JP3187021B2 - Screw structure of injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a screw structure of an injection molding machine.

[0002]

2. Description of the Related Art A general conventional example of a screw in an injection molding machine is shown in FIG. As shown in FIG. 6, the screw 100 of the injection molding machine has a supply section A for biting resin pellets supplied through a resin intake port of a cylinder.
A compression unit B for gradually compressing the resin sent from the supply unit A and melting it by shearing heat or frictional heating;
And it is integrally formed by the measuring part C for storing the molten resin.

Generally, a groove width W between flights 101 in a screw 100 is set within a range of 80% to 90% of a flight pitch P over the entire length of the screw 100. Further, the groove depth d is formed deepest in the supply section A for biting the resin pellets, gradually becomes shallow in the compression section B, compresses the resin, and melts the resin by shear heat and frictional heat. The molten resin is filled into the reservoir at the tip of the cylinder via the measuring section C and a check ring (not shown).

[0004] Adjustment of shear heat and frictional heat is performed by adjusting the ratio (compression ratio) between the groove depth d 'in the measuring section C and the groove depth d in the supply section A, but the compression ratio is too small. As a result, the amount of heat generated by shearing and the amount of heat generated by friction are reduced, and the melting of the resin becomes incomplete.

On the other hand, if the compression ratio is too large, the amount of heat generated by shearing and the amount of heat generated by friction become excessive, and problems such as decomposition of the resin arise. Generally, a compression ratio in the range of 1.0 to 3.0 is considered appropriate.

In a general molding operation, in addition to virgin pellets, a recycled material obtained by crushing a runner or a defective molded product with a crusher is often used as a pellet. Since it may be mixed, it is necessary to eliminate the bridge generated near the resin intake of the cylinder to improve the bite of the molding material. I have.

However, since a female screw for attaching a check ring required for preventing backflow of resin at the time of injection must be cut into the tip of the measuring section C, particularly,
In the case of the thin screw 100, it is difficult to design the groove depth d 'in the measuring part C deeply. If the groove depth d' in this part is too deep, the molten resin passes through the check ring. In this case, an extreme compressive force acts to cause an excessive shear heating effect or friction heating effect, which causes problems such as decomposition of the resin and breakage of the glass fiber in the resin. It is not preferable to increase the groove depth d 'in C.

Accordingly, if the groove depth d in the supply section A is formed deep to improve the biting of the resin pellet,
As a result, there arises a problem that the ratio of the groove depth d in the supply section A to the groove depth d 'in the measurement section C, that is, the above-mentioned compression ratio becomes unnecessarily large, and an appropriate compression ratio is realized. It is difficult to simultaneously achieve the condition of the groove depth of the supply unit A for achieving the condition of the groove depth of the supply unit A and the groove depth of the supply unit A favorable for the biting of the molding material.

As a screw structure for solving such a problem, the flight pitch P of the supply section A is fixed.
Japanese Unexamined Patent Publication No. 9-3 discloses a configuration in which the flight pitch P of the compression section B and the measuring section C is made larger than that of the compression section B to lower the compression ratio of the resin.
Japanese Patent Application Laid-Open No. 9-300413 proposes a device in which the flight pitch P is gradually increased between the compression section B and the measuring section C to lower the compression ratio of the resin. It only mentions the liquid phase resin after that, and the problems of the shear heat generation effect and the friction heat generation effect in the supply section A (particularly the heat generation and friction problem in the pellets in a solid state) and the resin in the supply section A No mention is made of the problem of pellet entrapment.

Further, as a configuration for preventing the generation of excessive shearing heat and frictional heating in the vicinity of the supply section A, the flight pitch P is kept constant at the upstream portion of the supply section A, and from the lower part of the hopper to the compression section. Japanese Patent Application Laid-Open No. Hei 9-314625 proposes a method in which the flight pitch P is gradually increased over B to lower the compression ratio of the resin.

However, in this case, since the flight groove depth d in the supply section A is constant, the supply section A is connected to the compression section B.
In order to communicate smoothly, the groove depth d of the supply section A must be adjusted to the groove depth of the compression section B, and the supply section A is adjusted to a depth suitable for biting resin pellets made of recycled material or the like. In some cases, the groove depth d cannot be increased. Also,
It merely mentions the resin in the liquid phase after it has been melted in the same manner as described above, and relates to the problem of the shear heat generation effect and the friction heat generation effect in the supply section A (particularly, the heat generation and the friction problem of the pellets in a solid state). Did not even mention.

[0012]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned disadvantages of the prior art, and to prevent an excessive shear heating action or friction heating action in a supply section without distinction between a solid phase and a liquid phase. In addition, the screw structure of an injection molding machine that can smoothly bite coarse resin pellets made of recycled materials, etc., and minimize resin melting unevenness in flight grooves To provide.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a resin flow path cross-sectional area in a screw groove (when a gap formed between a flight and a screw valley bottom surface and a cylinder inner peripheral surface is cut along a central axis direction of a screw). the size of the cross-sectional area) to the total feed portion
The above object has been achieved by providing a section in which a flight is formed so as to gradually expand from the upstream portion to the most downstream side over the region .

Since the cross-sectional area of the resin flow path in the supply portion of the screw is increased from the most upstream portion to the downstream side, excessive shear heat generation and frictional heat generation due to compression of the resin in the supply portion are prevented. Also, if the groove depth of the flight is changed from the upstream portion of the supply portion to the downstream side, the groove depth on the upstream side of the supply portion is increased to a depth suitable for biting resin pellets made of recycled material or the like. Even so, the groove depth on the downstream side of the supply unit can be set in accordance with the groove depth of the compression unit, and the supply unit and the compression unit can be smoothly communicated.
In addition, since the depth of the groove on the upstream side of the supply portion can be sufficiently maintained, the biting of the resin pellet is stabilized.

As described above, the groove depth of the flight at the most downstream portion of the supply section is appropriately 1.0 to 3.0 times the groove depth of the flight at the measuring section. In order to prevent excessive shearing heat and frictional heating due to the compression of the resin, the cross-sectional area of the gap formed by the flight and its groove and the inner peripheral surface of the cylinder along the center axis direction of the screw (flow path cutting) It is necessary to determine the groove depth of the flight so as to increase the size of (area).

[0016]

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a screw assuming that resin pellets made of recycled material of 5 mm square are injected into a large diameter screw having a diameter D of 40 mm and a groove depth dvari. 1 is one embodiment. Here, in the conventional shape, the screw compression ratio (the ratio of the groove depth of the measuring section to the groove depth of the supply section) = 2.0
A new screw based on the present application shall be designed to achieve the same compression effect as the screw defined as

According to the conventional design policy, the depth of the groove of the flight 2 immediately below the resin intake is 6.0 mm, which does not hinder the introduction of a 5 mm square recycled material. However, in the supply section A, the resin pellets receive the heat energy of the external heater by the heat transfer from the inner peripheral surface of the cylinder. If the supply unit groove depth is excessively large, there is a large difference in the heat energy received from the cylinder between the pellets located near the inner peripheral surface of the heater and the pellets located near the groove bottom, resulting in uniform melting. The resin does not become a resin, and the resin density and the molecular weight become uneven.

Therefore, in the screw 1 of the present embodiment, first, in order to smoothly bite the recycled material of 5 mm square, just below the resin intake, that is, in the flight 2 at the most upstream part in the supply part A, The groove depth dvari. Is set to 5 mm, which is necessary and sufficient. As described above, the groove depth dvari. Of the flight 2 in the measuring section C is 3 mm.

Further, the groove depth dvari. Of the flight 2 at the most downstream portion in the supply section A is set to 6 mm, and the design data of the boundary portion between the supply section A and the compression section B is matched with the screw according to the conventional design policy. That is, the shape from the boundary between the supply section A and the compression section B to the tip of the screw 1 is the same as that of the conventional screw.

Next, the flight pitch Pvari. Of the uppermost stream in the supply section A is determined. In this case, the flight pitch Pvari.
Is determined. If the groove depth is gradually changed from the most upstream part of the supply part A having the groove depth dvari. = 5 mm to the most downstream part of the supply part A having the groove depth dvari. = 6 mm, the flight 2 and its The size of the cross section in the axial direction of the screw (the cross-sectional area of the resin flow path indicated by the hatched portion X1 in FIG. 1) of the gap formed by the groove and the inner peripheral surface of the cylinder gradually increases from the upstream side to the downstream side. It expands and finally expands about 1.2 times at the most downstream part X2 of the supply section. For this reason, it is possible to suppress shear heat and friction heat generated when the resin is transported in the supply unit A.

As a result, the resin pellets are smoothly caught by the flight 2 at the most upstream portion of the supply section A, that is, immediately below the resin intake port, and at the same time, from the most upstream portion of the supply section A to the supply section A. Excessive shearing and frictional heat generation, which are problems when transporting the resin to the most downstream part, could be suppressed. In addition, it is possible to minimize variations in the temperature distribution of the resin in the flight grooves of the supply unit.

Further, in the present invention, since the shearing and frictional heat generation in the supply section are suppressed, it may be difficult for the resin to completely melt before the resin reaches the measuring section C. There is fear. For this reason, in the present embodiment, the subflight 3 is provided from the compression section B to the measurement section C so that the variation in the temperature of the injected resin is suppressed to a minimum. That is, as shown in FIG. 1, in a region G extending from the compression section B to the measurement section C, a sub height slightly lower than that of the main flight 2 and a clearance of approximately 0.5 mm between the sub flight and the inner diameter of the heating cylinder are formed. Flight 3 is provided.

FIG. 7A is an enlarged view of the subflight area G. FIG. 7B is a development view of the subflight and an explanatory diagram of the operation of the subflight 3. FIG. 7 (a)
, The subflight 3 is formed slightly lower than the main flight 2, and the pitch of the subflight 3 is formed larger than the pitch of the main flight 2. The subflights 3 are formed between the pitches so as to have three pitches.

Although the resin flows from the upstream to the downstream along the groove, the unmelted resin and the resin having a high viscosity are dammed by the subflight 3, and as shown in FIG. Only the lowered resin passes over subflight 3. As described above, only the resin having a high temperature and a low viscosity is selectively passed by the subflight 3, so that the variation in the temperature of the injected resin can be suppressed. Since the viscosity of the resin that passes over the subflight 3 has already been reduced, excessive heat generation due to shearing does not occur.

Although the subflight 3 is provided in the boundary area between the compression section B and the measurement section C as shown in FIG. 1, it may be provided only in the measurement section C or only in the compression section B. Is also good. Further, in the above-described embodiment, the groove depth dvari. Of the flight 2 is gradually increased from the most upstream portion to the most downstream portion of the supply unit A. However, in some sections or a plurality of sections of the supply section. The groove depth dvari. May be changed to increase the depth. Finally, it is sufficient that the groove depth dvari. = 6 mm at the most downstream portion of the supply section. Another embodiment will be described. FIG. 2 shows a measuring part C having a diameter D of 20 mm.
Is an embodiment of the screw 1 on the assumption that resin pellets made of recycled material of 5 mm square are injected into a screw having a small diameter of 2 mm and a groove depth dvari. Here, a new screw based on the present application is designed to obtain a compression effect equivalent to that of a screw whose conventional shape is defined as a screw compression ratio (ratio of the groove depth of the metering section to the groove depth of the supply section) = 2.0.

According to the conventional design policy, the depth of the groove of the flight 2 immediately below the resin intake is 4.0 mm, which hinders the introduction of a 5 mm square recycled material, and causes a bridge or the like.
This is a situation in which the resin is deteriorated due to shear heat and frictional heat generated by excessive biting.

Therefore, in the screw 1 of the present embodiment, first, in order to smoothly bite the recycled material of 5 mm square, just below the resin intake, that is, the flight 2 of the most upstream part in the supply part A is required. The groove depth dvari. Is set to 5 mm.

Further, the groove depth dvari. Of the furthest downstream flight 2 in the supply section A is 4 mm, and the flight pitch Pvari. Of the furthest downstream section in the supply section A is 20 mm, that is, 1.0 times the screw diameter D ( 0.9 times to 1.4 times), and the thickness T of the flight 2 is 3 mm over the entire section of the screw 1. Here, the flight pitch Pvari. Is set to 20 mm (0.9 mm of the screw diameter) at the most downstream portion of the supply section A.
The reason is that if the flight pitch is larger than 1.4 times the screw diameter, the inclination angle α of the screw flight described later increases, and as a result, the following equation (2) is used. Since the moving speed V of the resin in the screw axis direction shown in the drawing becomes extremely large, the shearing force applied to the resin from the inner peripheral surface of the cylinder becomes too strong, and it is impossible to achieve the suppression of heat generation due to the shearing which is the object of the present invention. is there. In addition, if the pitch is less than 0.9 times the screw diameter, it is not practical because the plasticizing ability is reduced, and if the screw rotation speed is increased to compensate for this, the shear force given to the resin by the screw rotation will increase. However, this is different from the object of the present invention of suppressing heat generation. or,
Since the groove depth dvari. Of the flight 2 in the measuring section C is 2 mm, the groove depth dvari. Of the flight 2 at the most downstream part in the supply section A is 2.0 times the groove depth of the flight 2 in the measuring section C. (Range of 1.0 to 3.0 times). Next, the flight pitch Pvari. Of the most upstream part in the supply unit A is determined. However, since the same design data as in the past has been decided to be applied to the compression unit B and the measurement unit C, the supply unit A The flight pitch Pvari. = 20 mm at the lowermost portion and the groove depth dvari. = 4 mm of the flight 2 at the lowermost portion in the supply section A are determined.

Further, as described above, since the groove depth dvari. Of the flight 2 at the most upstream part in the supply part A needs to be 5 mm, the most upstream part of the supply part A having the groove depth dvari. = 5 mm is required. To groove depth dvari. = 4mm, flight pitch Pv
ari. = 20 mm, in order to suppress the shear heat and the friction heat generated when the resin is conveyed to the most downstream portion of the supply section A having an allowable limit, the flight 2 and the valley bottom are formed by the inner peripheral surface of the cylinder. The size of the cross section taken along the central axis direction of the screw (the cross-sectional area of the resin flow path indicated by the hatched portion X1 in FIG. 2) of the gap to be formed is increased. In other words, the flight depth dvari.
That is, the flight pitch Pvari. needs to be gradually increased from m to 4 mm at the most downstream portion, and the flight pitch Pvari.

Meanwhile, there is a relationship between the flight pitch Pvari. Of the most upstream part in the supply part A and the feed amount of the solid pellets by screw rotation as shown in FIG.
If the flight pitch Pvari. Is smaller than 0.6 times the screw diameter D, the feed amount is drastically reduced, so that the weighing time is extended and the molding cycle time is extended too much, which increases the molding cost. Further, the distance (length of the flight groove) in which the resin moves downstream while contacting the inner circumferential surface of the cylinder in the flight groove of the supply section is short. In other words, the number of turns of the flight in the supply section is smaller than that of the conventional screw. When the amount decreases, the amount of heat that the resin receives from the external heater in the screw supply unit A decreases as compared with the conventional screw, but this means that the performance in the supply unit A decreases.

Accordingly, in the embodiment shown in FIG.
i. 0.6 times the screw diameter D = 20 mm = 12 mm (0.
(The range of 6 to 1.0 times) and the cross-sectional area X1 of the resin at the most upstream portion of the supply section A and the cross-sectional area X2 of the resin at the most downstream portion of the supply section A The area ratio was about 1: 2. Note that FIG. 3 was obtained from the formula of the feed amount Q of the solid pellets in the supply section A. Assuming that the pellets move in lump in the screw groove,

[0033]

(Equation 1)

(Equation 2) D: Screw outer diameter H: Screw groove depth V: Pellet moving speed in the downstream direction of the screw (screw axial direction) ψ: Pellet moving speed (see screw development diagram in FIG. 4) N: Screw rotation speed α: It is the inclination angle of the screw flight, and D, H, V, ψ, N are fixed, and the relationship between the feed amount and the inclination angle α of the screw flight is obtained.

[0034]

(Equation 3) Becomes Here, since the tilt angle α of the screw flight is uniquely determined by the flight pitch P, the relationship between the feed Q and {(flight pitch P) / (screw diameter D)} is determined as shown in FIG.

As a result, the resin pellets can be smoothly caught by the flight 2 from immediately below the resin inlet, that is, from the most upstream portion of the supply section A, and at the same time, from the most upstream portion of the supply section A to the supply section A. Excessive shearing and frictional heat generation, which are problems when transporting the resin to the most downstream part, could be suppressed.

In the embodiment of FIG. 2, the rising taper at the front and back of the flight 2 is 2.8 / 5 (however,
When the sizes X1s and X2s of the flow path cross-sectional areas X1 and X2 are roughly calculated as (axial / radial ratio), as shown in FIG. 5, X1s = 5. [(12-3-2.8.2) +2. 8] = 31 mm ² , and X2s = 4 · [(20-3-2.8 · (4/5) · 2) + 2.8 · 4 /
5] = 59.04 mm ² , and the size X2s of the flow path cross-sectional area X2 is about twice the size X1s of the flow path cross-sectional area X1.

In the embodiment shown in FIG.
The subflight 2 is provided in the boundary area between the compression section B and the measurement section C, as in the embodiment shown in FIG. The operation of the subflight 3 is the same as that of the embodiment shown in FIG.
or. It is the same as the embodiment shown in FIG. 1 that the subflight 3 may be provided only in the compression section B or the measurement section C or both.

In any of the embodiments, the measuring section C
And the groove depth dvari. On the upstream side in the supply section A can be formed according to the size (for example, 5 mm) of the recycled material pellet to be used without being restricted by the groove depth dvari. Therefore, the resin pellets can be smoothly engaged in the supply section A. In addition, since the resin injected from the resin inlet of the cylinder is not forcibly sheared, the generation of excessive shear heat and frictional heat is suppressed, and the flow path cross-sectional area in the supply section A gradually increases. Therefore, excessive heat generation due to careless compression in the supply unit A is also eliminated.

When the same design data as the conventional design data is applied to the compression section B and the measurement section C, that is, the flight pitch Pvari.
Even if i. is limited by design, the upstream section of the supply section A has a groove depth d that is smaller than that of the conventional screw structure (for example, JP-A-9-314625).
Since the vari can be formed deeply, it is advantageous in terms of smooth biting of the coarse resin pellets made of the recycled material.

[0040]

According to the present invention, it is possible to suppress the occurrence of excessive shear heat generation and frictional heat generation in the screw supply section, and to smoothly bite coarse resin pellets made of recycled materials and the like. Can be.

[Brief description of the drawings]

FIG. 1 is a side view showing a screw structure according to an embodiment of the present invention.

FIG. 2 is a side view showing a screw structure of another embodiment to which the present invention is applied.

FIG. 3 is a graph showing a relationship between a feed amount Q of a resin pellet and {(flight pitch P) / (screw diameter D)}.

FIG. 4 is an explanatory diagram showing a relationship between a feed amount Q of a resin pellet and {(flight pitch P) / (screw diameter D)} based on a screw structure.

FIG. 5 is a conceptual diagram illustrating a shape of a flight groove according to an embodiment, which is taken out from a downstream side and an upstream side of a supply unit by one pitch.

FIG. 6 is a view showing a general conventional example of a screw structure.

FIG. 7 is an enlarged view and a development view of a subflight area.

[Explanation of symbols]

Reference Signs List 1 screw 2 flight 3 subflight 100 screw 101 flight A supply section B compression section C measuring section D screw diameter W groove width P flight pitch d groove depth d 'groove depth Pvari. Flight pitch (variable) dvari. Groove depth (Variable) T Thickness of flight X1 Size of radial cross section of gap formed between flights X2 Size of radial cross section of gap formed between flights

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshio Ishiguro 3580 Kobaba, Oshino-za, Oshino-mura, Minamitsuru-gun, Yamanashi FANUC CORPORATION (56) References JP-A-10-2788082 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (5)

(57) [Claims] In the entire region of a screw supply section, the depth of a screw groove is gradually increased from an upstream portion to a downstream portion, and a resin flow path cross-sectional area in a screw groove formed between flights is increased. A screw structure for an injection molding machine, wherein the screw structure is formed so as to gradually increase in the entire region from the section toward the downstream section, thereby preventing the generation of excessive shear heat and frictional heat in the supply section groove. 2. The injection according to claim 1, wherein the depth of the screw groove at the most downstream portion of the screw supply portion is formed to be in a range of 1.0 to 3.0 times the groove depth of the measuring portion. Screw structure of molding machine. 3. In the entire region of the screw supply portion, the flight pitch continues to increase gradually from the upstream portion to the downstream portion, and the cross-sectional area of the resin flow path in the screw groove formed between the flights increases from the upstream portion. A screw structure for an injection molding machine, wherein the screw structure is formed so as to gradually increase in the entire region toward the downstream portion, thereby preventing the generation of excessive shear heat and frictional heat in the supply portion groove. 4. The flight pitch in the most upstream part of the screw supply part is 0.6 times to 1.times.
4. The screw structure of an injection molding machine according to claim 3, wherein the screw structure is formed so as to be in a range of 0 times. 5. The flight pitch at the most downstream portion of the screw supply section is 0.9 times to 1.times. The screw diameter.
5. The screw structure of an injection molding machine according to claim 3, wherein the screw structure is formed so as to be four times as large.