866
are lifted by hydraulic cranes, of which there arethree types. Bessemer’s, which is used mainly inEngland, consists of a strong cylinder casing fixedfirmly to the ground, and having glands at thetop and bottom. The ram is thicker at the toppart than at the bottom, and the difference in sec-tional area is the active surface to which the poweris applied. The jib is fixed to the top of the post,and is balanced by a heavy weight fixed to theopposite end. The American plan was designedby Holley. The ram works through a single glandin the top of the casing, and the whole sectionalarea is acted upon by the water pressure. Insteadof being guided, as in the English plan, by thelower portion of the ram working in a casing,the post is carried above the jib and is stayedfrom the roof of the building. Messrs. Tannett& Walker have recently introduced an ingeniousarrangement for the purpose of balancing the weightof the moving parts upon the column of water inconnection with the accumulator. For this purposethey employ two rams, one of which works in acasing which is in constant connection with theaccumulator, to act as the balance for the craneposts, jib, &c.; the other is worked by a valve, thediameter of the second ram being only sufficient togive the power needed for the maximum weightto be lifted. A strong guide ram is also fixed tothe crane head to insure stability. The arrange-ment works well, but requires very careful adjust-ment. A plan occasionally adopted is to fix thejib to the cylinder, and let it work on the ramwhich is fixed. This plan is only suited for specialcases.
Hydraulic Pumps are of various kinds. Those byArmstrong are ingenious and scientific, but arealways made with too short a stroke. There isnothing better than a good-sized ram with longstroke and very slow motion. Davey of Leeds hasapplied his differential valve gear to direct-actingpumps for high pressure with excellent results.Worthington’s pumps, which are somewhat similarto D avey’s, are used very largely in the United States .
The Accumulator , for regulating and storing thewater pressure, consists of a large ram weighted onthe top, and working in a strong casing through awell-packed gland.
Hydraulic Valves are a source of considerabletrouble in steel works, and a really good balancedvalve remains to be invented. Slide valves requiregreat power to move them. Three and four waycocks leak rapidly, and require constant grinding.Luthy’s valves, which are balanced, are ingeniousand easily worked; but the leathers are a source ofconsiderable expense in large works.
Present Mode of Conducting the Bessemer Process .—If the iron is to be taken direct from the blastfurnaces to the convertors in a molten state,all that is necessary is to take care that it is ofsufficiently good quality, that is, free from phos-phorus and sulphur, and that it contains from 1|to 2 per cent, silicon if little or no manganese ispresent. The lower the percentage of silicon and
manganese, the shorter will be the blow. Hencein Sweden five or six minutes often suffice to blowout sufficient carbon to leave the metal at the pointof steel. In England it generally takes from fifteento twenty minutes; but occasionally, when muchsilicon or manganese is present, the blow may lastfrom thirty to sixty minutes. If the iron is remeltedin a cupola, a proper system of charging must beadopted.
The old plan of arriving at uniformity in qualityof iron was to have a number of brands, and byexperiment to arrive at a mixture of these whichworked well; a similar mixture being supposed toanswer on all occasions. This was often foundto fail, and the proper mixture had then to befound by experiment again. The more correct andscientific method which is now followed where theprocess is properly conducted, is to analyze before-hand the stocks of iron, and then to make up acharge from an examination of the analyses. WithEnglish pig iron it is generally sufficient to find thepercentage of silicon, and to calculate the charge fromthis element. If the grade of the iron be not toolow—say a fair mixture of Nos. 1, 2, and 3 Bes-semer —a charge containing from 2J to 2^ per cent,silicon is found to work well, as it blows sufficientlyhot to leave no skull, and the silicon is not too highto endanger the quality of the steel by running therisk of leaving a variable quantity in the metal afterthe carbon has all been burnt out, or making thecharge so hot as to cut out the moulds and bottomplates during teeming. Supposing, then, we havefour stocks of iron, A containing 3‘5 per cent,silicon, B 3 per cent., C 2'5 per cent., and D 1-5per cent. If used alone, A would yield a steel thatwould be so hot as to cut the moulds on teeming,and the silicon would be so high that it would notall be burnt out by the time the carbon had beenoxidised, and a siliceous steel would be the result.B would still blow hot, and there would be somerisk of a siliceous steel. C would work well; butII would blow so cold that there would be insuf-ficient heat developed to make the metal hot enoughto remain fluid in the ladle during teeming, andthere would be great risk of the whole charge con-solidating in the ladle, forming a wasteful skull.But by mixing in the following proportions we geta charge that will use up all the samples withoutrunning any risk whatever:—
1 Ton A at 3-5,. 3-5
2 Tons B at 3. CO
2 “ C at 2-5,. 5-0
3 “ D at 1-5,. 4-5
8 19*0
Per Cent.
Average silicon,.= 2-37