A VISIT TO A BLUE LIAS CEMENT WORKS.
(From the Portland Cement Journal)
The use of Rugby Portland cement (Note 1) has during the past twenty years developed to an enormous extent, and a description of a visit to the most recently constructed works in the district may be interesting to our readers. The works we have selected are those of the Rugby and Newbold Cement Company, Limited, which have been entirely reconstructed and supplied with the most approved appliances for producing large quantities of cement from the Blue Lias strata.
Our managing editor, on arriving at Rugby Station and enquiring for the works, found that there were two cement works near Rugby. "Which do you want", said the ticket collector, "there's the works at New Bilton, and the big works at Newbold? (Note 2)" The latter we found to be the works we sought, and which we reached in a walk of twenty minutes. We were received by the resident secretary, who, as the manager was engaged, very courteously showed us over the laboratory testing rooms and offices; and we were particularly struck by the extreme care with which the testing was carried out, and remained for some time watching the operations of the man engaged in this department.
Although this is beginning our tale at the wrong end, we will tell it according to the course we followed. As our time was limited, and as the manager was otherwise engaged, it happened that the testing came before our notice first. We found the operator removing from brass moulds several briquettes (Note 3), which he told us he had gauged with neat cement twenty hours previously. The date of mixing had been neatly scratched on them before the cement was quite set. These briquettes were placed in water from which they were taken at intervals of four days, seven days, and fourteen days, and placed in a machine to ascertain their breaking tensile strain per square inch. Having had no notion of the extreme attention paid to this department of the manufacture, we remained in the test room some time watching other operations. The brass mould having been cleaned carefully and refilled for a fresh series of tests, several briquettes were taken from a tank in which they had been covered with water twenty-four hours after being gauged, and were alternately placed in a machine to determine their tensile strain.
The first one tried—four days old—bore a strain of more than 400 lbs. per square inch, and when the fracture took place, there ensued a report like the crack of a small pistol, which sufficiently testified to the extreme hardness or the material. Two other briquettes, one seven days and one fourteen days old, broke at strains of 670 lbs. and 840 lbs. The latter we understood to be a test of some specially selected cement required for a water works contract. The results of these proceedings were carefully recorded on the briquettes themselves, which were then arranged on shelves in the order of their date, and also in a book kept for the purpose. Examining this book we found a daily record, the figures in which indicated an average pretty close, as far as the four and seven day dates were concerned, to those recorded of the briquettes we had witnessed fractured just before. The great expense and care evidently expended in this department very much impressed us. The quality of any particular consignment of cement could, by the means taken here be ascertained at a moment's notice. Many more interesting details we could add on this subject, but we have given sufficient to show the thoroughness displayed in this matter of testing, a thoroughness which we found was characteristic of every part of the business.
Having spent some time in watching the manipulation of the manufactured article, the manager arrived, and we reversed the mode of our proceeding by visiting the quarry, whence the raw material was obtained, and, with the aid of the manager, we followed the limestone and shale in their course through the various processes undergone before subjection to the final ordeal in the test room. In order to get a better view of the limestones and shales, we descended the incline on which a tramway was laid for the purpose of hauling out, by means of a wire cable, the raw materials for manufacturing purposes, and were well rewarded for our pains by obtaining a view of a magnificent "face" of the Blue Lias formation, some eighty feet in depth. The large quantity of water draining into the quarry was pumped out by steam pumps made by Messrs. Tangye, working night and day, and throwing some 15,000 gallons per hour (Note 4). After a short search for fossils, which we found very abundant, we followed a truck load of rock on its way up the incline to the top of the quarry.
Three or four men were busily engaged in cleaning the stone from clay (Note 5) and in assorting the material. The first stage in the manufacture was the wheeling of the limestone and shales in due proportion (Note 6) to a powerful stonebreaker, whose enormous jaws quickly broke up the material into very small pieces. An elevator conveyed the broken material to a large hopper placed above mill-stones. These mill-stones, made from very hard "French Burrs", reduce the stone and clay to a very fine powder.
The powder is mixed into a thick paste, styled by the men, "Daub", and wheeled away to be dried, after being formed into bricks, in huge ovens. The bricks being baked, the next move is into domed kilns, where, by means of coke, they are calcined into clinker. This operation of heating the raw material to the point of vitrifaction is of the greatest importance. The next operation is the crushing of the clinker by large crushing machines. The broken clinker is finally reduced to a fine powder by the mill stones. This powder is afterwards passed by elevators to revolving screens, which effectually sift out any imperfectly ground particles. This process of screening is the final stage of manufacture, except storing in large cooling sheds and packing in sacks or casks.
The systematic testing which is carried out in these works renders it a matter of impossibility for an inferior article to be placed in the market. So closely is each step in the manufacture looked after, that we can quite believe the assurance of the manager that it was a rare occurrence indeed to have a sample of cement which would not endure the tests imposed upon it.
Having now seen the various processes just mentioned being busily carried out, we emerged from the mill houses, and made a visit to a long line of buildings adjoining. A couple of blacksmiths were busy in the first shop, and passing along we found carpenters, fitters, and coopers, each with a roomy shed for their respective trades; store houses for sacks and casks, stabling for horses, a mess room for the men—all with complete accommodation—which fully explained to us the necessity of the extensive building which had aroused our curiosity. Opposite these large buildings was another line of brick work, which we found to be a set of large lime kilns. There were some half-dozen of them varying in size, the largest capable of burning sixty or seventy tons.
The manufacture of lime is very simple. The kiln is filled up with limestone, intersected with coal in sufficient quantity to produce a dull red heat, in order that the carbonic acid gas may be discharged, and this is the sole operation. Our attention was drawn to a more modern kiln, which had been designed to burn continuously, lime being drawn every day from the bottom of the kilns and being replenished every day at the top, the fire being kept going for months at a time. This kiln was a formidable looking structure, and had evidently been erected at great expense.
Looking down from the lime-kilns we saw three large boilers, each about 30ft. long, and this reminded us that we had not yet seen the engines which drove the heavy machinery we had seen at work. We, therefore, made our way down, and in passing the boilers noticed that they were of modern design and fitted up with the latest improvements. The first engine we were shown was a large beam engine by Musgrave and Sons, and was of more than 100 horse power; but the second one, which had just been put down in connection with a separate set of stones and their attendant crushing machines and elevators, &c, was capable of working up to 300 horse power (Note 7).
That there was plenty of need for these powerful engines was evident, there being ten pairs of 4 ft. 6 in. mill-stones, four large stone breakers (all of the Blake principle), from the well-known Leicester firm of S. Mason and Co., to say nothing of elevators, screens, &c. Messrs. Glover and Sons, of Warwick, we understood, had the contract for the fixing of the greater part of the mills and engines; the remainder— the mill houses, drying floors, cement-kilns, lime-kilns, &c.—having been entrusted to the firm of Messrs. J. Fell, Limited, of Leamington. It was apparent that no expense had been spared in putting down very complete plant for the manufacture of cement and lime. The secretary was good enough to tell us that the company started with the idea of being able to equip the works with an outlay of £10,000, but, unfortunately, they had had to spend more than double that amount, and that the whole cost up to this had exceeded £24,000 (Note 8), and what they had done with this sum only enables them to turn out 400 tons of cement and lime per week, but with an additional expenditure £5,000, they contemplated being able to well-nigh double their output.
The secretary handed us copies of several certificates of tests made by cement experts, with a request that we would introduce them into this article; and, although such a course is somewhat unusual, we promised to give extracts. In the report made by Mr. Hy. Faija (who is probably the most eminent and best known cement expert), he states that the average tensile strength at seven days old was 830 lbs. to the square inch, and that on examining the samples for soundness he found no indications of either expansion or contraction. In the certificate and report made by Mr. G. A. Hird, C.E., he states that no effort was made in preparing the tests to imitate the scientific manipulation adopted by professional testers, and could conscientiously say that—"In my twenty years' experience of Portland cement in actual construction of works, I have never seen such high results as those noted. One briquette which I made with your cement in the moulds of the Hull Dock Company (and which had an area of 2.15 square inches) was put under strain the other day in the Company's own machine, but was not broken. The lever marked a strain of 1,160 lbs., and, although repeated attempts were made to break the briquette by moving the weight on the lever, the block remained unbroken".
Having now seen pretty nearly everything in the way of machinery and buildings, and, having a short time still to spare, we took a stroll around the outskirts of the works to see what facilities there were for despatching manufactured goods. We found that the Oxford Canal and the Midland Railway ran within a few hundred yards of the warehouses, tram lines being laid down to a wharf at each. The Midland Company have built a dock for the accommodation of the company, and the Oxford Canal Company have also gone to the expense of a suitable wharf. With the canal and railway so handy, it would be difficult to hit upon a better site for works of this kind At the canal wharf we noticed a very substantial building occupied by the manager. Allotments were provided for the men on the spare land, and cottages are about to be erected for some of the workpeople on a strip of land facing the highway to Rugby. in a line with the house occupied by the secretary.
No expense evidently had been spared on plant and buildings, and every detail dealt with in a very complete and effective manner; and, having imparted our opinions on this subject to the obliging officials who had shown us the various interesting stages in the manufacture of Blue Lias cement, and who had given us courteous assistance and every information we required, we ended a most instructive and enjoyable visit with an apology from the secretary for not being able to offer refreshments.