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KTB relies on SurTec for chromium(III) processes

2020-06-15

Since September 2019, Kunststofftechnik Bernt GmbH (KTB) has been gradually converting the previous chromium(VI) processes to the more environmentally friendly chromium(III) process developed by surface specialist SurTec. SurTec's new process is not only impressive in terms of colour and quality, but the cost of the chemicals is also approximately comparable. The new process can be integrated into existing plants with little effort.

When chrome-plated switches, buttons and trim strips shine in a car, it is probably Kunststofftechnik Bernt GmbH (KTB) in Kaufbeuren that is behind it. This is because 300 employees at the company in the Bavarian Ostallgäu, Germany, contribute to giving motorists a high-quality impression of their vehicle interiors: KTB manufactures injection moulded plastic parts and, if desired, finishes their surface with various surface coatings for interior and exterior applications in the company's own electroplating facilities. Various matt surfaces are just as much a part of the production spectrum as complex multi-component parts. Apart from car manufacturers, customers are also companies from the household appliance and sanitary sector. KTB has a state-of-the-art production facility in the Kaufbeuren industrial park. Two fully automated electroplating plants, injection moulding, assembly and toolmaking, all to the most modern standards, guarantee reliable delivery of high-quality components.

High demands on occupational safety and environmental protection
KTB also aims to be a leader in terms of occupational safety and environmental protection and, wherever possible, to use sustainable processes. This includes the substitution of SVHC substances where technically possible. Chromium trioxide is such a SVHC substance that is used in the chromium(VI) processes that have been in use up to now and which, according to the REACh regulation, may only be used with the appropriate authorisation since September 2017. KTB has submitted such an authorization application and expects to be authorized until at least 2024, but nevertheless KTB started already in 2018 to intensively analyze the market for trivalent coatings and finally to conduct a benchmark between the most promising approaches. This resulted in SurTec, the specialist for surface technology, achieving the most convincing results. For KTB and SurTec this is the beginning of a completely new cooperation, as the two companies had never worked together in the past. SurTec's experience in the production of large series using the chromium(III) process was also convincing. This includes the electroplating of metallic components as well as plastic components.

Convincing in colour and quality
An essential requirement that the new process had to meet were the specifications of the automotive industry, which are defined in the relevant standards of the manufacturers. These include above all the optical appearance, especially the b-value - an indicator of the blue colour tones on the L*a*b scale. The attractive white-blue color preferred in the automotive sector could previously only be achieved with chromium(VI) processes. The decision in favour of SurTec was preceded by extensive preliminary investigations with all process suppliers used at KTB.

SurTec 883 XT is an innovative chromium(III) process for decorative applications based on sulfate, which is a 100% substitute for chromium(VI) in colour and function. Thus, the corrosion protection and the colour properties are identical to chromium(VI) bright chromium. Among the special requirements that the new chromium(III) process must meet are:

  • Deposited layer thickness of 0.2 to 0.3 µm in maximum 6 minutes exposure time
  • Corrosion requirements: CASS-Test 120 hours | NSS-Test 1,200 hours
  • Colour stability over a defined current density range (4 to 6 A/dm2)
  • Color values (measured with Konica Minolta CM-700d)
    L = 83 to 85
    a = -0.5 to -0.8
    b = -0.5 to -1.5

Changeover in the shortest time
The coating of components with trivalent electrolytes was a completely new process for KTB, which had to be integrated into the existing process. The know-how of the specialists from KTB and SurTec complemented each other perfectly, so that the process could be introduced within a very short time. The existing infrastructure and the correct positioning in the coating process had to be taken into account. KTB had already provided space for the trivalent chromium plating when the electroplating shop was built, which simplified the implementation. The necessary changes included in particular the installation of new peripherals including a new electrolyte tank, ion exchangers, special anodes, dosing stations, storage tanks and the revision of the plant control system.

Further chromium(III) series planned
Following the start of the project in September 2019, the first components were produced in October and the first smaller series were produced in November. The previous throughput with the new process at KTB is just under 27,000 m2 at 500,000 Ah. Various components, also from the non-automotive sector, are already being produced in series. Further orders for new projects have been received and process approvals from several OEMs are nearing completion. This also includes the approval of car manufacturers.

The result for KTB after the conversion is not only the desired freedom from chromium(VI) in the coating process, but also a higher degree of efficiency during deposition and shorter exposure times. The product carriers can also be equipped with more components, which enables a higher production throughput. However, process monitoring is somewhat more complex and the system is more sensitive than the previously used chromium(VI)-containing process. Since the temperature of the bath must not fall below 40 degrees Celsius on a permanent basis, a higher energy input is also required. Added to this are the acquisition costs for the special anode technology. However, this enables a long service life and, in practice, up to 50 percent lower current density (amperes per square meter), which in turn makes energy savings possible elsewhere.

SurTec Chromium(III) process convincing in all decorative areas
Chromium(III) processes from SurTec are already replacing the previously used chromium(VI) applications in all decorative areas worldwide. Customers include plastics (POP) & metal coaters and the sanitary industry. In total, more than half a million liters of chromium(III) electrolytes are in use. SurTec's latest developments in this area include in particular chromium(III) electrolytes in all colour variants from light (L* value 85) to dark (L* value below 40). In addition, SurTec is currently working on a process to make the pre-treatment of plastic components completely free of chromium(VI) and thus meet REACh requirements.

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