Injection Molding Of Thermoplastics

Once molten plastic enters the mold, it is molded into a certain shape by the cold mold cavity.

The resulting shape is often the final product and no longer needs any other processing before installation or final use.

Many details, such as raised parts.

Ribs and threads can be molded in one step of injection molding.

The function of the clamping device is as follows: (1) the mold is closed under the pressure of injection; (2) the product is removed.

At present, there are two kinds of injection devices: screw type pre plasticizing device or two-stage device, and reciprocating screw.

The screw type pre plasticizing device uses the pre plasticized screw (first stage) to deliver molten plastic to the injection rod (level second).

These strengths are needed for pparent, thin-walled products and high production rates.

Its shortcomings include uneven residence time (resulting in material degradation), higher equipment costs and maintenance costs.

The powder or granular plastics in the hopper are melted and sent to the front end of the screw through the rotating screw. The plastic fluid flows through the front end of the screw and accumulates in front of the screw.

The accumulation of molten plastic in front of the screw drives the screw to the rear part of the injection device. The rotation of the screw, the accumulation of the molten material and the movement of the rear part continue until a certain amount of injection is formed.

In the next equipment working cycle, the end of screw ends are closed to prevent material from returning along the screw.

The role of screw tip and feed screw is as follows: injection plunger, plastic pressure.

These advantages are crucial when processing thermosensitive materials and when screw and barrel are used when the color material or resin varieties are changed.

The toggle clamping device is suitable for small tonnage equipment because its design is low in manufacture cost.

Its features include high mechanical benefits of lockout operations, slow clamping devices, slow mold damage and quick closing operation.

When the closing device is closed, the mechanical benefits are reduced, prompting the pressing plate to move rapidly.

When the pressure plate reaches the position where the die is closed, the elbow will be changed from high speed and low mechanical benefits to low speed and high mechanical benefits.

Low speed is the key to mold protection, and high mechanical benefits are needed to form large tonnages. Once ribs are fully stretched, hydraulic pressure is no longer necessary to maintain tonnage.

In order to open the clamping device, the hydraulic pressure is applied to the opposite side of the clamping plunger. In order to prevent the damaged products from being damaged, the mold must be slowly opened.

The clamping device is adjusted to fit the different die height through the movement of the whole elbow device and the movement of the pressing device along the pull bar (moving to the closing part of the die before fully extending the elbow device).

The advantages of the toggle clamping device include: quick clamping operation, lower energy consumption and lower equipment cost.

The disadvantage is that it is more complicated than the hydraulic clamping die, and the connecting pin and bushing should be repaired regularly.

However, the development of elbow bar design has reduced the maintenance of the toggle clamping device. These developments include oil-free bushing, which greatly reduces the need for compulsory lubrication.

These motors only provide the power needed to complete the functions of the machine. They greatly reduce the total energy consumption of each product.

With the aid of a pressurized tube (or external oil cylinder), the mold is rapidly closed, and the effect of large oil on small areas is very fast.

The fluid is asked to enter the rear part of the main piston with gravity from the high reservoir.

The mold should be in a low speed and low pressure protection state before the contact of the 2.5 die, which prevents damage caused by foreign objects, spills or products not taken out in the previous cycle.

When the die is closed, the priming fluid is closed to the outlet of the pre reservoir.

The rear part of the main piston produces tonnage clamping force.

After this injection cycle, the priming solution is opened, which urges the clamping device to open the mold flap gradually.

Within a short distance, the clamping device accelerates to the fast opening speed.

Since the mold clamping force can be generated at any part of the mold closing stroke, the mold can be connected to the contact points of the two valves by means of the control of the equipment.

The hydraulic mechanical clamping device combines the functions of both mechanical and hydraulic to move the clamping device and cause the mold clamping force at the tonnage level.

Hydraulic mechanical design is used as a clamping device because of the limited flow rate between the liquid filling units, which is from 1000 t to larger.

The speed of the clamping device is governed by the fluid flow controlled by pre charge.

The hydraulic mechanical design includes the following units: moving the movable pressure plate to two half mold valves, near the contacting hydraulic cylinders; (2) preventing mechanical locking plates from moving backward when large tonnage clamping forces are formed; (3) short stroke hydraulic cylinders for the last distance from the moving molds to the closed state and generating clamping force.

The multi microcomputer control system has been developed.

In order to match the new control device, the hydraulic part of the machine has also been improved.

It has increased flexibility and accuracy with servo controlled proportional valves and corresponding amplifying devices, and reduced the response time of machine functions.

The microcomputer control system and the servo proportional hydraulic device provide dynamic response to complete a real closed loop system.

The closed-loop system adjusts the machine to compensate for changes in oil temperature, material viscosity and machine variables.

High level control also appears on auxiliary equipment.

(dryer, cooling device and mold temperature control device), and make all machine and equipment adjusted and monitored by CRT and LCD.

The various machines connected to the main computer provide the whole workshop monitoring and production scheduling, and SPC provides real-time monitoring at the machine or main computer.

The heat generated by the barrel temperature and the mechanical heat generated by the screw rotation are all helpful to the processing of high quality melts. Two.

The most common situation is that most of the energy used in molten plastics is obtained by rotating the screw.

When the material moves along the screw, it repeats mixing and shearing until the plastic is completely melted.