Vertical injection molding machine pressure setting parameters

Date：2014-06-04 13:07:35

        With the development of all walks of life , increasing application of plastic products , their quality requirements are also increasing , especially for industrial products, more stringent requirements . However, the key to how to provide customers with high-grade , precision , can meet a variety of features and even more conducive to the protection of the mold process equipment , now is not the main problem in terms of the injection molding machine , which decided to achieve excellent performance that set the parameters of the injection molding machine . Especially in precision machining , plastic injection molding machine when the complex adjustment technique is more critical .
        To this end , I screw back pressure against the effects of injection molding machines , injection pressure , an important factor in holding pressure and clamping force and setting method to make a brief introduction.
        In a back pressure when the screw is rotated, the softened plastic is pushed through the stop valve and reaches the front of the screw. Since the melt constantly being pushed forward in this region will produce a pressure , and acts on the screw and the stop valve , push them in order to accommodate the additional melt , but also the back of the screw is connected to after the hydraulic cylinder piston to push the cylinder chamber pressure after oil will flow back to the tank through the pipe injection molding machine . If the oil pressure control speed , then the hydraulic pressure chamber to a pressure cylinder , the greater the reflux rate of pressure oil , the higher the pressure generated within the cylinder , this pressure is called backpressure. Backpressure of melt back pressure and screw / oil line back pressure. Usually called backpressure mostly screw back pressure. Screw back pressure and melt back pressure has a direct relationship with the injection molding machine structure ( for example, the diameter of the screw diameter and cylinder piston ) related. Usually about 10 times the melt back pressure in the back pressure of the screw . Table 1 is the recommended value of the back pressure of some molten thermoplastic material .
        2 injection pressure
        Injection pressure must be set sufficiently , it will determine the rate of injection and subsequent filling of the mold situation . Under optimum injection pressure , injection cycle variation should not exceed 0.2 5 , preferably 0.1 to control Chuan 9. If the injection cycle over 0.1 . , In addition to indicate a low injection pressure , there may be a melt uniformity or poor injection rate control problem.
        2.1 Inter- ending stream
        Screw stop valve in front of the return valve is known , its function is to prevent the injection stage before the melt front of the screw back to reflux . In order to achieve a constant closing stop valve , stop valve must be reset after the screw stays in the same location , the best reverse sew stop valve stroke should be less than the required effective stroke length closed 0.5 , the highest rate should be inverted index 20% to 30 % of the injected velocity.
        2.2 Pressure
        One reason for oil filling of the mold caused by temperature changes in the temperature of the oil pressure , which can affect the normal operation of the injection molding machine . Should drive the oil temperature rises to normal operation after production, to pay attention to the temperature of the hydraulic oil through the cooler . Ideal oil temperature should be controlled at 30 a 5 ℃ [2;.
        2.3 gate
        In many cases the injection rate can be set depending on the size and position of the gate , in particular a gate diameter reaches 1.5 mm 0.5 . When the melt at high speed through the gate when the small , they produce a lot of shear stress in the melt , the greater the speed the higher the shear stress , which is a huge stress to make a sharp rise in the temperature of the melt may cause degradation of plastics . If the diameter of the gate is slightly increased, the shear stress can be greatly reduced , the defect on the article will be avoided. If the gate is increased in diameter from 0.8 mm to 0.9 mm, the expansion of the gate area increased 0.134m , representing an increase of 21.07% of the area . After the gate increases, the lack of material can be partially filled , the surface quality of the corresponding parts have begun to improve, obviously , increase the gate diameter will help to improve the state of the cavity is filled .
        2.4 Injection Rate
        The injection rate of the melt into the cavity of the line speed , the filling stage of injection of the melt into the mold cavity must be controlled in order to adapt the speed of mold materials and product characteristics . For example, the injection rate should be set at the product , design and plastic properties of the wall thickness of the case as far as possible to allow faster , thin-walled parts will require very fast injection rates to ensure full product ; rather thick-walled parts you need to slow injection rate to prevent the formation of air pockets and flow marks . Injection can convert different injection rates at different screw position , in order to avoid the appearance of defects in parts , such as crazing , flash, scorch marks, weld lines , etc. , and controls the speed of the melt into the cavity , the speed can be the degree of molecular alignment and internal stress affect the products , different injection rate control is called " multi-stage injection ." Multi-stage injection can not only improve the quality of the finished product , but also to shorten the injection cycle a clever % 10% , and the injection rate can be obtained using stroke control separately into the melt flow channel system and the optimal position of the cavity. The principle of multi-level set injection rate is at the optimum condition, changes in general is not the injection cycle . If there is a greater change in the injection cycle , possible causes are poor melt uniformity , lack of injection pressure , improper operation of the hydraulic control system , pressure oil is not clean , the problem occurs filtration system , multi-stage injection rate is not set correctly , etc. .
        3 holding pressure
        Holding pressure when the cavity is the pressure used was just filled . The injection volume and the residual effect is compensated by the supply of the cooling cavity and the desired melt volume shrinkage that the cavity shape of the melt under pressure to cool the case . Thus, the product appearance requirements and dimensional tolerances in order to be guaranteed.
        3.1 packing value
        Holding pressure range is usually 30 to 70 MPa, and sometimes up to 90 a 10 M Pa. Affect the actual use of the main factors holding pressure has processed plastic types , runner and gate design, mold operating temperature , melt processing temperature , thickness of the product , the shape and complexity of the products , as well as the need to provide packing stage the injection volume and percentage . In general, the value of the holding pressure should be 25% of a 65% injection pressure may be as high as 95 % to 10% of the injection pressure of the production of thin-walled parts . Proportional to the residual value of the holding pressure injection volume and injection cavity should be used. The remaining injection volume is larger, the larger the required holding pressure , produced by the weight of product items the greater the change . Screw gasket ( article number of pieces needed to produce a given feed amount ) of the product piece weight value may reflect a change , the operator can use many of the injection screw values ​​to evaluate the stability of the level of the gasket production process . Dwell time is the position of the screw in the front is almost stationary time . Dwell time and part thickness , injection rate, gate design , plastic mold level and temperature. In addition, the injection pressure switch correctly set pressure point and turn segmented packing injection molding production is also essential when a holding pressure. Paul will have to use the pressure prematurely turn put too much pressure melt promote cavities , so it is prone to lack of material ; If you dwell too late products will be compressed too large, many parts of the formation of burrs and stress over high , stripping is not stable enough , increase product piece weight , etc.; segmented packing can better improve packing product defects only caused by a single pressure.
        3.2 Determination of the amount of the injection stage of the injection
        Should first find out the optimal parameters of products, and the products produced pieces weighing heavy , assuming this piece weight Wo, then holding pressure and dwell time of injection molding machine is set to zero , then the cavity only the amount of injection stage of the injection , the product thus obtained with a piece weight injection volume Gong only on the injection stage . Percentage of the amount of the injection stage injection = ( Rocky / Gong ) x lo%. When injected into the cavity of the people shall be the total injection volume of 95% a piece weight of 98% [3] . If the multi -cavity molds , filling each cavity shall ensure balanced . Z- Md d can be applied , such as injection molding analysis software for multi-cavity injection mold casting system runner and gate size to balance the flow optimized design .
        4 clamping force
        Mold clamping force is to provide a locking force injection molding machine , which can offset the melt in the cavity mold opening force generated . Many people like to use the largest injection molding clamping force , but rarely consider the size and design of molds and injection volume form molds and products , in fact, the need for economic and technical , to ensure product quality , under the premise should be clamping force to the required minimum. Thus , one can significantly save energy , on the other hand can reduce the degree of wear of injection molding machines and molds , injection molding machines and help extend the life of the mold , and the mold is also natural exhaust capacity can be increased , so that the mold filling state easier to control . The program sets the optimum clamping force is : ¹ First, the clamping force injection molding machine to the highest , followed by the normal automatic or semi-automatic production . º three parts were weighed and averaged gross . » The clamping force reduction st, until production stabilizes repeat º, to identify gross average. ¼ then clamping force reduction s t, and repeat º. Repeat ½ ¼, until a significant increase in the average gross weight . ¾ the obtained data lists , draw a workpiece clamping force GW curve. Figure 1 is produced by A BS dumbbell tensile specimens parts PcsWgt a clamping force curve. Figure 1 shows , when the clamping force is reduced from 70t 4O t, GW parts begin to increase the value , and then reducing the clamping force more parts gross value increases significantly , and produce burrs , so the production best clamping force under steady conditions is 4O t. For security molds , mainly low-pressure mold test , which uses the clamping pressure hierarchical control before the termination of the low-speed low- shift mode , only when the mold completely stickers timely boost to achieve the required clamping locking force .
        5 Conclusion
        When injection molding , injection molding machine pressure related to personal life , safety equipment and molds and injection molding machine , but it is also a prerequisite to ensure product quality. Therefore, the use of injection molding machine technology to process each tuned to optimize the injection molding process , so that the injection molding machine, mold , plastic combined maximum effectiveness will be able to play the most crucial factor of production. Stable level of production process can be investigated by the following phenomena : first , the injection cycle should be not more than 0.2 5 , preferably controlled within 0.1 5 ; Second, the use of a screw member to reflect changes in litter weight values ​​should be more stable.

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