XRF Analysis for Better Coil Coating Quality Control

Pre-painted, coil-coated metal is needed in the manufacturing of a vast amount of products: from home appliances to automotive panels to cooking tins. New applications are being developed all the time, which means that the coil coating industry is growing fast. In fact, the Global Functional Coatings Market size was valued at $368.5 million in 2017 and is predicted to reach $509 million by 2024; a CAGR of a healthy 4.8%.

Of course the demands of this growing industry are high. Suppliers of coil-coated metal face a competitive market that needs specialist equipment to meet tight specifications. It’s essential that the parts produced from the coil coated metal maintain their corrosion resistance, provide a good base for painting and look good for the lifetime of the finished product. The thickness of each coating is crucial for maintaining the integrity of the machined part, and it’s up to the supplier to ensure each layer falls right within the specification. As an accurate, fast and non-destructive measurement technique, XRF is perfect for coating thickness measurements and is described in the international standards ASTM B568-98(2014) and ISO 3497:2000.

You can either use XRF analysis during production to measure the coating thickness before moving on to the next stage, or you can use it during process optimisation to check which concentrations and immersion times result in the right thickness.

Let’s take a look at three types of coatings that XRF can analyse:

Phosphate-based conversion coatings

If you’re using ZnP, FeP or MnP as a conversion coating prior to powder coating or painting, you can use XRF to optimise your process. Newer and more advanced XRF instruments are able to measure the amount of phosphorus in these types of coatings in addition to thickness.

Zr, Ti and Cr pre-treatments

Right now, there’s a trend towards using new pre-treatment chemistries in place of the traditional phosphate-based conversion coatings. These pre-treatments cost less and have a lower impact on the environment. They use less water and don’t produce phosphate-containing waste, which can be hazardous and costly to dispose of. They also have lower energy demands as they can be applied at room temperature, rather than the high temperatures of the more traditional conversion coatings. They are also applied at a lighter coat weight, while still providing a high level of corrosion resistance and paintability. XRF is able to quantify the amount of Zr, Ti and Cr and therefore – given the right calibration setup and software configuration – can give you an accurate thickness for the pre-treatment coating before going to the next stage of production.

Zinc Magnesium Alloy Coatings (ZM)

ZM coating is one of the more recent breakthroughs in coating technology and is now fairly widespread in use. The addition of magnesium gives several advantages over a pure zinc coating. For example, ZM has similar corrosion protection to Zn at lower coating thicknesses. This helps when looking to reduce the weight of components, as is the case within the automotive, aerospace and military industries. The ZM coating also gives better corrosion resistance in demanding environments, such as marine environments. XRF can detect both zinc and magnesium and can ensure you are getting the right coating thickness and even distribution of the coating.

Hitachi XRF Analysers for Production

We’ve been designing our XRF analysers to cope with 24/7 production environments, such as plating and coil-coating facilities, for decades. We have a range of bench top XRF analysers that can sit alongside your production line for immediate analysis. We also have hand-held XRF analysers for spot checks at goods-in and within production. XRF is the standard measurement technique for many metal finishing applications – from checking the gauge of incoming steel to tight quality control of plating and conversion coatings.

For more information on how XRF can help you meet spec, get in touch with one of our experts.

You can get more information on our analysers here, including detailed technical information.




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Date: 12 July 2019

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