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Mechanical fasteners, fixing and joining, and equipment
News Release from: Arnold Umformtechnik | Subject: Chromiting process
Edited by the Manufacturingtalk Editorial
Team on 06 January 2005
Chromiting replaces hexavalent chromium
The EU End of Life Vehicles Directive forbids the use of hexavalent chromium, which is why a German manufacturer is supporting the 'Chromiting' technique for its fastener treatment.
The EU End of Life Vehicles Directive will come into force in July 200 For health reasons, the use of hexavalent chromium - formerly applied to galvanised (yellow and olive-black) chromated surfaces - will be prohibited in the automotive industry
This article was originally published on Manufacturingtalk on 20 Feb 2004 at 8.00am (UK)
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It is called Chromiting.
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Managers at Arnold Umformtechnik, the German fastener manufacturer in south-west Germany, have joined forces with the research engineers to put this innovative technology into practice.
To achieve their aim - zero health risk in corrosion protection - they needed to overcome a residual economic risk.
The partnership between the developers, the business administrators and the production engineers has worked perfectly, and has proven the suitability of this alternative to hexavalent chrome.
* Metal fasteners secure lasting connections between partners - thread-forming fasteners feature strongly in the product range offered by Arnold Umformtechnik, a medium-sized screw manufacturing enterprise, based in south-west Germany.
Taptite screws form a chipless thread in a pre-drilled hole.
The grooving or screw-in pressure torque must possess sufficient torque differential to the tensioning torque so as to provide a high level of operational reliability, while saving up to 80% in assembly costs.
And every one of the three billion screws produced each year at the plant in Forchtenberg meets the highest standards of quality and innovation.
The 450 employees at Arnold Umformtechnik are specialists in creating customised parts.
With its orientation towards innovation and creativity the company strategy is maintaining a clear course towards technical and market leadership.
It believes its principal resource to be its people.
And this is proven by the way business has developed in recent years.
Sales have doubled in the past 10 years.
Reinhard Barth, Product Development Manager, gives a figure of 8% as being the rate at which the company is developing, and, barely suppressing a smile, gives a further figure: "On average there are 250 Arnold fasteners in every car produced in Germany".
Half of the sales volume, which in 2004 amounted to around EUR 65 million, is generated from the screw fastener side of the business, supplying automotive manufacturers and suppliers.
These customers, and also clients in the electronics and consumer goods industries, are not simply buying fasteners, but commissioning a full package of services.
The services range from advice on application-specific development, or on production techniques, and include a complete safety guarantee to meet specific demands, as well as further design enhancements.
Some 20,000 different fastener models, each one developed for "a special purpose" are listed at the Forchtenberg plant.
About 600 of these are known as "living items" - these are the ones that, in collaboration with the clients, are always in continuous production and undergoing further development.
The main quality characteristics of the end product lie in their surface treatment.
The final processes performed on the formed screw include cleaning, hardening, galvanising, passivating and tempering, followed by the specific slide and other coatings.
Corrosion protection is the final crucial step of the manufacturing process.
The regulations aimed at eliminating hexavalent chromium have created a challenge.
Arnold Umformtechnik squared up to the challenge at an early stage.
In doing so it made the right decision; there are two reasons behind this.
While the conditions set by the "End of Life Vehicles" directive will take full effect on 1st July 2007, stricter conditions for handling the toxic chromium trioxide come into force much sooner - at the end of October 2005.
These stricter conditions were published in the relevant official bulletin on 16th June 2004 (see panel).
With the Chromiting solution the experts at Arnold are well equipped to comply with the new legislation.
As the first users they are setting the standards.
Creative laboratory solution finds practical application - 'Chromiting' is a registered trade mark and is an innovation in process technology.
It is used to apply a reaction-inhibiting barrier coating consisting of trivalent chromium onto galvanised metal surfaces.
This type of passivating differs from the conventional (yellow) chromating with hexavalent chromium, and also from blue chromating.
The latter contains the harmless trivalent chromium instead of the carcinogenic hexavalent chromium, but does not provide sufficient protection from corrosion.
The technology goes back to the research and development carried out by the surface coating experts at SurTec, based in the Hesse region of Germany.
Following a successful series of tests in cooperation with the Technical University of Darmstadt, documents containing all the results since 1996 are currently lodged at the Patent Office.
The researchers believe that chromiting is superior to the conventional chromating process, both with regard to its non-toxicity and to its corrosion-protection properties.
The verdict on its economic equivalence remains open until the theory can be transferred from laboratory to production.
That means varying, recording, and evaluating application data, ascertaining and comparing costs, and creating reproducibility and process reliability.
Strong business links had already been forged between the managers and the research scientists at SurTec and the application engineers at Arnold Umformtechnik when they started the "Chromiting in industrial practice" project.
"Ten years ago the End-of-Life vehicles directive was nothing more than a prophesy," recalls product manger Thomas Hager.
"But, like our partners at SurTec, we knew that we would one day be faced with the task of solving the problem.
So, right from the start, we understood it to be an issue that needed to be overcome jointly and in partnership." Both companies pursued many lines of development, both in research and in automotive development, using a high degree of sensitivity, aligning their strategies at an early stage.
"Based on our field research we tested the practical applications of Chromiting on a step-by-step basis, after which we were convinced that it was the appropriate method," commented Hager.
"When the EU End of Life Vehicles directive was adopted in September 2000, we were already prepared in our approach to customers." Barth summed up "and the result has been an extremely successful cooperation".
A foundation was formed by the standardisation of the Chromiting process or "thick layer passivating" in a number of company specifications and works standards.
In inter-laboratory tests on 56 systems carried out by the VDA SurTec achieved excellent success with its chromiting process.
This confirmed in principle that chromiting dominates.
* From laboratory to series production - based on trust and an assessment of the residual risks - Hager and Barth freely admit that there were aware of the element of risk and that they might have experienced a "hint of adventure" in their endeavours.
"The foundation of trust with our development partners at SurTec has evolved and been proven as firm over many years.
Reinhard Barth summed up: "That gave us the necessary courage." Meanwhile the system has established itself on the market, and is now a widely used and has become standard practice.
"With chromiting we can offer our customers added value at almost the same price as the discontinued yellow-chromated products.
Its certification to ISO TS 16949 is evidence of its quality", explained Barth.
This added value comes from the proven additional corrosion protection.
In particular smaller galvanised screws with diameters of less than 6mm now have a hexavalent-free passivating chromium layer.
These are used, for example, in airbag systems, navigation systems and other electronic components in the vehicle's passenger compartment.
Chromiting under production conditions - fasteners undergoing chromiting first progress through the multi-stage galvanising line, consisting of more than 20 baths.
Rinsing is very important during the process.
It reduces the risk of passing on contamination caused by the various cleaning and pickling fluids.
The fasteners are given their anodic zinc layer or zinc alloy inside a drum.
The thick-layer passivation, or chromiting, then follows - also in the drum.
This imparts the characteristic light green iridescent layer, which becomes colourless and transparent after sealing.
In salt-water spray tests to DIN 50/021 standard, this method has shown clearly that it provides protection against corrosion.
The thick layer, and thus the quality of corrosion protection, is controlled and set by varying the contact time, the temperature and the concentration.
Since the pickling acids used to shine steel surfaces before galvanisation have a detrimental hydrogen embrittlement effect, the parts are usually tempered immediately after the galvanising process.
The hydrogen particles emerge under the effects of heat.
Tempering is specified for steel parts from property class 100 upwards(1000N/mm2).
According to test results, chromited parts can be tempered, underlining the economic efficiency of the system.
Hager summarised the experience gained from the transfer of the chromiting process to practical applications: "Firstly the staff needs to be trained and secondly the plant technology has to be adapted and prepared.
Before converting to the new technology we needed to make strategic calculations of any possible interruptions to production, so that we could react to critical production bottlenecks.
And Barth added: "Since we were able to consider all the risks with the aid of an extremely competent partner, we could easily surmount this challenge." * The product and the company philosophy pass the market test - innovation and creativity are bywords that belong together, because new ideas can only come to light in the heads and from the hands of thinking and doing people.
A certain amount of risk undeniably goes hand in hand with creative innovation.
The managers and staff at Arnold Umformtechnik can apply their successful trials into the process reliability of chromiting as evidence that the process indeed meets all the required values.
"The two partners, SurTec and we at Arnold, have entered into the spirit of technical innovation and act accordingly.
Our reliable cooperation is founded on that premise," said Barth.
And proof that the innovative spirit of the company culture lives in every member of the staff is provided in the company's stringent quality management.
A high availability rate and economic efficiency guarantee a mature Supply Chain Management (SCM) and a Continuous Improvement Process (CIP), with individual responsibilities.
A bar-coded document containing dimensioned drawings, together with the crucial quality criteria and data and other specifications, accompanies every customer order from the moment it is received until it is packed and despatched.
The Statistical Process Control system (SPC) covers the entire chain at every production step.
The quality awareness of our staff, along with the electronic systems we have in place, ensure that every fastener meets the required, and sometimes specified demands for the highest of quality.
The inspection log is completed at every stage of the production process and has the status of a genuinely accurate and valid document.
"The secret of our success lies with our staff; their high level of qualification and motivation are our most important asset," says Hager.
"By this I mean everyone, from the trainees and the experienced and skilled staff, to the engineers and researchers." Added to this is an advantage with delivery lead times.
"With the rapid prototyping system we can cut consulting, development and trial times for specialist screws by more than two thirds," said Reinhard Barth.
The list of customers and references confirms the success: DaimlerChrysler, BMW, Bosch and many other national and international tier 1 suppliers.
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