Rheological design method of straight manifold hanger mold and its balanced flow channel

Abstract

The present invention discloses a straight manifold coat-hanger type mold and a rheological design method for a balanced flow channel thereof, wherein the flow blockage area of ​​the flow channel is designed as a flow blockage area I and a flow blockage area II with different thicknesses along the flow channel length direction, and the manifold is designed as a straight manifold with a constant cross-sectional size along the flow channel width direction. Without changing the inlet area, relaxation area and molding area of ​​the coat-hanger type mold flow channel, the flow behavior of the melt in the flow channel is analyzed, and based on the condition that the melt outlet flow rate is uniform along the flow channel width direction, the boundary curve of the two flow blockage areas is derived using rheological theory. The design method can theoretically design the flow channel structure and size of the coat-hanger type mold according to the molding conditions, and the designed flow channel has the advantages of a short flow blockage area length and good melt outlet flow rate uniformity.

Description

Technical Field

[0001] The invention relates to the technical field of mold design, and in particular to a straight manifold hanger-type mold and a rheological design method for a balanced flow channel thereof. Background Art

[0002] Hanger-type molds are widely used in the extrusion molding of plastic sheets and cast films. In order to ensure the uniformity of the transverse thickness of the product, the runner design of the hanger-type mold requires the melt to have a uniform outlet flow rate along the width of the runner. Based on the principle that the melt has a uniform outlet flow rate in the width of the runner and that the melt stays in the manifold and the choke zone for an equal time, the manifold size and trajectory are calculated for a single thickness choke zone. The designed hanger-type mold has a large choke zone length, which is difficult to use for the extrusion molding of wide sheets and cast films. The residence time of the melt in the manifold is extended to several times the residence time of the melt in the choke zone. The above method is improved to shorten the length of the choke zone of the runner, but the radius of the manifold increases, which significantly increases the residence time of the melt in the runner. The radius and trajectory of the manifold designed by this method are more complex, which increases the difficulty of mold manufacturing.

[0003] The runners of hanger-type molds used in industrial production mostly adopt the structure of straight manifolds and single-thickness flow-blocking areas. Due to the lack of design theory guidance, engineering usually adopts empirical design and improves the uniformity of melt outlet flow rate through mold trials and mold repairs. Adding a flow-blocking rod to the mold is also a common method to improve the uniformity of melt outlet flow rate. However, when the runner structure is poorly designed, it is difficult to make the melt outlet flow rate uniformity meet the molding requirements even if the flow-blocking rod is adjusted. Summary of the invention

[0004] The object of the present invention is to overcome the deficiencies of the prior art and to provide a straight manifold hanger-type mold with a short choke zone and good melt outlet flow rate uniformity.

[0005] Another object of the present invention is to provide a rheological design method for a balanced flow channel of a straight manifold coat-hanger type mold. The design method designs the flow channel obstruction area of ​​the coat-hanger type mold into two obstruction areas (i.e., obstruction area I and obstruction area II) with different thicknesses along the flow channel length direction (i.e., extrusion direction), and designs the manifold as a straight manifold with constant size along the flow channel width direction. Under the condition that the melt outlet flow rate is uniform along the flow channel width direction, the boundary curve of the two obstruction areas is deduced using rheological theory.

[0006] The technical solution of the present invention is: a straight manifold hanger-type mold, the flow channel of the straight manifold hanger-type mold includes an inlet area, a manifold, a flow blocking area, a relaxation area and a molding area arranged in sequence along the flow direction, the flow blocking area includes a flow blocking area I and a flow blocking area II designed along the length direction of the flow channel, the thickness of the flow blocking area I and the flow blocking area II are different, and the manifold is a straight manifold with a constant cross-sectional size along the width direction of the flow channel.

[0007] In the blocking area, the area close to the manifold is blocking area I, and the area close to the relaxation area is blocking area II; the thickness of blocking area I and the thickness of blocking area II are constant along the width direction of the flow channel.

[0008] The blocking zone I is provided with a spacing between the symmetry plane of the flow channel and the end of the flow channel and the manifold, and the blocking zone II is provided with a spacing between the symmetry plane of the flow channel and the end of the flow channel and the relaxation zone; the cross section of the manifold is circular, and the radius of the manifold remains unchanged along the width direction of the flow channel.

[0009] A rheological design method for a balanced flow channel of a straight manifold hanger-type mold is applicable to the flow channel design of a mold that is symmetrical along the width direction, and includes the following steps:

[0010] Constructing a physical model: Assumptions a. The melt is an incompressible fluid; b. The melt flow is a steady laminar flow, ignoring inertial force and volume force; c. The temperature of the melt remains unchanged during the flow; d. The melt flows only along the axial direction of the manifold in the manifold, and only flows along the extrusion direction in the flow resistance zone I, flow resistance zone II, relaxation zone and molding zone, and the flow of the melt in the manifold and the flow in the flow resistance zone I do not interfere with each other; e. Ignore the influence of the two side walls at the end of the flow channel on the melt flow;

[0011] Constructing the flow channel geometric model: the mold flow channel includes an inlet area, a manifold, a flow blocking area, a relaxation area and a molding area arranged in sequence along the flow direction; the flow blocking area is designed as a flow blocking area I and a flow blocking area II along the extrusion direction, and the thickness of the flow blocking area I and the flow blocking area II are different; the manifold is designed as a straight manifold with a constant cross-sectional size along the width direction of the flow channel;

[0012] The boundary curve between the choke zone I and the choke zone II is deduced using rheological theory: a coordinate system is constructed. Based on the uniform outlet flow rate of the melt along the width of the flow channel, the melt pressure in the manifold along the width of the flow channel is calculated, and the pressure drop from the entrance of the choke zone I to the exit of the choke zone II when the melt flows along the extrusion direction is calculated; based on the fact that the melt pressure in the manifold is equal to the melt pressure at the entrance of the choke zone I and the melt pressure at the exit of the choke zone II is constant along the width of the flow channel, the expression of the boundary curve between the choke zone I and the choke zone II in the coordinate system is obtained.

[0013] As a preferred embodiment, in constructing the flow channel geometric model, the area close to the manifold is the flow blocking area I, and the area close to the relaxation area is the flow blocking area II.

[0014] As a preferred embodiment, in constructing the flow channel geometric model, the thickness of the flow blocking area I and the flow blocking area II remains unchanged along the flow channel width direction.

[0015] As a preferred embodiment, in constructing the flow channel geometric model, the thickness of the flow blocking area I is less than the thickness of the flow blocking area II.

[0016] As a preferred embodiment, in constructing the flow channel geometric model, the thickness of the flow blocking area I is greater than the thickness of the flow blocking area II.

[0017] Preferably, the flow blocking area I is provided with a spacing between the position of the symmetric plane of the flow channel and the end of the flow channel and the manifold, and the flow blocking area II is provided with a spacing between the position of the symmetric plane of the flow channel and the end of the flow channel and the relaxation area.

[0018] As a preferred embodiment, in constructing the flow channel geometric model, the manifold cross section is circular, and the manifold radius remains unchanged along the flow channel width direction.

[0019] As a preferred embodiment, in constructing the flow channel geometric model, the thickness and length of the relaxation zone and the forming zone remain unchanged along the flow channel width direction.

[0020] As a preference, at any position in the flow channel width direction, the melt pressure in the manifold is equal to the melt pressure at the inlet of the choke zone I, and the melt pressure at the outlet of the choke zone II remains unchanged along the flow channel width direction.

[0021] As a preferred embodiment, the deduction process of rheological theory is:

[0022] The temperature of the melt remains unchanged during the flow process, and the viscosity of the melt is described by the power law model, that is,

[0023]

[0024] Where η is the melt viscosity; K is the consistency coefficient; is the shear rate; n is the power law exponent;

[0025] According to the symmetry of the flow channel in the width direction, half of the flow channel is taken for analysis. Ignoring the influence of the inlet area, the manifold cross section is circular, and the coordinate system is constructed with the flow channel width direction as the x-axis, the flow channel length direction as the y-axis, and the boundary line between the manifold and the flow resistance area I as the z-axis, as shown in Figure 2 shown.

[0026] The pressure gradient of the melt flowing along the manifold is

[0027]

[0028] Where p(z) is the pressure of the melt at point z in the manifold; Q(z) is the volume flow rate of the melt at point z in the manifold; R is the radius of the manifold;

[0029] Assuming that the volume flow rate of the melt at the flow channel inlet is 2Q0, and the melt outlet flow rate is required to be uniform along the flow channel width, the volume flow rate of the melt in the manifold along the manifold direction is

[0030] Q(z)=Q0(1-zsinθ / W) (3)

[0031] Where W is half of the channel width; θ is half of the expansion angle of the choke area;

[0032] Substitute equation (3) into equation (2) and integrate, assuming the melt pressure at the end of the manifold is p E ,have

[0033]

[0034] According to the coordinate system, we have

[0035] x=z sinθ (5)

[0036] p(x)=p(z) (6)

[0037] Where p(x) is the pressure of the melt at x in the manifold;

[0038] Substituting equations (5) to (6) into equation (4), we have

[0039]

[0040] Since the thickness and length of the relaxation zone and the forming zone are constant along the flow channel width, the melt pressure at the outlet of the blocking zone II is constant along the flow channel width when the melt outlet flow rate is required to be uniform along the flow channel width. The length of the blocking zone at the symmetry plane of the flow channel is L, and the melt pressure at the outlet of the blocking zone II (i.e. y = L) is p L At any position x in the flow channel width direction, when the melt flows in the obstruction zone along the extrusion direction, the pressure drop between the inlet of the obstruction zone I and the outlet of the obstruction zone II is

[0041]

[0042] Wherein, h1 and h2 are the thickness of the blocking area I and the blocking area II respectively; y is the boundary curve between the blocking area I and the blocking area II, which is a function of the coordinate x;

[0043] At the end of the channel width, that is, when x=W, y=y E , p(x)=p E , substituting into formula (8) we get

[0044]

[0045] From equations (7) to (9), we get

[0046]

[0047] The y in formula (10) is the expression of the boundary curve between the flow blocking area I and the flow blocking area II in the coordinate system.

[0048] As a preferred embodiment, the pressure drop of the melt flowing from the manifold inlet through the manifold and the choke zone along any path is equal, which can be expressed as the sum of the pressure drop of the melt flowing from the manifold inlet to the end of the manifold and the pressure drop of the melt at the end of the flow channel flowing through the end of the choke zone, that is,

[0049]

[0050] As a preferred embodiment, numerical simulation software is used to perform numerical simulation on the flow field of the melt in the flow channel, and the ratio of the volume flow rate per unit width at a certain position in the flow channel width direction at the melt outlet to the average volume flow rate per unit width is defined as the dimensionless flow rate of the melt outlet, which is used to reflect the uniformity of the melt outlet flow rate, and further verify the reliability of the dividing curve.

[0051] The principle of the present invention is as follows: in the flow channel of the hanger type mold, after the melt enters the manifold from the inlet area and flows along the manifold, a part of the melt enters the flow blocking area and flows into the relaxation area and the molding area along the extrusion direction. The melt pressure in the manifold decreases nonlinearly along the flow direction, that is, the melt pressure at the inlet of the flow blocking area decreases nonlinearly along the flow channel width direction. Under the condition that the cross-sectional shapes of the inlet area, the relaxation area and the molding area are not changed, the flow blocking area is designed as two areas (i.e., flow blocking area I and flow blocking area II) with different thicknesses along the flow channel length direction (extrusion direction), and the manifold is designed as a straight manifold with a constant cross-sectional size along the flow channel width direction. By designing the boundary curve between the flow blocking area I and the flow blocking area II, the pressure of the melt at the outlet of the flow blocking area II is constant along the flow channel width direction, or in other words, the pressure drop of the melt flowing from the manifold inlet through the manifold and the flow blocking area along any path is equal, thereby achieving the purpose of uniform melt outlet flow rate along the flow channel width direction.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The present invention designs the flow channel choke zone of the coat-hanger type mold into two areas with different thicknesses (choke zone I and choke zone II), and designs the manifold as a straight manifold with a constant cross-sectional size along the width direction of the flow channel. By analyzing the flow of the melt in the flow channel of the coat-hanger type mold, the flow channel structure and size are theoretically designed according to the rheological theory on the premise that the melt outlet flow rate is uniform along the width direction of the flow channel, and the boundary curve between the choke zone I and the choke zone II is deduced.

[0054] The present invention numerically simulates the flow behavior of the melt in the coat-hanger type mold runner designed by adopting the theoretical design method of the boundary curve between the choke I zone and the choke II zone, verifies the reliability of the boundary curve, and can be used to guide the design of the straight manifold coat-hanger type mold runner.

[0055] Compared with the existing design method of the straight manifold hanger type mold flow channel, the design method proposed by the present invention can effectively reduce the length of the flow resistance area and thus the length of the flow channel under the condition of uniform melt outlet volume flow rate.

[0056] Compared with the existing design method of straight manifold hanger type mold flow channel, the present invention can design the manifold radius, the length and expansion angle of the choke zone, the thickness of the choke zone I and the choke zone II and their boundary shape curve according to the molding requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 Schematic diagram of the runner structure of the straight manifold hanger-type mold designed for this patent.

[0058] Figure 2 Schematic diagram of the rheological design model of the straight manifold hanger-type mold flow channel in the embodiment.

[0059] Figure 3 It is the pressure contour line of the melt in the flow channel obtained by simulation calculation when n=0.4 in the embodiment.

[0060] Figure 4 It is the pressure contour line of the melt in the flow channel obtained by simulation calculation when n=0.6 in the embodiment.

[0061] Figure 5 It is the dimensionless flow rate per unit width along the width direction of one side of the flow channel obtained by simulation calculation when n=0.4 in the embodiment.

[0062] Figure 6 It is the dimensionless flow rate per unit width along the width direction of one side of the flow channel obtained by simulation calculation when n=0.6 in the embodiment.

[0063] As shown in the figure, 1 is the inlet area, 2 is the manifold, 31 is the flow blocking area I, 32 is the flow blocking area II, 4 is the relaxation area, and 5 is the forming area. DETAILED DESCRIPTION

[0064] The present invention will be further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0065] The present embodiment provides a rheological design method for a balanced flow channel of a straight manifold hanger-type mold, which is applicable to the flow channel design of a mold that is symmetrical along the width direction, and includes the following steps:

[0066] S1. Construct a physical model: Assumptions a. The melt is an incompressible fluid; b. The melt flows in a steady laminar flow, ignoring inertial force and volume force; c. The temperature of the melt remains unchanged during the flow; d. The melt flows only along the axial direction of the manifold in the manifold, and only flows along the extrusion direction in the flow resistance zone I, flow resistance zone II, relaxation zone and molding zone, and the melt flow in the manifold and the flow in the flow resistance zone I do not interfere with each other; e. Ignore the influence of the two side walls at the end of the flow channel on the melt flow.

[0067] S2. Construct the flow channel geometry model: Figure 1 As shown, the mold runner includes an inlet area 1, a manifold 2, a blocking area, a relaxation area 4 and a molding area 5 which are arranged in sequence along the melt flow direction; the blocking area is designed to be a blocking area I 31 and a blocking area II 32 with different thicknesses along the length direction of the runner, the area close to the manifold is the blocking area I, the area close to the relaxation area is the blocking area II, and the thickness of the blocking area I and the blocking area II are constant along the width direction of the runner; the blocking area I is provided with a spacing at the position of the runner symmetry plane and between the end of the runner and the manifold, and the blocking area II is provided with a spacing at the position of the runner symmetry plane and between the end of the runner and the relaxation area; the manifold cross-section is designed to be circular, and the radius of the manifold is constant along the width direction of the runner; the thickness and length of the relaxation area and the molding area are constant along the width direction of the runner.

[0068] S3. Use rheological theory to deduce the boundary curve between the flow-blocking zone I and the flow-blocking zone II: Construct a coordinate system, such as Figure 2 As shown, based on the uniform outlet flow rate of the melt along the width direction of the flow channel, the melt pressure in the manifold along the width direction of the flow channel is calculated, and the pressure drop from the inlet of the choke zone I to the outlet of the choke zone II when the melt flows along the extrusion direction is calculated; according to the melt pressure at the inlet of the choke zone I being equal to the melt pressure in the manifold and the melt pressure at the outlet of the choke zone II being constant along the width direction of the flow channel, the expression of the boundary curve between the choke zone I and the choke zone II in the coordinate system is obtained.

[0069] The deduction process of rheological theory is:

[0070] According to the symmetry of the flow channel width, half of the flow channel is taken for analysis. Ignoring the influence of the inlet area, the manifold cross section is circular and the size along the flow channel width direction is unchanged. Other shapes can be converted by the shape factor. The coordinate system is constructed with the flow channel width direction as the x-axis, the flow channel length direction as the y-axis, and the boundary line between the manifold and the flow blocking area I as the z-axis, as shown in Figure 2 shown.

[0071] The power law model is used to describe the shear viscosity of the melt, that is,

[0072]

[0073] Where η is the melt viscosity; K is the consistency coefficient; is the shear rate; n is the power law exponent.

[0074] The pressure gradient of the melt flowing along the manifold is

[0075]

[0076] Where p(z) is the pressure of the melt at point z in the manifold; Q(z) is the volume flow rate of the melt at point z in the manifold; and R is the radius of the manifold.

[0077] Assuming that the volume flow rate of the melt at the flow channel inlet is 2Q0, and the melt outlet flow rate is uniform along the flow channel width, the volume flow rate of the melt in the manifold along the manifold direction is

[0078] Q(z)=Q0(1-zsinθ / W) (3)

[0079] Where W is half of the channel width; θ is half of the expansion angle of the choke area.

[0080] Substitute equation (3) into equation (2) and integrate, assuming the melt pressure at the end of the manifold is p E ,have

[0081]

[0082] According to the coordinate system, we have

[0083] x=z sinθ (5)

[0084] p(x)=p(z) (6)

[0085] Where p(x) is the pressure of the melt at point x in the manifold.

[0086] Substituting equations (5) to (6) into equation (4), we have

[0087]

[0088] Since the thickness and length of the relaxation zone and the forming zone are constant along the flow channel width, the melt outlet flow rate is required to be uniform along the flow channel width, and the melt pressure at the outlet of the blocking zone II is constant along the flow channel width. The length of the blocking zone at the symmetry plane of the flow channel is L, and the melt pressure at the outlet of the blocking zone II (i.e. y = L) is p L At any position x in the flow channel width direction, when the melt flows in the obstruction zone along the extrusion direction, the pressure drop between the inlet of the obstruction zone I and the outlet of the obstruction zone II is

[0089]

[0090] Wherein, h1 and h2 are the thicknesses of the flow-blocking zone I and the flow-blocking zone II, respectively; y is the boundary curve between the flow-blocking zone I and the flow-blocking zone II, which is a function of the coordinate x.

[0091] At the end of the channel width, that is, when x=W, y=y E , p(x)=p E , substituting into formula (8) we get

[0092]

[0093] From equations (7) to (9), we can get

[0094]

[0095] The y in formula (10) is the expression of the boundary curve between the flow-blocking zone I and the flow-blocking zone I in the coordinate system.

[0096] It can be seen from formula (10) that the boundary curve between the choke zone I and the choke zone II is related to the flow channel width, the manifold radius, the thickness of the choke zone I and the choke zone II, the choke zone length and expansion angle, and the power law index n of the melt, but has nothing to do with the consistency and output of the melt.

[0097] When x = 0, the length of the flow blocking area I at the symmetrical position in the flow channel width direction can be obtained from formula (10):

[0098]

[0099] When designing the runner, it is necessary to comprehensively consider the dimensions of each part of the runner. At any position in the width direction of the runner, the flow blocking area I and the flow blocking area II should be properly spaced in the length direction of the runner to facilitate mold manufacturing.

[0100] The pressure drop of the melt flowing from the manifold inlet through the manifold and the choke area along any path is equal, which can be expressed as

[0101]

[0102] The first term on the right side of formula (12) is the pressure drop of the melt flowing from the manifold inlet to the end of the manifold, and the second term is the pressure drop of the melt flowing through the flow block I and flow block II at the end of the flow channel. When designing the flow channel, the extrusion pressure can be adjusted by designing the manifold radius, the thickness of the flow block I and flow block II, the length of the flow block, and the expansion angle.

[0103] S4. Verification: In order to verify the reliability of the boundary curve between the choke zone I and the choke zone II derived by the present invention, two melts with different power law indices are selected for flow channel design, and the flow field of the melt in the flow channel is calculated using numerical simulation software. The ratio of the volume flow rate per unit width at a certain position along the width direction of the flow channel at the melt outlet to the volume flow rate per unit width at the average unit width is defined as the dimensionless flow rate of the melt outlet, which is used to reflect the uniformity of the melt outlet flow rate and verify the reliability of the boundary curve between the choke zone I and the choke zone II derived above.

[0104] The sheet width (2W) is 2000 mm, the thickness and length of the relaxation zone are 4 mm and 40 mm, respectively, and the thickness and length of the forming zone are 2 mm and 20 mm, respectively. The power law model is used to describe the rheological properties of the melt, with n = 0.4 and K = 8000 Pa·s. -0.6 and n = 0.6, K = 8000 Pa·s -0.4 The radius of the manifold is 15 mm, the expansion angle (2θ) of the flow resistance zone is 177°, the length of the symmetric plane of the flow channel width is 40 mm, and y E Take 34mm, the thickness of the flow resistance zone II is 2.5mm, and the thickness of the flow resistance zone I is 1.2mm and 1.6mm when n is 0.4 and 0.6 respectively. The boundary curve between the flow resistance zone I and the flow resistance zone II can be calculated by formula (10). The flow channel is geometrically modeled using 3D design software, and half of it is taken for calculation according to the symmetry of the flow channel width direction.

[0105] Extrusion output (2Q0) is 80000mm 3 / s (i.e., the extrusion speed is 40 mm / s), and the melt pressure contours in the flow channel obtained by simulation calculation when n is 0.4 and 0.6 are as follows Figure 3 and Figure 4 As shown. It can be seen that when the melt leaves the choke zone, its pressure contour is parallel to the runner outlet, thus ensuring the uniformity of the melt outlet flow rate along the runner width direction. When n is 0.4 and 0.6, the pressure drop of the melt flowing from the manifold inlet along any path through the manifold and the choke zone obtained by numerical simulation is 4.91MPa and 8.28MPa, respectively, which is consistent with the calculation result of formula (12).

[0106] Figure 5 and Figure 6 The dimensionless flow rates of the melt outlet along the width direction of the flow channel obtained by numerical simulation when n is 0.4 and 0.6 respectively. The dimensionless flow rate of the melt outlet increases along the width direction of the flow channel and reaches the maximum value at about 20mm from the end of the flow channel. When n is 0.4, the dimensionless flow rate of the melt outlet increases from 0.995 to 1.005, and when n is 0.6, the dimensionless flow rate of the melt outlet increases from 0.997 to 1.003; then it begins to decrease, and only within a range of about 10mm from the end of the flow channel, the dimensionless flow rate of the melt outlet is less than 1. This is because the influence of the flow channel side wall on the melt flow is ignored in the theoretical derivation, and when the melt flow field is numerically simulated, there is a no-slip boundary between the melt and the side wall, which is consistent with actual production.

[0107] This embodiment is a straight manifold hanger type mold, such as Figure 1As shown, the flow channel of the straight manifold hanger-type mold includes an inlet area 1, a manifold 2, a flow blocking area, a relaxation area 4 and a molding area 5 arranged in sequence along the flow direction, the flow blocking area includes a flow blocking area 31 and a flow blocking area 32 designed along the length direction of the flow channel, the thickness of the flow blocking area I and the flow blocking area II are different, and the manifold is a straight manifold with a constant cross-sectional size along the width direction of the flow channel. In the flow blocking area, the area close to the manifold is the flow blocking area I, and the area close to the relaxation area is the flow blocking area II; the thickness of the flow blocking area I and the thickness of the flow blocking area II are constant along the width direction of the flow channel. The flow blocking area I is provided with a spacing at the position of the flow channel symmetry plane and between the end of the flow channel and the manifold, and the flow blocking area II is provided with a spacing at the position of the flow channel symmetry plane and between the end of the flow channel and the relaxation area; the cross section of the manifold is circular, and the radius of the manifold is constant along the width direction of the flow channel.

[0108] In addition to the methods mentioned in the above embodiments, for manifolds with other cross-sectional shapes, the melt pressure in the manifold can be converted by the shape factor, and then the boundary curves of the flow blocking zone I and the flow blocking zone II corresponding to the manifolds with different cross-sectional shapes are obtained. These transformation methods are all within the protection scope of the present invention.

[0109] In addition to the methods mentioned in the above embodiments, the boundary curve between the flow blocking area I and the flow blocking area II calculated by the above design method essentially determines the length of the flow blocking area I and the flow blocking area II at any position in the flow channel width direction. Therefore, the positions of the flow blocking area I and the flow blocking area II are swapped in the extrusion direction or decomposed into a combination of multiple areas to ensure that the outlet volume flow rate is uniform. These changes are all within the scope of protection of the present invention.

[0110] In addition to the above-mentioned embodiments, the chamfering or rounding transition between the flow blocking area I and the flow blocking area II does not affect the boundary curve between the flow blocking area I and the flow blocking area II. These changes are all within the protection scope of the present invention.

[0111] As described above, the present invention can be better implemented. The above embodiments are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention; that is, all equivalent changes and modifications made according to the content of the present invention are covered by the scope of protection required by the claims of the present invention.

Claims

1. A rheological design method for a balanced flow channel of a straight manifold hanger-type mold, characterized in that: The following steps are involved: Construct a physical model: set the conditions a. The melt is an incompressible fluid; b. The melt flow is steady laminar flow, and the inertia force and volume force are ignored; c. The temperature of the melt remains unchanged during the flow process; d. The melt only flows along the axial direction of the manifold in the manifold, and only flows along the extrusion direction in the flow blocking area I, flow blocking area II, relaxation area and molding area, and the flow of the melt in the manifold and the flow in the flow blocking area I do not interfere with each other; e. Ignore the influence of the two side walls at the end of the flow channel on the melt flow; Constructing the flow channel geometric model: the mold flow channel includes an inlet area, a manifold, a flow blocking area, a relaxation area and a molding area arranged in sequence along the flow direction; the flow blocking area is designed to be a flow blocking area I and a flow blocking area II along the length direction of the flow channel, and the thickness of the flow blocking area I and the flow blocking area II are different; the manifold is designed to be a straight manifold with a constant cross-sectional size along the width direction of the flow channel; Deducing the boundary curve between the choke zone I and the choke zone II: constructing a coordinate system, based on the uniform outlet flow rate of the melt along the width direction of the flow channel, calculating the melt pressure in the manifold along the width direction of the flow channel, and calculating the pressure drop from the entrance of the choke zone I to the exit of the choke zone II when the melt flows along the extrusion direction; according to the fact that the melt pressure at the entrance of the choke zone I is equal to the melt pressure in the manifold and the melt pressure at the exit of the choke zone II is constant along the width direction of the flow channel, the expression of the boundary curve between the choke zone I and the choke zone II in the coordinate system is obtained; In the blocking area, the area close to the manifold is the blocking area I, and the area close to the relaxation area is the blocking area II. The thickness of the blocking area I and the thickness of the blocking area II are constant along the width direction of the flow channel. The thickness and length of the relaxation zone and the forming zone remain unchanged along the width of the flow channel; The deduction process of rheological theory is: The temperature of the melt remains unchanged during the flow process, and the viscosity of the melt is described by the power law model. Where η is the melt viscosity; K is the consistency coefficient; is the shear rate; n is the power law exponent; According to the symmetry of the flow channel in the width direction, half of the flow channel is taken for analysis, the influence of the inlet area is ignored, the manifold cross section is circular, and other shapes are converted by shape factors. The coordinate system is constructed with the flow channel width direction as the x-axis, the flow channel length direction as the y-axis, and the boundary line between the manifold and the flow-blocking area I as the z-axis; The pressure gradient of the melt flowing along the manifold is Where p(z) is the pressure of the melt at point z in the manifold; Q(z) is the volume flow rate of the melt at point z in the manifold; R is the radius of the manifold; The volume flow rate of the melt at the flow channel inlet is set to 2Q0, and the melt outlet flow rate is required to be uniform along the flow channel width. The volume flow rate of the melt in the manifold along the manifold direction is Q(z)=Q0(1-zsinθ / W) (3) Where W is half of the channel width; θ is half of the expansion angle of the choke area; Substitute equation (3) into equation (2) and integrate, assuming the melt pressure at the end of the manifold is p E ,have According to the coordinate system, we have x=zsinθ (5) p(x)=p(z) (6) Where p(x) is the pressure of the melt at x in the manifold; Substituting equations (5) to (6) into equation (4), we have Since the thickness and length of the relaxation zone and the forming zone are constant along the flow channel width, the melt outlet flow rate is required to be uniform along the flow channel width, and the melt pressure at the outlet of the blocking zone II is constant along the flow channel width; the length of the blocking zone at the symmetric plane of the flow channel is L, and the melt pressure at the outlet of the blocking zone II when y=L is p L At any position x in the flow channel width direction, when the melt flows in the obstruction zone along the extrusion direction, the pressure drop between the inlet of the obstruction zone I and the outlet of the obstruction zone II is Wherein, h1 and h2 are the thickness of the blocking area I and the blocking area II respectively; y is the boundary curve between the blocking area I and the blocking area II, which is a function of the coordinate x; At the end of the channel width direction, when x=W, y=y E , p(x)=p E , substituting into formula (8) we get From equations (7) to (9), we get The y in formula (10) is an expression of the boundary curve between the flow-blocking zone I and the flow-blocking zone II in the coordinate system.

2. The rheological design method for a straight manifold hanger-type mold balanced flow channel according to claim 1, characterized in that: The thickness of the flow-blocking region I is smaller than the thickness of the flow-blocking region II, or the thickness of the flow-blocking region I is larger than the thickness of the flow-blocking region II.

3. The rheological design method for a straight manifold hanger-type mold balanced flow channel according to claim 1, characterized in that: The blocking zone I is provided with a distance between the symmetric plane of the flow channel and the end of the flow channel and the manifold, and the blocking zone II is provided with a distance between the symmetric plane of the flow channel and the end of the flow channel and the relaxation zone.

4. The rheological design method for a straight manifold hanger-type mold balanced flow channel according to claim 1, characterized in that: The cross section of the manifold is circular, and the radius of the manifold remains constant along the width of the flow channel.

5. The rheological design method for a straight manifold hanger-type mold balanced flow channel according to claim 1, characterized in that: At any position along the width direction of the flow channel, the melt pressure in the manifold is equal to the melt pressure at the entrance of the choke zone I, and the melt pressure at the exit of the choke zone II remains unchanged along the width direction of the flow channel.

6. The rheological design method for a straight manifold hanger-type mold balanced flow channel according to claim 1, characterized in that: Numerical simulation software is used to simulate the flow field of the melt in the runner. The ratio of the volume flow rate per unit width at a certain position along the width direction of the runner at the melt outlet to the average volume flow rate per unit width is defined as the dimensionless flow rate of the melt outlet. It is used to reflect the uniformity of the melt outlet flow rate, and then verify the reliability of the boundary shape curve.

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