Zawiercie Crystal Glass Factory Ltd.

About glass

Glass manufacturing process

The first phase in the process of glass manufacturing is the process of raw materials preparation, which at the later stages will be subjected to thermal processing. Chosen with the proper proportions and carefully mixed, the raw materials form the so-called ”glass set”. The majority of the currently used glass is manufactured through the process of heating the mixture of sand, sodium and calcium to the temperature of about 1500 degrees Celsius. Crystal glass is obtained through enrichment of the basic glass mass with lead oxide. Then, glass is heated in the glass ovens, huge baths, which are laid out with fire resistant clay. The temperature necessary for melting of glass is achieved using gas burners situated on both sides of the bath.

Prior to the addition of the other ingredients , some broken glass is thrown into the bath in order to speed up the process of glass manufacturing. Melted glass cools off slowly until it looks like a thin, sticky candy. It is then ready to be manually formed, with the application of cast forming machinery or to be pressed into sheets.

Glass in sheets is the cheapest type of glass, among others used in window manufacturing. Melted glass is pulled out of the oven with the use of a metal rod, during this manufacturing stage it reminds a thick syrup. Next it undergoes the processing in a press until flat sheets are formed. Since it is very soft, when coming in contact with the rollers of the press, it often gets scratched. The glass is completely flattened only during the process of pressing. Obtained sheets are machine ground and polished from both sides.

In 1952 Aalastair Pilkington invented the method of float glass processing. The method is based on the idea that the melted glass from the oven is put into a huge reservoir filled with melted tin. The melted glass is spread on a perfectly thin layer of tin. The heating is gradually decreased, until glass cools off so much so that it can be placed between cooling presses without the danger of scratching. Next, the glass is cut into smooth sheets.

During the process of manufacturing of jars, glasses, vases or bowls, the melted glass is fed into the forming devices, where compressed air forms their shape in accordance to the model form. The more complex shapes have each of their halves modelled separately and then joined while still being hot.

Some high quality glass products (for instance crystal glass) are still subject to manual blowing and formation. Hot and melted glass in the shape of a bubble is placed at the end of the long metal pipe referred to as the blow-pipe. Next the factory employee (glass-blower) forms the shapeless mass by the turning of the pipe and by blowing in air in such way that it slowly reaches the required shape.

After obtaining the required form and shape, when still hot, the products are subject to further phases of processing. The products are placed in a de-stressing device, where they cool off in a controlled manner. The aforementioned de-stressing device is a type of an oven. It has the length of dozen metres or so with a belt conveyor running through the middle, on which glass products are placed. The belt transports the products with very small speed throughout the bowels of the device, which are subject to the influence of various temperatures.

After the execution of the de-stressing process all of the products are passed to the decorative department. This mainly concerns crystal glass products, upon which cuts are formed or the product surfaces are painted. Decoration specialists execute original decorations (cuts) with the application of special devices and diamond discs, and the engraving specialists manually cut out unique decorations mirroring pictures of humans or the natural environment. Lead glass may also be decorated through gilding of the edges or through the process of sanding.

The next process, is the one of enhancement, during the execution of which crystal glass products as well as utility glass products without decorations are taken out of the de-stressing device, and are subject to the process thanks to which they become even more shining and aesthetic. The aforementioned process of immersion of glass products in the special acid, offers them a beautiful shine.


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