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News Release from: Keronite | Subject: Keronite technology
Edited by the Manufacturingtalk Editorial
Team on 18 September 2007
Mould surfaces made more durable
Aluminium is used as a replacement for expensive steel tools using patented chrome-free Keronite technology, improving durability and surface release properties.
In a variety of moulding applications, Keronite Plasma Electrolytic Oxidation (PEO) enables aluminium to be used as a replacement for expensive steel tools by improving both the durability and the release properties of the surface Using the patented, chrome-free Keronite technology, mould surfaces are transformed into a complex ceramic composite by anodic conversion under plasma discharge conditions in a non-toxic electrolyte solution
This article was originally published on Manufacturingtalk on 2 Jul 2002 at 8.00am (UK)
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Depending upon the alloy used and the thickness of the ceramic layer created by the process, the hardness of Keronite surfaces ranges from 500 HV to 2000 HV: well above the capabilities of hard anodising.
Aluminium surfaces can thus be rendered harder than steels, glass, and many silicon-containing compounds.
This hardness is great for improving the wear performance of surfaces, but it the combination of this hardness with compliance of the Keronite layer that really makes it ideal for wear resistance.
Further reading
Process hardens and protects magnesium, aluminium
Surface treatment process is building quite a reputation as the preferred treatment for magnesium and aluminium alloys, providing the hardest and most corrosion resistant surfaces.
Surface treatment toughens non-ferrous metals
Patented surface treatment technology allows automotive companies to use lighter metals to reduce vehicle weight, thereby saving fuel and decreasing emissions.
Electrolytic surface preparation is ISO approved
Keronite International has achieved ISO 9001:2000 certification for the application of advanced surface treatments using the Keronite Plasma Electrolytic Oxidation process.
Research at the University of Cambridge demonstrated that the stiffness of Keronite layers can be as little as 30 GPa, making them far more strain-tolerant than most ceramic layers.
When impregnated with PTFE, the wear resistance of Keronite surfaces can be even further enhanced.
Keronite is a conversion coating which grows into the surface of the aluminium in a uniform, controlled manner to form a defect-free interface with the original metal.
The Keronite layer therefore has far better adhesion to the substrate than most deposited coatings such as plasma sprayed ceramics.
As well as inward growth, the layer grows out from the original surface in a predictable manner.
The extent of outward growth depends on the alloy and is typically between 10% and 40%.
This can be allowed for in tool design or, if necessary, it is possible to polish the layer back to original surface dimensions.
The natural Keronite surface has surface roughness (Ra) of approximately 10% of the thickness of the applied layer but can be polished back to a very smooth finish if necessary.
The layer also has a very fine-scale pore structure which is ideal for retention of lubricants or can be used to make a tough, non-stick, or low-friction composite by impregnation with polymers such as PTFE.
DuPont declared Keronite a winner of the 2002 Plunkett award for innovation with Teflon: Keronite impregnated with Teflon provides a wear-resistant, non-stick surface with excellent adhesion to an aluminium substrate.
Moulded parts are thus easily released, time after time, without damaging the surface of the mould itself.
Aluminium moulds tend to wear along edges and on corners where conventional dip-plating or painting processes produce thinner layers of protection due to surface tension effects (also known as "dogbone" effects).
Hard anodising also offers limited protection to edges or sharp corners because its columnar growth results in wedge-shaped cracks on tight radii, again creating points of weakness.
Keronite, however, shows no defects or thinning on corners and edges; it can faithfully follow the contours of the component or even be thicker on sharp corners, offering much better edge protection than the rival processes.
Finally, because of the combination of excellent substrate adhesion and the low stiffness mentioned earlier, Keronite layers show good tolerance to strains such as those caused by differential thermal expansion.
Keronite layers therefore show good resistance to thermal cycling.
Keronite is being used in a wide variety of moulding processes, from the less aggressive blow moulding and vacuum forming, to those like injection moulding and resin-bonded sand core moulding where tool wear can be a real problem, particularly opposite injection points.
On blow, vacuum forming moulds, or paper and board moulds Keronite is used as a finish in its own right, particularly where a textured finish is required on the plastic surface.
Alternatively, where a very smooth but durable surface is required, bare Keronite can be polished using conventional methods, or by wet blasting with corundum, plastic media or nut shells in a liquid medium.
Where a non-stick, quick release finish is required, as is often the case with injection moulding, Keronite is used together with PTFE.
The best results are obtained with water based emulsions or thin solvent-based solutions which penetrate the Keronite layer to produce an extremely hard-wearing PTFE/ceramic composite.
This PTFE-impregnated composite structure can be polished back to give a very smooth surface, if required.
Keronite has been used successfully together with PTFE on rotary moulds for plastic balls, whereby plastic is spun to form a hollow ball.
In this application, the tool is subjected not only to abrasive plastic, but also to extensive thermal cycling.
Despite this aggressive environment, moulds treated with Keronite and PTFE then polished to produce a smooth, non-stick surface, have been in service for 3 years with no requirement for maintenance.
Keronite and PTFE have also been used to treat plastic roll forming tools used to produce corrugated polycarbonate sheeting.
This combination has proved very resistant to the extremely aggressive, hot plastic material.
In another application, Keronite with PTFE has been used to treat the surface of vacuum forming tools used to produce high volumes of food packaging.
Keronite is also being used together with PTFE as a replacement for hard anodising with PTFE to produce a harder wearing surface for the heating plates used to form fibre board blanks which are used inside car doors.
The treated surface has low friction and excellent release properties and remains stable under temperature cycling.
Many manufacturers have tried to replace their expensive steel tools with aluminium, but found that there is poor adhesion of the release agent (PTFE) and that aluminium tools tend to wear too quickly, particularly in the case of the more abrasive plastics with a high glass content.
Keronite has been successful in improving the adhesion of the PTFE and the resistance to wear.
In many cases, prototype tools can even be used for volume production, and tool life can be even longer than that of the conventional steel moulds.
In the sand casting industry, it has been possible to replace steel inserts with aluminium ones treated using the Keronite process.
The aluminium inserts treated in this way have proved to be four times more durable then the steel equivalents, bringing considerable cost savings through reduced downtime.
There are many applications where Keronite has been adopted as a much more durable alternative to hard anodising which has failed to meet the customer's requirements.
For example, Keronite has been used together with a water-based PTFE to treat moulds for plastic caps used in packaging.
In this particular example, the moulds have been in service since 2003 and are still going strong! Bare Keronite has also been used as an alternative to hard anodising to extend the life of vacuum forming moulds used to produce packaging for mobile 'phones, and of blow moulds for beverage packaging.
60 microns of Keronite with PTFE was found to be successful in treating the surface of equipment used in the manufacturing of paper cups.
Moving parts are constructed from wrought aluminium in order to reduce weight and to improve the heat transfer properties, but friction and wear can be problematic without the appropriate protective surface.
Keronite on aluminium not only provides a much harder surface than steel or hard anodised aluminium in most tooling and moulding applications, generally improving wear life, but it is also very effective in protecting the moulds against chemical attack from the chlorides or sulphides generated when plastic or rubber is heated.
By enabling the use of aluminium in applications where this was not previously possible, Keronite can also help to improve heat transfer in the moulding process and this in turn enables the use of water-based resins.
A further advantage of using Keronite in this industry is that it can be reprocessed if the tool needs to be altered, machined or welded for any reason.
The combined effect of all these benefits is a considerable cost saving when switching from steel to aluminium with Keronite.
Experts believe that savings of Euros 60-80,000 can be made when moulding an item of around 1 dm3.
If this is the case, expensive steel moulds may soon be a thing of the past!.
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