Analysis of the design of the extrusion die for th

Analysis of plastic extrusion die design

1 degree unevenness in rectangular hole and rectangular channel. Flow parents in different shapes such as pyramid Hugh; Brother. As well as the influence of the effect on the shape of the opening, the molding pressure size and the plastic lattice, the research shows that the geometry of the mold cavity through which the material flows must be smooth and streamlined, in order to reduce; 61. The length of the molding part of the extrusion die must be determined according to the rheological properties of different plastics, and the Chinese French classification No. D 83; 1241.62 plastic extrusion molding is a continuous molding method that heats and melts powdery or granular raw materials, and then cools and solidifies them through extrusion molding and setting mold

in the process of plastic melt briefly referred to as double material passing through the extrusion die, it experiences changes in temperature, pressure, viscosity and chemical structure. 1 the rheological characteristics of the flow state in the extrusion die forming on the melt 1 and the effect of extrusion are very important for the reasonable design of the shape and size of the inner cavity of the extrusion die, and directly affect the accuracy and quality of the extruded products. When setting the juice extrusion die

according to the shape and structure of different extruded parts, the + same rheological properties and effects of melt in the extrusion die cavity must be analyzed

1 flow rate characteristics of melt in the extrusion die cavity. The shapes of plastic extrudates are diverse, and the sectional geometry of the extrusion casting cavity is also very different. Therefore, the flow rate of melt in the film cavity is very complex, and its flow rate will change with the geometry of the mold cavity. Analysis of face classification

1.1 the flow of molten material in a smooth circular hole has been proved by practice that the velocity of flow at each point along the length of the radius is not equal. However, the flow velocity on each concentric circle in the circular hole, which makes it easier to display data and curves, is equal. If you connect the points of the same flow velocity, you can get the isokinetic line of the circular hole, 1 According to the introduction,

it is known from the Ge that the flow rate of fluid in the mold cavity only changes in the direction of the call. Then, the velocity of each point in the channel is perpendicular to the coordinate of the flow direction. Moreover, the velocity parallel to the inner wall of the cavity can be measured by coordinates. This type of flow is called dimensional flow. The velocity change of molten material flowing in this channel is only a function of variables, and the velocity change is only a function of radius factory, that is, the velocity of 12 molten material flowing in the rectangular hole at any point on the die cavity section cannot be in single coordinates, while the velocity of each point changes with the distance from the center of the square hole, and its isokinetic line is 2

the distribution of flow violations is symmetrical. The flow violations at each point can be determined by the distance from the point to the horizontal axis and the vertical axis. The material speed needs two coordinates. This flow type is called dimensional flow. The velocity change of molten material flowing in this channel is 1 water number, 1! 1.=.， 13. The flow of molten material in the rectangular channel with non parallel inner wall and conical prism shape. On the date of receipt, its flow violation changes not only along the vertical and horizontal directions of the section, but also along the flow direction. Therefore, it is called dimensional flow. The change of flow velocity in this channel is a function of coordinates. The shaped part of the melt in the extrusion die cavity is usually a parallel straight part and a part with a large pressure drop, which is almost dimensional flow

in the design of extrusion die, it is necessary to accurately analyze and distinguish the type of runner section according to the structural shape of products. It is very important to simplify the dimensional flow into dimensional flow for calculation, because the geometry of tangential flow can be calculated in the flow under different pressure drops

in special cases, the rectangular section is in a narrow shape, and the isokinetic lines are parallel to the long side, and the fillet area of the isokinetic line is only a small part of the whole section, 3 not

ignoring this part in the calculation has little effect. In the extrusion die of plate and film products, the melt flow in the die mouth of the extrusion die belongs to dimensional flow, but the calculation shows that when the ratio of die width to height is 7, the error is not large, and when it is 13. The error is not greater than the isokinetic line of 3 =

therefore, in fact, the slit channel of 510 is also an example of dimensional flow. 2 bar, s effect 83.18 when the melt leaves the gap at the die mouth of the extrusion die, the melt parison has an obvious human expansion effect, which is called extrusion human expansion or 831 Effect

influence practice has proved that the expansion degree of polymer bar melt leaving the die mouth of the extrusion die can exceed 3. Therefore, the change of the size of the melt parison leaving the extrusion die 1 can be ignored. Therefore, it is particularly important to analyze and master the degree of the expansion of the melt leaving the die for the design of the extrusion die

there are many factors that affect the die swell. Among them, the main one is the streamline convergence of molten material from the outlet of the extruder to the die mouth of the extrusion die, and the gradient of irregularity in the flow direction causes the tensile elastic deformation of the solder bucket. In the whole channel of the extrusion die, this elastic deformation has no time to relax, resulting in the elastic recovery at the die mouth of the extrusion die, making the melt swell in the direction of melt wall thickness or diameter. In addition, when making stable flow in the whole channel from the inlet to the outlet of the extrusion die, the melt will produce elastic deformation due to various stresses, which will inevitably lead to elasticity when leaving the die. The complex effect is mainly caused by the elasticity of the solder

generally speaking, when the flow rate is fast, the temperature is low, the shear rate is large, the die setting section is small, and the molecular weight of the melt is large, the melt will swell out of the mold

experiments show that at the same shear rate, higher temperature can reduce die swell; At a given temperature, people 1010, 3, etc. swell greatly

the expansion coefficient of melt release can be calculated by the following formula. It can be seen from the above that when designing the die opening of the extrusion die, it is far from enough to consider only an empirical coefficient of release expansion. To correctly give the extrusion expansion system and value, it needs to be determined by comprehensive consideration according to the specific analysis of the geometry, die structure size and process conditions of the plastic extruded by the extrusion die

ixsenic material production process is simpler and energy-saving

22 effect of melt on the geometry of plastic melt parison leaving the extrusion die. As the melt is forced to flow through the die, there is obvious expansion of the melt leaving the die. As a result, the parison section leaving the die is larger than the gap section of the die. If the flow channel is dimensional flow, it will swell along the direction of velocity gradient. For example, as a result of the expansion of the plastic round bar, its diameter is larger than the diameter of the mold hole, but the shape has not changed, and it is still round, which shows that the expansion is uniform, we know. If it is a flat rectangular plastic belt, it will expand greatly in the height direction, while the expansion in the width side is very small

if it is a dimensional flow, such as a square shaped section, the shear stress in all aspects is uneven. The opposite side of the square hole * is large, and the diagonal * is small. It can be imagined that the expansion * at the center of the two cavity walls received at the opposite corner * is large. And the expansion * at the corner is small. The melt leaving the die not only increases the cross-section, but also becomes not ldquo; There is no way to limit the output of square sections in the whole industry like coal. Its shape is between round and square, 41. From this, it can be seen that the angular flow channel will also cause the shape change of the melt leaving the die, polonium. Rectangular 1 parison section; The effect of the cross-section shape of the 2-inch flush die on the geometry of the off mold melt parison. It is ignored. Through the change relationship between 4 small elemens and the old shape of the mold release soldering body. We know 31 The influence of the effect on the geometry of the melt billet is still regular. However, the influencing factors are relatively complex, which are related to the cutting rate of the whole flow channel structure of the extrusion die, the degree of the shaped section of the die mouth and the plastic characteristics. There are 8 through analysis and excavation; 18 effect on the change law of the geometry of the Yu sheet die can be reasonably corrected in the design of the extrusion die. 416.

to sum up, in the design of plastic extrusion die, all channels through which molten material flows must have smooth streamline surfaces. In order to reduce the influence of 6 effect, the length of the molding part of the extrusion die should be determined according to the rheological properties of different plastics

1 Chen Quande. Material forming engineering. Xi'an Jiaotong University Press, 2000.446449 2 plastic mold design manual, writing group. Plastic mold design manual. Beijing Machinery Industry Press, 1998.44-4493 Wang Shuyun. Practical technology of injection mold design and manufacturing. Guangzhou South China University of Technology Press, 1993.2935