IMPACT MACHINE. :\ 1 



a flat-end plunger (/>') of 1 kg weight, which is pressed upon the 



briquette ('>) by two light spiral springs BUITOUnding the guide rods 



(7 y7 ). This plunger (j^ is bolted to a crosshead (#), A ^mall lever (./) 

 holding- a brass pencil (A') at its free end, is connected with tin- side 

 of the crosshead. by a link motion arranged so that it gives a vertical 

 movement to the pencil five times as threat as the inoveinent of the 

 <T<--head. The ])encil is pressed against a drum (.1), and il.s move- 

 inent is recorded on a slip of silicated j)aper fastened thereon. The 

 drum is moved automatically through a small angle at each stroke of 

 the hammer; in this way a record is obtained of the movement of the 

 crosshead during and after each blow of the hammer. To the oross- 

 head ((*) is fastened a steel rod (R] which passes up through the cross- 

 head (/) and through a piece of metal securely attached to the cone 

 rod (/'). At this junction a vernier scale is graduated, by means of 

 which the height of blow of the hammer can be accurately set to 0.1 

 mm. and by lowering the cone rod until it rests on the hammer cone 

 (L) the height of the briquette can also be measured to (). L mm. 



The standard fall of the hammer for a test is 1 cm (0.31) inch) and 

 this blow is repeated until the bond of cementation of the material is 

 destroyed. The blow producing failure is easily ascertained, for when 

 the hammer falls on the plunger, if the material beneath it can with- 



r 



ee Blows. 



FIG. 7. Diagram showing point of failure in cementation tost. 



stand the blow it recovers; if not, the plunger stays at the point to 

 which it is driven, and in either case the behavior of the test piece is 

 recorded on the drum. The automatic record thus obtained from each 

 briquette is tiled for future reference. A copy of one of these records 

 is shown in fig. 7. The number of blows required to destroy the bond 

 of cementation or resilience, as described above, is noted and the 

 average obtained upon five briquettes is given as the cementing value. 

 The problem of holding the test piece rigidly under the intervening 

 plunger, so that it would not be subjected to lateral movements and 

 transverse strains, is one which has given much difficulty. Tntil 

 recently a small brass plate with a beveled hole slightly larger than 

 the diameter of the briquette was used, but it was found that the te^t 

 piece was often seriously abraded by the side thrust developed. Later 

 attempts to secure the briquette by various clamping devices were not 

 satisfactory. Finally the method was adopted of placing a drop of 

 thick shellac on the bottom of the test piece, which caused it to adhere 

 firmly to the bedplate. Careful attention to such details as these is 

 necessary in order to get satisfactory results from thi- te-t. 



