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Annealed Glass

Annealed Glass is glass that has not undergone any treatment process like toughening, lamination or heat strengthening. Also known as 'normal' glass, it is most commonly used for residential windows. It is brittle and very strong in compression. The use of annealed glass is limited owing to its low toughness, low tensile strength and low thermal shock resistance. Sudden change in temperature can cause the glass to break. When annealed glass breaks, it forms sharp, knife-like fragments. Annealed Glass has minimal residual stress and the stress is uniformly distributed.

Tempered Glass

Tempered Glass is safety glass processed by thermal or chemical treatment. It is four times stronger than normal annealed glass. It is called safety glass because when it breaks, it shatters into small pieces that have much lower risk of injury. Tempered Glass has much higher tensile or bending strength and better thermal shock resistance. It can withstand temperature changes of up to 200 Degree Celsius without breaking.

What is Tempering?

Tempering is a process through which stress is developed in glass to increase the mechanical strength four times than that of annealed glass. The stress distribution created is such that the outer surface is under compression and the core is under tension. The compression on the outer surface gives glass the strength and the tension at the core gives it the property of shattering into small pieces when the glass fails and a breakage happens.

Types of Tempering

There are two types of Tempering:

Thermal Toughening

  • Horizontal Glass Flow
  • Chemical Glass Flow

Chemical Toughening

Thermal toughening is achieved based on the density difference between surface and midplate.

Chemical toughening is done similar to electroplating. It involves dipping the glass in salt bath in 400 Degree Celsius for 12 to 36 hours. It is not suitable for mass production.

Types of Furnaces

Radiation Type

This type of furnace is not recommended
for low E and soft coat.

Radiation and Convection

This has a lesser cycle time than the
radiation type.

High Convection

It has a heating time between 35 and 40 seconds
The set point is 650 to 680 Degree Celsius

Heat Soak Test

The Heat Soak Test conforms to EN14179. Glass is heated to 290 +/- 10 Degree Celsius. The testing time is for 2 Hours. This test is used to to reduce the possibility of Spontaneous glass breakage. Spontaneous breakage can occur in tempered glass due to the presence of activated Nickel Sulphide. Nickel Sulphide is present in glass as part of the glass composition but it can get activated only during the process of tempering.

Heat Strengthening

Heat Strengthened Glass is glass which has been heat treated to increase Mechanical Strength and Resistance to Thermal Breakage. Heat Strengthening is similar to the process of toughening except that cooling is done at a much slower pace. It increases resistance to mechanical and thermal stress up to 130 Degree Celsius. While Heat Strengthened Glass is twice as strong as annealed glass, its fragmentation pattern is the same as annealed glass.

Tempering vs Heat Strengthening

Heat Strengthened Glass is cooled down with much less pressure. The critical aspect in manufacturing is how to create sufficient stress level (not force of cooling co-efficient). The force of stress created depends on correct & even temperature of glass and heat transfer coefficient during cooling. It is difficult to control cooling coefficient during heat strengthening.

Applications of Heat Strengthened Glass

Heat Strengthened Glass is used where optical requirement is very high. Used in high wind load areas, it is intended for general glazing where additional strength and/or resistance to mechanical and/or thermal strength are desired. It is widely used in laminated glass for additional strength (overhead or sloped glazing). However, Heat Strengthened Glass cannot be used in any safety glazing applications.

Integrated Glazing Unit (IGU)

Definition of Insulating Glass (IG)

A combination of two or more panes of glass spaced apart with a spacer bar and hermetically sealed with primary and secondary sealant to form a single glazed unit with one or more air spaces in between; Also called Double Glazing.

Integrated Glazing Unit (IGU)

Desiccant

  • 3 A Grain Size
  • Desiccant should not absorb the inert gas used in the DGU.

01

Sealants

  • Primary Sealant : PolyIsoButylene or Butyl
  • Secondary Sealant : Silicone + Polysulphide

02

Types of Desiccants used

  • Molecular Sieve
    • Nominal pore diameter
    • Base : Aluminum Silicate
    • Cation : Potassium
  • Silica Gel
    • Similar to molecular sieve but has larger pore dia
  • Zeolite

03

Frame

  • Spacer : No oil, grease, dust
  • Spacer should not be kept on the ground
  • Monitor Spacer
    • While cutting
    • While bending

04

Lamination

Laminated glass has the same strength as ordinary glass but it consists of two pieces of glass containing a sandwich of plastic interlayer. If the glass does get broken this interlayer holds the whole piece in place so there is no hole left in the window for an intruder to get in through for example or large free shards that can cut..

Benefits of Lamination

Safe

Secure

Bullet-proof

Cyclone
and
blast resistant

Noise-free

Ensures Privacy

Components of Laminated Glass

01Outer Lite

Outer lite of a laminated glass combination can be tempered, heat strengthened or annealed. It could have a thickness in the range of 2mm to 19 mm.

02Inter Layer

The inter layer is a plastic film placed between the two sheets of glass. Polyvinyl Butyral (PVB) and Ethylene Vinyl.Acetate are two commonly used polymer inter layers. The inter layer has two extremely beneficial properties- it improves the impact resistance of the glass by distributing any impact force that acts on glass and in case of a breakage, it holds the two layers of glass together in the glass frame.

03Inner Lite

The Inner Lite can also be tempered, heat strengthened or annealed. It can have a thickness range of 2 to 19 mm.

Lamination Process

Storage Conditions

PVB is hygroscopic. Interlayer is kept below 10 Degree Celsius and moisture between .4 and .65%. Relative Humidity need not be controlled.

Assembly

Room Temperature is to be maintained at 18 Degree Celsius and Relative Humidity at 30%. High temperature leads to PVB shrinkage. Air should be dust-free. There should be limited passage and floors must be tiled. Use of protective clothing is mandatory.

De-airing

It is the process of removing the air trapped between glass and PVB and ensures adhesion between them. Seal the edges so that air does not penetrate during autoclaving. Poor de-airing leads to bubbles, delamination, poor thermal stability, etc. The temperature of the pre-heating tunnel should be maintained between 40 and 60 Degree Celsius to soften the glass. The temperature of the main heating tunnel should be kept between 65 and 115 Degree Celsius.

Pre-processing

Processes involved in preparing the glass before actual processing procedure to ensure quality of processing.


Storage

Sealed packs must be used within 6 months from the date of receipt, while unsealed packs should be used within 2 months. When it comes to unloading, fiche number/tag number has to be noted at crate level. The coating surface should be away from the operator, placed on racks. The crates must be opened with care. Tag number and photos must be recorded in case of any defects or breakages.

Storage Condition

  • The place should be dry and well-ventilated in order to prevent condensation on the surface.
  • It should be protected from rain and running water (reference to leaks to be detected).
  • The temperature and humidity levels should be suitable to store coated glass.
  • Glass should never be stored outdoors.

Cutting

Precautions should be taken to keep the table clean. Oil should be based on the recommendation ACECUT 5503. Templates should not touch the coated side.

The suggested interleaving materials are:

  • Cork pads
  • Paper interlayer
  • Fork pads
  • Corrugated cardboard strips

Grinding

There are two types of grinding : Rough Grinding and Crystal Edging. It is essential to keep the glass fully wet during the whole grinding process. Wash the glass within 30 seconds of rising. Manual grinding involves 100-120 grid belts for getting the raised section on the edges of the glass. The belt should run in downward direction to minimize the grit deposited on the surface. If the grinding is not done properly, then, the temperature in the furnace....?


No hammering should be done for breaking. Snapping pliers/ snappers have to be provided in the cutting line for the purpose. Cutting pressure has to be maintained such that a silver line of the score is seen.


Washing

Washing water quality:

  • For KT: 0 to 10 micro Siemens
  • For SKN and offline products : 0-20 micro Siemens

The brushes used are made of Polyamide for low E glass. The bristles must be 40 mm long and have 0.2 mm diameter. Water must be sprayed directly on glass, not on brushes. The glass should not stay inside within the machine. No water must remain on the coated glass after the drying process.

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