MACHINERY AND PLANT 71 



is about equal to the time of pressing, and one 

 kettle serves two presses. Simple measuring 

 boxes under the kettle, by being alternately 

 opened and closed at the top and bottom, deliver 

 sufficient meal for each cake. As charging 

 takes place, the ram is lowered and steel or 

 malleable iron plates are inserted between each 

 layer of meal. These plates are usually galva- 

 nised to prevent the adhesion of the oil cake 

 formed. Similar presses with solid cylinders 

 are used when making oil cakes from mixtures 

 of rich and poor residues, where no oil extraction 

 takes place. 



The second pressing is generally conducted in 

 plate presses. The cakes from the cage presses 

 are broken down in fluted roller mills, and the 

 material ground to break up further the oil cells 

 in the material. The meal is delivered into a 

 steam-heated kettle, measured and moulded to 

 form a compact cake in a cake-moulding machine. 

 The cake, with its press cloth folded over the sides 

 to prevent lateral flow, is slid between the plates 

 of the plate press ready for pressing. 



For this operation one kettle usually serves 

 four plate presses, so that the time of pressing is 

 four times that of charging and discharging. 

 After removal from the press the cakes are 

 trimmed in a cake-paring machine, by which 

 about 25 per cent, of the weight is removed 

 from their outer edges. The parings usually 

 contain 14 to 16 per cent, of oil, and are 

 returned for re-pressing. The expressed oil as 



