JP7458289B2 - Screws for injection molding machines, injection equipment and injection molding machines - Google Patents

Description

The present invention relates to a screw for an injection molding machine in which a step-like stepped portion, that is, a land portion is formed at the top of the flight, an injection device provided with the screw, and an injection molding machine.

The injection device of an injection molding machine is composed of a heating cylinder and a screw inserted into the bore of the heating cylinder. Flights are formed on the screw to melt and measure the injection material, and the flights come in various shapes.

In the so-called conventional screw, the top of the flight is formed from a single cylindrical surface. On the other hand, the screw described in Patent Document 1 has a stepped flight in which the top of the flight is formed into a step-like step. In the stepped flight, at the top of the flight, the upstream side of the stepped section, that is, the hopper side, is the large diameter section, and the downstream side, that is, the injection nozzle side, is the land section. According to Patent Document 1, the large diameter section and the land section are It is stated that the height difference should be within 0.5mm.

Special Publication No. 06-84035

By the way, the inventors have found that in the injection device equipped with the screw described in Patent Document 1, there is a problem of so-called color changing in which the color or type of the injection material is changed. Color changes require substantially complete replacement of old injection material with new injection material within the heated cylinder. This means that the molding cycle must be repeated until the injection material has been substantially completely replaced. However, in a screw equipped with stepped flights such as the screw described in Patent Document 1, old injection material that has entered the top of the flight is difficult to discharge, and the number of molding cycles required when changing colors increases. In other words, it was found that the number of wasted shots increases.

Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

The present disclosure provides a screw for an injection molding machine having the following configuration. That is, a stepped flight is formed in the screw. The stepped flight is a flight in which a step-like stepped portion is formed at the top of the flight, and a large diameter portion on the upstream side and a land portion on the downstream side are formed. In the stepped flight, the difference in level between the large diameter part and the land part is selected to be greater than 0.5 mm and less than 0.8 mm.

According to the present disclosure, it is possible to provide a screw for an injection molding machine that can reduce the number of unnecessary shots that are repeated before the old injection material is completely replaced with new injection material when changing the type of injection material.

FIG. 1 is a front view showing an injection molding machine according to the present embodiment. FIG. 1 is a front sectional view showing an injection device according to the present embodiment. It is a front view showing a part of screw concerning this embodiment. It is a sectional view showing a step part flight provided in a screw concerning this embodiment. A cross-sectional view showing the stepped flights provided in the screw according to the present embodiment, and a graph showing the lubricating pressure generated at the top of the stepped flights due to the injection material flowing between the stepped flights and the bore of the heating cylinder. be. It is a figure which shows typically the behavior of the viscous fluid which flows through the gap between a moving piece and a stationary piece. 1 is a graph showing the relationship between the size of the step formed in the stepped flight and the number of shots required to completely replace the injection material during a color change. When the screw is rotated within the heating cylinder, the screw vibrates and the rotating shaft becomes eccentric with respect to the central axis of the heating cylinder. The figure is a graph showing the degree of screw amplitude at various screw positions for three screws each having step flights with different step sizes and a conventional screw. It is a graph which shows the change of the load capacity coefficient when the shape of the top part of a flight is changed in a stepped flight.

Hereinafter, specific embodiments will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. For clarity of explanation, the following description and drawings have been simplified where appropriate. In each drawing, the same elements are designated by the same reference numerals, and redundant explanation will be omitted as necessary. In addition, hatching is omitted in some parts to avoid cluttering the drawings.

<Injection molding machine>
As shown in FIG. 1, the injection molding machine 1 according to the present embodiment includes a mold clamping device 2 provided on a bed B and an injection device 3 according to the present embodiment, which will be described next. It is roughly structured. The mold clamping device 2 includes a fixed platen 7, a movable platen 8, a mold clamping housing 9, tie bars 10 connecting the mold clamping housing 9 and the fixed platen 7, and a toggle mechanism. The molds 13 and 14 are provided on a fixed platen 7 and a movable platen 8. When the mold clamping mechanism 11 is driven, the molds 13 and 14 are clamped.

<Injection device>
The injection device 3 according to the present embodiment is provided so as to be able to move forward and backward with respect to the mold clamping device 2, and is configured to inject injection material into the molds 13 and 14 clamped by the mold clamping device 2. There is. As shown in FIG. 2, the injection device 3 includes a heating cylinder 17 and a screw 18 according to this embodiment. A hopper 19 is provided near the rear end of the heating cylinder 17, and an injection nozzle 20 is provided at the tip. When the injection material is put into the hopper 19 and the screw 18 is rotated, the injection material is melted, sent forward, and measured. That is, in the injection device 3, the hopper 19 side is on the upstream side, and the injection nozzle 20 side is on the downstream side.

<Screw>
The screw 18 according to the present embodiment is characterized by the shape of a part of the flight 21, which will be described next, but the screw 18 as a whole is as follows. The depth of the groove formed by the flight 21 of the screw 18 changes in each part of the screw 18, and the inside of the heating cylinder 17 is divided. That is, a deep groove is formed on the upstream side of the screw 18, and serves as a supply section 23 through which the injection material is heated and sent downstream. In the midstream, the groove depth gradually changes to become shallower, forming a compression section 24 where the injection material is melted and compressed, and downstream, the groove becomes shallower and becomes a measuring section 25, where the injection material is measured. ing.

The screw 18 according to the present embodiment is partially enlarged and shown in FIG. 3, and is characterized in that a part of the flight 21 is a stepped flight 28. The stepped flight 28 is shown in FIG. 4 in a cross section taken along line A--A in FIG. 3, and its top portion 29 is distinctive. That is, the stepped flight 28 has a top portion 29 formed in a step-like stepped portion, and is composed of a large diameter portion 31 on the upstream side and a land portion 32 on the downstream side. Since the land portion 32 has a smaller diameter than the large diameter portion 31 by the step 33, the gap H1 with the land portion 32 is smaller than the gap _H2 with the large diameter portion 31 with respect to the bore 35 of the heating cylinder ₁₇ . It's bigger. With this configuration, the stepped flight 28 is filled with molten injection material and generates appropriate lubricating pressure at the top 29, thereby preventing contact between the heating cylinder 17 and the screw 18.

In this embodiment, stepped flights 28 are provided in the compression section 24 and the metering section 25. When the screw 18 rotates, the screw 18 may oscillate and its rotating shaft may be eccentric from the axis of the heating cylinder 17, and the degree of this oscillation is relatively large in the compression section 24, and the second largest in the metering section 25. It is. Therefore, although the stepped flights 28 are provided in these sections, even if the stepped flights 28 are provided only in the compression section 24 where the degree of amplitude is large, contact between the heating cylinder 17 and the screw 18 can be prevented. can be obtained.

The screw 18 according to the present embodiment is characterized by the size d of the step 33 of the step flight 28, which is selected as follows.
0.5mm < d ≦ 0.8mm
With this selection, the injection material that has entered the top portion 29 of the stepped flight 28 is quickly discharged and replaced with new injection material at the time of color change. The size d of the step 33 is selected so as to obtain the effect of lubricating pressure from the step flight 28 and to reduce unnecessary shots during color change.The reason for selecting it as above is explained below. .

<Mechanism of generating lubrication pressure and lubrication load capacity W>
First, the mechanism by which lubricating pressure is generated in the stepped flight 28 will be explained, and the repulsive force that prevents the contact between the top 29 of the stepped flight 28 and the bore of the heating cylinder 17, that is, the lubricating load capacity W, will be shown by a mathematical formula.

When the screw 18 rotates within the heating cylinder 17, the step flight 28 is driven at a predetermined speed with respect to the bore of the heating cylinder 17, and this speed can be divided into a component parallel to the step flight 28 and a component perpendicular to the step flight 28. Can be done. Considering the component perpendicular to the step flight 28, the step flight 28 appears to be moving to the left at a speed U' with respect to the heating cylinder 17, as shown in FIG. If the step flight 28 is assumed to be fixed, the heating cylinder 17 can be considered to be moving at a speed U in the right direction. The velocity U is equal in magnitude and opposite in direction to the velocity U'.

The molten injection material enters the gap _H1 and is discharged from the gap _H2 . At this time, lubricating pressure is generated. The distribution of the velocity v of the injection material in the gaps H ₁ and H ₂ is schematically shown in FIG. 5 . The lubricating pressure p reaches a maximum value _Ps at the boundary between the large diameter portion 31 and the land portion 32, that is, near the stepped portion, and becomes substantially zero at both end faces of the stepped portion flight 28. The lubricating pressure p changes linearly in each of the large diameter portion 31 and the land portion 32. The reason why the lubricating pressure p changes linearly is that the flow of the molten resin with high viscosity becomes a laminar flow, and the laminar flow loses pressure in proportion to the distance over which it flows.

Here, we will consider the general behavior of a viscous fluid between two relatively moving planes. FIG. 6 shows a fixed piece 37 and a movable piece 38 that slides at a speed V relative to the fixed piece 37, and Newtonian fluid is filled between the fixed piece 37 and the movable piece 38. ing. Considering the balance of forces acting on the fluid minute element 39, one equation can be obtained from the balance of forces in the x-axis direction. Here p is pressure and τ is shear force.

１式と２式とから３式が得られる。

３式は、いわゆるナビエ・ストークスの式から得ることもでき、非圧縮流体の定常流れを表す式になっている。 The shearing force τ is given by two equations, where μ is the viscosity of the fluid and v is the flow velocity in the x direction.

From equations 1 and 2, equation 3 can be obtained.

Equation 3 can also be obtained from the so-called Navier-Stokes equation, and is an equation that expresses the steady flow of an incompressible fluid.

紙面に垂直な単位幅を考えると、隙間ｈを流れる流体の流量Ｑは４式を積分した５式で与えられることになる。

If the gap in the y direction between the fixed piece 37 and the movable piece 38 is h, then the fluid velocity v=0 at y=h. Also, when y=0, the velocity of the fluid is v=V. By solving Equation 3 using these as boundary conditions, Equation 4, which is a relational expression between flow velocity v and pressure distribution, is obtained.

Considering the unit width perpendicular to the plane of the paper, the flow rate Q of the fluid flowing through the gap h is given by Equation 5, which is the integration of Equation 4.

In the present embodiment, the range of the size d of the step 33 at the top 28 of the stepped flight 28 is selected based on consideration based on this formula 5 and through experiments, which will be explained later.

Now, the flow rate Qx of the molten resin flowing through the gap H ₁ and the gap H ₂ in the model shown in FIG. 5 is calculated using Equation 5. The flow rate Qx is equal in the gap H ₁ and the gap H ₂ . Here, assuming that the flight width of the step flight 28 is _B1 and the width of the land portion 32 is _B2 , the pressure gradient dp/dx is given by Ps/ _B2 in the gap _H1 , and in the gap _H2 . is given by (0-P _s )/(B ₁ -B ₂ ). Then, the flow rate Q _x is given by Equation 6.

When these 6 equations are solved for the maximum value Ps of the lubricating pressure, 7 equations are obtained.

なお、Ｋｗは負荷容量係数、ｍは隙間比つまり隙間Ｈ_１、Ｈ_２の比、βは形状因子つまりフライト幅Ｂ１とランド部３２の幅Ｂ２の比である。 The lubrication load capacity W per unit length in the step flight 28 is obtained by integrating the lubrication pressure p in the width direction of the step flight 28. By the way, as shown in FIG. 5, the lubricating pressure p changes like a triangle whose base length is _B1 and height is Ps. Then, the load capacity W will be given as this area. The load capacity W calculated in this manner is shown in Equation 8.

Note that Kw is the load capacity coefficient, m is the gap ratio, that is, the ratio of the gaps H ₁ and H ₂ , and β is the shape factor, that is, the ratio of the flight width B1 to the width B2 of the land portion 32.

The step flight 28 generates a repulsive force between the top 29 and the bore of the heating cylinder 17 due to the lubrication load capacity W shown in equation 8, preventing contact.

The lubrication load capacity W is proportional to the load capacity coefficient Kw, and the load capacity coefficient Kw is determined by the gap ratio m, which is the ratio of the gaps H ₁ and H ₂ , and the ratio of the flight width B ₁ and the width B ₂ of the land portion 32. It changes depending on a certain shape factor β. Therefore, the graph in FIG. 9 shows how the load capacity coefficient Kw given by Equation 8 changes when the shape factor β is changed for various gap ratios m. In order to increase the load capacity coefficient Kw,
0.6 ≦ shape factor β ≦ 0.9
It is preferable that

<Procedure for selecting the range of size d of the step 33 of the step flight 28 and reason for selection>
When performing a color change, the old injection material remaining in the groove between the flights 21 of the screw 18 is replaced with new injection material relatively quickly. This is because it is extruded by new injection material. On the other hand, the injection material tends to stay in the gaps H ₁ and H ₂ between the top 29 of the stepped flight 28 and the heating cylinder 17 . Then, the color change will not be completed unless the old injection material in these gaps H ₁ and H ₂ is completely replaced with new injection material. The present inventors thought that the speed of exchanging the injection material in the gaps H ₁ and H ₂ would affect the number of shots required for color change, and decided to study this. By the way, if the dimensions of the gaps H ₁ and H ₂ are selected to be small, the volume of the injection material filled in these portions will be reduced. A smaller capacity is more advantageous for exchanging injection materials. This is because the capacity to be replaced is small. On the other hand, when the dimensions of the gaps H ₁ and H ₂ are small, the flow velocity v at which the injection material flows through these parts becomes small. If the flow velocity v is small, it will be disadvantageous to replace the injection material. In other words, since there are contradictory effects, it is not possible to simply determine the gaps H ₁ and H ₂ .

Therefore, the inventors first excluded the gap _H2 and set only the gap _H1 as an object to be studied. The reason why the gap _H2 was excluded from consideration is that the dimensions of the gap _H2 have approximately a predetermined appropriate range and cannot be changed. Based on that, we focused on Type 5.

隙間H_１を流れる流量Q_１は２項の式からなる。まず、第１項を検討すると、この項による流量は隙間H_１に比例することがわかる。つまり隙間H_１の寸法に比例して流量が大きくなり射出材料の入れ替えが早まることを示している。しかしながらランド部３２に存在している射出材料の容量も隙間H_１の寸法に比例して大きくなる。そうすると、この第１項に関して隙間H_１の寸法の違いは射出材料の入れ替えに影響しない。 Considering the flow rate Q ₁ of the injection material flowing through the gap H ₁ of the land portion 32 based on Equation 5, Equation 9 is obtained.

The flow rate Q ₁ flowing through the gap H ₁ consists of a two-term equation. First, when considering the first term, it can be seen that the flow rate due to this term is proportional to the gap _H1 . In other words, this shows that the flow rate increases in proportion to the dimension of the gap _H1 , and the replacement of the injection material becomes faster. However, the capacity of the injection material existing in the land portion 32 also increases in proportion to the dimension of the gap _H1 . Then, regarding this first term, the difference in the dimension of the gap _H1 will not affect the replacement of the injection material.

Next, considering the second term, the flow rate according to this term is proportional to the cube of the dimension of the gap _H1 . Since the capacity of the injected material in the land portion 32 is proportional to the dimension of the gap _H1 , the effect of replacing the injected material according to the second term is proportional to the square of the dimension of the gap _H1 . Note that although the sign of the second term is negative, the pressure gradient is negative, so as a result, the effect of replacing the injection material according to the second term is as follows. In other words, the larger the dimension of the gap _H1 is, the higher the effect of replacing the injection material is, and the smaller the number of wasted shots during color change.

Therefore, the inventors decided to carry out the following first and second experiments to select the range of the size d of the step 33 of the stepped flight 28. The first experiment was aimed at confirming the effect estimated by the second term of formula 9, that is, that the number of shots during color change decreases as the size of the gap _H1 increases. The second experiment was aimed at investigating the conditions under which contact can be reliably prevented when the screw ₁₈ is rotated in the heating cylinder 17, even though the lubricating pressure changes depending on the size of the gap H1.

<First experiment>
Purpose of the experiment:
It is confirmed that the larger the size d of the step 33, which affects the gap _H1 of the step flight 28, the smaller the number of shots required for color change. Then, consider the range of the size d of the step 33 that is necessary to obtain the desired number of shots.

Preparation for the experiment:
As experimental screws, a screw S1 in which the size d of the step 33 in the stepped flight 28 was 0.2 mm and a screw S3 in which the step 33 was 0.8 mm were prepared.
Using the injection molding machine 1 according to the present embodiment shown in FIG. 1, a color change experiment was conducted using the respective screws S1 and S3 in the following procedure.

Experimental steps:
1) Perform a molding cycle to obtain a molded article using a white colored resin.
2) Change the color to transparent resin.
3) Repeat the molding cycle and check the number of molding cycles, that is, the number of shots, until a completely transparent molded product is obtained.

results of the experiment:
The number of shots required for color change was 11 for screw S1 and 9 for screw S3. From these results, the graph in FIG.
Observations:
It is preferable that the number of shots required for color change is within 10. Therefore, it is understood from this graph that the size d of the step 33 of the stepped flight 28 needs to be greater than 0.5 mm.

<Second experiment>
Purpose of the experiment:
The larger the size d of the step 33, which affects the gap _H1 of the step flight 28, the smaller the lubricating pressure becomes. This can be inferred from the fact that in Equation 8, the larger the gap _H1 and the larger the gap ratio m, the smaller the load capacity coefficient Kw, and the smaller the lubrication load capacity W. Therefore, an experiment was conducted to find out the range of the size d of the step 33 that does not affect the necessary lubricating pressure.

Preparation for the experiment:
The experimental screws were a screw S1 in which the step 33 in the stepped flight 28 had a size d of 0.2 mm, a screw S2 in which the step 33 had a size d of 0.5 mm, and a screw S2 in which the step 33 had a size d of 0.5 mm. Prepare an 8mm screw S3. Furthermore, a conventional screw S4 with a flat flight top was prepared as a comparative screw.
In the injection device 3 according to the present embodiment shown in FIG. 2, sensors for detecting the distance to the screw were embedded in multiple locations G7, G8, ..., G12 of the heating cylinder 17. Locations G7 to G9 correspond to the compression section 24, and locations G10 to G12 correspond to the measurement section 25.

Experimental procedure and results:
In the heating cylinder 17, screws S1, S2, S3, and SS were sequentially installed and rotated to measure the injection material. At this time, the screw amplitude ratio at each location was obtained from the distance to the screw detected at each location G7, G8,..., G12. The results are shown in the graph of FIG. Reference numerals 41, 42, and 43 are graphs of the screws S1, S2, and S3, respectively, that is, graphs in which the size d of the step 33 is 0.2 mm, 0.5 mm, and 0.8 mm. Reference numeral 44 is the graph of the screw S4, that is, the graph of the conventional screw. The screw amplitude ratio becomes 0.0 when the center axis of the screw 18 coincides with the center axis of the heating cylinder 17, and becomes 1.0 when the screw 18 and the bore of the heating cylinder 17 come into contact.

Consideration:
It was confirmed that if the size d of the step 33 was within 0.8 mm, the screw amplitude ratio was sufficiently smaller than that of a conventional screw, and the necessary lubricating pressure could be obtained. However, when the size d of the step 33 is 0.8 mm, the screw amplitude ratio is large at locations G7 to G9, and it is predicted that if the size is larger than this, sufficient lubricating pressure will not be obtained. From the results of this experiment, it was confirmed that the size d of the step 33 should be 0.8 mm or less.

<Selection of the range of the size d of the step 33 of the step flight 28>
From the results of the first and second experiments, the size d of the step 33 of the step flight 28 is set to be greater than 0.5 mm and less than 0.8 mm, as described above.

Although the invention made by the present inventor has been specifically explained based on the embodiments above, the present invention is not limited to the embodiments already described, and various changes can be made without departing from the gist thereof. It goes without saying that it is possible. The plurality of examples explained above can also be implemented in combination as appropriate.

1 Injection molding machine 2 Mold clamping device 3 Injection device 13 Mold 14 Mold 17 Heating cylinder 18 Screw 21 Flight 23 Supply section 24 Compression section 25 Measuring section 28 Step flight 29 Top section 31 Large diameter section 32 Land section 33 Step

Claims (12)

Injection molding machine screw with the following configuration:
(1a) A stepped portion whose top is a stepped portion and is a flight consisting of a large diameter portion on the upstream side and a land portion on the downstream side that has a smaller diameter than the large diameter portion. Flights have designated sections ;
(1b) A step difference between the large diameter portion and the land portion is greater than 0.5 mm and less than 0.8 mm. The screw according to claim 1, comprising:
(2a) Regarding the flight width B ₁ and the width B ₂ of the land portion in the direction perpendicular to the lead angle in the step flight, the width B ₂ is 0.6 to 0.9 times the width B ₁ . The screw according to claim 1 or 2, comprising:
(3a) When the screw rotates within the heating cylinder, the inside of the heating cylinder includes an upstream supply section where the injection material is supplied, a compression section where the injection material is compressed while being melted, and the injection material in a molten state. It is divided into a measuring section where the weight is measured;
(3b) The step flight is formed in the compression section. The screw according to claim 3, comprising:
(4a) The step flight is formed on the metering portion. An injection device consisting of a heating cylinder and a screw, the screw having the following configuration:
(5a) A stepped portion that is a flight whose top portion is formed into a step-like stepped portion and is composed of a large diameter portion on the upstream side and a land portion on the downstream side that has a smaller diameter than the large diameter portion. Flights have designated sections ;
(5b) The step difference between the large diameter portion and the land portion is greater than 0.5 mm and less than 0.8 mm. The injection device according to claim 5, comprising:
(6a) Regarding the flight width B ₁ and the width B ₂ of the land portion in the direction perpendicular to the lead angle in the stepped flight, the width B ₂ is 0.6 to 0.9 times the width B ₁ . The injection device according to claim 5 or 6, comprising the following configuration:
(7a) When the screw rotates within the heating cylinder, the inside of the heating cylinder includes an upstream supply section where the injection material is supplied, a compression section where the injection material is compressed while being melted, and an injection section in a molten state. It is divided into a measuring section where materials are measured;
(7b) The step flight is formed in the compression section. The injection device according to claim 7, comprising:
(8a) The step flight is formed in the measuring section. An injection molding machine comprising a mold clamping device that clamps a mold, and an injection device that injects an injection material into the mold, the injection device comprising a heating cylinder and a screw having the following configuration:
(9a) A stepped portion that is a flight whose top portion is formed into a stepped portion and is composed of a large diameter portion on the upstream side and a land portion on the downstream side that has a smaller diameter than the large diameter portion. Flights have designated sections ;
(9b) The step difference between the large diameter portion and the land portion is greater than 0.5 mm and less than 0.8 mm. 10. The injection molding machine according to claim 9, comprising:
(10a) In the step flight, the flight width B1 in the direction perpendicular to the lead angle and the width _B2 of the land portion are such that the width _B2 is 0.6 to 0.9 times the width _B1 . The injection molding machine according to claim 9 or 10, comprising:
(11a) When the screw rotates within the heating cylinder, the inside of the heating cylinder includes an upstream supply section where the injection material is supplied, a compression section where the injection material is compressed while being melted, and an injection section in a molten state. It is divided into a measuring section where materials are measured;
(11b) The step flight is formed in the compression section. The injection molding machine according to claim 11, comprising:
(8a) The step flight is formed in the measuring section.

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