EXTERIOR VIEW OF ENGLISH GLASS-MELTING FURNACE
Pot Trolley in foreground
The action of the glass upon the siege of the furnace is very active, and any leakage quickly destroys the blocks, leaving fissures which gradually increase in size until the blocks are eaten right through. Consequently, every care is taken to preserve the pots from losing metal. If by chance any pot develops a crack through which the metal leaks into the furnace, the glass working is ceased at that particular pot, and every endeavour is made to ladle out what remains of the metal, and so prevent any more running on to the siege and causing further mischief. The metal is ladled out of the pot by means of thick, heavy, iron spoons, with which the hot metal is scooped out of the pot and dropped into a large cauldron containing water. This is very exhausting work, but there is worse trouble still if the metal is allowed to continue to run through the crack in the pot and over the siege into the eye of the furnace, for it then fluxes with the ashes of the fuel, causing them to form into a big mass of conglomerate, which, lying in the fire, interferes with the draught and combustion of the fuel within the furnace, and before the furnace can be got to work properly again has to be cut away, piece by piece, through the firebars whilst hot, until it is all removed. At the sign of any glass running down into the fires and through the bars, the tizeur hurries up to give the word that a pot is leaking in the furnace, and when the pot is isolated the work of ladling the hot metal out into water begins in earnest. A pot which has cracked and leaks is useless for any further work of melting glass, and at a convenient time it has to be withdrawn from the furnace and a new pot must be substituted. Glass-melting pots form a very expensive item in the glass manufacturer’s costs; consequently, every care is taken to prevent the pots within the furnace from getting chilled by inadvertently allowing the fires to burn too low or allowing cold air to rush through the bars, through unskilful clinkering and inattention to the furnace fires. Sometimes these furnaces are fitted with a Frisbie Feeder. This is a mechanical firing arrangement fitted underneath the furnace bars, by which the fuel is fed upwards into the furnace box, so that all smoke given off by the fuel baitings has to travel through the hot fuel above, and thereby is more completely consumed, giving better combustion than when the black fuel is thrown on the top of the hot bed of fuel. A mechanically operated piston pushes up small charges of fuel from within a cylindrical-shaped box, which works on a swivel backwards and forwards as the fuel is fed into it.
In the old type of English furnace containing twelve pots, each 38 in. diameter and holding about 15 cwts. of metal, the furnace would be capable of melting 7 to 8 tons of glass a week, taking 40 tons of best fuel. The more up-to-date glass-melting furnaces are constructed upon a much better principle than the coal-fired old English type of furnace just described. These are usually producer gas-fired and give more economy and greater convenience in every way.
Fig. A
SIEMENS SIEGBERT TYPE OF REGENERATIVE GLASS-MELTING FURNACE
In these better types of modern furnaces some form of regeneration or recuperation of the waste heat is usually adopted. These furnaces are much smaller and more compact; being gas-fired, they give much higher temperatures, more complete combustion of the fuel, greater ease in regulation, cleaner conditions, and far greater production than the older types of English furnaces. Considering the reasonable initial cost that the latest types of these modern furnaces can be built for, it appears incredible that so many of the old out-of-date English furnaces remain in use in this country.
Fig. B
SIEMENS SIEGBERT TYPE OF REGENERATIVE GLASS-MELTING FURNACE
As examples of the types of regenerative and recuperative furnaces, a description will be given of the Siemens Siegbert Gas-fired Regenerative Furnace and the Hermansen Recuperative Furnace for glass-melting, which are extensively used on the Continent and are giving remarkably good results.
