Electroplating
Electroplating is the most widely used finishing method, zinc is electro deposited onto the base material and the zinc corrodes in preference to the base material.
To enhance the corrosion resistance of the zinc the surface can be given a conversion coating or passivate.
These coatings can contain hexavalent chrome (which is now a controlled material under the EEC’s End of life vehicle legislation). In the majority of cases the hexavalent chrome can be replaced with the harmless trivalent chrome, but this has a detrimental effect on the corrosion resistance. In these cases this can be further improved by the use of the Leach Seal process (JS500) or lacquers.
Hydrogen Embrittlement
All components made from steel which are subject to chemical or electro-chemical treatments in the course of the coating process may absorb hydrogen which is evolved during these processes. This absorbed hydrogen can cause premature failure if the component is made from higher tensile steel.
Parts are usually considered to be at risk if they have a tensile strength equal to or greater than 1050 MPa, 1000 N/mm2 or 65 tons/sq.in. (T class imperial fasteners and above) or have a hardness greater than 320 vpn. (10.9, fasteners and above).
Baking parts after coating will minimise the risk of failure, this process can never be guaranteed to be completely effective.
Additional reading – Extract from ISO 4042:1999
Mechanical Plating
Degreased parts are placed in a drum with a mixture of glass beads and zinc powder. The beads cold weld the zinc to the components. The parts can then be passivated to give various levels of corrosion protection. This process avoids the risk of Hydrogen Embrittlement.
Organic Coatings
These consist of a coloured pigment bonded with a heat curing polymer giving good corrosion resistance, controlled lubricity high wear resistance and no risk of Hydrogen Embrittlement.
Phosphating
Slight corrosion protection, used as an undercoat prior to painting, with the addition of oil increased corrosion protection can be achieved.
Hot Dip Galvanising
Products are immersed in molten zinc within temperature range 440 – 470 deg.C Coating thicknesses are 40 microns+ giving very high protection against corrosion.
Coating |
Colour |
Corrosion Resistance (Salt Spray Hrs) |
CR6
Free |
Potential for Hydrogen Embrittlement |
ELECTROPLATING |
Zinc + heavyweight trivalent passivate + top coat |
Silver-iridescent |
96w 384r |
Yes |
Yes |
Zinc + yellow + top coat |
Pale yellow |
180w 252r |
No |
Yes |
Zinc + clear |
Silver |
24w 96r |
Yes |
Yes |
Zinc + yellow |
Yellow |
96w 192r |
No |
Yes |
Zinc + heavyweight passivate |
Iridescent |
96w 240r |
Yes |
Yes |
Zinc, no passivate |
Silver |
48r |
Yes |
Yes |
Zinc + black |
Black |
72w 192r |
No |
Yes |
Zinc + olive drab |
Green – brown |
168w 360r |
No |
Yes |
Zinc + heavyweight passivate + nano particles |
Silver |
200w 600r |
Yes |
Yes |
Zinc clear + top coat |
Silver |
96w 240r |
Yes |
Yes |
Zinc nickel yellow |
Yellow-brown |
480w 1000r |
No |
Yes |
Zinc nickel + heavyweight |
Purple-blue |
120w 720r |
Yes |
Yes |
Zinc nickel + heavyweight passivate + top coat |
Silver-blue |
144w 1000r |
Yes |
Yes |
Zinc nickel + black |
Black |
240w 720r |
Yes |
Yes |
Zinc nickel no passivate |
Silver grey |
720r |
Yes |
Yes |
Zinc iron trivalent black |
Black |
500 |
Yes |
Yes |
Zinc iron trivalent clear |
Clear |
500 |
Yes |
Yes |
Zinc iron hexavalent black |
Black |
240w 480r |
No |
Yes |
um (bright ni cr) |
Silver metallic |
72+ |
Yes |
Yes |
Nickel/black chromium (black ni cr) |
Black |
72+ |
Yes |
Yes |
Nickel |
Pale yellow |
72 |
Yes |
Yes |
Magni 560 (on zinc plate) |
Silver-grey |
840r |
Free |
No |
MECHANICAL |
Zinc trivalent heavyweight |
Iridescent |
48w 120r |
Free |
No |
Zinc trivalent heavyweight + seal |
Iridescent |
|
|
|
Almac® (Zinc-Al) |
Matt silver |
200w 480r |
Free |
No |
Inverplex (Zinc-Tin) |
Matt silver |
72w 240r |
Free |
No |
Zinc trivalent TT15 |
Iridescent |
|
|
|
Zinc chromate |
Yellow |
|
|
|
SPECIALIST COATING |
Dry film lubricants |
Clear, grey, black |
Variable |
Free |
No |
Phosphate -manganese |
Grey |
24+ |
Free |
Yes |
Phosphate - zinc |
Grey |
24+ |
Free |
Yes |
ORGANIC |
Cathodic electrocoat |
Black |
1000r |
Free |
Slight |
E-Cote® |
Black |
72r |
Free |
No |
E-Cote® + seal |
Black |
120r |
Free |
No |
Xylan® |
Black, blue |
144+r |
Free |
No |
Xylan® Spray |
As required |
240+r |
Free |
No |
Spray Painting |
As required |
As required |
- |
No |
ZINC FLAKE |
Geomet® |
Silver-grey |
240-1500r |
Free |
No |
Delta Protekt® |
Silver-grey |
240-840r |
Free |
No |
Magni 565 |
Silver-grey |
840r |
Free |
No |
Zintek® / Tintek® Top / Techseal® |
Silver-grey |
840 |
Free |
No |
TOP COATS - Top coats can be applied to most coatings to modify colour and / or frictional coefficients. Some top coats also enhance corrosion performance of electro zinc and zinc flake base coatings. |
Delta Coll® GZ |
Various colours |
|
|
|
Magni B18 |
|
|
|
|
Finigard® 105 |
|
|
|
|
TNT 15 |
Clear |
|
|
|
Hydroclear lacquer |
|
|
|
|
PS100 |
Leach seal |
|
|
|
JS500 |
Leach seal |
|
|
|
TT15 |
lubricant |
|
|
|
Thread Locking & Sealing
 |
 |
 |
| Scotchgrip 2353 |
Tuflok 180 |
Precote 80 |
There are two main types of thread locking used:
Nylon Prevailing Torque Patch
Adhesive Patch
Nylon Prevailing Torque Patch
The Nylon is fused to the thread; on installation the nylon fills the available space between the threads causing a strong axial load between the threads which in turn provides the locking action.
Adhesive Patch
The adhesive patch is applied to the component and on installation ruptures to form a locking bond between the two parts.
Common Nylon Patched Used
Tuf Loc 180, 360
Esloc 180, 360
Common Adhesive Patches Used
Scotchgrip
Precote
Recommended Links for further information on Finishes, Thread Locking and Sealing:-
http://www.deltagbn.co.uk/
http://www.anochrome.co.uk/
http://www.prelok.com/uk.html
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