CL 01.06.2007 CL Technology GmbH – Zinc Solutions 1 Corrosion Resistant Coating Sophisticated Zinc Solutions Highest corrosion protection attractive look

CL

01.06.2007 CL Technology GmbH – Zinc Solutions 1

Corrosion Resistant Coating Sophisticated Zinc Solutions

Highest corrosion protection

attractive look

CL

01.06.2007 CL Technology GmbH –Zinc Solutions 2

Profile

Founded in Solingen, Germany in 2001 Distributors in 15 countries

Own laboratory for developments & analysisOur production facility is ISO 9001 certified

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Our Vision

Continuous development and realization

of innovative plating solutions

resulting in

significant economical benefits

for our customers

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Our portfolio

Pretreatment Decorative Processes Functional Processes Corrosion Protection

• Bright Chrome• Bright Silver• Bright Nickel• Satin Nickel

• Tin Nickel• Acid Copper• Tin Cobalt• Cyan. Copper

Plating-on-Plastics Post treatment Specialties Technical Services

• Instrumental Analysis(AAS, HPLC, UV, IR)

• Degreasers• Etchants and Pickling solutions• Chemical brightening & Deburring processes

• Acid zinc• Cyanide zinc• Cyanide free, alkaline zinc

• Semi bright nickel• Hard chrome • Bright Silver (reel-to-reel)• Electroless copper• Tin

• Acid Copper• Semi bright nickel • High sulphur nickel • Bright nickel• Micro-porous nickel • Bright chrome

• Corrosion protection and anti-tarnish for different metals.

• Technical Advice and Consulting• Electro polishing processes• Metal strippers• Waste water treatment

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The value of zinc/zinc-alloy plating as a rust proof finish for iron and steel has long been appreciated.

Although zinc/zinc alloys are considered to be similar in their galvanic behaviour to iron in most environments. They do differ in many of their physical deposit properties.

These differences should be considered in selecting one coating versus another for a given application.

In recent years electrode position of zinc/zinc alloys has made rapid strides and is now used extensively for finishing all manners of iron and steel products.

Corrosion Resistant CoatingZinc/Zinc-Alloy Plating

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Corrosion Resistant CoatingZinc/Zinc-Alloy Plating The protection afforded to iron and steel is largely due to its behaviour as

the anode in any electrochemical reaction that may occur.

From this it might appear that the protection would be of short duration, but in practise rapid corrosion does not occur, as the zinc develops upon its surface a film of oxide which resists further attack.

Corrosion of this sort usually can be minimized by application of chromate conversion finishes.

For general protective purposes it is usual to apply zinc/zinc alloy deposits from 5-25 microns.

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Zinc/Zinc Alloy PlatingStandard Process Sequence Soak Cleaner Rinse Acid Dip Rinse Electrolytical Cleaner (anodic) Rinse Rinse Zinc/Zinc-Alloy Plating Dragout Rinse Rinse Rinse Predip Passivation Rinse Rinse Topcoat Drying

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Zinc/Zinc Alloy PlatingZinc Plating Equipment

These solutions require plastic- or rubber lined mild steel tanks. Rubber lined equipment should be thoroughly cleaned before use.

A means of heating should be provided so that the solution can be raised to working temperature.

Mild steel heating and cooling coils are suitable or mild steel sheeted electric immersion heaters can be used.

For barrel plating the use of fully immersed barrels is advised. The normal barrel speed is 5-7 rpm.

On rack plating tanks it is advantageous to employ mild mechanical agitation, solution circulation or mild air agitation.

Continuous filtration is necessary.

Alkaline Solution

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Zinc/Zinc Alloy PlatingZinc Plating Equipment

Acid solutions require equipment which is similar to that uses for bright nickel plating, e.g.rubber lined steel tanks.

For solution heating, resp. cooling titanium steam heating coils may be employed.

The tanks should be fitted with air agitation pipes or mechanical cathode rod movement.

Continuous filtration is generally necessary.

Acid solutions are very corrosive because of their chloride content, so care should be taken to maintain all items which come into contact with the solution.

Acid Solution

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Zinc/Zinc Alloy PlatingZinc Plating Solutions

For the electrodeposition of zinc/zinc alloys various solutions are available, these differ considerably both in composition and in characteristics, but may be classified generally as being either of the acid or the alkaline type.

Alkaline non cyanid zinc

This type of solution gives a bright deposit with high efficiency and is used either where effluent requirements are strict and cyanide and organic complex ants cannot be tolerated. Suitable for rack or barrel.

Alkaline zinc-alloys

Offer in general excellent corrosion resistance, harder deposits than conventional zinc.

Accepts a variety of chromate conversion coatings, easy to operate.

Barrel has slower plating speed than acid formulation.

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Zinc/Zinc Alloy PlatingZinc Plating Solutions

Acid zinc

These can give dull or brilliant zinc deposits and can be used for the direct zinc plating of decorative and industrial iron and steel. The cathode efficiency approaches 100 %, therefore high tensile steel components can be plated with little risk of hydrogen embrittlement. Suitable for rack or barrel.

Acid zinc-alloys

The plating speed is faster than alkaline formulations, allowing barrel plating

at faster deposition speeds. Best formulations for reel to reel plating.

Deposit is typically more brittle than alkaline deposits.

Contains Ammonium, needs dual rectification for zinc-nickel.

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Degree of exposure Minimum thicknesses

Chromate Finish

Salt Spray Hours to white corrosion

Typical Application

Mild Exposure to indoor atmospheres with rare condensation and subjected to minimum wear and abrasion

5 micron NoneClearBlackIridescent Yellow

- 12-24 72-96 72-96

Screws, nuts, bolts, wire goods, fastener

Moderate-Exposure mostly to dry indoor atmospheres, but subject to occasional condensation, wear or abrasion

8 micron NoneClearBlackIridescent Yellow Olive drap

- 12-24 72-96 72-96150-300

Tools ZipperShelvesMachine parts

Severe-Exposure to condensation, perspiration, infrequent wetting by rain, cleaners

13 micron NoneClear BlackIridescent Yellow Olive drap

- 12-24 72-96 72-96150-300

Tubular furniture, Window-fittings, Builders Hardware

Very Severe-Exposure to bold atmospheric conditions and subject to frequent exposure to moisture, cleaners and saline solutions plus likely damage by denting, scratching or abrasive wear

25 micron None Plumbing fixture, pole line hardware

Zinc/Zinc Alloy PlatingSuggested Standards for Quality Zinc Coatings on Iron & Steel Products

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c.Protective ValueAs indicated earlier, specifying a minimum thickness of zinc, zinc-alloy is the best way to guarantee protective value of high performance. Some buyers require additional performance in the standard salt spray test as another acceptance requirement. A different test that is becoming more and more popular in the automotive industry is a cyclic test. In this test, the component parts are subjected to a cycle of salt fog and humidity dictated by the specifier.


Zinc/Zinc Alloy Plating Specifying the finish

a. ThicknessAtmospheric exposure tests in several countries have supported the generalization that the protective value of zinc, zinc alloy is proportional to their thickness.That is, a steel part coated with 10 microns of zinc will be protected from rusting about twice as long as another part coated with 5 microns and exposed for the same time. Thickness is, therefore, a very important item in a quality specification.

b.ChromateChromate finishes are the first line of defence against corrosive attack on the plated coating and these thin films do an outstanding job of enhancing the total protective value of the metal coating. The chromate coatings serve to improve appearances of the plated coatings in delaying formation of white corrosion products which might interfere with function of a component.

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Zinc/Zinc Alloy Plating Specifying the finish

c.AdhesionThe coating must remain adherent to the basis metal when subjected to bending, cutting or grinding. There is no accepted standard of adhesion and these tests can only be consideredqualitative.

d.AppearanceAppearance cannot be readily specified because it involves factors which are not easily assessed such as brightness, roughness, uniformity of colour, freedom of blisters, pits and othersurface defects. For chromated finishes the general appearance is automatically specified when the type of finish is selected.

f.Hydrogen EmbrittlementAll high strength steel parts are susceptible to embrittlement caused by absorption of hydrogen during the processing of the steel or in cleaning, pickling, plating operations.To avoid possible failure of such components on the shelf or in service due to delayed cracking, it should be noted that the parts shall be heated within 1-2 hours after plating for 3-4 hours at 191-205 degrees Celsius.(ASTM B 242)

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Zinc/Zinc Alloy Plating Protective Value a. Compound Cyclic Corrosion Test This test is comprised of a series of tests, usually consisting of neutral salt/fog spray, hot air blowing on parts and high humidity. The specifier can specify exactly which cycle is most meaningful. Some use an 8 hour cycle comprised of 4 hours salt fog, then 2 hours hot air blowing on the parts, then 2 hours high humidity. The cycle is repeated again and again until white corrosion and the red corrosion (failure) is observed and recorded. Some specifiers use a cycle that takes 24 hours to complete. The specification will typically detail how many “cycles“ the tested parts must complete to pass.

b. Salt Spray TestThe salt spray test has been used to asses the protective value of zinc coatings. However, the test do not correlate with any given service exposure. Most purchasers do use the salt spray test to assess the quality of chromate treatments on zinc, zinc alloys by specifying the number of hours to appearance of white corrosion products on a significant surface.

c. Lead Acetate Spot TestThe presence of clear chromate finishes is often hard to detect visually. On zinc coatingssuch films can be detected by spot testing with a drop of solution containing 5 % lead acetate in water. The time elapsed to the appearance of the coloured spot is compared within the time required for a spot to appear on an unchromated coating.There is no valid correlation with the salt spray test.

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operating conditions

a. alkaline cyanide zinc 10 - 35 g/l zinc 10-100 g/l sodium cyanide (free) 60- 75g/l sodium hydroxide proprietary additive

cathode current density: 1,5 - 3,0 amp/dm2 cathode current barrel: 0,5 - 0,8 amp/dm2temperature: 20 - 30°C anodes: zinc

b. alkaline non-cyanide zinc6 -10 g/l zinc80 -120 g/l sodium hydroxide proprietary additive

cathode current density: 1,0 - 4,0 amp/dm2cathode current barrel : 0,5 - 0,8 amp/dm2temperature: 20 - 30°C anodes: steel

c. acid zinc30-55 g/l zinc 140-180 g/l chloride proprietary additive

cathode current density: 1,0 - 4,0 amp/dm2cathode current barrel: 0,4 - 0,8 amp/dm2 pH : 4,5 - 5,5temperature : 20 - 30°Cagitation: air/cathode rod anodes : zinc

Zinc/Zinc Alloy Plating Suggested Bath Formulation – Operating Conditions

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d. zinc-cobalt alkaline (0,5% cobalt in deposit)8-12 g/l zinc 120-135 g/l sodium hydroxide 50-100 ppm/l cobalt proprietary additive

cathode current density: 0,5 - 5,0 amp/dm2 temperature: 20 - 40°C anodes: steel

e. zinc-cobalt acid (0,5 % cobalt in deposit)20-30 g/l zinc140-180 g/l chloride 20-30 g/l boric acid 20-100 ppm/ cobalt proprietary additives

cathode current density: 1,0 - 4,0 amp/dm2pH: 5 - 6temperature: 20 - 40°C anodes: zinc

Zinc/Zinc Alloy Plating Suggested Bath Formulation –Operating Conditions

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f. zinc- iron alkaline (0,5% iron in deposit)10-25 g/l zinc 50-350 ppm/l iron 120-150 g/l sodium hydroxide proprietary additive

cathode current density: 0,5 - 5,0 amp/dm2 temperature: 18 - 30°C anodes: steel

g. zinc- nickel acid (5-7% nickel in deposit)20-25g/l zinc20-25 g/l nickel 140-180 g/l chloride proprietary additive

cathode current density: 0,2 - 4,0 amp/dm2temperature: 45 - 55°C pH: 5,2 - 5,5 movement: air/cathode rod


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h. zinc-nickel alkaline (5-9%nickel in deposit)6,0-12,0 g/l zinc 1,3-1,8 g/l nickel 110-140 g/l sodium hydroxide proprietary additive

cathode current density: 1- 8 amp/dm2 temperature: 23 - 26°C anodes: nickel or nickel - plated steel

i. zinc-nickel alkaline (12-15% nickel in deposit)6,0-12,0 g/l zinc 1,3-1,8 g/l nickel 110-140 g/l sodium hydroxide proprietary additive

cathode current density: 2 - 5 amp/dm2temperature: 26 - 30°C anodes: nickel or nickel - plated steel


Documents

CL 01.06.2007 CL Technology GmbH – Zinc Solutions 1 Corrosion Resistant Coating Sophisticated Zinc Solutions Highest corrosion protection attractive look