September 20, 2017

Choice of Metallic Coating (2)

Metal Coating With Different Ways


This is just about the characteristic of every metal are different each other, one is easily to corrode and other more stand to corrosion. This character is use to protect each other using Coating Different Method. Because of the characteristic and the strong of coated by certain way of coating, so we just use the best way to coat metal.


Electrochemical Series


The metals above hydrogen in the electrochemical series, which have a more positive potential than hydrogen, are less pores to progressive corrosion in aqueous solutions. Those metals with the most positive potentials, such as gold and platinum metals, indeed have practically no tendency to pass into the combined state, accordingly they are designated noble metals.

Every metal have electrochemical characteristic, this character is different strength among them
Electrochemical Series

The position of iron in the electrochemical series should particularly be noted; it is more negative or base than hydrogen, and considerable more negative than copper, tin, and nickel, almost identical in position to cadmium, and considerable more positive than zinc.

Where two different metals are in electrical contact with each other an also with an aqueous solution, they form a galvanic cell or battery, because of their difference of potential. The metal with the more negative potential is stimulated to corrode faster, and the metal with the more positive potential is discouraged by the difference of potential. A current flows around the circuit made up from the two metals and the solution, it passes out of the corroding metal (the anode) into the solution and thence back into the protected metal (the cathode). The anode and the cathode may be some distance apart in this action, since both the metals and the solutions are electrically conducting to the electron transfer.

This situation of two different metals in contact being exposed to a corrosive liquid, arises when a protective metallic coating is discontinuous for some reasons. It may be inherently porous, or it may be locally deficient, or it may have become cut or damaged in service, or even by former corrosion. The corrosion of the basis or undermetal thus exposed will be stimulated or protected, according to the relative potentials in the electrochemical series of the coating and the basis metal. The more positive metal will always stimulate the corrosion of the more negative metal. If it is the corrosion of the basis metal which is stimulated in this way the effect can be serous, because the area exposed will be small compared with that of the undamaged coating metal, and therefore the current generated by the difference of potential will be concentrated on a small area of reactive basis metal. On the other hand, if the corrosion of the basis metal is inhibited by the adjacent presence of a more negative coating quite large gaps in the coating may not be very detrimental.

Metal Surface Coating Method

Anodizing Method


Anodizing Product


Electroplating Method

 









Metal Coating Method






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Coated With Copper

Copperplate and Sheet Metal

Pure copper plate and tube have been applied in many parts and application because pure copper have good characteristic like have good electrical conductivity and resistance to corrode. For this character make copper also good as coating material for other sheet metal in order more stand to corrode because of base metal is protected by copper. So the corrosion reaction can’t attack the base metal.

Copper plate is applied in several uses like in the below:
  • Electrical Cable and printed circuit board
  • Telecommunication network
  • Architecture Planning for For building art
  • Antimicrobial agent such as for fungicidal
  • Gasket and seal as on car engine part
  • Plumbing
  • Industrial tanks and vats
  • Electronic house hold such as tubing for Freezer agent
PCB is printed circuit board use copper circuit to make electric can run over the plastic
Printed Circuit Board

Sulfuric acid is used as solution which has two hydrogen ions. Copper is a metal atom of which has two easily removable electrons. Copper sulfate (CuSO4) is the copper salt of sulfuric acid. In aqueous solution the copper ions, each with two positive charges due to loss of two electrons, separate them selves from the doubly charged negative sulfate ion SO42

If two copper plates, which may be called electrodes, are dipped into the solution of copper sulfate and a direct current applied to them, one plate will become negatively charged and the other positively charged. The negatively charged plate is called the cathode. When a copper ion touches the cathode, two electrons will transfer themselves from the cathode to the copper ion, and thus turn it back into metallic copper, simultaneously, at the positive electrode, the anode, a metallic atom on the electrode will slip away into the solution as a copper ion, leaving its two electrons behind. In this way the aqueous solution remains electrically neutral, but two electrons have been able to move down to connecting wire into the cathode, and another two up from the anode along its connecting wire. In other words a current (of electrons) flows in the metallic circuit, and a metallic atom has disappeared from the anode and another has appeared at the cathode.

Ions (whether anions or cations) do not move so freely in a solution as electrons do in a metal, so the rate at which that the current can pass from the solution to the cathode and deposit smooth copper is somewhat limited. The amount of current is obviously related to the area of the solution/metal interface, so it is called a current density. Under ordinary conditions it is limited in this case to about 30 A/ft2 of cathode area. This may be compared with a safe current of at least 1000 A/in2 of cross section in a metal. However, this rate of 30 A/ft2 of area corresponds to a growth of thickness of the coating of about 0.002 in/h (25 mm). This is fairly typical for most electroplating process, so that it will be seen that electroplating is essentially a rather slow method of metal coating.

September 18, 2017

Copper Plating on Zinc

Copper Coating Solution


A copper strike applied in a copper cyanide solution is normally the first plating step for all die castings electroplated with nickel and chromium. The thickness of the strike should be at least 1.0 µm for castings that will be plated with nickel after copper striking. A thickness of 3 to 4 µm is recommended for die castings that will be subsequently electroplated with bright, leveling copper in copper sulfate-sulfuric acid solutions. The copper strike is a critical step in plating zinc die castings that is sometimes inadequately controlled.

Solutions containing 20 to 45 g/l of copper cyanide, 10 to 20 g/l of free sodium cyanide, and 15 to 75 g/l of sodium carbonate are customary for strike solutions. A solution containing 20 to 27 g/l of copper cyanide and 10 to 15 g/l of free sodium cyanide is relatively popular. A few formulations include the molecular equivalents of potassium cyanide in place of sodium cyanide. Other contain 15 to 25 g/l sodium hydroxide or 30 to 45 g/l of sodium potassium tartrate in addition to the major constituents. Agent such as sodium hydrosulfite that reduce hexavalent chromium ions are sometimes added to prevent the reduction in efficiency caused by only a few parts per million of Cr(VI). Periodic additions of such as reducing agent may be required, especially in solutions containing tartrate ions. Cathode current densities range from 2.3 to 5.5 A/dm2 and solution temperatures from 50 to 57oC should be avoided, or there will be danger of blister formation.

The average cathode current density dust be balanced with the free sodium cyanide and the temperature of the solution, or burning might occur at edges and other high current density areas. With an average cathode current density of 2.3 A/dm2 the cathode current efficiency varies from 30 to 60% for strike plating, depending on the free sodium cyanide concentration. Although a low concentration (10-15 g/l) favor a high efficiency, throwing power is reduced, so that recesses receive thin deposits that are unsatisfactory for protecting the zinc from chemical attack during nickel plating in acid solution. Ultrasonic agitation increases the cathode efficiency, the covering power in recessed areas, and the density of the copper deposit.

High purity copper anodes are recommended for copper cyanide strike solutions. Solutions should be continuously filtered to avoid the inclusion of small particles that nucleate nodules during subsequent plating operations. Anode bagging is sometimes adopted for ensuring smooth copper strike deposits. In this connection, the control of the free cyanide concentration is important. A relatively high free cyanide concentration is also to maintain satisfactory anode dissolution in solution operated at 50 to 57oC.

September 14, 2017

Metal Surface Protection

Metals are essentially artificial and unstable materials, that is to say, they are not found as such in nature (excepting gold and copper) and they tend, under the influence of the weather, waters and similar corrosive exposure, to revert back to a non-metallic state. It is convenient for reasons of cost, strength and ease of working to manufacture metallic articles without too much regard to their external appearance or to their behavior against corrosion, and then to deal with these purely surface characteristics by a subsequent treatment, which may therefore be designed in general as surface treatment of metals. Since iron and steel are by far the most commonly used metals, and also unfortunately among the most prone to rust, decay and corrosion, they figure very largely, but not by any means exclusively, in the general subject of the surface treatment of metals.

Process Stage of Surface Treatment of Anodizing


The main purpose of the surface treatment of metals are predominantly twofold, with emphasis on one or the other to different degrees in different cases, viz:
  1. To improve the appearance
  2. To improve resistance to corrosion, tarnish or staining under the conditions of use which are foreseen.

 Surface Protection using Paint

Surface Protection using plastic cover

 surface protection using electroplating

Surface Protection using Anodizing

There are other objectives, each important in its own sphere, but these together are only of minor importance compared with the above main purposes. Examples of these minor objectives are to provide resistance to scaling by heat, to facilitate other subsequent surface treatments or to change the surface hardness or other surface properties, or even to change the overall dimension.

The surface treatment of metal almost invariably consist of applying a coating of some kind to the metal, and thus providing an external skin which can be selected solely for its appearance and corrosion resistance. If such a coating can be applied without any discontinuities, and if it is firmly adherent to the behavior of the coating. However, such external coatings must inevitable be thin, unless the whole character of the article is changed. In the normal course of use these coatings therefore entail the risk of penetration through to the basis metal by mechanical damage or flexing; the effect of the small areas of basis metal thus exposed can't be ignored, not only because of the local corrosion of the exposed metal, but because of the risk that the remainder of the coating may be undermined and thrown off.

In the choice of surface treatment for any particular metallic article, many factors must be considered, such as cost, type of corrosive environment to be withstood, and compatibility with special materials such as foodstuffs or washing materials. In very many cases an additional factor of continuing good appearance must be considered. Metal surfaces, especially satisfying appearance. It is obviously appropriate to provide a metallic article with a metallic coating of higher corrosion resistance and more attractive appearance, so that the whole system is a unity. But very few metallic coatings are absolutely resistant to corrosive influences, and these few are the most expensive. In particular, metallic coatings are not completely resistant to some of the many chemical substances now involved in everyday life, such as washing chemicals, fruit acids and many foodstuffs. Nor do they provide much opportunity to introduce colors, including white, which may be desired to conform to decorative schemes or fashions. Thus non-metallic coatings, such as vitreous enamels, paint and lacquer, are applied to metallic articles for decorative as well as protective reasons.

Before any surface coating can be applied it is essential that a clean, sound surface must be provided on the article to be coated. In particular, scale and oxide, grease and dirt remaining from the manufacturing operations, must be removed; the surface usually must be smoothed or even polished. It may also need to be prepared physically or chemically to ensure satisfactory adhesion of the coating. These preparatory treatments are an integral part of the surface treatment process, and obviously have to be applied at the end of the main manufacturing process. For this reason these cleansing, protective and preliminary decorative treatments are almost invariably applied as the final stage of the manufacturing process of a metallic articles, to such an extent that the processes are often collectively referred to under the term 'metal finishing'. In the cases of hot dipping tinning and hot dipping galvanizing of sheet steel the protective films are applied to the semi-fabricated material; here, however, the subsequent process are limited to cutting, bending and joining; moreover, decorative effects are subordinate to economics.

November 7, 2014

Aluminum Anodized Price

Aluminum anodized metal have more expensive price because anodized aluminum already improved the properties. Anodized aluminum already stand to corrode because the surface of anodized aluminum already become oxides and will not react further on normal environment. Anodized aluminum can change their surface or damage if the condition of environment surround the product is acid or base environment. Base or Acidic atmosphere can broken the oxidized surface because the oxidized surface can react and change become normal aluminum metal and easily react with oxygen on the air.

Aluminum Anodized Product

Aluminum anodized price become expensive because their surface already improve become interesting color like, brown, black, orange, yellow, gold, bronze or other color. The current technology already can apply many kind of color can be develop on the aluminum anodized surface.

The price of aluminum anodized sheet as on the list below:

Thickness
Code
Color
50 pack, $
100 pack, $
250 pack, $
1000 pack, $
3.2 mm
D20
Solid Color
1.25
2.25
5.00
14.00
4.0 mm
F20
Solid Color
1.50
2.75
6.00
17.00
4.0 mm
F18
Solid Color
1.75
3.25
7.25
19.75
4.8 mm
H18
Solid Color
2.00
3.50
8.00
22.50
4.8 mm
H16
Solid Color
3.00
5.50
12.25
33.75
6.3 mm
L18
Solid Color
2.50
4.50
10.25
28.25
6.3 mm
L16
Solid Color
3.25
5.75
13.25
36.75