The remaining pictures for this article are in preparation.
The Holborough plant was set up as a private venture in 1923 by William Lee Henry Roberts - High Sheriff of Kent, Rochester Bridge Commissioner, native of Snodland, and previously manager of Lee's plant - and Percy Girouard of Armstrong Whitworth. The latter, no doubt, brought about the association of the plant with Vickers, at a very early stage in their development as plant suppliers. After the plant had been commissioned (December 1924), the Holborough Cement Company, Ltd. was set up in October, 1925, with Roberts as chairman, and on the board Percy Girouard, Ralph Montague Cook (also local, Roberts' brother-in-law), Henry Horne and Richard Lakin, so there was an incipient link with the Red Triangle group from the outset. Roberts retired almost immediately, and the company was formally merged into the Red Triangle group in August 1928. Horne was in the chair at the second AGM on 24/5/1928. Roberts died 18/10/1928.
The Red Triangle group finally crashed in 1931, and was nearly all acquired by Blue Circle. Holborough was selected as one of the four plants that were to be kept running, and as the best of the Blue Circle plants in the Medway area, with by far the best raw material reserves, it continued in operation as late as October 1984, by which time it was among the least efficient plants in Britain. Planning permission for a new cement plant (to be called Medway Works) was granted by the Secretary of State for the Environment on 26 November 2001, the intention being that it should replace the Northfleet plant. However, Northfleet closed in 2008, and after construction of a rail spur, no further development has taken place at Holborough (as of 2017). The chalk at Holborough is alleged to be very wet. Manufacturers have in general concentrated on installing new plant where dry raw materials are available, in the interests of energy conservation and CO2 reduction.
The following rather terse description of the Holborough plant appeared in an anonymous article in Cement and Cement Manufacture (II, Jan 1929, pp 7-13) in 1929, a few years after start-up. The article is believed to be out of copyright. No mention is made of the Red Triangle organisation. A training film made at Holborough in the 1940s can be viewed at British Pathé.
Values of imperial units (as of 1926) used in the text (alphabetical order): 1 acre = 0.40468424 Ha: 1 ft = 0.30479947 m: 1 gallon = 4.5460756 dm3: 1 HP (horse-power) = 0.7456998 kW: 1 inch = 25.399956 mm: 1 psi (pound-force per square inch) = 6.89478 kPa: 1 ton = 1.01604684 tonne: 1 yard = 0.91439841 m.
THE HOLBOROUGH WORKS, KENT.
Aerial view of works
The image used in the journal article is one of a number produced by Aerofilms, under contract to Allied Cement Manufacturers. For clarity, I have used the print of a similar image once kept at Blue Circle Southern Area Engineering Office.
The "Holborough" works of the Holborough Cement Company, Ltd. was erected four years ago in an area renowned for the quality of the cement produced, i.e. the Medway Valley. The plant is one of the most up-to-date in Great Britain, and is equipped entirely with machinery of British manufacture by Messrs. Vickers, Ltd. The output capacity is over a quarter of a million tons per annum. The works are situated on the left bank of the river Medway, at a point midway between Rochester and the village of Aylesford. Labour-saving devices of the most modern type are everywhere installed with a view to reducing costs to a minimum (Note 1).
An asset of the greatest importance is the nature and quality of the raw material deposit, a deposit of natural marl (Note 2) some 300 acres in extent being adjacent to the plant. The marl deposit is, as quarried from the pit, of such a chemical constitution and physical condition as to be eminently suitable for the production of Portland cement. The marl is excavated by four steam navvies, each capable of a 3-ton bite at each operation.
The quarried material is dumped into rail cars, railed to the opposite side of the quarry, and tipped into a battery of rough or primary washmills of 30-ft. diameter and capable of washing 150 tons of marl per hour. These primary washmills are fitted with slotted sieves having apertures of 5/64 inch (Note 3). The slurry is forced through these grids at the sides of the mills, and is then pumped to a second battery of washmills, which have sieves with openings of 1/50-inch diameter (Note 4).
After passing though the sieves of the secondary or finishing washmills, the slurry is pumped to a number of correction and mixing tanks. These tanks, constructed of concrete, are 50 ft. in diameter and have a total capacity of 4,000 tons (Note 5). The slurry feed presents no unusual feature in the most modern practice, being of the usual spoon-feed type.
The kilns are 200 ft. in length by 9-ft. diameter through the drying zone and enlarged to 10 ft. in the burning zone (Note 6). Induced-draught fans, driven by 40 H.P. Crompton motors, increase the kiln output in addition to enabling a smoother control of the burning to be maintained. The kilns are driven 60-H.P. slip-ring motors and have a total weight of well over 500 tons. All are direct-driven through gearing from the motor to the girth ring. A pulverising plant consisting of Raymond mills (Note 7) (supplied by Messrs. International Combustion, Ltd.), including magnetic sets for the elimination of any tramp metal in the coal, prepares the coal for burning. The pulverising plant and transference apparatus are situated immediately in front of the kiln hood.
The clinker, after passing through rotary coolers of 90 ft. length (Note 8) by 6 ft. 6 in. diameter, is conveyed by belt conveyors to stock or direct to the grinding mills. There is a clinker storage for 10,000 tons of clinker, these storages being constructed entirely of concrete (Note 9).
The grinding mills are of the compound tube-mill type, over 30 ft. long by 7 ft. in diameter, and are driven by synchronous motors, each of 600 H.P., driven through machine-cut helical gearing (Note 10). The mills are divided by slotted diaphragms into three compartments. They are loaded with approximately 45 tons of grinding media in the form of steel balls ranging from 4 in. to ¾ in. in size.
The cement transference machinery including screws, elevators, and inclines are all electrically driven. There is a cement storage capacity of 15,000 tons (Note 11); these storages, as in the case of the clinker storages, are constructed entirely in reinforced concrete, as also are all elevator casings, stages, etc.
The cement storage consists of several batteries of the modern silo type, with packing and loading equipment. The Bates' packers have a capacity of 250 tons per shift. Excellent facilities exist for packing the cement on rail, road or water-side loading stages; 400 tons a day can be despatched from the road loading stage alone. Railway sidings connect direct to the main line of the Southern Railway.
A wharf with 700-ft. frontage enables ten barges to be loaded at the same time. The wharf, and the permanent way to it from the factory, are electrically lighted, and cement loading goes on night and day (Note 12).
Coal is delivered direct from the Southern Railway to the coal plant, thus keeping handling costs to a minimum. The coal conveyor is of somewhat unusual design, as far as its use in cement works is concerned; the coal plant as a whole is claimed to be of the most efficient in the industry.
A total of 3,000,000 bags of cement are handled at this plant in the course of a year, and improvements are now being effected or are planned with a view to still further reducing production costs. The whole of the plant is electrically driven, the power being transmitted from Barking at a pressure of 33,000 volts, by means of underground cable (Note 13). This is transformed down to 440 volts at the plant sub-station. The social side of the lives of the workers is not neglected, and arrangements are in hand for welfare and social care, including sports grounds, etc.