Surface Treatment of Materials

History

In 1954, in Letecké opravovne Trenčín, a.s., for purpose of repair of aviation and ground technic, was built galvanizing workshop, which was used for plating parts and fasteners. Due to the large number of orders expanded to new, larger place. In new places was made surface treatments as a cadmium, anodized aluminum and hard chromium.
In 1995, was galvanizing workshop reconstructed. Complete reconstruction of galvanizing vats, building, air conditioning and suction of gas from galvanizing process. Since then, galvanizing workshop has undergone many modifications and modernizations.

Present

Letecké opravovne Trenčín, a.s. currently performs surface treatments such as cadmium, anodized aluminum, hard chrome and zinc phosphating.

Personnel

Personnel that is working in this workshop is well qualified and regularly recertified and capable to work with chemicals. There is also a lab for fixed analyzes of galvanizing baths.

External personnel from Department of Environment is regularly monitoring this galvanizing workshop. Discharged waste water is also monitored after neutralization where stringent ecological criteria for galvanized waste are set. The activities of the galvanizing workshop are technologically and chemically assured by technology workers. In preparing the procedures, the surface treatment guidelines use current information from literature, seminars and training.

Surface treatments

Cadmium

Cadmium is the electrolytic method of surface treatment of steel parts of Class 10-16. Alkaline cyanide cadmium is not recommended for the treatment of steels with a tensile strength of over 1370 MPa (HSM – high strength materials), cement and hardened steels and springs.
In addition to steel, cadmium is a suitable coating for alloy, brass and copper. Cadmium treated surface is soft and resilient, used as a protective coating with good corrosion resistance or as a basis for organic coatings.

Increased corrosion resistance of the cadmium coating can be achieved by an additional coating – chromating. Chromatography of the 5-15 μm cadmium layer improves the resistance of the layer and delivers a typical silver or yellow glare.

The required cadmium treatment is prescribed in accordance with standards ONL 1811, ONL1811.1 yellow passivation, ONL1811.2 white passivation that determines and describes the physical parameters required from individual components or parts.
We are able to quickly and qualitatively cadmium products of different sizes and shapes by agreement:

• non hinges in 2 vats / working dimensions length 60 cm, width 55 cm, depth 60 cm
• multiple / drum / cadmium suitable for cadmium e.g. screws, wedges, etc.

ANODIZING

Vat dimensions: working dimensions length 55cm, width 35 cm, depth 70 cm
Our company provides aluminum surface treatment with anodic oxidation – anodizing and subsequent coloring.

• White sealed in distilled water ONL 1831.12
• Yellow-yellow closed in sodium dichromate ONL 1831.11
• Blue concealed in color AlufinishONL 1831.15
• Red concealed in color AlufinishONL 1831.14
• Black concealed in color AlufinishONL 1831.17

Dimensions: length 140 cm, width 60 cm, depth 80 cm

Hard chrome

A very hard and abrasion-resistant coating with good corrosion resistance is applied on the surface of the component. The coating has a low friction coefficient and gives excellent characteristics in terms of abrasion and tear.
It is used for components where a hard, corrosion-resistant and abrasion-resistant surface is needed, for example, pistons, shafts and hydraulic parts.
For chrome plating, it is necessary to specify the thickness of the coating or the size of the part also with the coating (or the size of the workpiece after grinding), the place of plating and the places to be protected before application.
Custom dimensioning and tolerance (drawing) is required for custom chroming.
Vat dimensions: working dimensions length 60 cm, width 50 cm, depth 70 cm

Zinc phosphating

By phosphating, anticorrosive coatings are formed on the metal surface which are electrically non-conductive and therefore reduce the amount of corrosion current. In water or in organic solvents, they are not soluble and have very good cohesion with the base metal, which contributes to the protective characteristics of the phosphate layer and at the same time they are a good base for coatings. The crystalline phosphate layers that are formed on the surface can fulfill several functions:
• create corrosion protection of metal parts
• Cold forming of steel parts (pipe drawing, wire bending, pressing) improves lubricant adhesion to the surface and reduces friction
• prior to coating, they improve the adhesion of the paint to the surface of the metal and prevent sub-coating of the paint
• facilitate sliding and therefore are used for machining steel movable parts during their running
• serve as electrical insulators
The fundamental of phosphatizing is to convert soluble phosphate (which is the main component of the phosphating agent) into insoluble hydrogen-phosphate and phosphate of the metal concerned, which is caused by the reaction of the metal surface with the phosphatizing liquid.
Phosphating could be done for steels with a max. 1639 MPa. Steel with a strength of 1240 MPa and greater can´t be cleaned in acids. The steel must be cleaned only mechanically.
The required zinc phosphate treatment is performed according to the ONL 1821 standard, which determines and describes the physical parameters required from individual components or parts.
We make the following additional modifications:
Impregnation ONL 1821.1
Conservation ONL 1821.2
Paint ONL 1821.3

Vat dimensions: working dimensions 140 cm, width 60 cm, depth 80 cm