September 2012 Archives

#132 Zinc Alloy Plating

By システム管理者 on September 28, 2012 12:00 AM | No Comments | No TrackBacks

There are following two zinc alloy plating types being put to practical use.

(1) Zinc-Nickel Alloy Plating

This is an anti-corrosive plating for products used in harsh corrosive environments able to cope with heavy environmental loads where the coating film thickness would have to be considerable if it were the conventional zinc plating. It has established its position as a type of plating of highly anti-corrosive and thin plating film thickness.
Normally, it contains 5~10% nickel, and colored chromate processed specimen is highly anti-corrosive where it can withstand 2000 hours or more of salt water spray test without showing red rust. Additionally, it has good heat resistance characteristics and good post heat treatment corrosion resistance property and secondary workability.
In addition, since this plating does not cause hydrogen embrittlement, it is possible to apply highly corrosion resistant plating on carbon steels and alloy steels, occupying important positions such as on functional parts of automobiles and etc. Colored and Brown chromate treatments are implemented for this plating.

(2) Zinc-Iron Alloy Plating

This is a plating of 5µm coating thickness, and has high corrosion resistance of 2000 hours or more of salt water spray test result. The coating film contains 0.2~0.7% of Iron, but it said to show the highest corrosion resistance property when the Iron content is 0.4%.
Especially, the Black Chromate treatment has better corrosion resistance properties and more economical compared to the other zinc plating types. Also, the plating has good plating coverage characteristics as well as electro-deposition characteristics. There are: Glossy, Colored, Black Chromate treatments available, with the Black Chromate being the most popular in demand.

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Chromate Treatment
When zinc and cadmium plated objects are submerged in solutions containing chromic acid and dichromate salt, the plate coatings are partially dissolved and chemically complex films are formed on the surfaces. When these are stabilized and dried, chromate coatings are formed. The formulation of these films greatly increase the corrosion resistance characteristics. However lately, popularity of Chromium-free movements are causing transitions toward chromate processes that do not use the chromium.

#131 Chromate Treatment

By システム管理者 on September 21, 2012 12:00 AM | No Comments | No TrackBacks

Chromate treatment process [Figure] and types and characteristics [Table] applied over zinc plating (some cadmium plating also) are shown.

[Fig.] Zinc plating chromate treatment process

Fig.

[Table] Outline of various chromate treatments

Variety	Type	Exterior color tone	Application area
Gloss chromate	For exterior appearance	Silver blue white	Use where emphasis is on the aesthetics rather than the corrosion resistance as much.
Gloss chromate	Anti-corrosive	Blue~Light Yellow	Used where the anti-corrosion property is most important.
Colored chromate		Gold, Rainbow	Used where the anti-corrosion property is further emphasized.
Black chromate	For exterior appearance	Black	Good corrosion resistance. Often used for ornamental purposes. Used where anti-wear property is not of importance.
Black chromate	Anti-corrosive	Black	Used where corrosion resistance and weather resistance are of importance.
Green chromate		Olive color	Applied on parts used in highly corrosive enbironments.

Corrosion resistance example of various chromate treatments are shown in the [Table] below. The "white rust" is zinc oxide.

[Table] Corrosion resistance of various chromate treatments (Number of white rust spots, Test specimen 5 pcs.)

	Salt water spray time (H)
Coating	24	48	72	96	120	144	168	192	216	〜	500
Gloss chromate	0	2	4	5
Colored chromate	0	0	0	0	2	4	5
Black chromate	0	0	0	0	0	2	5
Green chromate	0	0	0	0	0	0	0	0	0	0	2

Fig.

#130 Zinc Plating

By システム管理者 on September 14, 2012 12:00 AM | No Comments | No TrackBacks

The zinc plating has been widely used as anti-corrosion plating for steel for a long time. Notably, in recent years it has been in ornamental use as well due to the advancements on plating baths and chromate processes have greatly improved not only the anti-corrosion properties but external appearance performances.

Also, the zinc plating is known for its good economy because it is possible to implement tumble plating easily.

Usual plating, called "Stationary Plating", uses racks (fixtures) to hold the objects to submerge in the plating bath to apply the DC current. On the other hand, with the Tumble (Barrel) Plating, the objects are placed in either a vertical or a horizontal barrel and tumbled and the electrical current is applied. The objects travel within the barrel while conducting the electrical current with each other. Therefore, the racks and racking of objects are not needed with tumble plating, offering great savings in power and labor.

Let us first look at the types of zinc plating.

[Table] Zinc plating bath types and characteristics

Type	Characteristics
Cyanide Bath	The most common type of bath widely used since the old times. Used in all areas such as complicated shaped pressed products and etc. due to the good coating thickness uniformity (good deposition uniformity) and post plating workability. This bath type has good characteristics but contains cyanide.
Zincate Bath	This is a bath with cyanide removed from cyanide bath, and has grown popular as environmentally preferable. After many improvements have been applied, the coating properties have become near that of the cyanide bath.
Acidic Bath	Has better electrical current efficiency in comparison with the previous two baths above, and enabled higher speed in plating. Also, this bath is being used for plating carbon steels, alloy steels and cast products since it caused little hydrogen embrittlement where the material absorbing hydrogen during the plating process.

The coating properties of each zinc plating bath differ. The Erichsen test shows the hardness of the coatings which become the issue on post plating workability. The cracks mean that the coatings are harder.

Fig

#129 Anti-corrosion Plating

By システム管理者 on September 7, 2012 12:00 AM | No Comments | No TrackBacks

Various products and parts are used mostly in the atmosphere.There are corrosive environments in the air, where the products are exposed to in some degrees, such as moisture, oxidizing atmosphere, sulfide atmosphere, and salts.The platings applied to the products in order to protect them from these environments are called "Anti-corrosive platings (also called Anti-rusting platings).
The most frequently used industrial material is steel and it is well known that the most suitable plating for steel is zinc plating.It is often used for ornamental products that require some degree of corrosion protection.The following are an outline of various anti-corrosive platings that can withstand harsher corrosive environments.

[Table]Anti-corrosive plating types and applications

Plating Type	Characteristics and Applications
Zinc Plating Plating bath types - Cyanide Bath - Zincate Bath - Acidic Bath	Due to the anti-corrosive property of zinc (Zinc is well known as a sacrificial anode of steel. This is because zinc's single electrode potential is less noble in comparison to iron, and the zinc dissolving before the iron prevents iron from dissolving.) and the anti-corrosive nature of the chromate process over the zinc plating, this is often used as anti-corrosive plating for steel. This is a zinc plating bath customarily has been in usage, and is used for press formed components, bolts & nuts and etc. It has good plating thickness uniformity and post plating machinability. The cyanide bath contains highly toxic cyanide, and the alternative bath containing no cyanide has harder plate coating than the cyanide bath. Compare to the two alkaline baths listed above, this has better electric current efficiency, and and steel and cast iron can be plated. Also, it causes little hydrogen embrittlement.
Cadmium Plating	This plating is indispensable for ships and aircrafts since it is especially resistant against salts. As with the zinc plating, chromate process is applied.
Tin-zinc alloy plating	It has anti-corrosive performance next to the cadmium plating. It has good solderability, paint coating adhesion, and post plating machinability, and often used for electrical components.
Zinc-Nickel Alloy Plating	This is an anti-corrosion plating of high corrosion resistance, and colored chromate processed plating shows multi-fold corrosion resistance of the zinc chromate processed products. Because it does not cause hydrogen embrittlement, it is used for automotive parts and etc. made of steel and steel alloys.
Zinc-Iron Alloy Plating	High corrosion resistance as listed above. Colored chromate processed plating has 5 micro-meters of coating thickness and withstands 2000 hours or more of salt water spray test. Glossy, colored, or black chromate process can be selected.

Fig

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