THE TECHNOLOGIST. [Sept. 1, 1864. 



64 ON THE MACHINERY FOR 



risk of fracture was great, from the number of times the plates were 

 handled. On leaving the annealing oven the plate was handled once in 

 conveying it to the grinding machine and bedding it there, and after- 

 wards a second time in turning it over for grinding the second side ; 

 and similarly it had to be twice handled for each of the subsequent pro- 

 cesses of smoothing and polishing, making six times of handling altoge- 

 ther before the plate of glass was finished on the machines, after which 

 it had still to be twice handled in the final operation of hand cleaning. 

 All these processes, he considered, ought to be effected without more 

 than twice laying the plate at all, by working on both sides of it simul- 

 taneously ; and in this respect, therefore, he thought there was a wide 

 field open for improvements in the plate glass manufacture. 



The revolving grinding table that had been described was a decided 

 improvement upon the old fly-frame grinding machine, since in all 

 mechanical operations it was better to get rid of a reciprocating action, 

 wherever practicable, and replace it by a continuous circular motion. 

 The new construction of grinding table was preferable to the old 

 grinding benches, on account of its protecting all the machinery below 

 it, so that the working parts and bearings are not exposed to injury from 

 the grit thrown off profusely from the grinding table. A further 

 advantage was the large size of the table, 20 ft. diameter, which afforded 

 room for working on the whole surface of a large plate of glass at 

 once. 



A serious cause of loss at present in the manufacture was the very 

 large proportion of the glass that had to be removed in the process of 

 grinding in order to obtain a level surface of the glass. The undulations 

 on the surface of the plates before grinding could not, he considered, be 

 produced by the roller on the casting table, as had been suggested, 

 because the roller was of great weight and was moved forwards steadily, 

 running at each end on a smooth strip of iron laid along each side of 

 the casting table, by which the thickness of the plate of glass was 

 determined ; the surface of the glass appeared level before the plate was 

 put into the annealing oven. The undulations after annealing were not 

 in parallel furrows across the plates, but were in the form of hills and 

 hollows ; altogether irregular in size and position. It therefore ap- 

 peared that the glass in annealing must contract irregularly, causing 

 this unevenness of the surface, particularly on the side which had lain 

 uppermost in the annealing oven, in consequence of which so large a 

 proportion of the glass had to be ground away as waste in order to 

 obtain a level surface. In the old annealing ovens the plates had to be 

 left a long time till the oven had cooled down of itself ; but the ovens 

 were now built with air channels under the bed, through which a cur- 

 rent of cold air passed, so that the heat was reduced as quickly as 

 practicable without injur} 7 to the glass, whereby a great saving of time 

 was effected. No method, however, had yet been devised for laying the 

 plates one on another in the annealing oven, and consequently a large 



