Manufacturing

Thermal spray coatings for manufacturing applications ranging from injection moulds to cookware coatings.

Backing Nickel Electroforms

Reason for use: To offer a fast and low cost alternative, reducing the potential in some cases of tool distortion due to high residual plating stresses.

Nickel electroforms are extensively used as tools for injection moulded plastics. Whilst they give excellent service, their production is slow and costly. In some cases, tool distortion may be caused by the high residual plating stresses. For these reasons, the Metallisation spraying processes have been adopted to reinforce thin electroformed shells to produce tools which are strong enough and thick enough to incorporate in injection moulding machine tool sets.

The most commonly used backing material is copper wire, sprayed by either the Flame spray or the Arc spray process. Copper provides an ideal blend of thermal conductivity, strength and low residual stress. Successful tools will be produced if the correct processing techniques are used.

Equipment: Metallisation Arc Spray or Flame Spray System (Contact us for further information)

Materials

Bond Coat Arc Spray with MSSA 75 Arc Bond - This Arc Spray Bonding Wire exotherms during spraying, producing very high bond strength coatings.

OR

Bond Coat Flame Spray with Metallisation T 405/1 - The Flame Spray Bonding Material will exotherm during spraying to produce very high bond strength coatings.

Main Deposit

Preparation

The back of the electroform must be free of any grease, oil, water or dirt. It must be roughened by grit blasting, preferably using aluminium oxide grit. The front face of the electroform must be adequately protected during preparation and subsequent processing.

Bonding

Good bonding of the backing to the electroform is essential. MSSA 75 Arc Bond is recommended when using the Arc Spray process. Metallisation T405/1 Bonding Material is recommended when Flame Spraying. The bonding material should be sprayed with acetylene fuel gas. Bond coats are intended to provide a key between the electroform and the backing coat. They should be sprayed to a thickness of 100 – 150μm (0.004-0.006 in). Excessive bond coat thicknesses offer no technical advantage and may impair the tool performance.

Backing

Copper Wire is applied with Arc Spray or Flame Spray Equipment, immediately after bonding. It is important that heat input is minimised and rapid movement of the pistol relative to the electroform is recommended. Additional cooling air jets should also be used to maintain the surface temperature below 50°C.

Pistol operating parameters should be set according to the equipment manual. When Arc Spraying, the current should not exceed 150A, for Flame Spraying 2mm diameter wires should be used. The backing should be built up gradually, until the required thickness has been achieved.

Temperature Control Tubes

If required, temperature control tubes may be built into the mould at any time after the initial deposit has been applied. The tubes should be prepared by degreasing and grit blasting and sprayed with a thin layer of the backing material before placing them in position.

Finishing the Electroforms

When sufficient material has been applied, the reinforced electroform should be machined to fit the moulding machine tool set. Turning, milling or shaping may be employed, but care must be taken to avoid excessive cuts. The use of cutting fluids is not recommended.

Alternative Backing Materials

Where the strength and thermal conductivity of the tool is less important than low residual stress, the copper backing may be replaced by a special brass (MSSA 13). This backing is mainly used for larger – less rigid electroforms.

Where strength is of primary importance and thermal conductivity is relatively unimportant, electroforms may be backed with steels. Only low stress steels such as MSSA S2 or MSSA 65 should be used. Because of the higher melting points of these materials, extra precautions must be taken to avoid overheating the tool during backing. Steel backings must be carefully ground to size (preferably without coolant) after spraying.

Manufacture of Sprayed Metal Moulds

Reason for use: Manufacture of low cost moulds and tooling.

For low pressure mouldings sprayed metal moulds can be used with every confidence as a production tool. In high pressure moulding such as injection moulding, the tool life may be only 50-100 mouldings (under favourable conditions 2500 mouldings have been produced from one tool and it has remained in a usable condition) but this is usually for prototype work. In the foundry industry, sprayed tooling gives lives greater than resin patterns and eliminates the problems of sand adhering to the pattern as a result of static build-up. The metal spraying process is used for mouldings in: Expanded Polyurethane, Polyurethane GRP (DMC and SMC), GF Nylon Polycarbonates, RIM, Acetal etc., on a prototype basis. Components ranging from vehicle seats, body panels, steering wheels, bumpers, spoilers, light clusters to jet engine intake nacelles, have all been produced from sprayed metal shells.

Tool Manufacture

Patterns

Patterns may be of almost any material. Wood and metal are often employed as are plastics, certain waxes, textiles etc. Existing components may be used. Textured surfaces will be reproduced on the sprayed tool surface. Care should be taken to minimise the incidence of deep, narrow holes and slots as these may be difficult to spray. Draw angles should be as generous as possible although, depending on shape and size, as little as half a degree may be acceptable. Wooden patterns should be varnished / sealed before spraying.

Preparation

The pattern should be mounted on a flat plate prior to spraying. Where an existing component is used as a pattern, the split line must be carefully chosen and a framework built along the split line on the outside of the part. Gaps between the pattern and the mounting plate must be completely filled with wax, plasticine etc. If this is not done, it may be impossible to extract the pattern after spraying.The surface of the pattern must be clean, dry and free from debris. A thin film of cleaning agent is particularly desirable if the sprayed tool is to be ‘”shocked” out. A film of Metallisation Release Agent 21115 is applied evenly to the surface with an air operated spray gun; several coats of ‘Crystic’ must be necessary to obtain the necessary uniform surface sheen. On highly polished surfaces, application of crystic may not be handled or contaminated after preparation; even finger prints may be reproduced in the moulded surface.

Materials

Moulds have been made in many materials, including tin-zinc, zinc, zinc alloys, brass, copper and aluminium. It may be possible to use other materials or combinations of materials in certain circumstances. Most commercial applications have centred around zinc or zinc alloy faced moulds offering a high degree of surface definition, insignificant shrink and in the case of tin-zinc, a virtually mirror finish, these materials providing excellent spraying characteristics.

Spraying

Using either arc or flame spraying equipment, it is normal to apply an initial deposit of zinc alloy to give high surface definition. This is normally done at a relatively low pistol throughput directing the spray stream first at corner radii and the bottoms of any slots, pockets etc. and then at the remainder of the surface. Rapid movement of the pistol relative to the pattern and air jet cooling are recommended. The above measures ensure that the initial coating is applied as evenly as possible and that excessive heat input (which could distort the pattern) is avoided. Surface temperatures should not exceed 35°C, hence particular care must be taken when utilising flame spraying equipment. Depending on size and geometry, when the deposit thickness has reached 750μm, (0.030”) the deposition rate may be increased and the spraying range (when arc spraying) reduced until the required thickness is reached, typically this will be 3mm (1/8”) maximum. The final 250μm (0.010”) may be sprayed with a coarse deposit of aluminium to aid the bonding of any backing material.

Incorporation of Temperature Control Tubes

Where necessary, Temperature Control Tubes may be built into the mould at any time after the initial deposit has been applied. The tubes should be prepared by de-greasing, abrasive blasting and spraying with zinc before placing them in position.

Backing

To provide additional strength and rigidity, it is normal to support the sprayed tool in a bolster and back with a suitable material. Selection of the backing material should be made carefully; the choice will depend on strength required, its ability to retain or dissipate heat and its ability to match the thermal expansion of the sprayed face. Materials used include epoxy resins (filled and unfilled), metal and concrete. If desired, temperature control tubes can be included in the backing.

Release

To provide additional strength and rigidity, it is normal to support the sprayed tool in a bolster and back with a suitable material. Selection of the backing material should be made carefully; the choice will depend on strength required, its ability to retain or dissipate heat and its ability to match the thermal expansion of the sprayed face. Materials used include epoxy resins (filled and unfilled), metal and concrete. If desired, temperature control tubes can be included in the backing.

Sealing

Sometimes, the inherent porosity is advantageous since it facilitates vacuum forming and allows the release of gases which may be evolved during curing of the moulding. However, where porosity is detrimental, the face of the tool may be sealed with Sprayseal M. This sealant must be allowed to cure fully before the tool is used since, if uncured, it may react with the moulding resin. Sprayseal M should not be exposed to temperatures greater than 150°C. Any backing materials should be fully cured prior to sealing with Sprayseal M since the solvents contained may react with uncured resins.

Reinforced Coating System for Cookware

Ceramic Coating

Reason for use: To reinforce fluoropolymer coating with a hard Ceramic coating. The application of Plasma sprayed ceramic powder 216 as a reinforced coating has been proven to increases the working life of many types of cookware. Even above that achieved by Arc sprayed Stainless Steel. By producing a thin Plasma sprayed layer the fluoropolymer coating penetrates the sprayed surface. This produces high bond strengths and allows the high wear resistant ceramic to protect the fluoropolymer coating (See Fig 1) from such items as cooking utensils.

Fig 1

Materials: Main Deposit: Ceramic Powder 216

Plasma Spray Process

Plasma is the term used to describe gas, which has been raised to such a high temperature that it ionises and becomes electrically conductive. In the case of Plasma Spraying, the Plasma is created by an electric arc burning within the nozzle of a plasma gun and the arc gas is formed into a plasma jet as it emerges from the nozzle. Powder particles are injected into this jet where they melt and then strike the surface at high velocity to produce a strongly adherent coating.

Method

Cleaning: The surface should be free from grease, oil or other contaminants as this would affect the adhesion of the sprayed coating.

Blasting: The surface should be grit blasted; the standard of surface cleanliness required is as Swedish Standard SA3. Surfaces not being treated should be masked before blasting.

Application of Sprayed Ceramic Coating

Spraying should begin as soon as possible after preparation and before any visible sign of deterioration occurs.

1. The Plasma Equipment should be set up in accordance with the MSSA Manual for the spraying of St/St or Titanium wire.
2. The area to be sprayed should be cleaned with a clean air blast to remove any loose particles of grit.
3. The Plasma 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.
4. Apply Ceramic coating to the required thickness.
5. Spraying parameters for Ceramic Powder 216.

Note:

1. Adjust secondary gas to achieve voltage.
2. Adjust Rpm to achieve Powder Feed rate GPM.
3. Air Jets at 80 psi parallel.

General

There should be the minimum of interruption from commencement of preparation to completion of spraying. At all times, the prepared surface should be protected from dust, dirt, moisture etc.

Stainless Steel Coating

Reason for use: To reinforce the fluoropolymer coating with Stainless Steel. The application of Arc sprayed Stainless Steel as a reinforced coating has been proven to drastically increase the working life of many types of cookware. By producing a thin Arc sprayed layer the fluoropolymer coating penetrates the sprayed surface. This produces high bond strengths and allows the high wear resistant Arc sprayed coating to protect the fluoropolymer coating (See Fig 1) from such items as cooking utensils.

Equipment and Materials: Metallisation Arc Spray system, Energizer: S350, Main Deposit: Stainless Steel or Titanium.

The Aluminium Spraying of Stud Welded Fasteners

Reason for use: To assist with attachment and produce a stronger weld as the aluminium acts as a fluxing agent.

To assist with attachment and produce a stronger weld, aluminium is being used as a fluxing agent on welding fasteners.

There are generally two methods of applying the aluminium to the fastener end. In some cases a small hole will be drilled in the centre of the fastener end then an aluminium ball of the same size inserted, being fixed into place under a press.

By using the Flame spray process, it is possible to apply a thin coating of aluminium over the total area to be welded giving all over fluxing and less change of debris inclusion into the weld area. In some cases, it is necessary to retard the welding process. If the Metallisation process is being used, it is possible to achieve this by spraying a thin coating of zinc on top of the aluminium.

Equipment: Flame Spray Equipment

Bond Coat: Pure Aluminium wire - has excellent corrosion resistance and electrical conductivity characteristics.

Cleaning: (a) Degrease by solvent vapour process, if material available. (b) Check all surfaces are free from contamination and debris.

Preparation

1. The fasteners should be packed tightly in rows into a steel tray approximately 15cm square leaving only the area to be sprayed exposed. The tray may hold up to 1,000 fasteners dependent on their diameter.
2. Thoroughly inspect for contamination prior to blasting.
3. Thoroughly blast the area to be sprayed with clean n° 30-36 grade aluminium oxide grit.
4. Ensure that areas to be treated are thoroughly blasted.
5. After blasting turn tray over to remove any unwanted grit from between the fasteners.

Masking

1. The fasteners are to be left in the steel tray for the spraying process. It may be necessary in some cases to apply masking tape to the outside edges of the tray to protect fasteners from overspray.
2. Check thoroughly area to be sprayed for contamination

IMPORTANT: Area to be sprayed should not come into contact with hands or other form of contamination. Delays between blasting and spraying should not exceed 2 hours.

Spraying

1. The Flame Spray pistol should be set up in accordance with the MSSA Manual for spraying Aluminium Wire.
2. The Flame Spray pistol should be held so that the spraystream is at a 90° to the surface being coated and traversed at an even speed to give a uniform deposit of the specified thickness (typically 25μm-50μm) ensuring all fastener ends are completely covered.
3. Spray Parameters Fine Spray Aluminium Wire, 2mm diameter.
   1. Range: 10cm
   2. Nozzle Air Pressure: 3.47 bar (50 psi)
   3. Oxygen Pressure: 2.08 bar (30 psi)
   4. Propane Pressure: 1.38 bar (20 psi)

Flowmeter Settings

Gas 1.5

Oxygen 1.5

Note: If Zinc is required on top of the aluminium to retard the weld, it should be sprayed immediately after aluminium spraying is completed.

Demasking

1. Remove all masking tape.
2. Remove all overspray taking care to prevent coating damage.
3. Remove all traces of No Bond with solvent.

Finish Grind

1. Grinding Wheel Type N° 46 Grit Blue V Grade.
2. Wet Grind to finished diameter, take light cuts using feed and speed in accordance with grinding machine manufacturer’s instructions.

Inspection

1. Check dimensions.
2. Check all specified areas are coated with aluminium.
3. Finished component is ready for packing.

Soap Chilling Cylinder Repair

The surface of this massive soap-chilling cylinder had been badly scored by the action of a stainless steel scraping blade used during the soap production process. 

A Metallisation Arc Spray system was used to carry out an ‘on the spot’ repair with the cylinder revolving in its own running bed, thus eliminating expensive dismantling and transport costs. During a thirty-hour period, a radial deposit of 3.175mm (0.125”) of S2 was applied, this material being chosen in order to improve the wear characteristics of the cylinder in relation to the stainless steel scraper blade. After spraying, the surface was machined and ground down to a highly polished finish. 

The cylinder is 1.676m (5’6”) in diameter, 1.89m (6’0”) long and weighs 3055kg (3 tons). The soap manufacturer concerned was quoted a twelve-month delivery for a new cylinder; the metal spraying process had the cylinder back in operation in one week at a fraction of replacement cost.

Carbide Coatings for Exhaust Fans with HVAF

Kermetico HVAF equipment provides an effective way to protect exhaust fan impellers from abrasive wear. Kermetico HVAF thermal spray systems deposit ductile, high-bond wolfram carbide coatings as hard as 1,600+ HV₃₀₀ and as thick as 3mm (0.120”). The gas impermeable HVAF coatings are superior to any other surfacing technology in dry or wet abrasion protection of exhausters.

The Abrasive Wear of Centrifugal Impellers

Centrifugal fans provide air for industrial processes like coal and lignite-fired power plants, cement, metal or woodchip manufacturing. Particles present in the air stream wear the fan surfaces.

This wear is induced both by very fine particles, for example, fumes, as well as by large particulate matter such as wood chips. Fan impeller blades are the most severely attacked components. Once they are worn-out, the resulting geometrical alteration can lead to dramatic efficiency drops. Furthermore, balance problems appear, affecting the service life of the ancillary equipment.

The resulting change in operational conditions increases energy and maintenance costs and leads to unplanned plant downtimes.

Advanced wear protection of equipment, as a preventative maintenance measure, reduces overall costs and diminishes the risk of unscheduled outages of exhaust equipment.

Thermal spray coating of a fan reduces severe wear, increases the fan productivity and prolongs intervals between planned repair cycles.

Kermetico HVAF tungsten carbide coatings are created for extreme abrasion, erosion and corrosion conditions where the abrasion resistance of regular steel or conventional abrasion-resistant coatings does not meet the need. The abrasion resistance of the Kermetico HVAF (tungsten) carbide is a hundred times better than that of regular steel, and many times better than weld overlays.

Kermetico HVAF and HVOF carbide abrasion resistant coatings lengthen the fan’s operational life and significantly reduce the wearing of the impeller and other fan components, which could lead to additional outages and premature repairs.

Surface Treatment to Protect Centrifugal Equipment from Corrosion and Wear

Carbide coatings deposited by using different high velocity technologies (HVOF, HVAF and Detonation), are extremely wear-resistant. Industry uses tungsten carbide in combination with cobalt, nickel or cobalt-chrome matrices preferably. The erosion and corrosion behavior of wolfram carbide coatings is a key element for the assessment of the coating application.

We use our Kermetico HVAF equipment to deposit tungsten carbide coatings that are wear resistant and tough enough to be effective at all angles of impingement.

We recommend WC-CoCr-bound powders because they exhibit the highest wear resistance coupled with adequate corrosion resistance in any environment except very high pH environments or hydrofluoric acid. Only 100 microns of our WCCoCr coating is gas-tight, protecting a base metal of a fan from corrosive agents as a barrier layer.

A Kermetico HVAF Ultra-Quality WC-CoCr Coating, Hardness 1,600 HV300

Kermetico's Multi-Purpose HVAF AK7 and AK5 are recommended for exhaust fans.

Aluminium Taper Rollers Repair

A batch of twenty four conveyor rollers which provide a hot strip delivery system in an aluminium strip mill has been treated by metal spraying after showing severe signs of wear. The rollers are designed with a double taper so that as the aluminium strips cool, they run progressively towards a central point. The taper can be seen in the photograph. In addition to wear on the roller surface itself; the carrying spindles were also severely worn.

A deposit of S2 was applied to the rollers, followed by some skillful finishing. The taper towards the centre section meant that the tailstock of the lathe had to be offset, the rollers being steadied on the parallel centre section to facilitate the skilled lathe work.

With an overall length of 3m (10ft) working faces of 2.44m (8ft) a diameter decreasing from 315mm (12½”) to 292mm (11½”) and a weight of 508kg (10 cwt) each, the twenty-four rollers together represented a considerable capital item to the aluminium mill concerned.

Bottle Pasteurising Plant

Metallisation System ZN6 has been used to provide an anti-corrosive protection on a Guinness Bottle Pasteurising Plant, designed and built in the UK, for commission in West Africa. The Plant treats 15,300 bottles per hour, and the very humid conditions created by the ambient atmosphere, plus the steam generated by the pasteurising process produce particularly corrosive conditions. System ZN6 has been applied to the inside of the main stream-heating tank and to all internal surfaces of the plant. The full advantages of positive cathodic protection is given to surfaces being treated ensure that the Guinness Bottling Plant will have a long and effective service life. ZN6 = 150 microns of Zinc spray.

Coin Production Slides

The surface treatment of Slideways, which are fitted to “Coinmaster” Presses, used in the production of coins and medals throughout the World, and manufactured by the HME Division of Cincinnati Milacron Ltd.

Depending upon the type of coins or medals being produced the press speed is up to 400 strokes per minute. The slide ways locate the main slide upon which the work-head is mounted, and it is vital that accurate and precise location is maintained at all times under high-speed operation.

Conductor Rolls

A considerable reduction in the cost of producing a set of continuous electro-tinning strip conductor rolls has been made possible by the use of the Arc Spray Process.  Existing methods of conductor roll manufacture have presented major problems, including lengthy delivery dates and high cost copper forgings.

Wean Ltd. of Croydon, UK decided to try an alternative means of manufacture by depositing a thick copper coating onto carbon steel tube, using arc metal spraying as the deposition process, a total of 916kg of copper was deposited on the 3.35M (11ft) long roll. The finished thickness of the copper coating ranged from 15.87mm (5/8”) on the 457mm (18”) diameter roll face to 38mm (1½”) on the journal ends. The roll face ends were also sprayed to provide a 19mm (¾”) copper coat.

The Arc Spray Process enables a heavier deposit to be achieved with higher conductivity than is normally obtained with ordinary metal spraying. Chrome plating to the copper coat is also made easier.

Cellulose Pressure Roll - Hard-wearing and Rust Free Coating Solution

A cast iron pressure roller used for crushing chemical wood pulp, and measuring approximately 70cm (2’3”) in diameter by 350cm (11’6”) long, has been sprayed with stainless steel by Norwegian company Metalliseringsverket – Olsen & Borge A/S in Oslo. These rolls are made of cast iron, therefore rust staining of the wood pulp is unacceptable. The coating of stainless steel not only presents a hard-wearing surface but also acts as a protective coating to prevent staining. After spraying and finishing to a thickness of over 3.2mm (1/8”) the surface is grooved to a width and depth of 1.5mm over the whole surface. This is another application, which started as a reclamation process and is now being used on new components to improve their life and performance. The coatings are applied by Flame, Arc and Plasma spray.

Drilling Spindle (High Speed)

The seal areas of the spindle shown on the photograph have been sprayed with Chrome Oxide to a thickness of 625 microns (0.025”) during manufacture. Before the final application of Chrome Oxide the components were undercut by 500 microns (0.020”) and an initial bond coating of Molybdenum applied to 125 microns (0.005”) thick to a freshly ground surface. Due to the very high speed involved the seals were having a very short life. The Chrome Oxide surface offers a much harder wearing surface thus prolonging the life of the components.

For more information on Metal Spray equipment or consumables, call us on 07 3823 1004 or email us using our contact form.