Wouldham Cement Co
of 35 Great St. Helens, London, cement makers; works at West Thurrock and Wouldham
General
1855 Company established
1875 of Moorgate St, London [1]
Acquired by S. Pearson and Son in order to supply the cement needed for their various contracts[2]
1900 The works at Wouldham on the Medway (Wouldham (Medway) Cement Works) became part of the Associated Portland Cement Manufacturers
1900 The company was registered as the Wouldham Cement Co (1900), to take over an established business of Portland cement manufacturers at Grays. [3]
1920 Formation of a joint marketing company with APCM, Martin Earle and Co and British Portland Cement Manufacturers, which would be called the Cement Marketing Co Ltd[4]
1925 The company was absorbed by British Portland Cement Manufacturers which previously held the shares in the company[5]
The Grays Works in 1902
See article in [1]
WOULDHAM CEMENT WORKS in 1912. [6]
The Wouldham Cement Company, Limited, established in 1855, whose well-known "Red Cross" brand of cement has a world-wide clientele, has now one of the largest works in the British Isles. The works to be visited are on the north bank of the Thames. They have an output of 4,000 tons per week, or 200,000 tons, equal to 1,200,000 barrels per annum.
Portland cement was the name given by Joseph Aspdin from its similitude in colour to Portland stone. It is manufactured by intimately mixing together calcareous and argillaceous materials, burning them at a clinkering temperature and grinding the resulting clinkers.
Base Materials.— The raw materials used on these works are white chalk, of which the company seems to have an almost unlimited supply in their quarry adjoining the works, and clay or alluvial mud obtained from the Medway Valley. The chalk is quarried by hand labour and "milled" so as to fall into wagons. These wagons when filled are taken to the washmills.
The clay, which arrives alongside the works in barges, is discharged by means of mechanical grabs into similar wagons to those used for the conveyance of the chalk. These wagons of chalk and clay are carefully weighed before being taken to the wash mills, where a thorough intermixing in the proportions desired is carried out. This work is done in circular washmills, in which heavily-weighted harrows revolve.
The raw materials are tipped from the wagons into the mills, sufficient water being added to assist the mixing process, which is continued through a series of mills and mixers with graded screens and sieves until the slurry is fine enough for calcination.
Extreme fineness in the mixture is essential, and as practically the whole of it will pass through a 180 by 180 or 32,400 holes per inch sieve, it will be realised that every care is expended by the Wouldham Company in this part of the process.
The chemist is also in continuous attendance controlling and determining the exact proportions required of the different materials.
Slurry Storage Tanks.— The slurry is now pumped into storage tanks. For this purpose two sets of three-throw plunger pumps are used. These tanks are four in number, and have a total storage capacity sufficient to maintain the continuous working of the rotatory kilns during week-ends and inclement weather or such times as the chalk or clay supplies are temporarily suspended. To prevent any settlement of the fine particles of chalk and clay in suspension in the slurry a very ingenious form of "stirrer" has been installed.
On a central pillar a lattice girder is fixed which can revolve on a roller bearing. On this lattice girder, which is driven by an electric motor, are four vertical harrow frames suspended from the lattice girder which revolve by means of crown and pinion wheels. The motion of these harrow frames whilst stirring the slurry act as propelling agents, and cause the lattice girder to circulate on the central pillar, so operating over the whole area of the tank.
Slurry pumps are again used to lift the slurry from these tanks as required to the back or inlet end of the rotatory kilns in which the calcination takes place.
Calcining.— The Wouldham Company's plant for this part of the process is of the best and most up-to-date procurable. A large number of intermittent stationary kilns have been entirely discarded in favour of the rotatory kilns. A patent was first taken out for this type of kiln by Mr. E. Ransome in 1885, but they were not in use in this country till 1901, when two companies, of which the Wouldham Co. was one, first installed batteries to manufacture by this process.
Enormous developments have taken place of recent years in this part of the cement-making process. Rule-of-thumb methods have been entirely displaced for mechanical and chemical precision and exactitude. Complete control of the rate of slurry feed to kiln in conjunction with that of fuel, temperature, draught in the clinkering zone, all tend to perfect and even calcining.
The kilns consist of revolving steel cylinders fixed at a slight incline, and lined throughout with fire-resisting material. The slurry or cement-making material is continually fed through a pipe into the upper end of the kiln, the fuel used being very finely ground coal, introduced by means of special mechanism and; air jet from a blast fan.
The fine coal is ignited, and a very high temperature is obtained at the lower end of the kiln. As the kiln revolves the slurry gradually descends to the lower end and through the zone of heat generated by the combustion of the finely-ground coal. Water present in the slurry evaporates, the material becomes heated to redness, and soon afterwards losing its carbonic acid, and then disintegrating into a large number of small round lumps, which passing through the burning zone are exposed to the very high temperature existing there, and after complete calcination is delivered on the outlet of the kiln into a rotating cooling cylinder, front which it is conveyed by means of a mechanical tray conveyor to the grinding mills.
Kiln Plant.— The whole plant is electrically driven, and the calcination is under the complete control of the burners. Special devices for the regulation of the slurry feeds, amount of coal and air supplied to the kilns and the dampers of the chimney shafts for the waste gases have had most careful attention. Each kiln is connected with a separate chimney shaft, varying in size according to the size of the kiln. In the largest kiln special water-cooled bearings have been installed, thus mitigating any possibility of overheating and attendant troubles in the runnings.
The coal drying and grinding plants are of necessity very extensive. A good quality coal has to be crushed and dried down to about 1 per cent. of moisture, and finally ground in Kominor and tube mills to an extremely fine powder. This is elevated to the hoppers and fed by means of screw feeds to the air blast.
Cold air, forced through the kiln cooler absorbs a considerable quantity of the heat units of the hot clinker, is passed from the cooler into ducts, and is used for drying the coal to the requisite degree of dryness, the surplus being forced into the kiln for the purpose of combustion.
Grinding.— The final stage in the process of manufacture is the grinding of the clinker to impalpable powder. Opinion seems unanimous on the point that the more finely ground the cement the better the quality. Broadly, assuming the previous stages of manufacture have been properly carried out, it is correct; but it should be borne in mind, however, that in allowing certain degrees of fineness it is most desirable to have as large a percentage of flour as is possible in the finished product.
The British standard specification, as revised in 1907, allows 18 per cent. residue on a 180 by 180 mesh to the square inch, and 3 per cent. on 76 by 76 ditto. Many well-known brands of cement will be found to be considerably under this specified allowance.
Methods of grinding have considerably changed during the past ten years. In the early days of the industry the preliminary crushing was done by means of stone crushers, and the resulting product finished by French Buhr millstones or edge runners. Pendulum roller mills have also been used, but in the most up-to-date and better-equipped works of to-day the preliminary grinding is carried out by the ball mill, and the resulting coarsely-ground material is then conducted to the tube mill, which completes the fine grinding process prior to its conveyance to the warehouse and storage mills.
Grinding Plant.— In their grinding plant the company, as in its rotatory kiln plant, have adopted, and are still installing, only the most efficient and up-to-date machinery. Generally the mills are all of the ball and tube mill type. The mills are of heavy calibre throughout, specially adapted for fine grinding and capable of complying with the most stringent specifications in this respect. Each unit is driven electrically.
The finished cement is conveyed to the warehouse by belts or band conveyors, from which it is shot into any desired bin.
Storage Warehouse.— The storage warehouse, a very fine example of ferro-concrete construction, is situated on the river side, and has a storage capacity of 35,000 tons, which is divided into bins of 500 tons capacity each. A covered-in loading platform gives excellent facilities for the casking of cement before stowing into steamer, craft, or barges. It is also specially adaptable for loading trucks.
For export trade the bulk of the cement is shipped in casks (capable of holding 375lbs.) made from fir staves and bound with four steel hoops.
Cooperage.— The company have their own cooperage plant, where the casks are manufactured from staves as shipped from the Baltic ports. Machines for jointing, tongue and grooving, crozing, printing, and trussing staves into casks, and also for the manufacture of riveted steel hoops, have been installed.
The casks produced from these machines show great advantages over the old handmade patterns.
Power Plant.— The power plant for so large a factory is of necessity very extensive. Electrification wherever possible has enabled the company to bring all the generating units to one station. The power house includes the following principal generating units:—
Compound reciprocating engines, fitted with Corliss and drop valve gear, high speed triple expansion units, mixed pressure turbine and generators.
A battery of tubular economic boilers, working at 160lbs. per square inch pressure, is responsible for the steam for the above units.
Direct current generators and motors are in use throughout the whole of the works at the voltage of 500.
It may here be mentioned that mechanical and electrical power and devices have been installed throughout the works with a view to economising labour and making the process of manufacture as continuous as possible. As a result no hand labour is required in the actual handling of the material during process between the time of first tipping the raw materials into the mixer mills and the packing of the finished cement into either casks or bags for export to customers.
Testing Laboratory.— The testing and examination of the raw materials and of the cement, both during its process of manufacture and the finished article, is carried out by a staff of specially trained chemists and assistants, whose duty it is to determine the exact proportions used, firstly of the raw materials, and to keep careful records and observations throughout the whole of the process.
Chemical and microscopical examinations, physical and mechanical tests quite unthought of by the general user, are daily and hourly applied to eliminate all possibility of the standard and desired properties of the cement fluctuating, and especially to make deterioration in quality absolutely impossible.
Cement has now to comply with many and varied specifications, each requiring a special course of manufacture. In the old days this product was largely the product of rule-of-thumb methods, but it has now become one of the world's biggest and most important industries. Works of this magnitude of necessity require well-equipped repair shops for the large amount of machinery in use. Excellent machine, blacksmiths' and carpenters' shops on the works enable the company with the aid of a trained staff to not only do most of their own repairs, but much of the engineering work incidental to the large amount of construction work in installing the =new plants they have from time to time erected.
Offices.— The offices, built entirely of crushed flints obtained from the chalk, and the company's own cement, are an excellent example of a concrete building.