Seeds usually contain impurities like sand, stone, stems of plant, earth, sutli, leaf, grass etc. Sometimes they contain iron and metallic pieces also. These impurities should be removed in order to obtain high quality of the oil. These impurities in spite of injuring the quality of the cake, lower the oil yield by absorption of certain amount oil and tends to wear out of the machinery.
Pre-Cleaning of the seed increase the life of expellers & minimizes unwarranted breakdowns and keeps the better quality of finished products.

Different types of seed cleansing machines are used in the oil mill industry :

Hand Cleaning Machines.
Stationary seed cleaning machines
Vibrating seed cleaning machines
Rotary seed cleaning machines
Brushing machines