注射成型介绍

1、Injection Molding"Injection molding is the most important commercial method for transforming thermoplastics into useful products. A thermoplastic polymer is one that can be reheated and reshaped many times. Themoset plastics set in a desired shape and cannot be reheated and remolded. During the

2、 injection molding process, plastics are heated until they soften into a molten state. The melted plastic is then forced at high pressure through a nozzle into a cold mold. The plastic cools in the mold and takes on the mold's shape. Once the plastic is cooled, the mold opens and the product is

3、released from the mold. The resulting product often needs no further work before being put into use since details such as ribs and screw threads can be formed during this process. Examples of injection molded items are cabinets for computers, computer screens, and computer keyboards, parts of plasti

4、c model or hobby kits, plastic bottle caps, brake and engine parts, reflectors and headlights, circuit breakers, toaster oven panels, power tool and lighting housings, and even tableware. These items can usually be identified by one or more of the following features: side parting lines or seams in a

5、n object formed where the two sides of the mold meet together, sharp corners, fine detail and precision, frequent flat areas, and the presence of a "gate". The gate looks like a dimple or bump of plastic. It is the entry point of the polymer melt into the mold cavity. The gate may be centr

6、ally located and a significant distance from the parting lines as in a waste basket, on the edge as in individual parts of a plastic model hobby kit, or submarine where the gate itself appears oval and is located below but near the parting lines.An injection-molding machine is really a combination o

7、f three machines: the plasticizing and injection machine, the clamp, and the mold. The purpose of the plasticizing and injection machine is to produce a molten volume of plastic under enough force to cause the plastic to fill the mold cavity. The pressure may be supplied by a plunger (also called a

8、ram or piston) or rotating screw. A hopper feeds the plastic resin into a heated cylinder or chamber while the ram is retracted. The ram then pushes forward rapidly and forces the resin into the cylinder compacting it around a centrally located torpedo or spreader. As the melt moves forward around t

9、he cylinder, it becomes more fluid. As the melt arrives at the nozzle, it is pushed rapidly forward and into the mold. (In screw injection molding machines, the screw's turning motion delivers the melted plastic to the mold.) Molds may have only one, or many cavities for a number of parts to be

10、molded simultaneously. When the mold cavities are filled, the plastic is allowed to cool so that an item holds it shape when ejected from the mold. The clamping unit supplies the motion and force to open and close the mold. It must also hold the mold closed with sufficient force to prevent the injec

11、tion pressure from opening the mold's cavity as it is filled. The molds themselves may vary greatly. They are highly complex structures using various metals and alloys to form their exact finished dimensions. However, all molds contain and guide molten polymers from the nozzle into the cavity, c

12、ool the polymer in the cavity to its solid state, and open to discharge the final item. Once an object has been injected from a mold, the machine is ready to fill the mold cavity again and start the process over. Most injection molding machines are automatically timed, and for many thermoplastic materials, it only takes 10 to 30 seconds to complete a cycle. The rapid succession of injection of the molten plastic and ejection of the solid molded object has permitted this process to become the leader in the mass production of plastic toy