Grinding mill system having proportioning feeder

In a grinding mill system for sand or the like, said system including a mill, classifying means for receiving ground materials from the mill and separating over-sized particles from finished product, first conveyor means for receiving said over-size ground material, a feed device including a feed channel, said channel including an entry end and a discharge end connected to said mill, second conveyor means movably mounted in said channel for advancing material to said discharge end, said second conveyor means including transverse separator portions extending into proximate spaced relation with the inner walls of said channel and dividing said channel into a series of longitudinally extending segments, a first receiver station in said channel adjacent said entry end and connected to said first conveyor means for receiving and introducing into said channel said partially ground materials from said first conveyor, a second receiver station interposed between said discharge end and said first receiver station, and gravity feed means at said second receiver station for introducing said raw material into the area beneath said second station and bounded by the surface of the material introduced at said first receiver station and said separator portions of said second conveyor at a rate to substantially fill said conveyor in said area beneath said second receiver station, whereby the quantity of said raw material introduced at said second station automatically varies as a function of the level of the material beneath said second station which was introduced at said first station.