JP3119745B2 - Vent type injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a vent type which is capable of smoothly supplying a raw material resin even though the entire length is equal to that of a non-vent injection molding machine, but in which a vent-up phenomenon does not easily occur. It relates to an injection molding machine.

[0002]

2. Description of the Related Art Resin pellets supplied to an injection molding machine contain moisture, air, volatile components, etc., and when they are kneaded and melted as they are and injected into a mold, bubbles are formed in a molded product, or silver is formed. It may cause streaks.

[0003] Therefore, a vent hole is formed in the heating cylinder and the screw is divided into two parts before and after, and the material supplied to the deep groove portion (supply part) of the rear first stage in a moist state is supplied to the first stage. The raw resin is melted and supplied to the shallow groove portion (first metering portion) while being sequentially heated and compressed. The molten resin passes through the first metering section and the vent throttle section and
It moves to the deep groove part (vent part) of the stage,
At this time, the groove depth suddenly increases and the space of the vent portion suddenly increases, and as a result, the pressure of the vent portion decreases, and the moisture and volatile substances in the resin are vaporized, and the entire resin is in a foamed state. Become. Then, the molten resin is kneaded by the rotation of the screw to break the bubble film enclosing the gas, and the gas is separated from the resin and discharged out of the heating cylinder through the vent hole.

[0004] The resin from which water and volatile substances have been separated in this way is sent to the shallow groove portion (second metering portion) of the second stage in the front part, and balances with a predetermined pressure (back pressure). When the pressure to keep is reached, it is sent in front of the screw. As the resin is fed into the storage space at the front end of the heating cylinder, the screw moves rearward, and when a predetermined amount of the resin is metered (that is, the predetermined amount of resin has accumulated in the front end storage space), the screw stops. One cycle of the measured resin is completed through a series of steps such as injection, pressure holding, and cooling.

[0005] As described above, the vent-type injection molding machine has the feature of reducing the defects of the molded product due to the active release of the moisture, air and volatile substances contained in the raw material resin. Occurs and closes the vent hole,
There is a problem that the vent effect is lost. Therefore the relationship between the amount of resin Q ₂ to which discharged to vent up is stored from the resin amount Q ₁ and a second stage that is sent from the first stage of the screw as a condition which is not generated in the second stage to the gap portion of the screw tip , Q ₂ ≧ Q ₁ . One way to satisfy this relationship is to
Conventionally, L / D (ratio of screw effective length to screw outer diameter) is 24 to 28, so that it is longer than non-vent screw (usually L / D = about 20). Venting-up prevention screws were installed in the supply device and vent port.

As described above, if the L / D is set to 24 to 28, which is longer than that of the non-vent screw, the position of the injection unit must be lowered by the length of the screw. Similarly, the length of the injection pipe must be increased by the length of the screw. The pinstone rod for nozzle touch must also be lengthened by the length of the screw. The longer the screw, the lower the rigidity of the screw. There have been various problems such as an increase in the overall length of the apparatus and an increase in space.

Also, since the vent screw is divided into two stages as described above, the length of the deep groove for material supply of the first stage at the rear portion is shortened by the wrinkling, and the screw reciprocates to reciprocate. In some cases, the supply of raw materials may vary, and as a result, there is a problem that a special supply device that can supply the raw materials while precisely defining the supply amount itself is required.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and the problem to be solved by the present invention is that despite the fact that the entire length of the screw is equivalent to that of a non-vent type injection molding machine. Another object of the present invention is to provide a vent-type injection molding machine capable of stably supplying a raw material resin without occurrence of vent-up and without a special raw material supply device.

[0009]

According to a first aspect of the present invention, there is provided a vented injection molding machine comprising: a heating cylinder having a vent hole and a raw material supply port provided on a rear upper surface thereof; And the heating cylinder
(1) Revolving and reciprocating inside, a spiral groove (3) is formed on the surface thereof, the first stage portion (A) located at the rear side of the heating cylinder (1) and the tip side of the heating cylinder (1) And a screw (2) having a rear portion of the first stage portion (A) formed in a deep groove portion (C) for supplying raw material. In the molding machine, the pitch of the spiral groove (3) of the first stage part (A) and the second stage part (B)
The ratio of the pitch of the spiral groove (3) to the pitch of the spiral groove (3) is set to 0.7 to 0.8: 1, and the front part of the first stage part (A) is formed in a shallow groove part (D + E). Shallow groove (D + E)
Is formed so that it becomes shallower toward the front end,
Length / outer diameter of the screw is in the range of 23 to 18 ”. Thus, the first stage (A)
Amount Q of resin supplied from the part to the second stage (B) part
₁ is the reservoir from the second stage (B) to the screw tip
Becomes smaller than the amount of resin Q ₂ to which is discharged to the reservoir (8), a vent-up phenomenon with a shorter screw length of pressure increase applied to the raw material resin can be suppressed bent portion (9) Can be suppressed.

Further, according to the vent type injection molding machine of the second aspect, in the configuration of the first aspect, the "first stay"
The length of the deep groove part in the
It is characterized in that it is set to approximately 30 to 35% of the portion . " This allows the raw material supply port (7) to be covered by the deep groove portion (C) over the entire length of the reciprocating movement of the screw (2),
The supply of the raw material resin in the first stage portion (A) can be stabilized.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments, but the present invention is not limited thereto. In FIG. 1, (1) is a heating cylinder, (2) is a screw, and a heating cylinder.
(1) It is arranged so as to rotate and reciprocate inside.
The drive mechanism of the screw (2) is omitted. Screw (2)
Is divided into two stages before and after the first and second stages (A) and (B).
A spiral groove (3) is formed on the surface. A nozzle (5) is attached to the end of the heating cylinder (1),
A band heater (4) is wound around the outer periphery of (1) and the nozzle (5). In addition, a raw material supply cylinder (6) is installed on the rear end upper surface of the heating cylinder (1), and a raw material supply device (not shown) such as a hopper is connected, and the raw material resin is heated. Screw (2) through raw material supply port (7) at the rear of cylinder (1)
To be supplied continuously.

Although the screw (2) is divided into the first and second stages (A) and (B) as described above, the deep groove portion (C) and the shallow groove portion (D + E) are provided for each of the first and second stages. , The deep groove portion (G) and the shallow groove portion (H + I) are formed with different groove depths of the spiral groove (3). Deep groove part (C) (G) is shallow groove part (D + E),
(H + I) is provided on the rear side, and shallow grooves (D + E), (H
+ I) is formed on the front end side so that the groove depth becomes slightly smaller. Raw material resin is from deep groove part (C) to shallow groove part (D + E),
The resin is narrowed down (F), deep groove portion (G), shallow groove portion (H + I), and so forth, and is metered and stored at the tip of the heating cylinder (1). As described above, the space between the first and second stages (A) and (B) is made slightly smaller than the inner diameter (J) of the heating tube (1), and the heating tube (1) and the screw (2) are Is provided with a vent throttle portion (F) formed so as to minimize the gap.

The screw pitch of the first stage (A) is finer than the screw pitch of the second stage (B). For example, the ratio of the screw pitch of the second stage (B) to the diameter of the screw (2) is 1: 1. In this case, the ratio of the screw pitch of the first stage (A) to the diameter of the screw (2) is (0.9 to 0.6): 1, and more preferably (0.8 to 0.6).
0.7): 1 >>, the first stage (A) is formed finer. In the present embodiment, the ratio is 0.8: 1. Also the first stage
The length of the deep groove portion (C) of (A) is 25% or more (30 to 35% in this embodiment) of the length of the spiral groove (3) of the screw (2), which is a conventional non-vent type. The length of the material supply deep groove (C) formed at the rear of the screw (2) is almost the same as that of the screw (2) and the material supply port (7 ) Is greater than or equal to the sum of the opening widths, thereby facilitating the supply of the raw material resin.

The ratio (L / d) of the effective length (L ) of the screw (2) to the screw outer diameter ( d) is 23 or less, more preferably 20 or less. Normally, about 20 to 18 mm, in this embodiment, the screw (2)
Is formed to be the same as the screw of the non-vent type injection molding machine, and (L / d) is 20. Therefore, it is characteristic that the overall length is very short as compared with the conventional vent type injection molding machine.

Thus, the raw material resin is continuously supplied from the raw material supply device to the raw material supply port (7) at the rear end portion of the heating cylinder (1). The screw (2) is continuously rotating, and the raw resin is continuously conveyed in the tip direction by the spiral groove (3). First
In this embodiment, the deep groove portion (= supply portion) (C) of the stage (A) is formed to be as long as 30% of the entire length of the screw (2). Even if the screw (2) retreats according to the storage in the section (8), the deep groove portion (C) does not come off from the raw material supply port (7), and the raw material resin is supplied stably.

The raw resin supplied into the heating cylinder (1) is heated by a band heater (4) and is transported forward by a screw (2). First, the resin raw material supplied in a wet state is supplied to the deep groove portion (supply portion) (C) of the first stage (A), and the raw material resin is supplied to the first stage (A) as the screw (2) rotates.
(A) is transferred while being compressed and heated to the first half (D) of the shallow groove portion, and is then supplied to the second half (E) while being heated and compressed, whereby the raw material resin is gradually melted. Shallow groove part is the first half
The groove depth gradually becomes shallower from (D) to the latter half (E) so that the raw resin can be continuously compressed.

The raw resin melted by the compression and heating passes through the vent throttle section (F) and moves to the deep groove portion (G) of the second stage (B), and as described above, the vent resin (9). Due to the pressure drop, the raw resin expands, and the whole resin becomes a foamed state, and the moisture and volatile substances inside are vaporized. Then, the molten resin is kneaded by the rotation of the screw (2) to break the bubble film surrounding the gas, and the gas is separated from the resin and discharged to the outside of the heating cylinder (1) through the vent hole (10).

Since the first stage (A) has a higher thread pitch than the second stage (B) as described above, the first stage (A) is supplied from the first stage (A) to the second stage (B). many people amount Q ₂ of the molten material is stored in the distal end of the quantities Q ₁ from the second stage of melting the raw material heating cylinder from (B) (1) that is, the (in other words, the first stage (a) The feed rate of the raw resin is lower than that of the second stage (B).)
In this space, the space is not filled with the molten raw material, and sufficient degassing is performed, and at the same time, no pressure is applied to the resin raw material transferred to the vent portion (9). Therefore, the molten resin does not enter the vent hole (10) and does not block the vent hole (10).

The raw resin from which moisture and volatile substances have been degassed is sent forward through the shallow groove portion (G) of the second stage (B) with the rotation of the screw (2). The transfer of the portion to the first half (H) is performed by reaching a pressure that balances with a predetermined pressure (back pressure) in the shallow groove portion (G). The screw (2) moves rearward as the raw material resin is fed into the front end storage section (8) of the heating cylinder (1), and when a predetermined amount of the measurement is completed, the screw (2) stops, and then the screw (2) ) Moves forward, injects the measured molten resin into a mold (not shown), performs pressure holding and cooling, opens the mold, and takes out the molded product. This completes one cycle.

(Embodiment) A vent-type injection molding machine of the present invention having an L / D = 20 was used.
D = 25 was used. As the raw resin used in the experiment, two types of PMMA (acrylic resin) and ABS resin were used. Experimental results show that the vent-type injection molding machine of the present invention has a lower charge rate of the raw material by about 10% than the comparative example, but the raw material supply is more stable because the deep groove portion of the first stage, which is the raw material supply section, is longer. However, the variation in charging speed and charging time and the heat history were small. The amount of heat required for melting the raw material resin was small, and almost no vent up or silver streak was observed. Also, the charge torque is low, and low-temperature molding is possible. Therefore, PMMA and A
Most suitable for molding BS resin.

The above test results (compared to L / D = 25) are shown in the table below. L / D resin charge Charge time Vent Silver Charge type Variability in speed Up Streak Torque PMMA -10% Small No No No Low Low temperature molding 20 possible ABS -10% Small Somewhat low Low (Note 1) Low temperature molding possible Note 1 ... Can be solved by installing a vent heater.

[0022]

According to the vent type injection molding machine described in claim 1 of the present invention, the screw pitch of the first stage portion is formed finer than the screw pitch of the second stage portion. Write from the second stage than the amount to Q ₁ fused raw material supplied to the stage of the amount Q ₂ of the molten material to be stored in the storage portion of the tip of the heating cylinder increases. As a result, the space in the vent portion is not filled with the molten material, and sufficient degassing is performed, and at the same time, no pressure is applied to the resin material transferred to the vent portion, and the molten resin enters the vent hole. Therefore, there is an advantage that the vent hole is not blocked, and as a result, the entire length of the screw can be shortened.

According to the vent type injection molding machine of the second aspect, the length of the deep groove for material supply formed at the rear of the screw is substantially equal to the moving distance of the screw and the opening width of the material supply port. Since it is formed to the sum length, the raw material supply port can be covered by the deep groove portion in the entire length of the reciprocating movement of the screw, the supply of the raw material resin in the first stage can be stabilized, and the charging speed and the like can be improved. I was able to keep the variation in charging time small.

[Brief description of the drawings]

FIG. 1 is a sectional view of a heating cylinder part of a vent type injection molding machine according to the present invention.

FIG. 2 is a sectional view taken along line bb of FIG. 1;

FIG. 3 is a sectional view taken along line aa of FIG. 1;

[Explanation of symbols]

(1) ... heating cylinder (2) ... screw (3) ... spiral groove (7) ... material supply port (10) ... vent hole (A) ... first stage (B) ... second stage (C) ... screw Deep groove for material supply formed at the rear

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/00-45/17 B29C 45/46-45/63 B29C 47/60-47/66

Claims (2)

(57) [Claims] 1. A heating cylinder having a vent hole and a raw material supply port on a rear upper surface thereof, and rotates and reciprocates in the heating cylinder.
A helical groove is formed on the surface of the first stage portion located on the rear side of the heating cylinder and the second stage located on the tip side of the heating cylinder.
A vent type injection molding machine having a screw divided into two stages and a rear part of the first stage part formed in a deep groove part for supplying raw material, wherein the pitch of the spiral groove of the first stage part and the two stages The ratio of the pitch of the helical groove to the pitch of the helical groove is set to be 0.7 to 0.8: 1, and the front part of the first stage part is formed in a shallow groove part. It is formed to be shallow, and the effective length of the screw / the outer diameter of the screw is in the range of 23 to 18.
A vent-type injection molding machine characterized by being enclosed . 2. The vent-type injection molding machine according to claim 1, wherein the length of the deep groove portion in the first stage portion is set to approximately 30 to 35% of the groove portion of the screw.