Pre-treatment
Pre-treatment is literally the key to successful powder coating.
The performance of a coated product is dependent on the materials of construction, its design, the pre-treatment, the coating system and the working environment.
In the UK 1 tonne of steel turns to rust every 90 seconds, it pays to protect it properly.
At Hydralon we have extensive pre-treatment facilities, including programmable microprocessor controlled aqueous systems which allow optimum conversion of a range of metals and forms whether sheet, extrusion, castings or fabrications. This, together with many years of experience from the field, our own extensive laboratory test facilities, and working closely with pre-treatment and materials suppliers, enable us to offer the latest, most appropriate pre-treatment and coating systems for your product.
A Hydralon Guarantee of up to 25 years can be provided on request depending on the substrate, use and working environment.
Work can be carried out to BS 6496/7 if required.
Hydralon's pre-treatment all to 6.45m are as follows:
- Aqueous degreasing
- Architectural trivalent (RoHS compliant) chromate 407-47
- Zinc Phosphate
- Grit Blasting (chilled angle iron)
- Bead blasting
In addition we have specialist magnesium chromating and alocrom 1200.
Details of RoHS Compliant Alocrom 407/47
Alocrom 407/47 is a trivalent chromate conversion coating with a light iridescent green colour. It is applied by Hydralon to components in a fully automated computer controlled plant which cleans, degreases, etches and chromates the metal surfaces.
This trivalent chromium pre-treatment is safer and more environmentally friendly than yellow hexavalent chromates, such as Alocrom 1200 and has outstanding corrosion protection.
This trivalent chromium pre-treatment is RoHS compliant.
The treatment chemically reacts with the metal and converts the surface layer to an integral and flexible non-metallic barrier consisting of a complex mixture of aluminium chromate, phosphate and fluoride. The chemically converted layer is insoluble and inhibits the start and spread of corrosion even from layers which have been damaged in service. The chemical conversion provides an excellent key for the subsequently applied powder coating which adheres very strongly to the surface.
Performance Characteristics
Alocrom 407/47 meets fully the requirements of BS 6496 : 1984 (1991) - Specification for "Powder organic coatings for application and stoving to aluminium alloy extrusions, sheet and preformed sections for external architectural purposes , and for the finish on aluminium alloy extrusions, sheet and pre-formed sections coated with powder organic coatings".
Laboratory tests carried out on nominally 1mm thick aluminium panels pre-treated with Alocrom 407/47 and coated with a level finish polyester powder - meeting the requirements of BS 6496 : 1984 (1991) with coating thickness between 50 and 70 microns, have given the performance standards.
| Physical Characteristic | Test Method | Result |
| Adhestion | 2mm Cross-Cut BS 3900 : Part E6 |
No failure Classification zero |
| Impact Resistance | Falling Weight BS 3900 : Part E3 |
Pass 2.5mm indentation, With no cracking of the coating. Nor any detachment from the substrate |
| Flexibility | Conical Mandrel Bs 3900 : Part E11 |
Pass 5mm diameter, with No cracking of the coating nor detachment from the substrate |
| Elasticity | Cupping Test BS3900 : Part E4 |
Pass 6mm indentation with no cracking of the coating nor any detachment from the substrate |
| Chemical Characteristics | Test Method | Result |
| Hot Salt Spray Resistance |
BS 3900 : Part F12BS 6496 : Clause 15 | No failure Classification zero |
| Acetic Acid/Salt Spray Resistance |
Excellent resistance to over |
Excellent resistance to Over 1,000 hours |
| Condensing Humidity Resistance |
BS 3900 : Part F2 BS 6496 : Clause 4.11 |
Excellent resistance to Over 1,000 hours |
| Pretreatment Quality | BS 6496: Clause 17 |
Pass |
Uncoated Performance and Electrical Resistance
A conversion coating of 20-50mg/m2 of Cr3+ (total coating weights of 60 - 150 mg/m2) will give electrical resistance values suitable for electronic applications. This will meet the US military specification M1L-C-554 of less than 5000 Ohms.
Uncoated performance against hot salt spray ASTM B117 is 325 hours.
Zinc Phosphate
Zinc phosphate is the premier chemical pre-treatment for mild steel, because of its crystalline structure, the zinc phosphate conversion coating provides an excellent key for the subsequent powder coating, resulting in superb adhesion. Moreover, as the zinc phosphate conversion layer is insoluble, it inhibits the spread of corrosion from areas where the powder coating may have been damaged in service. Consequently, it also prevents undercutting of the powder coating and thereby eliminates the problem of unsightly flaking paintwork. Expensive maintenance is greatly reduced, although some rust staining may still occur if the crystalline layer has itself been penetrated.
Polyester powder coated zinc phosphated mild steel panels pass 1000 hours in hot neutral salt spray to ASTM B117, this would give a useful life of 10 years in most UK environments.
Grit Blasting
Grit blasting is a process of propelling hard sharp angular grit at the item to be clean. It is an excellent way to remove oxide and rust from black or welded mild steel and provides an excellent surface for subsequent chemical pre-treatment or as a key for powder coating.
At Hydralon we use chilled angle iron grit for ferrous material and aluminium oxide or glass bead for stainless steel and non ferrous materials.
The quality of blasting is quantified by ISO 8501. Normally we would specify Sa 2½ prior to zinc phosphate for outdoor application.
Our technical support team would be pleased to assist your specification selection.
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