Tweco FP-235DC - Manual (Page 22)

Generally, all ferrous metals are affected by magnetism while the nonferrous metals are not. However, some
stainless steels are not magnetic.
COLOR TEST
The two main divisions of metal include the irons and steels which are indicated by their typical gray-white
color and the nonferrous metals which come in two general color classifications of yellow and white. Copper
may be easily identified due to its color (yellowish) as are brass and bronze. Aluminum, white metal, alu-
minum alloys, zinc and similar metals are all silver-gray (with shade variations) in color.
SPARK TEST
This method of identifying metals is widely used by welders to identify irons and steels. A power grinder is
used as the test equipment.
To help prevent eye injuries when grinding, you MUST ALWAYS wear
safety goggles. The grinder MUST be inspected to see that it is in good condition
BEFORE proceeding with the test.
When testing a metal sample, if you touch it to the rim of the revolving wheel lightly, the friction of the wheel
surface will heat the resulting metal particles to an incandescent and burning temperature.
The sparks resulting from contact with the grinding wheel contact will differ in character for different types of
steel. The lighter the contact, the better. Use a black background to better identify the sparks.
The theory of the spark test is that when a metal is heated, the different parts of each metal oxidize a different
rates and the oxidization colors are different.
Relatively pure iron, when heated by the grinding wheel, does not oxidize quickly. Therefore, the sparks are
long and fade out on cooling. As the carbon content of steel or cast iron increases, the compounds of carbon
and iron have different ignition temperatures. Consequently, the characteristics of the sparks differ.
Four characteristics of the spark generally tell the nature of the condition of the steel. Those characteristics are:
• spark color;
• spark length,
• the number of explosions (spurts) along the length of the individual sparks;
• and the shape of the explosions (forking or repeating).
ADDITIONAL SAFETY INFORMATION
Make sure you read and understand all of the information and instructions contained in this manual BEFORE
proceeding.
The National Electrical Code, Occupational Safety and Health Act (OSHA) regulations, local industrial codes
and local inspection requirements also provide a basis for equipment installation, use and service.
For additional information concerning welding safety, refer to the following standards and comply with them
as applicable.
• ANSI Standard Z49.1 - SAFETY IN WELDING AND CUTTING - obtainable from the American Welding
Society, 2051 N.W. 7th St. Miami, FL 33125 (305) 443-9353.
• ANSI Standard Z87.1 - SAFE PRACTICE FOR OCCUPATION AND EDUCATIONAL EYE AND FACE
PROTECTION - obtainable from the American National Standards Institute, 1430 Broadway, New York, NY
10018.
• NFPA Standard SIB - CUTTING AND WELDING PROCESSES - obtainable from the National Fire
Protection Association, 470 Atlantic Avenue, Boston, MA 02210.
18