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Vertical injection molding machine molded article shrinkage (IX)

Date:2015/10/23 2:37:53


        Chapter Four vertical injection molding machine molding material physical properties table
        4.1 Viscosity
        The study of fluid mechanics, according to consider whether the fluid viscosity, ideal fluid and viscous fluid into a River 1209}. No ideal fluid viscosity, fluid flow inside without internal friction. Ideal fluid actually does not exist, any fluid has viscosity occurs when the flow is bound to the internal friction. Viscous fluid is divided into Newtonian fluid and non-Newtonian fluids. It is a constant viscosity Newtonian fluid, a gas, liquid or solution of a low molecular compound belongs Newtonian fluid. Characteristics of non-Newtonian fluids are high molecular weight, high viscosity and viscosity is not constant.
        Non-Newtonian fluids is divided into a viscous system, there is a time-dependent systems and viscoelastic system 12 Sichuan three categories. Which is closely related with the injection molding system is viscous, the fluid flow force of such systems, only the viscosity of the applied shear stress and the size, time and length of the applied shear stress regardless of influence on the viscosity according to the shear stress in different ways, it is divided into 宾哈 fluid, pseudoplastic fluid and swelling fluid three. Polymer melt pseudoplastic fluid, which is characterized by "shear thinning", ie shear flow viscosity decreases. In the description of the vertical injection molding machine of pseudoplastic fluids empirical equation, the more commonly used is the power law model with CrosS model.
        4.1.1 The power law model
        In the power-law model, the viscosity is shear rate (ie shear strain per unit time) is a function of temperature. n called non-Newtonian index. For vertical injection molding machine pseudoplastic fluid, n but at low shear rates greater power law model error, for which researchers have proposed a strain rate applicable to a wider range of mathematical models.
        4.1.2 Cross Model
        CroSS model not only describes the power-law rheological behavior of the polymer melt at high shear rates, but also to describe the Newtonian rheological behavior near zero shear rate of the polymer melt. Ten shear viscosity, it expresses the shear rate is close to zero when the polymer melt flow properties of the material constants. When the shear rate is sufficiently large, the formula (4.2) simplify its forms and similar power law model; r when the shear rate approaches zero, the knife close to the knife. Approximates Newtonian fluids. On behalf of the rheological properties of the polymer melt transition from Newton area to shear stress level power rate zone, in this shear stress, the viscosity of the melt by the knife. Transition to power-law curve. Zero shear viscosity blade. At higher temperature, the viscosity of the calculated values ​​of five parameters cross model is consistent with the calculated value of the viscosity of the seven cross model parameters; when lower temperatures, precision cross seven parameter model was significantly higher than the five parameters cross model, so In this paper, because the viscosity is too large, seven-parameter model to calculate the viscosity cross filling and packing process in polymers. In order to prevent a temperature lower than the 'overflow and the advent of computers, in this paper to calculate the viscosity of program modules. ia. (Gradu, Wu p) stipulates that when T as the temperature rises, the polymer molecular thermal kinetic energy increases, the ability to enhance the thermal conductivity, thermal conductivity of the polymer becomes so large. By introducing the hyperbolic tangent function and its value is negative of gas, so the thermal conductivity of crystalline plastic vertical injection molding machine of mutation occurs at temperatures of about stick at, where the value is higher than the temperature T, the thermal conductivity and the value is very low (with PP, for example, has a value of roughly 0.175W / m nearby); when the value of the temperature T is lower than the stick, the thermal conductivity values ​​of people suddenly increased (with PP, for example, people value roughly 0.215w / m this. After the formation of grains reflect, narrowing the distance between the polymer, the thermal conductivity of the polymer is greatly enhanced.
        4.4 hematocrit
        At present, domestic and foreign general equation to calculate it using several polymer specific volume. But Tait equation only when the temperature change rate is fixed at the case of a measured value and temperature, pressure corresponding to the specific volume of data, if it varies greatly in vertical injection molding machine plastic molding process as the cooling rate in The hematocrit value, inevitably produce theoretical error. As for the vertical injection molding machine used to predict the shape and size of the computer-aided plastic analysis technology, vertical injection molding machine plastic hematocrit value calculated correctly or not, directly affect the prediction accuracy of the results. After Taiwan scholars and others with a cooling rate R.YChang factor on a non-crystalline plastic vertical injection molding machine Tait equation corrected to obtain the temperature change rate yield ring T relationship is different from the actual conditions, but it still can not be calculated cooling rates continue changes with temperature, pressure, hematocrit value corresponding to the polymer. In this paper, polymer relaxation effect of non-crystalline plastic vertical injection molding machine vertical injection molding machine with the crystalline plastics Tait equation is corrected to give the case of changing the cooling rate of vertical injection molding machine amorphous and crystalline plastics VT relationship several plastic vertical injection molding machine.
        4.4.1Tait equation
        Dual Domain Tait equation of state and speneer a single domain Gilmore state equation compared than by temperature dependence of capacity is divided into two areas leaving the melt and solid non-crystalline polymer specific volume change curve fitting even more After accurate, and in consideration of the specific volume mutant crystalline polymer occurs at a temperature near the crystallization, but also to express the relationship between VT only crystalline polymer, so it is widely used.
        Amendments to the Tait equation of 4.4.2 R.Chang etc.
        Taiwan scholars R.YChang and others believe, Tait equation only expresses the capacity of the pressure and temperature contrast effects, but did not express a cooling rate of comparative tolerance of. They use the cooling rate of the glass transition temperature Factor eve of amorphous plastic vertical injection molding machine was modified Tait equation. R.YChang, who proposed several VT equation of state of non-crystalline plastic vertical injection molding machine, although you can calculate the non-crystalline plastic vertical injection molding machine under different cooling rates of specific volume, but still requires changes in hematocrit during the cooling rate is constant. Vertical injection molding machine plastic molding process, the cooling rate is not possible to maintain a certain value. If on the cured initial vertical injection molding machine plastic cooling rate of a point has been great, but at this point in the late solidification cooling rate suddenly becomes small, then the application R.Ychang et al amended Tait equation to calculate the specific volume , it will cause a sudden drop in hematocrit at this point for a number, and hematocrit value regardless of how much the previous time step. This paper argues that the polymer in the hematocrit value with a certain time at this time is not only the temperature, pressure, and cooling rate, but also with the polymer at a time preceding the relevant hematocrit value. Calculated hematocrit value of the current time, it should be linked to the hematocrit value of the previous time. So this paper based on the relaxation properties of polymers, with hematocrit value at a cooling rate of the previous time correction Tait equation.
        4.4.3 polymers affect their relaxation effect P- ring T acts
        Let xt to external stimulation response time is equal to t value polymers, xco the polymer reaches the response value corresponding to equilibrium with the outside stimulation, and at a temperature well above the polymer glass transition temperature, Relaxation time is very short, can be considered the volume of the polymer is in equilibrium with the external stimuli. When it cooled down to another temperature, volume will readjust. Volume adjustment polymers, by segmental motion to achieve. As the temperature dropped, the relaxation time segmental motion of the rapid increase in the volume adjustment period will gradually become the seconds, minutes, hours or even days of magnitude. When the external stimulation time (equal to the reciprocal of the cooling rate on the value of q) to achieve the same magnitude and volume adjustment time, continue to cool down, the volume was adjusted to keep up with the external stimulation time period, the volume is no longer enough time to reach its equilibrium value, which is the glass transition. It is believed that when the glass transition temperature of the relaxation time of the small (a few), and give the glass transition temperature of the cooling rate of the reciprocal (1 / q) approximately equal in value. The larger the cooling rate, will begin at a higher temperature polymer exhibits a glassy state. The larger the cooling rate, the larger the value of the hematocrit solid. For simplicity, that the glass transition temperature of the polymer specific volume and more independent of the cooling rate, the cooling rate affects only the hematocrit value of the glass transition temperature of the polymer or less.
        4.4.4 Calculation of non-crystalline plastic hematocrit vertical injection molding machine
        For non-crystalline plastic vertical injection molding machine, often the temperature specific volume-temperature curve occurs when the deflection as the glass transition temperature lvl. With increasing cooling rate, specific volume-temperature curve deflection occurs at higher temperatures. When the cooling rate endless hours, set specific volume-temperature curve deflection does not occur, and it as pressure, hematocrit value corresponding to the temperature equilibrium state, with v. To represent. Specific volume calculation method according to the melt domain Tait equation to obtain the formula to calculate vco.
        4.4.5 crystalline plastic vertical injection molding machine specific volume calculation
        Crystalline plastic inner vertical injection molding machine comprising grains of different sizes, so from the beginning of melting to fully melt a fairly wide temperature range, typically the melting temperature and finally completely as the melting point Tm.
        Tm also be regarded as the temperature begins to crystallize during cooling time. For crystalline plastic vertical injection molding machine, by the influence of the cooling rate of a few or Tm, there is no clear conclusion. This paper argues that, Tm not affected by the cooling rate, the cooling rate can affect the jaw, for the following reasons: in less than a few and not higher than the crystallization temperature Tm, crystallization processes occurring in Van and between Tm. If the ambient temperature is less than a few, the micro-Brownian motion of the molecular chains is frozen, can not pass the necessary movement condensed into nuclei; the contrary, when the temperature is higher than Tm, although molecules with sufficient energy, enables segment Motion to lattice up, but due to the higher temperature of the system, even though there may nucleation but not stable enough, it is vulnerable to saboteurs thermal motion.
        Only in a few with a temperature range between Tm, can guarantee to produce stable nuclei without being destroyed, but also ensures that the molecular chains have enough athletic ability to the nucleation surface movement, so that nuclei grow into grains, This can happen crystallization. So this will be regarded as a few stop temperature (or melting temperature at the start of the heating process) crystallization takes place in the cooling process. Polymer at what temperature began to crystallize, depending on when the thermal motion of molecules slow down to allow the formation of stable nuclei, regardless of the cooling rate, because when the temperature is just below Tm, the relaxation time is still very short; and the polymer in What stopped crystallization temperature, cooling rate is a major factor, since the crystalline stop means segmental motion is frozen, that is, external stimulation time is less than the relaxation time at this time. For ease of calculation, the provisions when vt (P, T) is equal to vt (P, Wu 1) 1/6, the value of the temperature T is taken as a few. If the third expression according to formula (4.31) is calculated v, (p, Tm), makes specific volume-temperature curve projections in Wu 1, in order to maintain a crystalline plastic vertical injection molding machine specific volume-temperature curve continuity, v. (P, Tm) second expression according to equation (4.31) is calculated.
        The third expression by the formula (4.31) can be obtained formula (4.33) a few.
        Calculation methods and non-crystalline plastics same vertical injection molding machine, see (434). Calculation claw 'activation energy data needs polymers. Reference [69] provides a PP (HoechstPPN1060) in the cooling rates of 54 "C / s and 0.04" Tait equation of state material constants C / s when, under different pressures by both the cooling rate corresponding to the glass temperature into the equation in sacrifice .34), to detect changes in the activation energy △ E PP with pressure is very small, so the crystalline plastic vertical injection molding machine as a constant activation energy to deal with, for PP (HoeehstPPN1060), E two 5.05X106) / mol. After obtaining bite, the curve vr (P, T) a T crystalline portion extending (when q'q, the first expression, see (4.35) and the second expression) or truncated (when q > When qr, third expression see (4.35)) is to bite at, we get the curve, (P, T, q) of the crystalline portion of a T. For crystalline plastic vertical injection molding machine, it can not be exactly like the non-crystalline plastic vertical injection molding machine as a temperature curve deflection by hematocrit does not happen to get in the glass transition temperature less than the temperature and pressure corresponding to the equilibrium state, capacitance value because the slope of the crystalline portion is too large.
        For this reason, the T

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