Compared with ordinary runner molds, hot runner molds have obvious advantages such as time-saving and material saving, high efficiency, and stable quality. However, at one time, their widespread application was affected by the tendency to produce defects in application. With the improvement of skills in the mold industry, hot runner molding has made significant improvements in controlling the melt temperature of the runner, ensuring structural stability, and designing and manufacturing hot runner components. This has led to the re recognition and favor of hot runner technology.

1、 The residue at the gate is protruding or salivating, and the material and appearance are poor

1. Main reasons

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

2. Handling Measures

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

2) Reasonable temperature control. If the cooling water in the gate area is not sufficient, it will cause heat to gather and form salivation, material dripping, and wire drawing phenomena. Therefore, when the above phenomena occur, the cooling in the area should be strengthened.

3) Resin pressure relief. Excessive residual pressure in the flow channel is one of the main reasons for salivation. In general, injection machines should adopt buffering circuits or buffering devices to prevent salivation.

2、 Material discoloration, charring, or degradation

1. 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 a prolonged heating time of the resident material.

2. Handling Measures

1) Accurate temperature control. In order to accurately and quickly measure temperature fluctuations, it is necessary to ensure that the thermocouple temperature measuring head firmly contacts the flow channel plate or nozzle wall, and is located at the center of each independent temperature control zone. The distance between the head temperature sensing point and the flow channel wall should not be greater than 10mm, and the heating element should be evenly distributed on both sides of the flow channel as much as possible.

(2) Correct the size of the gate. Efforts should be made to prevent dead spots in the flow channel, increase the gate diameter appropriately within the allowable range, and prevent excessive shear heat generation. The melt of the internally heated nozzle has a large temperature difference in the radial direction of the flow channel, which is 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.

3、 Short injection quantity or no material injection

1. Main reasons

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

2. Handling Measures

1) During the design and processing of the flow channel, it is necessary to ensure that the melt flows to the curved wall surface for arc transition, so that the entire flow channel is smooth without any active dead corners.

2) Properly increase the material temperature without affecting the quality of the plastic parts, to prevent premature solidification of the gate.

3) Properly adding hot runner temperature to reduce the thickness of the condensation layer of the internally heated nozzle, reduce pressure loss, and then facilitate the filling of the cavity.

4、 Serious material leakage

1. Main reasons

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

2. Handling Measures

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

2) Choose appropriate leak stopping methods. 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 maintaining a secure contact condition at the leak stop contact area.

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

1. Main reasons

The distance between the wire channels is not sufficient, resulting in wire breakage; When installing the mold, the wires intersect and cause short circuits, leakage, and other phenomena.

2. Handling Measures

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

6、 Poor material or color change

1. Main reasons

Improper method of changing materials or colors; The unreasonable design or processing of the flow channel results in a large amount of residual material inside.

2. Handling Measures

1) Improve the structural design and processing methods of the flow channel. When designing the flow channel, efforts should be made to prevent dead spots in the channel, and circular arc transitions should be made at each corner as much as possible. Within the allowed range, the size of the flow channel should be as small as possible, so that there is less residual material in the channel and the flow rate of new material is high, which is conducive to rapid cleaning and cleanliness. When processing the flow channel, regardless of its length, it is necessary to process from one end. If the two ends are processed together, it is easy to form a non overlapping center of the hole, which inevitably leads to the formation of a stuck material area. Generally, the external heating nozzle can easily clean the flow channel because the heating device does not affect the melt activity, while the internal heating nozzle is prone to forming a condensation layer on the outer wall of the flow channel, which is not conducive to rapid material replacement.

2) Choose the correct refueling method. The process of material replacement and color change in the hot runner system generally involves pushing all the remaining materials directly out of the runner, and then moving the remaining materials on the runner wall forward, making cleaning easier. On the contrary, if the viscosity of the new material is low, it is easy to enter the center of the retained material and separate the retained material layer by layer, making cleaning more difficult. If the viscosity of the new and old materials is similar, rapid material replacement can be achieved by accelerating the injection speed of the new material. If the viscosity of the retained material is sensitive to temperature, it can be appropriately increased to reduce the viscosity and accelerate the refueling process.