What is it?
Electro-Chemical marking or Electromarking is recognized as one of the best methods of marking metal permanently without distortion. Electromarking is permanent because it created by etching out metal and then plating on the etched surface a stable compound of the base metal.
In most cases this stable compound is an oxide, and the Electromark is, in effect, a stable rust which will withstand additional corrosive action. This corrosion resistance can be shown by the extreme length of time the Electromark will stand up in a salt spray test.
The Electromark impression is dark in color. The degree of darkness depends on many things; however, the base metal is most important. For example, some stainless steels yield only a brown mark, whereas monel metal gives a jet black mark.
How does it Work?
Electromarking is accomplished by using a small amount of electric current, a harmless electrolyte, a marker with pad to hold the electrolyte to carry the current through the stencil with a image.
The current passes through these openings in the stencil and the electrolyte allows the image of the stencil to be transferred onto the base metal.
THE BASIC EQUIPMENT
Power Units
Power units which provide voltage and current to make the mark, come in a range of sizes. The size required depends on the area of the mark and speed of the etch. All units have an On-Off switch and an AC-DC switch to produce an AC mark or a DC etch. (The reverse is true in Aluminium). Most units have a rheostat to regulate the output voltage. The current required will automatically be produced by the unit unless it exceeds the output of the power unit, in which case a fuse or circuit breaker will blow. All units contain banana or polarity receptacles for making contact through cord sets. The power units on the market today range from 5 Volts to 40 Volts and have an ampere output from 0 to 40 amps.
Electrolytes
The electrolyte or marking solution required depends upon the alloy of the materials to be marked or etched. There are general purpose electrolytes for most products. For specific applications, however, it is best to send samples of the part to be marked to the manufacturer for his recommendations. Selection of the proper electrolyte is very important. Using an incorrect electrolyte can produce a mark with an unstable oxide which can be rubbed off after the mark is made. Most electrolytes cause an excess of oxides and thus clog the stencils, giving poor marks and short stencil life. Therefore on production runs particularly, it is imperative to use the self cleaning electrolytes which stop stencil clogging by controlling the amount of oxides created. These self cleaning electrolytes are identified with "SC" in the part number. In most parts books there is a list of the more popular electrolytes. These electrolytes do about 90% of the jobs. However, there are more than 100 electrolytes available and no list can be complete, nor should any list be considered the final word. Suitable liquids are available for nuclear grade are available.
Neutralytes
Because most electrolytes are salt solutions, any mark or etch must be neutralized by wiping it or soaking it in a neutralizing solution for a specified period of time. If the wiping operation is used the part should be dried before wiping with the neutralizer.
If a pad saturated with neutralizer is used to wipe the parts which have not been dried, soon the pad will have more electrolyte than neutralizer on it, and the corrosion problem will be aggravated instead of eliminated. Soaking in a solution specially prepared to counteract the action of the electrolytes is the other method of neutralizing. These solutions usually are diluted with water (up to twenty parts of water) depending upon the application. Soaking time is about ten minutes. After this, the use of proper neutralizing oils will ensure against corrosion. The type of oil depends upon the application.
Stencils
There are two basic types of stencils available. One type can be made by impression and is thus produced on an ordinary typewriter or dot matrix printer. Since any impression will create a design in a stencil, a metal die can be used to impress trademarks or logotypes. The limitation of this type of stencil is that, of necessity, it must be a fine line. Each impression on this stencil material can produce up to several hundred Electromarks. These are called die impression stencils.
The other basic type of stencil commonly used is made by a photographic process. It starts from black and white artwork. Thus any line thickness, broad or fine, and any character size can be made. Each design of this stencil can produce up to many thousands of Electromarks. The matrix or base of the photographic stencil can be made of paper or fabric. Thus a whole series of various stencils are available for different applications. They are called "perma" or "electrolast" stencils. It is best to contact the manufacturer for precise recommendations.
These stencils can be pre-formed into "caps" which fit any size marker cartridge. Rectangular caps usually mark names and part numbers. The round caps, particularly in small sizes, are used for inspection stamps.
Automation and Semi-Automation
In order to keep pace with greater production speeds of today's industry a semi-automatic or completely automatic marking systems can be used.
Extra long life stencils, electrolyte pumps and self cleaning electrolytes enable us to mark almost any metal at any production line speed. Our machines are readily adaptable to any line operation and can be moved or relocated in a matter of minutes.
The advantages of semi-automatic machines are several;
-First, with a small amount of inexpensive tooling the parts to be marked can always be positioned exactly under the marking head so that each part is marked identically.
-Second, each time the marking head comes down on the piece to be marked it applies the same pressure and dwell time, thus assuring identical marks.
-Third, the machine, when set in automatic mode will cause the marking head to move up and down at a predetermined rate. This can help increase production speeds.
Air operated automatic units are also available as a kit, or completely assembled with proper tooling can provide up to 20,000 marks per eight hour shift; low cost, versatile automation.
Questions & Answers
1. Can I mark round parts?
Yes by rolling on a bench marker or by using contour blocks
2. Can I mark plated parts?
Yes, as long as the parts conduct electricity
3. Can I mark anodized parts?
Not after anodizing. Mark deep before anodizing and the mark will show through after the process.
4. What type of repairs will be needed to the power unit?
Almost none. Most power units are guaranteed for six months.
5. Can I mark black oxide surfaces?
Yes, in most cases using low voltage, high pressure and proper electrolytes.
6. Can I mark Parkerized parts?
In most cases, No.
7. Is the electrolyte harmful?
No, it may stain clothes but it will wash out. If you swallow it drink a lot of water and see a doctor.
8. How deep can I go?
An AC mark is around 0.0003" deep. A DC etch can go as deep as 0.005" or more but generally 0.001" is
considered deep.
9. What is an etch?
The dark mark is a combination of an etch and a plate.
10. How long will the stencil last?
Depending on the kind and use of the configuration and the depth required you can get from one to thousands of impressions
11. Can I make my own stencils?
Yes by using a typewriter or dot matrix printer on the die impression stencils
12. How clean does the surface of the part have to be?
Just free of sharp particles which would cut the stencil. Light oil is fine
13. How rough a surface can you mark on?
A reasonably smooth forged or cast surface
14. Will this method of marking cause corrosion?
Yes, if not neutralized with the proper neutralizers
15. How well does this mark stand up in a salt spray test?
Excellent
