Pananaliksik sa Epekto ng Bilis ng Pag ikot ng Screw ng Injection Molding Machine sa Plasticizing Ability at Apparent Viscosity

0 Panimula

Injection molding machine is the main equipment for plastic molding, mainly by the injection system.System, clamping system, electrical control system, lubrication system, hydrostatic transmission system,Heating and cooling system, safety monitoring system, atbp. To improve product qualityQuantity, production efficiency, reducing energy consumption, people have conducted in-depth research on it.The research on injection molding machines is multifaceted, including the electrical control system.Intelligent transformation.Servo transformation of transmission system Energy saving of heating and cooling systemReform.The screw structure transformation of plasticizing ability. The screw is the core of the injection molding machineHeart components, whose parameters determine the injection volume of the injection machine, researchers have studiedMore. The better the plasticizing uniformity of the screw represents the repetition accuracy of the product.The higher the measurement accuracy, the performance parameter of plasticizing uniformity is apparent viscosity.Wherein the modification of the screw structure helps to reduce the apparent viscosity of the melt, the screw.

The capacity is determined by the screw structure and the screw speed, pressure, speed, temperature, etc.It is the main parameter to measure the performance of the screw. Wang XishMelting of injection screwBody transport was analyzed theoretically. Li Zhenget The effects of temperature and back pressure on snailInfluence of rod plasticizing ability. Plasticizing capacity represents the efficiency of injection molding machine production,It is necessary to improve the plasticizing ability of screw for the economic benefits of enterprises.

The plasticizing ability of the rod refers to the quality of plasticized materials per unit time of the injection molding machine screw.The quality of material storage is determined by the metering chamber, and the exit of the screw homogenization sectionConnected with the measuring room, the volume at the outlet of the screw homogenizing section can be measured.The plasticizing ability of the screw was determined by the pass rate.In the selection of materials, the viscosity is greatly affected by the shear rate and the temperatureThe degree of low sensitivity of polypropylene to facilitate detection and observation of experimental results. This paperThe flow field of PP melt in the homogenizing section of the screw is analyzed by Fluent software.

Using the research method of combining experiment and theoretical analysis, the screw rotation

Effects of different screw depths on temperature, apparent viscosity, velocity and plasticizing abilityThe volumetric pass rate at the outlet of the screw homogenizing section is analyzed to optimize theScrew speed of injection molding machine production process parameters.

1 Theoretical analysisIn this paper, the homogenization of LYH680 plastic injection molding machine is simulated by Fluent.Section of pipe fluid, set different screw speed, analysis of homogenization section of the pipeThe volumetric transit rate at the outlet of the propylene fluid homogenization section is obtained.The apparent viscosity of PP melt and the plasticizing ability of screw were investigated. Phase of injection molding machineThe relevant parameters are: the length of the homogenized section of the screw is 80 mm, and the temperature of the barrel in the homogenizing section is setSet at 220 C, the melt pressure in the homogenizing section is 1.5 MPa, and the depth of the screw groove is 2.2Mm, screw screw angle is 17.66 °, screw length-diameter ratio is 19.6, screw diameter32 mm; The melt density of polypropylene (PP) was 770 kg / m3The melting point is 170 °C, the thermal conductivity coefficient of the melt is 0.182W / (m · °C), and the melt ratioHeat capacity of 2900 J / (kg · C), melt viscosity of 421 Pa · s (453 K / 320)Pa·s（463 K）/250 Pa·s（473 K）。 In practical engineering, consider the fluidThe density changes little due to the fact that the molten polymer is sheared in the injection molding machine when premolded.Shear rate is less than 10-3 m / s, at which time the melt is located in the non-Newtonian rheological region of the first In this region, the melt polymer can be regarded as a Newtonian fluid, so the PP melt is regarded as an incompressible laminar Newtons fluid in the theoretical and experimental test analysis.

• Establishment of the coordinate system

The original rotating channel through which the material passes is stretched into a cuboid channel,The three-dimensional space model constructed from the origin is shown in Figure 1 sa Figure 3.

1.2 The Establishment of Fluid Governing Equation (φ) + div (π φ) = div (γ gradphi) + S. (1) Where φ is a generalized physical variable; The generalized diffusion coefficient corresponding to phi; S is a generalized source term.

According to the Guangyi method, the equation of conservation of mass and momentum is established at the entrance of the homogenization section of x-y plane (z = 0).

dV

ρ

Z = – del Pb + π F + δ V.

(2) In the dt formula: rho is the melt density, kg / m3; Vz is the flow velocity in z direction, m / s, entering the spiral groove in the homogenization region; F is the acceleration of gravity, m / s2; Pb is back pressure, Pa; Is the melt viscosity,

Pa·s; T for time, s; ▽为哈密顿算子，▽= ∂ i+ ∂ j+ ∂ k。 ∂x ∂y ∂z

Equation (2) is the momentum equilibrium equation (N-S equation) of viscous fluid, the fluid in the spiral groove is regarded as isothermal flow; The viscosity and density fields are uniform. The width of the spiral groove is much larger than the depth of spiral groove, and the effect of the screw side wall is ignored. The melt flows fully along the screw channel, ignoring the flow effect of the inlet and outlet, but considering the effect of the reverse back pressure. The N-S equation is simplified by the above conditions:

2

dp

dy=1·b。 (3) dy2eta dx

Integrate y twice and give boundary conditions (y = 0, Vz = 0; Y = h, Vz = π NDcos theta / 60). The flow velocity distribution state function in the direction of the melt is obtained, iyon ay

NDyπ cos theta hy-y2pb

Vz = 120h – 2eta × Lsintheta. (4)

Where h is the depth of the screw groove in the homogenization section, m; The helix angle of the screw, (°); L is the length of homogenized segment, m; N is screw speed, r a d / m i n; D is the straight diameter of the screw rod, m.

1.3 Calculation of theoretical plasticizing capacity

Substituting Eq. (4) into the flow definition equation, Q = WhVz = π DhVzsintheta, gives

22 32

Mpt = Qπ = π D Nhрsin θ cos θ – π Dhsin

Pitch. (5) 120 12 L where: W is the width of the fluid section, m; MPT is the Theoretical Plastic of Screw Type Plastic Injection Molding Machine

Chemical capacity, kg / s; Q is the volume pass rate of melt homogenization section, m3 / s. Through equation (5), it can be seen that the plasticizing ability of the screw is affected by a variety of process parameters such as screw diameter, screw groove angle, melt pressure and screw groove depth. The higher the screw speed, the stronger the plasticizing ability; When the apparent viscosity of melt increases, the plasticizing ability of screw increases.

Experimental results and simulation analysis

2.1 Simulation analysis and results

1) Conditions for simulation analysis.

The inlet end face: from the velocity distribution state function in the z direction of the melt (tulad ng (4)), the velocity at the inlet of the homogenizing section changes with the y value. Now N = 120, 140, 160, 180 rad / min are substituted into Vz respectively, and the initial simulated velocity along the spiral direction at the entrance of the homogenization section is determined through the function definition of Fluent with its own programming language UDF, iyon ay, the initial velocity under simulated and measured conditions; Dahil ang natutunaw na presyon sa inlet ay mas mababa kaysa sa presyon ng ulo ng tornilyo, ang presyon sa inlet ng seksyon ng homogenization ay 0; Ayon sa mga parameter ng proseso ng PP materyal at kagamitan, ang

Ang temperatura ng pagkatunaw ay nakatakda sa 465 K. Kaliwa at kanang bahagi ng pader: Eroplano ng Y-Z (x = 0), (x ay katumbas ng 3.2 × 10-2 m) bilang homogenization segments

Ang dalawang panig ng pader ng tornilyo groove ay nakatakda bilang mga pader na hindi madulas, at ang temperatura ng pagtunaw ay ang temperatura ng tornilyo, na nakatakda na 473 K according to the PP material characteristics and the actual condition of the equipment.

Upper and lower sidewalls: x-z plane (y = 0), (y = 2.2 × 10-3 m) as the lower and upper sides of the screw groove of the homogenization section, the lower side is regarded as a non-slip wall, the melt temperature is the screw temperature, and the temperature is set to 473 K according to the material characteristics of PP and the actual condition of the equipment; The upper side of the screw groove in the homogenization section is the contact surface of the melt and the barrel, the melt flow rate is the maximum, and the melt temperature is equal to the barrel heater temperature, na nakatakda na 493 K according to the production conditions of the PP material.

Outlet end face: the x-y plane (z = 0.264 m) as the outlet of the homogenization section, the pressure outlet boundary is adopted, where the pressure is opposite to the z direction, and the pressure is set to match the experimental equipment for easy analysis and comparison, and the back pressure is set to -1.2 MPa.

• Simulation analysis results

For x = 0.01, the curve diagram of velocity, temperature and viscosity at the exit of the homogenization section as a function of the depth of the spiral groove is shown in Figures 4 sa 6.

We can see from Figure 4 that with the increase of screw speed, the speed of the homogenization section at the exit also increases, with the increase of the depth of the screw groove, the speed first decreases and then increases, which is due to the shear force and viscosity on the upper and lower surfaces of the screw groove, in line with the polymer fluid in the plate.

Changes between. As we can see from Figure 4, with the increase of screw speed, The velocity at the outlet of homogenizing section also increases. With the increasing of the groove depth, the velocity decreases first and then increases. This is due to the large shear force and viscosity on the upper and lower surfaces of the groove, which is consistent with the change of polymer fluid between plates. Temperature change in the radial direction as shown in FIG. 5. The PP melt is in contact with the screw at the bottom (y = 0), above contact with the screw (y = 0.0022m) heat conduction occurs, heat from the bottom, the upper into the melt, the temperature from both sides inward downward trend, forming a concave temperature curve. With the increase of screw speed, the speed increases, the heating time in the runner decreases, and the temperature decreases with the increase of the number of revolutions. As shown in FIG. 6, the apparent viscosity of the melt first increases and then decreases with the increase of the spiral height, Contrary to the temperature curve, the apparent viscosity is the lowest at the top of the highest melt temperature, and the apparent viscosity is the highest at the middle of the lowest melt temperature. With the increase of screw speed, the apparent viscosity of the melt is higher and higher, and the apparent viscosity uniformity decreases. It can be seen that the apparent viscosity of PP melt is inversely proportional to temperature, which shows the accuracy of simulation.

It can be seen from Figure 6 that the viscosity is not fixed in the Fluent simulation, so we take the average viscosity at the exit of the homogenization section at x = 0.01 dito, because the viscosity changes here through the data comparison.

The viscosity that is closest to the theoretical calculation.

2.2 Measurement and Analysis of Plasticizing capacity

After preheating the injection molding machine, the polypropylene raw material is put into the funnel for plasticity. The rotating speed parameters of the screw are set at 120,140,160,180 r/min, the temperature of the homogenized section is set at 220 °C, and the melt pressure in the homogenizing section is set at 1.2 MPa. The storage time t at each rotating speed is recorded with a stopwatch, and then the empty feed is set.

Pagkatapos ng iniksyon, after the injection is cooled, the mass m of the injection is collected and measured, and the actual plasticizing ability mps is obtained by mps = 1000m/t. The comparison results with the theoretical plasticizing ability mpt under the same conditions are shown in Fig. 7.

Figure 7 shows that the theoretical plasticizing capacity and screw speed of the screw approximate a function

With the increase of screw speed, the plasticizing ability of screw is enhanced, and the actual screw screw

Rod plasticizing ability is lower than the theoretical plasticizing ability, the actual plasticizing ability of the injection molding machine at the speed of 120 ~ 180 rad / min accounts for 82% ~ 86% of the theoretical plasticizing ability, indicating that the injection molding machine screw plasticizing ability is above the average level. 2.3 Error analysis

There are differences between the actual plasticizing ability and the theoretical plasticizing ability of the screw, nothing more than these points: 1) part of the material forms a molten film during the plasticizing process, resulting in the leakage of the material; 2) The leakage of spiral pressure was not considered in the theoretical plasticizing ability analysis, which caused some materials to stay on the spiral edge. 3) In addition to the heat transmitted by the barrel heater, the material is more from the shear heat of the screw and the friction between the materials, resulting in the thermal decomposition of part of the material.

With the increase of screw speed, the actual plasticizing ability is slowing down, there are the following points: 1) With the increase of screw speed, the shear heat of the screw is increasing, resulting in the thermal decomposition of part of the material; 2) The increase in temperature reduces the viscosity of the material, increases the reverse pressure, hinders the progress of the material, and causes the actual plasticizing energy to slow down.

Conclusion With the increase of screw groove depth, the uniformity of temperature and apparent viscosity decreased, and the plasticizing ability increased, but the precision of product quality decreased. The plasticizing ability increased with the screw speed increasing, but the uniformity of temperature and apparent viscosity decreased with the increase of screw speed. Increasing the temperature of the screw helps to promote the apparent viscosity uniformity and improve the quality accuracy of the product; In order to ensure product quality and improve production efficiency, the depth, temperature and screw speed should be optimized.