Abstract: A pneumatic cylinder includes a cylinder body, a piston assembly, a connecting rod, and at least one pressure-relief valve. The cylinder body is formed with a cylinder chamber, and has an exterior disposed with at least one inlet-outlet passage and at least one pressure-relief opening, wherein the inlet-outlet passage is connected to the cylinder chamber. The piston assembly is contained within the cylinder chamber. The connecting rod is connected to the piston assembly, and protrudes out from the cylinder body. The pressure-relief valve is disposed in the pressure-relief opening, and has two ends connected to an outside of the pneumatic cylinder and the cylinder chamber respectively. When a gas pressure within the cylinder chamber is greater than a threshold value, the pressure-relief valve works to allow the cylinder chamber connecting to the outside for pressure relief.

Abstract: A pneumatic-fixation connecting having a body, a movable part, a plurality of spheres, a plurality of elastic units, and a plurality of stop units is disclosed, wherein each of the elastic units is disposed between the body and the movable part via each of the stop units, respectively. When an external force is applied on the movable part, the distance between the movable part and the body is reduced and the sphere does not block the connecting pin in the extension tube inside the body. When the external force disappears, the distance between the movable part and the body increases such that the sphere affixes the connecting pin and the body. The stop unit can be used, not only to adjust the length and elastic force of the elastic unit so as to extend the life cycle of the elastic unit, but also to help in changing the elastic unit which in turn enhances the efficiency of the replacement work.

Abstract: A molding changing apparatus having a holder, a cooling plate, and a mold set coupled to the cooling plate is disclosed. The cooling plate has at least one connecting pin disposed on the surface which is reverse to the surface where the mold set is disposed, and the holder has at least one pneumatic pin receptacle disposed thereon. The connecting pin of the cooling plate can be inserted into the connecting hole of the pneumatic pin receptacle of the holder, and the connecting pin is fastened by the pneumatic pin receptacle, thereby connecting the mold set and the cooling plate to the holder. Through the use of the connecting pin and the pneumatic pin receptacle, the mold set and the cooling plate on the holder can be changed rapidly and the efficiency of the plastic vacuum forming with mold sets is enhanced.