A device that can automatically close or secure an open door leaf to a location. Some have the function of hinges, and some have fire resistance. The main varieties are floor springs, door top springs, door slingshots, door gates, door clamps, magnetic door tips, etc. 1 floor spring: also known as the earth dragon. Installed in the lower part of the door and window (Figure 5). It is made of gray cast iron, carbon steel, spring steel, cast steel, etc., and is assembled. 2 door top spring: an automatic door closing device that closes the door leaf by the spring force of a spring or a spiral spring. A buffer cylinder is installed inside to reduce the closing speed. 3-door slingshot: It is made of low-carbon steel strip and is equipped with a low-carbon cold-drawn steel ram to close the door with elastic force. 4 Door gate: A brake door and a simple positioner that avoids collision of the door leaf with the wall (Figure 6). Installed in the outer lower corner of the door leaf, the door leaf can be positioned at any angle. 5-door chuck: A device that secures the door leaf. It consists of a knife-shaped base and a triangular steel collet. There are two types of horizontal (Fig. 7) and vertical. The base is cast in grey cast iron; the chuck is made of spring steel and the surface is treated with blue. 6 magnetic door suction head: the same function as the door clamp door and window hardware, the door is fixed by the suction force of the permanent magnet, and there is no noise when used. Pce Based Superplasticizer for concrete,pce based admixture,pce admixture,PCE water reducer,PCE concrete admixture Shanghai Hongyun New Construction Materials Co., Ltd , https://www.hongyunpce.com