Protection of Magnesium & AluminiumIndestructible Paint has been involved for more than 50 years with the development and production of surface coatings to provide corrosion protection for magnesium and aluminium. Our first experience with magnesium was as far back as the 1950's with the introduction of the Rockhard range of coatings, initially for the SRN1 hovercraft and the Westland Wigeon helicopter. These initial coatings were stoving (baking) systems, and still form the basis of the range, albeit with considerable and on going development in the ensuing years.
We believe that the American AMS 3132 phenolic based system which appears to be their standard magnesium protection is the fore runner of our Rockhard range of products. This was the technology used for protecting magnesium in the 1940's in the UK, and has been superseded a long while ago. However, some of the thin film principles are still used today in obsolete, but still called for, specifications.
As with many other industries, current aerospace prime manufacturers have been formed from the amalgamation of several older companies. As an example Rolls-Royce aero engines includes Hawker-Siddeley and Bristol Aerospace among others. Each of the companies had their own systems for magnesium protection; consequently the Rockhard range includes differing products released to differing specifications to achieve similar results. We still hear references to Glasgow systems, Derby systems, Bristol systems, and even Leavesdon systems.
Latest developments have included work on
both the traditional baking and cold cure (touch
up) ranges, to take account of improved
performance requirements, constantly evolving
environmental and safety legislation. These new
additions are detailed in the listing of products.
New work is on-going into low VOC cold cure 2
component systems to give corrosion and
protection performance to match the baking
products, a development
we consider to be particularly exciting.
Like all our product ranges, we continue to
engineer Rockhard products to meet specific
client requirements.
Pre-treatmentHistorically we have worked with commercially available pre-treatments which in the UK have been chromate based. In the USA, there has been a move to chrome free systems, and heavy anodizing and new anodic technologies including HAE, Tagnite, Magoxid and Keronite have been employed. This trend is now being seen throughout the world, and several additional chrome free systems are being introduced. We now believe that there needs to be more synergy between the pre-treatment and the sealing/priming operation, and we can now offer a chrome free immersion pre-treatment system for aluminium. This is undergoing ongoing development to improve the protection on magnesium. Please refer to our Iptreat information leaflet for full details.
However, we believe in aerospace applications all pretreatment methods benefit from the use of a full surface treatment system. On magnesium it is our conviction that the use of a penetrative sealant is essential, prior to application of further primers or colour coats. On aluminium, either a chromate, or nowadays more commonly, a chromate free primer is the choice.
Rockhard Baking SealantsThere are two basic ranges, both of which are used to successfully seal magnesium & aluminium. However, each have slightly different properties.
576-450-002-R1 has good high temperature capability; 1000 Hours at 220ºC is a normal test. It is also significantly better for intercoat adhesion for subsequent primer or decorative coats. However, it is less colour stable at temperature, the clear coat going a dark chocolate brown if cured correctly. White versions go a very dark cream/brown when used at elevated temperatures. The latest R-1 version is formulated to be ethyl glycol acetate free.
The product is widely used on magnesium helicopter gearbox castings, and is specified by a number of manufacturers such as Sikorsky. It is also used as the sealant on magnesium engine casings, prior to application of decorative colour coats.
A recent development, at a specific client behest, is a reduced VOC version, formulated for dip/flow coating application. Utilising latest generation formulation techniques to include reactive diluents, a greater than 25% reduction in VOC’s at application viscosity has been achieved. This is being adopted on aluminium heat exchangers. For further information, request our technical data sheet on IP576-4675.
985-111-800 clear is slightly more complicated in its application parameters, but it does have some distinct advantages. It is possible to build up quite thick coats by part curing between coats with a final full cure after application of the topcoat. This material then retains its colour better than the 961 grade and can be used as a decorative coating. 985 systems are understood to have slightly better resistance to chemicals used in anodising baths, making this range more suitable when reanodising is part of the production process.
Again, a recent development is a toluene free, reduced VOC version (IP985-547) which is now widely specified and used, with approvals from Turbomeca; Messier- Bugatti and Eurocopter.
In overhaul situations, it is not always possible to utilise high temperature baking sealants; components to be coated can include several differing metal parts, with resultant differing rates of expansion at elevated temperatures. For these types of application, we have developed a low cure version, which gives technical performance approaching the full baking grade. 985-111-002 has been adopted by McDonnell-Douglas Boeing for use on overhaul of Apache helicopter gearboxes.
A commercially available product from this low cure range, IP985-125 is being evaluated in several other aerospace and industrial areas where cure temperatures below 150°C are essential.
For protection of aluminium, it is possible to utilise a primer system in addition to, or as an alternative to clear sealants. It is also quite common to use a primer over both 576 and 985 sealants on magnesium.
The Rockhard primers are based on the 985 system, and have traditionally utilised chromate pigments, well proven as an anti-corrosive system. 700-155-003 has been used in many applications, including on aluminium fan cases on turbine engines. This is still the product specified by Rolls-Royce to MSRR 9226.
However, changes in environmental and safety legislation is forcing a move to chrome free systems. This is especially so in Europe and America. Much development work has been conducted into alternative chrome free anti-corrosive pigments; the resulting primer, IP985-6500 also being produced toluene free.
The primer has been tested at the Rolls-Royce main test laboratory to give over 6000 hours salt spray performance to ASTM B-117 on aluminium. The product has now been approved and adopted across the Safran group in France and by Eurocopter, where technical performance has actually been improved over the previous chrome containing system.
Rockhard Baking FinishesAs with Rockhard primers, the range of finishes are based on the 985 system, which ensures colour stability across a wider temperature range.
Black gloss (614-150-002), black matt (615-155-001) and aircraft grey gloss (985-000-693) have been used for many years on a variety of projects, including undercarriages, heat exchangers, engine casings and control gear. Normally released to DTD 5562, these products also meet the requirements of MSRR 9226.
Mirroring the work conducted with the 985 sealants and primers, an additional range of finishes (IP985 range) is now available with reduced VOC’s and toluene free. A wide colour range is available, and this range has been approved and is in use throughout the Safran group for both aerospace and military applications, and again by Euroopter. This range will of course still meets the requirements of DTD 5562 and MSRR9226.
Rockhard baking systems are extremely chemical resistant, very hard and erosion resistant. For example, both systems are still used for coating turbine blades and varying engineering parts in aerospace, military and other high performance applications.
Originally designed as touch up systems for Rockhard baking systems, Rockhard 2 component systems are used where baking/stoving is not desirable or possible, and where good corrosion or chemical resistance is required. By nature of their cold cure capabilities, these products can be used on temperature sensitive substrates, including composites, some plastics, and even wood and asbestos. As such specific products from the range have been used in untypical aerospace applications, including as the primer-filler of composite airframe panels on the HAL DHRUV advanced light helicopter.
A range of sealants, primers and finishes is available, in both traditional low solids, high VOC grade and the latest technology low VOC, HAPS solvent free grade. Again, to mirror the work conducted on the baking products, primers containing chromate and non-chromate anticorrosive pigments are available.
The products have been approved and are used against a wide range of specifications, including Def-Stan 80- 161(DTD 5555); MSRR 9064; LB568, PWA36568/9 and CPW 714/5.
Examples of the ranges include 750-450-004 (clear sealant); IP3-6600 (Low VOC Chromate free primer); 750- 152-009 & 700-155-005 (Gloss & Matt Black finishes), and the IP3 range of low VOC gloss colours.
Ongoing development work investigating methods of increasing surface hardness and corrosion and chemical resistance, including nano technology, will, we expect produce a range of cold cure products with equivalent performance characteristics to the baking ranges.
We hope this information gives an insight into our technologies for protecting magnesium and aluminium. Full technical details and application and cure information are available on all the products discussed; please ask your usual sales contact at Indestructible for further details.
The Rockhard Range of Coatings
Jet stream steel under carriage leg coated with Rockhard
THE ROCKHARD RANGE OF COATINGS
576-450-002 ROCKHARD CLEAR STOVING ENAMEL & MICROPOROUS CASTING SEALER
615-155-001 ROCKHARD STOVING MATT BLACK EPOXY COATING
690-115-010 SPRAYING, MULTI-COAT ATTRITION COATING
700-155-003 ROCKHARD STOVING ZINC CHROMATE PRIMER
700-155-005 ROCKHARD TWO PACK EPOXY MATT BLACK
750-450-004 ROCKHARD TWO PACK CLEAR EPOXY GLOSS
750-152-009 ROCKHARD TWO PACK EPOXY GLOSS BLACK
985-000-693 to 696 ROCKHARD GREY, GREEN, WHITE & BLACK STOVING ENAMEL
PROTECTION OF MAGNESIUM USING INDESTRUCTIBLE PAINTS ORGANIC COATINGS RANGE
Rockhard is the name of a range of coatings that is still being developed after 40 years.New uses and markets are still being found for these incredibly versatile chemical and erosion resistant products.
(to DTD 5562. 444/176 and IP9040 CPMC 79964)
Epoxy Phenolic 961
This product was designed for the original painting of aircraft 40 years ago, such as the Comet and Westland Wessex. It is so good that it and its variants are still specified today on aircraft such as the Tornado, VC10, Airbus and BAC-111. As a protective coating it is particularly effective on magnesium and aluminium alloys and as such is recommended by Magnesium Electron. It is also used on steel, titanium and other metals. It is highly resistant to weathering and a very wide range of chemicals up to 200ºC (see chart). The original MOD spec required the coating to resist 3 months exposure to distilled water at 60-70ºF, 3 months exposure to humidity (Def 1053 No.25) and 6 months exposure to salt spray (Def 1053 No.36). Rockhard is also very effective at curing microporosity in magnesium and is recommended for surface sealing particularly as protection against chloride ions. It can be centrifuged, sprayed, roller coated or dipped, on magnesium, aluminium, steel or titanium. Approved for use by British Leyland for use on Radiators etc and recently by Toyota. It is also used to coat computer chassis for insulation purposes.
(to DTD 5562), Allied Signal FP5109, BMW Rolls Royce.
Similar to the 576-450-002, this product is sometime preferred. It is slightly more acid resistant when magnesium is rechromated after machining. Rockhard 985 is high flash, low toxicity and low odour. It also has slightly better colour retention properties, slightly thicker film thickness, but is less tolerant to adverse conditions and application and does not have quite such good intercoat adhesion. 985-111-800 is a good dipping product having been formulated with high flash, low odour solvents, it is also easily sprayed. Both 985-111-800 and 576-450-002 are fully compatible and will not cause problems if mixed. Used by both Allied Signal and Textron, it has most recently been approved by BMW Rolls Royce for use on the BRR 710 gearbox.
(to DTD 5562. 444-1081 and IP9044)
A gloss black epoxy Stoving enamel proven for many years as a protective coating, particularly magnesium and aluminium alloys. With similar properties to the Rockhard clear, it is also resistant to weathering and a very wide range of chemicals at up to 200ºC. Its uses include heat exchangers and aircraft components, including the Rolls Royce Trent control apparatus, boxes and covers.
(to DTD 56D & Rolls Royce MSRR 9226. 444-80 and IP9045)
Aircraft under carriages, control gear, brake temperature cases and optical equipment have all been coated in this matt black. With similar properties to the Rockhard clear and gloss black it has also been used for many years.
(to DTD 5562, Rolls Royce RPS 534, AQD & RTO Approvals RP123)
Used for more than three decades on compressor blades by the UKI's turbine manufacturers both in jet engine units and electricity generators. Like the other Rockhard stoving products it is highly resistant to acids, alkali's, organic solvents and temperatures up to 200ºC.
(to Lycoming MS M4735)
A glossy grey epoxy stoving coating to Fed. Stan 595-16099 developed for engine and other use including process specs. P6426 and P6445. This product has similar properties to the Rockhard Clear 576-450-002. A 2 part air drying colour matched touch up is available - IP9158 A & B, which is approved for P6426-P6 and P6445-P4.
(to DTD 56D & British Aerospace S26.3506)
A glossy, grey, epoxy stoving coating to the colour grey. Proven over many years as a protectant, it is highly resistant to weathering and a wide range of chemicals. It is currently used, for example, on the BAe 146 wing sections, Sidewinder air to air missiles and the Airbus.
(to MOD AFS538, Rolls Royce MSRR 9226 & BAe S26.3506, 444-3097)
(588/006/2, DTD 300/4825, AFS 881)
Although environmentally unpopular, chromate based primers are wonderful anti-corrosion products. Formulated originally for the aerospace industry, it is suitable for use on magnesium alloys, steel and aluminium. These particular products have been used in aerospace and other industries for more than thirty years as part of a system for superior metal protection. Currently specified on the Airbus, its users include Westland and others.
An established, decorative maintenance product, used for over three decades. With the acknowledged properties of the Rockhard stoving products, it is used on magnesium alloys, steel and titanium.
Rockhard two pack coatings are for use where stoving is not possible and good corrosion, weathering, or chemical resistance is required. Rockhard two pack products can be used not only on metals, but a variety of their substrates including wood, asbestos and many synthetic rubbers and plastics.
(750-452-002, 444-709 & IP9041, AFS 641c)
Rockhard clear, two pack coating, is for use where stoving is not desirable or possible. Used on a variety of substrates including metals, wood, asbestos and many synthetics rubbers and plastics. Also as a touch up materials for Rockhard Clear Stoving.
Rockhard gloss black two pack coating is used as a decorative protectant. Normally dust free in 15-30 minutes, it achieves its full cure in approximately 7 days.
Two pack matt black coating is used on a wide variety of substrates. Resistant to corrosion, weathering and chemical attack, it can also be used to touch up Rockhard Matt black stoving 615-155-001, used by MOD in such diverse applications as Harrier fuel pump diaphragms, general engine touch-up, flexible fuel tanks, composites, and coating glass, prisms, etc.
The second part of the Rockhard Two Pack Coating used in a 1:1 mixing Rockhard Two Pack Clear (750-450-004) and Rockhard Two Pack Gloss Black (750-152-009) and 1:4 mixing ratio with Rockhard Matt Black Two Pack (700-155-005). (5 litres catalyst: 20 litres 700-155-005).
The normal thinners for both Rockhard stoving and two pack products.
For use with both Rockhard stoving and two pack products. Often used with two pack products to reduce drying time.
Occasionally, due to circumstances such as bad de-greasing, or problem applications, Rockhard can 'pinhole'. A small addition of anti-cyssing can overcome these problems.
Rockhard is the name of a range of coatings that is still being developed after 50 years. New uses and markets are still being found for these incredibly versatile chemical and erosion resistant products.
Please contact one of our technical team for a range of solutions.
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