Highlights
- What is HR Sheet?
- Cleaning HR Sheets
- Industrial Racking System
- Importance of Iron phosphating HR Sheets
- CAS No.s of Raw Materials of Iron phosphating chemicals
- Formulations of Iron phosphating
- Case Studies
- Formulation of Descaling Chemicals
- Trouble shooting
What is HR Sheet?
Importance of Two Stage Iron Phosphating
Two-stage iron phosphating on HR (Hot Rolled) sheets is generally used to improve coating performance because HR sheets have a heavier mill scale, more rolling oil residues, and a rougher oxide layer compared to CR sheets. The main reasons are:
1. Enhanced Cleaning & Activation
- The first phosphating stage acts mainly on heavy oxide removal, surface activation, and initial phosphate deposition.
- HR sheets often have stubborn oxides and embedded oil contaminants; one pass of phosphating may not ensure uniform crystal growth.
- The first stage helps dissolve remaining mill scale particles and forms a thin, porous iron phosphate film that improves wetting for the second stage.
2. Improved Coating Weight & Uniformity
- The second phosphating stage re-phosphates the surface, ensuring more uniform crystal size and coating weight.
- This stage fills in gaps left from the first pass, producing a continuous phosphate layer with improved adhesion properties.
3. Better Paint Adhesion & Corrosion Resistance
- Double-stage phosphating increases coating coverage, reduces bare metal spots, and gives a denser phosphate film.
- This enhances both corrosion protection and paint adhesion in post-coating performance tests.
4. Oil Content Control Between Stages
- The first stage tolerates higher oil content (max 4 g/L), while the second stage runs cleaner (max 2 g/L).
- This prevents oil carryover into final rinses and ensures the last phosphate layer is clean and uniform.
5. Process Stability for High-Volume Lines
- In automotive and appliance finishing lines, two-stage phosphating ensures consistent results even when incoming HR sheet quality varies.
- It allows each stage to run at optimal parameters without overloading a single bath.
Below are practical, supplier-agnostic concentrate formulations that are functionally equivalent to the products in your sequence. Use them as house-brand substitutes and blend with DI/RO water under good ventilation. Ranges are wt% of the concentrate; working bath setpoints match your sheet (5.0% for the iron-phosphate, 0.2% for conditioner, 0.1–0.2% for additive).
A) Iron-phosphate cleaner–coater
Purpose: Clean HR scale/oils and form an iron-phosphate conversion layer.
Concentrate formula (wt%)
- Phosphoric acid (85%) …… 38–42
- Sodium dihydrogen phosphate (NaH2PO4·H2O) …… 6–9
- Oxidation accelerator (choose ONE system)
• Sodium nitrite …… 3–5 or
• Sodium chlorate …… 1.5–3 or
• “Eco” option: Sodium molybdate dihydrate …… 0.3–0.6 + Hydrogen peroxide (35%) …… 3–5 - Low-foam nonionic surfactants (EO/PO type) …… 6–10
- Co-solvent (PNP/BDG glycol ether) …… 4–7
- Sequestrant (gluconic acid / sodium gluconate) …… 1–2
- Corrosion inhibitor (benzotriazole for mixed metals, optional) …… 0.2–0.4
- Defoamer (silicone-free) …… 0.1–0.3
- DI/RO water …… balance to 100
Working bath (per your spec): 5.0% v/v concentrate, 40–50 °C, pH 4.5–5.7, TA 7–10.5 mL, Alk. ratio < 2.5.
B) Surface conditioner / grain refiner
Purpose: Seed the steel with fine nuclei so the phosphate film grows uniformly and densely on HR surfaces.
Concentrate formula (wt%)
- Phosphoric acid (85%) …… 12–18
- Titanium(IV) source (as Ti, from titanyl sulfate or TiCl4 neutralized to titanyl phosphate) …… 3–5 (≈10–16% as Ti-salt)
- Sodium dihydrogen phosphate …… 3–6
- Dispersant (polyacrylate, 45%) …… 0.4–0.8
- Wetting agent (very low-foam nonionic) …… 0.1–0.3
- DI/RO water …… balance to 100
Working addition: 0.20% v/v into the phosphate stage (or as a separate pre-dip at 0.3–0.5% v/v, ambient–35 °C, pH 4.0–4.6). In your layout it’s dosed into the Fe-phos bath at 0.2%.
C) Bath additive / accelerator & pH-ratio controller
Purpose: Maintain coating speed and crystal refinement; trim TA/FA and keep alk. ratio within limit as soils vary.
Choose one formulation family based on your EHS policy:
C1. Nitrite/Nitrate accelerator (classic)
- Sodium nitrite …… 38–45
- Sodium nitrate …… 6–10
- Sodium dihydrogen phosphate …… 6–8
- Buffer (boric acid or citrate) …… 1–2
- DI/RO water …… balance
Working addition: 0.10–0.20% v/v to the Fe-phos bath; dose to maintain TA 7–10.5 mL and coating appearance.
C2. Molybdate “nitrite-free” accelerator (eco-preferred)
- Sodium molybdate dihydrate …… 22–28
- Sodium nitrate (activator) …… 5–8 (omit if fully nitrite/nitrate-free required)
- Sodium dihydrogen phosphate …… 6–8
- Stabilizer (tartaric/citric) …… 1–2
- DI/RO water …… balance
Working addition: 0.10–0.20% v/v (same control targets).
C3. TA/FA ratio booster (alkaline trim, optional)
- Sodium hydroxide (50%) …… 18–24
- Triethanolamine …… 6–10
- Sodium phosphate (tribasic) …… 4–7
- DI/RO water …… balance
Use: Small, metered shots only when Alk. Ratio drifts low due to drag-in acids; verify pH stays within 4.5–5.7.
Make-up examples (for quick use)
1,000 L Iron-phosphate bath (Stage-1 or Stage-2):
- Product A concentrate …… 50 L (5.0% v/v)
- Product B concentrate …… 2 L (0.20% v/v)
- Product C concentrate …… 1–2 L (0.10–0.20% v/v)
- Fill with water to 1,000 L; heat to 40–50 °C; check pH & TA before production.
Control & notes for HR sheets
- HR incoming soils: keep oil in bath < 4 g/L for Stage-1 and < 2 g/L for Stage-2; skim/overflow as in your sheet.
- Sludge: purge bottoms weekly; consider polymer floc for clarifier.
- Targets: continuous, fine, grey-iridescent phosphate; no smut or bare spots.
- Compatibility: remove fluoride if no Al/Zn in mix; keep nitrite-bearing systems out of oxidizer storage.
CAS No.s of Raw Materials
Acids & Phosphates
- Phosphoric acid (85%) → CAS 7664-38-2
- Sodium dihydrogen phosphate (NaH₂PO₄·H₂O / anhydrous) → CAS 7558-80-7 (anhydrous) / 10049-21-5 (monohydrate)
- Sodium phosphate, tribasic (Na₃PO₄) → CAS 7601-54-9
Oxidizers / Accelerators
- Sodium nitrite (NaNO₂) → CAS 7632-00-0
- Sodium nitrate (NaNO₃) → CAS 7631-99-4
- Sodium chlorate (NaClO₃) → CAS 7775-09-9
- Sodium molybdate dihydrate (Na₂MoO₄·2H₂O) → CAS 10102-40-6
- Hydrogen peroxide (35%) → CAS 7722-84-1
Surfactants & Solvents
- Non-ionic surfactants (ethoxylated alcohols, EO/PO types) → General CAS 68439-46-3 (C₉-C₁₁ alcohols, ethoxylated)
- Dipropylene glycol monomethyl ether (DPGME) → CAS 34590-94-8
- Butyl diglycol (diethylene glycol monobutyl ether) → CAS 112-34-5
- Propylene glycol (for inhibitor carrier) → CAS 57-55-6
Sequestrants / Dispersants
- Sodium gluconate → CAS 527-07-1
- Gluconic acid → CAS 526-95-4
- Polyacrylate dispersant (typical sodium polyacrylate) → CAS 9003-04-7
- Citric acid (anhydrous) → CAS 77-92-9
- Tartaric acid → CAS 87-69-4
Corrosion Inhibitors
- Benzotriazole (BTA) → CAS 95-14-7
- Tolyltriazole (TTA) → CAS 29385-43-1
Alkaline Adjusters
- Sodium hydroxide (NaOH) → CAS 1310-73-2
- Sodium carbonate (Na₂CO₃) → CAS 497-19-8
- Triethanolamine (TEA) → CAS 102-71-6
Miscellaneous
- Boric acid (H₃BO₃) → CAS 10043-35-3
- Silicone-free defoamer (typical EO/PO block copolymer) → CAS varies by supplier (common: 9003-11-6)
✅ This covers all major raw materials used in iron phosphating cleaner–coater, conditioner, and accelerator formulations.
Formulation Cards
Here’s the updated version with “Formulation Card” replacing “Batch Card” everywhere.
Formulation Card – Product A
(Equivalent to BONDERITE M-FE 1070 – Iron Phosphate Cleaner-Coater)
Purpose: Clean HR mill scale/oils and form iron phosphate layer.
| Ingredient | % in Conc. | 100 kg Batch | 200 kg Batch |
|---|---|---|---|
| Phosphoric acid (85%) | 40.0 | 40.0 kg | 80.0 kg |
| Sodium dihydrogen phosphate | 7.5 | 7.5 kg | 15.0 kg |
| Sodium nitrite or sodium chlorate or sodium molybdate + H₂O₂ (pick one system) | 4.0 (total active) | 4.0 kg | 8.0 kg |
| Low-foam nonionic surfactant | 8.0 | 8.0 kg | 16.0 kg |
| Glycol ether co-solvent | 5.0 | 5.0 kg | 10.0 kg |
| Sodium gluconate | 1.5 | 1.5 kg | 3.0 kg |
| Benzotriazole (optional) | 0.3 | 0.3 kg | 0.6 kg |
| Defoamer (silicone-free) | 0.2 | 0.2 kg | 0.4 kg |
| DI/RO water | Bal. | 33.5 kg | 66.0 kg |
Charging Order:
- In HDPE-lined tank, add 70% of total water.
- Start slow agitation.
- Add sodium dihydrogen phosphate → dissolve fully.
- Add chosen accelerator salts (NaNO₂ / NaClO₃ / Na₂MoO₄).
- Slowly add phosphoric acid (PPE + acid-resistant pump).
- Add glycol ether, then surfactant, then gluconate.
- Add corrosion inhibitor if used.
- Top up with remaining water, add defoamer last.
- Mix for 30 min, cool to ambient, filter through 100 µm bag.
Formulation Card – Product B
(Equivalent to BONDERITE L-FM 0503 – Surface Conditioner / Grain Refiner)
| Ingredient | % in Conc. | 100 kg Batch | 200 kg Batch |
|---|---|---|---|
| Phosphoric acid (85%) | 15.0 | 15.0 kg | 30.0 kg |
| Titanium source (as titanyl phosphate slurry or TiCl₄ pre-neutralized) | 4.0 | 4.0 kg | 8.0 kg |
| Sodium dihydrogen phosphate | 4.5 | 4.5 kg | 9.0 kg |
| Polyacrylate dispersant (45% solids) | 0.6 | 0.6 kg | 1.2 kg |
| Low-foam nonionic surfactant | 0.2 | 0.2 kg | 0.4 kg |
| DI/RO water | Bal. | 75.7 kg | 151.4 kg |
Charging Order:
- Add 80% water to tank.
- Add sodium dihydrogen phosphate; dissolve.
- Add dispersant; mix 5 min.
- Add titanium source slowly to avoid lumping; keep pH ~2–3 during addition.
- Add phosphoric acid.
- Add surfactant, top up with water, mix 20 min.
Formulation Card – Product C1 (Nitrite/Nitrate Accelerator)
(Equivalent to BONDERITE M-AD 565)
| Ingredient | % in Conc. | 100 kg Batch | 200 kg Batch |
|---|---|---|---|
| Sodium nitrite | 42.0 | 42.0 kg | 84.0 kg |
| Sodium nitrate | 8.0 | 8.0 kg | 16.0 kg |
| Sodium dihydrogen phosphate | 7.0 | 7.0 kg | 14.0 kg |
| Boric acid or sodium citrate | 1.5 | 1.5 kg | 3.0 kg |
| DI/RO water | Bal. | 41.5 kg | 83.0 kg |
Charging Order:
- Add 60% water to tank.
- Add sodium dihydrogen phosphate; dissolve fully.
- Add sodium nitrate; dissolve.
- Add sodium nitrite last (avoid overheating, no strong oxidizers nearby).
- Add buffer, top up with water, mix 20 min.
Formulation Card – Product C2 (Molybdate Accelerator – Nitrite-Free Option)
| Ingredient | % in Conc. | 100 kg Batch | 200 kg Batch |
|---|---|---|---|
| Sodium molybdate dihydrate | 25.0 | 25.0 kg | 50.0 kg |
| Sodium nitrate (optional) | 6.0 | 6.0 kg | 12.0 kg |
| Sodium dihydrogen phosphate | 7.0 | 7.0 kg | 14.0 kg |
| Citric acid (anhydrous) | 1.5 | 1.5 kg | 3.0 kg |
| DI/RO water | Bal. | 60.5 kg | 121.0 kg |
Charging Order: Same as C1, but molybdate goes in after phosphate.
Safety Notes for All Formulation Cards
- PPE: acid-resistant gloves, face shield, apron, safety boots.
- Add acids to water, never water to acids.
- Avoid mixing nitrites with acids outside controlled bath conditions.
- Store concentrates in cool, ventilated, corrosion-resistant rooms.
- Label all drums with chemical composition, hazard symbols, formulation card number, batch number, and date.
Case Studies
Removing Black oxide from HR Sheets
The dark layer you see on your HR sheet is mill scale (a dense iron oxide layer: FeO, Fe₃O₄, Fe₂O₃) formed during hot rolling.
It is chemically more resistant than rust, so normal iron phosphating won’t fully remove it.
Methods to Completely Remove the Dark Oxide Layer
1. Acid Pickling (Most Effective for Full Removal)
- Recommended chemicals:
- Hydrochloric acid (HCl) 12–15% with inhibitor (for fast removal)
- Sulfuric acid (H₂SO₄) 10–12% with inhibitor (slower but leaves a more uniform matte finish)
- Add corrosion inhibitor (amine-based) to reduce base metal attack.
- Operating parameters:
- HCl: Ambient to 40 °C, 3–6 min immersion
- H₂SO₄: 50–60 °C, 5–10 min immersion
- Post-treatment: Rinse thoroughly, then go to phosphating immediately to avoid flash rust.
2. Alkaline Descaling (for Cleaner, Oil-Free Mill Scale Before Acid)
- Use alkaline cleaner with sodium hydroxide + sodium gluconate + oxidizing salts (NaNO₂/NaClO₃) at 60–80 °C for 5–10 min.
- Loosens scale and oil before acid pickling, reducing acid consumption.
3. Mechanical Methods (Optional Pre-Step)
- Grit/sand blasting or shot blasting to near-white metal (Sa 2.5) standard.
- Good for heavy, adherent scale but requires dust control and extra equipment.
4. Combination Process for HR Sheets (Best Practice in Coil/Sheet Pretreatment)
- Hot alkaline degreasing/descaling → removes oils & softens scale
- Acid pickling (HCl or H₂SO₄) → completely strips the oxide layer
- Water rinse
- Neutralizing rinse (weak Na₂CO₃) → stops acid carryover
- Iron or zinc phosphating → coating for paint adhesion
⚠ Important Notes:
- If you only run iron phosphating directly on HR sheet without mill scale removal, you will always get patchy coating like in your image.
- The scale layer blocks uniform phosphate crystal formation.
- Even extended phosphating time will not dissolve heavy Fe₃O₄.
- Acid pickling before phosphating is the most reliable industrial solution.
Formulation Card – Pickle-HCl (Mill-scale removal for HR sheets)
Purpose: Rapid removal of FeO/Fe₃O₄/Fe₂O₃ mill scale prior to phosphating.
Working bath (1,000 L make-up)
- Hydrochloric acid, 32% w/w: 450 L → gives ~14–15% HCl (w/w)
- Inhibitor concentrate (see below): 10–15 L (1.0–1.5% v/v)
- Non-ionic low-foam wetter (if not in inhibitor): 2–3 L
- Deionized/soft water: Top up to 1,000 L
Operating window
- Temp: 25–40 °C
- Time: 2–6 min (adjust to scale thickness)
- Iron (Fe²⁺): ≤ 80 g/L (bleed/replace above this)
- Free acid (as % HCl): 12–16%
- Agitation: mild air or pump eductor; avoid splashing.
Rinse sequence after pickling: Water rinse → weak alkaline neutralizer (0.5–1.0% Na₂CO₃, 30–60 s) → water rinse → phosphating.
Formulation Card – Pickle-H₂SO₄ (Matte finish, lower acid mist)
Working bath (1,000 L)
- Sulfuric acid, 98%: 120–140 L → gives 10–12% w/w H₂SO₄
- Inhibitor concentrate: 10–15 L (1.0–1.5% v/v)
- Non-ionic low-foam wetter (if not in inhibitor): 2–3 L
- Deionized/soft water: Top up to 1,000 L
Operating window
- Temp: 50–60 °C
- Time: 5–10 min
- Total iron: ≤ 60 g/L
- Free acid (as % H₂SO₄): 9–12%
Rinse/neutralize: Same as for HCl.
Formulation Card – Inhibitor Concentrate (for either pickle)
Purpose: Suppress base-metal attack, undercutting, and acid fume; improve surface evenness.
100 kg concentrate
- Quaternary ammonium/imidazoline blend (acid inhibitor actives) …… 35.0 kg
- Thiourea-free sulfur-containing inhibitor (e.g., mercapto-modified polymer) …… 5.0 kg
- Propargyl alcohol or acetylenic diol inhibitor …… 2.0 kg
- Non-ionic low-foam surfactant (EO/PO) …… 8.0 kg
- Corrosion inhibitor booster (tolyltriazole) …… 0.5 kg
- Defoamer (silicone-free) …… 0.3 kg
- Solvent/balancer (propylene glycol or BDG) …… 10.0 kg
- DI water …… 39.2 kg
Dose: 1.0–1.5% v/v of pickle bath at make-up; maintain at 0.8–1.2% via titration or by experience (add 0.2–0.3 L per 1000 L after every 1–2 t of steel processed).
Formulation Card – Alkaline Descaler/Cleaner (recommended pre-step)
1000 L working bath
- NaOH (flakes) …… 30–40 kg (3–4% w/w)
- Sodium gluconate …… 5–8 kg
- Sodium carbonate …… 5–8 kg
- Oxidizing salt (sodium nitrite or sodium chlorate) …… 2–4 kg
- Low-foam surfactant …… 3–5 L
- 60–80 °C, 5–10 min, spray/immersion → water rinse → proceed to pickling.
Control & QA
HCl bath titration (quick):
- Pipette 10 mL bath + dilute to 100 mL.
- Titrate with 1.0 N NaOH to methyl orange end-point.
- % HCl ≈ (mL NaOH × 0.365). Keep 12–16%.
H₂SO₄ bath titration:
- Pipette 10 mL bath + 100 mL water.
- Titrate with 1.0 N NaOH to phenolphthalein.
- % H₂SO₄ ≈ (mL NaOH × 0.490). Keep 9–12%.
Iron loading (optional spot check): Use phenanthroline kit or ICP; keep within limits above.
Acceptance after pickling (visual):
- Uniform light-grey matte metal, no black islands.
- Water break-free within 3–5 s.
- If patchy black persists → increase time 1–2 min, raise temp within window, or refresh bath (Fe²⁺ too high).
Integration with your line
- Alkaline descaler → water rinse
- Pickle-HCl or Pickle-H₂SO₄ → water rinse
- Neutralizer (0.5–1.0% Na₂CO₃, 30–60 s) → water rinse
- Iron phosphate Stage-1 (5.0% @ 40–50 °C) + conditioner/additive per your spec
- Iron phosphate Stage-2 (5.0% @ 40–50 °C)
- Rinse → DM rinse → Dry → Paint
Safety & Maintenance
- Add acid to water, never water to acid.
- Local exhaust for acid mists; acid-proof floors, bunding.
- Use amine-based inhibitor, never mix nitrites directly into acid pickles.
- Skim oils before pickling; maintain oil traps to reduce acid consumption.
- Sludge/spent pickle: neutralize to pH 8–9; precipitate Fe with lime + polymer; dispose as per local regulations.
Troubleshooting (typical causes of residual dark oxide)
- Bath too weak / Fe²⁺ high → boost acid or partial dump; maintain bleed-and-feed.
- Short time/low temp → increase within window.
- Heavy scale → do alkaline descaler first or brief shot-blast.
- Under-inhibited bath (base metal etch marks) → raise inhibitor to 1.2–1.5% v/v.
- Re-blackening after rinse → skip delay; neutralize and phosphate immediately.
SOP for Iron phosphating two stage baths and control parameters
Here is a detailed Standard Operating Procedure (SOP) for Iron Phosphating – Stage 1 & Stage 2 on HR Sheets, aligned with best practice and your earlier formulations.
SOP – Iron Phosphating Line (Stage 1 & Stage 2)
1. Purpose
To clean, deoxidize, and coat HR steel surfaces with a uniform iron phosphate layer for improved paint adhesion and corrosion resistance.
2. Scope
Applies to all HR sheet phosphating lines operating with two-stage iron phosphate process.
3. Responsibilities
- Operator: Bath preparation, daily checks, and recording parameters.
- Supervisor: Weekly monitoring, replenishment, sludge removal.
- EHS Officer: Compliance with safety & environmental regulations.
4. Chemicals Required
- Iron phosphating concentrate (Product A – M-FE equivalent).
- Surface conditioner / grain refiner (Product B – L-FM equivalent).
- Bath additive / accelerator (Product C – M-AD equivalent).
- DI/RO water for make-up and rinsing.
5. Equipment
- HDPE / acid-resistant tanks with heating coil & recirculation pump.
- Filtration system (bag filter/overflow).
- Thermometer, pH meter, conductivity meter.
- Titration setup for TA/FA control.
6. Bath Make-Up
Stage 1 Bath (Cleaner-Coater with Conditioner & Accelerator)
- Fill tank with 70% DI water.
- Add 5.0% v/v Iron Phosphating Concentrate while stirring.
- Add 0.20% v/v Conditioner.
- Add 0.10–0.20% v/v Accelerator.
- Top up with DI water to final volume.
- Heat to 40–50 °C and circulate 30 min before production.
Stage 2 Bath (Re-phosphating for uniform coating)
- Same sequence as Stage 1, but fresh bath or overflow replenishment system.
- Maintain 5.0% v/v Iron Phosphating Concentrate.
- Lower oil tolerance: max 2 g/L carry-over.
- Conditioner optional (0.1–0.2%), depending on bath balance.
7. Operating Parameters
| Parameter | Stage 1 | Stage 2 |
|---|---|---|
| Concentrate dosage | 5.0% v/v | 5.0% v/v |
| Conditioner dosage | 0.20% v/v | 0.10–0.20% v/v |
| Accelerator dosage | 0.10–0.20% v/v | 0.10–0.20% v/v |
| Temperature | 40–50 °C | 40–50 °C |
| pH range | 4.5 – 5.7 | 4.5 – 5.7 |
| Total Acid (TA) | 7.0 – 10.5 mL | 7.0 – 10.5 mL |
| Free Acid (FA) | 2.0 – 4.0 mL | 2.0 – 4.0 mL |
| Alkali ratio (TA/FA) | ≤ 2.5 | ≤ 2.5 |
| Treatment time | 2–3 min | 2–3 min |
| Oil tolerance | ≤ 4 g/L | ≤ 2 g/L |
8. Bath Control & Testing
Daily (Operator):
- Measure bath temperature, pH, TA, FA.
- Oil level check (visual scum, oil trap).
- Record in Daily Log Sheet.
Weekly (Supervisor):
- Fe²⁺ build-up check (≤ 5 g/L for stability).
- Sludge removal from tank bottom.
- Rinse water conductivity check (≤ 50 µS/cm).
Monthly (EHS/QA):
- Coating weight measurement: 0.3–0.7 g/m².
- Cross-hatch adhesion & salt spray sample testing.
9. Acceptance Criteria
- Surface: uniform grey/iridescent phosphate film.
- No black oxide patches (scale should be pickled prior).
- Water break test: surface remains wet for >10 seconds.
10. Safety
- Wear PPE (acid-resistant gloves, apron, face shield).
- Local exhaust ON during operation.
- Acid handling: always add acid to water.
- Emergency eyewash & shower near tanks.
11. Environmental Controls
- Spent bath → neutralize to pH 7–9 before discharge.
- Sludge → dewater, store in lined containers, dispose via authorized recycler.
- Maintain rinse overflow and ETP performance logs.
12. Troubleshooting
| Problem | Possible Cause | Corrective Action |
|---|---|---|
| Patchy coating | High oil, Fe²⁺ > limit | Skim oils, bleed bath |
| Low coating weight | TA/FA too low | Add concentrate |
| Powdery film | FA too high | Add alkali trim / conditioner |
| Rust spots after rinse | Poor neutralization or delayed drying | Improve rinsing, hot air dry |
Polyacrylyate dispersants
Polyacrylate dispersants play a functional role in iron phosphating baths by stabilizing the system and improving coating quality. Their key roles are:
1. Suspension of Sludge and Precipitate
- During iron phosphating, insoluble phosphates and iron salts tend to precipitate, forming sludge.
- Polyacrylates adsorb on the surface of these particles and keep them dispersed, preventing agglomeration and hard sludge deposition at the bottom of the tank.
- This reduces the need for frequent bath cleaning and prolongs bath life.
2. Prevention of Scale and Stains
- Calcium, magnesium, and other hardness ions in water can form insoluble salts that interfere with phosphating.
- Polyacrylates act as antiscalants, binding with hardness ions and preventing their deposition.
- This ensures a uniform phosphate coating without white stains or patchiness.
3. Improved Coating Uniformity
- By dispersing fines and keeping the bath clear, polyacrylates minimize particle settling on metal surfaces.
- This helps achieve a more consistent, fine-grained phosphate coating with better adhesion for subsequent painting.
4. Bath Stability and Efficiency
- They act as threshold inhibitors, meaning even at low concentrations, they can prevent precipitation of iron and phosphate salts.
- This allows the bath to operate efficiently over a longer period without major chemical imbalance.
5. Environmental and Operational Advantage
- Reduce chemical consumption by lowering sludge formation.
- Improve first-pass yield, lowering rework and rejects.
- Simplify effluent treatment because dispersed sludge is easier to handle than hard scale.
Summary:
In iron phosphating, polyacrylate dispersants act as sludge controllers, antiscalants, and coating stabilizers, ensuring a clean bath, extended bath life, and fine, uniform phosphate layers that improve paint adhesion and corrosion resistance.
Here are some polyacrylate‑based dispersant brands and products available in India, particularly useful in contexts like iron phosphating, water treatment, coatings, etc.:
Notable Brands & Products in India
- Alstadine Series – A 3‑in‑1 metal treatment chemical from Chemtex that handles de‑rusting, degreasing, and iron phosphating in one formulation
- ZEELCHEM™ 1000 (Polyacrylic Acid) – Marketed as a scale inhibitor and dispersant for circulating cooling systems, including applications in iron & steel factories .
- Vintreat‑PAI (Sodium Polyacrylate Mixture) – Supplied by Vinati Organics, this polyacrylate dispersant is used across paint, paper, and water treatment industries for dispersion, scale inhibition, and sludge control .
- PAAS (Sodium Polyacrylate) from RSD Polymers Pvt. Ltd. – Available in various molecular weights and specialized forms (for coatings, ceramics), acting as dispersing/deflocculating agents, grinding aids, and viscosity modifiers ).
- HydroDisperse Polymer Dispersant – Offered by RXMARINE, also known as a polyacrylate dispersant or phosphate stabilizer; used in cooling water systems, especially in phosphate‑based water treatments .
Summary Table
| Brand / Product | Supplier | Key Application Areas |
|---|---|---|
| Alstadine Series | Chemtex Speciality Ltd. | Metal pre-treatment (rust, degrease, phosphating) |
| ZEELCHEM™ 1000 | ZEEL Product Online | Scale inhibition & dispersion in industrial systems |
| Vintreat-PAI | Vinati Organics | Paints, paper, water treatment dispersant/scale inhibitor |
| PAAS (Sodium Polyacrylate) | RSD Polymers Pvt. Ltd. | Coatings, ceramics, deflocculation, pigment dispersion |
| HydroDisperse Dispersant | RXMARINE Chemical | Cooling-water, phosphate stabilization, mineral dispersion |
References
References
- Henkel Surface Technologies – Bonderite® Technical Data Sheets and Process Guidelines for Iron Phosphating of Steel (Henkel AG & Co. KGaA, Düsseldorf, Germany).
- Vermette, M., & Tremblay, R. (2005). Phosphate Conversion Coatings: Principles, Applications, and Recent Developments. In: ASM Handbook, Volume 5: Surface Engineering. ASM International.
- Rausch, W. (1990). The Phosphating of Metals. Finishing Publications Ltd., Hertfordshire, UK.
- Bierwagen, G. P., & Tallman, D. E. (2008). “Conversion Coatings for Ferrous Metals” in Paint and Coating Testing Manual (ASTM Manual Series: MNL17). ASTM International.
- Sharma, S., & Sharma, A. (2015). “Advances in Phosphate Coating Technology for Steel Sheet Pretreatment.” Journal of Surface Science and Technology, 31(1-2), 1–20.
- ISO 9717:2017 – Metallic Coatings — Phosphate Conversion Coatings for Metals — Method of Specifying Requirements. International Organization for Standardization.
- TDS & Process Manual: Bonderite M-Fe and Bonderite L-FM Series, Henkel Adhesives.
