Coil Coating Effluent Guidelines | US EPA

Coil Coating Effluent Guidelines | US EPA

The Environmental Protection Agency (EPA) established the Coil Coating Effluent Guidelines and Standards (40 CFR Part 465) to regulate both direct and indirect dischargers, providing necessary measures for compliance. The guidelines are integrated into National Pollutant Discharge Elimination System (NPDES) permits for direct dischargers and into permits or other control mechanisms for indirect dischargers, as described in the Pretreatment Program.

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Understanding the Coil Coating Industry

Coil coating refers to the series of processing steps utilized in transforming a metal coil—a long strip of metal rolled into a coil—into a pre-painted coil suitable for various industrial applications. The primary materials involved include steel, galvanized steel, and aluminum, while minor applications extend to materials like brass and coated steels. The production of coated coils typically follows three core processes:

1. Cleaning to eliminate contaminants such as soil, oil, and corrosion.
2. Chemical conversion coating, which treats the metal surface with chromate, phosphate, or other complex oxide materials.
3. Application of and drying polymeric materials like paint.

Water Usage in the Process

Water plays a vital role throughout the coil coating processes. Cleaning operations often utilize water-based alkaline cleaners and occasionally acid pickling solutions to remove oxides and corrosion. After cleaning, rinsing the strip with water is standard, and most chemical conversion coating methods also depend on water solutions. Post-painting, the strip undergoes baking in an oven to dry the paint, followed by cooling with water to prevent damage to the organic coating. The characteristics of wastewater produced during the coil coating process can vary based on the base material and selected cleaning and conversion processes.

Major Pollutants of Concern

1. Toxic pollutants: including chromium, zinc, nickel, lead, copper, and cyanide.
2. Conventional pollutants: such as suspended solids, abnormal pH levels, and oil and grease.
3. Unconventional pollutants: including iron, aluminum, phosphorus, and fluoride.

Given the significant concentrations of toxic metals present, the sludges formed during wastewater treatment typically contain considerable amounts of these substances.

Canmaking Processes

The Canmaking Subcategory was integrated into regulations through a subsequent amendment addressing the manufacturing of shaped metal containers used in food and beverage storage. Seamed cans are primarily constructed from flat metal sheets formed into containers with seams that are either clinched or welded, while seamless cans are produced from single pieces of metal with top closures formed from sheet metal. By the last rulemaking, around 300 plants in the United States were dedicated to seamed can production.

Seamless cans, made through several forming methods, necessitate washing with water-based alkaline cleaners to eliminate oil lubrication before they can proceed to further processing.

Key Pollutants in Canmaking

1. Toxic metals: such as chromium and zinc.
2. Toxic organics: classified as total toxic organics (TTO).
3. Nonconventional pollutants: including aluminum, fluoride, and phosphorus.
4. Conventional pollutants: like oil and grease, total suspended solids (TSS), and abnormal pH levels.

Due to the presence of toxic metals, sludges from wastewater treatment in this sector also carry substantial toxic metal levels.

Currently, 88 of approximately 425 can manufacturing plants in the U.S. release wastewater before treatment.

Exclusions within Canmaking

The production of seamed and seamless cans from coated (e.g., coil coated) stock is excluded, as this process does not utilize oil and does not require washing following forming.

NAICS Classification

Coil coating and canmaking are categorized under the following NAICS codes:

• 3312: Metal Can Manufacturing
• 3328: Metal Coating, Engraving (excluding Jewelry and Silverware), and Allied Services for Manufacturers.

Further details on the coverage of the Coil Coating category can be found in the Applicability sections of 40 CFR Part 465.

Facilities Covered by Regulation

This regulation completes coil coating operations that are categorized as follows, based on base material:

1. Steel
2. Galvanized (including zinc-coated steel and brass)
3. Aluminum (and aluminum-coated steel)

Subpart D specifically addresses canmaking operations.

Guidance and Historical Rulemaking

Recent Amendments

Subpart D was added through a subsequent amendment to address various operational sectors.

Initial Rulemaking Overview

• Subparts A-C documents include:

  • Final Rule (December 1, ).
  • Development Document (November ).
  • Industry description, wastewater characterization, treatment technologies, regulatory compliance costs, and pollutant loadings for the finalized rule.
  • Proposed Rule (January 12, ).

Further Assistance

For more information regarding National Coil Coating Effluent Guidelines, please reach out to Erica Mason or call 202-566-.

What Are Coil and Can Coating?

Coil and can coating encompass the application of organic materials on rolled metal strips through a continuous process featuring cleaning, chemical pre-treatment, as well as the application of liquid paints or powder coatings followed by curing and lamination. The procedure includes twelve steps which enhance quality and efficiency.

Modern Coil Coating Steps

• Step 1: Mechanically stitching the strip to its predecessor.
• Step 2: Cleaning the strip.
• Step 3: Power brushing.
• Step 4: Surface treatment through chemical conversion.
• Step 5: Drying the strip.
• Step 6: Priming on one or both sides.
• Step 7: Curing in the oven.
• Step 8: Cooling the strip.
• Step 9: Coating the finish.
• Step 10: Second curing in the oven.
• Step 11: Cooling to room temperature.
• Step 12: Rewinding the coated coil.

Reasons to Utilize Coil and Can Coating

Traditionally, post-coating processes are expensive and time-consuming, often leading to environmental issues. Coil coating presents a continuous, highly automated process that efficiently coats metal coils, ensuring full surface coverage.

Applications of Coil and Can-Coated Materials

Pre-painted metals are widely utilized across various sectors including construction, appliances, and automotive parts, providing diverse application possibilities without losing coating quality. This technology offers sustainability, flexibility in design, and a significant advantage in various industrial applications.

Materials Used in Can and Coil Coatings

A combination of chemicals, including polyesters and laminating films, underpin the formulation of can and coil coatings, ensuring optimal performance and longevity.

Conclusion

The can and coil coating processes are advanced, leading to enhanced metal sheeting outcomes compared to traditional methods. Technologies like 2-Methyl-1,3-Propanediol (MPO) improve productivity, offering benefits in process handling and product quality. For detailed information on line 2 line coatings, please get in touch with our technical team at Gantrade to explore improved production efficiency and performance.