JP7192405B2 - Mold and mold design method - Google Patents

Description

The present invention relates to a mold and a method of designing a mold.

Patent Literature 1 discloses an invention about a mouthpiece attached to a cylinder of an extruder for extruding a rubber composition. According to Patent Literature 1, by forming a retention space on the surface of the die plate including the die on the side where the rubber composition flows, it is possible to contribute to the improvement of the quality of the molded rubber sheet.

JP 2018-086734 A

According to Patent Document 1, in the die plate in which the retention space is formed, the shape of the end portion in the width direction of the rubber sheet is formed better than in the die plate in which the retention space is not formed. However, as the pressure of the viscoelastic material increases in the retention space, the viscoelastic material exerts a force to open the gap between the die plate and the holder used together with the die plate, and the viscoelastic material may protrude from the gap. be. The protruding viscoelastic material may adhere to the molded product and affect the shape of the molded product.

An object of the present invention is to provide a mold and a method of designing the mold for obtaining a molded product with a good shape.

A mold according to a first aspect of the present invention is a mold used for extrusion molding, and includes a channel defining portion defining a channel in which a viscoelastic material flows. The outlet of the channel has a longitudinal direction and a lateral direction, and the channel defining portion is arranged at at least one end of the channel in the longitudinal direction from a portion other than the at least one end. The channel is defined so that the length of the channel is also short.

A mold according to a second aspect of the present invention is the mold according to the first aspect, wherein the flow path defining portion has a short length of the flow path at the at least one end near the outlet. It is notched so that it becomes

A mold according to a third aspect of the present invention is the mold according to the second aspect, wherein the flow path defining portion includes a die plate. The die plate is notched near the outlet such that the channel length is reduced at the at least one end.

A mold according to a fourth aspect of the present invention is the mold according to the third aspect, wherein the flow path defining portion further includes a preformer. The preformer is notched near the outlet such that the length of the channel is reduced at the at least one end.

A mold according to a fifth aspect of the present invention is the mold according to any one of the first aspect to the fourth aspect, wherein the flow path defining portion has a length of the flow path along the longitudinal direction. The flow path is defined so as to be continuously variable.

A mold according to a sixth aspect of the present invention is the mold according to any one of the first aspect to the fifth aspect, wherein the flow path defining portion is provided at both ends of the outlet in the longitudinal direction. The channel is defined so that the length of the channel is shorter than that of the portion other than the portion.

A mold according to a seventh aspect of the present invention is the mold according to any one of the first aspect to the sixth aspect, further comprising a relief surface continuous to the outside of the outlet of the flow path defining portion.

A method for manufacturing a molded article of viscoelastic material according to an eighth aspect of the present invention comprises the following.
(1) Prepare a mold according to any one of the first to seventh aspects.
(2) molding the viscoelastic material by flowing the viscoelastic material through the channel of the mold;

A method of designing a mold according to a ninth aspect of the present invention is a method of designing a mold used for extrusion molding, and includes the following.
(1) Determining the shape of the outlet of the flow path through which the viscoelastic material flows in the mold.
(2) determining the length of the channel so that at least one end of the channel in the longitudinal direction of the outlet is shorter than a portion other than the at least one end;

The mold defines the shape of the molded product by the shape of the outlet of the flow channel inside. At the longitudinal end of the outlet of the flow path, the frictional resistance of the inner wall surface of the mold against the flow of the viscoelastic material is greater than the frictional resistance at other portions, and the flow speed of the viscoelastic material tends to be extremely reduced. As a result, the speed at which the viscoelastic material is expelled from the mold varies greatly along the length of the exit, causing partial contraction and relaxation of the molded product. As a result, irregularities may occur in the shape of the molded product, and the ends of the molded product may be partially broken. According to the mold according to the first aspect of the present invention, the flow path defining portion defines the flow path so that the length of the flow path becomes short at at least one end in the longitudinal direction of the outlet. With this configuration, the frictional resistance at the ends is reduced, and the decrease in the flow velocity at the ends is suppressed. As a result, unevenness and breakage occurring in the molded article can be suppressed, and the viscoelastic material can be molded into a favorable shape.

Sectional drawing of the metal mold|die which concerns on one Embodiment of this invention. FIG. 4 is a perspective view of a flow channel shape defined by a head and a mold; The perspective view of a die plate. The perspective view of a die plate. The shape of the channel outlet. FIG. 4 is a perspective view of the upper plate portion of the die plate; The shape of the channel defined by the mold according to the example. The shape of the flow path defined by the mold according to the comparative example. Graph of velocity distribution at the exit obtained by simulation.

A mold and a mold design method according to an embodiment of the present invention will be described below with reference to the drawings.

<1. Overview of Extrusion>
A mold 1 according to this embodiment is a mold used for extrusion molding, and constitutes a part of an extruder. The mold 1 is attached to the head 100 at the tip of the cylinder of the extruder for the viscoelastic material 5, and is a mold for molding the viscoelastic material 5 discharged from the head 100 into a predetermined shape. It has a plate-like appearance. The viscoelastic material 5 put into the extruder is heated and melted in the cylindrical cylinder. At the same time, the screw housed inside the cylinder and extending in the axial direction of the cylinder rotates, kneading the viscoelastic material 5 and pushing it out to the head 100 . FIG. 1 shows a cross-sectional view of a mold 1 according to this embodiment mounted on heads 100 , 100 . In the example shown in the figure, two heads 100, 100 at the ends of two cylinders are both connected to the mold 1. As shown in FIG. The direction of the arrow indicates the direction in which the viscoelastic material 5 flows. The viscoelastic material 5 extruded from the two heads 100, 100 may be the same type of material or different types of material.

The viscoelastic material 5 discharged from the heads 100 , 100 flows from the outlets 101 , 101 of the heads 100 , 100 into the mold 1 through the inlet 20 , which is an opening on the upstream side of the mold 1 . The viscoelastic material 5 that has flowed in flows through the flow path defined by the flow path defining portion 10 provided in the mold 1, and is continuously discharged as the molded product 6 from the outlet 31, which is an opening on the downstream side of the mold 1. Or it is discharged intermittently. The molded product 6 is taken up at a constant speed by a device such as a take-up conveyor located downstream of the extruder and sent to the next process.

<2. Composition of mold>
A mold 1 according to this embodiment is configured by combining a preformer 2 defining a flow path of a viscoelastic material 5 and a die plate 3 . That is, the flow path defining portion 10 in this embodiment includes the preformer 2 and the die plate 3 . The preformer 2 is located on the most upstream side (on the side of the heads 100 and 100) in the mold 1, and is the part where the inlet 20 of the mold 1 is formed. The preformer 2 defines a first channel 22 for preforming prior to forming the viscoelastic material 5 . The first flow path 22 is defined by the inner wall surface 21 of the preformer 2 . The viscoelastic material 5 flows into the preformer 2 from the inlet 20, flows through the first channel 22, and then enters the die plate 3 through the receiving port 30 of the die plate 3 connected to the outlet 23. and discharged. FIG. 2 shows a perspective view of the shape of the flow path of the viscoelastic material 5 defined by the heads 100, 100, the preformer 2 and the die plate 3. FIG. The code in parentheses is the code of the portion that defines the portion of the channel.

3A is a perspective view of the die plate 3 showing the receiving port 30 side of the die plate 3, and FIG. 3B is a perspective view of the die plate 3 showing the discharge port 31 side of the die plate 3. FIG. The die plate 3 is used in a state of being integrated with the preformer 2 by bolts or the like. The die plate 3 of this embodiment is formed by integrating an upper plate portion 3a and a lower plate portion 3b with bolts or the like, and has a substantially plate-like appearance as a whole. The upper plate portion 3a has a curved flow path forming surface 32 on the side facing the lower plate portion 3b, and the lower plate portion 3b has a flat flat surface 33 on the side facing the upper plate portion 3a. In a state in which the upper plate portion 3a and the lower plate portion 3b are integrated and the flow path forming surface 32 and the flat surface 33 face each other, the flow path forming surface 32 and the flat surface 33 define a second flow path .

FIG. 4A shows the shape C of the outlet of the second channel 34 . The shape C is a shape obtained by projecting the shape of the outlet of the second flow path 34 when viewed from the discharge port 31 side onto a plane orthogonal to the direction in which the viscoelastic material 5 flows. The circumscribing quadrilateral of shape C is a horizontally long rectangle. The direction in which the long sides of the rectangle extend is referred to as the longitudinal direction, and the direction in which the short sides extend is referred to as the lateral direction. The two longitudinal ends of shape C are called E1 and E2, respectively. Note that the shape C substantially matches the shape of the molded product 6 molded from the viscoelastic material 5 .

FIG. 4B is a perspective view of the upper plate portion 3a showing the discharge port 31 side. The flow path forming surface 32 extends continuously downstream from the receiving port 30, and the downstream terminal portion L (indicated by a broken line in the figure) of the flow path forming surface 32 terminates the flow path of the viscoelastic material 5. stipulate. That is, the outlet of the second flow path 34 is defined by the downstream end portion L and the flat surface 33 . As shown in the figure, the downstream end portion L is located closest to the discharge port 31 at the central portion in the longitudinal direction, and the upstream end portion L is located farther from the discharge port 31 as it approaches the ends E1 and E2 from the central portion. located on the side. As a result, as shown in FIG. 2, at the ends E1 and E2, the length of the channel of the viscoelastic material 5 starting from the outlet 101 of the head 100 (or the inlet 20 of the preformer 2) is It is formed so as to be shorter than the length of the channel in other portions. Although not limited to this, in the present embodiment, the length of the channel changes continuously over the longitudinal direction.

A downstream end portion L of the flow path forming surface 32 continues to the relief surface 35 . The relief surface 35 is a slope that continues to the outside of the outlet of the second flow path 34 and that is inclined with respect to the direction in which the second flow path 34 extends. incline. That is, the die plate 3 is formed so that the cross-sectional area of the opening expands from the outlet of the second channel 34 toward the discharge port 31 . Note that even if the viscoelastic material 5 passes through the space defined by the relief surface 35 and the flat surface 33 after being formed by the second flow path 34, the viscoelastic material 5 is not formed by that space. Therefore, the space defined by the relief surface 35 and the flat surface 33 is distinguished from the channel through which the viscoelastic material 5 flows.

The mold 1 is made of metal, typically steel. The preformer 2 and the die plate 3 may be made of different materials or may be made of the same material. Also, the upper plate portion 3a and the lower plate portion 3b may be made of different materials, or may be made of the same kind of material.

The viscoelastic material 5 is a polymeric material having both viscous and elastic properties, and includes rubber, resin, compositions containing rubber, compositions containing resin, and the like.

<3. Mold design method>
Below, the design method of the metal mold|die 1 which concerns on one Embodiment is demonstrated.

First, the shape of the outlet of the channel in the mold 1, that is, the shape C of the outlet having the longitudinal direction and the lateral direction of the channel through which the viscoelastic material 5 flows is determined. The shape C is a shape obtained by projecting the shape of the outlet of the flow path of the mold 1 when viewed from the outlet side, onto a plane perpendicular to the direction in which the viscoelastic material 5 flows. Here, the longitudinal direction is the direction in which the long sides of the circumscribing rectangle of the shape C extend, and the lateral direction is the direction in which the short sides of the circumscribing rectangle of the shape C extend. The shape C substantially matches the shape of the molded product 6 molded from the viscoelastic material 5 and is appropriately determined according to the shape of the molded product 6 .

Next, the length of the flow path inside the mold 1 is determined. At this time, at least one end portion E of the shape C is formed to have a relatively shorter flow path than portions other than the end portion E. FIG. For example, the flow path can be relatively shortened by cutting out a portion of the flow path forming surface 32 that forms the flow path and forming the downstream end portion L on the upstream side of the end portion E. If the mold 1 is composed of multiple parts such as the preformer 2 and the die plate 3 , the downstream end L may be formed across the preformer 2 and the die plate 3 . Preferably, the downstream terminal portion L is formed continuously along the longitudinal direction.

Furthermore, it is preferable to form the die plate 3 with a relief surface 35 continuous to the outside of the outlet of the flow path defined by the downstream terminal portion L and the flat surface 33 . The relief surface 35 can be formed in the vicinity of the ejection port 31 of the die plate 3 by, for example, chamfering or grooving. When the relief surface 35 is formed by chamfering, the relief surface 35 preferably inclines toward the ejection port 31 by about 10 degrees or more with respect to the direction in which the viscoelastic material 5 is ejected.

<4. Features>
(1)
The mold 1 of the above embodiment defines the shape of the molded product 6 by the shape C of the outlet of the second flow path 34 inside. At the longitudinal end of the outlet in the second channel 34, the channel is formed to be relatively short. With this configuration, it is possible to reduce the extent to which the flow velocity of the viscoelastic material 5 at the ends is reduced relative to the flow velocity at other portions, and the flow velocity distribution along the longitudinal direction becomes nearly uniform. . As a result, shrinkage or relaxation of each part of the molded product 6 is reduced, and unevenness (wavy) in the shape of the molded product 6 is less likely to occur. In addition, the end portion of the molded product 6 is prevented from being partially broken (edge breakage), and the molded product 6 with a good shape can be obtained. Moreover, the mold 1 of the above-described embodiment can be applied to viscoelastic materials, which have been conventionally considered unsuitable for extrusion molding because they tend to cause waviness and edge breakage. Therefore, it can contribute to quality improvement of the molded product 6 and expansion of variation.

(2)
Furthermore, the mold 1 of the above-described embodiment has relief surfaces 35 near the ends E1 and E2. With this configuration, the flow paths at the ends E1 and E2 can be formed short. Furthermore, even if a phenomenon (die swell) occurs in which the molded product 6 swells after ejection, it is possible to prevent the molded product 6 from adhering to the mold 1 or adversely affecting the shape due to contact with the mold 1 . The relief surface 35 is formed by, for example, preparing a mold in which the length of the flow path is constant along the longitudinal direction, and cutting the flow path forming surface 32 of this mold from the upstream side with a reverse taper end mill. may be formed. As described above, the mold 1 can be manufactured easily by processing a mold having a constant flow path length, and thus has excellent productivity.

(3)
The mold 1 of the above-described embodiment can mold a molded product 6 with a good shape without providing a retention space like the die plate disclosed in Patent Document 1. Therefore, the force that causes the viscoelastic material 5 to widen the space between the upper plate portion 3a and the lower plate portion 3b is hardly applied to the die plate 3, and the viscoelastic material 5 does not protrude from the gap between the upper plate portion 3a and the lower plate portion 3b. is prevented.
(4)
In the method of designing the mold 1 of the above-described embodiment, the flow velocity distribution in the longitudinal direction can be made nearly uniform by forming the flow path short at least at one end of the outlet of the flow path. That is, since the shape C determines the portion where the flow path should be formed to be short, the effort of trial and error for designing the mold is saved, and the design efficiency of the mold 1 is improved. In addition, since the flow velocity is extremely reduced particularly at the ends in the longitudinal direction of the outlet, a sufficient effect can be obtained simply by shortening the flow path at the ends by, for example, notching.

<5. Variation>
Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the scope of the invention. For example, the following changes are possible. Also, the gist of the following modified examples can be combined as appropriate.

<5-1>
The mold 1 may contain only the die plate 3 without the preformer 2 . Further, as long as the die plate 3 is positioned on the most downstream side in the mold 1, the flow path defining portion 10 that defines the flow path of the viscoelastic material 5 is included in addition to the preformer 2 and the die plate 3. good too.

<5-2>
The die plate 3 is not limited to the structure formed from the upper plate portion 3a and the lower plate portion 3b as in the above embodiment. For example, the upper plate portion 3a and the lower plate portion 3b may be formed from a plurality of parts. Alternatively, the flow path of the viscoelastic material 5 may be formed inside one metal plate to form the die plate 3 . Further, the surface of the lower plate portion 3b forming the second flow path 34 may be a curved surface like the flow path forming surface 32 instead of the flat flat surface 33 .

<5-3>
The preformer 2 may be formed of, for example, an upper plate portion and a lower plate portion, like the die plate 3 of the above embodiment.

<5-4>
The number of heads 100 to which the mold 1 is attached is not limited to two, and may be one or three or more.

<5-5>
The portion where the channel is formed short is not limited to the end portion. For example, in addition to shortening the flow path at the ends, the distance is relatively smaller than other parts in the transverse direction of shape C, and the flow velocity of the viscoelastic material 5 is higher than that in other parts in the longitudinal direction. The channel may be formed short even at the relatively lowered position.

Examples of the present invention will be described below. However, the following examples are merely illustrative of the present invention, and the present invention is not limited thereto.

Three types of molds X, Y and Z were designed as an example, comparative examples 1 and 2. The mold X is the same mold as in the above embodiment. Further, the molds Y and Z differ from the mold 1 of the above embodiment only in the shape of the portion corresponding to the upper plate portion 3a of the die plate 3. As shown in FIG. A perspective view of the shape of the flow path defined by the die plate 3 included in the mold X is shown in FIG. 5A together with the dimensions of each part (unit: mm). In the die plate 3 of the above-described embodiment, the mold Y does not have the escape surface 35 formed on the upper plate portion 3a, and the length of the flow path of the viscoelastic material 5 does not change (the downstream terminal portion L and the discharge port It has the same configuration as the mold X except for the point that the periphery of the mold 31 is almost the same. The mold Z has retention spaces P1 and P2 formed by notching flow passage forming surfaces 32 in a substantially spherical shape at both ends of the receiving port 30 of the upper plate portion 3a. The mold Z has the same configuration as the mold Y except for the above points. A perspective view of the shape of the flow path defined by the die plate 3 included in the mold Z is shown in FIG. 5B together with the dimensions of each part (unit: mm). Moreover, the maximum length of the flow path of the die plate 3 included in the molds X, Y, and Z is 15 mm.

<1-1. Simulation>
Assuming that the same viscoelastic material is extruded under the same conditions for each of the molds X, Y, and Z, the flow velocity distribution of the viscoelastic material at the outlet of the flow channel of each mold is measured using a known CFD. simulated by the method. Analysis software used was STAR-CCM+ (registered trademark). The viscoelastic material 5 is a mixed material of the rubber composition 1 and the rubber composition 2 having different physical properties, and was modeled as a viscous body in the simulation. The simulation conditions are shown in Table 1 below. Also, the viscosity coefficient μ of the rubber composition is calculated by the following formula (1). In formula (1), G, H, and I are constants specific to the rubber composition, e is the base of natural logarithms, and T is the temperature (K) of the rubber composition. γ is the shear rate (1/s) and represents the velocity gradient of the rubber composition in the direction perpendicular to the wall surface. The wall slip velocity (m/s) is determined using F _slip (constant) and e (constant) in Table 1 by the method disclosed in applicant's patent No. 5,564,074. Here, α is the volume ratio of the rubber composition 1 contained in the viscoelastic material 5, and 0≦α≦1.

<1-2. Simulation results>
The flow velocity distributions of the viscoelastic material 5 at the outlets of the flow channels of Example, Comparative Examples 1 and 2 obtained by simulation are shown in the graph of FIG. Flow velocity is the flow velocity in the middle of the transverse distance. The vertical axis of the graph is dimensionless obtained by dividing the flow rate of the viscoelastic material 5 by the extrusion rate of the extruder. The horizontal axis of the graph is the non-dimensional position of the outlet of the channel in the longitudinal direction, and 1 and 0 in the longitudinal direction are both ends. As can be seen from the graph, in Comparative Example 1, the flow velocity was extremely low at both ends, whereas the flow velocity was high near the center in the longitudinal direction (0.4 to 0.8). In Comparative Example 2, compared with Comparative Example 1, the flow velocity near the center in the longitudinal direction (0.4 to 0.8) was lower, and the flow velocity at both ends was slightly higher. In the example, the speed at both ends was higher than in the comparative examples 1 and 2.

<2-1. Experimental conditions>
The molds X, Y, Z designed above were fabricated to mold the viscoelastic material 5 under conditions substantially similar to the simulation conditions described above. For molds X, Y, and Z, the shape of the molded product was confirmed visually.

<2-2. Experiment results>
As a result of visual observation, the following results were confirmed.
Comparative Example 1: Waviness occurred in the molded article 6 at a position corresponding to the vicinity of the center in the longitudinal direction of the outlet of the flow channel. No edge breakage was observed.
Comparative Example 2: Edge breakage and waviness did not occur, but the viscoelastic material 5 protruded from the gap between the upper plate portion 3 a and the lower plate portion 3 b of the die plate 3 .
Example: A molded article 6 having a good shape was obtained without edge breakage, waviness, or protrusion of the viscoelastic material 5 .

From the above experimental results, it was found that the embodiment prevents edge breakage and waviness, prevents the viscoelastic material 5 from protruding due to the provision of the retention space, and is effective in molding the molded product 6 satisfactorily. I found out.

1 Mold 2 Preformer 3 Die Plate 5 Viscoelastic Material 6 Molded Product 10 Channel Defining Part 22 First Channel 32 Channel Forming Surface 34 Second Channel 100 Head C Shape L Downstream End

Claims (9)

A mold used for extrusion,
A flow path defining portion defining a flow path in which the viscoelastic material flows,
The outlet of the channel has a longitudinal direction and a lateral direction, and has a shape in which the length along the lateral direction changes along the longitudinal direction ,
The flow path defining portion defines the flow path such that at least one end of the flow path in the longitudinal direction is shorter than the length of the flow path at a portion other than the at least one end. do,
Mold. The flow path defining portion is notched in the vicinity of the outlet such that the length of the flow path is shortened at the at least one end.
A mold according to claim 1 . The flow path defining portion includes a die plate,
The die plate is notched near the outlet such that the length of the flow channel is shortened at the at least one end.
A mold according to claim 2. the flow path defining portion further includes a preformer,
the preformer is notched at the at least one end near the outlet such that the length of the flow path is shortened;
A mold according to claim 3. wherein the flow path defining portion defines the flow path such that the length of the flow path changes continuously along the longitudinal direction;
A mold according to any one of claims 1 to 4. The flow path defining portion defines the flow path so that the length of the flow path is shorter at both ends in the longitudinal direction of the outlet than at portions other than the both ends.
A mold according to any one of claims 1 to 5. further comprising a relief surface continuous to the outside of the outlet of the flow path defining portion;
A mold according to any one of claims 1 to 6. preparing a mold according to any one of claims 1 to 7;
shaping the viscoelastic material by flowing the viscoelastic material through the channel of the mold;
A method of manufacturing a molded article of viscoelastic material. A method of designing a mold used for extrusion, comprising:
The shape of the outlet of the flow path through which the viscoelastic material flows in the mold has a longitudinal direction and a lateral direction, and a shape in which the length along the lateral direction changes along the longitudinal direction. and
Determining the length of the channel so that at least one end of the outlet in the longitudinal direction of the channel is shorter than a portion other than the at least one end.
How to design the mold.

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