Coatings FAQ

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 [1].

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.

[1] Francis, L. F., & Roberts, C. C. (2016). Chapter 6-Dispersion and Solution Processes. Materials Processing.

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 [2].

[2] 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

Polymer coatings are designed to improve function or appearance of components by taking advantage of the inherent material properties such as self lubricating properties, corrosion and chemical resistance.
 

Our coatings range is built of references using different polymer matrixes that allow different levels of load capacity and operating temperature as well as suitability to work in different media.

GGB offers coatings made from polymers across the entire spectrum of mechanical and thermal properties they have to offer. The polymers of GGB coatings are epoxy, PFA, PES, PAI, PAEK and PBI. Commodity polymers like PE, PP, PET or ABS and not considered because they have insufficient mechanical/thermal performance to cope with tribological solicitations. 

Coatings exist in organic and inorganic form with the most common industrialised coatings catagorised as either polymer, metal and ceramic based. GGB Tribological coatings are principally based on carefully formulated polymer technology to minimise friction and take advantage of their self lubricating properties.  Such coatings are relatively inexpensive and can be applied using traditional spray painting technology.  By contrast, metal and ceramic coatings require more specialised equipment, are more costly and although more durable with higher temperature resistance, they are less suited to tribological applications due to the higher friction.  

Surface coating technology generally refers to the application of a thin film or layer or a dissimilar material onto a substrate that enhances the surface characteristics in some way. The surface coating may be designed to specifically provide chemical or corrosion protection, improve hardness and durability, provide self-lubricating characteristics if relative motion and contact with other bodies, or may even simply be for decorative purposes. The technology aims to ensure an effective mechanical or chemical bond between coating and the underlying surface. GGB surface coating technology is dedicated to extending the life of moving parts by modifying coating surfaces to reducing energy consumption and improving efficiency by minimising friction, simplifying design through self lubrication behavior that eliminates need for third party lubrication such as grease or oil, and extending durability by reducing risk of seizure damage. The GGB coating used in this way serves as the sacrificial element protecting the more expensive substrate component.

UV Protective coatings generally refer to coatings purposely engineered and applied to protect against the damaging or ageing effects of ultraviolet radiation and sunlight. The coating is designed to act as a barrier, absorbing UV rays and preventing penetration to the underlying surface. This technology is commonly used to create the protective film on sunglasses to protect eyes or as protective clear paints that prevent discoloration of the underlying colored surface e.g. car body paintwork.  

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 enables 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.
 

Although solvents are used to help process coatings, the GGB polymer coatings in their finished applied form are non toxic. GGB purposely develops its formulations with safety in mind avoiding the use of prohibited or legislatively controlled substances. 

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. 

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 component 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.

A nominal thickness of 25 µm is the most common guide for liquid spray coating. However, some polymers can achieve up to 50-80 µm by tuning viscosity and/or number of passes. The typical thickness and respective tolerance for each coating in the table below:

Please note that tolerances may change based on part geometry and complexity of the coated area (needs to be reviewed project by project). For these cases, please consider an increase in tolerance to ±10 µm.
The choice of material and process will be based on functional requirements. Therefore, the best thickness for a specific application depends on which coating material and the process selected.  
 

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.

Yes. 

Almost all of our coatings provide electrical insulation in varying degrees that are connected to the part geometry, coating thickness level, and dielectric strength of the specific coating. The exception to this is TS742, that is a static dissipative coating, implying that it is inherently conductive.

Only TS742 provides static dissipative properties and therefore conducts electricity, ~104 Ohm surface resistivity.
 

The colors of our coatings are black (TS225, TS650, TS742) and dark brown (TS651). To change the color, a new formulation development is required, and it needs to be discussed with an expert.

The curing cycles currently performed for GGB’s coatings are the following:

* Stated temperatures refer to the substrate temperature during the curing process.

Yes, but it depends on the coating and melting point of the plastic substrate.  The coating requires to be cured. If the coating or plastic substrate is a thermoplastic, the curing temperature must be compatible with the melting temperature of the substrate. However, with a thermoset coating, the curing can be controlled to maintain temperature within reasonable levels, giving more opportunity. We have shown that fiber reinforced composite material can be coated with an epoxy coating if necessary to the OD.

The “coated/functional area” is the area where the coating is applied within the coating requirements that are defined in the drawing.

The “area that may have overspray” is the area where some traces of coating can be found, due to the spraying process. It’s important to make sure that this overspray doesn’t affect the final performance of the coated component.

The “coated area with no thickness control” is the area where coating is applied but as there are no particular tribological requirements, there is no need to control the applied thickness.

The “masked area” is the area where there should be no traces of coating as the functionality of the part may be affected.

No.
If we are solving a purely tribological problem, it is sufficient to apply the coating to the area that represents the sliding surface.  However, be aware that in order to confine the coating to a designated surface, this may have implications: 

• Risk of overspray on the non-designated sliding surface (this should always be verified as acceptable by customer)
• Need for masking, which can be laborious and costly. Often it can be cheaper to coat the whole component than to mask
• Need for special carrier tooling (cost implications)
• If the sliding component is at risk of corrosion or chemical resistance, then there may be value in coating the whole component since most of GGB’s coatings provide an effective barrier to corrosion or chemical attack.  In this latter case, one must be careful on how the component is held during coating.

The identified materials are all metals except high copper containing alloys and some plastics. However, other substrates may be considered. The first factor to consider is which coating is to be applied as this dictates the curing temperature and the substrate exposure temperature and duration during the coating process.  In other words, the substrate must be able to withstand this thermal cycle without any impact on the key properties of the component. You should routinely inform the customer that his substrate will be subjected to high temperature.

Yes.
Most coating systems require higher curing temperature which can range between 200°C to 420°C during, for up to 25 minutes. This exposure will behave as an annealing process and shall be considered when a coating operation is envisaged.
 

Yes, by pyrolysis or surface treatments like blasting or laser cleaning.  
Note that each time the coating is removed, the process of grit blasting will also remove a small thickness of substrate. This leads to the fact that the coating removal/re-application can only be performed a finite number of times before it starts to impact the final dimensions of the coated part.