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The Roller Coating Process Explained

What is it and Why is it so Popular?

Roller coating is considered to be an ideal method of applying thin coats of finishing material to flat substrates of wood, metal and plastic. It’s so effective because it’s expert method of design is both precise in application and also safe for the environment – offering near 100% transfer efficiency. The principle behind this method is ancient – based upon the physics of transferring a layer of coating from the surface of the roller to that of the substrate. As famously uttered by Leonardo Da Vinci: ‘simplicity is the ultimate form of sophistication’.

But How Does it Work?

The roller coating machine setup begins with the initial adjustment of the application roll to the desired height – this application roller is typically set at light compression with the substrate (a function of roller durometer and substrate texture).

Science tells us that there are numerous bonding requirements behind this to ensure that the amount of coating material which is supplanted onto the substrate is almost entirely independent to the properties of the fabric. The effectiveness of this roller coating is technically determined by the rheology of the fluid being used set against the two individual speeds of the rotation surfaces (generally known as the “doctor roller” and the “application roller”).

So – What Exactly is the Process?

Well, explained in more simple terms, the speed of the conveyor and application roller are set and synchronised based upon production requirements (what needs to be coated) Following this, the process of transferring a layer of coating from the roller requires multiple crucial components. Let’s roll this process out specifically:

  • A conveyor belt  moves the substrate under the application roller to enable the coating transfer
  • The application roller carries the coating film which will then be transferred to the substrate
  • The roller is covered with various materials and densities to facilitate a range of coating applications
  • The metal metering roller then works in conjunction with the application roller in order to form a pocket of coating which is called the nip.
  • Initial doctor roller rotation speed can be set at a percentage of the conveyed speed and adjusted accordingly for coating of specific items
  • The distance between the doctor and application role is then set to create the NIP and to transplant the film thickness onto the application roller below
  • The film thickness on this application role is ultimately determined by the distance between the two rollers (doctor roller and application roller) and the speed and direction of these individual rollers
  • Coating is loaded and fluid begins circulating within the system via a pick-up tube
  • A scraper blade is usually used in order to remove the coating from the back of the roller and return it to the NIP above – whilst simultaneously keeping the coating from dropping down below onto the conveyor when the doctor roller is run backwards
  • A recirculation system fluid pump pulls coating from a container and pumps it carefully between the rollers into the NIP
  • It is wholly crucial to have fluid constantly circulating, to mitigate the danger of damage to the application roller
  • The final adjustment is based on keeping the nip at a constant fluid level – ultimately determined visually by a “test piece”
  • Once this test has been run, someone will often initially appraise by eye for any clear imperfections, then determined the accurate weight of the coding film onto a scale
  • The resulting weight can be used to make coating adjustments with the NIP, the roller speeds and the application height as well
  • Production is ready to proceed!

The Different Coating Methods

Although there are different types of coating methods, the most common type of roller coating is the differential direct style in which moving components are adjusted individually in speed and direction, in order to ensure maximum control of the coating process. These can be used highly effectively for the application of UV oil, waterbase and a wide range of other coatings onto various materials, stemming from plastics, woods and metal.

Standard Roller Coating

As detailed above, the standard roller coating machine is expertly engineered in order to roller coat a wide range of materials – suitable for application of stains, primers and top coats.

The top of the range models, such as Cefla Smartcoater EVO, are also available in a range of configurations; with fixed or self-levelling floating head and automatic longitudinal and transverse adjustments – which makes them ideal for those who are implementing their roller coating onto any panels that are not perfectly calibrated.

Curtain Coating

The top end of curtain coating machines are able to offer impeccable performance and consistency through being designed to apply any type of coating with varying levels of viscosity to semi-finished panels of material.

The Cefla SmartCurtain models, for example, are all fully equipped with removable coating heads, alongside material trolleys and tanks, three adjustable-speed conveyor belts and enclosed heavy-duty stainless steel tanks to protect against any damaging, imperfection inducing vibrations within the system itself.

UV Radiation Curing Ovens

UV radiation curing ovens are a highly effective method of curing the UV coatings applied which combine systemic elements of the process into a single method of sophistication: the conveyor, control panel and UV unit. This innovative plug and plot solution is popular due its versatility, compact nature and performance efficiency – making it easily integrated even within complex finishing lines. It is also available within a variety of configurations in order to meet any specific curing needs.

The conveyor system can be configured with a slatted or belt conveyor which is integrated within the framework of the machine itself. As an optional extra, you can choose to install a highly innovative liminar air flowing cooling system which is able to disperse heat at the point of generation. The operator interface is usually a touch-screen PLC integrated into the machine body itself – affording the simple, efficient control of all the working parameters of the machine. The control panel is also conveniently installed into the body of the machine again – meaning no additional space in the line layout is required.

In terms of eco-efficiency, the Cefla UV-R Radiation Curing Oven has an electronic system built in which effectively regulate the power of each individual lamp within the system. This system is also able to automatically activate its sophisticated energy saving function, via constantly monitoring whether there is or is not material placed under each individual lamp. The technology on hand for this specific model is now a cutting-edge, highly innovative tool throughout a wide range of industry; with an LED source of cold UV light which is considered to be an advantage for substrates (e.g. wood) which are more sensitive to high pressure and therefore diminishing the chances of heat damage to the material itself.

How We Can Assist You

Have any more questions or enquiries about how roller coaters can satisfy your industry demands? With long-standing partnerships with Industry renowned names including Cefla, Wandres and CMA Robotics; MPS Machines Ltd provides the complete service and package for the furniture production sector – providing high quality, innovative equipment and solutions to the entire woodworking industry.

Contact us today at sales@mpsmachines.co.uk or give us a call on +441162401795 (phone) / +447799896769 (mobile).

High Barn

3 Cedars Courtyard

High Street

Fleckney

Leicestershire

LE8 8DN

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