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Runner Analysis

Hot runner molding Fault Analysis and Countermeasures

2.1 residues highlight the gate drops or salivation poor materials and surface appearance

2. 1.1 Select the main gate structure is unreasonable, improper temperature control, the presence of a melt flow channel within a larger residual pressure after the injection.

2. 1.2 Solutions

Improvement (1) gate structure. Typically, the gate length is too long, the gates will stay longer in the plastic surface of the material, while the gate diameter is too large, easily lead to drooling drool phenomenon. When the failure occurs, you can consider changing the focus of the gate structure. Common forms gate hot runner sprue, point gate and valve gate.

Sprue gate, which is characterized by coarse channel diameter, it is not easy to condense the gate, to ensure a smooth melt deep cavity injection products; not fast condensation, the minimum residual stress of plastic parts, suitable for forming a multi-cavity mold deep cavity products, but the gate easier to produce salivation and drawing phenomenon, and a large gate scars, even leaving the cylindrical material, so the gate material temperature is not too high, and need stability control; the basic characteristics same, but the scars on plastic parts is relatively small; characterized by plastic residual stress is small, moderate condensation rate, salivation, drawing phenomenon is not obvious; can be applied to most plastics, is currently the runner at home and abroad molded using more gates in the form of a class of high quality plastic parts, leaving only tiny traces of surface; with small scars, low residual stress, and does not produce salivation, drawing phenomenon, but the wear and tear than the valve port Obviously, with the gap in use along with the increase salivation phenomenon will appear, and you should promptly replaced the valve, the valve nozzle. Selection and is closely related to the performance of the molded resin gate form. Low viscosity resin prone salivation, choose valve gate. Crystalline resin forming a narrow temperature range, the temperature at the gate should be appropriately high, such as POM, PPEX and other resins can be used with a gate in the form of heated probe. Amorphous resins such as ABS, PS, etc. forming a wide temperature range, due to the formation of a melt torpedo head nozzle core insulating layer, the gate does not contact the heating element, it is possible to accelerate coagulation.

(2) the reasonable control of temperature. If the gate area of cooling water is not enough, it will cause heat concentration, causing salivation, drool and drawing and, therefore, the above phenomenon should strengthen the cooling area.

(3) the resin pressure release. Residual pressure within the flow channel is one of the main causes excessive salivation. Under normal circumstances, the buffer circuit injection machine should be taken to prevent drooling or cushioning device.

2.2 Material discoloration or degradation of coke feed

2. 2.1 main reasons: improper temperature control; runner or gate size is too small to cause large shear heating; dead spots within the flow channel leading to prolonged heat retention materials.

2. 2.2 Solutions

(1) precise temperature control. In order to be able to quickly and accurately measure the temperature fluctuations, thermocouple head can * make contact manifold or nozzle wall, and it is centrally located in each individual climate zones, the head temperature sensing points and runner wall distance should be no more than 10mm is appropriate, should try to make heating elements on both sides of the road uniform flow. Thermostat can be used intelligent central processor operating under the fuzzy logic technology, which has a temperature limit alarm and automatic adjustment feature that allows the melt temperature control within the accuracy of claims.

(2) amend the gate size. Avoid dead runner, and increase gate diameter within the permitted range, to prevent excessive shear heat even in. Melt in the heat nozzle flow channel radial temperature, and are more likely to focus material degradation phenomenon, so pay attention to the flow channel design radial size is not too large.

Shortage of 2.3 injection amount or no material injection

2. The main reason 3.1

Obstructions or dead appeared in the flow channel; gate blockage; a thick layer of condensation occurs within the flow channel.

2. 3.2 Solutions

(1) flow channel design and processing, should ensure that the melt flow corner arc transition wall, so that the whole passage smooth flow without the presence of the dead.

(2) Without prejudice to the quality of plastic case, an appropriate increase in material temperature, to avoid premature condensation of the gate.

(3) appropriate to increase the temperature of the hot runner, in order to reduce the thickness of the condensate layer of heat-type nozzle, reducing the pressure loss, thereby facilitating the cavity is filled.

Severe leakage of material 2.4

2. The main reason 4.1 Sealing element is damaged; heating element burned uneven expansion caused manifold; nozzle and sprue bushing center dislocation, or stanch the melt ring decisions insulating layer on the nozzle of the projected area is too large, leading to the nozzle back.

2. 4.2 Solutions

(1) Check the sealing element, heating element for damage, if damaged, carefully check before replacing the component quality problems are the result of structural problems, or normal life caused.

(2) Select the appropriate stanch way. According adiabatic way nozzle to prevent leakage of material o-ring or nozzle can be contacted two structures. It should be noted so that the contact area remains available * o contact state.

Within the allowable range strength, to ensure that the projected area of the melt between the nozzle and the sprue bushing as small as possible, in order to prevent generated when the excessive back pressure injection nozzle backward. When using stanch the way, the contact area between the nozzle and the direct sprue bushing to ensure that both the center due to the thermal expansion caused by the dislocation, it will not happen resin leakage. However, contact area can not be too large, so as to avoid heat loss increases.

2.5 runner can not be normal or elevated temperature for too long

2. The main reason 5.1

Wire channel spacing is insufficient, resulting in broken wires; shorted wires intersect, leakage and other phenomena mold assembly.

2. 5.2 Solutions to choose the correct processing and installation process to ensure that all the wires can be placed, according to the requirement to use high-temperature insulation materials, regular testing wire breakage.

2.6 refueling or change color bad

2. 6.1 The main reason: the color change refueling or improper way; runner design or process caused by an irrational stranded inside there are more material.

2. 6.2 Solutions

(1) structural design and processing methods to improve the flow channel. Design flow channel, should try to avoid dead spots runner, each corner of the arc transition should seek. Within the allowable range, the flow channel dimensions as small as possible, staying less material flow path within this new material flow rate greater conducive to rapid clean. The processing flow channel, regardless of how long runner, from one end of the process must be carried out, if the process from both ends at the same time, could easily lead to the center of the hole do not overlap, so the material is bound to form part of the residence. Usually the heating means due to the outer heated nozzle does not affect the melt flow, can be more easily cleaned flow path, and the inner layer is easy to form a heated nozzle is condensed in the flow channel wall, which is not conducive to rapid refueling.

(2) Select the correct method for refueling. Hot runner systems refueling, changing color process generally consists of the direct introduction of all new material streams stranded tract, then the flow channel wall material stuck to move forward as a whole, and therefore relatively easy to clean. Conversely, if the new low viscosity material, it is easy to enter the detention center material, layer by layer separation stranded material, cleaning up on more trouble. If the viscosity when both old and new material is similar, the new material can be injected by accelerating speed to achieve rapid refueling. If stranded material viscosity is sensitive to temperature, may be appropriate to raise the temperature to reduce the viscosity of the material, in order to speed up the refueling process.

Note 3 to select and apply the hot runner

For as to exclude or reduce the use of the fault, when the selection and application of hot runner systems note the following.

Select 3.1 in heating mode

(1) heating. Heat nozzle structure is more complex, higher cost, difficulty replacement parts for electric components higher. The heater is placed in the middle of the flow channel, will produce an annular flow, increasing the capacity of the body friction area, pressure drop may be externally heated nozzle 3 times. However, since the heating element is a heated torpedo provided in the nozzle body, heat is supplied to all the material, so that heat loss is small, can save energy. If using point gate, torpedo body tips to keep in the center of the gate after the injection sprue and conducive to condensation due to the gate late leaving lower residual stress of plastic parts.

(2) heating. By external heat nozzle, you can eliminate cold film to reduce the pressure loss. And because of its simple structure, easy processing, and thermocouples installed in the middle of the nozzle allows accurate temperature control, etc., currently has widespread application in production. But externally heated nozzle greater heat loss, as energy-saving heat nozzle.

3.2 Gate choice of form

Gate design and selection directly affect the quality of the plastic parts. In the application of hot runner systems should be based on the flow properties of the resin molding temperature and product quality requirements in the selection of the appropriate form of the gate to prevent drool, drool, drool, and change color and poor phenomenon.

3.3 Temperature control

When determining the form of the gate, control the melt temperature fluctuations will play a key role in the quality of the plastic parts. Very often the focus of the material occurs, degradation or flow blockage phenomenon is mostly caused by improper temperature control, especially heat-sensitive plastic, often require the reaction temperature can be quickly and accurately fluctuations.

For this reason, it should be reasonable to set the heating element to prevent overheating, ensure that the heating element with the gap with manifold or nozzles to minimize heat loss, and should try to choose the more advanced electronic thermostat to satisfy the thermostat Claim.

Computing content 3.4 after the hot runner system structure determination

Temperature and pressure (1) The balance is calculated for each runner. The purpose of the hot runner system is injected from the injection molding machine nozzle thermal plastic, at the same temperature by the hot runner and to equalize the pressure distribution of the melt to each gate of the mold, so the response to the temperature of each heating zone of the distribution channel and flows into the respective gate melt pressure is calculated.

Nozzle and sprue bushing center offset (2) the calculation of thermal expansion. That should ensure that the thermal (expansion) of the nozzle and the cold (no expansion) centerline gate sets are accurately aligned position.

(3) heat loss calculations. The heated flow channel is surrounded by a cooling jacket and the support of the mold, it should be possible to accurately calculate the amount of heat loss due to thermal radiation and direct contact (conduction) caused, otherwise, the actual path of the flow path because the flow path thickened wall condensed layer becomes smaller.

Install 3.5 runner boards

Should take full account of insulation and injection pressure to bear two issues. Usually set between pads and supports manifold and templates, this area can withstand injection pressure, in order to avoid the flow channel plate deformation of the material leakage phenomenon, on the other hand can also reduce heat loss.

Maintenance 3.6 Hot Runner System

For hot runner mold, hot runner components use regular preventative maintenance is important, this work including electrical testing, the sealing element and wiring inspection and cleaning of dirt and other elements.