Heat Treatment

 

Heat-Strengthened and Fully Tempered Glass

 

The principle

Heat treatment is a transformation process that is very similar to that of basic annealed glass. The glass is heated to about 650° C, and then cooled rapidly by fan-blown air. This immediate and sustained application of air quench produces the temper. The glass is made resistant to impact, mechanical loads and thermal stress breakage. Heat treatment does not change the spectro-photometric properties of the glass. There are two distinct heat-treated glass products: Heat Strengthened and Fully Tempered.

 

Heat-strengthened glass is made using a heating process similar to that of tempered glass. The cooling cycle takes place gradually, however. Because heat-strengthened glass has a breakage pattern comparable to that of annealed glass, it is not ideally classified as a safety glass. It is particularly suitable for use in applications subject to thermal stress but not governed by mandatory safety requirements. It is also ideal for applications requiring mechanical strength greater than that of annealed glass but less than that of tempered glass.


A spontaneous breakage of tempered glass can sometimes occur due to nickel-sulfide inclusions during the glass manufacture process. To prevent this, a ‘heat-soak’ test can be conducted to check for any inclusion of Nickel-Sulfide.

 

Heat-Strengthened Glass Vs. Tempered Glass

 

 

Feature

Heat-Strengthened Glass

Tempered Glass

Surface Compression

3,500 – 10,000 psi

10,000 psi or more

Edge Compression

5,500 – 9,700 psi

9,700 psi or more

Strength

2 times as strong as Annealed Glass of similar thickness

4-5 times as strong as Annealed Glass of similar thickness

Breakage Pattern

Similar to Annealed Glass

Fractures into small, relatively harmless fragments

Optical Distortion

Less compared to Tempered Glass

More than Heat-Strengthened Glass

Processing

Edge-work, Holing, etc., are possible to a very small extent after the glass has been Heat-Strengthened

No processing is possible once the glass has been Tempered. Processing will cause the glass to shatter into tiny bits.

Applications

  • Vision and Spandrel areas where added mechanical and thermal strength is required
  • Laminated Skylights and Solariums
  • High wind-load areas
  • Use where Safety Glazing is required
  • High windload areas
  • Fire knock-out panels
  • Glass Entrances and Storefronts
  • High-Risk Human Contact Areas
 

How do we produce heat-strengthened/tempered glass?

 

Step 1: Glass pane cutting  
 A large sheet glass (usually 4200 mm x 3210 mm) is cut to the required dimensions, as specified by our customer.
Step 2: Processing  
Because Heat-Treated glass is used whenever the demands of mechanical strength are great (such as for doors and side panels), it is crucial that all processing work – such as edge-grinding and drilling – be carried out prior to the treatment process. Processing of glasses post heat-treatment, will result in the glass shattering in the case of Tempered glass, and can result in the breakage of Heat-Strengthened Glass.
Step 3: Washing  
Post Processing, every piece/pane is carefully cleaned under controlled conditions to ensure that no impurities are present on the surface of the glass.
Step 4: Heating process  
The cleaned, annealed panes are now furnace heated to a temperature of 650-680 °C, just above the melting point of glass.
Step 5: Tempering process  
The glass is cooled rapidly by fan-blown air which makes the surface contract. The inner core of the glass takes longer to harden. This results in permanent, compressive stresses in the surfaces of the glass, that lend to the enhanced mechanical and thermal strength.
 Step 6: Labeling, Packaging, and Transportation  
Labels outlining full order details are affixed to the finished, Heat-treated glass. A protective film is also pasted on the surface of the glass to prevent scratches during transportation.
Applications  
  • Doors
  • Wall cladding
  • Partition walls
  • Floors & stairs
  • Shower Cabins
  • Skylights