Finishing

Different finishing treatments – such as annealing, toughening, and coating – can be used to influence product characteristics

Annealing aims to reduce the strain in the glass by slowly reheating the glass in an oven, called a lehr. The glass product is first heated to a high temperature, varying between 400°C and 500°C, depending on the product, and then is gradually reduced to a temperature at which no further strain can be induced. Next, the product is cooled by fan air to room temperature. This process is usually completed in less than an hour – actual times depending on the size of the product and its wall thickness

Thermal toughening includes re-heating the glass product uniformly to just above deformation temperature and then rapidly cooling the surfaces by jets of air. Rapid cooling of both surfaces leads to the build-up of a compressive stress layer upon further cooling, since the hot core glass can still contract. Thermal strengthening can be applied to flat glass or simple shapes like curved car windscreens or tumblers. For thermal toughening to be applicable, the glass should have a minimum and uniform thickness and the shape of the article must be such that all surfaces can be uniformly cooled at the same time. Bottles cannot be toughened in this way, and require a chemical process for toughening.

The coating of glass surfaces (e.g. mirrors, strengthening of bottles, and coloring) gives glass new physical, chemical, and optical properties. Lightweight glass containers are coated with organic compounds to give the surfaces a degree of lubricity, thus preventing abrasion in handling. This adds strength to the container and has enabled glass manufacturers to make a lighter and better product (Worrell et al., 2008. p. 13).

FinishingTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Optimizing Plant Layout

Quantitative information not available. 

Quantitative information not available. 

Quantitative information not available. 

Commercial
Oscilating Combustion for Glass Production

Reported fuels savings are 2 to 5% (Worrell et al., 2008. p.73).

Demonstration
Product Drying System Upgrade

In a US based plant, by reduced the drying time from 58 to 72 hours to only 11 hours per batch energy savings were 179,200 kWh/year obtained (Worrell et al., 2008. p.73)..

Non-energy benefits, including reduced operation and maintenance costs of reduced drying times in the US based plant were $14,637 per year. Costs for the project were $43,630. With energy costs of 5 cents/kWh, this would yield a payback of less than 2 years (Worrell et al., 2008. p.73).

Commercial
Minimizing Air Leakage to the Lehr

Quantitative information not available. 

Quantitative information not available. 

Quantitative information not available. 

Commercial
Scheduling Advisory System

A glass-lined steel vessels and parts producer in the UK reduced the energy consumption in its electric glass coating furnaces by 12% (Worrell et al., 2008. p. 72)..

The expert system US $55,000 /year in electricity, $43,000 in reduced labor, maintenance and repair and $74,000 [1989 values] for reduced work in progress (one-time savings). The total system cost was $161,000 (1987), yielding a payback of 10 months (Worrell et al., 2008. p. 72).

Commercial
Glass Coating with Microwave Systems

The investment cost of installing a microwave-vacuum coating system in Germany with an annual capacity of 3 million m2 is estimated to $15 million [1995 values] (Worrell et al., 2008. p.73)

Commercial
Improved Insulation of the Annealing Lehr

Quantitative information not available. 

Quantitative information not available. 

Commercial

Finishing Publications

Page Number: 

13

Finishing Reference Documents

Best Available Techniques (BAT) Reference Document for the Manufacture of Glass

As a reference of the EU Industrial Emissions Directive (2010/75 EU) this new version provides extensive information on Best Available Techniques (BATs) applicable to European Glass Manufacturing Industry for reducing environmental impact. The document is prepared by the  Institute for the Prospective Technological Studies of European Commission's Joint Research Center. 

Page Number: 

54-90