Description
Manufacturing Process
Reinforcing steel bars are sprayed with epoxy powder (blue) which adheres to the pre-heated surfaces and cures instantly, forming a thin film that protects the steel against all corrosion, thereby prolonging the life expectancy of the steel and concrete structure or building.
Coating Process
The coating process involves four steps:
- Surface preparation
- Heating
- Powder application
- Cure
1. Surface Preparation
Rebars are blast-cleaned to a near white metal finish using abrasive grit. This cleans the steel of contaminants, mill scale and rust. It also roughens the surface to give it a textured anchor profile. During this process, salt contamination is also removed.
2. Heating
Bars are heated to approximately 232-239°C, using electrical induction heaters.
3. Powder Application
The heated steel is 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-steel surface providing even coating coverage. When the dry powder hits the hot steel, it melts and flows into the anchor profile (i.e., the microscopic peaks and the valleys on the surface) and conforms to the ribs and deformations of the bar. The heat also initiates a chemical reaction that causes the powder molecules to form complex cross-linked polymers which give the material its beneficial properties.
4. Cure
Following powder application, the coated rebar is cured with distilled water which quickly reduces the bar temperature to facilitate handling and testing.
Quality Inspection & Control Stage
While quality tests are done after each successive production stage, the final coating inspection is conducted at the end of the procedure to ensure that the coating:
- Is sound and free from abrasion and pores,
- Has acquired the right thickness,
- Is strongly adhered to the steel surface and is bendable.
Quality Assurance & Quality Control Standards (ASTM – CRSI – ACI)
Why have bending Codes?
Within the ASTM codes for the manufacture of the high tensile deformed reinforcement steel, there are varying grades of steel (e.g. A615, A616, A617), and for each of these grades the correct bending radius must be applied.
Considerable testing has shown that when the bending radius on a high tensile steel rebar is too accurate, then stress fractures occur in the steel. These fractures change the electrochemical make-up of the steel, allowing corrosion to commence earlier and at a faster rate. When bars are bent using the correct radius, this problem is eliminated.
| Standard Bar Weights – Standard Bar Length 12M | |||||
|---|---|---|---|---|---|
| Nominal Diameter (MM) | Nominal Weight (Kg/M) | No. of Bars/Ton | Kg/Bar | S. Aramco Standards Mandrel dia.(MM) | A.C.I. Standard Mandrel dia.(MM) |
| 8 | 0.395 | 211 | 4.740 | 64 | 48 |
| 10 | 0.617 | 135 | 7.404 | 80 | 60 |
| 12 | 0.888 | 94 | 10.656 | 96 | 75 |
| 14 | 1.210 | 69 | 14.520 | 112 | 84 |
| 16 | 1.580 | 53 | 18.960 | 128 | 96 |
| 18 | 2.000 | 42 | 24.000 | 144 | 108 |
| 20 | 2.470 | 34 | 29.640 | 160 | 120 |
| 22 | 2.980 | 28 | 35.760 | 176 | 132 |
| 25 | 3.850 | 22 | 46.200 | 200 | 150 |
| 28 | 4.830 | 17 | 57.960 | 224 | 224 |
| 32 | 6.410 | 13 | 76.920 | 256 | 256 |
Correct Bending Codes can save on Steel Costs
If you take two lengths of steel and bend one of them using the correct ACI bend radius (as shown in the table above) and the other with a more acute bend radius, the ACI bar will be shorter. While the amount of steel saved on one length may be small, if applied throughout a project, the saving is significant.
Bar Bending Mandrels for Coated Rebars
Procoat has a comprehensive stock of Nylotron mandrels to use with epoxy-coated rebars. Nylotron is a hardwearing material that will not damage the coating when used in the bar bending process.
Resources
- Quality policy statement
- Certificate of PVC coating tie wire specification
- Two-part epoxy touch-up kit for fusion bunded epoxy coating rebars
- Two-part touch-tp kit for fusion bunded epoxy coating rebars
