Steklarna Hrastnik, one of the largest producers of glass containers for premium food products in Slovenia, announced in October 2004 that it was to undertake the construction of a special purpose glass container and tableware production plant in the Podkraj industrial zone near Hrastnik in central Slovenia, on the right bank of the Sava river adjacent to the Hrastnik commune.

The new plant required an estimated investment of €27m and was completed and operational by autumn 2005. The construction process started in December 2004 and was planned to take ten months putting the opening date on 28th September 2005. The new plant is a response to the opening of new markets in the European Union and the United States where the majority of the products will be distributed. The new facility is believed to be of strategic importance for the long-term development of the company.

The plant employs 210 personnel and has an annual production capacity of 33,000t/yr. The new factory represents one of the largest investments in Slovenia in 2004 and is one of the most modern of its kind in Europe. The facility produces a wide variety of glass containers suitable for the packaging of products such as food (bottled vegetables and sauces), olive oil, perfume, soft drinks, spirits and wine. Containers are produced in a range of sizes for these applications from 40ml up to 1,000ml.

In 2007, in response to internal organisational changes the quality systems at the Steklarna Hrastnik organisation were changed with an emphasis on the improvement of management processes based on target managing. Because of these changes it is now possible to check the efficiency of individual processes according to given aims and take corrective measures on an as-needed basis.

Changes

Steklarna Hrastnik has four divisions: Vitrum, a glass products manufacturing company, Opal, a lighting manufacturing company, Stedek, a glass processing and decoration company and Special who were responsible for the new plant. In August 2006 Vitrum, Stedek and Special became a single entity under the Steklarna Hrastnik Ltd umbrella (590 employees) while Opal remained independent (225 employees). In August 2008 Opal introduced new semi-automatic processes into its hand production set up a including a new carousel for one-side acid etching to complement the original acid etching. Opal has also achieved fabrication of larger pieces including a globe with a diameter of 600mm and a narrow square ceiling light with a length of 720mm.

Construction of the new facility

In October 2004 RUDIS d.d. Trbovlje was awarded the turnkey Engineer, Procure, Construct (EPC) construction contract for the new facility. The contract was for the complete factory including fabrication of the building and construction and installation of the furnaces and glass moulding equipment. RUDIS was involved in the investment from the very beginning when Steklarna Hrastnik started to consider the new facility.

RUDIS started work on the project with Steklarna Hrastnik in spring 2004 on planning the implementation of the project and by producing building permit documentation, and the structural and basic design of the plant. The new plant has been designed around four furnaces and four production lines.

RUDIS constructed the facility in a standard steel frame, concrete block and aluminium panel design and then supplied and installed all of the mechanical, electrical and pipe services (completed in June 2005). By August 2005 the construction was over and the natural gas furnaces had been built.

RUDIS were also involved in the installation of several furnace pre-silos, flue gas purification (scrubbers to remove NOx and other environmentally problematic gases), conveyor belts to feed the furnaces with cullet and other raw materials and air-cooling systems (for cooling the product containers).

Furnaces

The new furnaces use oxyfuel firing as this is now widely recognised as the most energy efficient and environmentally friendly process. The oxyfuel furnace reduces a glass manufacturer’s fuel use by 15% to 45%, NOx emissions by 80%, and particulates by 60%. The process also increases productivity by 25%. However, because of higher temperatures and production of alkali vapours, refractories corrode significantly faster in oxyfuel furnaces; furnace crown life can be shortened by a factor of two to three. The four new furnaces at Hrastnik have been installed with a new extended life refractory lining which will also reduce long-term maintenance costs.

Production lines

The furnace produces the molten glass which is then divided into hot-glass melt gobs by dosage devices with special shears, which are then passed into suitable moulds on a moulding machine. The gobs’ form, weight, speed and temperature are programmed and depend on the product required. The moulding process (pressed, blown, etc.) is carried out and a hot form of the product is shaped, which then needs to be cooled (using air cooling systems).

Following this, products are reheated later for fire polishing so that the product has smooth surfaces and so that all characteristic traces of automatic production are removed. Each product is then put into a cooling/annealing furnace, to remove tensions in the glass by slow cooling (since initially the temperature is between 900°C to 1,000°C and is quickly reduced to 400°C, which could cause defects). At the end of the cooling furnace products are inspected by quality control and rejects removed. In mid-2008 a further production line was added to the plant to allow the production of a larger range of glasses and domestic items at the plant for sale in the European and US markets.