Anodising, chromating, hard anodising & more

surface is everything

The anodising company DIENER & RAPP GmbH & Co. KG has specialised in the surface treatment of aluminium since 1978. We anodise clear and in many different colours and offer hard anodising with and without colouring, Surtec 650 aluminium passivation and yellow chromate, vibratory grinding of small parts, as well as various pre- and post-treatments.


El-ox-al is the name given to electrolytically oxidised aluminium. The surface of the aluminium is chemically transformed by an electrochemical process and forms a porous, protective oxide layer. After the anodising process, the pores are closed by sealing and the chemical intermediate compound is transferred to its final form. If the components are immersed in a suitable dye immediately after anodising, the organic dye diffuses into the resulting aluminium oxide layer. Lighter or darker colour variations can be achieved by changing the immersion time and the dye concentration.

The dye is then encapsulated in the anodised pore by the post-compaction process and is therefore inseparably bonded to the aluminium. The metallic character is nevertheless retained. The colouring is individually influenced by the alloy and surface of the customer's material. You can therefore rely on our many years of experience and intensive consultation.


Chromating & passivation. When chromating aluminium in an acidic solution, the resulting layers are thin and electrically conductive. The main tasks of the chromating layers are applications that require corrosion protection or as an adhesion primer for components that are painted and powder-coated in a later work step. Chromating layers are also available in different colours. Which depend on the components of the electrolyte. We have a yellow chromate coating available, as well as a colourless, chromium6+ - free conversion coating, which achieves almost the resistance of the classic yellow chromate coating and is also ROHS-compliant.
With chromating, the layer thickness is a few nanometres and cannot be measured. These coatings can become micro-cracked above 80°C, which can worsen the corrosion protection.

Highest Quality


The chromate coating can be colourless or yellow. Alternatively, we can offer you a colourless conversion coating that comes close to the resistance of classic yellow chromating, but is ROHS-compliant. This process is called Surtec 650.


Layer thickness

With chromating, the layer thickness is a few nanometres and cannot be measured. These coatings can become micro-cracked above 80°C, which can worsen the corrosion protection.

Electrically conductive


The electrical contact resistance of chromate coatings is very low. It is usually more favourable than the electrical resistance of untreated parts. Chromate coatings are therefore very suitable for aluminium enclosure parts that must be conductively connected to each other to ensure the shielding effect of the enclosure.

      Hard anodising

      The technical hard anodising process is a combination of physics and chemistry. The hard and dense layers have an extremely high resistance - especially to abrasive stress. Hard anodised parts can be used wherever abrasive stresses occur. Due to the density and structure of the layer, hard anodised layers also have a high corrosion resistance. The dielectric strength per µm is 20 to 30 V per base material. Hard anodised coatings can also be impregnated with Teflon, which improves the sliding properties.

      High-tech made in Germany

      We have been audited and certified in quality management and environmental management since 2008. The highest standards are a matter of course for us and are reflected in great acceptance and customer satisfaction.

      We keep emissions low through modern filter systems and save resources through energy recovery.

      A photovoltaic system generates electricity for our own use and is designed for expansion. Other measures such as waste avoidance and proper disposal are a matter of course for us.

      Our service

      Quality is not just a buzzword for us, it is our philosophy. Various test procedures ensure flawless results in surface finishing. Furthermore, we can carry out a full analysis of all metals. This enables us - especially in hard anodising - to alloy precisely. These and other procedures enable us to guarantee our customers the best quality in the finishing of their products.

      Quality Service

      Personal contact

      It is important to us to be available to you directly and unbureaucratically. That is why you will have direct contact partners at all levels. We do not have telephone hotlines or stalling tactics. Clear communication and simple contact options have always led to optimum Diener & Rapp customer service.

      perfect coatings

      Surfaces are often more than meets the eye. They can be resistant protective layers, electrical conductors, haptic experiences and much more. In the field of aluminium surfaces, anodising and passivation still hold a fascination of their own. For us, for our customers and for our customers' customers.