to improve the formability and adherence of the zinc coating.
Excellent paint adhesion is achieved and corrosion resistance enhanced by careful preparation of the steel surface prior to paint application. Rigid quality control testing is carried out on each coil to ensure conformance to specification.
The atmospheric conditions to which the CHROMADEK® sheeting will be subjected, will determine which of the following paint systems should be specified:
Standard CHROMADEK® is intended for use under rural, mildly chemically polluted or moderate marine conditions, and is composed of Z200 hot-dip galvanised substrate pre-primed with an epoxy/chrome free primer (dry film thickness (DFT) of 4-6 microns) and finished with a final paint coat (DFT 18-22 microns) on the top surface. A single backing coat (DFT 8 microns) is normally applied to the reverse side of the sheet.
CHROMADEK® PLUS is intended for heavy industrial or marine conditions, and is composed of Z275 hot-dip galvanised substrate, pre-primed with a primer with DFT of 20-25 microns (4-times thicker than the standard CHROMADEK® primer coat) and finished with a final coat (DFT 18-22 microns) on the top surface, giving a total coating thickness of 38-47 microns.
The bottom surface can either be coated with the CHROMADEK® top surface paint system i.e. 4-6 microns primer and 18-22 micron topcoat, or the CHROMADEK® PLUS top surface paint system.
Paint System
CHROMADEK® is produced in a range of 14 standard colours, which were selected after consultation with both Specifiers and Architects. Special pigments are used to ensure that the paint will withstand extended outdoor exposure under the harsh S.A. conditions (high UV-radiation).
The availability of other colours for large projects is subject to enquiry.
Standard Colours
Table 1 Standard Colours

Name

Colour
% Gloss at 60°
(± 5 %)

ArcelorMittal Steel SA

Reference number
Fish Eagle White
White Lion
Gemsbok Sand
Sandstone Beige
Kalahari Red
Buffalo Brown
Traffic Green
Aloe Green
Umhlanga Wave
Azure Blue
Kingfisher Blue
Dove Grey
Dark Dolphin
Charcoal Grey
White
White
Dark Beige
Beige
Red-Brown
Brown
Green
Light Green
Turquoise
Blue
Light Blue
Light Grey
Dark Grey
Dark Grey
30
30
30
30
30
30
30
30
30
30
30
30
30
30
N14128
N15010
N15366
N15365
N06541
N09412
N03002
N03283
N02103
N01109
N01029
N13639
N13030
N13012

Note:
For an indication of the colours, refer to Data Sheet: CHROMADEK®, Standard Colours (Data Sheet C1.9).

Table 2 Paint System Properties

Property
Test conditions
Method
Typical values
Chromadek
Chromadek Plus
Resistance to UV Weathering (Colour Change)
QUV-A
ASTM G154
ISO 7724/1/2/3
After 2000 hrs:
DE < 2
After 2000 hrs:
DE < 2
Resistance to UV Weathering (Chalking)
QUV-A
ASTM G154
ASTM D659-04
After 2000 hrs:
Rating No 8
After 2000 hrs:
Rating No 8
Resistance to corrosion:
- Edge creep
- Blister size
Salt Spray

ISO 7253

ASTM D1654
ISO 4628/2
After 500 hrs:

5mm max
2-S2
After 1000 hrs:

5mm max
2-S2
Flexibility:
T-bend test

ASTM D4145
2T
No adhesion loss
7T
No Cracks
2T
No adhesion loss
7T
No Cracks
Flexibility:
Reverse impact

ISO 6272
No adhesion loss
No adhesion loss
Pencil Hardness

ASTM D3363
F – H
F – H
Scratch Hardness

ISO 1518
25 – 40 N
25 – 40 N
Dry Film Thickness

ISO 2808, 5B
23 µm minimum inclusive of primer
38 µm minimum inclusive of primer
Specular Gloss at 60°
At time of coating
ISO 2813
25 – 35%
25 – 35%


Mechanical properties

The substrate used for CHROMADEK® is produced to any of the galvanised steel specifications listed in Table 1 of Data Sheet: Galvanised: Availability and Properties (Data Sheet C1.1)

Dimensions

The nominal thickness includes the zinc coating, but excludes the paint system.

Table 3 Standard Dimensions

Nominal Thickness (mm)
Nominal Width (mm)
0.47
0.50
0.53
0.58
0.80
925, 1225
925, 1225
925, 1225
925, 1225
925, 1225

Tolerances

Shape and dimensions

Tolerances on shape and dimensions are given in the data sheet: Galvanised Sheet Tolerances (File 
Ref Data Sheet C1.2)
Design considerations

In areas with frequent rain followed by long periods of relatively high humidity, the following design factors must be addressed:

Ø Overlapping of sheeting (end laps) is to be avoided if possible, as waterproofing of lapped areas is seldom successful in the long term.  The use of full-length sheets is recommended.
Ø The slope of the roof shall be such that water can drain freely from it without forming ponds. The minimum recommended slope for Box Ribbed or S-Rib sheeting is 5°.
Ø In a marine climate, certain areas for example sheltered areas on the undersides of roof overhangs, canopy type roofs and loading bay canopies could result in accelerated corrosion from the under side. Sea salts or aggressive contaminants tend to accumulate on these surfaces, as they are not periodically washed down by rain.  Designers should avoid this type of design or allow for additional protection in coastal or highly polluted industrial areas by means of light ceilings or specifying a full paint coat on the reverse side of the sheet.

Ø CHROMADEK® is recommended for applications greater than 5 Km from either marine or industrial environments whereas within the area between 1 - 5 Km from the salt spray zone CHROMADEK® PLUS must be used.  Both CHROMADEK® and CHROMADEK® PLUS used within 1 Km from either Marine or Industrial environments are excluded from any warranty by ArcelorMittal Steel South Africa Limited.

Expected Performance


Paint fading is the natural phenomenon associated with the gradual decrease of colour intensity resulting from the exposure of coloured paints to natural weathering. 





Packaging, transportation and handling

CHROMADEK® is a finished material with decorative coatings and good general abrasion resistance, but must be handled with care to prevent damage to the coatings. During de-coiling the coil should not be allowed to unwind freely, as slippage between interleaving surfaces could lead to paint pick-off in these areas.  No paint pick-off complaints will be entertained if tension control is not kept with a pinch roll before the strapping is cut during de-coiling.  De-coiling tension must be lower than the coiling tension.
The thinner backing coats are more prone to scuffing damage (paint pick-off) and orders should specify the correct packaging in line with the mode of transport and the final destination.  To avoid pressure marks coils should not be stacked, and should be dispatched ‘eye-to-the-sky’ (with the coil axis vertical) to prevent the occurrence of surface defects during transportation.

Forming

1. Roll-forming

Roll-forming rather than press braking is recommended for the forming of sections and components from pre-painted steel sheet, since there is less chance of damaging the paint coating.  A multitude of sections can be roll-formed provided the necessary adjustments are made in roll clearances.

Bend diameters should also be larger than the bend to which the material was subjected to during Quality Control Testing.

2. Lubricants

The organic coatings used for CHROMADEK® usually act as excellent dry film lubricants.  Where lubricants are needed, the water-soluble types are recommended.  If emulsified compounds are used, it is important that they are completely removed immediately after roll-forming, in order to prevent staining of the paint coating.

Touch up and Site Practice

Air-drying touch-up paints, such as water based acrylic roof paints, are recommended for over-painting.  However, the ultraviolet resistance of air-drying touch up paints is generally lower than the oven-cured CHROMADEK® finishes.  Accordingly, touching-up of scratches should be undertaken with a thin paintbrush to minimise unnecessary over-painting.  Slight scratches which may occur during erection or handling can generally be left as is, because they will not be visible from a distance, while the galvanised substrate will offer adequate protection against corrosion.

Anyone walking on roofing panels must wear soft-soled rubber shoes.  Such traffic across the roof must be restricted to a minimum.  It is recommended that soft material of some form be used to protect the paint coat temporarily in areas of traffic.

Abrasive cutting or trimming of CHROMADEK® sheeting on top of roofs should be avoided.  However, if unavoidable, the iron particles must be removed from the roof surface by means of a bristle brush or broom, as it is not easily washed down by rain.  If left on the roof the iron particles will start to rust, tarnishing the CHROMADEK® paint surface.

The recommended method of cutting sheets on site is by using a sheet nibbler, which gives a clean edge and does not damage either the sheet or paint coating.  It is imperative that all steel particles (swarf) and other debris are removed as roof erection proceeds, since they can cause damage, discoloration or corrosion. A thorough building clean up after completion of construction should be conducted to remove all loose particles, objects and dust from walls and roofs.

Maintenance

Rainfall alone is often sufficient to keep exterior surfaces looking clean and bright. However to achieve maximum life from the CHROMADEK product, it is important that accumulations of dirt and debris which are not removed by normal rain washing are removed by regular cleaning every six months.
Washing may be carried out with a hose and soft bristle brush, using fresh water. In areas where heavy dust deposits dull the surface, a solution of fresh water and good quality household detergent or propriety cleaner may be applied to ensure thorough cleaning, followed by rinsing with clean water to eliminate the possibility of residue
.
Compatibility

Most materials used in contact with traditional galvanised steel can be safely used with CHROMADEK®.  However, run-off water from COR-TEN®, lead or copper products may cause staining and should not be allowed to come into contact with the painted surface.

Mixing of Material

Where different brands of prepainted material are used on the same building, differences in colour, gloss, and weathering performance may appear obvious in a short period of time. This is due to the different formulations used by the various manufacturers.   
ArcelorMittal will not accept liability for problems caused by the mixing of brands.
By the very nature of colour, some slight variation can occur between coils produced at different times through the paint line therefore all profiles for a single elevation should be manufactured from the same production batch. Building contractors and erectors should aim to ensure that this practice is followed during the installation of the roof sheets.

Edge protection

Generally cut edges on CHROMADEK® sheets do not present a corrosion problem, even in coastal areas, as the zinc of the galvanised substrate will cathodically protect the exposed edge. Small traces of white deposits on cut edges should therefore not be a reason for concern.

Warranty

ArcelorMittal South Africa guarantees the prime quality of the product and that the material will have a functional life prior to weathering in the natural elements of a minimum of 10 years from the date of supply. However, ArcelorMittal South Africa cannot accept liability for scratches or other damage to the material sustained during and after profiling, transport to or storage at the building site or after erection.
For warranty purposes ArcelorMittal South Africa may be approached for a:

Ø Provisional warranty (warranty of intent) during the tendering stage; and
Ø Warranty of the material on the building after erection.

Please note that no warranty is deemed to be valid unless ArcelorMittal Steel South Africa Limited has formally issued a warranty after specific request by the purchaser.

Quality Assurance

A quality assurance system that complies with SANS 9001 is in operation throughout the manufacturing process, and the galvanised substrate used for ArcelorMittal South Africa’s CHROMADEK products conform to the requirements of both SABS ISO 3575 and SABS ISO 4998.

Branding

All CHROMADEK material is marked with the ArcelorMittal logo, on the reverse side at intervals of approximately 900 mm, parallel to the length of the strip and 140 mm in from the edge.

Supply conditions

CHROMADEK® is supplied in terms of Price Lists 145 and 147 with ArcelorMittal South Africa’s General Conditions of Sale.
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