Epoxy Coated Steel Reinforcing Bars
FREE CRSI VIDEO
Fabrication of
Epoxy-Coated Rebar
See how most CRSI-certified epoxy coating facilities manufacture
and test the quality of epoxy-coated reinforcing bar.
Epoxy coating starts out as a dry powder produced by combining organic epoxy resins with curing agents, fillers, pigments, and flow control agents. When heated, the powder melts and the constituents react to form complex cross-linked polymers. Once cured, the coating will not soften at higher temperatures.
Epoxy coatings are environmentally friendly materials. Unlike many paints, the fusion-bonded epoxy coatings used for steel reinforcement do not contain appreciable solvents or other environmentally hazardous substances. Very little material is lost to the atmosphere during the coating process — and there is very little waste.
Coating
In North America, epoxy coating plants typically coat bars in straight lengths (typically 40 to 60 feet long), then fabricate (cut and bend the bars) to meet requirements of the project. Some facilities are capable of coating reinforcing steel — either bars or welded wire fabric — after fabrication. In this process, individual cut and bent bars are hung from a conveyor system and moved through the coating process.
Coating straight bar has the advantage of being more cost effective and corrosion tests indicate little difference between the two. Coating the bars prior to fabrication also allows for a "n car" "off-the-shelf" availability.
The Manufacturing Process
The application of fusion-bonded epoxy coating to steel reinforcing bars is a highly controlled, meticulous process. When performed by a CRSI-certified epoxy coating plant, the highest standards of product quality are met. Here's how they do it:
Surface Preparation
The reinforcing bar is abrasive blasted to near white metal which assures maximum adhesion between the steel and the coating.This removes contaminants, mill scale, and rust. It also roughens the surface to give it a textured anchor profile (i.e., microscopic peaks and the valleys on the surface). The surface roughness "keys" the coating to the steel and provides anchorage.
Coating
After the reinforcing bars have been blast-cleaned, they are heated to approximately 450 degrees Fahrenheit. The heated bars are then passed through a powder spray booth where the dry epoxy powder is emitted from a number of spray nozzles.As the powder leaves the spray gun, an electrical charge is imparted to the particles. These electrically charged particles are attracted to the grounded bar.
When the dry powder hits the hot bar, it melts and flows into the anchor profile and conforms to the ribs and deformations. The heat also initiates a chemical reaction that causes the powder molecules to form complex cross-linked polymers.
Curing
Following powder application, the coating is allowed to cure a short period (approximately 30 seconds) during which time it hardens to a solid. The curing period is often followed by an air or water quench that quickly reduces the bar temperature to facilitate handling.
