Dr E. Ramanathan PhD
Formula-1
Hot Dip Type Combined Degreasing + Derusting Concentrate Formula
Single-bath process for both oil removal and rust removal before trication phosphating
Formulation (Concentrate – by weight %)
| Ingredient | % w/w |
|---|---|
| Phosphoric acid (85%) | 35.0 |
| Sodium metasilicate (5H₂O) | 15.0 |
| Sodium carbonate | 10.0 |
| Non-ionic surfactant (NP-10 or equivalent) | 3.0 |
| Thiourea (acid inhibitor) | 0.5 |
| Benzotriazole (flash rust inhibitor) | 0.5 |
| Wetting agent (e.g., sodium lauryl sulfate) | 1.0 |
| Water (to make 100%) | 35.0 |
Usage Conditions
- Dilution: 10–15% in water
- Temperature: 50–60°C
- Time: 5–10 minutes (adjust for degree of contamination)
- Application: Dip or spray
- pH: 2.5–4.0
- Rinse thoroughly with water after treatment
Advantages
- Saves time and space by combining cleaning steps
- Removes both oil and rust in a single stage
- Prepares surface adequately for trication phosphate coating
- Minimizes process tank count
Formula-2
Low-Temperature & Spray-Optimized Combined Degreasing + Derusting Formula
Efficient at 30–45°C; suitable for spray and dip applications.
Concentrate Formula (by weight %)
| Ingredient | % w/w |
|---|---|
| Phosphoric acid (85%) | 25.0 |
| Citric acid (monohydrate) | 10.0 |
| Sodium metasilicate (5H₂O) | 15.0 |
| Sodium gluconate (chelating aid) | 5.0 |
| Non-ionic surfactant (low foam type) | 2.5 |
| Amphoteric surfactant (foam control) | 1.0 |
| Benzotriazole | 0.5 |
| Organic acid inhibitor (e.g., thiourea or proprietary) | 0.5 |
| Wetting agent (optional, SLS) | 0.5 |
| Water | 40.0 |
Usage Parameters
- Dilution: 10–12% in water
- Temperature: 35–45°C
- Spray pressure: 1.5–2.5 kg/cm²
- Time: 3–5 minutes (spray), 6–10 minutes (dip)
- pH: 3.0–4.5
- Rinse: Soft/RO water recommended
Features
- Functions efficiently at lower temperatures → energy saving
- Compatible with spray systems (low foam)
- Safer on sensitive steel parts
- Reduces flash rusting due to corrosion inhibitors
Comparison of these two formulae
Comparative Table: Combined Degreasing + Derusting Formulas
| Parameter | Standard Formula | Low-Temperature & Spray-Optimized Formula |
|---|---|---|
| Main Acids Used | Phosphoric acid | Phosphoric acid + Citric acid |
| Alkaline Builder | Sodium metasilicate + Sodium carbonate | Sodium metasilicate |
| Chelating Agent | None | Sodium gluconate |
| Inhibitors | Thiourea + Benzotriazole | Thiourea/BTA + organic inhibitor |
| Surfactant System | Non-ionic + Wetting agent (SLS) | Low-foam non-ionic + amphoteric + SLS (opt.) |
| Dilution for Use | 10–15% | 10–12% |
| Operating Temperature | 50–60°C | 35–45°C |
| Application Method | Dip or spray | Spray-optimized; also suitable for dip |
| Contact Time | 5–10 minutes | 3–5 min (spray), 6–10 min (dip) |
| pH (at use) | 2.5–4.0 | 3.0–4.5 |
| Foaming Behavior | Moderate foaming | Low-foam formulation |
| Rust Removal Efficiency | Strong (faster scale removal) | Moderate to good (gentler on surface) |
| Steel Safety (Flash Rusting) | Basic protection (benzotriazole) | Enhanced with dual inhibitors |
| Energy Consumption | Higher due to temperature | Lower |
| Recommended For | Heavily rusted/oily parts | Lighter rust/oil, continuous spray lines |
Tank Fabrication
Recommended Metal Components for Equipment Handling Derusting + Degreasing Chemicals (Citric/Phosphoric Based):
These materials must withstand acidic, chelating, and surfactant-rich environments at 30–60 °C.
1. Tank and Piping Materials
| Component | Recommended Material | Remarks |
|---|---|---|
| Tank body | PP (polypropylene), HDPE, or FRP lined MS | Best for acid + chelant resistance |
| SS316L (optional for cleanroom/high-grade use) | More expensive but durable; avoid SS304 in acidic mix | |
| Piping | PP, PVC, CPVC | Acid + temperature resistant |
| Teflon/PTFE (for small high-resistance sections) | For critical dosing lines |
2. Heating Coils (if used)
- Teflon-coated coils, Titanium, or Quartz
(Avoid copper or MS – will corrode rapidly in acidic media)
3. Agitators and Shafts
- PP-coated MS, SS316, or Hastelloy C (for long life)
(Avoid plain MS or aluminum)
4. Pumps
- Magnetic drive pumps with PP, PVDF, or Teflon internals
- Suitable for both circulation and spray systems
5. Spray Nozzles (for spray systems)
- PVDF, PP, PTFE, or ceramic-lined nozzles
- Resist acid + surfactant wear
6. Racks/Baskets (for components)
- PVC coated MS, SS316, or acid-resistant polymer frames
- Ensure good drainage and chemical resistance
Avoid
- MS, GI, SS304 (especially in presence of chelators like citric acid)
- Copper, brass, or aluminum components – severely attacked
Conclusion:
For long service life and corrosion-free operation, polymer-lined materials (PP/HDPE/PVDF) or SS316/FRP-lined structures are ideal. Design should consider thermal expansion, chemical resistance, and ease of maintenance.
Metal components to be coated
Metal Components That Can Be Cleaned Using the Combined Degreasing + Derusting Chemicals (Citric + Phosphoric Based)
These formulations are mildly acidic, chelating, and surfactant-rich, making them suitable for a wide range of ferrous and non-ferrous metals—especially when formulated with proper inhibitors.
✅ Suitable Metals for Cleaning
| Metal | Suitability | Notes |
|---|---|---|
| Mild Steel (MS) | ✔️ Highly suitable | Removes oil, rust, and mill scale without aggressive attack |
| Cast Iron | ✔️ Yes | Effective rust removal; use inhibitors to minimize surface pitting |
| Carbon Steel | ✔️ Yes | Efficient degreasing and derusting; post-treatment rinse needed |
| Stainless Steel (SS 304, 316) | ✔️ With care | Minimal rust removal; may show slight etching—rinse well after |
| Galvanized Steel (GI) | ✔️ With inhibitor | May react with phosphoric acid; use with ammonium bifluoride control |
| Aluminum (Pure or Alloy) | ⚠️ Limited | Citric acid is safe, but phosphoric acid may etch—use only with inhibitors |
| Zinc Coated Surfaces | ⚠️ Caution | Citric acid is better than phosphoric; test before large-scale use |
| Copper/Brass | ⚠️ Limited | Citric acid is safe in low concentration; phosphoric may cause staining |
| Nickel, Chrome plated | ⚠️ Not recommended | Surface may dull or get attacked over time |
❌ Not Recommended For
- Magnesium and its alloys – very reactive to acid
- Bare tin, cadmium, or lead surfaces – potential for chemical attack
- Anodized aluminum – surface finish may be damaged
Conclusion:
These cleaning chemicals are best suited for mild steel, carbon steel, and cast iron, and can be extended carefully to stainless steel and galvanized parts with proper formulation control. For non-ferrous or sensitive metals, consider diluted citric acid with corrosion inhibitors only.
