2. Grinding — Shelled corn and alfalfa pellets must be ground be- 

 fore being mixed with other ingredients. They are moved by screw con- 

 veyor or gravity to the feeders on the hammermills which are used in the 

 model mills. The ground ingredients are then elevated into bins by a 

 pneumatic system. 



3. Mixing — The mixing stage consists of the following sequence 

 of steps : moving ingredients to the mixing center, weighing, mixing, con- 

 ditioning and conveying the batch to the next stage. A number of tech- 

 niques exist for performing each step. 



Bulk ingredients are moved from bins to the mixer by "weigh bug- 

 gies'' or conveyors. Weigh buggies are used in conjunction with vertical 

 mixers in small size mills. The ingredients are weighed into the buggy 

 and pushed to and dumped into the mixer sink. 



The movement of bulk ingredients by conveyors is the practice in 

 the large size mills since large quantities nuist be moved in short periods 

 of time to keep mixers operating at capacity. Feeder screws move ingre- 

 dients into a weigh hopper over the mixer. The quantities of the differ- 

 ent ingredients fed into the hopper are controlled from a central panel 

 either by an operator or by automatic devices. 



The bagged ingredients are brought from the warehouse periodic- 

 allv. For each batch the bags are opened, weighed, and dumped into the 

 mixer. Fat is pumped directly into the mixer, the amount being controll- 

 ed manually or automatically. However, if the batch is to be pelleted, 

 the full amount is not generally added at this stage, since a high propor- 

 tion of fat in the mix makes pelleting extremely difficult. 



A batch is mixed for a predetermined length of time to oljtain a 

 thorough blend of ingredients. The specific time required depends on 

 the formulation and characteristics of the mixer. Generally, the mixino; 

 time is between eight and ten minutes in a vertical mixer and three and 

 five minutes in a horizontal. The time is controlled manually or by an 

 automatic timing device. 



The mixed batch is moved from the vertical mixer by conveyor to a 

 bucket elevator. Batches mixed in a horizontal mixer are dumped into a 

 surge bin from which they are moved by conveyor to a bucket elevator. 

 The use of a surge bin results in a substantial increase in mixer capacity. 



The mixed batch is elevated and passed through a conditioner to 

 remove any foreign material and to break up lumps. The conditioned 

 batch is moved by self-cleaning chain drag conveyors to the finished 

 mash bins or to holding bins for pelleting. 



4. Pelleting or Crumbling — This stage consists of several different 

 series of steps depending on the desired finished form of the feed and 

 the formulation. These steps include pelleting, crumbling, and fat appli- 

 cation. The pelleting stage starts with mash being fed into the pellet mill 

 where it is conditioned by steam and forced through the pellet die. The 

 continuous flow of hot pellets is gravity fed into a vertical cooler, and 

 then conveyed directly to the grading shoe. If the desired output is 

 crumbles, the cooled pellets are fed into a crumbier and then conveyed 

 to the grading shoe. Fines and oversizes are screened off on the shoe 

 and conveyed back to the pellet mill. Formulations in pellet or crumble 

 form that require additional fat are routed through a fat applicator 



10 



