Toughened / Tempered Glass
Toughened (tempered) glass is float glass that has been heated to around 620–650 °C and rapidly cooled, making it about four to five times stronger than ordinary glass. If it breaks, it shatters into small, blunt pieces, which is why it is used for machine guards, panels, doors and safety glazing.
What it is
During toughening, the glass is heated close to its softening point and then quenched with air jets. The outer surfaces cool and harden first, leaving them in compression while the core is in tension. This balance gives the strength and the safe break pattern.
Because the stress is locked in, toughened glass cannot be cut, drilled or edge-worked afterwards. All sizing, holes, notches and edge finishing must be done before toughening, so an accurate drawing is essential.
Typical applications
- Machine guards and inspection windows
- Equipment, cabinet and oven doors
- Control panel and display covers
- Partitions, railings and architectural glazing
- Furniture tops and shelving
Materials & grades
- Clear float glass (3–19 mm)
- Extra-clear (low-iron) glass
- Tinted and reflective glass
- Frosted or printed glass (screen printing before toughening)
Points to consider
- Give final sizes, hole positions and edge finish on the drawing; nothing can be changed after toughening.
- Holes should be at least the glass thickness in diameter and kept away from edges and corners (as a rule of thumb, at least about twice the thickness from an edge).
- Rare spontaneous breakage from nickel sulphide inclusions can be reduced by heat soak testing, recommended for overhead or high-risk glazing.
- Toughened glass can show slight roller-wave distortion; mention it if optical clarity is critical.
- For higher temperatures or chemical exposure, borosilicate or ceramic glass may be more suitable.
Frequently asked questions
Can toughened glass be cut or drilled?
No. Any cutting, drilling or edge work after toughening will shatter it. All processing is done on the annealed glass before it goes into the toughening furnace.
How much stronger is toughened glass?
Typically four to five times stronger than ordinary annealed glass of the same thickness, and it also withstands much larger temperature differences.
What is the difference between toughened and laminated glass?
Toughened glass breaks into small blunt pieces. Laminated glass has a plastic interlayer that holds the broken pieces together, keeping the opening covered. The two can be combined for high-safety uses.
What thickness of toughened glass do I need for a machine guard?
It depends on size, support and impact risk. Small guards often use 5–6 mm and larger panels 8–10 mm or more. Polycarbonate may be preferred where heavy impacts are possible; share the details and we will advise.