Fishing Boat Corrosion Protection - Image Provided Courtesy of ESpray Greece
The Metal Spray process is used in saltwater environments all over the world in order to provide anti-corrosion coatings, anti-slip coatings and also as a method to reclaim worn components. The Metal Spray process is used to combat the very harsh conditions of a Marine environment in which ships can be at sea for months at a time with limited regular maintenance. Metal spray is much more durable than paint and independent European standards (EN14713 and EN2063) show that a life to first maintenance of 20+ years or can be achieved in sea water splash zones.
To ensure the long-term anti-corrosion protection of ocean-going vessels, Metal Spray is used on various parts of the vessels with an aluminium and zinc coating. Many parts of the vessels are specified to be Metal Sprayed for improved safety, durability and life-cycle costs. The deck and the hull, which sit above the waterline, have to be metallised in order to protect them against the harsh saltwater environment. Other parts of vessels that are metal sprayed include: Refrigerated Sea Water (RSW) tanks (where fresh fish are stored on board), fish processing rooms, chutes into the fresh fish tanks, net winching sheaves and drums, masts and the trawl boards. Not only are these elements exposed to the harsh, destructive sea environment, but also to the daily ravages of wear and tear of the equipment used in the trawling process. Other areas where Metal Sprayed anti-corrosive coatings are applied include, but are not limited to: Radar Masts, Steam pipes, Exhaust pipes, Ladders, Lifeline Stanchions, Diesel Exhaust Stacks and Steam Riser Valves. The durability of metal sprayed coatings means that maintenance downtime is greatly reduced.
Reclaiming parts on ocean-going vessels is another area where Metal Spray is utilised. The reclamation of worn parts for ships is usually subject to Lloyd's Register, particularly on larger vessels. Reclamation applications include, but are not limited to: Propeller Shaft Bearing Journals, Turbo Hydraulic Pump, Rudder, Bilge Pump, Main Circuit Pump, Stabilisers, Capstan and Winches.
Metal/thermal spraying is a technology that protects or extends the life of a wide variety of products in the most hostile environments and in situations where coatings are vital for safety and performance. Durable non-slip coatings can be applied for use on steel floors, ship decks and panels across diverse industries, from train steps and manhole covers to oil platforms and ships.
The images below show the stern of vessel being sprayed with Zinc using an aerial work platform and the Arc Spray process.
Metallisation Equipment Protecting Fishing Boats
Fishing Boat Arc Spray Anti-Corrosion Protection
Final application after grit-blast, Arc Spray coating, followed by paint top-coat.
Images Provided Courtesy of ESpray Greece
Sea corrosion is a major problem for the shipbuilding and fishing industries.
Reason for use: Corrosion protection.
Metallisation’s thermal spraying equipment has been protecting a diverse range of surfaces, structures and vessels for over ninety years and continues to be the chosen solution for many industry sectors.
Another project has yet again proven the longevity of thermal sprayed surfaces. Parkol Marine Engineering, based in Whitby, UK, applied a thermal sprayed zinc coating to a new whitefish trawler, the Resilient LK195, to protect it from corrosion. At the same time as the Resilient was being coated, the 26m single rig whitefish trawler, the Guardian Angell LK272, was back at the Whitby boatyard for a refurbishment.
Coating Effectiveness
The effectiveness of the zinc coating process can clearly be seen to the rear of the Guardian Angel where the trawl doors are brought back on board. Despite extensive paint damage, the robust thermal sprayed zinc base layer clearly remains and continues to protect the hull from rust. Parkol Marine, established in 1988, offers a full range of marine engineering services and has used Metallisation equipment and consumables for a number of years. From new builds to repairs and refurbishment its reputation has been built on quality.
Parkol is renowned for building successful commercial fishing vessels for the North Sea and UK fishing fleets. The company’s shipbuilding yard has two work sheds, large building births that can accommodate new builds up to 25m long and a dry dock with a capacity of up to 5m draft, 42m long and 10.5m beam. Parkol is proud to continue the long Whitby tradition of boat building and repairs.
The anti-corrosive properties of the metal spraying process are widely recognised in the shipping and marine industry, where steel super structures and vessels are subjected to very damaging corrosion from the sea and salt laden air of the world’s shipping and fishing industries.
Parkol opted for the Metallisation ARC150 Arc Spray system and a 20 metre supplies pack, which makes the system very flexible, enabling the engineer to move easily around the boat and gain access to all spray areas.
Metallisation also supplied an extension trolley that included another 20m supplies pack, this ensures the energiser can be kept well away from the spray area. Due to the nature of the project, Parkol engineers used MIG reels to spray from, as they are much easier to move around and load compared to drums. In the last twelve months they have sprayed over one tonne of zinc on to trawlers of all shapes and sizes Prior to zinc coating and painting of trawlers, the surface is grit blasted to SA2.5 cleanliness and a profile of around 75 microns.
Within four hours the zinc coating is then applied which instantly cures. Finally, the zinc is then sealed and finished with several coats of marine grade paint. The Metallisation ARC150 arc spray system has been designed for high throughput coatings.
At 500A, it can apply up to 52kg/hour of zinc or 12kg/hour of aluminium. This high capacity, combined with the flexibility of the system makes it ideal for coating large areas such as boat hulls, offshore oil platforms and other large steel fabrications.
Arc Spray Process
The spray rate and pistol are easy to control, also making it suitable for spraying more intricate areas like deck rails and hardware. The coating finish is very fine, which creates an ideal base for the final paint top coats. In the Arc spray process, two electrically charged wires are driven and guided so that they converge at a point and form an arc. An air nozzle atomises the molten metal produced from the wire and projects it towards the work piece using high pressure air. This spray solidifies when it hits the surface of the work piece to form a dense coating, which protects against corrosion. The driving of the wires is typically either by air motor or electric motor and gearbox arrangement.
Protecting Ships and Trawlers from Corrosion
Reason for use: The anti-corrosive properties of the metal spraying process are widely recognised in the shipping and marine industry.
Metal/thermal spraying is a technology, which protects or extends the life of a wide variety of structures in the most hostile environments and in situations where coatings are vital for safety and performance. Thermal spraying is carried out in a wide range of anti-corrosion or engineering markets. Typical applications include the spraying of ships, trawlers and other ocean going vessels.
The anti-corrosive properties of the metal spraying process are widely recognised in the shipping and marine industry, where steel super structures and vessels are subjected to very damaging corrosion from the sea and salt laden air of the world’s shipping and fishing environments.
Metallisation’s Arc Spray equipment is regularly used within the shipping industry to protect ships and trawlers from corrosion and has been involved in a number of projects. One of those saw Chorro Naval, a customer of Metallisation’s Spanish distributor, Descon Quimica S.L, metal spraying a wide range of vessels using the Arc Spray 140 system (superseded model). Chorro Naval is a renowned shipyard based in Vigo, Spain, and has many years’ experience in maintaining, repairing, restoring and building ships. The company has vast expertise in maintaining all types of ship including, fishing trawlers, merchant ships, cement carriers, supply ships, ferries and chemical carriers. The company offers a wide range of services to the shipyard industry including, hull shot blasting in dry dock, tank coating and a wide range of ship restoration and painting services.
In five separate projects, Chorro Naval has metal sprayed a variety of shipping components with pure zinc. On a Spanish tuna fishing boat they metal sprayed the inside of the tunnel and the fishing hold with a zinc aluminium alloy (85/15). On two trawlers, built in a Vigo shipyard and destined for the Faroe Islands, Chorro Naval metal sprayed all external areas of the boats with zinc. The external areas of a Danish patrol boat and an oceanographic Spanish ship were also sprayed with pure zinc. The final ship the ‘Ronja Polares’, a Norwegian fish carrier, was also metal sprayed at the Vigo dry dock, which is fully kitted out to accommodate restoration and metal spraying work. The external areas metal sprayed during these projects included the hull, all external decks, superstructures, the bridge, mast and chimney.
Prior to metal spraying, surfaces of the ship’s components, both internal and external, were shot blasted to Standard SA 2.5 to clean and prepare the surface. The zinc and zinc aluminium alloy coatings were then applied using the Arc spray system. The Metallisation Arc Spray equipment is the ultimate solution to today’s demands for high performance Arc Spray coatings.
In Turkey, Metallisation customer, Celiktrans Shipyard (an expert shipyard that builds specialised vessels for local and foreign ship owners), recently metal sprayed a 3,588 tonne Norwegian fishing trawler. Using the Arc spray 140 system (superseded model), Celiktrans metal sprayed nearly 5000m2 of zinc to the internal and external surfaces of the vessel. The long supplies pack (unique to Metallisation) enabled the operators to metal spray this large capacity vessel efficiently and safely, as the energiser could remain securely located on the ground. Celiktrans is a specialist ship builder and provides, supply vessels, fishing vessels, ferries, tugboats and offers complex tailor made building projects to its customers.
The photograph above shows the base of a trawler deck-house being grit blasted prior to metal spraying. The upper section has already been sprayed with 150mm (0.006”) of zinc, and the base will be similarly treated. The economics of using this most efficient method of anti-corrosive protection are being recognized more and more in industries where corrosion presents a serious day-to-day problem.
An application in New Zealand, saw the ship Moana III arc sprayed with 100 microns of zinc on a blasted SA3 surface using Metallisation’s Arc Spray System. The coating was finished with an epoxy sealer, 2 undercoats and 1 finish epoxy coat. After 19 years, the vessel was been repainted on the hull, and no corrosion was apparent in areas where the zinc arc spray was applied.
In the Arc Spray process, two electrically charged wires are driven and guided so that they converge at a point and form an arc. An air nozzle atomises the molten metal produced from the wire and projects it towards the work piece using high pressure air. This spray solidifies when it hits the surface of the work piece to form a dense coating, which protects against corrosion. The driving of the wires is typically either by air motor or electric motor and gearbox arrangement.
Major advantages of the Arc Spray process are that the coatings are available for almost immediate use. There is no drying or curing time, no risk of damaging the component and the deposits possess a higher degree of bond strength than many other sprayed coatings.
To read the "Winning the War on Corrosion Onboard Passenger Ships" article from the Autumn/Winter 2018 International Cruise & Ferry Review, Click Here.
Deflected Flame Extension used on RNLI Launch Carriers
Reason for use: Corrosion protection.
The Metallisation deflected flame spray extension has been used to protect a Supacat Launch and Recovery System (L&RS), which has been designed for the RNLI, UK (The Royal National Lifeboat Institution).
Deflected Flame Extension
The deflected flame spray extension was launched in July 2010 and Perryfields was one of the first companies to purchase the new equipment. Perryfields Limited, painting and finishing specialists, based in Dorset, added the flame spray extension to its existing range of metal spraying equipment because of its ability to apply a better quality coating in difficult to access areas, where line of sight is not always possible. The Metallisation deflected flame spray extension comes in three lengths, 150mm, 300mm and 450mm and can angle the spray up to 90º. It can be used with either 1/8” (3.17mm) or 3/16” (4.76mm) wires.
The Supacat Launch and Recovery System is the latest project in which Perryfields has used the deflected flame spray extension. Supacat Limited has developed the new L&RS in association with the RNLI to meet the need for an up to date, highly mobile transport system for a new class of lifeboat. Perryfields Limited has been working with Supacat for many years and has metal sprayed the chassis of the new L&RS with zinc to protect it from corrosion. Supacat is an innovative engineering and design company that produces and supports high mobility, all terrain vehicles.
The L&RS was the first of its kind for the RNLI and it incorporates several unique and innovative features. The L&RS has a permanent software controlled Four-Track-Drive system, which gives exceptional mobility in all beach conditions. The cradle, the main interface with the boat, rotates through 360 degrees, which enables a ‘Bow First’ launch and recovery. This unique facility meets the RNLI’s requirements for rapid turnaround from recovery to relaunch.The L&RS will be consistently exposed to harsh seawater environments and therefore needs to be protected from corrosion. Supacat specified metal spraying with zinc as the most effective corrosion protection and commissioned Perryfields to complete the project. The front and rear chassis’ have been specified by Supacat to be metal sprayed with zinc, as have the two sections of the engine bay, the cradle, and the main trailer structure.
Due to the many difficult to access areas of the large L&RS, Perryfields used the 300mm extension. This flexibility enables the extension unit to be sprayed directly forward or at a deflected angle, ranging from 0º to 90º by varying the deflector air pressure. The deflection nozzle can also be rotated through 180º, to allow spraying in a 360º arc around the pistol, making it very easy to apply high quality coatings in the recessed areas of the chassis.Metal spraying a zinc coating is a process in which molten particles of zinc are applied by impact onto a substrate. The zinc spray is then applied to the substrate within hours of it being cleaned using grit blasting, a process used to prepare the substrate to enable the adhesion of the zinc. The zinc is normally 99.9% pure and is not contaminated in the spraying process, or suspended in organic compounds, ensuring maximum cathodic corrosion protection, similar to galvanising.
Flame spray coatings form a dense, strongly adherent coating suitable for corrosion protection. Major advantages of the flame spray process are that the coatings are available for almost instant use, with no drying or curing times. In addition, there is no risk of damage from heat distortion that can sometimes happen during galvanising.
The Launch and Recovery System is a pre-production system that is being used by Supacat to prove various upgrades to the previous prototype vehicle. This was in preparation for the production build, which was due to begin towards the end of 2011.
"We have been using metal spraying for many years, but the new Metallisation extension is a great addition to our equipment. It is really easy to use and allows us to get into all the difficult to reach areas, making sure the Launch and Recovery Equipment is fully protected from corrosion. The Metallisation Team has been really supportive and I would definitely recommend them.”
Notes
The RNLI is the charity that saves lives at sea. Its volunteers provide a 24-hour search and rescue service around the United Kingdom and Republic of Ireland coasts. The RNLI operates over 230 lifeboat stations in the UK and Ireland and has more than 150 lifeguard units on beaches around the UK. The RNLI is independent of Coastguard and government and depends on voluntary donations and legacies to maintain its rescue service. Since the RNLI was founded in 1824 its lifeboat crews and lifeguards have saved over 139,000 lives.
Reclamation of Rudder Posts
The following application can be completed with an Arc Spray or Flame Spray System. This particular example explores the Arc Spray System being utilised.
Reason for use: Reclamation of worn rudder posts.
Materials
Bond Coat - MSSA 75 Arc Bond.
Main Deposit - MSSA S16 Wire - Used to produce a dense corrosion resistance coating.
Cleaning
- Steam clean if equipment available.
- Degrease by solvent vapour if equipment available.
- Inspect for longitudinal distortion, cracks or faults taking the shaft below the manufacturers recommended operating tolerances.
NOTE: Metal sprayed deposits do not impart any strength to base materials.
Pre-Machining
Rough turn or grind areas being reclaimed to a depth of 1.25mm (0.050”), machining their length the width of the bearings plus an allowance of 25mm (1”) either side.
Recommended Depth of Undercut
| Diameter of Shaft | Depth of Cut | |
| mm | 0.001 inch | |
| 50 -100mm (2 - 4") | 1.25 | 50 |
| 100 - 150mm (4 - 6") | 1.50 | 60 |
| Over 150mm (Over 6") | 1.75 | 70 |
- Mask all machined surfaces adjacent to area requiring treatment with a heavy duty masking tape.
- Thoroughly inspect for contamination prior to blasting.
- Thoroughly blast with clean n° 30-36 grade aluminium oxide grit, the standard of surface cleanliness required is as Swedish Standard SA3.
- Ensure that areas to be treated are thoroughly blasted, paying particular attention to edges of machined areas.
Application of Sprayed Coating
Masking
- Apply No Bond masking fluid using a small brush to all areas adjacent to the area being sprayed.
- Ensure fluid is not applied to area being metal sprayed (Small amounts of masking fluid on area to be sprayed can be removed with emery cloth).
- Check thoroughly that area to be sprayed is free from contamination.
- IMPORTANT: Areas to be sprayed should not come into contact with oil, grease, hands or any other form of contamination.
- Delays between blasting and spraying must not exceed 20 minutes.
Bonding
- The Arc Spray equipment should be set up in accordance with the MSSA Manual for spraying of 75 Arc Bond Wire.
- The area to be sprayed should be cleaned with a vacuum cleaner or clean air blast to remove any loose particles of grit.
- Apply 75 Arc Bond coat to a depth of 75-100μm (0.003”-0.004”) using multiple passes.
- The propeller shaft should be rotated to give a minimum surface speed of 18 metres/minute.
- The Arc Spray pistol should be set so that the spray stream is at 90° to the surface being coated and traversed at an even speed, giving a uniform coating.
- Spraying Parameters Bond Coat:
- Range: 100mm (4”)
- Nozzle Air Pressure: 3.7 bar (55 psi)
- Voltage before spraying: 38V
- Voltage during spraying: 34V
- Amperage: 200A
Note: Parameters may differ in accordance with type and length of power cables being used. S16 Deposit (To be applied immediately after bond coat)
- The Arc Spray equipment should be set up in accordance with the MSSA Manual for spraying S16 Wire.
- Apply S16 final deposit to the specified thickness including grinding allowance i.e. finished ground dimension plus: 0.375mm - 0.50mm (0.015”-0.020”) grinding allowance.
- The propeller shaft should be rotated to give a minimum surface speed of 18 metres/minute.
- The Arc Spray pistol should be set so that the spray stream is at 90° to the surface being coated and traversed at an even speed to give a deposit of not more than 0.13mm per pass.
- Using pre-set callipers, check final sprayed deposit thickness to ensure there are no areas below finished sprayed diameter.
- Remove loose particles on surface with wire brush or clean air blast.
- Allow to cool thoroughly, preferably whilst rotating.
- Spraying Parameters:
- Range: 15cm (6”)
- Nozzle Air Pressure: 4.3 - 4.6 bar (65-70 psi)
- Voltage before spraying: 38V
- Voltage during spraying: 35V
- Amperage: 250A
- Apply Sprayseal "M" in accordance with Metallisation Sprayseal "M" instructions. Keep surface wet by re-application for a period of approximately one hour.
- Allow to dry thoroughly.
- Remove uncured sealer from surface with clean, disposable cloths or paper towels.
- Remove all masking tape.
- Remove all overspray thoroughly taking care to prevent coating damage.
- Remove all traces of No Bond with solvent.
- Grinding Wheel Type N° 46 Grit Blue V Grade.
- Wet grind to final diameter taking light cuts using feeds and speeds in accordance with grinding machine manufacturer’s instructions.
- Check dimensions.
- Check for cracks, defects in sprayed coating, i.e. large pores or protrusions and loose particles.
- Clean to remove all traces of grinding abrasive and loose particles.
- Clean to remove any traces of grinding abrasive and loose particles.
- Wash with petroleum spirit/paraffin.
- Dry the surface with clean, disposable cloths or paper towels.
Reclamation of Propeller Shafts
The following application can be completed with an Arc Spray or Flame Spray System. This particular example explores the Flame Spray System being utilised.
Reason for use: To repair the worn bearing areas on a ships propeller shaft.
Equipment: Metallisation Flame Spray Pistol
Materials
Bond Coat - Metallisation T405/1 Flame spray Bonding Material exotherms during spraying which produces very high bond strength coatings.
Main Deposit - MSSA S16 Wire - Used to produce a dense corrosion resistance coating.
Cleaning
-
Steam clean if equipment available
-
Degrease by solvent vapour if equipment available
-
Inspect for longitudinal distortion, cracks or faults taking the shaft below the manufacturers recommended operating tolerances.
NOTE: Metal sprayed deposits do not impart any strength to base materials.
Pre-Machining
Rough turn or grind areas being reclaimed to a depth of 1.25mm (0.050”), machining their length the width of the bearings plus an allowance of 25mm (1”) either side.
Recommended Depth of Undercut
|
Diameter of Shaft |
Depth of Cut |
|
|
mm |
0.001 inch |
|
|
50 -100mm (2 - 4") |
1.25 |
50 |
|
100 - 150mm (4 - 6") |
1.50 |
60 |
|
Over 150mm (Over 6") |
1.75 |
70 |
-
Mask all machined surfaces adjacent to area requiring treatment with a heavy duty masking tape.
-
Thoroughly inspect for contamination prior to blasting.
-
Thoroughly blast with clean n° 30-36 grade aluminium oxide grit, the standard of surface cleanliness required is as Swedish Standard SA3.
-
Ensure that areas to be treated are thoroughly blasted, paying particular attention to edges of machined areas.
Application of Sprayed Coating
Masking
-
Apply No Bond masking fluid using a small brush to all areas adjacent to the area being sprayed.
-
Ensure fluid is not applied to area being metal sprayed (Small amounts of masking fluid on area to be sprayed can be removed with emery cloth).
-
Check thoroughly that area to be sprayed is free from contamination.
-
IMPORTANT: Areas to be sprayed should not come into contact with oil, grease, hands or any other form of contamination.
-
Delays between blasting and spraying must not exceed 20 minutes.
Bonding
-
The Flame Spray Equipment should be set up in accordance with the MSSA manual for spraying T405/1 Bond Wire.
-
The area to be sprayed should be cleaned with a vacuum cleaner or clean air blast to remove any loose particles of grit.
-
Apply T405/1 Bond coat to a depth of 75-100μm (0.003”-0.004”) using multiple passes.
-
The rudder shaft should be rotated to give a minimum surface speed of 18 metres/minute.
-
The Flame spray pistol should be set so that the spray stream is at 90° to the surface being coated and traversed at an even speed, giving a uniform coating.
-
Spraying Parameters Bond Coat:
-
Range: 100mm (4")
-
Nozzle Air Pressure: 3.7 Bar (55 psi)
-
Oxygen Pressure: 2.0 Bar (30 psi)
-
Acetylene Pressure: 1.02 Bar (15 psi)
-
Flowmeter Settings Bond Coat
Gas: 5.5
Oxygen: 2.2
S16 Deposit (To be applied immediately after bond coat)
-
The Flame Spray Equipment should be set up in accordance with the MSSA manual for spraying S16 Wire.
-
Apply S16 final deposit to the specified thickness including grinding allowance i.e. finished ground dimension plus: 0.375mm - 0.50mm (0.015”-0.020”) grinding allowance.
-
The rudder shaft should be rotated to give a minimum surface speed of 18 metres/minute.
-
The Flame Spray pistol should be set so that the spray stream is at 90° to the surface being coated and traversed at an even speed to give a deposit of not more than 0.13mm per pass.
-
Using pre-set callipers, check final sprayed deposit thickness to ensure there are no areas below finished sprayed diameter.
-
Remove loose particles on surface with wire brush or clean air blast.
-
Allow to cool thoroughly, preferably whilst rotating.
-
Spraying Parameters:
-
Range : 15cm (6”)
-
Nozzle Air Pressure : 4.51 bar (65 psi)
-
Oxygen Pressure: 1.5 - 1.8 bar (25-30 psi)
-
Acetylene Pressure: 1.02 bar (15 psi)
-
Flowmeter Settings Main Deposit (S16)
Gas: 5.5
Oxygen: 2.25
Sealing
-
Apply Sprayseal "M" in accordance with Metallisation Sprayseal "M" instructions.
-
Keep surface wet by re-application for a period of approximately one hour.
-
Allow to dry thoroughly.
-
Remove uncured sealer from surface with clean, disposable cloths or paper towels.
De-Masking
-
Remove all masking tape.
-
Remove all overspray thoroughly taking care to prevent coating damage.
-
Remove all traces of No Bond with solvent.
Finish Grinding
-
Grinding Wheel Type N° 46 Grit Blue V Grade.
-
Wet grind to final diameter taking light cuts using feeds and speeds in accordance with grinding machine manufacturer’s instructions.
Inspection
-
Check dimensions.
-
Check for cracks, defects in sprayed coating, i.e. large pores or protrusions and loose particles.
-
Clean to remove all traces of grinding abrasive and loose particles.
White Metal Bearing on Cruise Ship
This white metal bearing was flame metal sprayed in Australia in June 2005. The bearing has a diameter of 450mm and a length of 350mm.
The bearing is from the P&O Cruise Liner - Pacific Sky. The Pacific Sky caters for 1550 passengers on 11 decks and is 240m long. The ship was built in 1984, weighs 46,000 tonnes and has a top speed of 21 knots.
Ships Walkways
Reason for use: Corrosion protection. Can also be sprayed as a rough coating or with Al-Oxide for non-skid surface.
The structural steelwork of a ship walkway is protected against the severe corrosion of the marine environment in which it is situated in by means of the Arc Spray process.
The application calls for grit-blasting and aluminium spraying to a depth of 150µm (0.006”) in accordance with BS EN.22063. The sprayed surface is then treated with an Olive Green single pack inhibitive Sealer, followed by a coal tar epoxy paint system.
River and Canal Vessels
Canal barges are Metal Sprayed for anti-corrosion protection. The below narrowboat was metal sprayed with Zinc using an ARC150 Arc Spray system and top-coated with paint.
"Bringing the technology from the factory to the ship has been demanding"
When the Navy/RAF’s new stealth fighters enter service in 2018, they will launch from the Navy’s two new massive aircraft carriers to provide what the Government calls a “formidable fighting force”.
Currently the most advanced jets in existence, the F-35B Lightning II fighters will take off from a short ramp and land vertically on the decks of the warships. But the heat and force of the exhaust gases from the jets are so extreme, this demands innovative technology to protect the decks of the aircraft carriers: the traditional coatings aren’t tough enough.
Engineers have devised an innovative thermal “paint” (actually metal spray) to withstand the extreme high temperatures from the supersonic jets. It’s a metallic compound of aluminium and titanium which is melted and sprayed on to parts of the four-acre deck of the carrier. So resilient is the thermal coating, it can withstand temperatures of up to a staggering 1,500°C.
But applying it hasn’t been easy, says David Thomson, flight deck and coating manager at the Aircraft Carrier Alliance, which is responsible for building the carriers. The Scottish weather hasn’t always behaved.
He’s been working at Rosyth Dockyard where HMS Queen Elizabeth and HMS Prince of Wales are being built by the Alliance, which includes BAE Systems. His team needs to keep temperatures stable and the air dry.
“It is a challenge,” admits Mr Thomson. “We’ve had to maintain tight environmental controls: we’re working on open decks and it rains a lot in Scotland”
The team has been working in an enclosure which is kept at 22°C and at a humidity below 60 per cent in all weathers. “We’ve made 10 air changes an hour through extraction, to make sure the air is kept clean,” explains Mr Thomson. “We spray on the coating but it generates aluminium dust which is flammable, so it needs to be removed.”
Specialist machinery has been developed in order to apply the coating. Robots fire powdered metal through a jet of plasma at temperatures of around 10,000°C. The molten droplets then flatten and solidify, creating a tough coating.
A first application ensures the “paint” sticks to the steel deck, a second coat is for strength, and the third application has added sand to provide non-slip friction, both for the jets and crew.
It’s a laborious process and has taken a year to complete. This type of durable coating has been used in the oil industry to protect rigs from corrosion from salt water, but this is the first time it has been used on the deck of warships.
According to the engineers it will protect decks throughout the carriers’ 50-year lives. Rather than coat the complete deck, the team has protected three landing spots. “The high standards of the aviation sector have required lots of independent testing,” says Mr Thomson. “Bringing the technology from the factory to the ship has been demanding.”
The first of the two warships, HMS Queen Elizabeth, completed sea trials in 2017 and then flight trials in 2018, before its sister ship, HMS Prince of Wales, went through the procedure. The new fighter jets, meanwhile, employ stealth technology to avoid radar detection, and the RAF plans to have 24 aircraft available on the two new carriers by 2023.
Sea Dock Hydraulic Rods Hard Chrome Replacement
Thermal spray applications that can be completed with Kermetico HVAF technology cannot be accomplished as well with traditional thermal spray processes. One particular area is the replacement of hard chrome plating on hydraulic rods.
Traditional coatings and hydraulics have never worked long enough. Even with a sealer, the porosity eventually allows the hydraulic fluid under pressure to penetrate the coating. Once the pressurized fluid hits the substrate, it spreads out under the coating and lifts it off.
Kermetico coated about 30 hydraulic rods used at a local refinery on their dock cranes. They had been getting only six months out of the chrome plated rods. Kermetico coated them with HVAF WCCoCr 86-10-4. The first ones that were sprayed have been in service for over five years. A report of a visual inspection about six months ago was, “They still pretty much look like they did when we first put them in.”
Ship Building
ESpray Greece is adopting thermal spray into their ship building applications. Utilising Metallisation’s 145(19) arc technology, they are providing exceptional lifespan to first maintenance and creating corrosion resistant coatings, as well as non-slip flooring applications.
Other Marine Applications
Jet Pump Dredger
Since the metal spraying process was pioneered in the U.K. by Metallisation Ltd. of Dudley, West Midlands, one of its principal applications has been as an anti-corrosive protective treatment for structural and other steelwork. The Zinc Spraying of a Jet Pump Dredger provides an interesting example of the very widespread use of metal spraying. The dredger extracts sand by high-pressure suction jet, and has an output of 250 tons of sand per hour.
The vital statistics of the dredger are length 41m (135ft), width 6.7m (22ft), and height from the water line to the top of the hoist 4.55m (15ft). Fabricated in mild steel the dredger will spend its entire working life afloat on the quarry lake, so that the problem of corrosion is quite considerable.
Using Metallisation Flame spray equipment, the contractor Thomas Gilks & Son, UK has grit blasted the steelwork and sprayed with zinc. Below the water line a deposit of 100mm (0.004”) zinc has been applied followed by two coats of bitumastic paint; above the water line the dredger hull and deck structure have been grit blasted and zinc sprayed to a thickness of 100mm (0.004”).
In addition to the normal corrosive attack of water, the method of operation creates corrosive and abrasive conditions above the water line so that the best available anti-corrosive treatment is essential. It is anticipated, that the metal sprayed zinc will protect the dredger throughout its entire operational life without further treatment.
Sea Water Mains
A series of 1.8m (6ft) diameter pipes fabricated in mild steel to form a massive Sea Water Main at a Chemical Plant in the UK. As part of the chemical process, seawater is pumped through the Main, which is obviously subject to very considerable corrosive attack from the seawater. To afford the best possible anti-corrosive protection therefore, these massive pipes were grit blasted and then metal sprayed with 100mm (0.004”) zinc using Flame Spray equipment. The metal sprayed surface was then followed by a zinc chromate primer and a finishing coat.
Armature Shaft – Falmouth Dry Dock
The armature shaft on the No 2 main pump motor head, became so badly worn that it was deemed un-serviceable. A deposit of S20/S2 chrome steel was sprayed to a depth of 2.5mm (0.100”) using the Arc Spray system. No disconnection of the armature windings was necessary, a simple cardboard mask preventing the ingress of metal dust during spraying, and after re-machining the component was back in service in less than 24 hours.
Marine Piston
The illustrated piston from a massive marine diesel engine provides an interesting example of more than one characteristic of arc spraying.
The piston, which is 508mm (20”) in depth and approximately 305mm (12”) in diameter, came from a marine engine that had been in use for a considerable number of years, it was not possible to obtain a replacement.
The outer surface was so badly worn that an overall deposit of 1.56mm (1/16”) on the radius was necessary, with heavier build-ups in localised areas where the wear was excessive. Before spraying, the piston was machined and the recessed areas were masked with a No Bond masking compound to prevent adhesion of the sprayed deposit in these areas. A bond coating of aluminium bronze was deposited without any prior grit-blasting, followed by a final deposit of S20/S2 steel. After spraying, the piston was machined and ground to finished size. A point, which is well brought out by the photograph, is the sharp definition, which was achieved on the edges of grooves, holes and recessed surfaces.
Submarine Hull
The above image shows a submarine hull subjected to the thermal spray process in the 1930's. In this instance the hull was sprayed using Zinc with the MK16 Flame Spray Pistol (superseded model). Examples like this give an insight into the history of the Metal Spray process and how long it has been in use.
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