Such machines take advantage of planet gear speed reducers and alloy steel blades with high intension and anti-milling characters. Their four shafts rotate at different speeds with tearing, extrusion and bite functions. Electric part has the automatic detecting overl-oad protection function, with Siemens and electric components programme control. They have advantages in regularly deloading materials and easily controlling material size, low rotation speed, low noises, large torque and high efficiency. They fit for shredding large and hard objects such as plastic pail, plastic frame, plastic bottle, metal can, metal pail, intertexture bag, fridge, electric circuit board, paper box and so on.