Screw for injection molding machine, injection device, and injection molding machine

Abstract

A screw for an injection molding machine, an injection device, and an injection molding machine are provided. A stepped flight (28) is formed in a screw (18) of an injection molding machine (1). The stepped flight (28) is a flight (21) in which a stepped portion is formed in a top portion (29) thereof. The top portion (29) of the flight (21) is composed of a large-diameter portion (31) on an upstream side and a shoulder portion (32) on a downstream side. With respect to a gap H1 between the shoulder portion (32) and a cylinder bore (35) of a heating cylinder (17) and a gap H2 between the large-diameter portion (31) and the cylinder bore (35), a gap ratio m is selected to be 2.3 ≤ m ≤ 6.4 when the gap ratio m = H1 / H2.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a screw for an injection molding machine in which a stepped portion, i.e., a shoulder portion, is formed on the top of a flight, an injection device provided with the screw, and an injection molding machine. BACKGROUND

[0002] An injection device of an injection molding machine is composed of a heating cylinder and a screw put into a bore of the heating cylinder. The screw is formed with a flight for melting and metering an injection material, and the flight has various shapes.

[0003] For example, in the screw described in Patent Literature 1, a stepped portion screw in which a stepped portion is formed on the top of a flight. The stepped portion screw is at the top of the flight, the upstream side of the stepped portion, i.e., the hopper side, is a large diameter portion, and the downstream side, i.e., the injection nozzle side, is a shoulder portion.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent No. 4977258 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, the inventors have found that in the injection device provided with the screw described in Patent Literature 1, there is a problem in that it is desired to improve plasticizing ability in the screw provided with the stepped portion screw. The screw provided with the stepped portion screw has a smaller extrusion amount of the injection material than the screw having the same diameter as the so-called conventional screw in which no stepped portion is formed on the top of the flight. This is because the gap between the top of the flight and the bore of the heating cylinder is small only in the large diameter portion, and at the shoulder portion, the gap becomes large. And it is because the sealing effect at the top of the flight is smaller than that of the conventional screw.

[0009] Therefore, in the present disclosure, a screw having high plasticizing ability, an injection device, and an injection molding machine are provided.

[0010] TECHNICAL SOLUTION FOR SOLVING THE PROBLEMS

[0011] The present disclosure is a screw for an injection molding machine provided with the following structure. That is, a stepped portion screw is formed on the screw. The stepped portion screw is a screw in which a stepped portion is formed on the top of a flight to form a large diameter portion on the upstream side and a shoulder portion on the downstream side. With respect to the shoulder portion and the large diameter portion, when the gap of the bore of the heating cylinder is set to H1, H2, respectively, and set to a gap ratio m = H1 / H2, it is selected to be 2.3 ≤ m ≤ 6.4.

[0012] EFFECT OF THE INVENTION

[0013] According to the present disclosure, with respect to a screw having a stepped flight, when the gap ratio m is selected to be 2.3 or more and 6.4 or less, an effect of increasing the extrusion amount can be obtained. That is, the plasticizing capacity becomes high. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a front view showing an injection molding machine to which the present embodiment is applied.

[0015] Figure 2 is a front sectional view showing an injection device to which the present embodiment is applied.

[0016] Figure 3 is a front view showing a part of a screw to which the present embodiment is applied.

[0017] Figure 4 is a sectional view showing a stepped flight provided to a screw to which the present embodiment is applied.

[0018] Figure 5 is a sectional view showing a stepped flight provided to a screw to which the present embodiment is applied, and a graph showing a lubrication pressure generated at a top of the stepped flight due to an injection material flowing between the stepped flight and a cylinder bore of a heating cylinder.

[0019] Figure 6 is a graph schematically showing behavior of a viscous fluid flowing in a gap between a moving sheet and a fixed sheet.

[0020] Figure 7 is a graph showing a change in a load capacity coefficient related to a lubrication pressure at a top of a flight when a shape factor β is changed in a stepped flight.

[0021] Figure 8 is a graph showing a change in a load capacity coefficient related to a lubrication pressure at a top of a flight when a gap ratio m is changed in a stepped flight.

[0022] Figure 9 is a graph showing that, when a screw is rotated in a heating cylinder, the screw generates an amplitude and a rotational axis is eccentric with respect to a central axis of the heating cylinder. The graph is a graph showing degrees of the amplitude of the screw at various screw positions with respect to three screws having stepped flights with different gap ratios m and a conventional screw.

[0023] Figure 10 is a sectional view showing a stepped flight of a screw to which the present embodiment is applied provided to a heating cylinder.

[0024] Figure 11 is a graph showing a relationship between a gap ratio m and a load capacity coefficient.

[0025] Figure 12is a sectional view of the upper half of the center axis of the stepped flight of the screw involved in the present embodiment, which is provided to the screw of the present embodiment. DETAILED DESCRIPTION

[0026] Hereinafter, a detailed description will be given of the specific embodiments with reference to the drawings. However, the embodiments are not limited to the following. In order to make the description clear, the following description and the drawings are appropriately simplified. In each drawing, the same reference numerals are assigned to the same elements, and repeated description is omitted as necessary. In addition, in order not to complicate the drawings, there are parts in which hatching is omitted.

[0027] The present embodiment will be described.

[0028] <Injection molding machine>

[0029] As shown in Figure 1 , the injection molding machine 1 involved in the present embodiment is roughly composed of a clamping device 2 provided to a machine tool B and an injection device 3 involved in the present embodiment, which will be described below. The clamping device 2 is composed of a fixed disk 7, a movable disk 8, a clamping housing 9, connecting rods 10, 10,..., which link the clamping housing 9 and the fixed disk 7, and a clamping mechanism 11 composed of a toggle lever mechanism. Molds 13, 14 are provided to the fixed disk 7 and the movable disk 8. When the clamping mechanism 11 is driven, the molds 13, 14 are clamped.

[0030] <Injection device>

[0031] The injection device 3 involved in the present embodiment is provided so as to be freely advanced and retracted with respect to the clamping device 2, and injects an injection material to the molds 13, 14 clamped by the clamping device 2. As shown in Figure 2 , the injection device 3 is composed of a heating cylinder 17 and a screw 18 involved in the present embodiment. A hopper 19 is provided near the rear end portion of the heating cylinder 17, and an injection nozzle 20 is provided to the front end portion. When an injection material is put into the hopper 19 and the screw 18 is rotated, the injection material is melted and fed to the front, and is metered. That is, in the injection device 3, the hopper 19 side is the upstream side, and the injection nozzle 20 side is the downstream side.

[0032] <Screw>

[0033] In the screw 18 according to the present embodiment, the flight 21 has a feature in the shape of a portion of the flight 21, which will be described below, but the entire shape is as described below. In the screw 18, the depth of the groove formed by the flight 21 varies in each portion of the screw 18, which divides the inside of the heating cylinder 17. That is, the upstream side of the screw 18 is formed with a deep groove, which becomes a supply portion 23 in which the injection material is fed downstream while being heated. Also, the groove depth gradually becomes shallower in the middle stream, which becomes a compression portion 24 in which the injection material is compressed while being melted, and the downstream side is formed with a shallow groove, which becomes a metering portion 25 in which the injection material is metered.

[0034] The screw 18 according to the present embodiment is shown enlarged in a portion thereof Figure 3 characterized in that a portion of the flight 21 becomes a stepped flight 28. In the stepped flight 28, the cross section taken at A-A of Figure 3 is shown in Figure 4 characterized by a top 29 thereof. That is, the top 29 of the stepped flight 28 is formed into a stepped portion, and the stepped flight 28 is composed of a large diameter portion 31 on the upstream side and a shoulder portion 32 on the downstream side. Since the diameter of the shoulder portion 32 is smaller than the diameter of the large diameter portion 31 by an amount of a step 33, the gap HI between the shoulder portion 32 and the bore 35 of the heating cylinder 17 is larger than the gap H2 between the large diameter portion 31. As a result of this, the stepped flight 28 generates an appropriate lubrication pressure at the top 29 by the injection material entering, which prevents contact between the heating cylinder 17 and the screw 18.

[0035] In addition, in the present embodiment, the stepped flight 28 is provided in the compression portion 24 and the metering portion 25. This is because, when the screw 18 rotates, there is a case where the screw 18 generates an amplitude in which the rotational axis is eccentric from the axis of the heating cylinder 17, and the degree of the amplitude is relatively large in the compression portion 24, and the degree is next largest in the metering portion 25. Therefore, although the stepped flight 28 is provided in these sections, even if the stepped flight 28 is provided only in the compression portion 24 in which the degree of the amplitude is large, the effect of being able to prevent contact between the heating cylinder 17 and the screw 18 is obtained.

[0036] When the screw 18 rotates to feed the injection material forward, the stepped flight 28 is formed with the shoulder portion 32 compared to the flight of a conventional screw, and the injection material easily flows in correspondence with the large amount of the gap HI, and the plasticizing ability is lower than that of the conventional screw. However, the screw 18 according to the present embodiment is characterized by the numerical range of the gap ratio m, and the plasticizing ability is made higher despite the stepped flight 28. The gap ratio m is the ratio of the gap HI to the gap H2, that is, m = HI / H2, and is specifically selected to be in the following numerical range.

[0037] 2.3 ≤ m ≤ 6.4 (numerical range A)

[0038] If the gap ratio m is thus selected, the plasticizing ability becomes high. This fact is clarified by experiments explained later. However, according to a theoretical study based on a model explained later, the ideal range of the gap ratio m is 1.65 or more and 2.15 or less. This is because a high lubrication pressure can be obtained in this range. The numerical range A of the gap ratio m selected in the present embodiment is a range of a value larger than this ideal range.

[0039] Now, two problems arise. The first problem is that, although the numerical range A is larger than the ideal range, the plasticizing ability is higher than that of a screw in which the gap ratio m is in the ideal range. The larger the gap ratio m, the larger the gap Hl at the shoulder portion 32, and the more easily the resin material flows, and the plasticizing ability should be smaller. However, this is contrary to the expectation. The second problem is whether the necessary lubrication pressure is generated even if the gap ratio m deviates from the ideal range. In the case of the first problem, as described above, it is clarified by experiments that the plasticizing ability of the screw 18 according to the present embodiment is higher than that of a screw in which the gap ratio m is in the ideal range. In the case of the second problem, it is also confirmed by experiments that the necessary lubrication pressure can be obtained. These are described.

[0040] First, the behavior of the injection material in the step portion flight 28 is theoretically studied by a model.

[0041] <Mechanism of generating lubrication pressure and load capacity W of lubrication>

[0042] First, the mechanism of generating the lubrication pressure in the step portion flight 28 is described, and the load capacity W of the lubrication that prevents the contact of the top 29 of the step portion flight 28 with the cylinder bore of the heating cylinder 17 is expressed by a formula.

[0043] When the screw 18 is rotated in the heating cylinder 17, the step portion flight 28 is driven at a prescribed speed with respect to the cylinder bore of the heating cylinder 17, and this speed can be divided into a component parallel to the step portion flight 28 and a component perpendicular to the step portion flight 28. When the component perpendicular to the step portion flight 28 is considered, as shown in Figure 5 , the step portion flight 28 seems to move in the left direction at a speed U' with respect to the heating cylinder 17. If the step portion flight 28 is regarded as being fixed, it can be considered that the heating cylinder 17 moves in the right direction at a speed U. The speed U is a speed equal in magnitude and opposite in direction to the speed U'.

[0044] The molten injection material enters the gap Hl and is discharged from the gap H2. At this time, the lubrication pressure is generated. The distribution of the speed v of the injection material in the gaps Hl, H2 is schematically shown in Figure 5The lubrication pressure p becomes a maximum value Ps in the vicinity of the step portion at the boundary of the large-diameter portion 31 and the shoulder portion 32, and substantially 0 at both end surfaces of the step portion screw ridge 28. Further, the lubrication pressure p changes linearly in the large-diameter portion 31 and the shoulder portion 32, respectively. In addition, the lubrication pressure p changes linearly because the flow of the molten resin having a high viscosity becomes laminar flow, and the laminar flow loses pressure in proportion to the distance of the flow.

[0045] Here, the general behavior of a viscous fluid between two planes that are moving relative to each other is considered. Figure 6 A model composed of a fixed plate 37 and a moving plate 38 that slides relative to the fixed plate 37 at a speed V is shown, and a Newtonian fluid is filled between the fixed plate 37 and the moving plate 38. If the balance of forces acting on an infinitesimal element 39 of the fluid is considered, the following equation 1 is obtained from the balance of forces in the x-axis direction. Here, p is the pressure, and τ is the shear force.

[0046]

[0047] When the viscosity of the fluid is set to μ, and the flow rate in the x direction is set to v, the shear force τ is given by the following equation 2.

[0048]

[0049] The following equation 3 is obtained from the equations 1 and 2.

[0050]

[0051] The equation 3 can also be obtained from so-called Navier-Stokes equations, and becomes a formula that represents the steady flow of an incompressible fluid.

[0052] When the gap in the y direction between the fixed plate 37 and the moving plate 38 is set to h, the velocity v of the fluid at y = h is 0. In addition, at y = 0, the velocity v of the fluid is V. When these are solved as boundary conditions, the following equation 4 that is a relationship formula of the flow rate v and the pressure distribution is obtained.

[0053]

[0054] If the unit width perpendicular to the paper is considered, the flow rate Q of the fluid flowing in the gap h is given by the following equation 5 obtained by integrating the equation 4.

[0055]

[0056] According to the equation 5, the following is calculated Figure 5The flow rate Qx of the molten resin flowing in the gap Hl, the gap H2 in the model shown. The flow rate Qx is equal in the gap Hl, the gap H2. Here, when the rib width of the stepped rib 28 is set to Bl, and the width of the shoulder portion 32 is set to B2, the pressure gradient dp / dx is given by Ps / B2 in the gap Hl, and is given by (0-Ps) / (Bl-B2) in the gap H2. Then, the flow rate Qx is given by the 6 formula.

[0057]

[0058] If the 6 formula is solved for the maximum value Ps of the lubrication pressure, the 7 formula is obtained.

[0059]

[0060] The load capacity W of lubrication per unit length in the stepped rib 28 is obtained by integrating the lubrication pressure p in the width direction of the stepped rib 28. However, as shown in the 6 formula, Figure 5 the lubrication pressure p varies like a triangle whose base length is Bl and height is Ps. Then, the load capacity W is given as its area. The load capacity W thus calculated is expressed by the 8 formula.

[0061]

[0062]

[0063] In addition, Kw is a load capacity coefficient, m is a gap ratio, that is, a ratio of the gaps Hl, H2, and β is a shape factor, that is, a ratio of the rib width Bl to the width B2 of the shoulder portion 32.

[0064] The stepped rib 28 generates a repulsive force between the top portion 29 and the bore of the heating cylinder 17 due to the load capacity W of lubrication shown in the 8 formula, thereby preventing contact.

[0065] The load capacity W of lubrication is proportional to the load capacity coefficient Kw, which varies depending on the gap ratio m, which is a ratio of the gaps Hl, H2, and the shape factor β, which is a ratio of the rib width Bl to the width B2 of the shoulder portion 32. Therefore, for the load capacity coefficient Kw given by the 8 formula, the changing condition when the shape factor β is changed with respect to various gap ratios m is shown in the graph of Figure 7 . In addition, the changing condition of the load capacity coefficient Kw when the gap ratio m is changed with respect to various shape factors β is shown in the graph of Figure 8 .

[0066] When the gap ratio m and the shape factor β are the following conditions, the load capacity coefficient Kw becomes 0.2 or more.

[0067] 1.65 ≤ m ≤ 2.15

[0068] 0.63 ≤ β ≤ 0.79

[0069] At this time, the load capacity W is maximum, and the contact of the top 29 of the stepped flight 28 with the cylinder bore 35 of the heating cylinder 17 is reliably prevented by the high lubrication pressure. The above is a theoretical investigation based on a model.

[0070] As described above, in the stepped flight 28 of the screw 18 according to the present embodiment, the gap ratio m is selected to be in the numerical range A. This selection is made based on the following experiments.

[0071] The first experiment will be described.

[0072] <First Experiment>

[0073] Purpose of the experiment:

[0074] In the screw 18 having the stepped flight 28, the relationship between the gap ratio m and the plasticizing capacity was made clear.

[0075] Preparation of the experiment: A heating cylinder 17 having an inner diameter of 91.8 mm, and five screws X, Y, A, B, and C having the same screw diameter and the same flight groove depth were prepared. The screw X is a conventional screw having a flat flight top, and the screws Y, A to C are the screw 18 according to the present embodiment having the stepped flight 28 formed in the compression section 24 and the metering section 25. Further, for the screws Y, A, B, and C, the gap ratio m = H1 / H2 was changed. Specifically, it was set to 2.00, 2.33, 4.33, and 6.33, respectively.

[0076] Method of the experiment:

[0077] The screws X, Y, A, B, and C were sequentially set in the heating cylinder 17, and polypropylene (PP) and polyethylene (PE) were supplied as the resin material, and the extrusion amount was measured. This extrusion amount becomes an index of the plasticizing capacity in the case where the rotation speed of the screw is the same. That is, it can be said that the more the extrusion amount is, the higher the plasticizing capacity is. The measurement of the extrusion amount was performed in accordance with the following conditions 1 and 2.

[0078] "Condition 1": The screw was rotated for 90 seconds, and the weight of the extruded resin material was measured.

[0079] "Condition 2": The screw was rotated for 10 seconds and stopped for 10 seconds, the screw was rotated for 10 seconds and stopped for 10 seconds,..., such repetition was performed 10 times, and the weight of the extruded resin material was measured.

[0080] The test results are shown in Table 1.

[0081] [Table 1]

[0082]

[0083] Unit: g

[0084] Summary of the experiment:

[0085] The gap ratio m of the screw Y fell within the ideal numerical range obtained by the model-based theoretical investigation, but the extrusion amount was small compared with the screw X which was a conventional screw. In contrast, the gap ratio m of the screws A, B, C deviated from the ideal numerical range and became large, but the extrusion amount became large compared with the screw Y.

[0086] However, if the flow rate Ql of the injection material flowing in the gap HI of the shoulder portion 32 is considered based on the equation 5, the following equation 9 can be obtained.

[0087]

[0088] Originally, if the gap ratio m becomes large, the gap HI necessarily becomes large, and therefore the flow rate Ql should become large according to the first term of the equation 9. The flow rate Ql is considered to be the leakage of the injection material at the top 29 of the flight 21, and therefore the extrusion amount should decrease when the gap ratio m becomes large. However, the result of the experiment showed an effect contrary to this expectation.

[0089] According to Figure 10 An investigation was conducted. It was considered that in the case where the gap ratio m was large, that is, in the case where the gap HI was larger than the gap H2, the stagnation of the injection material occurred in the region indicated by the reference numeral 41 near the step 33. Due to this stagnation, the effect of pushing back the injection material occurred, and the thickness of the flow of the injection material at the shoulder portion 32 became thin. Due to this, the apparent gap HI' became smaller than the actual gap HI. Therefore, it was considered that the flow rate Ql indicated by the equation 9 became small. It was considered that the larger the gap ratio m, the larger the region 41 where the stagnation occurred, the smaller the apparent gap HI' compared with the actual gap HI, and as a result, the flow rate Ql became small and the extrusion amount became large.

[0090] Summary of the experiment:

[0091] It was found that in the screw 18 provided with the stepped flight 28, the plasticizing capacity of the screws A, B, C having the gap ratio m of 2.33, 4.33, 6.33 was higher compared with the screw Y having the gap ratio m of 2.00. From the viewpoint of the plasticizing capacity, it can be said that the above-mentioned numerical range A is preferable as the gap ratio m. More preferably, 2.3 or more and 4.3 or less is preferable as the gap ratio m.

[0092] Next, for the screw 18 provided with the gap ratio m of such a numerical range A, a second experiment was conducted in order to confirm whether the necessary lubrication pressure was generated or not.

[0093] [Second Experiment]

[0094] Purpose of the experiment:

[0095] For the screw 18 in which the gap ratio m is in the range of values A, it was confirmed whether or not the lubrication pressure was appropriately generated to reliably prevent the top 29 of the flight 21 from coming into contact with the bore 35 when it was rotated in the heating cylinder 17 to meter the injection material.

[0096] Preparation for the experiment:

[0097] In the injection apparatus 3 of the present embodiment shown in Figure 2 In the injection apparatus 3 of the present embodiment shown in

[0098] Process and results of the experiment:

[0099] In the heating cylinder 17, the screws X, A, B, C were sequentially arranged and rotated to meter the injection material. At this time, based on the distance between the screw and the heating cylinder 17 detected at each of the positions G7, G8,..., G12, the screw amplitude ratio at each position was obtained. The results thereof are shown in the graph of Figure 9 The numerals 46, 47, 48 are graphs of the screws A, B, C, respectively, i.e., graphs in which the gap ratio m is 2.33, 4.33, 6.33. Also, the numeral 49 is a graph of the screw X, i.e., a graph of a conventional screw. Further, the screw amplitude ratio is 0.0 when the central axis of the screw 18 coincides with the central axis of the heating cylinder 17, and is 1.0 when the screw 18 comes into contact with the bore of the heating cylinder 17. From the graph of Figure 9 the screw amplitude ratio of the present embodiment is in the range of 0.17 to 0.82.

[0100] Investigation:

[0101] For the screw C in which the gap ratio m is 6.4, it was also confirmed that the screw amplitude ratio was sufficiently small compared to the conventional screw, and that the necessary lubrication pressure was obtained. However, the shape factor β of this screw C was 0.94, and according to the equation 8 as a theoretical equation, the load capacity coefficient Kw was 0.056, and it was theoretically predicted that a sufficient lubrication pressure could not be obtained. However, in reality, it was confirmed through the experiment that the necessary lubrication pressure was obtained. If the reason therefor is presumed, as investigated in the first experiment through Figure 10 it is possible that the apparent gap H1' becomes thin compared to the gap H1 at the shoulder portion 32 in the case where the gap ratio m is large. Thus, for example, the graph showing the relationship between the gap ratio m and the load capacity coefficient Kw when the shape factor β is 0.9, shown in Figure 8 is as shown in Figure 11The graph 50 is actually shown as a broken line as illustrated schematically.

[0102] Summary of the experiment:

[0103] In the screw 18 having the stepped flight 28, it was confirmed that the screws A, B, and C having the clearance ratios m of 2.33, 4.33, and 6.33 were able to obtain the necessary lubrication pressure, and the contact with the cylinder bore 35 of the heating cylinder 17 was appropriately prevented. It was found that the clearance ratio m was not problematic from the viewpoint of obtaining the necessary lubrication pressure, from the numerical range A.

[0104] According to this second experiment, it was found that the lubrication pressure was sufficiently obtained even when the shape factor β was 0.94. According to the graph of Figure 8 , it was found that the theoretical load capacity coefficient Kw was read as 0.056 or more when the shape factor β was 0.5 and the value of the clearance ratio m was 4.6 or less, and the theoretical load capacity coefficient Kw was read as 0.056 or more when the shape factor β was 0.6 and the clearance ratio m was 5.2 or less. Furthermore, it was found that the theoretical load capacity coefficient Kw was read as 0.056 or more when the shape factor β was 0.95 and the value of the clearance ratio m was 6.5 or less. It was found that the actual load capacity coefficient Kw became larger than the theoretical value when the clearance ratio m was large, and thus the necessary lubrication pressure was able to be obtained. It can be said that the range of the shape factor β is preferably 0.5 or more and 0.95 or less.

[0105] Next, the preferable condition was investigated also with respect to the diameter of the screw 18. In the compression section 24, as shown in Figure 12 , the injection material 51 in a solid state and the injection material 52 in a molten state were mixedly present inside the heating cylinder 17. The injection material 51 in a solid state was stacked at the back of the flight 21, that is, the upstream side, and thus a solid bed 54 was formed. A molten film 55 composed of the molten injection material was formed between the solid bed 54 and the cylinder bore 35 of the heating cylinder 17, and a molten pool 57 composed of the molten injection material was formed at the upstream side of the solid bed 54.

[0106] When the screw 18 was rotated, as explained, the lubrication pressure was generated at the top 29 of the stepped flight 28, and a negative pressure was generated at the molten film 55. The negative pressure became a cause of the vibration of the screw 18 when the screw 18 was rotated, and the thinner the thickness H3 of the molten film 55, the larger the magnitude of the negative pressure. That is, if the thickness H3 of the molten film 55 was thin, there was a risk that the screw 18 contacted the cylinder bore 35 of the heating cylinder 17.

[0107] However, the larger the diameter of the screw 18, the thicker the thickness H3 of the molten film 55. That is, if the injection device 3 is large, the thickness H3 of the molten film 55 becomes thick. This is because the larger the machine, the more efficiently the injection material needs to be melted, and thus the heating cylinder 17 is heated more efficiently. In addition, this is because the larger the machine, the smaller the rotation speed of the screw 18, and the more the time for melting the injection material increases. In the industry, a device in which the diameter of the screw 18 is 70 mm or more is generally regarded as a large machine, but for the screw 18 having a diameter of 70 mm or more, the thickness H3 of the molten film 55 becomes sufficiently large, and the influence of the negative pressure generated by the molten film 55 can be ignored. Therefore, the diameter of the screw 18 is preferably 70 mm or more. For example, the diameter of the large diameter portion 31 of the screw 18 is 70 mm or more. In addition, the diameter of the large diameter portion 31 of the screw 18 is, for example, 450 mm or less, preferably 200 mm or less, and more preferably 130 mm or less.

[0108] The above describes the invention completed by the inventors of the present application based on the embodiments, but the present application is not limited to the described embodiments, and various modifications can of course be made within the scope of the gist thereof. The above-described multiple examples can also be appropriately combined to be implemented.

[0109] Reference Signs List

[0110] 1 injection molding machine

[0111] 2 mold clamping device

[0112] 3 injection device

[0113] 13 mold

[0114] 14 mold

[0115] 17 heating cylinder

[0116] 18 screw

[0117] 21 screw flight

[0118] 23 supply portion

[0119] 24 compression portion

[0120] 25 metering portion

[0121] 28 stepped portion screw flight

[0122] 29 top portion

[0123] 31 large diameter portion

[0124] 32 shoulder portion

[0125] 33 step

Claims

1. A screw which is inserted into a cylinder bore of a heating cylinder of an injection molding machine, wherein the screw has flight surfaces, a stepped portion is formed on a top of a part of the flight surfaces of the screw, the flight surface on which the stepped portion is formed becomes a stepped portion flight surface, the stepped portion flight surface is composed of a large diameter portion on an upstream side and a shoulder portion on a downstream side, a clearance ratio m = H1 / H2 between a clearance H2 between the large diameter portion and the cylinder bore and a clearance H1 between the shoulder portion and the cylinder bore is 2.3 or more and 6.4 or less, and a width B2 of the shoulder portion and a flight surface width B1 in a direction perpendicular to a lead angle in the stepped portion flight surface satisfy that the width B2 is 0.5 times or more and 0.95 times or less of the width B1.

2. The screw according to claim 1, wherein a diameter of the large diameter portion is 70 mm or more.

3. The screw according to claim 1 or 2, wherein when the screw is rotated in the heating cylinder, the heating cylinder is divided into a supply portion on an upstream side which supplies an injection material, a compression portion in which the injection material is compressed while being melted, and a metering portion which meters the injection material in a molten state, and the stepped portion flight surface is formed in the compression portion.

4. The screw according to claim 3, wherein the stepped portion flight surface is formed in the metering portion.

5. An injection device which is composed of a heating cylinder having a cylinder bore and a screw, a stepped portion is formed on a top of a part of flight surfaces of the screw, a part of the flight surfaces of the screw becomes a stepped portion flight surface, the stepped portion flight surface is composed of a large diameter portion on an upstream side and a shoulder portion on a downstream side, a clearance ratio m = H1 / H2 between a clearance H2 between the large diameter portion and the cylinder bore and a clearance H1 between the shoulder portion and the cylinder bore is 2.3 or more and 6.4 or less, and a width B2 of the shoulder portion and a flight surface width B1 in a direction perpendicular to a lead angle in the stepped portion flight surface satisfy that the width B2 is 0.5 times or more and 0.95 times or less of the width B1.

6. The injection device according to claim 5, wherein a diameter of the large diameter portion is 70 mm or more.

7. The injection device according to claim 5 or 6, wherein when the screw is rotated in the heating cylinder, the heating cylinder is divided into a supply portion on an upstream side which supplies an injection material, a compression portion in which the injection material is compressed while being melted, and a metering portion which meters the injection material in a molten state, and the stepped portion flight surface is formed in the compression portion.

8. The injection device according to claim 7, wherein the stepped portion flight surface is formed in the metering portion. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 9. An injection molding machine comprising a clamping device that clamps a mold, and an injection device that injects an injection material into the mold, the injection device comprising a heated cylinder having a cylinder bore, and a screw, a portion of the screw having a stepped portion formed at a top of a flight to become a stepped portion flight, the stepped portion flight comprising a large diameter portion on an upstream side and a shoulder portion on a downstream side, a clearance ratio m = H1 / H2 between a clearance H2 between the large diameter portion and the cylinder bore and a clearance H1 between the shoulder portion and the cylinder bore being 2.3 or greater and 6.4 or less, in the stepped portion flight, a flight width B1 in a direction perpendicular to a lead angle and a width B2 of the shoulder portion satisfy width B2 being 0.5 times or greater and 0.95 times or less of width B1.

10. The injection molding machine according to claim 9, wherein the large diameter portion has a diameter of 70 mm or greater.

11. The injection molding machine according to claim 9 or 10, wherein when the screw rotates in the heated cylinder, the heated cylinder is divided into a supply portion that supplies the injection material on an upstream side, a compression portion in which the injection material is compressed while being melted, and a metering portion that meters the injection material in a molten state, the stepped portion flight being formed in the compression portion.

12. The injection molding machine according to claim 11, wherein the stepped portion flight is formed in the metering portion.

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