This is a frequently encountered problem, but it is also relatively easy to solve. When it is really not solved by technological means, it can be improved from the design and manufacture of molds, which can generally be solved.
1 . Equipment:
(1) The capacity of the injection molding machine is small. When the quality from the product exceeds the actual maximum injection quality of the injection molding machine, it is obvious that the amount of material supplied will not make ends meet. If the top quality of the product is close to the actual injection quality of the shot molding equipment, there is a problem of insufficient plasticization. The heating time of the material in the barrel is usually insufficient. As a result, the appropriate melt cannot be provided to the Cnc Machining mold in time. In this case, the problem can only become solved by replacing the injection molding machine with a large capacity. Some plastics such as nylon (especially synthetic 66) have a narrow melting range and a large specific heat. An injection molding machine having a large plasticizing capacity is required to ensure the supply of materials.
(2) The temperature displayed by the thermometer is not true, the bright high is definitely low, and the material temperature is too low. This is because the temperature control device such as thermocouple and its wiring or the temperature difference millivoltmeter fails, or because the heating coil far away from the heat measurement point is aging or burned, heating failure has not been found or has not been repaired and replaced with time.
(3) The diameter in the inner hole of the cnc turning nozzle is too large or perhaps too small. If it is too small , due to the small flow diameter, the specific volume of the strip will increase, which will easily be cooled, block the feed channel or consume the injections pressure; The condition of low force. At the same time, plastic materials such as uhmw machining cannot reduce the viscosity because of the lack of large shear warmth, which makes it difficult to fill the mold.
The nozzle can be not well matched with the inlet of the main runner, as well as the overflow with the mold plus the filling on the mold are often unsatisfactory. The nozzle itself has high flow resistance or is blocked by foreign matter, plastic carbonized deposits, etc .; the spherical surface of the nozzle or the primary runner inlet is damaged or deformed, which affects the good cooperation with the other party; edm Machining faults or deviations cause the nozzle and the main runner axis to have an inclination displacement or the axial pressing surface area to separate; the nozzle ball diameter is certainly larger than the main runner entrance ball diameter, due to the gap at the edge, the nozzle axis gradually increases under the squeeze of this overflow The pushing pressure will cause the plastic gear to be dissatisfied.
(4) The plastic material frit blocks the feeding channel. Because the plastic is normally partially melted and agglomerated in the hopper dryer, or the temperature inside the feed section of the barrel is too high, or the plastic grade is going to be not selected properly, or maybe the plastic contains too much lubricant, the clear plastic will enter the feed port or screw at the reduced diameter position. Premature melting in the deep groove of your screw end, the pellets and the melt are bonded to each other to form a “bridge”, which blocks the channel or envelops the screw, and slides circularly with the mess rotation, and cannot move forward, causing interruption of feeding or irregular fluctuations. This situation can only end up being fundamentally resolved after the passage is cut through as well as the material blocks are eliminated.
(5) The nozzle cold material enters the mold. Injection molding machines usually only install straight-through nozzles due to pressure loss. However , if the temp of the front end of the barrel and the nozzle is too large, or there is too much material at the front end of the barrel or clip under high pressure, “salivation” will occur, which will cause the vinyl to accidentally enter the key runner entry before the injection is started and the plastic mold is open. And it becomes hard underneath the cooling effect of the template, which usually prevents the melt from entering the cavity smoothly. At this time, the temperature belonging to the front end within the barrel plus the nozzle should be lowered, the storage capacity for the barrel must be reduced, and the back pressure ought to be reduced to avoid excessive dissolve density at the front end of the barrel.
(6) The treatment cycle is actually short. Due to the short cycle, the material heat is too late to keep up, which will also cause material shortage, especially when the voltage fluctuates greatly. The period should be adjusted accordingly according to the supply voltage. Generally, the injection and holding pressure time are not considered during the adjustment. The main consideration is to adjust the time from the completion of the holding pressure to the return from the screw, which in turn does not affect the filling and molding conditions, and can extend or shorten the preheating time of the pellets in the barrel.
2 . Mould:
(1) The mildew casting system is defective. The flow channel is too small , too thin or perhaps too long, which will increases fluid resistance. The primary runner should increase the size, and the athlete and branch runner needs to be round. The runner and also the mouth is too large, as well as the injection force is inadequate; the jogger and gate are clogged by impurities, foreign matter or carbide; the runner and door are rough with scars, or have sharp angles, plus the surface roughness is poor, which impacts the material circulation;
The athlete does not have a cold slug well or the chilly slug well is too small , and the opening direction is without question wrong; for multi-cavity molds, the jogger and gate size distribution should be carefully arranged, otherwise there will be only the main runner or the thick and short gate. The situation where the cavity can be filled but other cavities cannot be filled. The diameter in the runner need to be increased appropriately to reduce the pressure drop of the burn flowing towards the end with the runner, and the gate on the cavity farther from the main runner should be enlarged to make the injection pressure and materials flow velocity of each tooth cavity basically the same.
(2) The mold design is unreasonable. The mold is too complex, with many turns, improper selection of the feed inlet, too narrow runner, limited number of gates or improper form; the partial portion of the product is very thin, the thickness of this entire product or part should be increased, or an auxiliary must be set near the insufficient filling Runner or gate;
It is not uncommon intended for inadequate venting measures inside the cavity to cause dissatisfaction with the parts. This defect mostly occurs in the corners of the item, deep recesses, thin-walled parts surrounded by thick-walled parts, and thin-walled parts formed simply by side entrance. The bottom of your bottom shell, etc .
The design to eliminate this defect includes opening effective vents, selecting a reasonable door position to help make the air easy to discharge in advance, and when necessary, deliberately making a certain part of the trapped area of the cavity into an insert to make the air escape from your insert. Gap overflow; to get multi-cavity forms that are prone to unbalanced gateway distribution, the number of injection cavities should be decreased if necessary to ensure that other cavity parts are qualified.
(1) Improper give food to adjustment, lack of material or perhaps excessive material. Inaccurate nourishing metering or abnormal feeding control system operation, abnormal injection routine caused by hypodermic injection molding machine or form or operating conditions, low pre-plastic back pressure, or low particle density in the clip or barrel may cause materials shortage. For large particles, Pellets with many voids and plastics with large crystalline specific volume changes, such as polyethylene, polypropylene, nylon, etc ., as well as materials with higher viscosity, including ABS, ought to be adjusted to a higher volume. If the temperature belonging to the material is undoubtedly high, the volume should be modified.
When there is certainly too much material at the end within the barrel, the screw will certainly consume extra injection pressure to compress and push the excess stock in the gun barrel during injection, which greatly reduces the effective shot pressure for the plastic entering the mould cavity. The product is hard to fill.
(2) The injections pressure is actually low, the injection time is brief, and the plunger or twist returns too early. Molten plastic has larger viscosity and poor fluidity at lower working temperatures, so it needs to be injected at higher pressure and speed. For example , in the production of ABS color parts, the high temperature resistance of the colorant limits the heating heat range of the barrel, which has to become compensated by simply higher treatment pressure and longer hypodermic injection time than usual.
(3) The injection speed is slow. The injection speed is of great significance for some products with complicated shapes, huge thickness changes, and long processes, as well as plastics with high viscosity, such as toughened ABS. When the product can not be filled with ruthless, high-speed shot of ptj machining parts should be considered to overcome the problem of filling discontentment.
(4) The material temperature is too low. The temperature of the front end from the barrel is low, as well as the viscosity in the molten materials entering the cavity rises too early to the point where it is difficult to flow as a result of cooling a result of the shape, which hinders the filling of the far end; the rear part of the barrel or clip is a plastic with low temperature and substantial viscosity Difficult flow slows the forward movement with the tsmachining screw. As a result, it seems that the pressure displayed by the pressure gauge is sufficient, but the melt actually enters the cavity in low pressure and low speed;
If the nozzle temp is low, it may be that the nozzle is in contact with the cold black mold for a long time throughout the fixed feeding and loses heat, or perhaps the nozzle heating system ring is usually insufficiently heated or has poor contact, resulting in cold, frigidity, frigidness, coldness of the material, which may block the feeding channel on the mold; if the mold does not have cool material Well, with self-locking nozzles and post-feeding procedures, the valve can maintain the necessary temps; the nozzle is too frosty when it is just turned on, and sometimes a flame gun can be used for external heating to accelerate the temperature of this nozzle.
Four, raw materials:
Plastic has poor fluidity. Plastic Machining Service often uses recycled components, and recycled materials often reflect a tendency to increase viscosity. The experiment pointed out that the unit volume denseness of molecular chain scission generated by oxidative cracking increased, which increased the viscosity of your flow in the barrel and cavity, plus the regenerated scraps promoted the production of more gaseous substances, which caused the injections pressure to get lost. Increased, causing difficulty in filling the mold.
In order to improve the fluidity of the plastic material, it should be considered to add exterior lubricants just like stearic acid or its salts, preferably silicone oil (viscosity 300~600cm2/s). The addition of lubricants not only improves the fluidity of the clear plastic, but also improves the stability and reduces the air level of resistance of gaseous substances.