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Apticote, the case for Mould Release Coatings

/live/stories/tyre-mould.jpgAPTICOTE, THE CASE FOR MOULD RELEASE COATINGS

A spokesman for surface coating specialist Poeton Industries suggests that coating moulds is a more cost-effective and environmentally friendly solution than the traditional aerosol release agent, and he offers advice on the right coating for a wide range of applications.

Perhaps I should start by answering the question most customers ask - "Why do I need a coating?"

In most moulding applications there is a need for some form of mould release to speed up production, maintain product quality and reduce or eliminate costly mould stripping and cleaning time.

The traditional solution, a manually or automatically applied aerosol spray release agent, can have serious cost and environmental implications when examined more closely. For example, consistency of application can be difficult to control, leading to patchy product release if it's uneven. Coverage can be difficult to measure accurately, and over-spray is both wasteful and potentially harmful to the operator. And if you are using cans, disposal of the 'empties' can be a costly.

Historically, release agents were solvent-based and this produced serious cost, HSE and environmental issues, which led to a move to water-based products. Whilst less costly and friendlier to the user and the environment, they can often be less effective at, leading to higher usage of the release agents. The water can also cause corrosion problems on hot moulds, leading to costly mould repairs.

If the release agents are water-based waxes, the contamination of the mould and the surrounding areas by wax overspray can be a serious problem, leading to high wastage and cleaning costs. For example, a large PU foam moulding company calculated the cost of spraying, wastage and general cleaning of the mould and surroundings, at £75,000 per annum!

Replacing conventional spray release agents with a specialised coating provides considerable cost and operational benefits. Carry-over of release agent onto the product is eliminated, the high cost of release agents and disposal of aerosols is eliminated, and as most moulds can be stripped and re-coated, their working life can be hugely extended.

After this explanation, most customers agree that it's worth looking at the benefits of coating technology in more detail.

In today's manufacturing and processing environments speed is of the essence. If products can be released quicker, more can be produced and they reach the customer sooner. Choose the optimum coating and it will deliver consistent quality throughout the life of the mould - whether it's operating short runs of a few hundred or long runs of many thousands. And the clean release of the product will save many hours of stripping and cleaning moulds.

Choosing the right coating means seeking advice, preferably at a very early stage of production engineering, and working closely with a surface coating specialist, because they will not only advise on coatings, but also on the materials from which the moulds are manufactured. This is important because, for example, in some applications aluminium will be better than steel, and some coatings can be applied more effectively to aluminium. There are also many different types of materials, which means that curing and setting temperatures vary widely (in the case of plastics and rubber these can vary from 140ºc to 340ºc). It is also far cheaper to coat a new mould than to try to clean a contaminated production tool. And of course, there are many different types of moulding!

Here's a brief overview:

Flow Moulding

Commonly used for plastic pipes, plastic sheet, rubber tube, etc., forces material through a set of dies in semi-liquid condition as a continuous stream. The material is then set using water to produce the end product.

Spin Moulding

Used where flow moulding cannot produce the shape. Very dense and durable materials can be used to produce products such as toilet seats, some children's toys, etc.

Blow Moulding

Used for high volume applications, for example to produce containers such as bottles for milk, soft drinks etc.

Compression Moulding

Applies high pressure to powders such as polyethylene, or synthetic rubbers which are then heat-cured for items such as tyre moulds.

Vacuum Moulding

Used to produce a wide variety of products from baths and sinks, to margarine and yoghurt tubs, by sucking an already partially cured sheet of material into a mould form.

Injection Moulding

Feeds material in pellet form into a hopper, where it is heated to flow conditions and forced into a mould.

The fact that each method of moulding will require a different release agent is further complicated by the many different types of materials used to manufacture moulds. Here are some examples of materials, applications, and the type of coating that should be specified.

Rubbers

Rubber comes in many forms, nowadays all synthetic.

The aluminium segmental moulds used to produce tyres will require different coatings for different rubbers. For standard silicon rubber, an anodic composite coating such as Apticote 350 will be ideal, whereas carbon black rubber will require a nickel alloy or nickel composite coating such as Apticote 450,460G or 200A. Applied correctly, they will last for years. Steel moulds will accept Apticote 400 and 450 but not Apticote 350, which is designed for light alloys.

The steel moulds used to produce Viton and Neoprene seals will need a coating such as Apticote 460G. Its combination of hardness and lubricity is designed to produce the best results and long life for high volume applications.

And the steels moulds used for very abrasive memory rubbers will need a nickel composite such as Apticote 450, a unique nickel alloy composite designed for even lower friction and greater load carrying capacity. However, depending on the application speed and volume, even using this coating, moulds could need re-coating every 3 months.

Coatings such as Apticote 200, 350, 450 and 460, which are already used extensively for tyre moulding applications, have excellent release properties and are extremely resistant to the high temperatures and aggressive materials used in tyre manufacture.

For the production of larger tyres, where sidewall plates are used, special Apticote nickel/chrome duplex coatings have been developed with exceptional wear and corrosion resistance, to reduce the pitting corrosion caused by heat and carbon gases.

Coatings can also be modified to provide the gloss or matt finishes that are required to meet the standards of certain high-end OEMs.


Plastics

Again there are many types. UPVC, for example is commonly used for pipes, sheet, window frames etc. When using aluminium moulds with UPVC a coating such as Apticote 350 is again ideal. For steel moulds a hard chrome coating such as Apticote 100 is tougher than steel and provides excellent abrasion resistance without needing after-plate grinding.

Polyethylene is self-lubricating plastic used for artificial implant joints, etc. The ideal coating for use with steel mould is a nickel composite such as Apticote 460, which adds the protective power of low friction polymers to the natural hardness and corrosion resistance of nickel. Different coatings will also need to be considered for different types of mouldings. Spin moulding, for example, will require an inert low friction polymer coating such as Apticote 200G to provide outstanding non-stick and dry-slide properties. Vacuum forming moulds need coatings such as Apticote 350. And for heat sealing bars/pads polymer composites such as Apticote 200A or Apticote 200G provide dry lubricity and can resist temperatures up to 285 Deg C.

Food Products

When using moulds for food products, coatings must be FDA compliant. Where moulds are in direct contact with food a hard anodic coating such as Apticote 350F or 200N should be used on aluminium moulds to provide a combination of permanent dry lubricity and exceptional corrosion and heat resistance. A high-hardness nickel composite such as Apticote 460 G needs to be applied to steel and stainless steel moulds. Both can be washed or cleaned.

Where products are very abrasive, they will need coatings such as Apticote 100, 350, 450, and 460 or a mix of flame spray and polymer such as Apticote 810TP, all of which are specially designed for these types of conditions.

Coating technology is already used extensively in the moulding industry and for many companies the benefits of applying coatings to replace release agents are proven. An added benefit is that most Apticote coatings can be stripped and the moulds re-coated.
Moulding companies who prefer the slower spray and mould routine could find that the extra cost and time of 'sticking' with traditional methods puts them at a disadvantage against competitors using perfectly matched high-quality coated moulds.

Before making the change however, they should consider that the selection and testing of the correct coating system requires a careful blend of skill and experience - so seek advice.

Trevor Amos

Poeton Group Sales Manager

19 April 2010

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