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Anticorrosion treatments

Chain lubricants can be a  valid  resistance against  slight exposion.   In the event of a long period of inactivity in  the open or in the presence of elements meanly aggressive, lubrication, as an anti-corrosive protection, is no longer sufficient.

In these cases you must utilize chains with surface coating treatments which aim to protect the chain parts against foreign agents.

Here following several anti-corrosive treatments in use:

Zinc plating (click here to open)

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 (click here to open)

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 (click here to open)

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 โ€‹โ€‹( ~ 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

Plasma nitriding (click here to open)

Plasma  nitriding

In all its variants , the nitriding is a thermochemical treatment that increases the surface hardness of a steel component through the diffusion of nitrogen ( and not carbon as in cementation) and the precipitation of nitrides ( high hardness ) in the superficial layers of the pieces , while maintaining the strength and toughness to the heart of the component.
The plasma  nitriding is a particular type of nitriding in which, thanks to an electric discharge stable triggered between the components to be treated ( + ) and the walls of a "cold" furnace under vacuum ( - ) , the surfaces of the pieces are literally " bombed " from ionized atomic nitrogen (ie nitrogen ions, differentiated by molecular nitrogen / ammonia , forming a layer very similar to plasma). Heating ( 350 ÷ 500 ° C ) of the surfaces of the components caused by this "bombing" promotes the formation of nitrides ( obtained from the reaction of the nitrogen atom with the metal elements of alloy of the surface layers "hot" pieces ) and the resulting surface hardening by precipitation
Despite being more expensive than conventional the plasma  nitriding is able to offer several advantages :

  • greater number of operational parameters independent of each other (temperature, pressure , gas composition , potential difference and current intensity ), with a large possibility of specific nitriding  (in terms of chemical composition, mechanical properties and hardness of the various surface layers ), calibrated on the specific use to which it is intended the component discussed
  • optimization of the typical layers of nitriding, with more compact ( less porous layer of the compounds ), and less frailty surface (reducing the thickness of the "white blanket")

  • High surface hardness (900 to 1000 HV) with hardened layers of small thickness , and the possibility to obtain better results using filler metals (titanium, boron, aluminum)
  • further reduction of deformations and thermal distortions associated with treatment
  • Increased resistance to corrosion ( as well as greater durability surface chemistry )
  • possibility to act also on stainless steels , leaving practically unaltered the corrosion resistance
  • removal of any contaminated or oxidized layers on the surfaces of the pieces before hardening 
  • surfaces of excellent quality, with a decrease in the coefficient of friction and increased resistance to wear
  • an increase in resistance to fatigue (due to a general increase in surface compressive residual stresses induced by treatment)
  • reduction of processing temperatures and the time required to process

It should however be kept in mind that the plasma  nitriding can be carried out effectively ( with good results) only on certain types of steels (classified as nitriding steels ) having surfaces that are not heavily work-hardened and not excessively decarburized or oxidized . In order to impart good mechanical strength and toughness at heart, before nitriding treatments are performed usually for cleaning , stress relieving and final mechanical finishing (since the nitriding treatment is normally a "final" that do not follow other technological operations ) .

The plasma  nitriding is performed exclusively on the elements of rotation of the chain (pins, bushes and rollers) in order to improve the resistance to wear , each time it is particularly important  in the articulation of the chain.

In the light of what has been seen so far, it appears evident the considerable variety of areas in which the plasma  nitriding is effectively used . To give you  an example, the plasma  nitriding has proved to be an excellent solution when applied to the elements of rotation ( made โ€‹โ€‹of specific materials ) for chains designed to operate inside food and bread  ovens with medium - high temperatures (300 to 450 °C).

"Pink" surface treatment for stainless steel execution (click here to open)

"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.

Latest test on chains with hard chromium plated pins (click here to open)

Latest test on chains with hard chromium plated pins

Unlike chromising, “hard chromium” is a chromium coating. Therefore the hard chromium underneath doesn’t undergo chemical alterations during the process. For this reason the component (pin) can be, and it is, casehardened. Therefore the hard chromium adds the exellent characteristics of the chromium coating to the already good characteristic of a casehardened pin.

During the useful life of the chain, wear and tear will be quite limited because first of all, there’s the particularty hard layer of the chromium and then the casehardened layer. The layer of hard chromium reaches 40 - 50 micron with hardness of 1000 - 1100 HV. Underneath, the casehardened layer reaches a hardness of 700 - 800 HV for the depth of useful casehardening.

The hard chromium adds to the exellent characteristic of resistance to wear and tear, an anti-corrosive protective power which makes it particularly suitable even for the applications in the open; the importance of the coating thickness enables the pin to resist with greater easiness to eventual abrasive and/or corrosive inclusions.

During the useful life of the chain, first the coated chromium will be consumed and successively and partially the casehardened layer. The max. stretching of the chain will take place before this last layer will wear away.

The Hard Chromium coating is being used by ROSA CATENE S.p.A. for several years now in the agricultural field with considerable satisfaction and recognition on behalf of the national and international customers.

Documentation of hard chromium process (PDF english)

Hard chromium (PDF deutsch)

Hard chromium (PDF french)

Hard chromium (PDF italian)

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.