Here at European Springs, we aim to have our products function to their full potential long after they have left our hands. We use protective sealants and coatings to ensure high quality life spans for our items, complete to ultimate customer satisfaction. The following are examples of the most common and popular types of surface treatments we use for protecting our products and maximising their functionality.
Zinc plating
Zinc plating is a common surface treatment which is mainly used on light springs as it works together with supplementary treatment of Cr+3 chromates or other sealers to form a good protection against corrosion. There is a risk of hydrogen embrittlement and hydrogen reduction by heating but it is necessary for completing the plating. We advise that some high strength materials should not be plated. An alternative to zinc plating which entails a very small risk of hydrogen embrittlement is mechanical zinc coating (also referred to as Rotalyt). This is where the surface coating is applied mechanically by tumbling zinc powder, glass balls and the goods to be coated in a drum. The balls act as zinc powder carriers and are removed after the treatment is completed, leaving the product plated and protected.
Galvanized wire and strip
Galvanized wire or strip material is in many cases an excellent and economical alternative to stainless metals, especially when component weights increase and there are reasonable demands for corrosion resistance. Galvanizing is made hot before cold rolling or drawing which eliminate the risk for hydrogen contamination.
Nickel plating
Nickel is used for decoration and corrosion protection but should not be used on springs where the wire will be subjected to considerable twisting. This is because the surface layer is hard and will be a victim of cracking at rates of high deflection. Examples for which Nickel is often used include the underlying coating for tin, silver, gold etc.
Chrome plating
We use Chromium with underlying nickel plating because it can be polished to a very bright surface, meaning it is generally used for decoration purposes. The fascinating element of this type of plating is how the surface becomes very hard and wear-resistant. We do advise our customers however that chrome plating should not be used on springs with large deflection.
Tin plating
We generally use tin plating in order to make soldering easier; making sure it also gives good corrosion protection. As with Chromium plating, Nickel is also the underlying substrate.
Silvering/gilding
Mainly used for decoration and corrosion protection for components in electrical and electronic equipment. This electrolytic silver plating is chosen in many applications because of its excellent electrical conductivity and its bright attractive finish.
Phosphating
There are many different types of phosphates but the one we choose for springs is normally zinc phosphate. It is generally used as substrate before the painting as it gives good protection against creep corrosion if the paint layer happens to receive any defects. Iron phosphate is used as substrate before powder painting when the demand for resistance against corrosion is lower. Iron phosphate is also used without paint for decoration as it needs to be sealed with oil if corrosion wants to be avoided. Phosphate increases the adhesion between steel and paint so becomes an ideal coating to use for springs which are used for continuous momentum
Black oxide
Used to increase the resistance against corrosion and also for decoration, Black Oxide consists of a layer of iron oxide. We make sure the product is oiled after treatment to achieve maximum functionality.
Electro-polishing
Electro-polishing is a treatment which is used for stainless steels and metal alloys. This particular surface treatment removes the material resulting in an even surface, giving off a high gloss finish. The fatigue limit for the spring is raised as well as corrosion resistance being dramatically increased.
Painting
Painting generally depends on the specific demands for corrosion resistance, meaning it sometimes must be sprayed with salt spray to test performance. Painting can be used for various types of systems of protection and cosmetic appearance. Wet, powder, primers and zinc paint systems are all used but generally are dismissed for tension coil springs with initial loads.
Delta MKS
This particular coating system can consist of a base coat alone, or can simply be a base coat as well as an organic/inorganic top coat depending on specific requirements. These types of coatings are stove systems which mean they chemically crosslink at temperatures below 250 °C. The zinc lamella systems, DELTA PROTEKT KL and DELTA -Tone are micro layer forming base coats which are packed with zinc and aluminium lamellae providing cathodic corrosion protection. This type of protection can be greatly increased by applying an organic top coat such as DELTA – Seal or using silicate water-based products from the DELTA-PROTEKT® VH series. These particular systems give good protection against corrosion and do not give any risks for hydrogen brittleness, something which we are always aiming to solve here at European Springs. For the highest adhesion, the components can be alkaline washing, shot peening and fine crystalline zinc phosphated before the treatment.
Teflon (PTFE)
A suitable surface treatment where there is a requirement for low friction, good insulation and chemical resistance, with an added working temperature range of -190 – +260°C.
Risk of hydrogen embrittlement!
Hydrogen can easily contaminate steel at certain contents making the steel brittle. Adding to this, very low stresses can lead to a rupture if hydrogen is present. Hydrogen absorption occurs during all reactions where hydrogen is produced on the surface of the steel. This is why European Springs supplies Surface treatments which include pickling in non-oxidising acids, cathodic cleaning and cathodic surface treatment to avoid hydrogen embrittlement. Oil tempered spring wire forms and flat springs which have been hardened after forming are specially sensitive to embrittlement, however the risk for embrittlement and failure is reduced the lower the ultimate tensile strength is. We have found that in general, no hydrogen embrittlement occurs in steel below 1000 MPa or hardness below 30 Vickers as a large proportion of the hydrogen can be removed by heating processes. We can also provide you with much information on how to avoid hydrogen problems.
Testing
The corrosion resistance for different treatment can be verified by many different testing methods, we give out recommendations of test methods and can also arrange tests if you have any queries.
