General Properties of Aluminum and Aluminum Alloys

Aluminum

Aluminum is the most widely used nonferrous metal, being second only to steel in world consumption. Aluminum is produced in both “pure” and alloyed forms. Aluminum is commercially available up to 99.8% pure. The most common alloying elements are copper, silicon, magnesium, manganese, and zinc, in varying amounts up to about 5%. The principal advantages of aluminum are its low density, good strength-to-weight ratio (SWR), ductility, excellent workability, castability, and weldability, corrosion resistance, high conductivity, and reasonable cost. Compared to steel it is 1/3 as dense (0.10 lb/in3 versus 0.28 lb/in3), about 1/3 as stiff (E = 10.3 Mpsi {71 GPa} versus 30 Mpsi {207 GPa}), and generally less strong. If you compare the strengths of low-carbon steel and pure aluminum, the steel is about three times as strong. Thus the specific strength is approximately the same in that comparison. However, pure aluminum is seldom used in engineering applications. It is too soft and weak. Pure aluminum’s principal advantages are its bright finish and good corrosion resistance. It is used mainly in decorative applications.

General Properties of Steel Alloys

Cast Steels

Cast steel is similar to wrought steel in terms of its chemical content, i.e., it has much less carbon than cast iron. The mechanical properties of cast steel are superior to cast iron but inferior to wrought steel. Its principal advantage is ease of fabrication by sand or investment (lost wax) casting. Cast steel is classed according to its carbon content into low carbon (< 0.2%), medium carbon (0.2–0.5%) and high carbon (> 0.5%). Alloy cast steels are also made containing other elements for high strength and heat resistance. The tensile strengths of cast steel alloys range from about 65 to 200 kpsi (450 to 1380 MPa).

General Properties of Cast Iron Alloys

Cast Iron

Cast irons constitute a whole family of materials. Their main advantages are relatively low cost and ease of fabrication. Some are weak in tension compared to steels but, like most cast materials, have high compressive strengths. Their densities are slightly lower than steel at about 0.25 lb/in3 (6920 kg/m3). Most cast irons do not exhibit a linear stress-strain relationship below the elastic limit; they do not obey Hooke’s law. Their modulus of elasticity E is estimated by drawing a line from the origin through a point on the curve at 1/4 the ultimate tensile strength and is in the range of 14–25 Mpsi (97– 172 MPa). Cast iron’s chemical composition differs from steel principally in its higher carbon content, being between 2 and 4.5%. The large amount of carbon, present in some cast irons as graphite, makes some of these alloys easy to pour as a casting liquid and also easy to machine as a solid. The most common means of fabrication is sand casting with subsequent machining operations. Cast irons are not easily welded, however.

Types of Heat Exchangers

A heat exchanger is a system used to transfer heat between two or more fluids. Heat exchangers are used in both cooling and heating processes. There are different types of heat exchangers

1. Double-pipe (pipe-in-pipe) heat exchanger - simplest type of heat exchanger consists of two concentric pipes of different diameters. Following two types of flow arrangement are possible

Types of Steel and its Manufacturing

Steel is an alloy of iron and carbon, with carbon content up to a maximum of 1.5%. Most of the steel produced now-a-days is plain carbon steel or simply carbon steel. Steel is divided into the following types depending upon the carbon content:

• Dead mild steel — up to 0.15% Carbon
• Low carbon or mild steel — 0.15% to 0.45% Carbon
• Medium carbon steel — 0.45% to 0.8% Carbon
• High carbon steel — 0.8% to 1.5% Carbon

Inspection Methods to Find Defects in Casting

In casting process, first few castings will be inspected dimensionally and the pattern is qualified afterwards, only few random inspection will be done. Every casting must be inspected to find out the defects in casting process.

Different methods of inspection to find out defects in casting process are discussed below

• Radiographic Examination
• Ultrasonic inspection
• Visual Inspection
• Hydrostatic Pressure Test
• Magnetic Particle Inspection
• Dye Penetrant Inspection
• Coin Testing

Types of Couplings Used in Shafts

Couplings are mechanical elements that ‘couples’ two drive elements which enables motion to be transferred from one element to another. The driven elements are normally shafts. Application of couplings are mainly seen in automobiles, for example the drive shaft which connects the engine and the rear axle in an automobile is connected by means of a universal joint.

In order to transmit torque between two shafts that either tend to lie in the same line or slightly misaligned, a coupling is used. There are various types of coupling available based on the area of application. They are generally categorized in the following varieties

Effects of Welding on Your Eyes?

Between UV radiation and flying debris, welding can certainly cause damage to your eyes, but only if you don’t observe the correct safety protocol. Since 25% of all welding injuries are eye-related, proper eye protection on the job is a serious issue.

The good news, though, is that most of these eye injuries are preventable, and the bulk are also reversible. To put that into perspective, fully 95% of welders sustaining eye injuries are back at work within a week, while over 50% return within two days.