Coatings & Additional treatments | Bossard Sweden

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Coatings & Additional treatments

The listed coatings are standard coatings according to ISO or DIN with corresponding composition and defined thickness. If the required coating is not displayed, we will be pleased to make you an individual offer. According to the product weight and definition of the packaging, parts are coated as rack plated or barrel plated parts.

Coatings

Anodizing black/colorless

Anodizing according to DIN 17611, color C-35 black/C-0 colorless, thickness 10-20 µm. (Rack plated parts)

  • In the anodizing process, the surface of the workpiece is specifically electrolytically oxidized - the top layer is converted into a stable oxide compound AL203.
  • By varying the process parameters, the layer thicknesses can be varied between 5 and 25 μm. The main purpose of anodizing is to give aluminium workpieces better corrosion resistance.
  • By introducing dyes into the AL203 layer, anodizing also enables the permanent color coding of work pieces or their visual enhancement.
  • It should be noted that not all aluminium alloys are suitable for anodizing.
  • Dimensional accuracy of anodized layers: During anodizing, the layer is made from the basic material provided. It consists of aluminium oxide AI203, which requires more space than the aluminium. Therefore, the layer grows to about 1/3 of the total layer thickness above the original surface level. With a layer thickness of 15 µm, the layer grew about 5 µm above the original level which means for bores, the diameter is reduced by 10 µm. This must be taken into account when designing workpieces - especially with fits and threads.

Chrome plating

Bright chrome plating, according to ISO 1456 --> Fe/Cua/Nib/Crmc, chrome layer thickness 0.5-1 µm

  • For the electrochemical production of chrome coatings, the previously electrochemically nickel-plated workpiece (made of iron, copper, brass) is dipped into a bath and switched as a cathode. The chrome layer adheres much better to a thin nickel layer than directly to iron.
  • For this reason, the galvanic chromium plating process is only used in combination.
  • The copper-nickel-chrome coating is used as standard. This combination offers a high level of corrosion protection and at the same time guarantees a high-quality surface.
  • Due to the low layer thickness, chrome is not a suitable corrosion protection. Protection can only be increased in conjunction with a suitable intermediate layer (usually copper and nickel).
  • With a nickel layer only, the corrosion protection is only slightly better, since layers with thicknesses under 25 μm are usually porous and therefore susceptible to pitting.
  • For this reason, workpieces are copper-plated (undercoppered 3-5 μm) before the nickel and chrome coating to achieve better corrosion protection.
  • Please note that galvanic chromium plating is generally carried out on the frame as a suspended part.
  • Example of a typical coating: ISO 1456 --> Fe/Cu3a/Ni5b/Crmc
    • ISO 1456: valid standard
    • Fe: chemical symbol of the base material, Fe for ferrous materials
    • Cu: Galvanic coating of copper / undercopper
    • 3: smallest local layer thickness μm
    • a: Type of copper coating, ductile copper
    • Ni: Galvanic coating of nickel
    • 5: smallest local layer thickness μm
    • b: Type of nickel coating, in this case bright nickel (for decorative nickel coatings)
    • Cr: Galvanic coating of chrome
    • r: regular chrome coatings (glossy) with smallest local layer thickness of 0.5 μm
  • Dimensional accuracy of a copper, nickel, chromium layer combination; with a layer thickness of 10 µm the diameter increases by 20 µm for waves. This must already be taken into account in the design of components - especially for fits and threads (gauge accuracy).

Nickel plating

Nickel plating according to ISO 1456 --> Fe/Nib, thickness 3-5 µm. (Rack plated parts or barrel plated parts)

  • With galvanic nickel plating according to DIN EN ISO 1456, nickel ions are deposited from an electrolyte by applying an electrical voltage.
  • The resulting layer is silvery with a slight shade of yellow. Corrosion protection is limited, as layers with a thickness of less than 25 µm are mostly porous and are therefore prone to pitting.
  • Multi-layer systems with chrome as a top layer have proven to be more durable here.
  • Dimensional accuracy of nickel layers. With a 5 µm layer thickness, the diameter is reduced by 10 µm for bores. This has to be taken into account when designing workpieces - especially with fits and threads.

Zinc blue

Zinc plated, blue passivated (CrVI)-free according to ISO 4042 --> Zn/AN/T0, thickness 3-5 µm. (Rack plated parts or barrel plated parts)

  • In zinc plating according DIN EN ISO 4042, zinc ions are deposited from an electrolyte by applying an electrical voltage.
  • Without customer-specific requirements, the standard layer thickness remains between 3 and 5 µm.
  • Passivation is a process in which metal surfaces are made more resistant to corrosion by non-metallic protective layers called conversion layers.
  • The zinc-coated steel components are provided with a Cr (III) -containing protective layer or conversion layer in an electroless process by immersion in chromium (VI) -free solutions. This protective layer is an inorganic passivation layer with a layer thickness in the nanometer range.
  • The different passivation processes blue passivation, thick layer passivation, etc. - differ in terms of corrosion protection, optic / color.
  • Dimensional accuracy of zinc layers: With a 5 µm layer thickness, the diameter is reduced by 10 µm for bores. This has to be taken into account when designing workpieces - especially with fits and threads.

Zinc thick layer passivation

Zinc thick layer passivation Cr(VI)-free according to ISO 4042 --> ZN/Cn/T0, thickness 3-5 µm (Rack plated parts or barrel plated parts)

  • In zinc plating according DIN EN ISO 4042, zinc ions are deposited from an electrolyte by applying an electrical voltage.
  • Without customer-specific requirements, the standard layer thickness remains between 3 and 5 µm.
  • Passivation is a process in which metal surfaces are made more resistant to corrosion by non-metallic protective layers called conversion layers.
  • The zinc-coated steel components are provided with a Cr (III) -containing protective layer or conversion layer in an electroless process by immersion in chromium (VI) -free solutions. This protective layer is an inorganic passivation layer with a layer thickness in the nanometer range.
  • The different passivation processes blue passivation, thick layer passivation, etc. - differ in terms of corrosion protection, optic / color.
  • Dimensional accuracy of zinc layers: With a 5 µm layer thickness, the diameter is reduced by 10 µm for bores. This has to be taken into account when designing workpieces - especially with fits and threads.

Tin plating

Tin plating according to ISO 2093 --> Cu/Ni2Sn3b, layer thickness 3-5 µm. (Rack plated parts or barrel plated parts)

  • In electroplating according to ISO 2093, the objects to be tinned are immersed in a tin electrolyte after a suitable pretreatment. By applying an electrical voltage, a tin coating is deposited on the surface of the objects. With this process, even very thin layers of a few µm can be realized. 
  • Without customer-specific requirements, the standard coating thickness remains between 3 and 5µm.
  • For electroplated tin plating on copper and brass (CuZn alloys), a nickel barrier layer is generally applied to prevent the diffusion of zinc into the tin coating. Zinc reduces the resistance to tarnish/oxidation of the tin coating. In addition, the zinc reduces the solderability.

Avoid the risk of so-called whisker formation (whiskers are hair-shaped single crystals that can "grow" several hundred micrometers out of the surface and pose a short-circuit hazard in electronic components)

  • A nickel barrier layer also improves corrosion protection.
  • Example Designation according to standard: ISO 2093 --> Cu/Ni2Sn3b
    • Cu: Basic material copper
    • Ni2: Nickel barrier layer 2µm
    • Sn3: Tin layer 3-5µm
    • b: Glossy
  • Dimensional accuracy of tin layers, with a layer thickness of 5 µm, the diameter of bores is reduced by 10 µm. This must be taken into account in the design of components, especially for fits and threads.

Zink nickel

Zinc nickel iridescent (bluish – silver-gray) passivated (CrVI)-free, according to ISO 4042-->ZnNi/Cn/T0, layer thickness 3-5 µm. (Rack plated parts or barrel plated parts)

  • In galvanically applied zinc nickel coatings according to DIN EN ISO 4042, zinc and nickel ions are simultaneously deposited from an electrolyte by applying an electrical voltage.
  • The zinc-nickel process is characterized by a very high corrosion protection compared to galvanized blue.
  • Without customer-specific requirements the standard layer thickness remains between 3 and 5µm.
  • Passivations are processes in which metal surfaces are made more resistant to corrosion by non-metallic protective layers, so-called conversion layers.
  • The ZnNi coated steel components are provided with a Cr(III)-containing protective layer or conversion layer in an electroless process by dipping them into chromium(VI)-free solutions. This protective layer is an inorganic passivation layer with a layer thickness in the nanometer range.
  • The appearance of a passivation layer can vary from transparent, clear to blue iridescent.
  • Dimensional accuracy of zinc-nickel coatings, with a coating thickness of 5 µm, the diameter of holes is reduced by 10 µm. This must be taken into account in the design of components, especially for fits and threads.

Additional treatments

Vibratory grinding

Vibratory grinding / vibratory finishing in barrel process. Deburring and rounding the edges, improving the surface roughness.

  • The workpieces are placed in a container together with numerous grinding tools and various additives. The workpieces get ground down by the oscillating or rotating movements of the container.

Ultrasonic cleaning

Surface free of oil, grease, and chips by visual final inspection. Packed in mini grip bags or according to customer specifications.

  • Cleaning can be done in closed or open, fully automatic or manually operated cleaning systems.
  • For sensitive surfaces with low roughness values or materials with low strength and hardness, ultrasonic should not be used for bulk goods in order to prevent damage on the surface.
  • Without customer's definition, the appropriate cleaning process is selected by Bossard based on geometry and raw material.

Heat treatments

Heat treatments according to special specification. Requirements for processes, hardness, surface roughness, hardness depth must be defined in an additional document or included in the technical drawing.

  • Dimensional stability: Depending on the structural condition after tempering with hardening and tempering or after a thermochemical treatment such as case hardening, nitriding etc., the dimensional stability is influenced (by warpage or volume increase).
  • When nitriding, for example there is a slight increase in volume due to the absorption of nitrogen.
  • The nitriding layer is usually composed of two zones.
  • The inner zone or diffusion layer is characterized by the formation of nitride needles (nitride needles are the chemical compounds of nitrogen with another element, for example iron) in the edge area of the work piece. The usual layer thickness is between 0.2 and 1.5 mm.
  • The outer zone on the workpiece surface with a thickness between approximately 5 and 30 μm is called the connection layer. This non-metallic layer consists of iron nitrides or nitrides of any alloying elements.
  • The change in size due to diffusion-related volume expansion is influenced by the connection layer since the connection layer partially grows on the surface. For example, the diameter increase of a nitrided cylindrical body is in the order of 30 to 50% of the connecting layer thickness.
  • In this case a typical connection layer thickness would be between 8 and 16 μm. This means that the layer increase on the surface is max. 4-5 μm.

For more information about coatings and treatments use the following links Coatings and surface treatments.