Anticorrosion treatments

Zinc plating

The zinc-plating process (also called cold galvanizing) aims to achieve zinc-plating on the base metal through electrolysis. It’s able to bestow, according to thickness, a good resistance to atmospheric corrosion. The electrolytic zinc coatings can be improved in appearance and protective power with a final “passivating” treatment. This passivation bestows particular colourings; for this reason electrolytic zinc-plating is also called “zinc-chromating”. Naturally, according to the application conditions and environment, it may be necessary to increase the coating thickness.

On request, Rosa Catene can supply zinc-plating free from Chromium VI (Cr VI) and therefore in accordance with the RoHS directive.

Nickel-plating

The nickel-plating process (also called cold galvanizing) is the same as the zinc-plating process except that the coating is made of nickel. It’s able to bestow, according to the thickness, a good resistance to atmospheric corrosion and however, better, compared to various types of zinc-plating. Between the nickel coating and the base material, a layer of copper is deposited with the task to increase adhesion of the layer of nickel and avoid the “exfoliation” phenomenon.

Chemical Nickel-plating

The process of chemical nickel (often based on industrial method Kanigen) allows to coat, with a layer (thickness 10μm ÷ 50μm) consisting essentially of nickel (90%) and phosphorus (10%), the surfaces of a mechanical component, in order to improve the surface characteristics in terms of hardness, resistance to wear and corrosion
The hardness of the surface layer and the wear resistance (but with them also the fragility and friability surface) increased by the amount of phosphorus contained in the layer, and the age of the deposit by heat treatment of heating at medium temperatures.

The hardness of the deposited layer ( ~ 550 HV , just deposited , at environment temperature) increases with the duration and temperature of heating . High hardness values ​​( ~ 1100 HV) can be achieved.
It should however be kept in mind that this heating process is problematic for components previously subjected to cementation : heating could affect the hardness of the hardened layer located immediately below the layer typical of the nickel plating. In these cases ( nickel- high hardness of cemented components ) are advised to contact our technical department in order to find a compromise solution more effective.
A secondary effect of this treatment is to obtain a good compromise between hardness / wear resistance and fragility / friability .
As mentioned above , it is possible to obtain higher hardness by heating at higher temperatures ( 280 ÷ 350 ° C )
The final visual appearance of the deposited layer is polished with slight yellowish tinge with phosphorus or ~ 10 % after heat treatment at high temperatures , to become progressively more opaque ( and visually similar to that obtained with nickel electroplating ) to decrease the levels of phosphorus or of the treatment temperature .

Although more expensive (4 to 5 times ) than the Galvanic / electrolytic nickel plating offers several advantages ( which makes it a viable alternative to hard chrome plating ) :

greater hardness and compactness of the surface layer , resulting in increased resistance to wear
layer uniform and precise , also on internal surfaces / cavities or complex geometry , with possibility of adjusting the thickness , respecting the original roughness and avoiding further final machining
excellent adhesion of the deposit to the base metal (no need to interpose substrates ) , giving the surfaces of the piece the ability to respond well to push-ups, expansions and changes in temperature ( -192 ° C to +200 ° C) , without the effects of ” flaking ” or cracking
good abrasive wear resistance and low coefficient of friction due to the self-lubricating properties of phosphorus
better corrosion resistance (making effective treatment even on stainless steel) , especially in alkaline environments , thanks to the very low porosity of the deposited layer and the presence of phosphorus ( and compounds Ni3P )
expanding the range of materials effectively treatable ( ferrous metals, aluminum alloys , stainless and special steels , heat-resistant plastic and ceramic – it is not possible to deal directly lead alloys or zinc)
the absence of electric currents, eliminating the presence of “point effect” and avoiding the brittleness of the material
The advantages that characterize the chemical nickel also highlight what may be cases in which it may find application as a valid alternative to the nickel plating and chrome plating .

The electroless nickel plating can be performed on all components of the chain, before they are assembled .

Typical areas in which it is used electroless nickel plating are those that require high resistance to corrosion.
Definitely worthy of note is the food field , where chains are required that can operate in contact with highly aggressive atmospheres , ensuring maximum corrosion resistance and compliance of hygienic – sanitary

“Pink” surface treatment for stainless steel execution

Progress and market demand always searching for advanced products with regard to quality/services and improvements in the life performance of the base product called “chain” brought us to develop and study, with regard to stainless steel, resolutions of problems concerning premature wear and tear caused by “mild” material of the cylindrical contact elements such as pins and bushes.

For this purpose, today we suggest a new surface treatment called “PINK” with a nonconsiderable cost in comparison to the results obtained and which offers the following characteristics:

The treatment is carried out on the cylindrical parts exposed to wear and tear and that is, bush/pin and eventually, roller
Treated components appears black colour
The surface hardness reaches 1100/1200 Vickers (contrary to 750 of the normal cementation of the carbon alloyed steel) with a thickness of 40/50 Micron which implies a major resistance to wear with the consequent life extension of the chain
Self-lubricating and anti-seizing up thanks to the presence of anti-adhesion compounds on the hard surface which prevent the forming of micro-cracks caused by friction stresses with reduction of the friction coefficent between the chain components
Resistance to saline fog between 300/400 hours
It result effective at temperatures between -40°C/+500°C
This treatment is obtained by spreading, same as hardening, and not by coating as for the “hard croming”, “chemical nickel plating” etc. therefore it avoids the risk of exfoliation of the covering treatment which causes scaling which could be dangerousin specific applications such as the food industry.

Another interesting feature always for the food industry is that it doesn’t eliminate the dust which generate among the components of the chain due to the wear, but thanks to above characteristics of hardness/wear resistance its appearance is delayed.

This treatment doesn’t have a specific homologation for the food industry and it’s inadvisable where the chain acts as a fulcrum for the food-product, i.e., where the chain is in direct contact with the product; while, it is suggested in any application in which the chain is not in contact with the product, therefore normally, even in the food industry.

Other types of coatings

On request, we carry out other types of protective coatings like hot galvanizing or like Delta Seal Silver GZ which guarantees an extremely high resistance to oxidation.
Since it’s a matter of special coatings with particular characteristics, we must previously study if it can be done.

General Informations

The mentioned coatings are superficial protective deposits which increase the resistance to oxidation of the coated material but they don’t make it an “anti-oxidant” material. The life of such coatings depends on numerous variations which can compromise the resistance. Naturally, besides the variable time (working hours), you must also take into consideration the working temperature, the presence of abrasive substances and the use of aggressive detergents which can negatively influence the protective characteristics of the coating.