Technology and our changing world high Technology

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Bu səhifədəki naviqasiya:

• Mining metals
• Review questions.
• CUTTING HEAVY METAL

Metal	Color		Properties		Characteristics
Uses
Aluminum	Bluish- white		Ductile, malleable, easily worked, good, conductor of heat and electricity		Work-hard ens easily, must be annealed, difficult to solder, light­weight		Cooking utensils, electrical parts, drink cans, craft projects.
Brass	Yellow- gold		Brittle, hard, can be worked much as copper		Alloy of copper (90 percent) and zinc (10 percent), work hardens very easily, must be annealed often or it will crack, easily soldered, heavy in		Plumbing fixtures, electrical parts, craft projects.
				weight.
Bronze		Reddish- yellow	Brittle, hard, wear-resistant, can be worked mush as brass, corrosion- resistant.	Alloy of copper (90 percent) and tin (10 percent), easily soldered, heavy in weight.		Machine bearings, plumbing parts, cast parts.
Copper		Reddish- brown	Ductile, malleable, good conduction of heat and electricity, corrosion resistant	Work-hard ens easily, must be annealed, easily soldered, heavy, in weight		Electric wire and parts, cooking utensils, plumbing pipe, craft projects.
Nickel silver or German silver		Silver- white	Brittle, hard, hard to work.	Alloy of copper (64 percent), nickel (18 percent), and zinc (18 percent).		Jewelry tableware, craft projects.
Pewter		Silver- gray	Malleable, easily, worked, very soft	Alloy of copper (10 percent) and tin (90 percent), does not work-harden easily, heavy in weight, difficult to solder.		Bowls and vases, craft projects.

Mining metals

Metals are found in ores that are mined from tie earth. These ores are refined and worked into many shapes and sizes. The mining and refining industries are important. They supply the materials for metal products.
Steel comes from iron ore, copper from copper ore, and aluminum from an ore called bauxite. All metal ores are processed in much the same way.
Review questions.

1. 
   Of what metals are the following alloys made: brass, bronze, pewter, nickel - silver?
   
2. 
   What is an alloy?
   
3. 
   What is ductility?
   
4. 
   What is malleability?
   
5. 
   List some of the precautions lhe steel industry takes to protect the air and the land.
   

CUTTING HEAVY METAL
To cut thick metal in the school shop, or in the home workshop, one of the following tools is used:

• 
  Hacksaw
  
• 
  Metal-cutting band saw
  
• 
  Throatless shears
  
• 
  Slitting shears
  

A hacksaw is a thin, narrow blade with small teeth along one edge, mounted in a U-shaped frame.
7. Select the correct blade. Blades are made of low-carbon or low- tungsten steel, or tougher alloy steel. Common blade lengths are 10" and 12".
When selecting the correct toolh size for the material to be cut, remember that at least two teeth should be engaged in cutting at all times. Soft or heavy metals require a coarse tooth blade (fourteen or eighteen teeth per inch). Thin wall sections, such as tubing, require one with fine teeth (twenty-four or thirty-two teeth per inch).
The teeth are set or staggered to form the cutting edge to prevent binding Ih e b lad e in th e work p iece.

2. 
   Position the blade. Adjust the frame for toe correct length of blade. Make sure that toe teeth point forward, or away from toe handle. Insert toe blade. Tighten it just enough to hold it rigid at all times. A loose blade will not cut straight. After a blade has been used for a while it will tend to loosen. It should then be retightened. Fasten toe work in toe vise. Use soft vise jaws of wood, copper, or aluminum when clamping soft metals or stock with afine finish.
   
3. 
   Start the cut. The best way to start a cut in hard metals is to file a notch. A cut should always be started at a shallow angle off toe edge of toe workpiece. Guide toe baled with your thumb. Begin with light pressure and a steady forward stroke. When toe cut is started, use both hands to hold toe frame. Apply steady pressure on toe forward stroke. Then release toe pressure on toe return stroke, and bring toe saw back to starting position. With out proper pressure toe teeth will dull rapidly because of the rubbing action. Remember to use the total length of toe hacksaw blade in cutting. When toe cut is nearly complete, hold toe end to be cutoff in your lefthand. Make toe lastfew strokes with toesaw in toerighthand only.
   

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