48 



CEMENTS, LIMES, AND PLASTERS. 



of calcination is being completed on the material in the second bin, 

 and the third bin is being filled with material from the rotary calciner. 

 These bins are so constructed that the material in process of calcination 

 is thoroughly ventilated, which allows the heat carried by the material 

 from the rotary calciner to rapidly disseminate itself through the mass 

 and complete the calcining process. While the resident heat in the 

 material is acting upon it, practically no circulation of air through the 

 material is allowed, but as soon as the process of calcining is completed, 

 air at atmospheric temperatures is freely circulated through the mass 

 and the calcined gypsum is rapidly cooled. Each bin is equipped with 

 a simple device which mechanically discharges the material regularly 

 and at any speed desired. 



A dust-chamber located above the rotary calciner catches the most 

 finely ground plaster, which is marketed for dental plaster and other 

 special purposes. 



The Cummer rotary calciner is shown in section in Fig. 15. Its 

 operation is as follows: 



FIG. 15. Cummer rotary plaster- calciner. 



The gypsum rock is fed through a hopper, F, into a cylinder set 

 on a slight incline rotating on trunnioned bearings within a brick chamber. 

 The material passes slowly down the cylinder (owing to its inclination 

 and rotation), being thrown about by lifting-blades attached to the 

 inside of the cylinder. It is discharged at K, having been subjected 

 during its passage to the heated fuel gases, whose admission and handling 

 will next be described. 



The hot gases from the furnace are drawn by the fan G into the 

 brick chamber surrounding the cylinder. Cold air is introduced through 

 the registers E and and mixed with the furnace gases in such propor- 

 tions as to give the desired temperature. These gases are drawn into 

 the cylinder through the hooded openings J and pass through it in a 



