OUR INDUSTRIES.

Otago Witness, Issue 2087, 22 February 1894, Page 35

OUR INDUSTRIES.

THE MILBURN CEMENT WORKS.

Portland cement from its initiation by Joseph Aspdein, to whom a patent was granted in England in the year 1824, to the present date has made more rapid strides in respect to the quantity used than any other building material, although it is questionable whether any very appreciable improvement has been made during the past 25 years in point of quality. The approximate production of Portland cement in Europe amounts to over 20,000,000 barrels. The manufacture was first introduced into Germany in 1852. At the present date there are over 60 large works turning out a similar quantity to England. In France the output has increased from 750,000 barrels in 1880 to 1,800,000 barrels to-day. The largest works are at Boulogne-aur-Mer, which turn out 800,000 barrels. Belgium makes about 800,000 barrels, whilst Italy scarcely makes any, Denmark, Norway, and Sweden combined equal the output of Belgium. America has scarcely succeeded in making Portland cement, but has an excellent natural cement (Rosesdale), which largely takes the place of Portland. Whilst England and Germany are the great rivals who run each other closely for the trade of the world, almost every country and colony is endeavouring to produce cement eince it has become an article of absolute necessity to the engineer and architect. Recognising the importance of such an industry, and the prospects of bringing the same to a successful issue, the Milburn Lime and Cement Company (Limited), of Dunedin, have so far succeeded in overcoming the numerous disadvantages inherent in all local industries that they may be Baid to be thoroughly established as cement manufacturers. A brief history of this company may be of interest. About six years ago the valuable and well-known Milburn lime deposit, together with a small cement works, was disposed of by auction and acquired by a syndicate of Dunedin gentlemen. This syndicate at once formed a more powerful company, with a capital of £30,000, registered as the Milburn Lime and Cement Company (Limited). The quality of the lime was too widely known to cause the directors any anxiety, and from the start a satisfactory business was done, but with the other branch of .cement making difficulties came quickly. The works were then situated at Walton Park — a site that seemed to possess every disadvantage, involving costly carriage of clay, lime, coke, general stores, and finished cement, combined with unsuitable machinery. After a few months' working the directors, recognising the gravity of the position, called a special meeting of shareholders to decidewhother the company should retire from cement making or acquire a new site and boldly erect modern works. Fortunately, the latter proposal was carried, or certainly there would be no such works in New Zealand as we now find at Pelichet Bay. The site selected has the advantages of both water and rail communication, besides having an unlimited supply of clay. From its position in the harbour, and the "breezy nature" thereof, the assistance in burning off and drying the " slurry" is invaluable.

Portland cement is a chemical product, obtained by a preliminary mechanioal process of combining silica and alumina with lime. The name of " Portland " was not given to it from any other reason than its resemblance 'to the well-known Portland building stone. It is practically an improved hydraulic lime, and may be made from many various materials containing suitable quantities of lime, silica, and alumina. The raw materials used by this company are : — Lime obtained from the company's own kilns at Milburn, and cl&y from the harbour. The process is as follows -.—Carefully weighed quantities of lime and clay are wheeled into & large wash mill, which has two powerful barrowa, revolving at a speed of 1000 ft per minute, where the materials are washed with sufficient water to enable it to flow; thence the "slurry" (as it is technically called) is passed through fine gratings to an elevator conveying it to horizontal millstones, in which it is ground co fine as not to leave more than 5 per cent, residue on a sieve of 3600 meshes per square inch. This practically completes the mixing. On this part of the process greatly depends the ultimate quality of the cement. From the millstones the "slurry" falls by gravity to a powerful force-pump (capable of lifting 15,000 gallons in eight hours), which elevates it to the chambers, where it is dried by the waste heat from the kilns. The kilns and chambers are of a modified Johnson type, built in brick and concrete, covering about 5000 Bquare feet. The principle is to utilise the waste heat from the kilns by passing itethrough a chamber containing the "slurry" intended for the following charge. The kilns are loaded in the usual way by alternate layers of coke and slip, and ignited from the bottom with straw and wood. After the kiln is burnt off and allowed to cool, it is drawn, the product being "clinker." The transformation from slip to clinker shows the high heat attained in the kiln — nearly 1600 centigrade — converting the white soft slip into a hard, dark green clinker, besides effecting the desired chemical change — viz., uniting the lime and silica, forming silicate of lime, and then at the highest heat uniting the silicate of lime with alumina. The clinker is next conveyed to the dry mill where it is pulverised by Askham Bros', patent plant (the largest size made, and capable of reducing three tons of clinker per hour to almost impalpable powder.) The grinding plant is the latest and most complete procurable, and there is no further handling from the time the material is fed into the crusher until it is delivered into the warehouse. The warehouse is a large building 150 ft long, containing about 1000 tons of cement ready for bagging and stored about 7ft high. There are three doorways opening on to the company's siding, which greatly facilitates the delivery. The power is supplied by a compound engiae 200 i.h p, and the waste hot salt water used for condensing is to be conveyed to a large public swimming bath in Frederick Btreet, now being erected by Messrs Morgan and Co.

The method of testing is considered to be as thorough and efficient as possible. In the first place a chemical analysis is made daily of the " slurry" to regulate the proportions. Mechanical and analytical tests are also daily made of the finished cement. The tensile is ascertained by lin briquettes, broken with an Adie machine at seven, 14, and 28 days, also up to 12 months, and the result is noted in the company's register. The average of these shows that the cement made is thoroughly sound, and that a higher standard is reached than many English makers attain. Our representative on visiting the works was invited to select a briquette out of a bath containing probably 50, and this proved to be one three months old, which stood the highest tenbile the machine was capable of breaking — viz., 8201b per square inch, a result that speaks for itself. The company claims that their cement is stronger and better made than the average English. Owing to the work being upon a smaller scale, the supervision

is more thorough, and greater attention is given to the proportions of raw materials. The output has gradually increased from 20 tons per week at the start to 60 at the present time, and there is no reason to doubt it will continue to prosper. As a colonial industry it is thoroughly bonafide. Everything used in the manufacture —fuel, clay, lime, coke, labour, and capital — being locally obtained. Given a continuance of the liberal support by the public generally, and the Government in particular (since the present Government has been in power the Premier has insisted upon using the colonial production instead of an imported article), the work of cement making will become one of vast importance to Dunedin and the colomy generally. As a factor in coping with the unemployed difficulty it is worthy of support. At present the company pay about £4000 a year for labour, and from £4000 to £5000 to the Railway department, and it uses from 100 to 200 tons of fuel per month. The present board of directors are : Mr Jno. White (who has held the chairmanship of the company since its formation), Mr Thomas Brydone (of the New Zealand and Australian Land Company), and Mr J. W. Brindley (of the Victoria Insurance Company). From what is known of the business abilities of these gentlemen, and of the energy of the manager (Mr F. Oakden) it may be taken for granted that the interests of the shareholders will be well looked after, and as a good dividendpaying concern — the great desideratum in all such enterprises — it must eventually be permanent and solid.