The hottest mold to automatically cut off the gate

2022-09-23
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Mold that automatically cuts off the gate (three plate mold and four plate mold)

in order to eliminate the secondary operation of cutting off the gate, gastrow has designed an injection mold that automatically cuts off the plastic parts and runner system with the help of the mold opening action as early as 1938. It is urgent to apply for a patent for this technology, but after the end of the Second World War, there was no application for a patent for this technology, so that the technology of automatic gate cutting has no patent protection

principle of automatic gate cutting

the mold that automatically cuts the gate requires two parting surfaces. On the first parting surface, the melt is distributed by the main channel through the shunt channel, and then the melt flows through the vertical channel set on the intermediate plate, and the gate leading to the mold cavity is set at the end of the vertical channel. A molded plastic part is arranged on the second parting surface of the mold. When the mold is opened, the parting surface containing the runner system is opened first, and the runner system is left on the fixed mold side, in order to cut off the gate and plastic parts on the intermediate plate. It must be considered that the opening distance of the parting surface should be appropriate. Once the parting surface is opened at an appropriate distance, the shunt channel and the main channel can be ejected. Then the second parting surface containing the plastic part is opened again. After the second parting surface is opened by the required distance, the plastic part is ejected in the common way. For the mold, opening the two parting surfaces in turn requires a large enough opening stroke, which is unfortunately not considered in the planning of many injection molding machines. And the mold also needs a relatively large installation height, especially for deep plastic parts. Therefore, for the driving device of two-stage mold opening, it is necessary to provide enough empty units to form the main machine: melting room. Surprisingly, it has been found that the so-called point gate (always in the form of three plate mold or four plate mold) is sufficient if certain prerequisites are met. It is also found that the point gate is better for filling the mold of thin-walled plastic parts than the gate set on the parting surface. For thick wall plastic parts, it is easier to prevent pit collapse with a point gate than with a larger gate on the parting surface: the explanation of this phenomenon is likely to be; If the point gate is properly designed, although there is a significant pressure drop at the narrow gate, the melt is suddenly heated as a result of this pressure drop, resulting in good mold filling

the local heating of steel around the gate is a further influence, because the local rise in the temperature of the steel surface prevents the premature solidification of the gate. For this reason, the melt can continue to be injected into the mold cavity through the point gate under the pressure retaining pressure for feeding. However, in order to easily fill the mold and maintain the pressure holding pressure, a basic prerequisite is that the shunt channel should be large enough. On the one hand, in order to prevent premature solidification of the melt, on the other hand, in order to prevent excessive pressure drop when flowing through the shunt channel, today we will share the relevant data of 1.5 gold tool torque detection equipment. At the beginning of injection, the point gate always needs high injection pressure

on hydraulic driven machines, this prerequisite can always be met. On the other hand, if the injection rate is limited by the driving form, the plunger injection molding machine driven by the spindle and elbow mechanism is usually like this. When the achievable plunger speed changes, the pressure that forces the melt to pass through the point gate may be too low due to the high flow resistance at the narrow section of the gate. In this case, the point gate must be increased to reduce the flow resistance

it is possible to set the gate at the center of gravity of the plastic part, for example, set the gate at the center of the plastic part of the disc. According to the reasons related to flow, the gate usually set at the center of gravity of the plastic part is more practical than the edge gate. On the one hand, the material flow route is shortened by half, on the other hand, the weld mark is avoided, because the weld mark always reduces the strength of the plastic part. Set the point gate at a certain position of the plastic part, and if the plastic part is stuck to another part afterwards, the trace of the gate will be invisible, which is usually very possible. Produce small plastic covers, which are finally glued to another part. Because the gate may protrude 0.1 ~ o.2mm after cutting off the gate, set the gate in a small pit on the back of the cover, so that the gate will not hinder the bonding of the cover

in order to cut the gate cleanly, the cutting action must take place on the firm and close inserts, and the mold structure must ensure this. For flat plastic parts, the runner must be left on the fixed mold side of the mold, and the mold must first be opened along the runner parting surface, so as to achieve this. In order to ensure that the mold is opened in turn, the fixed mold insert fixing plate a is pushed by the Butterfly Spring B, and the force of the butterfly spring is greater than that required to cut off the point gate. In this mold opening stroke, each vertical channel is reliably left on the fixed mold by the pull rod C. Therefore, when the parting surface between templates a and D is opened, the sprue and shunt system remains on the stripping template D. Because the Butterfly Spring B can only move for a short distance. The second parting surface where the cover is located must still be closed in some way. Its purpose is to first ensure the sufficient opening distance required to eject the runner system at the runner parting surface. For this reason, the fixing plates a and C are tightened together by the draw hook F. only after the runner parting surface is opened by the required distance, the draw hook is disengaged by the demoulding rod s bolted to the fixed mold fixing plate. At the beginning of the mold opening stroke, the fixing plate a is guided by three demoulding bolts h, and is in contact with the nut I shortly before the end of the mold opening stroke. These nuts are fixed on the guide sleeve K, which has no shoulder behind the demoulding plate D. At the end of the mold opening stroke of the runner parting surface, the template D is pushed forward by the guide sleeve by about 10mm until the nut 1 touches the washer M. After the nut 1 touches the washer m, the travel of the fixed plate a is limited, and the flow channel is pushed out of the pull rod C. At this time, the sprue has also been pulled out by 10mm, but it has not completely left the sprue bushing. Since the sprue has loosened in the sprue bushing, the effect of spring n can effectively push out the sprue, so the runner system can fall automatically at this time. However, the premise for the smooth falling of the runner system is that the nozzle does not have the phenomenon of wiredrawing salivation, because this is usually the case in PS. if there is no proper structure to close the nozzle, the runner condensate will hang there due to the phenomenon of wiredrawing salivation

when the mold continues to open, the parting surface between the two fixing plates a and, opens until the push rod. It is pushed out, and the push rod pushes the push plates P and Q forward. The push tube R is fixed between the two push plates by the shoulder, and the push tube pushes each cover of the measuring amplifier out of the core

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