Short shots, also called underfills, refer to partial incompleteness at the end of the stream or partial filling of a cavity in a multi-cavity, especially in the thin-walled region or the end region of the flow path. The performance is that the melt condenses without filling the cavity, and the melt does not fill completely after entering the cavity, resulting in product shortage. The main reason for the short injection is that the flow resistance is too large, causing the melt to continue to flow. Factors affecting melt flow length include: part wall thickness, mold temperature, injection pressure, melt temperature, and material composition. If these factors are not handled well, it will result in a short bet.
1. Improper equipment selection
When using the equipment, the maximum injection volume of the injection molding machine must be greater than the total weight of the plastic parts and the nozzle, and the total weight of the injection should not exceed 85% of the plasticizing amount of the injection molding machine.
2. Insufficient supply
At present, the commonly used method for controlling feeding is a fixed volume feeding method, in which the amount of the roll material is uniform with the fruit particles of the raw material, and there is no "bridge" phenomenon at the bottom of the feeding port. If the temperature at the feeding port is too high, it will also cause poor material feeding. In this regard, the feed port should be dredged and cooled.
3. Poor fluidity
When the fluidity of raw materials is poor, the structural parameters of the mold are the main reasons for the lack of injection. Therefore, the stagnation defects of the mold casting system should be improved, such as the proper placement of the runner, the expansion of the gate, the size of the runner and the injection port, and the use of larger nozzles. At the same time, an appropriate amount of additives can be added to the raw material formulation to improve the flow properties of the resin. In addition, it should also check whether the recycled materials in the raw materials are excessive, and appropriately reduce the amount.
4. Lubricant excess
If the amount of lubricant in the raw material formulation is too large, and the gap between the anti-reverse ring of the injection screw and the barrel is large, the backflow of the melt in the cylinder may cause insufficient supply, resulting in a low injection. In this regard, the amount of lubricant should be reduced and the gap between the barrel and the shot screw and the check ring should be adjusted to repair the equipment.
5. Cold material impurities block the material channel
When the impurities in the melt block the nozzle or block the cold material
When the gate and runner are in the way, the nozzle should be folded down to clean or enlarge the cold hole and runner section of the mold.
6. Pouring system design is not reasonable
When a multi-cavity is used, the appearance of the plastic parts is often unreasonable due to the unreasonable design of the gate and sprue balance. When designing the pouring system, pay attention to the balance of the gate. The weight of the plastic parts in each cavity should be proportional to the size of the gate, so that the cavity can be filled at the same time. The gate position should be selected at the thick wall, and the runner can also be used. Balanced layout design. If the gate or runner is small, thin, and long, the pressure of the melt is too large along the path during the flow, and the flow is blocked, which is prone to poor filling. In this regard, the flow passage section and the gate area should be enlarged, and if necessary, a multi-point feeding method can be employed.
7. Die exhaustion
When a large amount of gas remaining in the mold due to poor exhaust gas is squeezed by the flow material to generate a high pressure greater than the injection pressure, the melt is prevented from filling the cavity and causing a low injection. In this regard, it should be checked whether the cold material hole is set or its position is correct. For the mold with deep cavity, the exhaust groove or vent hole should be added in the unfilled part;
On the clamping surface, a venting groove with a depth of 0.02 to 0.04 mm and a width of 5 to 10 mm can be opened, and the venting hole should be placed at the final filling of the cavity. When using materials with excessive moisture and volatile content, a large amount of gas is also generated, resulting in poor mold discharge. At this time, the raw materials should be dried and the volatiles removed.
In addition, in the process operation of the mold system, it is possible to improve the exhaust failure by increasing the mold temperature, reducing the injection speed, reducing the flow assist of the pouring system, reducing the mold clamping force, and increasing the mold gap.
8. The mold temperature is too low
After the melt enters the low temperature cavity, it will not be able to fill all corners of the cavity due to the cooling too fast. Therefore, the mold must be preheated to the temperature required by the process before starting the machine. When starting up, the throughput of the cooling water in the mold should be properly controlled. If the mold temperature does not rise, check if the design of the mold cooling system is reasonable.
9. The melt temperature is too low
Generally, in the range suitable for molding, the temperature of the material and the length of the filling are close to a proportional relationship, and the flowability of the low-temperature melting material is lowered, so that the filling length is shortened. When the material temperature is lower than the temperature required by the process, check that the barrel feeder is intact and try to increase the barrel temperature.
At the beginning of the machine, the temperature of the barrel is always lower than the temperature indicated by the barrel heater meter. It should be noted that after the barrel is heated to the temperature of the meter, it needs to be warmed for a while to start. If it is necessary to take a low-temperature injection in order to prevent the melt from decomposing, the injection cycle time can be appropriately extended to overcome the deficiencies. For a screw type injection molding machine, the temperature of the front section of the barrel can be appropriately increased.
10. The nozzle temperature is too low
During the injection process, the nozzle is in contact with the mold. Since the mold temperature is generally lower than the nozzle temperature and the temperature difference is large, the frequent contact between the two causes the nozzle temperature to drop, causing the melt to freeze at the nozzle.
If there is no cold pocket in the mold structure, the cold material solidifies immediately after entering the cavity, so that the hot melt behind the plug cannot fill the cavity. Therefore, the nozzle should be separated from the mold when the mold is opened, and the influence of the mold temperature on the nozzle temperature is reduced, so that the temperature at the nozzle is kept within the range required by the process.
If the nozzle temperature is low and does not rise, check the nozzle heater for damage and try to increase the nozzle temperature. Otherwise, the pressure loss of the material will cause too much.
11. Injection pressure or insufficient pressure
The injection pressure and the filling length are close to a proportional relationship, the injection pressure is too small, the filling length is short, and the cavity filling is not full. In this regard, the injection pressure can be increased by slowing down the speed of injection and appropriately extending the injection time. In the case where the injection pressure cannot be further increased, it can be remedied by increasing the temperature of the material, lowering the viscosity of the melt, and improving the melt flow property. It is worth noting that if the material temperature is too high, the melt will thermally decompose, which will affect the performance of the plastic parts.
In addition, if the holding time is too short, it will also lead to insufficient filling. Therefore, the dwell time should be controlled within a suitable range, but it should be noted that too long dwell time will cause other failures, and the molding should be adjusted according to the specific conditions of the plastic parts.
12. Injection speed is too slow
The injection speed is directly related to the filling speed. If the injection speed is too slow, the melt filling is slow, and the low-speed flowing melt is easily cooled, causing the flow property to further decrease to cause a low note.
In this regard, the injection speed should be appropriately increased. However, it should be noted that if the injection speed is too fast, it is easy to cause other molding failures.
13. The structural design of the plastic parts is unreasonable
When the thickness of the plastic part is not proportional to the length, the shape is very complicated and the molding area is large, the melt is easily blocked at the entrance of the thin portion of the injection molded part, making the cavity difficult to fill. Therefore, when designing the shape structure of the plastic part, it should be noted that the thickness of the plastic part is related to the limit flow length of the melt filling.
In injection molding, the thickness of the plastic part is 1~3mm, and the large plastic part is 3~6mm. The recommended minimum thickness is 0.5mm, cellulose acetate and cellulose acetate butyrate 0.7mm. Ethylcellulose plastic 0.9mm, polymethyl methacrylate 0.7mm, polyamide 0.7mm, polystyrene 0.75mm, polyvinyl chloride 2.3mm. In general, the thickness of the plastic part exceeding 8 mm or less than 0.5 mm is unfavorable for injection molding, and such a thickness should be avoided in design.
In addition, in the process of molding complex structural plastic parts, the necessary measures must be taken in the process, such as reasonable determination of the position of the gate, appropriate adjustment of the flow path layout, increase of injection speed or rapid injection. Increase the mold temperature or use a resin with good flow properties.
Solution
(1) Improper control of process conditions. Should be adjusted appropriately.
(2) The injection capacity of the injection molding machine is less than the weight of the plastic part. Should be replaced with a larger size injection molding machine.
(3) The runner and gate sections are too small. Should be appropriately increased.
(4) The flow distance of the melt in the cavity is too long or has a thin wall portion. A cold pocket should be provided.
(5) The mold is poorly exhausted, and residual air in the cavity causes a low injection. The exhaust system of the mold should be improved.
(6) The flow properties of the raw materials are too poor. Resin with better flow properties should be used.
(7) If the temperature of the cylinder is too low, the injection pressure is insufficient or the injection time of the feed is too short, it will cause a low injection, and the control quantity of the relevant process parameters should be increased accordingly.
This is a pair of carbon brushes complete with the holder suitable for Ceset motors.
Washing machines have electric motors and some motors have carbon brushes, the purpose of these brushes are to conduct electricity from the fixed parts of the motor through the moving parts of the motor.
These motors are fitted across a large range of different manufacturer's washing machines including Bosch, Indesit, Whirlpool and Zanussi.
Compare your existing carbon brushes to the picture, paying special attention to the position of the screw holes and positioning lugs on the side of the holder. The carbon brush itself is held captive in the holder by a small plastic hook which would be removed during fitting allowing it to extend out to the motor armature.
Please check model fit list to ensure this part is correct for your model.
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