Northpoint is an approved applicator of powder organic coatings, servicing the construction and architectural industries across the UK.
What is BS EN 13438: 2013?
EN 13438: 2013 is a document prepared by Technical committee CEN/TC 139 “Paints and Varnishes”.
It’s a reference standard for Powder Organic Coatings for hot dip galvanised (HDG) or sherardized steel products for construction purposes.
It specifies the performance requirements for organic powder coatings to be applied as finishes for construction purposes. It does not set out the specific processes requirements but does provide guidance on cleaning and pre-treatment of HDG prior to coating application.
Substrate Materials Covered – HDG steel in accordance with ISO 1461, EN 10346, or sherardized steel in accordance with EN 13811. Ideally the steel parts should be free of die lines, spikes, dross or other surface imperfection but the pre-treatment is the responsibility of the powder applicator.
Coating Powders – the powder manufacturer or supplier if different shall provide the applicator with:
- Manufacturer name
- Trade name
- Colour ref.
- Gloss level
- Type of resin
- Batch number
- Product reference code
- Date of manufacture
- Date of dispatch
It’s important that the powders are stored in unopened containers for up to 12 months or less is specified by the manufacturer at less than 25oc, again unless specified otherwise by the manufacturer. There’s also a set of requirements for performance which are detailed in Annex A of the standard.
Clause 6 of the standard deals specifically with the application of the powder. Annex B deals with cleaning and pre-treatment. Annex C provides recommendations on application conditions of the powders.
Points to be aware of:
- Powder thickness should be not less than 60 µm
- No scratches through to the substrate shall be visible from 3 m or further away
- A slight degree of orange peel is expected – this can be reduced at the design stage by removing the need for differing section thicknesses on the same product or part
- The coating shall adhere to the substrate
Guidance on Cleaning
The parts should be free from contamination and/or zinc corrosion products when delivered in from the HDG process. The cleaning action of a chemical pre-treatment process is not likely to remove zinc oxides but should be able to cope with an amount of oils, grease, lubricants and other residues that can be removed by the washing process. Continuously HDG products may also have a temporary layer of corrosion protection (sometimes called passivation) which will have to be removed before pre-treatment conversion coating can effectively take place.
Pre-treatment is a chemical process, or a mechanical process, or a combination of the two (mechanical should always take place before the chemical process). There are many alternative pre-treatment systems that can be used and will be compliant with the standard.
Types of Pre-Treatment
- Chemical – conversion coating applied to a rust/corrosion, grease, dust free surface and not consisting of a powdery type deposit when viewed after drying. Typical processes might be chromate conversion, phosphate conversion, silane/zirconimum based process or another suitable alternative.
- Mechanical – sweep blast cleaning but in such a way that the HDG remains intact after the process. Blast abrasives such as carborundium of aluminium oxide are typically used at a pressure of not more than 300 kPa.
Methods of Powder Coating Testing
- Surface Appearance – illuminate the significant surfaces as ISO 3638 and examine at an oblique angle with normal or corrected vision
- Colour – colour match in accordance with ISO 3638
- Thickness – determine the total thickness on each significant surface in accordance with ISO 2808, you then have to subtract the zinc thickness to arrive at the powder coating thickness
- Gloss – assessed at an angle of 60o in accordance with ISO 2813
- Adhesion – test and record the results in accordance with ISO 2409
Packing and Handling
Powder coatings are generally robust but should still be handled with care so as to avoid damage and/or contamination. Its recommend that when packing coated parts that recycled materials should be used wherever possible and labels attached to each bundle of coated parts, ideally warning that care should be taken when handling. Additional care should be taken when handling coated parts in low temperatures.
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Blog Author – Philip Dawson, Technical Advisor, email@example.com for technical and specification enquiries