Thursday 6 February 2014

Charlton Glassworks 1946


(Up until the early 1960s the largest glass works in Europe was in Anchor and Hope Lane, Charlton - some of their site is now the new Sainsbury's depot.  The following document, produced by the Company in 1946 describes processes at the works)

At the Charlton works, high quality glass containers of all sizes and types are manufactured in colourless (flint) and in amber glass. The glass making machines operate continuously day and night, 24 hours per day, 7 days per week, 52 weeks per year; the machines only stop finally after eighteen months or two years when furnaces have to be closed down for repairs.
About 200 million glass containers are produced per annum, in the Charlton works alone.


Power House

This is the nerve centre of the factory; it provides (together with the waste heat boilers) steam for producers, for heating, and for the thousand and one other duties, from two Babcock & Willcox boilers which operate on coal fuel. Compressed air is provided, for blowing the bottles, and for separating liquid fuel burners, etc. Vacuum pumps provide the suction required by most of our glass-making machines.

Circulating pumps drive creosote pitch fuel from incoming barges to large storage tanks, and from thence to mains around the factory, finally to burners and furnaces or revolving pots. The creosote pitch has to be kept warm in the storage tanks and in the circulating mains, because of its viscous nature at room temperature; it has to be heated to, 200 ° F before it can be atomised.

The Power House contains much electrical equipment, needed for the many electrical services required throughout, the factory.

A new and complex automatic water softening plant has recently been installed, to supply the Power House and producer plant with softened water.

Wharf and Rail Traffic

In peace time, the raw materials used for glass making, and sand in particular; came to the works by sea. Coal and creosote pitch, our war time substitute or fuel oil, still arrive  by ship or barge but much of our sand during wartime, comes in by rail, English rather than foreign sands now being employed for glass-making.

Quite a number of our bottles are exported by sea; in peacetime they went to many countries but during the war, export has been restricted.

Batch Plant.

The sand as received whether Dutch, Belgian or Fontainebleau in pre-war days, or the English sands at the present time, is dried.  This ensures the most accurate control of glass composition. After drying, the sand is elevated to its appropriate concrete storage silo, each of which holds about 600 tons. In other silos, we store limestone, soda ash (sodium carbonate) and cullet the name we give to broken bottles). Before elevating to the silos, the cullet is washed, sorted and crushed, to reduce its Impurities to the minimum. The batches or mixtures for U.G's. bottle glass are  prepared by mixing sand , limestone and soda ash with cullet., the proportions of those major ingredients being carefully controlled to yield a glass composition of :

Silica (SiO2) 72-75
Lime (C20) 10-8
Sodium oxide (Na20)
Alumine (Al203) 16-15
etc, etc.

Besides the major ingredients, decolourising agents are added for colourlessness glass, or colouring media for the amber glass. For the highest quality flint glass, we must avoid iron oxide in the raw materials, for iron gives an undesirable green tint to otherwise colourless glass; the same effect, in even greater intensity, is produced by chromium oxide. Any iron oxide present must be decolourised with arsenic in combination with selenium and. cobalt; in addition, such oxidising agents as salt cake (sodium sulphate) or nitre (sodium nitrate) have to be present.

For amber glass, carbon in some appropriate form (we use producer soot), and sulphur (added as sodium sulphate) are included in the batch to impart the desired yellow-amber tint. Amber cullet in fairly high proportions is added to the other raw materials. Sands which contain higher percentages of iron oxide can be used for amber or other coloured glasses, but such sands would be quite unsuitable for colourless glass.

With the aid of a travelling, weighing batch-car, which runs on a track beneath the silo, the appropriate weights of sand, limestone and soda ash, with cullet, are taken from their respective silos, and are conveyed to the mixer , the minor ingredients of arsenic, salt cake , nitre and decolouriser- being added in the case of the colourless glasses immediately before mixing.

When mixed, the batch is elevated, and by means of a second, high-levc1 batch, car, is transported to the large hopper immediately above the furnace.

Gas Producers and Producer Gas

The present furnaces at Charlton can be fired by producer gas or, alternatively by creosote pitch fuel. The former method of firing is cheaper and yields glasses of higher quality and better colour; in war- time, however, coal supplies have to be restricted, and at times it has been necessary to use the 1ess convenient and more expensive creosote pitch liquid fuel.

In our Chapman gas producers, the coal fuel (from Northumberland, Durham, Scottish or Yorkshire coal-fields) is converted, by partial burning in an atmosphere of steam and limited air, to the combustible carbon monoxide and hydrogen. Gaseous fuels are controlled much more easily than solid fuels.  The producer gas, containing 25-27% carbon monoxide, with 12-14% hydrogen, at a temperature of approximately 600 passes along insulated flues, provided with water seals, to the gas regenerators. Rising though the gas regenerators, the producer gas is preheated by the hot brickwork to about 900 o C before reaching the furnace ports.  In these ports, which are virtually large burners, the preheated gas meets air which has been preheated to about 1OOO C., and the mixture ignites to give an intense flame within the combustion space of the furnaces i.e. in the zone immediately above the batch or glass. Waste gases Leave the-furnace and pass to the chimney via regenerators which are gradually raised in temperature.

(Since September, 1946 heavy fuel oil (Pool) has replaced creosote pitch, the lower viscosity of the new liquid fuel enables circulation to be made at lower temperatures)

Our tank furnaces are continuous and are of the cross-fired, regenerative type. They fire from alternate sides, 1/2 hour from the east, then 1/2 hour from the west, and so on. Batch materials are fed at regular intervals, or if desired, continuously, while the glass is constantly being drawn off by the machines.

The furnaces hold 120-140 tons of molten glass at temperatures of 1450 to 1480 °C. With present design and with existing refractory material, the furnaces last from 15 months to 2 years between repairs and they may yield as much as 25,000 tons of glass during their useful life. These standards may be raised still further in the next few years, as furnace design improves and as better refractories become available after the war.

As structural materials we use fireclay or sillimanite (an aluminous material), or electrocast (electrically fused) blocks, to form the bottom and side walls of the refractory bath or tank (some 42" in in depth) which contains the molten glass. The furnace super-structure i.e. the portion above the glass level, is mainly built in silica materials

The furnace is made up of two main parts, the melting and the working ends. The former is much the larger-of the two, being some 23 to 30 ft in length and 19 to 20ft in width, while the working end is smaller, some 8 ft long by 14ft wide. Melting end temperatures are kept at 1450 to 1480 C. to melt the batch and refine the glass, i.e. remove bubbles, sand, etc.; working end temperatures are usually about 100C. lower.
As the glass passes from the melting end to the working end, it descends and passes through a submerged throat, which effectively prevents unmelted raw materials passing to the glass-making machines.

Intense cooling is applied to the throats of our furnaces, and also to the outside of the lower side-walls of the tank, at the flux- line 1evel corresponding with the surface of the molten glass.

Loads up to 65 tons per day may be drawn from each of our four furnaces, although the average aggregate load is probably nearer to 160-170 tons of glass from all four furnaces.

Revolving Pots.
From the working end of the furnace, the glass flows through a spout, into the revolving pots. The latter are some 1O-ft. in diameter, are made of fireclay material and normally contain a 4" depth of molten glass at temperatures from 1150-1350°C.; small glassware needs a higher temperature in the revolving pot for a small mass of glass loses heat more quickly than a large mass. .

As their name implies the pots rotate so that whenever  the blank moulds of the Owens machine dip into the surface of the glass, a fresh area of molten glass is exposed, the cold glass r resulting from previous cut offs being avoided .'This arrangement with correct speeds of rotation of the machine and the pot (which rotate in opposite senses) enables the highest quality of glass containers to be produced and maintained.
The glass in the revolving pots is kept at the desired temperature by an automatic temperature control system which allows a greater or a lesser quality of fuel to enter the creosote or pitch oil burner, thus raising or lowering the revolving- pot temperature, as desired

Glass Making machines
When all four furnaces are in operation we use

8 Owens (American) machines
4 Reirant Machines
1 CSH Machines
(All suction machines)

An J.O’Neill feeder-fed machine
The Owens are the largest machines and account for a high proportion of the total Charlton production. The type of Owens machine worked at Charlton rotates continuously and has ter heads. The moulds on each head may be single, double or triple so that each complete rotation of the machine delivers 10, 20 or 30 bottles.  It is possible using the Owens machine to make bottles varying for 1/8 oz. capacity to 10 oz. capacity at speeds respectively 300 and 27 bottles per minute; these are equivalent to 3,000 gross and 170 gross per 24 hour.

The O’Neill feeder-fed machine receives the gob of glass by gravity, the correct weight bang dispensed by the feeder. The machine has rotating tables but the operation is not continuous. Bottles with internal screw finishes can be made on this machine although they cannot be produced on the Owens.

The Roirant and CSH machines deal with smaller orders that cannot be made economically on the large Owen machines these smaller machines operate on an 'in ‘and 'out' principle– they  are not of the rotating type.

The method of glass bottle manufacture on the Owens machine is as follows :

The molten glass is drawn from the revolving pot into the bottom of the blank (or parison) mould by applying suction.  when the blank mould  is completely filled, the continuous column of molten glass  still rising from the revolving  pot to the lower- opening of the blank mould , it is-cut by a swinging knife. The blank mould now opens and we see a 'sausage' of hot glass suspended by its finish, with air being puffed inside it, from the top; the lower portion of the glass parison is solid at this stage.  when the two halves of  the blank mould have swung out of position , the finishing mould rises from below , on a cam system, finally closing around the 'sausage' of hot glass. When the finishing mould has closed compressed air is applied, and the glass is blown out to take on the desired configuration which is determined by the shape of and decoration on the finishing mould. Equal thickness of wall in the finished bottle is realised by correct shaping of the glass blank, and by correct temperature distribution in the mould equipment.
The other bottle making machines operate on somewhat different principles.  

Annealing Lehrs
When the bottles leave the glass making machine they slide down a chute and are set up by takers-in on a stacker conveyor. The latter carries bottles to the lehr, where an automatic stacker packs them closely together in rows and columns. With modern automatic glass making machines the bottles enter the lehr at such a temperature and in such numbers that very little additional heat is required in the electrically heated lehrs. Annealing is thus carried out in a very economical manner.

As they pass through the lehrs which are some 80-90ft in length the bottles are cooled according to a definite schedule so chosen as to minimise the final stresses in the glass when the latter is sold.  If glass is allowed to cool quickly very great stresses are set up (largely because of the poor heat conductivity, and the viscous nature of all glassy materials) and bottles treated in such a manner usually shatter. They would be quite unsuitable for general use by the public. All our UGB glassware is carefully annealed to give optimum service.
Sorting and inspection

Travelling on a continuous wire mattress belt the bottles take about two hours to pass through the lehr.  At this stage they are cool enough to be handled and inspected . Every UBG bottle is inspected for perfection of glass quality, desired shape and dimensions and freedom from flaws or defects of any kind. Any faulty bottles are rejected and remelted as cullet.
The standard of annealing is checked at frequent intervals

The good ware is packed into wooden c rates of dimension chosen to suit the various sizes of bottles. In peacetime paper packing is used freely to avoid any damage to the bottles in transport but during the war this high standard of packing has had to be relaxed somewhat because of the shortage of paper
Warehouse and Despatch

After sorting and packing, the filled crates are taken by electric or petrol transveyor, to warehouse, or direct to lorry or rail way wagon or barge. Most of the bottles made at Charlton, are distributed in the Greater London area and the transport is largely by road . In peacetime road deliveries go further afield, but under war conditions ,the greater distances involve rail transport. Some glassware travels by sea
Nowadays the main users of our glassware are hospitals , dairies , breweries ,or factories making important commodities which have to be stored or transported in glass bottle

Special Subsidiary Procedures
In recent years  glass ware has had to withstand increasing severity of treatment. During the war, we have had to produce special glass containers for blood, sera, drugs, chemicals etc., all of which have very stringent requirements . To impart the desired chemical durability such U.G.B glass ware is subjected to a special patented process. Such specially processed, highly durable U. G. B. bottles and vials have helped and are still helping to save many lives during the war years.

Some bottles have enamel lettering put on them.. Enamel, in the wet state is transferred via a silk screen to the bottles to be so treated and this glassware is afterwards fired and -annealed a. permanent and durable form of decoration being obtained.
UGB bottles are washed and in some cases sterilised and capped before despatch to customers . Special departments deal with these branches of glass bottle production.

Ancillary departments
The direct sequence of bottle manufacture could not continue for long if it were not for the very important ancillary departments.  To mention only a few there is the MOULD SHOP where new moulds are made, and oId moulds as well as the glass making machines themselves , are re-conditioned.  The Engineering Maintenance Department keeps all, factory services in operation, and provides the means of running the works

We have special departments of Electricians, Carpenters, Wagon and Locomotive builders, Painters, Welders and sections for block grinding and sand blasting etching etc. The stores fill a most important function and we have offices dealing with personnel, warehouse, transport, despatch, wages, income tax deductions and so on. We have our own welfare department and our own nursing and first aid services
Research Laboratories and Engineering Design Departments

The Company's Central research Laboratories and the company's central design Department, are located at the Charlton factory.
Problems from all U.G.B. factories, at Charlton, Sherdley, Ravenhead, Castleford Shettleston (Glasgow),  Portobello (Edinburgh) and Kinghorn , are dealt with by these central departments

Research and control work on a number of important problems are always in progress, and every effort is made to improve the quality of our- U.G B. product and the efficiency of our processes. New machinery and new methods are constantly being sought and developed in an endeavour to provide the public with even better U. G.B. bottles

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