Glass Production – Types and Processes

In this article, we will explain the general glass production techniques and the general products from this material. You will have brief information about these topics here.

What is Glass?

We can say that glass is a state of material under certain circumstances at solidification. If we want to obtain a glassy state from a material, we must not allow the crystalline structure to occur on that material. So, for a glassy state, we need to provide a non-crystalline structure for that material. Obtaining a non-crystalline structure is about to solidify speed. Also, at low solidification speed, crystallization occurs in most materials. For a non-crystalline state of a material, we must establish high-speed solidification.

Commercial Glass Production as a Material

Also, there is a ‘glass’ term for a specific material that all of us know. In that commercial, we use this material in bottles, windows, etc. The main constituent of them is ‘silica’. As we stated in another article about it, they obtain silica from ‘quartz’ and they obtain quartz from sandstone and silica sand. In engineering, they call this material ‘silica glass’.

Properties of Silica Glass Material in Production

It is a very thermal resistant material and the thermal expansion of most types is very low. Because of that, they can use this material in high-temperature applications. The thermal shock phenomenon is not a prominent thing for them.

As we stated above, silica is the main constituent in them. But a slight amount of oxides was also added to the structure. That SiO2 constituent provides much more control over solidification, and with this slow solidification rate, they can shape easily. It prevents the occurrence of crystalline structure for this material. Also, oxides of silica are called ‘glass former’ materials in the market.

Reasons to Add SiO2 into Glass Production

• SiO2 acts as a flux.
• Retarder. SiO2 retards devitrification upon crystalization of them.
• SiO2 reduces the thermal expansion characteristics of this material.
• SiO2 gives resistance to chemical attacks of acids etc. to them.
• Gives fluidity to glass in a molten state.

How is the Glass Production?

Silica is one of the most important raw materials which we generally use to produce glass. Also, we use recycled material to produce a specific amount of it production.

They obtain silica from sand. There is a raw material for glass inside sand that we call ‘quartz’ in production. To obtain this quartz, they wash sand and ‘classified’. So, the process which we call ‘classifying’ includes a bunch of sub-processes to removing unwanted impurities from sand and classifying sand according to the shape and size of sand grains.

When they apply the proper washing and purifying operations to sand, sand is classified to obtain sand grains around 0.1 to 0.6 mm and are separated for glass production.

This obtained special sand is mixed with other additives;

• Special minerals,
• Soda ash,
• Limestone,
• Aluminum oxide.

Furthermore, this mixture constitutes the starting form of this material as sand. We melt this mixture by using special furnaces to obtain the required glass for special applications and production.

Glass Melting Operations in Production

To work with glass production, such as shaping them, they must obtain a liquid form. They melt the starting sand to produce this material around 1500-1600C degrees around 24-48 hours. Also, there are various kinds of shaping operations are available for different glass applications and productions. So, we must obtain the required viscosity according to the application.

The viscosity of the molten state is dependent upon its temperature. With the increasing temperature of it, viscosity decreases. So, they adjust the required viscosity for the specific glass shaping process.

Glass Melting Furnaces

The sand which they mix with various additives to melt in furnaces we call ‘charge’. They charge this ‘charge’ to furnaces for melting. Typically, there are four types of glass melting furnaces that they generally use in the glass production industry;

• Electric Furnaces: For various product ranges of glasswares, they use electric furnaces to melt the sand.
• Day Tanks: They burn various fuels to melt the material for bigger production rates of molten state.
• Pot Furnaces: For smaller production rates of molten ones, they heat small ceramic pots, which includes charge inside these pots.
• Continuous Tank Furnaces: These tanks are best suited for serial production manner for glassware. There is a long heated tank that charge is given from one side. On another side, a molten state is obtained. The charge is provided continuously to these kinds of melting equipment.

As you understand above, they produce it in the glassware production sites generally, because of the requirement of molten glass for production.

What are The Glass Shaping Processes?

After they produce glass from its raw materials, they shape these molten glasses into the required shapes to produce the required glass products. In here, we explain the general shaping processes available in the industry.

Casting Operations of Molten Glass in Production

They melt it sufficiently to cast it inside molds to obtain special glassware. They make the casting of these materials done for the casting of big telescope lenses and kinds of applications like this. And also, slow solidification is very important to prevent internal crackings of products.

Spinning Operations

This is a very basic process that they use in the production of cathode tubes and television tubes. There is a spinning metal mold that a piece of molten state is put inside it. With the rotation, molten material takes the shape of a spinning metal mold. This is a similar process to the centrifugal casting of metals.

Rolling Operations of Glass

They apply the rolling operations to a molten state to obtain flat shapes such as window applications. A bunch of rollers gives a flat shape to them which is came from melting furnaces. They apply the required annealing and additional processes after rolling this material to obtain flat, parallel, and smooth shapes.

Centrifugal Spraying of Molten Glass

A special bowl that has very small holes around that they rotate. And molten state flow on this bowl. With centrifugal force, molten glass flow from these holes. So, we obtain very thin glass wools. We use these wools generally in both thermal insulation and sound insulation.

Floating Process of Molten Glass

In the floating process also, we obtain flat shapes. But the smoothness of produced flat glasses is superior to the rolled glasses. And there is no need for the application of the additional process to obtain the required smoothness. Molten metal directly comes from a melting furnace, and it floats on the liquid tin. When we obtain the uniform thickness of the material, the glass is drawn to the annealing section.

Pressing Operation

Pressing processes are the most common process that we apply to molten glasses to obtain customer products such as kitchenware, automobile headlights, etc. Very basic pressing mechanisms we use obtain required shapes from the molten state.

Glass Tube Production with Drawing Operations

This is a very special process that molten material comes onto a rotating mandrel which blows air from the edge. With the airflow, they give a hollow shape to the fluxing molten glass. The size of the mandrel and the rate of airflow determines the thickness and size of the tube. Laboratory glassware, fluorescents, and products like them are produced.

Glass Filament Production

We generally use glass filaments in fiber-glass reinforced composites. They produce these with special plates which have hundreds and thousands of holes on them. Also, they produce these plates from platinum alloy. They draw a molten state on this plate. When molten metal passes through these holes, we obtain filaments. These filaments roll on spools. But before rolling, we generally coat them with some additives for protection.

Blowing 

Blowing is a very old technique to obtain containers and shapes like that. But in today’s technology, we apply to blow with fully automated techniques. There are two types of blowing operations;

• Multiple Blowing: We apply multiple steps of blowing operations to molten pieces to obtain the required shapes.
• Blowing After Pressing: They blow the molten state piece right after pressing it to obtain the required shapes.

This is one of the most important materials for our civilization. There are lots of engineers labor forces and scientists that are working on the development of glass production processes.

In general, in every application, the types of ingredients of this material are the same. But the compositions of these ingredients change according to application.

Glass Products

There are different kinds of products which we produce from glass.

Glass Containers

Glass containers are a very important aspect of our life. Almost in every home, people use these containers made from this material. We use basic soda-lime compositions to produce containers or bottles by blowing processes in history. Chemical stability is very important for containers. So we adjust the lime and soda compositions of these products for that purpose. In general, lime gives fluidity to glass. But also lime decreases the vitrification which eliminates with rapid cooling of products. Soda also decreases the chemical reaction affinity and solubility of products.

Window Glasses

Again, soda and lime compositions produce vitreous and chemically stable windows that adjust empirically throughout history. But in today’s technology of glass production, they add a slight amount of MgO to prevent devitrification.

Light Bulb Glasses

We call these types of them ‘thin glasses’. We use these materials in other applications such as ornaments and drinking bottles. Thin materials must be high in soda and low in lime composition. In today’s thin material manufacturing technology, we use continuous production and melting furnaces for the serial production of the light bulb.

Its ingredients of it change according to application. But the types of ingredients of glass products are generally the same. They adjust these ingredients empirically in history to obtain required properties according to application.

Glasses for Optics

This category of products includes lenses, eyeglasses, and optical instruments for cameras, microscopes, and teşescopes. Optics must be produced in high homogeneity. Also, refractive indices are very important for optical ones. ‘Crown glass’ has low refractive indices and ‘flint glass’ has high refractive indices.

Laboratory Glassware

Glasses or containers that are used for chemical and laboratory purposes must have very good thermal resistance and resistance to chemical attack. To obtain that high thermal resistance, laboratory glasswares are high in silica content. The trade name of these high silica content materials is ‘Vicor’ in the market. We add boric oxide (B2O3) also to silica to obtain very low thermal expansion. Pyrex is also high thermal-resistant glass material.

Glass Fibers

Fibers that they produce from this material have very important applications in engineering, Fiber-reinforced plastics, fiber optics, and insulation wool are examples of applications of fibers. E-Glass is the type of fiber that they use in fiberglass-reinforced plastics. The Cao and Al2O3 composition of these glasses are very high. The tensile strength characteristics of e-type are very good. S-type fiberglass is also very high in strength, but it is not economical as E-type. Glasses used for insulation are lime-soda-silica glass. And they are used at fiberoptics and must have a high refractive index. The outer layer of these fiber optic ones has low refractive index than the inner layer. The inner layer also must have high transmittance to transmit the information for long distances.

These three categories of glass industries comprise high technologies. Because of that, these markets are very valuable and high in profit.

Heat Treatment of Glass Products

Like metals, we apply heat treatment processes to these products after the shaping processes are applied to glasses. Types of heat treatment processes differ according to the type of shape, thickness, and other parameters of products defined below. In general, there are two types of heat treatment processes that we apply to products;

•  Annealing of glasses,
• Tempering

Why Glass Products are Annealed?

After the shaping processes such as blowing, pressing, etc. there are unwanted internal stresses which make these products flimsy. These internal stresses take place after the solidification of the molten state. To compensate for these internal stresses, we apply annealing processes to these glasswares.

Annealing is a process in which the produced glassware is held at elevated temperatures inside special heat treatment furnaces. These furnaces are generally in the shape of tunnels.

This heat application relieves the internal stresses in glasswares. So, the annealing temperatures of general products are around 500C degrees.

The time of heat application changes according to the shape of the product. But in general applications, the annealing time is proportional to its thickness of it.

Cooling after the annealing must be slow. This slow cooling of this material prevents the formation of new internal stresses.

Like metals again, we apply the tempering process also to these products.

Tempering Applications to Glass Products

Tempered applications are very important in today’s technology. Tempered ones are much stronger than conventional annealed ones. We fabricate automobile windshields, windows of tall buildings, and doors generally from tempered ones.

When a tempered fracture, fractures are not dangerous to cut someone else. Because the fractures are fracturing into very small pieces because of the nature of tempered ones.

There is also another kind of glassware application that conventional glasses are attached to the two sides of high-strength polymer sheets to obtain high-strength products. They use this type of application in automobile windshields to prevent fragmentations which can be harmful to drivers. We call this application also ‘laminated glass’.

Unlike annealing, the purpose of tempering heat treatment application, create internal stresses that will result in more strong and tough structures. Like tempering applications that applied to metals, they heated products to temperatures above annealing temperatures.

Again unlike the annealing application, cooling is very rapid. They apply this rapid solidification with quenching application of metals inside water or special oils. In the annealing of glasswares, external surfaces are rapidly cooled. And also, internal sections are cooled after the surface of the product. This leads to a contracting effect due to the difference between the cooling of internal and external sides of products. This contraction leads to the very good compressive strength of tempered glass.

Finishing Operations Applied to Glassware Products

They apply to grinding, polishing, and cutting of products generally according to commercial purposes, as end processes in manufacturing sites. After it melts inside special furnaces, they apply required shaping operations to obtain the required glassware shapes. After that, heat treatment operations are applied to obtain the required mechanical properties.

The last processes to be applied to glass products in production are grinding, polishing, and cutting operations. Here, we explain these processes that we apply to glassware products.

General Operations

They produce some glasswares with blowing and pressing operations in which seam marks form because of the split type of dies used. So, we can compensate for these seam marks with polishing operations after heat treatment applications.

Drawing and rolling of molten products are also very important applications to obtain containers. Because of the rolling and drawing tooling and machinery, surfaces of glasses can have scratches and other defects which are not desirable on a commercial basis. So, they can apply some polishing and grinding operations to clear off these defects after heat treatment processes again. So heat treatments are important in glass production.

We produce some decorative and sightly glassware products. In the production step of these types of them, we can apply some polishing, grinding, etching, and coating operations.

Cutting operations that they apply to glassware products are generally related to the production of long tubes and other flat products. They produce these types of products continually. So, cutting off this glassware must complete into standard sizes on a commercial basis. Like other finishing operations that they apply to glassware products, cutting operations are done after heat treatment operations.

Conclusion on Glass Production

Glass is one of the most important materials for our civilization. There are lots of engineers labor force and scientists that are working on the development of production processes. Also, they produce it in the glassware production sites generally, because of the requirement of molten glass for production.

This article includes very basic information about the general forming processes that they use in industry. You can determine the general production process of a glassware product with this article.

And also, as you might understand the finishing operation that they apply to products are the same as the ones that they apply to metals.

If you have additional information about finishing operations of glasswares, it can be very helpful for people who are searching for information about it.

Heat treatment applications are also very important for glassware to obtain high-strength glassware. Heat treatment applications for glasses are just like the ones that they apply to metals.

Finally, do not forget to leave your comments and questions below about glass production and glass fabrication.

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External Link: https://www.elsevier.com/books/glass-science/eitel/978-0-12-236307-8

FAQs About Glass Production