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PPA 571 Frequently Asked Questions

If you have a question about the PPA571 series, it may be answered here. If not, look at the rest of our technical information or relevant Data Sheets.

Table of Contents

What is corrosion and how does it occur?

Corrosion is the damage caused to a material when it reacts with its environment. In a humid atmosphere; metals are usually corroded by the combined action of water and oxygen. This process may be greatly accelerated by chemical agents such as salts or exhaust fumes. As a result, a metal component may corrode within a relatively short time to the point where it can no longer perform its intended function.

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What is Plascoat PPA571?

Plascoat PPA571 is a high performance coating powder, based on an alloy of thermoplastics and modified with functional groups. PPA571 is specially developed to provide a long-lasting, tough coating for exterior applications that require excellent protection against corrosion.

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Is Plascoat PPA 571 available in various colours?

Yes, Plascoat PPA571 is supplied in a range of standard colours, most of which are to RAL standards. Non-standard and special colours can also be supplied subject to minimum quantities.

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How is Plascoat PPA 571 applied?

Plascoat PPA571 coatings can be applied by the fluidised bed process, by electrostatic spraying, flame spraying, flock spraying, rotational sintering and/or pouring.

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What is the fluidised bed process?

A vessel is filled with Plascoat PPA571 powder, the particles varying in size from 80microns to 250microns. The powder rests on a porous plate, through which air is then blown in such a way that the powder is 'aerated' and therefore behaves almost like a liquid. The pre-treated metal articles, which have been heated to between 180 and 380°C, are dipped into this "bath" for just a few seconds. By virtue of Plascoat PPA571's low melting range (approx. 105°C), the heat content of the metal parts is sufficient to make the powder sinter on and then fuse completely after the article has been removed from the tank to give a smooth coating.

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Why are metal parts coated with Plascoat PPA 571?

The application of Plascoat PPA571 by the fluidised bed coating method or by electrostatic spraying gives metal articles highly effective, long-term protection against corrosion in a single operation.

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When Plascoat PPA571 is applied by the fluidised bed method, is the work piece coated evenly all over?

This is one of the advantages of the fluidised bed process. Unlike almost any other method, fluidised bed coating with Plascoat PPA571 results in a coating of relatively constant thickness so that even cavities, drill holes, corners and edges are reliably protected against corrosion.

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What is the maximum service temperature for articles coated with PPA 571?

Parts coated with Plascoat PPA 571 can be used constantly at temperatures up to 60°C in dry air. The coating can withstand short-term temperature peaks of up to 65° C. If the product is in constant contact with warm water please contact Plascoat. If higher temperatures than this are required, other products in the Plascoat range may be suitable. Please contact Plascoat.

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How thick is the coating?

For fluidised bed coating, the thickness of the coating is determined by the temperature to which the metal part is heated and by the dipping time, and is normally between 300microns and 600microns. Coatings more than 1000microns thick are to be avoided.

For electrostatic spray coating, the thickness of the coating is determined by the spray time and is normally between 200microns and 350microns. The absolute minimum recommended thickness is 150microns.

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How thin can Plascoat PPA 571 coatings be?

For technical reasons (particle size, temperature, dipping time), coatings less than 250microns thick cannot normally be applied by the fluidised bed process under practical conditions. Plascoat PPA571 ES is an electrostatic sprayable version, which can be applied at lower thicknesses. The minimum recommended thickness is 150microns.

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What area can be coated with 1 kg of Plascoat PPA 571?

An area of 3.3 square metres can be coated to a thickness of 300microns. There is virtually no wastage of powder using the fluid bed coating method.

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Can very large items be coated in PPA 571?

Yes, depending on the equipment available.

For fluidised bed dipping this means the size of the preheat oven and the fluidised bed tank. For electrostatic spraying this relates to the size of the spray booth and the cure oven. Large items are often flock sprayed if there is a constraint on the size of the spray booth.

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What advantages does a coating of Plascoat PPA 571 thermoplastic have to offer over a thermosetting powder paint?

Plascoat PPA 571 gives a coating of consistently high quality, since no chemical reaction is necessary after it has fused. The coating is tough and elastic, and has excellent oxygen and water vapour barrier properties. Thicker coatings can be applied more quickly, there are no unpleasant odours and any damage to the coating can be easily repaired.

A comparison between PPA 571ES and polyester coatings

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What are the properties of a Plascoat PPA 571 coating?

The typical advantages of a Plascoat PPA 571 coating are:

  • Extreme long life
  • Corrosion resistance in hostile environments
  • Aesthetic longevity
  • Low toxicity
  • Low fume toxicity
  • Warm to the touch
  • Low fungal growth
  • No primer required
  • Graffiti resistant – easily removed with no staining
  • Water & food contact approvals
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Can aggressive media penetrate the Plascoat PPA 571 coating and still cause corrosion?

Diffusion through a plastics layer is always possible, but very few substances are known to cause corrosion through a Plascoat PPA 571 coating. Two such media, however, are bromic and chromic acids. Please contact Plascoat for more details.

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What is meant by 'chemical resistance' in the case of PPA 571?

A coating is resistant if it is not perceptibly changed or rendered ineffective through contact with the chemical concerned. Plascoat has tested the resistance of Plascoat PPA 571 to a wide variety of reagents; in most cases the test duration was I year at temperatures of 20 and 60°C.

A Guide to Chemical Resistance of PPA 571

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Does PPA 571 have good UV, light and weather resistance?

Plascoat PPA 571 is UV resistant as well as having good light stability and outdoor resistance. No damage to the coating was detected after 3 years of weathering tests in Florida, under a 45°angle pointing to the south. No significant colour changes or gloss reduction were observed, and the Plascoat PPA 571 coating still gives effective protection against corrosion for many years.

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How does Plascoat PPA 571 behave in aggressive soils?

Plascoat PPA 571 gives full protection against corrosion even in contact with aggressive soils.

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Could PPA 571 be used, for example, in outdoor applications on the Arabian peninsula or in areas of similar climate?

Plascoat PPA 571 is already used in such areas and has demonstrated its outstanding effectiveness against corrosion in coastal areas of the Arabian peninsula. For example, the atmosphere is aggressive throughout the year, i.e. the air has a high salt content, humidity is high and the weather is hot. Also, the air cools considerably at night, i.e. there are considerable temperature fluctuations. Under these conditions, zinc coating will be destroyed within months, and Plascoat PPA 571 therefore provides the optimum corrosion protection because it has excellent resistance to both weathering and abrasion.

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What results have been obtained with Plascoat PPA 571 in salt spray tests?

The salt spray test to ISO-7253/ASTM B117 (5% sodium chloride solution at 35°C) was carried out both on pre-treated Plascoat PPA 571-coated steel panels with across-cut and on PPA 571-coated aluminium panels. The subsurface corrosion at the cross-cut after 1,000 hours was 0 mm with the aluminium panels and <1mm with the steel panels.

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How long has Plascoat PPA 571 been used for protecting steel or cast iron from corrosion?

Plascoat PPA 571 has already been in use since 1989 and has been shown to provide effective, long-term corrosion protection provided it is correctly applied.

See case studies on PPA571

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Why is the service life of Plascoat PPA 571 not presented in tabular form?

A coating of Plascoat PPA 571 forms a barrier to aggressive substances in the atmosphere, i.e. it provides passive corrosion protection. It is not consumed electrochemically, as is a layer of zinc. All tests and field experience indicate an extremely long service life.

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How quickly is a zinc layer destroyed under a Plascoat PPA 571 coating?

Where there is an unbroken layer of Plascoat PPA 571, the zinc will not be consumed, as no electrolyte (moisture, salts) can penetrate through to the zinc/steel interface. Where the Plascoat PPA 571 coating has been damaged, however, only the zinc layer can protect the steel from corrosion. When this happens the zinc layer exposed will be consumed at a rate depending on the environment.

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How does the PPA 571 coating behave under mechanical impacts?

By virtue of its ductility, Plascoat PPA 571 offers a degree of physical protection which depends on the thickness of the coating. Whereas hard coatings may flake or crack under impact loading, this does not occur with Plascoat PPA 571.

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Is Plascoat PPA 571 resistant to abrasion?

The Plascoat PPA 571 film is smooth, ductile and abrasion resistant. The abrasion measured is 60 mg weight loss (in accordance with Taber ASTM D4060/84, H18, 500 g load, 1000 cycles).

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What pre-treatment is required before metal parts are coated with Plascoat PPA 571?

The surface of the items to be coated must be free from rust, grease, scale and other impurities. A fully satisfactory substrate is obtained by blasting with sharp-edged materials until the standard purity rating SA 2½ to DIN 559 28, Part4, is reached.

Chemical activation and de-rusting with subsequent phosphating is also possible and yields excellent substrate for coating. For steel surfaces, good results have been obtained by iron phosphating for dip coating and zinc phosphating for electrostatic spraying; with galvanised articles, chromating or special zinc phosphating processes have proved effective.

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Are the support points also coated?

At the point where the article was held while being dipped in the fluidised bed tank, the coating is inevitably absent. This can easily be remedied, however, by:

  • Subsequent application of powder to the metal while it is still hot
  • Heating with a naked flame and application of powder
  • Application of a Plascoat PPA 571 film using a soldering iron
  • Flame spraying
  • Application of a recommended touch-up paint
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How can damage to a PPA 571 coating be repaired?

The substrate in the relevant areas should be cleaned to SA 2½to DIN 559 28, Part 4. Where damage has occurred or when two previously coated parts have been welded together, the following techniques may be employed:

  • Flame spraying with Plascoat PPA 571
  • Application of a Plascoat PPA 571 film with a soldering iron or a hot-air gun
  • Powder application after heating the part with a naked flame, e.g. Fluidised bed powder
  • Spraying or pouring
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Does material accumulate at the edges or around apertures in the metal part?

The coating thickness does not vary either way in such areas, except that accumulations of material may be difficult to avoid in the case of very small holes.

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How much time should elapse between pre-treatment and coating with PPA 571?

The coating should be applied very soon after pre-treatment, so that rust does not have time to re-form or the pre-treatment to de-activate.

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What is the cost of a fluidised bed coating plant?

This depends largely on the design of the plant. The largest single cost factor is probably the oven for heating the parts to be coated. A further consideration is how elaborate the pre-treatment is to be (mechanical roughening, or chemical de-rusting plus iron phosphating). All the other equipment is very inexpensive compared to an electrostatic unit with its special safety precautions and powder recovery facilities.

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What precautions should be taken when parts coated with PPA 571 are drilled, screwed, riveted or welded?

Plascoat PPA 571 is tough and elastic, but not hard. Coated articles should therefore be treated more or less like painted components. For screwing operations, large washers made of VA steel or plastics should be used. If holes are to be drilled in coated parts, scratching by hot drill chips can be avoided if the area at risk is protected with adhesive tape. Coated parts can also be welded, but the coating in the vicinity of the weld must be subsequently repaired.

For more demanding applications, see PPA 571H and PPA 571HES.

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Can Plascoat PPA 571 be painted where necessary to ensure uniform appearance?

It is better to apply Plascoat PPA 571 in the desired colour from the start, although subsequent colouring is possible by spraying or painting. Two-component polyurethane paints are suitable for this purpose since they adhere well to Plascoat PPA 571. Also, soon after coating epoxy/polyester paints can be over-sprayed on PPA 571, whilst the coating has not got too cold, with good inter-coat adhesion.

Further information on PPA571 Overspray.

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