What is glass?

Glass is a hard, brittle, and transparent substance produced by fusing a mixture of metallic silicates or borates of sodium, potassium, calcium, lead, or other alkali metal. Glass melts at extremely high temperatures, approximately 1400 to 1600 degrees Celsius or 2550 to 2900 degrees Fahrenheit Throughout history, glass has been used in innumerable applications from beakers to windshields to chandeliers.

Properties of glass

Glass is such a common material, it seems silly to describe it, but there are certain fundamental properties of glass. Glass is:

• Transparent
• Amorphous
• Hard and brittle
• Refractive
• Electrical insulator
• High compressive strength
• Absorb and transmit light
• Highly Recyclable

Types of glass

Glass can be generally divided into four types:

• Annealed glass
• High strength glass
• Toughened glass
• Laminated glass

Annealed glass

Annealed glass is a basic type of glass, and it is also termed "float glass". It is less hardened and durable than other types of glass.

High strength glass

High strength glass is a glass with higher silicon oxide, which increases its strength compared to annealed glass. It is commonly used indoors windows, and other applications that require high durability.

Tempered glass

Tempered or "toughened" glass as the highest strength of all other types described here. It is considerably harder and more durable than annealed glass. Tempered glass forms small granular pieces during breakage. It is commonly used for electronics, such as cell phones or televisions.

Laminated glass or safety glass

Laminated glass, also known as "safety glass", contains multiple sheets of glass with intermediate layers of plastic. When broken, the small pieces of glass are stuck within the plastic layer, which prevents shattering. The most common use of this type of class is in automobiles.

What is glass working?

Glassworking is the process by which glassware is manufactured using various techniques like glass blowing, glass sculpture, and many more.

Following is the process sequence in glass working:

• Preparation of raw material and melting
• Shaping
• Heat treatment

The diagrammatical representation for the process sequence in glass working is shown as:

Preparation of raw material and melting

The major component in all glasses is silica or silica oxide, and other components like soda ash, limestone, aluminum oxide, potash, and others are added in proportions to achieve the desired composition.

The raw material is heated above its melting temperature; the viscosity of molten glass is inversely related to its temperature.

Shaping

Shaping is described as a process to fabricate glass products or glass art. It is classified into three categories:

• Discrete processes
• Continuous processes
• Fiber-making processes

Discrete processes

Discrete processes are used to manufacture glass pieces ware like bottles, jars, light bulbs, glass spheres, and many more.

Following are the various types of piece ware shaping processes:

• Spinning
• Pressing
• Press and blow
• Blow and blow
• Casting

Spinning

Spinning is a process similar to the centrifugal casting of metals. In this process, a gob of hot glass is dropped into a rotating mold to spread molten glass on the mold and create a hollow shape. After cooling or solidifying, the glass is removed from the mold, and the desired product is achieved.

Pressing

Pressing is a process used for the mass production of flat products like dishes and television tube faceplates. In this process, the hot glass gob is fed into a mold and pressed into the desired shape by the plunger. The plunger is retracted, and the fished product is removed.

Press and blow

The press-and-blow process is used for manufacturing wide-mouth containers such as jars. In this process, the molten gob is fed into a mold cavity and pressed to form a parison. The parison is transferred to blow mold and blown to the final shape. The diagrammatical representation of the press and blow process is shown as:

Blow and blow

Blow and blow processes are used for manufacturing smallmouth containers like cola bottles, light bulbs, and many others. In this process, the gob is fed into the covered mold cavity, then the first blow step partially formed piece is repositioned in second blow mold, and blown to final shape.

Casting

Casting is the process of manufacturing large items such as astronomical lenses and mirrors. In this process, molten glass is heated until it is sufficiently fluid and then poured into a mold. After cooling and solidifying, the piece must be finished by lapping and polishing.

Continuous processes

Continuous processes are used to manufacture flat glass and tubing goods like glass sheets, test tubes, labware, and many more.

Following are the processes for producing flat glass:

• Rolling of flat plate
• Float process

Following is the process for producing glass tubes:

• Danner process

Rolling of flat plate

In the rolling of flat plate process, the molten glass from the furnace is squeezed through opposing rolls, grinding and polishing for parallelism and smoothness is also done.

Float process

In the float process, molten glass flows onto the surface of a molten tin bath, achieving uniform thickness and smoothness in the glass sheet. Grinding and polishing are not required for glass sheets manufactured by the float process.

Danner process

Danner process is used for drawing glass tubes. In this process, molten glass flows around a rotating hollow mandrel, and the air is blown through it, and glass is drawn.

Fiber making processes

The fiber-making processes are used for manufacturing fiber used in insulation and optical fiber. Glass fibers are subdivided into two categories:

• Fibrous glass
• Long continuous filaments

Fibrous glass is used for thermal insulation, acoustic insulation, and air filtration. Fibrous glass is produced by using the centrifugal spraying method.

Long continuous filaments are used for fiber-reinforced plastics or fiberglass, fabric, and fiber optics, among other things. The drawing process produces long continuous filaments.

Heat treatment

Heat treating is a process in which glassware is heated to an elevated temperature to eliminate stresses and temperature gradient, then slowly cooling the ware to overcome stress formation, then rapid cooling to room temperature.

Common Mistakes

• The crystal structure of glass can take two forms; it is either amorphous or crystalline.
• While used in similar applications and known for its strength, tempered glass differs from laminated glass. Tempered glass is created through heating, high-pressure, and chemical treatment procedures, while laminated glass is created by layering glass between sheets of plastic or other synthetic materials.
• While the flat plate and float process create glass that is similar in shape, these processes are very different.

Context and Applications

The topic of glass and glass working is significant in various courses and professional exams of undergraduate, graduate, postgraduate, doctorate levels. For example:

• Bachelor of Technology in Mechanical Engineering
• Bachelor of Technology in Production Engineering
• Diploma in Mechanical Engineering
• Bachelor of Science
• Master of Technology in Production Engineering
• Doctorate of Philosophy in Production

Related Concepts

• Crystalline and amorphous solids
• Silica Manufacturing
• Glass blowing
• Lamp working

Practice Problems

Q1. Glass is a(n) ______ material?

1. Amorphous
2. Crystalline
3. Semi-crystalline
4. None of these

Correct option - (a)

Q2. Which type of glass contains an intermediate plastic layer?

1. Annealed glass
2. High strength glass
3. Tempered glass
4. Laminated glass

Correct option- (d)

Q3. Which of the following process uses the centrifugal effect for producing glass arts?

1. Rolling
2. Blowing
3. Spinning
4. Pressing

Correct option- (c)

Q4. Which of the following process is used for the manufacturing of a torch bulb?

1. Danner process
2. Glass blowing
3. Pressing
4. Spinning

Correct option- (b)

Q5. The grinding and clearing are not required for glass sheets manufactured by the ____?

1. Float process
2. Danner process
3. Rolling of flat plate
4. None of these

Correct option- (a)