Fascination Glass!

Glass as a material

01 Introduction

Strictly speaking, glass is a congealed liquid.
In the physical sense, the material is a supercooled liquid.

02 What is glass

Glass as a material

What is glass actually?

solid

malleable

liquid

At room temperature, glass is solid.

 

02 What is glass

Glass as a material

solid

malleable

liquid

At roughly 1,000 °C, glass becomes pliable and shapeable.

02 What is glass

Glass as a material

solid

malleable

liquid

At roughly 1,400 °C, the material liquefies.

02 What is glass

Glass as a material

solid

malleable

liquid

Glass as a material

Glass components

The fascinating thing about glass is that it is made exclusively from natural inorganic raw materials.

 

The most important of these materials include: quartz sand (silicon dioxide), lime (calcium carbonate) and soda (sodium carbonate). Of course, it may also contain dolomite (calcium-magnesium-carbonate) or feldspar (a silicate mineral).

 

It may include a number of other materials depending on the properties desired for the glass.

 

It is no wonder that there is a multitude of formulas for producing the impressive variety of glass products.

The significance of the Manufacturing Process

 

02 What is glass

The significance of the Manufacturing Process

The formula alone is not responsible for determining the properties of the glass product. The manufacturing process significantly affects the result.

 

Among other things, the cooling process applied to the molten glass has a significant effect. Each glass product has its own cooling period, which may take between 30 minutes and several months.

 

Cooling down the glass slowly can prevent tension in the glass product. In contrast, faster cooling can develop tension in the glass product, which will contribute to the stability of the glass product.

02 What is glass

Glass:

• Resists high temperatures

Tunable properties

• Retains its shape, but is also malleable

• Provides a gas-tight seal

• Has a neutral taste

• Does not react with other materials

• Can be recycled multiple times

Thanks to these exceptional properties, there is a multitude of ways to use glass.

Glass as a material

Property

02 What is glass

Glass as a material

High chemical resistance to water and chemicals, in particular acids and organic solvents

Field of application

Glass containers for pharmaceutical products, i.e., syringes

Property

02 What is glass

Glass as a material

Non-combustible and resists high temperatures

Field of application

Fire viewing panels, fire-resistant special glass...

Property

02 What is glass

Glass as a material

Retains its form when temperatures fluctuate

Field of application

Cooktops, oven doors and so on

Property

02 What is glass

Glass as a material

Non-conductive material

Field of application

Insulation of electrical cables

Property

02 What is glass

Glass as a material

Transmits visible light easily, which means high transparency and clarity deviation of light,

such as for prisms

Field of application

Telescopes, objectives for cameras and microscopes as well as oculars

Glass is a material with manifold properties, even though its basic composition does not change. Let’s have a closer look at three types of glass.

02 What is glass

Glass as a material

Types of glass

Optical

glass

Technical

glass

Glass-

ceramics

02 What is glass

Glass as a material

Types of glass

Optical glass

The focus of optical glass are the optical properties themselves. The requirements for optical glass are very high. The glass must be homogeneous and without any defects, such as bubbles, inclusions, or cords/streaks.

Each optical glass product is created for a very specific purpose, such as for lenses or optical filters. For that reason, the glass must comply with certain specifications for transparency (the transmission and absorption of light) and the refraction of light (the refractive index and deviation of light).

On the Abbe-Diagram, glasses are arranged according to their refractive index and their Abbe number. The measure of dispersion is represented by the Abbe number.

Such a diagram makes it clear how unbelievably multi-faceted the world of optical glass is.

Many kinds of glass belong to the same type of glass as technical glass products. However, they require specially selected, pure raw materials and, in part consist of up to 14 different components.

Optical

glass

Technical

glass

Glass-

ceramics

02 What is glass

Glass as a material

Types of glass

Technical glass

Technical glass is defined as a kind of glass that is used in products whose main area of application does not involve optics.

As a rule, technical glass products are used in the chemical industry, in laboratories, in technology, pharmaceutical industry, optical-electronics and in households.

They are distinguished from optical glass by the use of fewer raw materials. The requirements and the purity of the raw materials are often less strict than those placed on optical glass products. The manufacturing processes are also significantly different.

 

Technical glass products can be divided into roughly six categories based on their composition.

Optical

glass

Technical

glass

Glass-

ceramics

• Borosilicate glass

• Alumino-silicate glass

• Aluminum borosilicate glass

• LAS glass-ceramics

• Alkali-lead-silicate glass

• Alkaline earth metals-silicate glass

02 What is glass

Glass as a material

Types of glass

Glass-ceramics

Glass-ceramics are a special category of technical glass, which is an inorganic, partial glass and partial crystalline material.

 

It has unique properties that neither glass nor ceramic materials exhibit by themselves.

Optical

glass

Technical

glass

Glass-

ceramics

  • The partial crystalline structure resists heat better than pure glass alone
  • The expansion coefficient of certain glass-ceramic materials is nearly zero. For that reason, the material does not change when there are temperature differences
  • However, because the crystals in the material are microscopic, it can be either transparent or translucent

Manufacturing processes

03

Glass

Manufacturing

SCHOTT has developed glass products that meet exceptional requirements.

 

At the same time, SCHOTT has developed Manufacturing Processes that were the first to focus on the unique properties of glass products.

 

Here's a look at the most important manufacturing processes.

Ultra-thin glass and float glass

Drawing and floating

Drawing and floating

03

Glass

Manufacturing

Ultra-thin glass products:

The Down-Draw process

Drawing and floating

A unique manufacturing process has been developed for ultra-thin glass products: the Down-Draw technology.

 

A belt of glass will be drawn through the annealing furnace for this process. The process speed determines the thickness of the glass.

03

Glass

Manufacturing

Drawing and floating

03

Glass

Manufacturing

Manufacturing float glass products using float process

Drawing and floating

In the float process, a continuous ribbon of glass moves from the end of the melting tank through the tin bath in the direction of the cooling lehr. The glass ribbon floats on the surface of the liquid tin and is drawn to the desired width by top roller machines.

 

As a consequence of the surface tension of the molten glass, tin and bath atmosphere, the glass is shaped naturally into an absolutely flat, parallel ribbon.

 

When the glass leaves the tin bath, keeping the temperature in the range of 600 °C is the decisive factor. The glass ribbon must have the necessary mechanical rigidity for lifting the glass off from the surface of the tin.

 

In the cooling channel and the subsequent conveyor will cool down the glass to room temperature.

03

Glass

Manufacturing

Fiber drawing

03

Glass

Manufacturing

Two types of glass:

Two refractive indices

Fiber drawing

Glass optical fibers are manufactured from two different types of glass.

 

They have a core with a higher refractive index and a cladding with a lower refractive index. When light comes at the right angle to the boundary between the glass with a higher refractive index and the glass with a lower refractive index, the light is reflected and carried further along the fiber.

03

Glass

Manufacturing

Two become one

Fiber drawing

The bottom of the tube and rod will be heated, drawn downwards and at the same time melted together.

 

The speed at which the tube and cladding are drawn will determine the desired diameter of the cladding and the core. If the glass is drawn quicker, the fibers will be thinner. If the glass is drawn slower, the fibers will remain thicker. This allows the diameter to be controlled precisely.

 

If the fibers have the desired diameter, they will be given a protective lubricant as a protective mantle, which makes the bundle of fibers flexible.

03

Glass

Manufacturing

Glass powder and glass-to-metal sealed housings

Reliable protection for sensitive electronics

Glass powder and glass-to-metal sealed housings

03

Glass

Manufacturing

Glass powder

Glass powder is an important primary material for manufacturing glass-to-metal sealed housings as well as many other products.

In order to produce glass powder, the glass is first melted and cast in larger pieces called ribbons.

 

Afterwards, the ribbons undergo a grinding process, reducing their size and turning them into glass powder.

Glass powder and glass-to-metal sealed housings

03

Glass

Manufacturing

Sintered glass preforms

Glass powder can be processed into a glass preform and used as solder and sealant in glass-to-metal sealed housings and feedthroughs.

 

To create glass preforms, a binding agent is mixed into the glass powder. This process creates a glass granulate that is then pressed into a variety of calculated shapes.

 

During the subsequent sintering process, the binding agent is burned out. This leaves an exceptionally stable and precisely-shaped glass part.

Glass powder and glass-to-metal sealed housings

03

Glass

Manufacturing

A hermetic connection between glass and metal

What is a Glass-to-Metal Seal (GTMS)?

  • A glass-to-metal seal is an electrically isolated combination of glass and metal
  • Sealing glass to metal creates a non-permeable seal
  • Glass seals do not suffer from aging as organic sealing materials do
  • Glass-to-metal seals are the preferred housing technology when sensitive electronic or electro-chemical components need reliable, long-term protection

Glass powder and glass-to-metal sealed housings

03

Glass

Manufacturing

Tube-drawing and hot-forming

Glass tubing and pharmaceutical primary packaging

Tube-drawing and hot-forming

03

Glass

Manufacturing

The tube-drawing process

In the tube-drawing process, the molten glass is drawn over a hollow, rotating ceramic cylinder, so-called the Danner mandrel. The so-called drawing onion is formed at the tip of the mandrel, from which a freely suspended glass tube is drawn onto a horizontal pulling line. Compressed air is blown through the hollow mandrel to prevent the glass tube from collapsing.

Tube-drawing and hot-forming

03

Glass

Manufacturing

The hot-forming process

The glass tubes are formed into the desired shape by heating them. This process is called hot-forming and is used for all product groups.

 

The glass tube is fixated and evenly heated from all sides through continuously turning it. As soon as it is hot enough, the tube can simply be pulled apart in order to achieve the desired length. Afterwards, while still hot, the tube is shaped into a container with the appropriate tools.

Tube-drawing and hot-forming

03

Glass

Manufacturing

Rolling

Glass-ceramics

Rolling

03

Glass

Manufacturing

The cooling process

After being rolled, the glass that is processed into glass-ceramic is cooled extremely slowly and continuously from roughly 900 °C to roughly 100 °C.

 

Doing this reduces the tension in the glass. The result is a robust material that is exceptionally resistant and durable.

Rolling

03

Glass

Manufacturing

Post processing

As a cooktop, CERAN® needs special post-processing.

The raw glass is cut to the customer’s specification and holes are drilled for the control components.

 

ROBAX® is post-processed in a similar way. However, the plates can also still be formed into the desired shapes.

 

Each plate can be custom-printed. There are no limits on the decoration that can be created. The result is a highly modern design.

Rolling

03

Glass

Manufacturing

The ceramization process

Each plate is heated to roughly 900 °C. At that temperature, the molecular composition of the glass changes.

 

A part of the glass crystallizes. This means that the glass has a partial crystalline structure and thus becomes a mixed glass-crystalline component.

 

This mixed component provides the desired properties, high resistance to temperatures and no expansion of the material when the temperature changes.

Rolling

03

Glass

Manufacturing

Tank-melting

and pressings

Optical Glass

Tank-melting and pressings

03

Glass

Manufacturing

The pressing process

Pressed glass is optical glass preforms with a matte surface formed under heat and pressure. Pressed glass already exhibits the shape of the final optical components, such as lenses, prisms and so on.

  • Less material is lost

  • The shape is as close as possible to the final contours
  • Pressing is a very quick and economic process

Tank-melting

and pressings

03

Glass

Manufacturing

Glass pressings have several advantages.

The fine annealing process

Fine annealing involves heating and cooling the glass in a specific manner. This can change the optical properties and the stress birefringence. In order to precisely adjust the properties such as the refractive index, dispersion and stress birefringence precisely, the temperature vs. time profile of the annealing is precisely defined.

Tank-melting

and pressings

03

Glass

Manufacturing

Casting and ceramization

Glass-ceramic

Casting and ceramization

03

Glass

Manufacturing

Melting and casting

When the raw materials are heated up, a liquid melt is generated. Bubbles in the melt, emerging from the chemical reactions are removed in the refining process.

 

To ensure that the molten glass becomes truly homogeneous, it is stirred additionally. Then the liquid glass is cast from feeders and shaped in formats according to the specifications of the order.

Casting and ceramization

03

Glass

Manufacturing

The ceramization and cooling processes

Once the product has been cast, the casted format is cooled down to room temperature in a controlled process.

 

All surfaces of the casted format are roughly machined in a first step. During the subsequent ceramization, the temperatures are slowly increased to enable crystal seed generation. After a holding period that determines the number of seed, the temperature is increased again in order to let the crystals grow.

 

Once the crystals have reached the desired size, the format is cooled down again.

 

The extremely low thermal expansion of ZERODUR® is based on the combination of roughly 70 percent crystals and 30 percent remaining glass phase in the material.

Casting and ceramization

03

Glass

Manufacturing

THE END