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## Vertical injection molding machine molded article shrinkage (VIII)

Date：2015/10/22 0:13:25

Chapter Three vertical injection molding machine injection molding process control equation
Since the injection molded article somewhere shrink vertical injection molding machine is a pressure drop in here is equal to the atmospheric pressure occurs later, so in order to analyze the contraction process vertical injection molding machine injection molding products, not only to the inner mold cooling stage and the die temperature cooling stage vertical injection molding machine injection molding products calculation, but also on the flow and dwell phases temperature and pressure vertical injection molding machine injection molding products is calculated to obtain the initial temperature distribution and pressure distribution within the mold cooling stage . This chapter hydrodynamics continuity equation, motion equation, energy equation, make appropriate assumptions and vertical injection molding machine according to the characteristics of injection molding approximation derived equations vertical injection molding machine injection molding products temperature and pressure. Vertical injection molding machine injection molding products temperature and pressure boundary conditions as described in detail in Chapter VI.
The basic equations of fluid mechanics 3.1
Hydrodynamics purpose is to seek the flow state under the given boundary conditions. For the spatial coordinates (e.g., Cartesian coordinates x, y, :) and the time t four independent variables, usually have fluid velocity vector v (containing three components u,., W) and the thermodynamic quantities (pressure p, temperature T, density p, internal energy e, braised h, entropy :) any two amounts, a total of five unknown scalar function. To solve these five unknown functions, necessary condition is that they must abide by the law of conservation of mass, momentum conservation law and the energy conservation law, which is due to momentum space vector, momentum conservation law is given three scalar relationship, so there are five equations the number of unknown function is equal to the number of the equation, indicating simultaneous equations is closed, the problem can be obtained in principle in accordance with various boundary conditions Special Solution 12031.
3.1.1 Continuous equation root
According to the law of conservation of mass, a mass airtight timber system remains constant. Therefore, the internal volume of unit density with changes in time, necessarily fully reflected in the material out or leave the premises of the flow rate. Per unit time (minus the mass flow of effluent into the mass), must be equal to the quality of the reduced volume element per unit time flowing through the surface of the net volume of the cell mass.
3.1.2 the equation of motion (Navier Stokes equations a)
In classical mechanics, the equations of motion of the object is expressed by Newton's second law, namely two mass x acceleration force acting on the object, another representation of Newton's second law is the law of conservation of momentum: Momentum rate of change of the system equal effect on the system's power. Acting on the unit mass of the viscous fluid forces, in addition to two external N (Nx, where from), and the internal stress F = (Fx, where, who) o the fluid side length accounted x, representing y, accounting for: the small cubes, force is uniformly applied to the inner cube volume force (such as gravity) on the fluid, and the internal stress is acting on the fluid micro yuan per unit surface area of ​​the force, the internal stress can be decomposed into plane perpendicular to the role of law and a stress parallel shear stress of the face: they are the two components y ,: direction is a two, 0 ,, is a positive direction at the time line, the subscript indicates the direction normal; for Ding, when its direction of action extrajudicial face, as when it is a positive direction along the axis positive direction, the two foot mark, the normal direction of the surface stress before a showing, the latter represents the direction of stresses.
3.1.3 energy equation according to the law of conservation of energy, increase the energy of the system is equal to the work done and the heat of the system and added to the system. 3.2 Basic assumptions and approximate the basic equations derived 3.1 (continuity equation, N-S equation, energy equation), the number of unknown function and the number of equations is consistent, simultaneous equations is closed, but left intact The direct application of nonlinear simultaneous equations to solve any liquidity problems is impossible. Moreover, even the uniqueness of the N-S equation has not yet been proven.
It is necessary to make various assumptions and approximations based on the nature of the practical problems in order to make it simpler. If the assumptions made and the approximation is appropriate, then we can accurately grasp the actual flow, to give the project a meaningful solution. Next, the vertical injection molding machine injection molding characteristics were analyzed to derive equations for the vertical injection molding machine injection molding process the various stages of preparation.
(1) Due to the high viscosity of the plastic melt, compared with the viscous force, inertial force and the external force is negligible. Acting on behalf of the left (3.4) per unit mass of the fluid in the inertial force, the first term representative of an external force, the second term represents the force caused by the pressure gradient, the third term represents the viscous force, N one S represents the force balance equation is equation.
Than the Reynolds number Re characterization of inertial forces to viscous forces, by examining Re's size, we can infer the degree of influence of viscous forces. Wherein said flow rate in U, L represents to the characteristic length of the flow characteristics through time L / U, the inertial forces have the effect of the turbulent-flow growth, and to make the turbulent viscous forces have inhibitory effects, according to the experimental Reynolds to the inner diameter of tube and the thickness direction of the average flow rate of feature size and characteristics of the flow rate, the Reynolds number less than 2300 for the laminar flow, the Reynolds number is higher than the beginning of the transition to turbulence value.
For the plastic melt, if we take Xi = loookg / m ,, U = 0.5m / S, five = 0.0o2m, knife = 1000Pa · s, then Re = 0.001 a. Usually when Re <0.01 it is called creep flow, inertial forces can be omitted. External force acting on the fluid is usually due to gravity or electromagnetic field is applied potential caused by substandard, vertical injection molding machine plastic injection mold cavity melt neither electromagnetic fluid, its flow state is also affected by gravity rather then "so It will force an omitted.
(2) Due to the small thickness of the vertical injection molding machine injection molding products, but also the larger the viscosity of the plastic melt, so the plastic melt flow in the mold cavity belonging to laminar flow, speed friction components can be ignored in the thickness direction, that w two o. - In fact, with the process of filling the cavity around the melt pressure continues to improve, there is a center layer from the melt point of the surface layer of compression in the thickness direction, but the flow in the thickness direction of the resulting extremely weak, It can not be considered; in the melt front of the fountain flow area, the flow in the thickness direction is very clear, but in the initial temperature of the melt front temperature taken as the upper reaches of the core layer to reflect the effect of the temperature flowing fountain, take w 20 The practice did not make the melt front temperature distribution and pressure distribution calculation be much affected, for the calculation of the specific volume change process had been sufficient.
(3) vertical injection molding machine injection molding products in the thickness direction of the velocity gradient, the velocity gradient is much greater than the flow plane. Considering only the thickness direction of internal friction between the layers, and in the flow surface is reduced to a non-viscous flow.
(4) The specific heat c, instead of the constant volume specific heat c.
(5) Assuming isotropic thermal conductivity vertical injection molding machine injection molding products. In this paper, the various stages of the vertical injection molding machine injection molding are considered the vertical injection molding machine injection molding products within the flow surface of the heat conduction, but the resulting problems related to the value of the thermal conductivity of plastics in different directions. The essence of heat conduction from the thermal motion of an atom (or molecules) pass to another atoms (or molecules), because the covalent bond strength along the polymer main chain of a lot better than the polymer between Van der 华力强, therefore molecular orientation along direction thermal conductivity greater than the thermal conductivity perpendicular to the direction of molecular orientation of the 1207] 1208], that is, the thermal conductivity anisotropy.
But to obtain anisotropic thermal conductivity, we must first get the vertical injection molding machine injection molding products inside the polymer orientation situation, which requires the use of heat viscoelastic constitutive model to calculate the flow stress change in the flow and packing Analysis process, and to gauge the thickness of the melt front and the direction of flow, so that the problem becomes more complicated, in addition Polymer relationship between the degree of orientation and thermal conductivity has not yet been solved. For these reasons, this paper thermal conductivity vertical injection molding machine injection molding products taken as isotropic. (6) plastic melt filling status as an incompressible fluid to deal with. We do this just to make equations are simplified, and at each time step of the filling process should be calculated on the specific volume of plastics, not so hematocrit value remains unchanged.
Equations 3.3 vertical injection molding machine at all stages of the injection molding process
According to the assumption of the foregoing vertical injection molding machine made by injection molding and approximate, may put the continuity equation, equation of motion, energy equation some items slightly off, draw vertical injection molding machine is suitable for injection molding analysis equations for each phase.
3.3.1 Flow Stage
(1) the continuity equation (2) the equations of motion (3) the energy equation
3.3.2 packing stage
(2) the equations of motion (1) the continuity equation
(3) the energy equation
3.3.3 cooling stage
During the cooling phase, one that the cavity completely stop the flow ratio, is no longer needed and the continuity equation to solve the equations of motion plastic melt flow field velocity distribution and pressure distribution (which does not mean that the internal vertical injection molding machine injection molding products The pressure has fallen to atmospheric pressure), leaving only the energy equation for solving temperature field of vertical injection molding machine injection molding products.

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