Chemically Strengthen Glass

Overview

Terminology

  • Mechanical Properties
  • Thermal Properties
  • Optical Properties
  • Units

Mechanical Properties

Impact & Flexural Bending Strengthens Are The Two Most Critical Mechanical Properties Of Chemical Strengthen Glass

Strengthened glass has excellent impact and flexural (bending) strength. Strength is specified by a Modulus of Rupture (MOR) test, surface compression test, and/or by Depth of Layer (DOL) test.

Chemical strengthened glass is classified by two strength components, surface compression and depth of layer (DOL). Surface compression values relate to flexural (bending) strength (MOR), impact strength, hardness penetration (scratching) and thermal shock resistance.

Depth of layer values relate primarily to the amount of sustained abrasion resistance and the impact resistance of the surface compression layer.

For a thermal heat strengthen glass to break it requires a stress 5 times higher than the stress imparted to float glass, to break a chemically toughened glass 10-15 times more stress in required.

In addition to higher flexion resistance, the other important feature of chemically heat strengthen glass is impact resistance.

If a thermal heat strengthen glass has an impact resistance of approximately 2.5 times than ordinary float glass (using a steel ball), the resistance of a chemical strengthen glass is 5 times higher than the resistance of float glass.

Processing times and temperatures as well as pre-heat/cool-down procedures affect both values and are determined based upon the application requirements. Because the chemical strengthening process treats the entire surface and all edges, fabrication processes should be completed prior to treatment.

Thermal Properties

Strengthened Glass Resist Thermal Shock

Strengthened glass has a resistance to thermal shock cycling that will vary based upon the actual surface compression created. In applications requiring capability to withstand thermal shock, heat tempered or chemically strengthened glass should be specified.

Optical Properties

Chemical Strengthening Process Does Not Affect Original Glass Optical Properties

During chemical processing, the glass temperature is lower than glass melting temperature and meanwhile, the glass does not move. So the optical quality is much better than those glass done by thermal tempering which the glass oscillates and travel on ceramic roller at softening temperature.

There will be a visible stress pattern observed when the part is placed between polarizing sheets that are oriented to each other at 90 degrees. This stress pattern is a result of the residual surface and edge compression introduced by heat strengthening.

Units

Terminology Of Strengthened Glass Is Always Expressed In Several Units

There are several international units system adopted to indicate the data relevant to the measurements of strength and pressure/stress.

NEWTON (N)

  • It is the force required to impact to a mass of one kilo the acceleration of a meter in a second per second.
  • Strength: mass x acceleration
    F=ma
    1 kgf = 1 kg x 9.81 m/s2 = 9.81kg x m/s2 = 9.81N
  • To simplify the calculation:
  • 1 kgf = 10N
  • 1 KN (Kilo-Newton) = 103 N
    1 MN (Mega-Newton) = 106 N

  • PASCAL (Pa)

  • It is the relationship between strength and surface

  • 1 Pa= 1 N/m2
  • To define the material's resistance characteristics, the mega pascal (Mpa) is used.
    1 Mpa = 1 N/mm2
  • The relationship between the international system of measuring and the technical one is decoded by the following equivalence factors:
  • 1 Kg/cm2 =0.1 N/mm2 (MPa) = 10 N/m2 (Pa)
  • 1 N/mm2 (MPa) = 10 Kg/cm2 = 10 N/m2 (Pa)

  • PSI (Pound Per Square Inch)

  • It is used to indicate the surface compression level of the glass after the toughened cycle.

  • 1 Mpa = 145 PSI
    1 PSI = 0.07031 kg/cm2