Tetrahedrons and Spherical Balls Compared: An interested operator furnished 1,000 pounds of tetrahedrons for comparison with spherical balls. The tetrahedrons were all about the same size and the average weight of each was the same as for a 1 3/8- inch spherical ball. Four pairs of tests with tetrahedrons and round balls, respectively, are shown in table 22. The loads weighed 796 pounds each.
In the first pair of tests with chert the tetrahedrons were deficient in crushing the coarse particles and they also failed in capacity and efficiency. In the second pair of tests, when dolomite was ground, the type of grinding was about the same, but otherwise the failure of the tetrahedrons was marked.
Since the tetrahedrons were of one size, it seemed best to make further tests and compare them with a load of closely sized balls. Similarly, the ore feed was sized, first plus 10-mesh chert and then 28- to 35-mesh chert. The 1 3/8-inch balls that were used in the sized-ball load were known to be slightly too small for the coarse ore charge and too large for the finer ore charge.
The tetrahedrons failed on the plus 10-mesh ore charge, and when the finer ore charge was ground the two media gave the same type of grind; but, as in all the other tests, the tetrahedrons failed in both capacity and efficiency.
The keying effects of the tetrahedrons against each other is evidenced by examination of the power records—the tetrahedrons required about 10 percent more power than the balls. All in all, they failed by about 15 or 20 percent. Possibly on account of the large area of the plane surfaces exposed to contact, the tetrahedrons would serve better for grinding excessively fine material.