ELECTROPLATING
Electroplating – Our modern plastic electroplating facility is designed to give a surface finish to plastic blanks made of ABS or ABS-PC. KTB has many years of comprehensive expertise in the electroplating of plastic parts for interior and exterior applications using various chrome surfaces (polished or matte in various degrees of gloss). By electroplating plastic, the metal coatings lend the surfaces a decorative appearance, make them extremely scratch-resistant, give them a firmer bond with better heat-resistance, and protect them from static charge, electrical disturbances (shielding) and the influence of UV light. Due to the different geometries, specifications, surfaces etc. a specific processing programme is set up for each individual item in the electroplating machine management system.
Marginal conditions for electroplating
• Cr VI may in future only be used with official authorisation
• KTB has applied for its own official authorisation and expects to be authorised for a period of 7 to 12 years
• Cr VI is present in the plating baths (pickling) and chrome plating process
• Cr III is a possible alternative for chrome plating
Status
• As part of the FGK test series, the Cr III process now achieves a very
similar quality and colour to the Cr VI chrome plating process
• KTB tests using sulphur-based systems have also impressed OEM customers.
Implementation
• Cr III Electroplating series production since October 2019
• Cr III dark chrome in series production since June 2021
Electroplating plastic is a complex process, the main features of which are explained below.
Electroplating – Pretreatment
Pickling:
Butadiene, a constituent part of an ABS polymer, is released from the resin structure on the surface area. The hollows and voids that result form the basis for the adhesion of the electroplating coatings.
Germing:
In order to be able to precipitate a thin, conductive, metallic coating without using current, the roughened surface of the ABS must first be germed using palladium as a catalyst. To ensure that the palladium remains in suspension in the electrolytes, it is surrounded by a protective tin colloid. In this process stage, the palladium deposits are absorbed by the roughened ABS surface.
Acceleration:
During the acceleration phase, the protective tin colloid is removed by an acid mixture, as it would have a negative influence on the subsequent coating process. Only active palladium remains on the surface.
Chemical nickel:
The absorbed palladium on the surface of the plastic triggers a reaction in the chemical nickel electrolyte. A layer of nickel measuring approx. 0.5 µm grows evenly across the ABS surface. The surface of the part is now conductive.
Electroplating Coating
Precopper
The items are then immersed in a copper sulphate solution where several atomic layers of the copper are deposited in a charge exchange, making the surface more conductive and preventing the burning through of the chemical nickel layer.
Bright copper
The highly polished copper layer is 20 – 30 µm strong and ductile, which enables it to balance out the different expansion coefficients between the metal and the plastic.
Semi-gloss/Bright nickel
A double layer of nickel is deposited to provide anti-corrosive properties and lower surface tensions. The nickel layer is high-gloss and scratch-resistant due to its hardness.
Matte nickel/Aluminium design
The nickel deposit is briefly interrupted by the static dispersion of extremely finely dispersed organic substances in the cathode film. Visually, this surface disruption turns the directional light reflection of the original polished coating into a diffuse reflection. Finally, a thin layer of chromium approx. 0.3 µm thick is deposited onto the matte nickel.
MIcro porous nickel MPS
In order to achieve improved corrosion protection, a layer of nickel approx. 1 – 2 µm thick is deposited onto the bright nickel layer. This MPS nickel layer forms very small pores which positively influence the corrosion behaviour. Cracked nickel is primarily used for exterior car parts.
Bright chrome plating
Bright chrome plating is done in very thin layers, measuring 0.3 to 0.8 µm.
The composition of the electroplated nickel base is crucial for the quality of the chrome plating.
After the items have been chrome-plated and dried, they are removed, inspected and packed. As well as the usual visual inspection criteria such as degree of gloss, pores, scratches, marks, roughness, flow lines, seams or faulty coatings, the following tests are carried out:
– Coat thickness measurement using X-rays
– Thermal shock resistance in accordance with DIN 53496
– CASS test in accordance with DIN 50021
– Temperature stability
– Test of adhesive strength (cross-cut test, Tesa test)
– Dimensional tolerance
– STEP test (coulometric measurement)
Chrome III plating
Chrome III is an alternative to chrome VI and will Chrome III will gradually replace Chrome VI in the coming years. At KTB chome III is available in bright and in dark colour.
KTB Quality Control
After the items have been chrome-plated and dried, they are removed, inspected and packed. As well as the 100% visual inspection, which identifies and rejects variations in the degree of gloss, pores, scratches, marks, roughness, flow lines, seams or faulty coatings, the following tests are carried out:
– Coat thickness measurement using X-rays
– Thermal shock resistance according to DIN 53496
– CASS test according to DIN EN ISO 9227
– Temperature stability
– Test of adhesive strength (cross-cut test, Tesa test)
– Dimensional tolerance
– STEP test (coulometric measurement)
Rinsing
After any chemical or electrolytical work process, liquid residues adhere to the work pieces and need to be removed or eliminated with thorough rinsing. The rinsing serves to remove the film of the previous process electrolytes that has stuck to the surface so that it does not affect the subsequent process steps. During the final process step, the parts are rinsed so clean that no corrosive or allergenic substances remain on the surface and the parts can be dried spotless.
Rack Plating
An individual rack plating system is developed for each part requiring electroplating. The ultimate aim is to achieve an optimal electroplating result with perfect thickness but without warping the plastic part. The plating racks are made of brass due to its good conductivity, with the actual contacts made from stainless steel or titanium (spring effect). The spring force of the contacts is adjusted to the lower strength of the plastic. Equally important is the rack insulation, which has to be fired at high temperatures so that the rack itself is not coated with metal.
Coating Variations
– Bright copper
– Double nickel
– Bright nickel
– Matte nickel/Aluminium-look (various colours possible)
– Bright chrome
– 3Q7
– Rover Aluminium
– Pearl gloss
– Silver Shadow
– Galvano silver 09
– others
– MPS in combination with matte chrome
– All layer systems are also available with a final chrome III layer
Technical specifications for electroplating at KTB
– Number of process baths: 30
– Number of process baths inc. rinsing and deposit stations: 108
– Bath volumes 2600 to 12000l
– Bath sizes 2500 x 1200 x 500
– Rack – carrier size 2500 x 1200
– Special sizes also possible
– Processing time 2 to 3.5 hours (depending on the programme)
– Max. 240 rack – carrier per plating line (2 lines available)
– Surface max. 65 sqm/hour or 1400 sqm/day
– Electroplating machine with 10 transport vehicles and 2 transverse transport vehicles
– Work areas: Jigging, quality control, laboratory (chemical/physical), waste water treatment, planning and process technology, production
KTB Laboratory
In order to ensure a stable electroplating process, the electrolytes are tested and prepared each day in our modern in-house laboratory and used chemicals are supplemented according to the analysis results.
This involves the use of wet chemical analyses and modern analytical methods (atomic absorption spectroscopy).
Here we also monitor compliance with the limit values of our waste water.
KTB Environment
The processes used in plastic electroplating require us to treat the substances used with extreme caution in terms of people and the environment. Environmental and safety issues are therefore always paramount in everything we think and do. We uphold this philosophy through our highly evolved safety management system and through our technical facilities. As early as 2015 we became certified in accordance with ISO 14001 (environment), ISO 50001 (energy) and ISO 18001 (HSE), all of which form part of our Integrated Management System (IMS).
All the relevant process baths in our electroplating facility are fitted with an extraction system. The extracted air is fully purified in our exhaust air system in line with the latest technical and chemical research. We verify the effectiveness of the purification by taking regular monitoring measurements.
In our modern water treatment plant we turn the waste water from the rinsing and process baths back into pure water. In this process, every batch of water is analysed in the final inspection and only released if it meets our high standards. All these analyses are subject to inspection by external laboratories and the relevant authorities.
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