How to Coat Steel Media

Application Summary

The following information is intended as a guideline for the coating of steel substrates where the end use requires a high performance exterior coating systems. Intended end use markets would include light poles, commercial industrial equipment, and agricultural implements.

Primer Description and Powder Characteristics
Product Type: Epoxy Based Powder Coat Primer
Product Code: PT-ES49-ES09 (Or Equivalent)
Particle Size: d(0.5) 36 – 44um
Storage Temp: Do Not Exceed 80F
Description: ATP AG M Gray Epoxy Primer
Specific Gravity: 1.8 +- .02
Substrates: CRS, HRS, Aluminum, HDG, Galvanneal
Film Thickness Range: 2-7 mils
Test Substrate: Unpolished CRS w/Iron Phosphate
Film Characteristics – Internal QC PT Test Reference ASTM Test for Specifications    
60 Deg Gloss: PT-310.080 D523 50 +/- 5 Units
Pencil Hardness: PT-310.110 D3363 2H  
Adhesion (Crosshatch): PT-310.090 D3359-B PASS  
Flexibility (Conical Mandrel): PTL-310.210 D522 1/8 PASS @ 2.5 mils.
Direct Impact: PTL-310.060 D2794 120 min. in lbs. @ 2.5 mils
Reverse Impact: PTL-310.060 D2794 120 min. in lbs. @ 2.5 mils
Environmental Performance Characteristics PT Test Reference ASTM Test for specifications    
Solvent Rub: PT-310.070 (90/10)   50 Double Rubs Softens, Recovers with Slight Loss of Gloss
Salt Spray: PTL-310.310 D1654 >= 2000 Hours Steel Substrate – Blast
Salt Spray: PTL-310.310 D1654 >= 3000 Hours Steel Substrate – Blast and Phosphate
Chip Resistance   D3170 5A ATP Polyester
QUV: PTL-310.320 G154 Not Applicable Not UV Resistant – Requires Topcoat
Humidity:   D2247 1000 Hours + No Blistering, or Discoloration
PENTABOND TGIC Polyester Topcoat – AAMA 2604
Film Characteristics – Internal QC PT Test Reference ASTM Test for specifications    
60 Deg Gloss: PT-310.080 D523 30 - 90 Units
Pencil Hardness: PT-310.110 D3363 H – 2H  
Adhesion (Crosshatch): PT-310.090 D3359-B PASS  
Flexibility (Conical Mandrel): PTL-310.210 D522 1/8 PASS @ 2.5 mils.
Direct Impact: PTL-310.060 D2794 80 min. in lbs. @ 2.0 mils
Reverse Impact: PTL-310.060 D2794 80 min. in lbs. @ 2.0 mils
Test Substrate: Unpolished CRS w/Iron Phosphate        
Environmental Performance Characteristics PT Test Reference ASTM Test for specifications    
Solvent Rub: PCI #8 Reagent B   50 Double Rubs Softens, Recovers with Slight Loss of Gloss
Salt Spray: PTL-310.310 D1654 1000 Hours Typical CRS Iron Phos wSealer
Salt Spray: PTL-310.310 D1654 3000 Hours Typical Shot Blast Steel + ATP Primer + Pentabond
QUV: PTL-310.320 G154 2500 Hours Typical less than 50% loss in gloss
Humidity:   D2247 1000 Hours Typical No Blistering, or Discoloration

Substrate: Mild Steel and Cast Iron

The objective is to remove any mill scale and soils. If mill scale is not removed, the powder coating will bond to this strata and subsequently field failures will result with dis-bondment between the scale and underlying substrate. Any soils that are not removed will result in poor adhesion andor potential boiling of material which will result in a discontinuous coating film.

Step 1: Blast using a media that will result in a target 1.5 – 2.5 mil surface profile. SSPC SP7 Brush Off Blast Cleaning Minimum.

Step 2: Grinding of Surface Defects. Any remaining surface defects should be ground and the immediate area air blasted.

Step 3: Final inspection to be completed and approved by a trained operator. A suitable surface profile gauge should be used periodically to insure an appropriate surface profile is achieved.

Note: Any additional cleaning and conversion coating after surface profiling is acceptable and encouraged. For additional guidelines, please contact either your chemical pre-treatment andor pre-treatment supplier.

Application Parameters

Application of Primer: Please refer to the link "How to determine powder coating curing". This document details the proper application and cure determination in order to insure maximum inter-coat adhesion between the primer and topcoat.

Application of Topcoat: The topcoat should be applied immediately after the priming process is completed. For optimal transfer of powder topcoat to primer and substrate, part temperature should be above ambient and below 200F. Once primer is applied, any delay in topcoat application may result in surface contamination of primer film that could result in defects of topcoat. The Cure Curve chart below should be used in order to achieve the desired properties of the topcoat applied. All PTI Pentabond topcoats follow the parameters outlined below. Final cure testing of the topcoat needs to be performed using the PCI #8 test method. This is a destructive test method so an inconspicuous spot shall be selected.

Cure Curve – Substrate Temperature  
HANDLING Do not use near sources of ignition, spark or open flame.
  Store in dry area below 80 °F away from all sources of heat.
PRECAUTIONS Provide adequate dust control and use approved dust mask.
  Avoid skin contact. Wash with soap and water if contact occurs.
  Use only in well ventilated areas. Wear proper eye protection.

Cleaning

Surface cleaning should be accomplished using non-abrasive cloths or brushes in conjunction with warm water and a mild detergent. For removal of heavy deposits of salt, a citric acid cleaner may be used. A citric acid concentration of 10% should not be exceeded. For removing grease, oil, or other hydrocarbon deposits, the use of mineral spirits is suggested. Stronger solvents should not be used.

After any cleaning, the item should be thoroughly rinsed with warm water.

Repairing – Field

Surface preparation will depend on the degree of damage to the coated item.

For cases where the damage has not penetrated to the substrate, a medium-fine grit sand paper should be used to scuff the surface prior to priming. A high quality air dry surface primer should be applied, followed by an air dry topcoat matched to the color of the original coating.

For cases where the damage has penetrated to the substrate, a wire brush should be used to remove any remaining loose film and abrasion of the substrate should be completed.Use a medium-fine grit sand paper for final prep. Priming and top-coating should be prepared.

Note: Performance of the field repair in most cases will not be equal to the original coating system. Specifically, unequal fading of the repaired section compared to the original coating system should be expected, along with decreased corrosion resistance. The higher the quality repair paint, the better.