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Coating solutions

Application: Step by step to optimal corrosion protection

The requirements for the coating of components are diverse: from protection against environmental influences to specific tasks such as defined friction and sliding properties, media resistance and colouring.

Dörken MKS offers different coating technologies, each of which require an individual application technique. Dörken MKS ensures consistently high quality via a process tailored to the individual components. This is how application is undertaken, step by step:

1

Pre-treat­ment

2

Coat­ing

3

Cur­ing

4

Cool­ing

Prior to coating, components must be free from rust, scaling, dirt and dust, oil and grease, as well as being dry. Typical forms of pre-treatment include alkaline degreasing, blasting with various materials (e.g. stainless steel grains, steel grains, glass beads etc.) or chemical pre-treatment such as phosphatising or pickling. In the case of zinc flake coating for example, alkaline degreasing plus blasting is recommended.

Mineral additives can be used to aid the blasting process. These keep the blasted surface cleaner (oil-free) and thus enable longer operation.

Coating may occur without the use of current, in the form of physically-applied painting, or with electrical current used to deposit the material on a component.

Zinc flake technology (electroless coating)

Zinc flake systems are applied in multiple, similar coating stages. Firstly, the zinc and aluminium base coat is applied and pre-dried. This is followed by annealing at a product-dependant temperature (typically above 180 °C). This enables the coating to achieve its protective function.

Application of the topcoat follows the same procedure. Annealing and drying occur at different temperatures, depending on specifications.

Various coating procedures are available, depending on component type.

 

Dip-spin process

The dip-spin process is ideal for small parts that are coated as bulk products. Depending on the quantity, geometry and volume of the parts there are varyingly-sized baskets that are immersed in a coating bath with a liquid coating before being spun at a defined speed. This means that the desired coat thickness can be achieved - even for difficult geometries.

In addition to the dip spin process for bulk products, the same technology also exists for racked goods. Larger components are kept apart for the coating process, without these damaging one another during the spin movements.

 

Spraying

Spraying is also an alternative for large parts. This may occur manually or via robots. This procedure is particularly suitable where a partial coating is required. An e-static unit can be used to reduce overspray

 

Dip-draw process

The dip-draw process is suitable for large parts. Here the coat thickness is achieved via a defined withdrawal speed and defined viscosity of the coating material.


KTL technology (with electricity)

The KTL is applied to the component in liquid form. Racked goods are typically moved through enormous tanks. The application of direct current deposits the required coat thickness to the component.

The KTL from Dörken MKS takes a different approach: larger bulk products (max. 10 cm, 150g) are not suspended from a rack, but instead coating directly in a drum. The drum unit is loaded and dipped into the liquid KTL medium, with rotation and the application of electricity depositing the KTL evenly. The drum is then moved to an ultrafiltrate rinser to remove excess material.

The twin line specially developed by Dörken MKS functions with a similar principle, with the difference that two drums work in parallel, making a higher throughput possible.

The EC-Automat 2000+ (the "worm"), is particularly well-suited to very small parts such as bolts <M6, including with self-tapping thread. The Archimedean form of the drum interior means that the small parts are coated in a throughput process.

At the end of each coating process the coated parts are transported directly to the furnace (usually a continuous furnace) via a conveyor belt, where they are annealed at a defined temperature and duration.

Electroplating technology (with electricity)

In the galvanic process application occurs using the drum or rack procedure, depending on the component. The components pass through various pre-treatment stages before the galvanisation process begins. Depending on system requirements, the components are coated with an acidic or alkaline zinc electrolyte. In the DELTA-PROZINC® process they pass through two passivation stages, including intermediate drying. Finally, a seal is applied and dried. In the drum process drying occurs in centrifugal dryers or rack dryers.

Depending on type of coating and component, various types of furnace can be used. Both the zinc flake basecoats and the matching organic system topcoats need to be cured in order to form a film. Depending on product, the inorganic topcoats are also cured or force dried. The following furnace types are typically available: conveyor furnace (continuous furnace), rack furnace or chamber furnace. Increasingly, inductive drying and infrared drying are also used. Decisive for choice of furnace is in particular the degree of automation of the coating process as a whole.

After the curing process the components should always be cooled back down to ambient temperature. The dew point should never be reached in this, particularly for zinc flake coatings, to avoid condensation of water from the air onto the component, which would affect later coating processes.

 

1Pre-treat­ment

Prior to coating, components must be free from rust, scaling, dirt and dust, oil and grease, as well as being dry. Typical forms of pre-treatment include alkaline degreasing, blasting with various materials (e.g. stainless steel grains, steel grains, glass beads etc.) or chemical pre-treatment such as phosphatising or pickling. In the case of zinc flake coating for example, alkaline degreasing plus blasting is recommended.

Mineral additives can be used to aid the blasting process. These keep the blasted surface cleaner (oil-free) and thus enable longer operation.

2Coat­ing

Coating may occur without the use of current, in the form of physically-applied painting, or with electrical current used to deposit the material on a component.

Zinc flake technology (electroless coating)

Zinc flake systems are applied in multiple, similar coating stages. Firstly, the zinc and aluminium base coat is applied and pre-dried. This is followed by annealing at a product-dependant temperature (typically above 180 °C). This enables the coating to achieve its protective function.

Application of the topcoat follows the same procedure. Annealing and drying occur at different temperatures, depending on specifications.

Various coating procedures are available, depending on component type.

 

Dip-spin process

The dip-spin process is ideal for small parts that are coated as bulk products. Depending on the quantity, geometry and volume of the parts there are varyingly-sized baskets that are immersed in a coating bath with a liquid coating before being spun at a defined speed. This means that the desired coat thickness can be achieved - even for difficult geometries.

In addition to the dip spin process for bulk products, the same technology also exists for racked goods. Larger components are kept apart for the coating process, without these damaging one another during the spin movements.

 

Spraying

Spraying is also an alternative for large parts. This may occur manually or via robots. This procedure is particularly suitable where a partial coating is required. An e-static unit can be used to reduce overspray

 

Dip-draw process

The dip-draw process is suitable for large parts. Here the coat thickness is achieved via a defined withdrawal speed and defined viscosity of the coating material.


KTL technology (with electricity)

The KTL is applied to the component in liquid form. Racked goods are typically moved through enormous tanks. The application of direct current deposits the required coat thickness to the component.

The KTL from Dörken MKS takes a different approach: larger bulk products (max. 10 cm, 150g) are not suspended from a rack, but instead coating directly in a drum. The drum unit is loaded and dipped into the liquid KTL medium, with rotation and the application of electricity depositing the KTL evenly. The drum is then moved to an ultrafiltrate rinser to remove excess material.

The twin line specially developed by Dörken MKS functions with a similar principle, with the difference that two drums work in parallel, making a higher throughput possible.

The EC-Automat 2000+ (the "worm"), is particularly well-suited to very small parts such as bolts <M6, including with self-tapping thread. The Archimedean form of the drum interior means that the small parts are coated in a throughput process.

At the end of each coating process the coated parts are transported directly to the furnace (usually a continuous furnace) via a conveyor belt, where they are annealed at a defined temperature and duration.

Electroplating technology (with electricity)

In the galvanic process application occurs using the drum or rack procedure, depending on the component. The components pass through various pre-treatment stages before the galvanisation process begins. Depending on system requirements, the components are coated with an acidic or alkaline zinc electrolyte. In the DELTA-PROZINC® process they pass through two passivation stages, including intermediate drying. Finally, a seal is applied and dried. In the drum process drying occurs in centrifugal dryers or rack dryers.

3Cur­ing

Depending on type of coating and component, various types of furnace can be used. Both the zinc flake basecoats and the matching organic system topcoats need to be cured in order to form a film. Depending on product, the inorganic topcoats are also cured or force dried. The following furnace types are typically available: conveyor furnace (continuous furnace), rack furnace or chamber furnace. Increasingly, inductive drying and infrared drying are also used. Decisive for choice of furnace is in particular the degree of automation of the coating process as a whole.

4Cool­ing

After the curing process the components should always be cooled back down to ambient temperature. The dew point should never be reached in this, particularly for zinc flake coatings, to avoid condensation of water from the air onto the component, which would affect later coating processes.

 

Coating solutions

Our service: how to find the optimal coating technology

It is important that the right corrosion protection and multifunctional characteristics are already worked out in the design stage. The Dörken MKS technicians support designers, engineers and planners in their choice of the right coating technology, as well as the planning of suitable plant. In this we always look at the process as a whole; because only a customised and refined process will enable the perfect coating result for the respective component.

HIGHEST QUALITY, GUARANTEED WORLDWIDE

For quality assurance we regularly audit the entire application process of the licensed coating partners n order to ensure consistent and uniform quality on the market. In addition, each coater can also consult our specialists regarding questions or problems, for prompt and expert assistance.