Glass production

Different glass types, colours, desired quality, raw material purity/availability, and furnace design will affect the batch recipe.

Types of furnaces used in container glass making include "end-port" (end-fired), "side-port", and "oxy-fuel".

Typically, furnace size is classified by metric tons per day (MTPD) production capability.

Modern furnaces use electric heating methods that improve energy efficiency compared to traditional fossil fuel systems, contributing to reduced pollution and emissions.

[4] Electrodes made from molybdenum, graphite, or alloys are used in glass furnaces to conduct electricity and generate energy.

Both processes start with the gob falling, by gravity, and guided, through troughs and chutes, into the blank moulds, two halves of which are clamped shut and then sealed by the "baffle" from above.

The first stage moulds all the details ("finish") around the opening, but the body of the container is initially made much smaller than its final size.

Sections make either one, two, three or four containers simultaneously (referred to as "single", "double", "triple" and "quad" gob).

However in recent times servo drives have been implemented in the machines which achieve a better digital control of the forming process.

Furnaces, compressors, and forming machines generate large quantities of waste heat which are generally cooled by water.

This is usually accomplished through the injection of a sulfur- or fluorine-containing gas mixture into bottles at high temperatures.

An annealing oven (known in the industry as a lehr) heats the container to about 580 °C (1,076 °F), then cools it, depending on the glass thickness, over a 20 – 60 minute period.

At the hot end a very thin layer of tin(IV) oxide is applied either using a safe organic compound or inorganic stannic chloride.

At the cold end a layer of typically, polyethylene wax, is applied via a water based emulsion.

This makes the glass slippery, protecting it from scratching and stopping containers from sticking together when they are moved on a conveyor.

Typical faults include small cracks in the glass called "checks" and foreign inclusions called "stones" which are pieces of the refractory brick lining of the melting furnace that break off and fall into the pool of molten glass, or more commonly oversized silica granules (sand) that have failed to melt and which subsequently are included in the final product.

In the "press and blow" forming, if a plunger and mould are out of alignment, or heated to an incorrect temperature, the glass will stick to either item and become torn.

In addition to rejecting faulty containers, inspection equipment gathers statistical information and relays it to the forming machine operators in the hot end.

This is carried out by automatic machines (palletisers) which arrange and stack containers separated by layer sheets.

[9] Glass container manufacture is also a geographical business; the product is heavy and large in volume, and the major raw materials (sand, soda ash and limestone) are generally readily available.

Despite its positioning as a mature market product, glass does enjoy a high level of consumer acceptance and is perceived as a "premium" quality packaging format.

How glass containers compare to other packaging types (plastic, cardboard, aluminium) is hard to say; conclusive lifecycle studies are yet to be produced.

Compounding this is that because they are mature market businesses, they often have been located on the same site for a long time and this has resulted in residential encroachment.

Of the one tonne, roughly half is evaporated to provide cooling, the rest forms a wastewater stream.

Most factories use water containing an emulsified oil to cool and lubricate the gob cutting shear blades.

Factories usually have some kind of water processing equipment that removes this emulsified oil to various degrees of effectiveness.

Nitrogen oxides are a natural product of the burning of gas in air and are produced in large quantities by gas-fired furnaces.

Manipulating the batch formula can effect some limited mitigation of this; alternatively exhaust plume scrubbing can be used.