November 20, 2019
Thinking Outside the Circle, Applied Tribology a Key to Impr
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Not all Coatings are created equal.
Equipment manufacturers are facing greater demand to deliver faster than ever reliable parts that meet higher performance expectations. Advances in polymer engineering during the past decade mean that tribo-coatings can now offer a means to achieve a product´s goals, helping to improve performance through reduced friction, increased wear life, reduced system noise and improved corrosion resistance. It is possible to do all this while reducing system costs.
Polymer coatings are thin layers of polymer applied to either flat or irregular substrates. Polymeric coatings can be functional, protective or decorative. They are also used to modify surfaces (paper coatings, hydrophobic coatings). Although polymeric coatings are mostly organic, they can also include ceramic or metal particles to increase durability, functionality, or aesthetics .
Applications often require a combination of bulk and surface properties at different locations, timing and in a function of the circumstances. Polymer coatings are often used to modify the substrate surface properties and enhance their performance. Therefore, coatings have become a key branch of the tribological materials science.
 Francis, L. F., & Roberts, C. C. (2016). Chapter 6-Dispersion and Solution Processes. Materials Processing.
The majority of polymeric coatings are thermoplastic polymers. With the thermoplastic polymers, the individual macromolecules of polymer are entangled but still largely independent from each other. Therefore, thermoplastic coatings featuring high flexibility, good elongation capability and high impact resistance but lower scratch resistance. They provide excellent corrosion protection.
Some of the most advanced polymer coatings are thermosets. They are infinite three-dimensional networks of covalently interconnected macromolecules of polymers. This three-dimensional network offers excellent resistance of polymer layers to solvents, chemicals, and mechanical stress. Their high hardness enable them to be extremely resistant against scratches and wear.
Thermoset coatings are applied as liquids on a substrate and start with short molecules which are cross-linked together during the curing at a given temperature to form a permanent three-dimensional network on an irreversible chemical reaction. This need for curing is inevitably reflected in the choices of substrate material.
The term polymer coating suggests that such a coating comprises predominantly polymers. However, coatings formulations are composed of organic and inorganic ingredients: binders, fillers (or pigments), additives, and solvents .
 Gijsbertus de With, (2018). Polymer coatings: A guide to chemistry, characterization, and selected applications, Wiley-VCH Verlag GmbH and Co., ISBN 978-3-527-80633-1
The coating system selection does depend on a large set of considerations and is obviously application dependant. That is the reason why we encourage you to fill out the contact form, so our Applications Engineering team can work with you in determining what the best solution should be.
GGB is capable of coating parts from as little as a few millimeters in dimension to a maximum part size of 5 m x 2.5 m x 2.5 m (16.5 ft x 8.25 ft x 8.25 ft). However, geometry complexity may place some restrictions.
Depending on the coating selected, curing temperatures can range from room temperature to a maximum of 420°C. For those subjected to higher curing temperatures, consideration should be given to the potential annealing effect on the substrate.
Coatings can be applied to specific areas of a part by means of either masking the surfaces where the coating is not permitted or using those areas as sacrificial handling points during the manufacturing process. However, coating the entire component will provide the advantage of full protection against corrosion and chemical attack and, in most cases, not be more expensive.
The surface finish requirements for a components to be coated is considerably more relaxed than traditional surface specifications for tribological components, thus potentially providing cost savings for the customer. The surfaces prior to coating can accept a roughness up to 1.6Ra since the coating process integrates a surface modification step to ensure optimum adhesion.
The thickness will depend greatly on the type of coating being applied, its composition, application process and final intended use. In general, the target thickness will be around 10 µm to 35 µm but coatings can be as thick as 300 µm.
There is no limit to the depth that the coating can be applied to, but there is a limitation on the aspect ratio of said hole/recess. The general guideline is that up to a hole diameter of 50 mm, we can control the coating thickness if the depth/diameter ratio is no higher than 3. If the hole/recess has an opening larger than 50 mm, then special spraying tools can be used to reach its entire length and deposit a controlled coating thickness.
A tribological performance coating can be applied to most substrates, including but not limited to metals, polymers and composites, regardless of shape or form. The coating feasibility is driven by the substrate thermal and chemical properties as it needs to survive the application and curing process.
Coatings are specifically designed to reduce friction between interacting surfaces in relative motion. TriboShield™ coatings are self lubricating, and thus specifically designed for low friction and good wear resistance.
For specific applications, GGB is also able to formulate high friction coatings still keeping the low wear rate as a key property of the coating.
We have a range of coatings which are FDA compliant. The actual approval is granted for each specific use and needs a specific certification process to be performed by a third party laboratory.
The difference in weight between coating & bearing is negligible so should we not emphasise the fact that it can be applied directly onto light weight materials such as aluminium, magnesium or titanium.
In many cases, the coatings are applied directly to the customers component, eliminating the need of assembling and simplifying the bill of materials. The component to be coated does not require fine machining, and a roughness of 1.6 μm Ra can be specified. In addition, the usual hardening and/or polishing of the surfaces can also be eliminated.
Polymers generally provide an effective barrier to corrosion or chemical attack. By coating the full part, the coating can potentially satisfy both your tribological and chemical resistance needs. The dampening characteristics of polymer coatings can also help reduce noise, vibration and hardness leading to quieter operation.
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