Disadvantages

Toughened glass is difficult to break therefore has limited break glass use. Assumingly, there are situations where you would WANT glass to break, I personally can’t think of any, but there you have it. In that situation, toughened glass would not be appropriate

Limited design – confined to simple shapes. Quite simply, complicated glass shapes are difficult to be made tough. More often than not, toughened glass is made in the form of simple shapes and sizes, such as a large square for a French window perhaps.

Advantages

Now then I’ve already spoken about how the glass shatters into small cubes, thus reducing the likeliness of injury. I’ve also mentioned how, when compared to a piece of glass of the same thickness, toughened glass will be the stronger (again quite obviously)

Toughened glass also has a higher resistance to heat.

Two types of heat treated glass

Now then, there are two main types of heat treated glass. heat strengthened and fully tempered. Now those sound like some pretty complicated things, but fear not, I’m here to explain them.

First let’s start with Heat strengthened Glass:

Heat strengthened glass is twice as strong as annealed glass. The heat puts the molecules under pressure and this makes the glass much stronger.

Fully tempered glass is typically four to six times the strength of annealed glass and withstands heating in microwave ovens. The difference is the residual stress in the edge and glass surface. Fully tempered glass in the US is generally above 65 Mega Pascal while Heat Strengthened glass is between 40 and 55 Mega Pascal.

Manufacturing

In 1952 Alistair Pilkington invented the float glass process. This process used a horizontal method whereby glass was drawn over top of a bath filled with molten tin. This method is still the most common method of glass manufacture today.

Toughened glass is essentially made in the same way as normal, annealed glass. The only difference is that there is an extra stage at the end of the manufacturing process which adds around 3~ 5 times greater strength than the ordinary annealed glass.

Uses

So what are the Uses of Tough Glass?As you can see, it is used primarily in car windows

Also used in buildings for unframed assemblies such as frameless doors

 

They’re also used in payphone cubicles, but as you can see tp the right, toughened glass is anything but unbreakable

 

Basically it’s used anywhere ordinary glass might cause harm, namely car windows.

The Properties of Toughened Glass

So I hear you asking, “what are the properities of to

ughened Glass, Simon?”

Well this slide should explain

Obviously, it’s going to be stronger than ordinary lass

It also has Enhanced thermal resistance

And instead of breaking into sharp shards, it breaks into small cubes, which means it’s less likely to cause injury.

How is Toughened Glass different to Ordinary glass?

Ordinary glass will break when it is under a stress that it cannot withstand. This stress can be caused by sudden impact, increasing pressure upon certain points of the glass, or by cracks developing in the glass' surface.

So how is Toughened Glass different?

Any cracks in the surface of the glass serve to raise the stress in a particular part of the glass. But, cracks can only grow in areas of tensile stress, where adjacent molecules are already being pulled apart. This makes it easy for the cracks to spread. Because the surface of toughened glass is in compression, these small cracks have little effect upon the glass, because the internal compression forces act against their force upon the glass.

What IS toughened Glass?

So what is Toughened glass? Well, as the name might suggest, it is glass that is tough.

 

It’s basically just ordinary glass that has been processed to increase its strength. This can be done by either:

 

Controlled thermal or chemical treatments.

 

The term toughened glass is generally used to describe fully tempered glass but is sometimes used to describe heat strengthened glass as both types undergo a thermal 'toughening' process, however, we’ll come back to that a little bit more later.