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Fastener Coatings & Finishes

Home-screw/fastener    Fastener Coatings & Finishes

The reason for coating is primarily for corrosion resistance but can also be for thread lubrication and in many instances for aesthetics for furniture and similar industries.

Fastener finishes and coatings are applied by electroplating, dipping, or spraying.Fastener coating can be done by the manufacturer in their own plating plants, or subcontracted to a local coater.
 

1.Self-colour
Fasteners in the plain uncoated finish are also called ‘Black’ or ‘Self Colour’ finish. Fastener products described in these ways have no additional coating, generally, they are oil quenched giving them a surface oil residue that gives a minimal amount of protection.

  
2.Zinc Plating/ZINC PLATED ELECTRO

Fasteners are electroplated with zinc for better corrosion resistance, zinc being the prime material for electroplated fasteners; Zinc plating applies a thin coating of zinc to fasteners, giving them a layer of protection from the surrounding environment. Zinc plated fasteners will rust if placed in a wet environment and are not suitable for outside use.  

Fasteners that have been zinc plated and clear passivated have a shiny, silvery appearance and are also available in zinc and yellow passivation that has a shiny yellow gold appearance; passivation is available in a range of colours. 
 
3.Black Zinc
Bolts electroplated with an electro zinc flash coating and black chrome passivation are described as Black zinc. This finish is used where a colour coating is important for identification or aesthetics.
 
4.Zinc-Cobalt
 
Zinc-cobalt plating of fasteners is a process that achieves enhanced corrosion resistance compared to traditional zinc plating of the same thickness. Zinc-Cobalt gives Bolts and screws have a bright lustre. By electroplating zinc and cobalt the end result is a uniform ductility that will withstand up to six times the corrosion resistance of conventional zinc plating. 

 

5.NICKEL PLATING

Screws Nickel plated are initially copper plated and the Nickel coat is electrolytically applied to the copper finish. Used in fasteners for electrical appliances and areas of condensation. 

 

6.Electro Brass

Electro brass is used for decorative fasteners; Appears similar to brass and is used in furniture or architectural fittings

 

7.TIN PLATED

Nuts and bolts of steel and copper can be electro tinned. Tin plating increases the performance and durability of objects is it added to and improves corrosion resistance.The conductive properties of tin ensure that it is commonly used in the electrical and electro-mechanical industries. Tin plating is also widely implemented in the food packaging trade thanks to its non-toxic and corrosion resistant properties

 

8.Chromium Plating

Fasteners are chrome plated and often polished for appearance.Chrome plating provides similar corrosion resistance to zinc plating.Fasteners decoratively chrome plated are designed to be aesthetically pleasing and durable. Thicknesses range from 0.05 to 0.5 μm and are usually between 0.13 and 0.25 μm. Chromium plating is applied on top of bright nickel plating. Fastener base materials range from steel; copper or zinc alloys and aluminium. Because of the double coating, decorative chrome plating is corrosion resistant but can be problematic if applied to very small threaded parts.

 

9.Copper coatings

Electroplated copper is used as a base for nickel plate or for improved conductivity.

Light Bronze Antique

Copper electroplated and chromate dipped for a medium brown for matching oxidised copper fittings 

Dark Florentine Bronze

Copper electroplated and chromate dipped dark brown for matching oxidised copper fittings  

 

10.Chromate Passivation
The corrosion resistance of fastener coatings is improved by a ‘passivation’ barrel process, which builds up a passive shield layer of metal oxide on top of the zinc layer on the bolt or screw and can add colour identification. Chromates have been used in passivation for many years.

 

11.Hot Dip Spun Galvanizing  HDS/HOT DIP SPUN GALVANISED

One of the most effective coatings for steel fasteners both performance and cost is hot dipped spun galvanized zinc. Hot dip zinc finish is dull and rougher then electroplated zinc coating. Typical coating thicknesses are 50 microns (μm), this is the thickest zinc coating to go onto the fastener resulting in superior corrosion resistance.

Due to the thickness of the coating and the concentration of zinc deposits is in the thread roots and internal corners, thread diameters of less than M10 are not normally galvanised. 

Hot dipped galvanized fasteners are frequently used outdoors, especially in coastal and severe marine environments.

 

12.Mechanical zinc

A mechanical barrel method of applying thick coatings of zinc is available which gives thick coatings and similar corrosion protection to hot dip galvanizing. This is sometimes called mechanical galvanizing or mechanical zinc.  A low-temperature process, so there is no tempering back allowing for high-grade fasteners to be coated.  

 

13.Sherardized coatings/SHERARDIZED

Sherardize coating is the main competitor to Hot dip spun galvanising.Sherardizing gives a good coverage, and the long-term corrosion resistance is excellent since the coating is thick and well bonded. 

 

14.Chemical black/BLACKODIZE

Blackodized, Black oxide, Gun barrel blue and blackening are all names for this conversion coating. It is used to add mild corrosion resistance, for appearance and to minimise light reflection. To achieve improved corrosion resistance the black oxide must be impregnated with oil or wax. The advantage over other coatings is its minimal build-up and is used where close tolerances need to be maintained.

 

15.Black Japaned

Wood screws and other fasteners can be black enamel dipped finished and this is called black japanning. Black is common and japanning is often assumed to be synonymous with japanning, other colours are available. Primarily used in black fittings or furniture, and historically was a popular screw head finish for furniture.

 

16.Phosphate conversion coating/PHOSPHATE

Phosphate coated fasteners have a thin dull grey coating obtained by immersing the steel fasteners in a phosphoric acid bath.  Gives a lower level of protection than zinc in mild environments, but gives an excellent base for painting and lubrication. Often used in automotive industry plain or with an oil coat .

 

17.Organic coatings
Fasteners Organically coated provide a barrier to corrosive media and impede the access of moisture. The thickness of the organic coating determines how much protection the fastener will receive. Fasteners are subject to scratching and surface damage in service, and if broken protection ceases; organic coatings are not suitable for all applications .


18.Zinc flake cured coatings
The coatings consist predominantly of Zinc Flakes usually with a small quantity of Aluminium.These coatings have relatively good coverage and can give good dimensional control and excellent corrosion protection. Examples that are widely used are the Dacromet and Geomet  branded range of coatings that are used extensively by the Automobile Industry to give salt spray resistances exceeding 600 hours with a thin coating, making them ideal for fasteners. 

This coating does not induce Hydrogen Embrittlement, which means that high tensile fasteners can be safely coated.
 

19.Spray Coatings /PTFE XYLAN TUFLON 

High resistance to solvents, acids, and bases.

 

20Rilsan

Rilsan’ s outstanding features are abrasion resistance, impact resistance, flexibility, thermal resistance, weathering and chalking, it has low water absorption high dimensional stability, good resistance to stress cracking and a low coefficient of friction. 

 

21.STAYBLACK

Stayblack is a chemical conversion which modifies the passive oxide layer of the stainless steel leaving the stainless steel matt black. The primary applications of this are fasteners and small pressings which need to retain a consistent and durable black appearance. It is used more specifically in military applications where a black, matt, non-reflective surface is essential. Stayblack is specified for components in medical, optical and scientific equipment as well as for many varied aerospace applications.


22.ANODISED FASTENERS.

Anodising increases corrosion resistance, wear resistance and provides better adhesion for paint primers. Anodic films can also be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add interference effects to reflected light. 

2021-11-26 10:25

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