Thermoplastic Injection Molding This method is to melt the plastic material and then inject it into the film chamber. Once the molten plastic enters the mold, it is cold-formed into a shape by the mold cavity.
The resulting shape is often the final product, no further processing is required until it is installed or used as a final product. Many details, such as protrusions. Ribs, threads, can be molded in one step in injection molding.
Injection molding machine has two basic components: the injection device and the mold clamping device for melting and feeding plastic into the mold. The role of mold clamping device is: (1) the mold to withstand the injection pressure closed; (2) the product removed.
The injection device melts the plastic before it is injected into the mold and then controls the pressure and speed to inject the melt into the mold. There are two designs of injection devices currently used: screw pre-plasticizers or two-stage devices, and reciprocating screws. Screw pre-plasticizer using pre-plastic screw (first) and then give the molten plastic injection rod (second level).
The advantages of screw pre-plasticizers are constant melt mass, high pressure and high speed, and precise injection volume control using mechanical thrust devices at both ends of the piston stroke. These are the benefits that are required for transparent, thin-walled products and high production rates. Disadvantages include uneven residence time (leading to material degradation), higher equipment costs and maintenance costs.
The most common reciprocating screw injection unit melts and injects plastic without the need for a plunger. The hopper in the powder or granular plastic melting, screw rotation through the screw to the front end of the anti-room, the plastic flow through the front end of the screw and piled in front of the screw. The accumulation of molten plastic in front of the screw pushes the screw toward the back of the injection device, the rotation of the screw, the accumulation of melt and the movement to the rear continue until a certain injection volume is established. In the next device working cycle, the screw tip stop inversely shut down to prevent material from returning along the screw. The role of the screw tip and feed screw, such as injection plunger, the pressure plastic mold.
Advantages of reciprocating screws include reduced plastic retention time, self-cleaning screws and screw tips. These benefits are key when machining thermosensitive materials and when using screw-type materials or resin varieties to change both the screw and the barrel.
Currently widely used clamping device design includes: toggle lever clamping device, hydraulic clamping device and a hydraulic mechanical clamping device. Knuckle-tie clamping devices are suitable for small tonnage equipment given the low cost of their design. Features include high mechanical efficiency of the lockout operation, built-in clamping slowing device, slow mold damage, and fast mold clamping.
Clamping cylinder to push the horizontal roof forward, so that the elbow extension and the pressure plate forward movement. When the mold closing device is closed, the mechanical benefits are reduced, which prompts the pressure plate to move rapidly. When the platen reaches the position where the mold is closed, the elbow is switched from high speed to low speed and low speed to high mechanical advantage. Low speed is the key to mold protection, and high mechanical benefits are required to create large tonnages. Once the ribs are fully extended, the hydraulic pressure is no longer necessary to keep the tonnage. In order to open the mold clamping device, the hydraulic pressure is applied to the opposite side of the mold clamping plunger, in order to prevent the molded product from being damaged, the mold should be slowly opened. The mold clamping device is adjusted to accommodate different mold heights by the movement of the entire toggle means and the movement of the platen means along the pull bar (to the extent that the toggle means are fully extended to open the front mold closure). The advantages of the toggle-lever clamping unit include: Fast clamping operation reduces energy consumption and lower equipment costs. The disadvantage is that compared with the hydraulic mold clamping complex, connecting pins and bushings to be frequently repaired. However, the development of the toggle lever design has reduced the maintenance of the toggle lever clamping device. These developments include oil-free bushings, which have greatly reduced the mandatory lubrication.
One of the advances is that all motors use the precision ball screw machine technology currently available combined with advanced AC servo motors to replace hydraulic power units. These motors provide only the power needed to perform the machine's functions, which greatly reduce the overall energy consumption of producing each product.
Hydraulic clamping device is widely used in 150-1000t equipment, and most are used in 250-700t equipment. With the booster tube (or external cylinder) quickly clamping, the effect of a large amount of oil on the small area is very fast. The fluid is scheduled to enter the rear of the main piston by gravity from the high reservoir. The mold should be protected from low pressure and low pressure before the two mold halves come into contact. This condition prevents foreign objects, flashbacks or damage to products that have not been removed in the previous cycle. When the mold is closed, the priming fluid closes the outlet to the pre-reservoir. The main piston rear ton-class clamping force. After this injection cycle, the priming fluid is turned on, prompting the mold closing device to gradually open the mold flap. Within a short distance, the clamping unit accelerates to a fast opening speed.
The hydraulic clamping unit provides flexibility in the installation and operation of the equipment. As the mold clamping stroke in any part of the ton-level clamping force can be generated, so long as the control of the device to adjust the position corresponding to the contact between the two mold halves can be connected to the mold. The hydromechanical clamping unit combines the functions of both mechanical and hydraulic to move the clamping unit and create a ton of clamping force. Hydraulic machinery design due to the flow of liquid between the limit, to make a clamping device, are from about 1000t to greater. The speed of the mold clamping device is governed by the fluid flow rate controlled by the priming fluid. Hydraulic machinery design includes the following units: the movable platen to move the mold halves, almost in contact with each other at the hydraulic cylinder;
(2) a mechanical lock plate that prevents the rearward movement of large tonnage clamping forces; and (3) a short stroke hydraulic cylinder that moves the last section of the mold to a closed position and generates a mold clamping force.
Machine control part of the coordination of all machine functions. Has progressed to the use of multi-computer control system. In order to match the new control device, the hydraulic part of the machine has also been improved. With servo-controlled proportional valves and the corresponding amplification device to increase the flexibility and accuracy, while shortening the machine function response time. Microcomputer control system and servo proportional hydraulic device to provide dynamic response to complete a true closed-loop system. The closed-loop system adjusts the machine to compensate for changes in oil temperature, material viscosity and machine variables. High level of control also appears on the auxiliary equipment. (Dryers, coolers and mold temperature control devices) and make all the machinery and equipment set and monitored by the CRT and LCD. The various machines attached to the host computer provide the entire shop floor monitoring and production scheduling, and the SPC provides real-time monitoring at the machine or host computer.
Important factors in plastic processing include: temperature, consistency, pigment distribution and melt density. Both the conduction heat generated by the barrel temperature and the mechanical heat generated by the rotation of the screw contribute to the processing of a good quality melt. The most common situation is that most of the energy used to melt the plastic, obtained by screw rotation.
As the screw rotates and kneading takes place between the threads, the surface of the plastic pellets is melted and plasticized. As the material advances along the screw, mixing and shearing are repeated until the plastic is completely melted. 【Suzhou Mold Casting】