DAIRYING 27 



268. In other words, for 1000 revolutions a minute the dis- 

 tance from the center R being 1 foot, the centrifugal force is 340 

 times the weight of the matter; R being 2 feet, it is 680 times; R 

 being 3 feet it is 1020 times the weight, etc. Supposing the 

 weight of a particle of fat in the milk to be 10 weight units, and 

 that of an equally large particle of milk serum to be 11 weight 

 units, then the force by which the fat is naturally driven towards 

 the surface by gravity only will be 11 10=1, while the centrifugal 

 machine making 1000 revolutions a minute with an average radius 

 of 1 ft. the force will be 340X1 1340X1 0=340. Thus the tendency 

 of separation is increased 340 times by the centrifugal forces, 

 and if the speed is 5000 revolutions per minute, the increase will 

 be 8500 times. This gives an idea of the efficiency of centrifugal 

 creaming as compared with any gravity process, and also suggests 

 the enormous strain to which the drum of a separator is sub- 

 jected. Supposing a stick to make 1000 revolutions a minute 

 around its center in the horizontal plane, at each end carrying 

 a pail with milk weighing 60 pounds, and supposing the average 

 radius to be 2 feet, then the force with which each pail will pull 

 the stick is 340X2X60=40,800 pounds or about 20 tons." 



269. Besides showing the difference between the force of 

 gravity and centrifugal force these figures give some idea of the 

 tremendous strain there is exerted on separator bowls run at a 

 high speed. It should be noticed in the figures given that the 

 pull on the balance does not increase directly in proportion to the 

 increase of the speed or the velocity, but to its square. Doubling 

 the speed or velocity quadruples the centrifugal force. 



These brief statements show that the strain on the walls 

 of a separator bowl is influenced by three things, the weight of the 

 material revolved, the diameter of the bowl, and its velocity. The 

 smaller the bowls, the higher the speed at which they may safely 

 run. 



Pail and Drum Separators 



270. Many experimental machines were made for the purpose 

 of separating cream from milk before any satisfactory results were 



