Reference cited in this section

7. D.B. Freeman, Phosphating and Metal Pre-Treatment, Industrial Press, Inc., 1986, p 76-77 Phosphate Coating Selection

Table 16 provides guidelines for choosing phosphate coatings based on application, coating weight requirements, and recommended process parameters.

Table 16 Process parameters for selected phosphate coatings

Coating type

Accelerator

Process type

Tank material

Coating weight

Operating conditions

Immersion

Spray

Time

Temperature

Time

Temperature

g/m2

oz/ft2 X 10-2

s

min

°C

°F

s

min

°C

Paint bonding applications

Iron phosphate

Chlorate

Stripline alkaline phosphate

Mild steel

0.2-0.5

0.070.16

8-20

6677

151171

8-20

6677

151171

Molybdate

Multimetal lightweight alkali metal phosphate

Mild steel

0.3-0.5

0.100.16

2-5

4070

104158

1-2

4060

104140

Chlorate

Lightweight iron phosphate

Mild steel

0.3-1.0

0.100.33

1

7075

158167

Nitrate (molybdate)

Combined cleaner/coater

Mild steel

0.2-0.5

0.070.16

1-2

3570

95158

Molybdate

Low-temperature liquid cleaner/coater

Mild steel

0.2-0.5

0.070.16

1.53.0

2535

77-95

Molybdate

Multimetal lightweight alkali metal phosphate

Mild steel

0.2-0.5

0.070.16

2-5

4060

104140

1-2

4060

104140

Zinc phosphate

Chlorate

Low-temperature immersion zinc phosphate

Mild steel

1.5-2.0

0.490.66

5-10

2530

77-86

Spray zinc phosphate

Mild steel(d)

1.4-2.0

0.460.66

1-2

5060

122140

Chlorate/metanitro-benzene sulphonate

Spray zinc phosphate

Mild steel(d)

1.4-2.0

0.460.66

45120

4550

113122

Low-temperature spray zinc phosphate

Mild steel(d)

1.4-2.0

0.460.66

80180

2535

77-95

Hydrogen peroxide

Spray zinc phosphate for closed-loop operation

Mild steel(d)

1.4-2.0

0.460.66

1-2

5560

131140

Nitrite

Zinc phosphate

Mild steel

3-7

0.982.3

5-15

6070

140158

Spray zinc phosphate

Mild steel

1.6-2.4

0.520.79

1-2

4560

113140

Multimetal spray zinc phosphate

Mild steel(d)

2.0-3.5

0.661.1

1-3

5570

131158

Multimetal zinc phosphate

Mild steel(d)

2-3

0.660.98

1-3

5580

131176

1-3

5580

131176

Nitrite/chlorate

Spray zinc phosphate (low zinc)

Mild steel

1.6-2.0

0.520.66

1.52.0

5055

122131

Nitrite

Calcium modified zinc phosphate

Mild steel

2.0-4.5

0.661.5

2-5

6070

140158

Zinc manganese phosphate

Nitrite

Low-temperature zinc phosphate

Mild steel

1.8-2.4

0.59-Ü.79

1-2

2535

77-95

Chlorate/metanitro-benzene sulphonate

Low-temperature spray/dip zinc phosphate®

Mild steel(d)

1.4-2.Ü

Ü.46-0.66

1.53.0

2530

77-86

1530

2530

77-86

Zinc iron phosphate

Nitrite

Immersion zinc phosphate (low zinc)

Mild steel(d)

2.8-3.4

0.921.1

2-4

5560

131140

Chlorate/metanitro-benzene sulphonate

Spray/dip zinc phosphate®

Mild steel

2.Ü-2.5

0.660.82

2-4

5053

122127

2030

5053

122127

Rustproofing applications

Iron phosphate

Heavy iron phosphate

Mild steel(d)

7.5-15+

2.5-4.9+

1530

9699

205210

Manganese iron phosphate

Manganese phosphate (unaccelerated)

Mild steel(d)

1Ü-3Ü

3.39.8

3090

95100

203212

Nitrate

Manganese phosphate

Stainless steel or rubber-lined

7.5-15+

2.5-4.9+

5-30

9699

205210

Nitroguanidine

Manganese phosphate

Mild steel(d)

7.5-15

2.54.9

1530

8595

185203

Zinc iron phosphate

Nitrate

Zinc phosphate

Mild steel(d)

7.5+

2.5+

1030

8090

176194

Antifriction applications

Manganese iron phosphate

Nitrate

Manganese phosphate

Mild steel(d)

7.5

2.5

5-15

9699

205210

Wire drawing applications

Zinc phosphate

Nitrite

Zinc phosphate (in-line operation)

Mild steel(d)

4-8

1.32.6

1030

9095

194203

Tube and wire drawing applications

Zinc phosphate

Chlorate

Zinc phosphate

Mild steel

6-12

2.03.9

2-15

5570

131158

Nitrite

Zinc phosphate

Mild steel

10-20

20

5595

131203

Nitrate

Low-temperature zinc phosphate

Mild steel

4-10

1.33.3

5-15

4050

104122

Zinc calcium phosphate

Chlorate

Zinc calcium phosphate

(batch)

Mild steel(d)

8-10

2.63.3

3-10

70-75

158167

Zinc calcium phosphate (in-line)

Mild steel(d)

8-10

2.63.3

2030

7580

158176

Nitrate

Zinc phosphate (low sludge)

Mild steel

6-10

2.03.3

4-10

6575

149167

Tube drawing lubricant applications

Iron

Combined phosphate

Stainless steel

2-5(p) 10-

0.661.6®

5-15

65-

149-

phosphate/lubricant

lubricant

4.9(q)

80

176

Cold extrusion applications

Zinc phosphate

Nitrite

Zinc phosphate

Mild steel(d)

6.6+

2-10

5595

131203

Cold-forming aluminum applications

Zinc phosphate

Nitrate

Zinc phosphate

Mild steel(d)

4-12

1.33.9

7-10

5257

126135

Galvanized steel applications

Zinc phosphate

Stripline zinc phosphate

Mild steel(d)

1.6-2.0

0.520.66

5-15

6269

143156

5-15

6269

143156

Chromate/phosphate for aluminum applications

Chromium phosphate

Chromate/phosphate

Stainless steel or PVC-lined mild steel

0.155.00

0.051.6

1-3

40

104

3060

25

77

Coating type

Control parameters

Other

Comments

Total acid

Free acid

mL

gal x 10-3

mL

gal x 10-3

Paint bonding applications

Iron phosphate

910

2.42.6

(a)

1416

3.74.2

0.53.0

0.130.79

Requires precleaning. Superior performance to cleaner/coaters

910

2.42.6

(b)

Requires precleaning. Superior performance to cleaner/coaters

4.55.0

1.21.3

No precleaning necessary. Gives iridescent to gray coatings, blue when molybdate-accelerated

4.55.0

1.21.3

(c)

Single liquid chemical. Low operating temperature. Suitable for use with automatic control equipment

1012

2.63.2

May be formulated as cleaner/coater for spray application

Zinc phosphate

2830

7.47.9

1.31.5

0.340.40

Additions of neutralizer needed to control free acid

16-17

4.24.5

2.02.8

0.530.74

10-12

2.63.2

0.81.0

0.210.26

24-26

6.36.9

0.71.0

0.180.26

May contain fluoride and nickel for treatment of galvanized steel and limited quantities of aluminum

14-16

3.74.2

0.71.2

0.180.32

Can be incorporated in closed-loop system to give total recycling of rinse water and no liquid effluent

15-20

4.05.3

6-10

1.62.6

(e)

Tends to give coarse coatings after strong alkali cleaning or acid pickle without refining pre dip. Requires regular nitrite additions

10-12

2.63.2

0.40.6

0.110.16

15-20

4.05.3

(f)

Treats steel and galvanized steel in any proportion, together with maximum 15% aluminum

14-16

3.74.2

0.52.5

0.130.66

Treats steel, galvanized steel and limited quantities of aluminum

20-24

5.36.3

(g)

Control of zinc content may be necessary

18-22

4.85.8

(h)

Refined coatings after alkali or acid cleaning without refining prerinse. Particularly suitable for one-coat finishes. Requires regular nitrite additions

Zinc manganese phosphate

1525

4.06.6

0.21.0

0.050.26

(i)

Low-temperature, low-stain. May have multimetal processing ability when fluoride-containing

2426

6.36.9

0.71.0

0.180.26

May contain fluoride and nickel for treatment of galvanized steel and limited quantities of

aluminum

Zinc iron phosphate

1921

5.05.5

0.81.1

0.210.29

Submerged agitation and activating predip required

2325

6.16.6

1.21.4

0.320.37

Rustproofing applications

Iron phosphate

2832

7.48.4

"Working-in" of solution required. Will remove light rust. Minimum rinsing satisfactory. Not ideally suited for intermittent working

Manganese iron phosphate

2832

7.48.4

2832

7.48.4

Coating weight and crystal structure dependent on cleaning method. Activating pre dip may be required for smooth coatings.

3840

10.010.6

May be used without subsequent rinsing

Zinc iron phosphate

3842

10.011.1

(k)

Separate makeup and replenishment concentrates

Antifriction applications

Manganese iron phosphate

8.4(1)

1.3e1'

(k)

Coating weight and dimensional build-up dependent on pre-cleaning. Activating pre dip may

be required for smooth coatings.

Wire drawing applications

Zinc phosphate

6G-7G

15.818.5

(m)

Mild steel, stainless steel for longer life. Normally self-generating in nitrite

Tube and wire drawing applications

Zinc phosphate

1822

4.85.8

Single chemical process. Has a higher consumption than more modern processes

1822

4.85.8

(m)

Autogeneration of nitrite when used at 40+ points.

3842

1G.G-11.1

(m)

Total acid

4G-5G

1G.6-13.2

(n)

Low sludge. Activating pre dip required

Zinc calcium phosphate

1822

4.85.8

Single chemical replenishment. Stable accelerator

6575

17.219.8

Single chemical replenishment. Stable accelerator

2G-24

5.36.3

(o)

Tube drawing applications

Iron phosphate/lubricant

(r)

No rinsing. Tubes drained at 515° slope for 30 min after treatment

1

Cold extrusion applications

Zinc phosphate

1822

(m)

Wide range of operating conditions to produce wide range of coating weights. Multichemical process

Cold-forming aluminum applications

Zinc phosphate

4550

2-4

Regular fluoride additions required

Galvanized steel applications

Zinc phosphate

27-29

Chromate/phosphate for aluminum applications

Chromium phosphate

(s)

Coating weight controlled by fluoride level. Lighter coatings for paint bonding, heavier coatings for bare corrosion resistance

(a) 0.5-1.5 mL (1.3 x 10-4 to 4.0 x 10-4 gal) acid consumed.

(b) 1.5-3.5 mL (4.0 x 10-4 to 9.2 x 10-4 gal) acid consumed.

(c) 0.5-2.0 mL (1.3 X 10"4 to 5.3 x 10"4 gal) acid consumed.

(d) Stainless steel for longer life.

(e) 2-3 mL (5.3 x 10"4 to 7.9 x 10"4 gal) accelerator.

(f) 0.5-2.5 mL (1.3 x 10"4 to 6.6 x 10"4 gal) accelerator.

(g) Gas points (saccharometer, 0.5-2.0 mL (1.3 x l(r4 to 5.3 x 10"4 gal).

(h) 1.0-2.5 mL (2.6 x 10"4 to 6.6 x 10"4 gal) accelerator.

(i) 3-4 mL (7.9 x 10"4 to 1.1 x 10"4 gal) accelerator, (j) Combinations of spray and dip.

(m) Accelerator starch/iodide paper.

(p) Phosphate contribution.

(q) Lubricant contribution.

(s) Chromate pointage, 4-5 mL (1.1 x 10"3 to 1.3 x 10"3 gal).

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