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To ensure a successful welding job, it is important to understand the composition of the metal before welding.
Metalworkers and welders must be able to identify different metal products in order to apply the correct work methods. Every engineering drawing must be examined to determine which metal is being used and how it will be treated.
After some practice, welders will be able to recognize that not all parts of equipment or machines are cast iron. Other parts are often forgings.
Metal Composition Tests
To identify metals, there are seven different tests that can be done in the shop.
The table summarizes six of the various tests. These tables should be supplemented with table 7-1 and table 7-2 which show the physical and mechanical properties and table 7-3 which shows hardness data.
These tests are:
The appearance metal composition test covers the color, and the appearance of machined and un-machined surfaces. The identity of the metal is determined by its form and shape.
The shape of the metal can be descriptive. For example, it could include cast engine blocks, automobile bumpers, and reinforcing rods.
The form of the part should be taken into consideration. It may reveal how it was made, such as castings with obvious surface appearance and parting lines or hot rolled wrought materials, extruded, or cold rolled with smooth surfaces.
The pipe can be cast or wrought. The color of metal can be used as a strong indicator. It can identify many metals, including copper, brass, and aluminum as well as magnesium, precious metals, and even magnesium.
To determine the color of unoxidized metals, you can scrape off the oxidation if they have been oxidized. This allows you to identify copper, magnesium, and lead.
This is a sign that the steel has oxidized or rusted. It can be used to distinguish between plain carbon steels and corrosion-resistant steels.
You can quickly identify metal by inspecting the surface of the damaged part or looking at chips made with a hammer, chisel, and/or a chisel.
The color of the base metal will be visible on the surface without any oxidation. This is true for copper, lead, and magnesium. Other cases will show a structure by the roughness or coarseness of the surface.
It is also a sign of its ductility or lack thereof. Also, It is considered to be one of the most ductile metals if it bends easily and doesn’t break. It is considered one of the more brittle metals if it breaks easily, with little to no bending.
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The spark metal composition test can be used to classify steels and iron based on their composition. It is done by looking at the sparks that are formed when metal is held against a high-speed grinding wheel.
Although this test is not a replacement for chemical analysis, it is a fast and convenient way to sort mixed steels with known spark characteristics.
The sparks produced by different types of iron and steel can be held against a grinder wheel. They are varied in length, shape, color, and size. To get a good spark stream, the grinding wheel should be rotated at a speed of at least 5kft (1525m) per minute.
The grinding wheels should be durable enough to withstand wear, but soft enough to maintain a cutting edge. Spark testing should only be done under dimmed light as the spark’s color is crucial. It is better to compare the sparks of standard metal samples with the test sample in all cases.
Nonferrous metals like coppers, aluminum, and nickel-base alloys are not suitable for spark metal composition testing, as they don’t exhibit spark streams of any significance. This is however one way to distinguish ferrous from nonferrous metals.
Spark Test Results
Spark testing isn’t very useful for nonferrous metals like coppers, aluminum, and nickel-base alloys. They don’t exhibit spark streams that are significant. This is one method to distinguish ferrous from nonferrous metals.
The metal composition test spark should be directed down and studied. Material characteristics such as the color, shape, length, activity, and size of the sparks are all affected.
There are specific items in the spark stream that can be identified. Carriers lines are straight lines. They are often solid and continuous.
They may split at the end of the carrier lines into three shorter lines or forks. A sprig is a spark stream that splits into multiple lines at the end.
There are also sprigs at various places along the carrier lines. These are known as fan bursts or star bursts. Sometimes, the carrier line may expand slightly for a very brief length, then continue to enlarge for a shorter length.
These heavier parts are known as spear points or buds when they occur at the ends of the carrier lines. These thicker areas in the carrier lines and spearheads are caused by high sulfur.
Cast irons have very short streams, while low-carbon and most alloy steels have long streams. Cast irons have reddish or straw yellow sparks while steels typically have white to yellow colors.
A 0.15 percent steel has sparked in long streaks and some tendency to burst with sparkler effects. A carbon tool steel displays pronounced bursting.
Steel with 1.00% carbon exhibits brilliant and minute sparklers or explosions. The intensity of bursting will increase with increasing carbon content.
This metal composition test has a major advantage: it can be used for the metal in all stages, bar stock in racks and machined forgings as well as finished parts.
Spark testing is best done by keeping the steel still and touching a portable grinder at high speed to the specimen.
The grinder will apply enough pressure to produce a horizontal spark stream of approximately 12.00 inches. (30.48 cm) in length and at right angles to the line of vision.
It is important to keep the wheel pressure against the work. An increase in pressure will cause the temperature of the spark stream to rise and create the appearance of higher carbon content.
You should observe the sparks around and near the wheel, as well as the spark stream’s middle and the reaction of incandescent particles towards the end.
Attention: Be cautious when using the torch metal composition test. It may cause damage to the part being tested. Magnesium can also ignite if heated in an open atmosphere.
The oxyacetylene torch allows the welder to identify different metals by looking at how quickly the metal melts, how the molten metal and slag look, and the color changes that occur during heating.
The rate at which a piece of white metal is melting can be determined by the sharp corners. If the material is made of aluminum because of its high conductivity, it won’t melt until enough heat is applied.
Zinc is used if the part is zincThe sharp corner will melt quickly because zinc is not a good conductor. Copper is the case if the sharp comer melts it will usually be de-oxidized copper.
It is electrolytic copper if it doesn’t melt after much heat has been applied. If they are made of lead, copper alloys will boil. Apply the torch to filings to distinguish aluminum and magnesium.
Magnesium is a good choice. It will glow with a bright white flame. Before melting, steel will display its characteristic colors.
A small magnet can quickly be used to test the magnetic metal composition. It is possible to distinguish a strong magnetic material from a weakly magnetic one with experience.
It is easy to recognize nonmagnetic material. The strong magnet materials are the low- and carbon-alloy steels as well as iron alloys and pure nickel.
Monel, high-nickel alloys and stainless steel of the 18chrome 8 nickel type can produce a slightly magnetic reaction when cold worked such as in a seamless tub.
Materials that are not magnetic include:
- Alloys made from copper-base
- Aluminium-base alloys
- Zinc-base alloys
- Annealed 18 Chrome 8 Nickel Stainless
- Precious metals
- Chisel Test
To identify metals, you can also use the chip test or chisel-metal composition test. A banner and a cold chisel are all you need.
The cold chisel can be used to hammer the corner or edge of the material being examined. A measure of the metal’s hardness is how easy it is to produce a chip. A chip that is continuous is a sign of a ductile material, while chips that break apart are an indication of a weaker metal.
The chips can be used on aluminum, mild steel, and malleable metals. They can be easily chipped and do not tend to split apart. Gray cast iron chips are fragile and break down into small pieces.
High-carbon steel has a hard time finding chips due to the material’s hardness. However, they can be obtained continuously.
Test for Hardness
Table 7-3 lists the hardness values for the different metals. Also, see the information above about the three most commonly used hardness tests.
The file test, which is less exact in hardness testing, is an alternative. Table 7-6 shows a summary of the reaction of filing, the approximate Brinell hardness, and the possible steel type.
You must use a sharp mill file. The part must be steel. A file test can help you identify the type of steel. Approximate Hardness of Steel as Tested by File Test – Table 7.6
To identify a material, there are many chemical metal composition tests that can be performed in the shop.
One drop of nitric acids can be applied to the surface to distinguish Monel from Inconel. It will turn blue-green with Monel but not on Inconel. A few drops of 45 percent phosphoric Acid will cause bubbles on low-chromium Stainless Steel.
Silver nitrate can distinguish magnesium from aluminum. This will leave a black spot on magnesium but not aluminum. These tests can be complicated and are not covered here.
- Color Code for Marking Steel Bars
- SAE Metal Classifying and Grading System
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The United States Department of Commerce’s Bureau of Standards has a color code to make steel bars.
You can apply the color markings in the code by painting the ends to bars. Solid colors are usually carbon steel. Twin colors signify alloy and free-cutting.