Monday, 24 February 2020

Glass made in Charlton


One of the ‘forgotten’ factories in Greenwich was the largest glass bottle works in the world. The following article, by R.D.Goodson, appeared in the London Electricity Board magazine in February 1961.

A bottle - who gives more than a passing thought to it other than in respect of its contents. Down in Greenwich in the South Eastern District a lot of people do. At United Glass Ltd’s Charlton factory some 2,100 employees of that organisation spend all of their working life designing, planning and making literally millions of bottles and in connection with the electricity supply, the Board's District Staff watch over its electrical well-being with an almost parental care, as may be expected a consumer who can set up a maximum demand of 4-6 MW with a high load factor is looked upon as a particular asset to the district.

The company originated under the title of Moore and Nettlefold and has carried on glass bottle manufacture on the same site as far back as 1911. It is of interest to note that even at that early date electricity played an important part in production. It is on record that the factory contracted to take an electricity supply of approximately 500 kW capacity. In those days Foreign labour, mostly drawn from East European countries, was used extensively. Production continued up to the outbreak of World War 1. Recommencing in 1920, the original plant was replaced by more modern equipment to meet the ever-increasing need for greater efficiency and economic working. 

Rapid development of the glass industry demanded modernisation of plant. and today the Charlton works rank high in glass-producing efficiency. "There have been changes in the Company title. Quite recently the well-known United Glass Bottle Manufacturers Ltd. (U.G.B) became United Glass Ltd. an organisation of nation wide interest and high reputation. The factory occupies an area of 37 acres, flanked by the River Thames in the vicinity of the Royal Naval College. Within the curtilage of the works is a well-planned system of internal roads, together with some 5.5 miles of railway lines, the latter constituting a veritable private marshalling yard. Goods in and out of the factory area are handled by road, rail or river, whichever is most convenient for the particular purpose. 

Access by river for export overseas is facilitated by a well-equipped wharf - always served by a sufficient depth of water in the Thames at that point. The buildings, apart from the production area, include an administrative block, drawing office, engineering workshops, research laboratory and storage sheds, supported by a miscellany of ancillary accommodation. The 2.100 people regularly employed include technical and administrative staff. Their shift-to-shift requirements are catered for by an efficient canteen service, which operates throughout the 24 hours in each day. Electricity is supplied at high voltage with a service capacity of 6,600 k VA delivered to two main substations known respectively as North and South.

The summated maximum demand recently recorded over the two points of supply is 4,600 kW with an annual consumption of over 30 million units. Security of supply is of paramount importance and with this in mind the Board’s engineers in designing the supply arrangements, provided a supply at 10.4 kV direct from Blackwall Point Main Substation, consisting briefly of 0.15 sq in feeder ring (unit protected) incorporating the two substations (North and South) in the United Glass works with a further injection feeder (also unit protected) from Blackwall Point main substation to the North substation. In addition to this, further security of supply is given by interconnection at three points on the Main Substation High Voltage feeder network. Glass production is a most interesting process and is carried on continuously throughout the year by means of four large oil fired furnaces with electrically driven fan cooling and electrically operated boost melting device each boost has an electrical capacity of 6500 kW. 

An interesting feature of glass bottle manufacture is that all scrap is remelted. It is the practice to feed this broken glass into a large hammer mill. The material when ground to a fine powder in known in the trade as ‘cullet’. Cullet is mixed with sand, soda ash and limestone. This is the raw material used in modern manufacture, of glass.

Colour variations are obtained by the introduction of chemicals to the mixture. In the Charlton factory white flint, green and amber bottles are produced. Raw materials stored in silos are always available for immediate transference to an electrically driven "batch" car. This vehicle is, in effect, a mobile hopper with a built-in weighing machine. The driver halts the vehicle under each silo in turn until the correct quantity of material required for the particular process, is collected. The contents, known as the "batch", are eventually tipped into a drum mixer, similar in design to a large concrete-mixer. Bucket elevators move the "batch" into hoppers above the furnaces, from where the material is gravity fed into them. The quantity of feed is carefully regulated by electronic control. 

Due to modern development of refractories and to electric boost melting, the output of the furnaces, which have been in existence for some while, has been increased from 180 tons per day to 440 tons per day. The electric boost melting applied to each furnace enables the manufacturers to obtain an additional 30 tons output per day per furnace. With the regenerative type of furnace installed in the factory, boost melting is achieved by passing an electric charge through the molten glass in the furnace. The old type of furnace used in 1911, it is of interest to note, had an output of approximately 30 tons per day. Electricity is continuously required by the present day furnaces for oil atomization and cooling. The molten glass is normally held at a temperature of 1,500 degrees C. and it needs little imagination to realise the importance of continually cooling the exterior of the furnace. In the early days of glass manufacture, production was hampered by the comparatively short life of the furnaces, not more than 6-8 months. Modern design however, provides a furnace life of 3 to 4 years. The process is continuous. Once ignited, a furnace is producing molten glass until rebuilding is necessary. At the end of its useful life the furnace is "tapped" and the remaining molten glass drawn off. This is an important part of the life operation for if the glass is allowed to cool in the furnace the solid mass would present an almost impossible task to break out. The drawing-off in molten state enables the glass to be used over again as "cullet” when the renewed furnace is again commissioned. 

At Charlton, the process known in the trade as "tank furnace" practice operates with fascinating continuity. The quantity of molten glass in the tank is controlled with infinite care, a depth of 42 inches being maintained throughout with a maximum tolerance of one-tenth of an inch. Approximately 110,000 tons of batch material are used in the four furnaces each year. An apparently never-ending flow of glass passes on its fiery way like lava from an erupting volcano. Continuously channelled into the insatiable maws of the bottle-forming machines. The visitor will inevitably experience an illusion of Dante's Inferno. This, however, is quickly dispelled by the well-ordered stream of perfect bottles, which emerge and move, inexhaustibly, towards completion stage. 

Two types of bottle-making machines are used. One operates on a flow principle, while the other incorporates a suction method. The difference briefly, is that the former is gravity fed by molten glass, while the latter sucks the material from a revolving pot furnace. With each type of machine a small quantity of glass known as the "gob", having a consistency of treacle, is passed into a preliminary mould known as a "blank" or "parison". It is at this stage that the first shape is formed by injecting a small quantity of compressed air into the "gob". The "parison" is important as it plays a major part in determining the thickness of the glass and strength of the finished product. The first stage complete, the "parison” is transferred mechanically to the finishing mould, where compressed air is again introduced to blow the glass to its final shape. The bottle still red hot is moved by conveyor belt on its next stage to an annealing oven or Lehr. Careful control of cooling is essential. The bottles are annealed by slow baking in the Lehr in gradually diminishing heat. The bottles, cool by now, are handled for the first.. and only time, when they are inspected for Haws. Periodic sample tests for quality, size, shape and liquid capacity ensure that the finished article is to specification. Bottles are then cartoned and despatched by road and rail or exported by ship direct from the Company's wharf.

United Glass Ltd. is proud of their product and use only the finest quality material. Their product has an ever expanding market both at home and abroad. Their exports at present represent approximately 10 per cent of their production and are marketed principally in Holland and the Scandinavian countries. At home, the firm supply bottles to milk, pharmaceutical, brewery and other similar trades. It is their proud claim that the customer has only to state the shape of the bottle, the quantity and the order will be satisfied. This they do to the tune of six to seven million bottles a week. How important the glass industry is to our modern way of life! Just imagine a world without bottles, windows, mirrors, drinking glasses, and television tubes!

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