The machine in the picture below is an injection molding machine. Iwako and Zensinsyoji use these machines to make the parts for the Jaspanese erasers. Many plastic parts are made this way, from the keys on my computer that I am using to write this, to the dashboard on my car.
On the left side of the injection molding machine, you can see a stainless steel cone shape which is a hopper where the plastic bits are fed. The hopper sits on a black box like thingy and extending from the right hand side of black box is a big tube. Inside the big tube is a big heated rotating screw that takes the plastic bits from the hopper. As the plastic is forced along by the heated rotating screw, the plastic becomes molten, and this liquid mixture is pushed into the mold. There the mixture hardens, and the new eraser parts are ejected. They move down a conveyor belt into the carboard box. There is a picture of these boxes full of Japanese erasers parts in an earlier post.