2022 HSC Engineering Studies Paper Theory Revision Quiz

Which of the following correctly describes the thermal toughening process for glass?

• Cooling glass slowly to remove internal stresses

• Heating glass to ~550–650 °C and then rapidly cooling the surface layers

• Adding reinforcing fibres to glass before cooling

• Applying compressive loads mechanically during shaping

Answer explanation

The thermal toughening process involves heating glass to ~550–650 °C and then rapidly cooling the surface layers, which creates compressive stresses that enhance strength and resistance to thermal shock.

In thermal toughening, why does the surface of the glass end up in compression?

• The outer layers cool first and contract before the inner core, locking in compressive stresses

• The inner core cools faster than the surface, creating tension on the outside

• The glass is chemically treated to expand the surface

• Reinforcement rods are added to the surface during cooling

Answer explanation

In thermal toughening, the outer layers of glass cool first and contract, while the inner core remains hot. This difference in cooling rates creates compressive stresses on the surface, making it stronger.

What is the effect of surface compression in toughened glass?

• Makes the glass more flexible but weaker in tension

• Increases its resistance to surface cracks and impact forces

• Reduces transparency and makes the glass opaque

• Prevents the glass from shattering when overloaded

Answer explanation

Surface compression in toughened glass increases its resistance to surface cracks and impact forces, making it more durable and less likely to break under stress.

Which alternative method can also be used to manufacture toughened glass?

• Extrusion

• Chemical toughening

• Rolling

• Lamination

Answer explanation

Chemical toughening is a process that enhances the strength of glass by introducing compressive stresses on its surface, making it a viable alternative method for manufacturing toughened glass.

During thermal toughening, the glass is typically heated to which temperature range?

• 100–200 °C

• 300–400 °C

• 550–650 °C

• 900–1000 °C

Answer explanation

During thermal toughening, glass is heated to 550–650 °C to increase its strength and thermal resistance. This temperature range is optimal for achieving the desired properties in the glass.

What is the first step in the thermal toughening process of glass?

• Rapidly cooling the surface layers

• Heating the glass to about 550–650 °C

• Adding reinforcing fibres

• Applying compressive forces externally

Answer explanation

The first step in thermal toughening is heating the glass to about 550–650 °C. This process prepares the glass for subsequent rapid cooling, which increases its strength and thermal resistance.

In thermal toughening, why is the surface of the glass placed in compression?

• The surface cools and contracts after the core

• The inner hot core contracts as it cools, forcing the surface into compression

• Reinforcement rods are added to the surface during manufacture

• The glass is laminated with plastic layers

Answer explanation

In thermal toughening, the inner hot core of the glass cools and contracts first. This contraction pulls the surface inward, creating a state of compression on the surface, which enhances the glass's strength.

Which property of glass is improved by placing the surface in compression during toughening?

• Transparency

• Impact resistance and crack prevention

• Electrical conductivity

• Thermal insulation

Answer explanation

Toughening glass involves placing its surface in compression, which significantly enhances its impact resistance and prevents cracks. This process makes the glass more durable compared to untreated glass.

Which of the following is an alternative method to produce toughened glass?

• Annealing

• Chemical toughening (ion exchange)

• Extrusion

• Rolling

Answer explanation

Chemical toughening (ion exchange) is an effective method to produce toughened glass by replacing smaller ions in the glass surface with larger ones, enhancing its strength. Other options like annealing do not achieve the same toughness.

During chemical toughening, how is the glass surface strengthened?

• By replacing smaller ions in the glass with larger ions

• By heating to 900 °C then cooling slowly

• By coating with an external polymer

• By laminating glass sheets together

Answer explanation

During chemical toughening, the glass surface is strengthened by replacing smaller ions with larger ions. This ion exchange creates compressive stresses on the surface, enhancing its strength and resistance to breakage.