Haochen 20 years of focus on multimode cavities and small spacing hot runner

1. Material discoloration, coking, or degradation

Main reasons:

Improper temperature control; The small size of the runner or gate causes significant shear heat generation; The dead center in the flow channel leads to prolonged heating of the trapped material.

Solution:

Accurate temperature control. In order to accurately and quickly measure temperature fluctuations, it is necessary to ensure that the thermocouple temperature measuring head reliably contacts the flow channel plate or nozzle wall, and

It is advisable to locate it at the center of each independent temperature control area, and the distance between the head temperature sensing point and the flow channel wall should not be greater than 10mm. The heating element should be as close as possible to
Both sides of the flow channel are evenly distributed. Temperature control can use intelligent fuzzy logic technology operated by the central processing unit, which has temperature exceeding alarm and automatic adjustment

Function, capable of controlling melt temperature changes within the required accuracy range.

Correct the gate size. Try to avoid dead spots in the flow channel and increase the gate diameter appropriately within the allowable range to prevent excessive shear heat generation. Endothermic type
The melt of the nozzle has a large radial temperature difference in the flow channel, which makes it more prone to coking and degradation. Therefore, it is important to note that the radial size design of the flow channel should not be too large.

2. The residue at the gate is protruding or salivating, and the material and surface appearance are poor

Main reasons:

The selection of gate structure is unreasonable, temperature control is improper, and there is significant residual pressure in the melt in the injection channel after injection.

Solution:

Improvement of gate structure. Usually, if the length of the gate is too long, it will leave a longer gate handle on the surface of the plastic part, and if the gate diameter is too large, it can easily lead to
The occurrence of salivation and material dripping. When the above faults occur, it is important to consider changing the gate structure. The common gate forms of hot runner include straight gate
Point gate and valve gate.

Reasonable control of temperature. If the cooling water in the gate area is insufficient, it will cause heat concentration, causing salivation, material dripping, and wire drawing, resulting in
When describing the phenomenon, the cooling of the area should be strengthened.

Resin pressure relief. Excessive residual pressure in the flow channel is one of the main reasons for salivation. In general, the injection machine should adopt a buffer circuit or
Buffer device to prevent salivation.

3. Insufficient injection volume or no material injection

Main reasons:

Obstacles or dead corners appear in the flow channel; Gate blockage; A thicker condensation layer appears in the flow channel.

Solution:

When designing and processing the flow channel, it is necessary to ensure the arc transition of the melt flow towards the wall at the turning point, so that the entire flow channel is smooth without any dead corners.

Under the condition of not affecting the quality of the plastic parts, increase the material temperature appropriately to avoid premature solidification of the gate.

Increase the temperature of the hot runner appropriately to reduce the thickness of the condensation layer of the internally heated nozzle, reduce pressure loss, and facilitate filling the cavity.

4. Serious material leakage

Main reasons:

Damaged sealing elements; The heating element is burnt out, causing uneven expansion of the flow channel plate; Misalignment of the nozzle and sprue sleeve center, or melt isolation determined by the sealing ring
The projection area of the edge layer on the nozzle is too large, causing the nozzle to retreat.

Solution:

Check the sealing and heating components for damage. If there is any damage, carefully check whether it is a component quality issue, structural issue, or normal before replacement
The result of service life.

Choose an appropriate leak stopping method. According to the insulation method of the nozzle, two structures can be used to prevent leakage: a sealing ring or nozzle contact. Attention should be paid to stopping
Maintain reliable contact with the leaking contact area.

Within the allowable range of strength, it is necessary to ensure that the projected area of the melt between the nozzle and the sprue sleeve is as small as possible to prevent excessive back pressure during injection
The nozzle retracts. When using a leak proof method, the direct contact area between the nozzle and the gate sleeve should ensure that the center of the two is misaligned due to thermal expansion,
There will also be no resin leakage. But the contact area should not be too large to avoid increasing heat loss.

5. The hot runner cannot heat up normally or the heating time is too long

Main reasons:

Insufficient spacing between wire channels, resulting in wire breakage; Short circuits, electrical leakage, and other phenomena occur when the wires intersect during mold assembly.

Solution:

Choose the correct processing and installation process to ensure that all wires can be placed, and use high-temperature insulation materials according to regulations, and regularly detect wire damage.

Choose an appropriate leak stopping method. According to the insulation method of the nozzle, two structures can be used to prevent leakage: a sealing ring or nozzle contact. Attention should be paid to stopping
Maintain reliable contact with the leaking contact area.