DURNI-COAT®, abbreviated to DNC, is a process for functional surface treatment of metals which matches the material with treatment and the end use. Names for this process include electroless nickel, chemical nickel or Durnicoating.
Metallic workpieces of various kinds are nickel plated chemically in aqueous solution. The chemical deposition takes place without an external power source. The process solution usually has a temperature of 90 °C and a defined content of nickel and hypophosphite ions. During the coating process, these ions are reduced to metallic nickel. The necessary electrons originate from the hypophosphite ions and act as a chemical reaction partner. They are oxidised into orthophosphite during the reaction and are also responsible for the phosphorus content of the deposited DURNI-COAT® coating. A nickel-phosphorus alloy layer forms on the surface of the workpiece, which differs substantially in its mechanical, chemical and physical properties from phosphorus-free electro-deposited or metallurgically produced nickel.
The property spectrum of the DURNI-COAT® coating ranges from chemical resistance, dimensional accuracy and optimal anti-friction properties through electrical conductivity to increased hardness. DURNI-COAT® layers are deposited uniformly on active material surfaces. The surface contours of geometrically complex workpieces are faithfully reproduced. Sharp edges and recesses, accessible cavities or holes are coated with the same layer thickness everywhere.
The wear and corrosion behaviour of electroless nickel plating using the DURNI-COAT® process is controlled by the phosphorus content of the coating. This content can be adjusted between 3% and 14%.
The layer thickness affects the resistance of the electroless nickel coatings. DIN EN ISO 4527 defines the following layer thickness ranges:
- 2 to 10 µm for mild corrosion loads
- 5 to 10 µm for mild wear loads
- 10 to 25 µm for more moderate loads
- 25 to 50 µm for heavier loads
- more than 50 µm for very heavy loads
Corrosion conditions, type and characteristics of the base material and its surface, the tribological system and the required service life all have to be considered when choosing the DURNI-COAT® variant and the coating thickness.
The following metallic materials are durnicoated at AHC Hangzhou:
- Aluminium alloys
- Nonferrous metals such as copper, brass or bronze
- Stainless steel
- Cast iron-based materials
- Low-alloy ferritic steels
- Sintered metal materials
We are very happy to clarify the suitability of other materials for coating by performing trials on samples.
The versatile DURNI-COAT® coating has been proven by the large number of suitable materials which can coated in diverse industries.
- Automobile manufacturing
- Chemical industry
- Communication technology
- Defence technology
- Electrical engineering
- Energy and reactor technology
- Food industry
- General Engineering
- Household appliance industry
- Hydraulics and pneumatics industries
- Measurement and control technology
- Office and data technology
- Pharmaceutical and medical equipment manufacturing
- Printing machines
- Textile industry
- Valve manufacturing
Overview of Process VariantsDNC 471
The process variant DNC 471 creates a lead-free, corrosion-resistant and especially ductile layer with a phosphorus alloy content of 10 to 14 percent (incl. alloying elements). [Phosphorus content of coatings (30 µm), determined in defined measurement ranges, steel base material, stationary, measurements in accordance with DIN 4527.] more
This layer is suitable for metal fittings with a stainless steel look as well as for components with high corrosion and chemical stresses.
- Elongation at break: The layer shows an elongation at break in the order of 1.0 to 2.0 percent after measuring foils using the dome method.
- Abrasion amounts to ≤ 35 mg. after 1,000 revolutions in the Taber-Abraser test using CS 10 wheels.
- The hardness amounts to about 570 HV 0.05.
- Corrosion resistance: As an example, a coating with a thickness of 50 μm, a surface roughness RZ of ≤ 1 μm and on a St 52 base material is resistant to more than 500 hours in the so-called acetic acid salt spray test according to DIN EN ISO 9227. In the Kesternich test according to DIN 50 018, the same coating is resistant to more than 7 cycles SFW 2.0.
DNC 571 is a process variant of electroless nickel DURNI-COAT®, which results in a lead-free and especially corrosion and wear resistant layer with a phosphorus alloy content from 9 to 13 percent (incl. alloying elements). [Phosphorus content of layers (30 μm), determined in defined ranges, steel base material, stationary, measurements in accordance with DIN 4527.] more
The lead-free coating can be found on pump casings and stopcocks for the oil and gas sector, on machine parts in the food industry as well as nozzles, compressors or screw fittings from the automotive engineering, electrical engineering, electronics and gear manufacturing sectors.
- The layer shows an elongation at break in the order of 0.5 to 1.0 percent after measuring foils using the dome method.
- Abrasion amounts to ≤ 35 mg after 1,000 revolutions in the Taber-Abraser test using CS 10 wheels.
- The hardness amounts to about 570 HV 0.05; heat treatment increases the hardness up to about 1,000 HV 0.05.
- Corrosion resistance: As an example, a coating with a thickness of 40 µm, a surface roughness of RZ ≤ 1 µm and on a St 52 base material is resistant to more than 200 hours in the so-called acetic acid salt spray test according to DIN EN ISO 9227. In the Kesternich test according to DIN 50 018, the same layer is resistant to more than 3 cycles SFW 0.2.
DNC-AL is a process variant of electroless nickel DURNI-COAT® for aluminium and its alloys. more
All the advantages of an electroless nickel coating on aluminium materials come to fruition: corrosion resistance, wear resistance, ductility, faithful reproduction of the base material surface contours, non-porous surface.
The finishes are suitable for components of textile machinery, printing and packaging machinery, as well as for control technology, electronics and electrical engineering.
Thus, electroless nickel plating of aluminium materials provides the opportunity of soldering with other materials in the electronics industry. Even a thin layer of a few micrometers is sufficient to aid soldering. Semiconductor components, heatsinks, housing parts or contact pins can then be combined. Thicker layers are recommended for high corrosion protection. The problem of contact corrosion in the assembly of materials with different electrochemical properties is also solved. In this way coated aluminium parts can be attached with stainless steel screws. An essential prerequisite however, is a closed electroless nickel coating.
In the automotive sector, workpieces treated with DNC-AL are, for example, used as passenger car diesel pistons. The coating protects these vehicle components against cavitation erosion. Aluminium compressor wheels for turbochargers also belong to the automotive sector. Through the use of turbochargers or compressors, designers have more opportunities for a smaller engine cylinder capacity. With electroless nickel plating the thermo-mechanical load capacity of the compressor wheels is significantly increased. This affects mainly in the supply of exhaust gases on the compressor side of a turbocharger because here very fine particles place extreme demands on the compressor at immense speeds.
Please note that nickel-phosphorous coats deposited on aluminium substrates exhibit diverging phosphorous alloy contents within the first 10 µm of the coatings thickness.
The PTFE-DURNI-DISP process is a variant of the DURNI-COAT® process in which solid polytetrafluoroethylene (PTFE) is incorporated and homogeneously distributed in the electroless nickel coating. more
In a PTFE-DURNI-DISP coating the fluoroplastic polytetrafluoroethylene (PTFE) is homogeneously dispersed at 20 to 30% by volume. Therefore, this coating is also called dispersion coating. It combines the good properties of the DURNI-COAT® coating with the advantages of PTFE. Depending on the tribological system, the coefficient of friction of PTFE-DURNI-DISP is between 0.1 and 0.2 with a mixed hardness of 230 HV 0.01. To produce the special coating properties, layer thicknesses from 7 to 15 µm are usually sufficient. The PTFE-DURNI-DISP coating offers outstanding adhesive wear resistance and excellent dry running properties. It is compatible with high temperatures and has excellent anti-friction and anti-adhesive properties. It shows a good corrosion resistance when in combination with an intermediate layer.
PTFE-DURNI-DISP primarily offers a near perfect dry lubrication. The layer can also be used as anti-adhesion coating for mould tools.
- improves release properties and wear resistance, for example, injection moulds
- adds anti-friction properties and improves wear resistance
- adds anti-friction properties and improves corrosion resistance
- adds anti-friction properties and magnetic properties
- acts as permanent lubrication combined with wear resistance and corrosion resistance
- develops anti-adhesion effects and protects, for example, heating elements from limescale deposits