Fusion bonded Epoxy coating commonly referred as FBE coating is widely used to protect concrete reinforcing bars steel pipes, piping connections,etc. used in construction. FBE coatings are in the form of dry powder at normalatmospheric temperature.The powder is applied electrostatically to the surface of cleaned hot steel bars and cured to form a protective film after undergoing various chemicalprocesses.The Epoxy coated bars last longer duetothe protectivefilm and therebycontributetothe quality of construction.
- The superior corrosion protection can extend the life of the Epoxy coated TMT bar, resulting in signiﬁcantly lower lifecycle costs over time.
- It needs little maintenance that leads to substantial savings in labour costs. It is ﬂexible to allow straight bars to be bent during fabrication on a special mandrel to protect the coating from damage.
- Epoxy powder coated bar is a sustainable solution that is friendly to the environment, a primary concern for construction companies everywhere these days.
- Studies have shown that structures built with Epoxy last longer than similar structures made with black steel. Epoxy coating is very cost eﬀective as it adds very little to the overall cost of the structure and lifecycle. As the technique is factory based, better quality control is achieved. It gives uniform thickness of coating. The bonding of coating with steel TMT Bars is high as it has excellent adhesive property.
- The Fusion Bonded Epoxy Coating acts as an insulator for electrochemical cells and oﬀer barrier protection to steel which prevents entry of chloride ions through it.
|PARAMETER||ASTM A775 : 2007||BIS 13620 : 1993||ET EPOXY PROTECT|
|Bar Anchor profile||1.5 – 4.0 miles||Nearly white metal||Nearly white metal & 1.5 – 4.0 miles|
|Coating Thickness||7-12 miles 170-300 (microns)||100-300 microns||100-300 microns|
|Coating Holidays||3 holidays/m (Max)||6 holidays/m (Max)||5 holidays/m (Max)|
|Coating Flexibility (Achieved)||18°0bent using 8D||120°(after rebound)||120°(after rebound)|
|Cathodic Disbondment test||Yes||Yes||Yes|
TMT bar is cleaned for surface contamination such as grease and oil by solvent cleaning. Shot blast cleaning is the most commonly used method for preparation of steel surfaces. This effectively removes rust, scales, slats, etc., from the surface and produces an industrial grade of a clean and rough surface finish.
Heating can be achieved by using several methods, but the most efficient method is induction heating. TMT bars are passed through a high frequency alternating current along with magnetic field, which heats according to the required FBE coating application temperature. Typical application temperature for a stand- alone FBE is 225°C to 245°C.
Epoxy Powder Application
The FBE powder is placed on a fluidization bed. The heated TMT bar is passed through the coating booth with number of electrostatic epoxy spray guns and the dry powder is sprayed (cloud formation) on to the hot TMT bar. Here, the powder particles are suspended in a stream of air which is electrically charged due to which epoxy powder particles are attracted to the grounded TMT bar. As soon as the charged epoxy powder
particles hit the hot TMT bar, they melt and flow into the anchor profile. The heat also initiates a chemical reaction which causes the epoxy powder molecules to form cross linked polymers which gives the coating its beneficial properties.
Curing & Cooling
Epoxy coated TMT bar is given a thermal treatment by keeping it at 225°C for a duration recommended by Epoxy powder manufacturer resulting in fully cured coating. The coated bars are passed through a cooling tunnel after curing, where water is sprayed on to the bars to cool them. The bars are then kicked-off on to the final inspection rack for testing and inspection.
Chemical Resistance Test
Chemical resistance of the Epoxy coating is evaluated according to BIS 13620 : 1993 standard test method for chemical resistance of TMT bar coatings.
Coating ﬂexibility is evaluated using the method described in section of BIS 13620 : 1993 where three 4- [1.2 m] long coated bars are bent 120º (aer rebound) around mandrels of diﬀerent diameters. (Based on job diagram)
Cathodic Disbondment / Resistance Voltage
Cathodic disbondment testing is performed in accordance with ASTM A775 : 2007 standard test methods for cathodic dis bonding of coatings.
Salt Spray Resistance Test
Salt spray resistance is evaluated by exposing coated specimens in accordance with ASTM A775 : 2007 standard practice for operating salt spray (fog) apparatus.
The abrasion resistance of the coating is evaluated in accordance with BIS -13620:2004 standard test method for abrasion resistance of organic coatings by the taber abraser.