1. The nozzle melt usually flows from the nozzle to the nozzle, but in some molds, the nozzle is part of the mold as it extends to the bottom of the mold. There are two other types of nozzles at the other end: the open firing nozzle and the closed firing mouth.
In injection molding, open nozzles should be used more often because they are both cheaper and less likely to remain, and even if the injection molding machine is equipped with a pressure relief device, even low viscosity melters can be used. Sometimes you must use a closed nozzle, this nozzle as a stop valve role in the injection cylinder plastic shade to ensure that the nozzle properly access the nozzle sleeve, the top hole than the nozzle sleeve , Which makes it easier for the nozzle to be withdrawn from the mold.The hole in the nozzle sleeve is 1mm larger than the nozzle, ie the nozzle radius is 0.5mm thinner than the nozzle sleeve.
2. Impurities in filters and modular nozzles plastics can be removed with an extended nozzle filter that melts and plastic flows through a channel that is partitioned by the insert into a narrow space that can remove impurities and improve Plastic mix.
So they can be extended to use fixed mixers for better mixing.These devices can be installed between the shooting cylinder and the nozzle to separate and re-mix the work of the melt, the majority of the melt through the stainless steel Channel.
3. Exhaust Some plastics need to be vented at the injection jets to allow the gases to escape during injection molding, in most cases they are just air, but it may be water or a single molecule of gas that has been released by the melt, and if these gases are not released When melted and compressed into the mold, it expands and bubbles in the product.
To get rid of the gas before it reaches the nozzle or mold, reduce or reduce the diameter of the screw root to decompress the melt in the shooting pot where the gas can be discharged from holes or holes in the shooting pot. Then the screw root diameter increases, and the degreasing glue to the nozzle nozzle equipped with this facility is called the exhaust injection molding machine injection molding machine above the exhaust catalyst should be very good A good smoke evacuator removes the potentially harmful gas.
4. Increasing backpressure In order to obtain a high quality melt, the plastic should be heated or melted in unison and thoroughly mixed, properly melted and mixed using the right screw and with enough pressure in the shooting cylinder (or back Pressure) in order to achieve mixing and thermal uniformity.
Increasing the resistance to oil return creates a back pressure in the firing cylinder, but the screw takes longer to reset, so there is more wear and tear in the injection molding machine's drive system, keeping the back pressure as isolated from the air as possible , Also need to melt temperature and the degree of mixing is consistent
5. Stop valves, regardless of the type of screw, are usually equipped with a stopcock at the tip. To prevent the plastic from flowing out of the nozzle, a decompression (cords) or special firing nozzle is also fitted.
The use of stop-flow supply and marketing must be checked regularly as it is an important part of the firing cylinder. At present, switch-type nozzles are not commonly used because the firing nozzle equipment is prone to plastic leaks and decomposition. There are specified types of firing nozzles.
6. Screw Back (Nibbler) Many injection molding machines are equipped with a screw retract or retract device that is hydraulically withdrawn to draw plastic back into the tip of the nozzle. This device allows the use of an open nozzle. The number of feet may be reduced because entering the air can cause problems for some plastics.
7. Most screw injection molding cycle should be adjusted during the turn screw village, so that when the screw injection is completed, the majority will be a small amount of padded plastic, this will ensure that the screw to achieve effective propulsion time and maintain a fixed shooting pressure.
Small injection molding machine pad is about 3mm; Large injection molding machine is 9mm. No matter how much the use of screw padding value, we must maintain the same. Now the size of the screw padding can be controlled within 0.11mm.
8. Screw Rotation Speed The speed of rotation of a screw significantly affects the known level of stability of the injection molding process and the amount of heat acting on the plastic. The faster the screw rotates, the higher the temperature. As the screw rotates at high speeds, the friction imparted to the plastic Cut) The energy increases the plasticization efficiency, but also increases the non-uniformity of the melt temperature.
Due to the importance of the screw surface speed, the screw speed of a large injection molding machine should be lower for a smaller injection molding machine because of the shearing heat generated by the larger screw than the small screw at the same rotational speed, Different, screw rotation speed is also different.
9. Injection Molding Machine The injection molding machine is usually evaluated in terms of the amount of PS that can be injected per injection, possibly in ounces or grams. The other ranking system is based on the volume of melt that can be injected by the injection molding machine.
10. Plasticizing Capacity The evaluation of the injection molding machine is usually based on the amount of PS material that can be uniformly melted within 1 hour, or the amount of PS heated to a uniform melt temperature (in pounds Kg), this is called the plasticizing ability.
11. Estimation of plasticization ability To determine whether the quality of cement can be maintained throughout the production process, a simple formula for yield and plasticization can be used as follows: t = (total shot gX3600) ÷ (amount of plasticizer kg / hX1000)
t is the minimum cycle time, such as the mold cycle time is lower than the t value, the plastic injection molding machine can not be fully plasticized in order to achieve uniform melt viscosity, so the injection molded parts often appear deviations .More attention to injection thin wall Or precision tolerance of the quality of the system, the shot amount and plasticizing amount must cooperate with each other.
12. Pellet retention time The decomposition of plastic is dependent on the temperature and the time. For example, plastics decompose after a period of time at high temperatures; however, they take longer to decompose when exposed to colder temperatures.
Therefore, the retention time of plastic in the shooting cylinder is very important.The actual residence time can be determined experimentally by measuring the time required for the colored plastic to pass through the shooting cylinder and can be roughly calculated by the following formula: t = Cylinder rated gX cycle time S) ÷ (shot gX300), please note that some of the plastic in the shooting cylinder residence time longer than the calculation of the time, because they can be assembled in the shooting cylinder.
13. The Importance of Calculating Dwell Time As a general rule, the dwell time of a plastic on a particular injection molding machine should be calculated, especially when a large injection molding machine uses less amount of shot, the plastic is easily broken down, not from the point of view of detectable To
If the residence time is short, the plastic will not be able to plasticize evenly, and the retention time will be long if the properties of the plastic deteriorate. Therefore, the residence time must be consistent. Method: Ensure the plastic input to the injection molding machine has stable composition, uniform size and shape. If any parts of the injection molding machine malfunction or wear and tear, must report to the maintenance department.
14. Injection Cylinder Temperature Environment It should be noted that the melt temperature is important and any jet cylinder temperature used is guidance only. If you do not have any experience with a specific plastic, start with the lowest setting.
Normally, the temperature in the first zone is set to a minimum to prevent the plastic from prematurely melting and blocking in the feed in. The temperature in the other zones then gradually increases until the nozzle is reached, and at the tip of the nozzle tends to be slightly warmer to prevent dripping The mold is also heated and cooled, and because of the size of many molds, the molds are also differentiated, but unless specified, the zones should be sized to the same size.
15. Melt temperature can be measured either on the nozzle or in air jets. With this latter measurement, care must be taken to ensure that no accident occurs when cleaning the hot-melt plastic because the hot plastic can burn or even cause skin corrosion.
In an injection molding plant, there is an accidental burn, so gloves and masks should be worn to deal with the danger of hot plastic or molten plastic in. To ensure safety, the tip of the hot needle should be preheated to the point where it is to be measured The temperature of each plastic has a specific melt temperature, to achieve this temperature injection actual injection cylinder value also depends on the screw speed, back pressure, injection volume and injection molding cycle may be.
16. Mold Temperature It is important to constantly check if the injection molding machine is set and operated at the temperature specified on the log. This is important because the temperature will affect the surface finish and yield of the injection molded parts. All measured values must be recorded and, Check the injection molding machine at the specified time.
17. Uniform cooling The injection molded parts that are injection molded must be cooled evenly, meaning that different parts of the mold must be cooled at different rates so that the entire product cools down evenly. The injection molded parts must be cooled as quickly as possible, Will have defects, such as the surface is not smooth, physical properties change and so on.
The parts of the injection molded parts must be cooled at the same rate, but in a non-uniform manner to cool the mold, for example by feeding cold water into the inner core of the mold and warmer water on the outside of the mold to cool the syringe. This technique should be used even for large products that have a longer melt flow in the water or in the spout.
18. Temperature and cooling checks It is important to check frequently that the injection molding machine is set and operated at the temperature specified on the log. This is important because the temperature affects the surface finish and yield of the injection molded parts. All measured values must be recorded , And according to the specified time to check the injection molding machine.