Bulk coating for rotationally symmetrical components
Zinc flake systems - reliable corrosion protection
Fasteners such as screws, nuts or bolts are small components with great significance: they secure assemblies, withstand high loads and must function reliably over the long term - even under extreme conditions. To meet these requirements, BENSELER relies on zinc flake coating using the bulk material process.
With established systems such as GEOMET® and DÖRKEN®BASE, the surface specialists achieve cathodic corrosion protection at the highest level - economically, reliably and reproducibly. This process is particularly suitable for rotationally symmetrical components weighing up to 300g or in a pourable design.
What is zinc flake coating?
Zinc flake coating with GEOMET® or DÖRKEN®BASE is a high-performance corrosion protection system for components with special requirements. Whether complex geometric parts, small bolts with washers or internal attacks as well as hollow or scoop components - many things can be coated with this surface. BENSELER coating systems from a wide range of manufacturers can be used. The GEOMET® and DÖRKEN®BASE zinc flake systems are based on water or solvents and consist of a baked film of zinc and aluminum flakes that are connected by a predominantly inorganic matrix.
As a basecoat, BENSELER generally applies a coating with a high proportion of zinc and aluminum flakes. During drying, the zinc flake layer forms a conductive connection between the metal pigments and the substrate. This layer protects the underlying metal from environmental influences and corrosion; the cathodic protection mechanism of the zinc and the targeted passivation of the flakes in the layer play a significant role in this.
The GEOMET® and DÖRKEN®BASE zinc flake coatings fulfill other, often very specific requirements in addition to corrosion protection. In combination with coordinated topcoats, properties such as defined coefficients of friction for threaded parts can be precisely adjusted or a specific final color finish can be achieved.
Application techniques for zinc flake coating
BENSELER applies the coating systems using different processes. Depending on the requirements and weight of the articles, bulk coatings are applied using the dip-spin technique or processed as rack goods. The zinc flake coating process for bulk goods is described below.
The process in detail
At BENSELER, coating with GEOMET® zinc flake or DÖRKEN®BASE for bulk goods is carried out automatically in large-scale production systems. Pre-treatment, basecoat and topcoat are applied one after the other.
Pre-Treatment
In the first step, the application is divided into batches. The components are transported automatically via a basket and tray system. The specialists at BENSELER ensure the lowest possible drop heights and gentle handling of the parts (soft handling).
Depending on the delivery condition, the raw material is evaluated. The pre-treatment is defined on this basis. Pre-treatment involves a multi-stage alkaline hot degreasing process with rinsing and final drying. Depending on the delivery condition, blasting may also be carried out.
Basecoat application and thermal cross-linking
This is followed by coating with GEOMET® or DÖRKEN®BASE by dipping the basket with the bulk material into the coating system. In this way, each component is wetted and a subsequent defined centrifugal process takes place. This process removes the excess material from the component before drying takes place in the oven: The parts are baked at a specified baking temperature and for a specific duration.
Depending on the corrosion protection requirements, BENSELER repeats the coating process with the basecoat at least once more.
After the cooling process, a resistant basecoat layer of the coating system is created, which is firmly cross-linked with the base metal.
Topcoat
To finish the surface, a topcoat is applied, which allows specific properties to be set and has a sealing effect.
This can be used to set friction value windows for threaded parts, create a colored final finish or improve chemical resistance. BENESLER uses the same coating technology for the topcoat: Dipping, spinning, drying and cooling.
Quality assurance
After coating with GEOMET® or DÖRKEN®BASE, the parts are removed from the system, packed in labeled customer containers and subjected to a documented quality inspection. In this way, BENSELER ensures that the zinc flake coating for bulk goods meets the highest requirements.
Properties of the zinc flake coating
The zinc flake coating in the bulk material process has the following properties:
- Cathodic corrosion protection in silver or black
- Depending on the coating, special friction values can be achieved
- Defined screwing with high coefficients of friction possible
- Abrasion-resistant surfaces
- UV-resistant top coats can also be realized in black
- Special aluminum coating possible
- Prevention of contact corrosion
- Suitable for even the smallest screws or special applications
- Fulfills technical delivery conditions of the automotive industry
Products used by BENSELER
BENSELER uses various products for zinc flake coating in bulk material. In addition to the leading manufacturers such as GEOMET® (NOF) and DÖRKEN®BASE, products from Atotech or other manufacturers are also processed at the customer's request. Although GEOMET® is a water-soluble zinc flake coating system and DÖRKEN®BASE is a solvent-based zinc flake coating system, both systems have the following properties with different characteristics:
- 5-25 µm mean value of coating thicknesses, depending on requirements
- Meets global automotive industry specifications, Reach compliant, ELV
- Over 1500 hours salt spray test according to DIN EN ISO 9227 NSS possible
- No risk of hydrogen embrittlement
- Can be painted with common value paints and KTL paints
- High resistance to coolants and brake fluids, diesel and gasoline, engine oils
- High resistance to organic solvents
- Metallic silver-grey
- Other colors also possible in combination with topcoat
- Adaptation to specific requirements in combination with different topcoats
GEOMET®- thin-film corrosion protection from NOF
The most frequently used product at BENSELER is the GEOMET® product family from NOF. GEOMET® products are used in particular in rack technology in the dip-spin process or in the electrostatic spraying process.
BENSELER processes both GEOMET® and DÖRKEN®BASE in the bulk solids sector.
DÖRKEN®BASE - Thin film corrosion protection from DÖRKEN®
DÖRKEN®BASE is the most frequently used solvent-based zinc flake process. Often combined with matching DÖRKEN®SEAL topcoats, DÖRKEN®BASE products reliably fulfill the requirements of OEMs and VDA recommendations - especially in the automotive industry.
What is DÖRKEN®BASE?
A DÖRKEN® zinc flake coating is a corrosion protection coating composed of zinc and aluminum flakes held together by an inorganic matrix.
DÖRKEN®BASE products are used for the corrosion protection of fasteners and for a wide variety of metal components. DÖRKEN® products can be combined with DÖRKEN®SEAL topcoats to achieve specific properties, such as friction coefficient windows.
The system formerly known as DELTA-PROTEKT® KL120 is, especially with the topcoat VH301.1, the system that is most frequently specified in the German automotive industry. The main advantage of this system is the good coverage of the bolting requirements according to the VDA recommendations as well as the specifications of the OEMs.
Advantages of the ®BASE product family at a glance
- DÖRKEN®BASE products offer high corrosion protection at low coating thicknesses of 5-25 µm (600h to >1500h according to DIN EN ISO 9227)
- DÖRKEN®BASE products meet automotive industry specifications worldwide
- DÖRKEN®BASE products are REACH compliant
- DÖRKEN®BASE products comply with the EU End-of-Life Vehicle Regulation 2000/53
- DÖRKEN®BASE products have a continuous temperature resistance of 200° (while maintaining the corrosion protection)
- The setting of defined friction coefficient windows leads to very good screwing properties of threaded parts (even with multiple screw connections)
- No risk of hydrogen embrittlement as the coating is not applied electrolytically
- There is no infiltration of the coating by corrosion, in contrast to paint coatings
- Good chemical resistance to organic solvents, oils, greases and brake fluids
- The lower hardness compared to electroplated zinc coatings can be an advantage for assembly processes
Examples of applications for zinc flake with GEOMET® or DÖRKEN®BASE in the bulk material process are:
- Fasteners (screws, nuts, bolts)
- Wood screws, self-tapping screws
- Washers (washers, spring washers)
- Clips and small springs (if pourable)
- Tapping screws for body covers (cars)
- Nuts for wheel bolting (trucks, trailers)
- Smaller parts in the steering train (e.g. screws, pins)
Additional customer services for zinc flake coating
In addition to bulk coating, BENSELER offers you the following additional services:
- Thread-locking coating of screws and nuts
- Individual testing and packaging
- Measuring 100% sorting
- Packaging and labeling for the end customer
- Direct delivery to the end customer or consignment warehouse
Further special services are available on customer request!
Download
BENSELER technical information for DÖRKEN® coating
BENSELER technical information for GEOMET® coating
To ensure that the product is perfectly suited to your requirements, the BENSELER sales team will be happy to provide you with personal advice at any time.