1. For plastic injection molding, the melt is injected into the air. If the material flow is uniform, smooth, without bubbles, and the color is uniform, the barrel temperature is considered to be appropriate; if the material flow surface is rough, silver or discolored, it means that the barrel temperature is not suitable.
2. Directly observe the appearance of the product in plastic injection molding. If there is no defect, it is considered that the temperature of the barrel is appropriate. Pay attention to the following issues in barrel temperature control.
① The adjustment of the barrel temperature should ensure that the plastic is well plasticized and can be injected and filled smoothly without causing decomposition. Only under the premise of sufficient plasticization, the plastic entering the cavity can fill the cavity with a smooth flow, and nearly completely reproduce the shape of the cavity to meet the perfect requirements.
If the plasticizing temperature is too low and the plasticizing is not uniform, the surface of the plastic injection molded product will have wavy marks and dull color. If the plasticizing temperature is too high, some plastic will be vaporized due to decomposition, and the surface of the product will be "frosted" in light, and silver streaks and blistering will appear in heavy.
In production, sometimes due to the poor resistance to high temperature of colorants, etc., the plasticizing temperature is intentionally lowered, and the injection pressure or injection speed is forced to fill the mold. The internal stress of the obtained product increases, which is easy to be stored or stored. Deformed, cracked or destroyed in the use environment. Therefore, to take care of the appearance quality of the product, first of all, the mechanical strength and durability of the product must be guaranteed. To do this, the sufficient plasticization of the material is a necessary prerequisite.
② The melting temperature of plastic not only affects the processing performance, but also affects the surface quality and color of plastic injection molding products. The maximum temperature near the end of the barrel is higher than the flow temperature (or melting point), which is the basic guarantee for processing.
However, in order to improve the apparent quality of the product, the melting temperature should be increased before the plastic decomposition temperature is reached, so that the surface gloss of the product increases and the color is more uniform. Generally speaking, it is best to increase the melting temperature by 20-30°C higher than the temperature required to fill the cavity.
③ Because of different injection molding machines, the temperature difference between the material temperature and the barrel temperature is different, so the temperature indicated on the temperature measuring millivoltmeter cannot be regarded as the actual temperature of the melt in the barrel at any time, but only as the actual temperature. Reference or adjustment basis. The temperature indicated by the millivoltmeter of the screw injection molding machine is close to or slightly lower than the actual temperature of 1I ~ 17 ° C; while the plunger injection molding machine is 11 ~ 17 ° C higher, and the difference between the two is 20 ~ 40 ° C.
In addition to the motion state of the material flow in the plastic injection molding barrel, the equipment of the temperature measuring device is also the cause of the difference. From a safety point of view, the thermocouple is preferably inserted above the horizontal barrel, which is the hottest point in the circumferential direction of the barrel, so as to avoid local overheating that may be caused by errors.
④ The relationship between the melt viscosity and temperature of plastics with different properties is different, and different temperature control focuses should be adopted.
⑤ The process of process debugging generally focuses on adjusting the temperature. Although it takes a lot of time to adjust the temperature of each section of the barrel, it can open the way for normal production by a more "gentle" method. If the pressure is frequently increased, it will not only increase the power consumption and mechanical loss, but also prone to machine and mold accidents.