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Surface Coating - The clean and cost effective alternative to messy, wasteful spray release agents

Keith Stevens, R&D director for surface coating specialist Poeton Industries, suggests that applying a non-stick coating to moulds is a more cost effective and environmentally friendly alternative to the traditional aerosol release agent.

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 is an aerosol spray release agent that is manually applied by a machine operator. Whilst this method may appear to be the easy option it can have serious cost and environmental implications when examined more closely.

Consistent application of the spray agent can be difficult to control and coverage can be difficult to measure accurately. The coating can be uneven, leading to patchy product release, and over-spray can be wasteful and potentially harmful to the operator.

Disposal of the empty cans may also prove to be a costly problem.

Environmental legislation puts a limit of 250 on the number of aerosols that can be disposed of in a single skip. With a waste management company charging approximately £200 for each load, disposal can become a significant cost.

Even if automated spray equipment is installed there can still be environmental concerns about spray particles in the atmosphere.

A thorough investigation of the actual and environmental costs would surely suggest seeking a viable alternative.

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 greatly reduced, and as most moulds can be stripped and re-coated, their working life can be extended significantly.

A number of Poeton's Apticote coatings are already being used to solve specific production problems in moulding applications.

For example, an inert low-friction copolymer coating combines excellent wear properties with permanent dry lubricity to extend mould life and eliminate the need for expensive chemical mould release agents. Throughput and machine running speeds are both increased, and downtime is greatly reduced as tools need changing less frequently and many cleaning operations are eradicated.

Another can operate at extremes of temperature from -200ºC to +285ºC and is chemical resistant and FDA compliant.

Advanced Apticote hard anodic composites combine excellent low-friction and release properties to offer a unique approach to precision hard anodising, providing a completely uniform surface layer of predictable thickness. As surface growth is 50% of the total coating thickness, final dimensions can be accurately predicted to eliminate the need for costly mould finishing operations.

An electroless nickel composite offers the opportunity to substantially reduce material costs by coating low cost materials to meet the needs of high performance moulding applications.

For example, moulds manufactured from low carbon steel and coated with this Apticote coating can be used to replace more expensive alloy moulds with no loss of performance. And costs are further reduced because moulds can be machined from more workable and readily available metals.
And a special coating has been developed for rubber and polymer moulding applications that require permanent mould release properties. It is designed to provide excellent mould release where maximum chemical and abrasion resistance is required.

USDA and FDA compliant Apticote coatings are ideal for food and drink, cosmetic and pharmaceutical applications. They have achieved four times the wear resistance of electroless nickel in Tabor Abrasor Tests, outperform hard chrome in dry running applications and will operate at temperatures from -115ºC to +260ºC.

Using a specialised coating, Poeton helped solve a sticky packaging problem for Rexam, one of the world's top-ten consumer packaging suppliers and a leading European supplier of thin wall plastic containers for the food industry.

At its factory in Yate near Bristol in the UK, Rexam has developed a proprietary process to mould high volume trays using PET, an advanced packaging material that is specified by major food brands because its clear finish allows consumers to see the product inside the pack.

However, whilst PET has obvious advantages for Rexam customers it can be difficult to process in high volume moulding machines, being both abrasive and sticky.

Its abrasive properties cause aluminium moulds to wear quickly and its stickiness makes it difficult to remove trays from moulds - problems that have a seriously affect on high volume production. Also, because trays stick together when stacked, de-nesting is also difficult and slows down the customer's production lines.

Both problems were experienced recently at Rexam on a line producing trays for a major food product line.

To overcome the de-nesting problem Rexam had been grit blasting the mould to roughen the surface, and blending an expensive migrating wax additive with the PET. Whilst this approach improved de-nesting it didn't solve the mould wear problem and, as the additive left a residue, the mould also needed regular cleaning.

At this stage the issue of pack clarity became secondary to the high volume needs of the customer and Paul Hawkins, technical manager at the Yate site, called in Poeton to advise on coatings, primarily to improve the long-term wear characteristics of the moulds.

Poeton's engineers recommended a coating to reduce wear in the mould cavity; and bead blasting rather than grit blasting as a more effective pre-treatment for use with the coating.

Initial trials were carried out on a 120-cavity drum mould with twenty cavities coated. After six weeks of running twenty-four hours a day and seven days a week there were no signs of wear in the coated cavities and Rexam were sufficiently impressed to have the whole tool coated.

Whilst the result was good news for high volume production, the real surprise came when Rexam ran trials of the coated cavities with reduced amounts of the de-nesting additive in the PET. With only half the amount of the expensive additive (the optimum result) de-nesting was significantly improved and additive costs reduced.

The process now produces 1.5 million of the twin-cavity trays each week to feed a production line that is operating every day of the week.

Commenting on the project, Paul Hawkins says: "Poeton coatings proved the ideal solution for the wear problems we encountered with this combination of long running, high-volume process and abrasive, sticky material.

"The improvements in de-nesting and the reduction in additive use is a very welcome bonus!"

Naturally, different methods of moulding - e.g. flow, spin, blow and vacuum injection - require different release agents. And there are many different types of material, which in turn means curing and setting temperatures vary widely.

Fortunately there are also many different surface coatings and, with more than eighty Apticote treatments to choose from, Poeton engineers work closely with customers to advise on the right coating and even the right mould material.

To discuss surface treatments, sample part processing or technical advice call Poeton Industries now on 01452 300500.

14 April 2010

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