Injection molding machine

Abstract

This invention provides an injection molding machine that can suppress leakage of molding material and simultaneously suppress contact between the plunger and the injection cylinder, and can set the gap between the injection cylinder and the plunger to be relatively large. The invention provides an injection molding machine including a plasticizing section for plasticizing molding material, an injection section for metering and injecting molding material, a connector connecting the plasticizing section and the injection section, and a control device. The plasticizing section includes a plasticizing cylinder and a screw. The injection section includes an injection cylinder, a plunger, and a sealing ring disposed at the rear end of the injection cylinder for the plunger to pass through. A first gap, serving as the interval between the plunger and the injection cylinder, is larger than a second gap, serving as the interval between the plunger and the sealing ring. The sealing ring is configured to be coolable, causing the molding material flowing between the plunger and the sealing ring to solidify or thicken.

Description

Technical Field

[0001] This invention relates to an injection molding machine, and more particularly to a screw pre-plunger type injection molding machine. Background Technology

[0002] Injection molding machines plasticize the molding material, measure a specified amount, and inject it into a mold to form the desired molded product. Currently, practical injection molding machines are mainly divided into two types: in-line screw type and screw pre-plasticizing plunger type.

[0003] A screw-pre-plasticized plunger injection molding machine includes a plasticizing cylinder, a screw rotatably disposed within the plasticizing cylinder, an injection cylinder, and a plunger rotatably disposed within the injection cylinder. The screw rotates within the plasticizing cylinder, plasticizing the molding material and conveying it to the injection cylinder. Then, the plunger in the injection cylinder retracts to meter the molding material; after metering, the plunger advances to inject the molding material.

[0004] To prevent jamming, a certain clearance must be provided between the outer surface of the plunger and the inner surface of the injection cylinder. Sometimes, the plasticized molding material leaks slightly from the rear of the injection cylinder through this clearance. If the leakage is large or uneven, the molding stability is compromised. Therefore, the clearance is usually kept as small as possible to reduce and maintain a constant leakage amount, thus achieving stable molding.

[0005] For example, Patent Document 1 discloses a structure in which the gap is kept at an optimal value by separately controlling the temperature of the plunger and the injection cylinder in a screw pre-plasticizing plunger injection molding machine.

[0006] [Existing technical documents]

[0007] [Patent Literature]

[0008] [Patent Document 1] Japanese Patent No. 2549357 Summary of the Invention

[0009] [The problem the invention aims to solve]

[0010] For some molding materials, if the gap between the plunger and the injection cylinder is too small, it may result in poor molding or severe wear of the components.

[0011] In molding materials, various fillers are sometimes added in addition to resin to improve physical properties. Furthermore, molding materials sometimes use fillers such as metal powder or ceramic powder as the main material, with resin acting as a binder mixed in. In this specification, fillers used in the resin mixture are broadly referred to as fillers, regardless of their shape or mixing ratio. When such a material containing resin and filler is used as a molding material, the filler entering between the plunger and the injection cylinder may be squeezed against the plunger or injection cylinder and become fixed in place as the plunger advances or retracts. This fixation is particularly prone to occur when the filler is metallic. If the filler becomes fixed in the component, the slippage of the plunger may deteriorate, leading to unstable molding, or the plunger or injection cylinder may wear out.

[0012] Furthermore, depending on the molding material, corrosive outgassing may occur during plasticizing, sometimes leading to corrosion of the plunger or injection cylinder. If injection is repeatedly performed while the surface hardness is reduced due to corrosion, a portion of the steel constituting the plunger or injection cylinder may dissolve into the molding material when the plunger contacts the injection cylinder. This dissolution can cause molding defects such as black streaks or blurring on the surface of the molded article.

[0013] To avoid filler adhesion or to prevent contact between the plunger and the injection cylinder, increasing the gap between the plunger and the injection cylinder is considered. However, simply increasing the gap increases the leakage of molding material and compromises molding stability. Moreover, a large gap can cause the plunger to wobble within the injection cylinder, potentially inducing contact between the plunger and the injection cylinder.

[0014] The present invention was made in view of this situation, and its object is to provide an injection molding machine that can suppress the leakage of molding material and simultaneously suppress the contact between the plunger and the injection cylinder, and can set the gap between the injection cylinder and the plunger to be relatively large.

[0015] [Technical means to solve the problem]

[0016] According to the present invention, an injection molding machine is provided, comprising: a plasticizing section, on which a molding material comprising at least a resin is supplied to plasticize the molding material; an injection section, which measures and injects the molding material from the plasticizing section; a junction, connecting the plasticizing section and the injection section; and a control device, controlling the plasticizing section and the injection section. The plasticizing section includes: a plasticizing cylinder on which the molding material is supplied; and a screw rotatably disposed within the plasticizing cylinder. The injection section includes: an injection cylinder on which the molding material is conveyed from the plasticizing cylinder; a plunger rotatably disposed within the injection cylinder; and a sealing ring disposed at the rear end of the injection cylinder for the plunger to pass through. A first gap, which is the distance between the plunger and the injection cylinder when the central axis of the plunger coincides with the central axis of the injection cylinder, is larger than a second gap, which is the distance between the plunger and the sealing ring when the central axis of the plunger coincides with the central axis of the injection cylinder. The sealing ring is configured to be coolable, so that the molding material flowing between the plunger and the sealing ring solidifies or thickens.

[0017] [The effects of the invention]

[0018] In the injection molding machine of the present invention, a sealing ring configured in a coolable manner is provided at the rear end of the injection cylinder. The molding material flowing between the plunger and the sealing ring solidifies or thickens, supporting the plunger and suppressing leakage of the molding material. Therefore, even if the gap between the plunger and the injection cylinder is set relatively large, leakage of the molding material is suppressed. Furthermore, the rear part of the plunger is supported by the sealing ring itself or by the solidified or thickened molding material within the sealing ring, thereby suppressing plunger wobbling and preventing contact between the plunger and the injection cylinder. Attached Figure Description

[0019] Figure 1 This is a schematic structural diagram of the injection unit of the injection molding machine according to this embodiment.

[0020] Figure 2 This is an enlarged view of the area around the sealing ring.

[0021] Figure 3 This is a three-dimensional view of the sealing ring, retainer, and temperature control block.

[0022] Figure 4 This is a cross-sectional view of the sealing ring.

[0023] Figure 5 Indicates the first gap and the second gap.

[0024] Figure 6 This is a front view of the retainer.

[0025] Figure 7 This is a cross-sectional view of the temperature control block.

[0026] Figure 8 This indicates the state of the plunger, which is tilted downwards as far as it can go.

[0027] Figure 9 for Figure 8 Enlarged view of the area around the sealing ring.

[0028] Figure 10 for Figure 8 A magnified view of the area around the tip of the plunger.

[0029] Figure 11 for Figure 8 A magnified view of the area around the tip of the plunger.

[0030] [Explanation of Symbols]

[0031] 2: Plasticizing Department

[0032] 3: Connecting parts

[0033] 4: Injection Section

[0034] 6: Control device

[0035] 21: Plasticizing tank

[0036] 23: Screw

[0037] 41: Injection cylinder

[0038] 42: Plunger

[0039] 51: Sealing ring

[0040] 53: Holder

[0041] 55: Temperature regulating block

[0042] 57: Temperature sensor

[0043] 556: On / off valve

[0044] C1: First gap

[0045] C2: Second gap Detailed Implementation

[0046] Hereinafter, embodiments of the present invention will be described using the accompanying drawings. The various modifications described below can be implemented in any combination.

[0047] The injection molding machine of this embodiment is a screw pre-plasticizing plunger injection molding machine. The injection molding machine includes an injection unit 1, a clamping unit (not shown), and a control device 6 for controlling the injection unit 1 and the clamping unit. The injection unit 1 plasticizes the molding material, measures a predetermined amount, and then injects it into a mold (not shown) held by the clamping unit. The clamping unit is configured to open, close, and lock the mold. During injection of the molding material, the clamping unit closes the mold and applies a predetermined clamping force to the mold. After the molding material injected into the mold cavity cools and becomes a molded article, the clamping unit opens the mold to discharge the molded article and closes the mold again. The clamping unit can employ well-known structures such as direct-pressure or toggle types.

[0048] like Figure 1 As shown, the injection unit 1 includes a plasticizing part 2, a connecting part 3, and an injection part 4. Figure 1 In the diagram, a portion of the structure is shown in cross-sectional view. Furthermore, unless otherwise specified, the following will refer to one side of the injection-molded material (…). Figure 1 The left side of the middle is set as "front", and the side supplying the forming material is set to the "front". Figure 1 The right side of the text is designated as "after" for explanation. Furthermore, the following explanation uses a horizontal injection molding machine as an example, but injection molding machines can also be vertical or other types.

[0049] Plasticizing section 2 plasticizes the supplied molding material and conveys it forward. Plasticizing section 2 includes plasticizing cylinder 21, screw 23, check valve 25, screw drive device 27, and heater 29.

[0050] Plasticizing cylinder 21 is a cylindrical body to which molding material is supplied. A material inlet 211 is formed on the rear side of plasticizing cylinder 21, and molding material is supplied to the material inlet 211 via a hopper (not shown). Plasticizing cylinder 21 is heated to a specified temperature by heater 29.

[0051] The screw 23 is rotatably mounted inside the plasticizing cylinder 21. The screw 23 plasticizes the molding material supplied to the plasticizing cylinder 21 using the heat and shear heat provided by the heater 29, while conveying it forward.

[0052] The check valve 25 is, for example, a single-acting cylinder that advances the screw 23 to block the flow path when metering is complete, preventing the backflow of molding material during injection. Alternatively, other check valve mechanisms, such as ball valves, may be used instead of the check valve 25.

[0053] The screw drive 27 can be any actuator that rotates the screw 23, such as a hydraulic motor or an electric motor.

[0054] The coupling 3 connects the plasticizing section 2 and the injection section 4. The molding material fed from the plasticizing cylinder 21 is conveyed to the injection cylinder 41 through the connecting passage in the coupling 3. In addition, a heater may be provided in the coupling 3 to form the coupling in a heatable manner.

[0055] The injection unit 4 measures the molding material delivered from the plasticizing unit 2 and injects it into the mold. The injection unit 4 includes an injection cylinder 41, a plunger 42, a nozzle cylinder 43, a nozzle 44, a connecting component 45, a plunger drive device 46, a coupling 47, and heaters 48 and 49.

[0056] The injection cylinder 41 is a cylindrical body for metering the molding material fed from the plasticizing cylinder 21. The injection cylinder 41 is heated to a specified temperature by the heater 48.

[0057] The plunger 42 is a generally cylindrical component that is freely movable within the injection cylinder 41. However, the tip of the plunger 42 may also have a conical portion. During metering, the plunger 42 retracts due to the pressure of the molding material supplied to the injection cylinder 41. The position of the plunger 42 is detected using an encoder (not shown), thereby metering the required amount of molding material within the injection cylinder 41. However, during metering, the plunger 42 may also be actively retracted using a plunger drive device 46. After metering the specified amount of molding material, the plunger 42 is advanced at a specified speed or pressure, extruding the molding material within the injection cylinder 41 towards the nozzle 44.

[0058] A nozzle cylinder 43 is provided in front of the injection cylinder 41. The nozzle cylinder 43 has: a flow path connected to the connecting member 3 and conveying the molding material from the plasticizing cylinder 21 to the front of the injection cylinder 41; and a flow path conveying the molding material extruded from the injection cylinder 41 by the plunger 42 to the nozzle 44. The nozzle cylinder 43 is heated to a specified temperature by the heater 48.

[0059] A nozzle 44 is mounted on the front surface of the nozzle cylinder 43, and the nozzle 44 abuts against the gate of the mold, at least during injection. The molding material extruded by the plunger 42 is injected into the mold from the tip of the nozzle 44. The nozzle 44 is heated to a specified temperature by the heater 49.

[0060] The injection cylinder 41 is connected to the plunger drive device 46 via a connecting member 45 at its rear. The plunger drive device 46 can be any actuator that moves the plunger 42 forward or backward, such as a hydraulic cylinder or an electric cylinder. The piston of the plunger drive device 46 is connected to the plunger 42 by a coupling 47.

[0061] Here, as Figure 2 and Figure 3 As shown, the injection section 4 includes a sealing ring 51, a retainer 53, a temperature regulating block 55, and a temperature sensor 57.

[0062] The sealing ring 51 is a cylindrical body located at the rear end of the injection cylinder 41 and constructed in a coolable manner. Furthermore, cooling of the sealing ring 51 refers to adjusting its temperature to a relatively lower temperature compared to the injection cylinder 41. For example... Figure 4 As shown, the sealing ring 51 has an inner hole 511 for the plunger 42 to pass through.

[0063] Here, as Figure 5 As shown, when the plunger 42 is located at the center of the injection cylinder 41, that is, when the central axis of the plunger 42 is aligned with the central axis of the injection cylinder 41, the distance between the plunger 42 and the injection cylinder 41 is defined as the first gap C1, and the distance between the sealing ring 51 and the injection cylinder 41 is defined as the second gap C2. The injection cylinder 41 and the sealing ring 51 are configured such that the first gap C1 is greater than the second gap C2. By setting the sealing ring 51, the first gap C1 can be set to be relatively large.

[0064] During molding, molding material passing between the plunger 42 and the injection cylinder 41 sometimes flows between the plunger 42 and the sealing ring 51. The molding material flowing between the plunger 42 and the sealing ring 51 cools down due to the sealing ring 51, causing it to solidify or thicken. Hereinafter, the solidified or thickened molding material will be referred to as the solidified / thickened material. The solidified / thickened material seals between the plunger 42 and the sealing ring 51, inhibiting the inflow of more molding material and thus reducing the amount of molding material that might leak from the rear end of the sealing ring 51 through the space between the plunger 42 and the sealing ring 51. Furthermore, the rear of the plunger 42 is supported by the sealing ring 51 itself or the solidified / thickened material, thus preventing the plunger 42 from wobbling within the injection cylinder 41. In addition, if the temperature of the sealing ring 51 is properly maintained, the force exerted by the solidified / thickened material to hold the plunger 42 is significantly lower than the force required to move the plunger 42 forward or backward, thus the solidified / thickened material will not hinder metering or injection.

[0065] The retainer 53 holds the sealing ring 51 and fixes the sealing ring 51 to the injection cylinder 41. Specifically, in this embodiment, the retainer 53 passes through the rear end of the sealing ring 51, and the retainer 53 is fixed to the connecting member 45 by bolts (not shown). Thus, the sealing ring 51 is positioned at the rear end of the injection cylinder 41. Figure 6 As shown, the retainer 53 has an inner bore 531 for the plunger 42 to pass through, and an insertion hole 532 for at least a portion of the temperature sensor 57 to pass through. Multiple grooves are formed circumferentially on the inner surface of the inner bore 531. This structure suppresses contact between the plunger 42 and the retainer 53, and the molding material discharged from the sealing ring 51 is appropriately discharged rearward through the grooves of the inner bore 531. The grooves of the inner bore 531 make the amount of discharged molding material uniform, or keep the sliding resistance of the plunger 42 approximately constant.

[0066] The temperature regulating block 55 abuts directly or indirectly against the sealing ring 51, cooling the sealing ring 51. In this embodiment, the temperature regulating block 55 abuts against the retainer 53, cooling the sealing ring 51 via the retainer 53. Figure 7 As shown, the temperature regulating block 55 has a medium flow path 551 through which the temperature regulating medium can flow, and an inner hole 552 for the plunger 42 to pass through. Connectors 553 and 554 are respectively provided at the inlet and outlet of the medium flow path 551. The inner hole 552 only needs to be formed to a sufficient size so that the plunger 42 does not contact it. The molding material discharged from behind the sealing ring 51 falls downwards onto the connecting member 45 through the inner hole 531 of the retainer 53 and the inner hole 552 of the temperature regulating block 55. A receiving dish for receiving the discharged molding material may also be provided at the falling position.

[0067] In this embodiment, the temperature-regulating medium is specifically compressed air. This embodiment includes a pressure-reducing valve 555 for adjusting the temperature-regulating medium to the required pressure, an on / off valve 556 for switching the supply of the temperature-regulating medium to the medium flow path, and a flow valve 557 for adjusting the temperature-regulating medium to the required flow rate. Compressed air supplied by an air compressor (not shown) is regulated to a specified pressure and flow rate via the pressure-reducing valve 555, the on / off valve 556, and the flow valve 557, and then delivered to the medium flow path 551 via connector 553. The compressed air that has undergone heat exchange through the medium flow path 551 is discharged from the temperature-regulating block 55 via connector 554. Furthermore, in this embodiment, the temperature-regulating medium supplied to the temperature-regulating block 55 is compressed air, but other fluids such as water or oil may also be used.

[0068] Temperature sensor 57 is a sensor for detecting the temperature of sealing ring 51. Temperature sensor 57 can be any sensor, such as a thermocouple. In this embodiment, temperature sensor 57 indirectly detects the temperature of sealing ring 51 by directly measuring the temperature of retainer 53. Temperature sensor 57 is inserted into insertion hole 532 of retainer 53 and fixed by sensor cover 533.

[0069] In this embodiment, the control device 6 controls the opening and closing of the valve 556 based on the detection value of the temperature sensor 57, so that the sealing ring 51 reaches the desired temperature. That is, the control device 6 performs feedback control on the temperature of the sealing ring 51. Preferably, the control device 6 performs proportional-integral-derivative (PID) control on the temperature of the sealing ring 51. If set in this way, the temperature management of the sealing ring 51 can be performed more accurately. The temperature of the sealing ring 51 is set to be lower than the temperature range in which the molding material can be formed. In other words, the temperature of the sealing ring 51 is set to be lower than the temperature of the plasticizing cylinder 21, the injection cylinder 41, the nozzle cylinder 43, and the nozzle 44. Although it also depends on the type of molding material, the set value of the temperature of the sealing ring 51 is, for example, around 100°C.

[0070] The control device 6 controls the injection unit 1, which includes the plasticizing section 2 and the injection section 4, as well as the mold clamping unit. More specifically, the control device 6 controls at least the check valve 25, the screw drive 27, the plunger drive 46, the heater 29, the heater 48, the heater 49, and the on / off valve 556, based on the set values ​​of each part and the detection values ​​of various measuring devices, including the temperature sensor 57. The control device 6 can be constructed by arbitrarily combining hardware and software to achieve the required control, for example, it may have a central processing unit (CPU), random access memory (RAM), read-only memory (ROM), auxiliary storage devices, and input / output interfaces.

[0071] In an injection molding machine with the structure described above, even if the first gap C1 is set to be relatively large, the cured / thickened material inside the sealing ring 51 seals the plunger 42 with the sealing ring 51, thereby suppressing leakage of the molding material. Furthermore, the rear of the plunger 42 is supported by the sealing ring 51 itself or by the cured / thickened material, thus suppressing the wobbling of the plunger 42 and preventing contact between the plunger 42 and the injection cylinder 41.

[0072] Here, the molding material used in the injection molding machine of this embodiment will be described. Regarding the molding material, molding materials comprising at least resin can be widely used. Of these, the present invention is suitable for molding materials comprising resin and filler. It is particularly suitable when the filler comprises a material with high affinity for the steel of the injection cylinder 41 or plunger 42. Materials with high affinity for the steel of the injection cylinder 41 or plunger 42 are, for example, metals, and more specifically, stainless steel, nickel-chromium alloys, titanium, etc. Furthermore, the present invention is suitable for molding materials that generate corrosive gases during plasticizing.

[0073] Materials containing resin and metal fillers include, for example, metal injection molding (MIM) materials and plastic magnet materials. MIM materials are a type of powder injection molding material, formed by mixing metal powder as a filler with resin as a binder. Plastic magnet materials are formed by mixing magnetic metal powder as a filler with resin as a binder.

[0074] The filler can be in powder or fibrous form. Hereinafter, the particle size of powdered fillers and the fineness of fibrous fillers will be collectively referred to as diameter.

[0075] Examples of molding materials that readily generate corrosive gases during plasticization include materials that generate corrosive gases from the resin itself or materials containing flame retardants. Examples of materials that generate corrosive gases from the resin itself include fluoropolymers or polyvinyl chloride. Materials containing flame retardants often include acrylonitrile butadiene styrene, polystyrene, polypropylene, polyethylene, polycarbonate, polycarbonate-acrylonitrile butadiene alloy, modified polyphenylene ether, olefin-based thermoplastic elastomers, polyamides (including aliphatic polyamides, semi-aromatic polyamides, and aromatic polyamides), polybutylene terephthalate, and saturated polyesters (including polyethylene terephthalate).

[0076] Here, the appropriate values ​​for the first gap C1 and the second gap C2 are explained.

[0077] The second gap C2 is set according to the molding material. When using a molding material containing resin and filler, the second gap C2 is ideally set to be relatively large to prevent filler adhesion or wear caused by the filler. Specifically, the second gap C2 is preferably a value obtained by dividing the maximum diameter of the filler by 2 or more. The second gap C2 is preferably 5 μm or more. On the other hand, if the second gap C2 is too large, it may lead to an increase in the amount of molding material retained in the injection cylinder 41, or an increase in pressure loss during injection, or an increase in the amount of molding material leakage. Therefore, the second gap C2 is preferably less than or equal to the maximum diameter of the filler. When using molding materials other than these, the second gap C2 can be the same size as the gap between the plunger 42 and the injection cylinder 41 in conventional injection molding machines. Specifically, the second gap C2 can be 5 μm or more and 100 μm or less. Moreover, even when using a molding material containing filler, if the filler contains a material that is not easily adhered to the steel of the injection cylinder 41 or the plunger 42, the second gap C2 can be 5 μm or more and 100 μm or less.

[0078] In this embodiment, the rear of the plunger 42 is supported by the sealing ring 51 itself or by the cured / thickened material. This suppresses the wobbling of the plunger 42, but it is also possible for the plunger 42 to tilt around the support position within the sealing ring 51. Therefore, it is ideal to set the value of the first gap C1 in such a way that even when the tilt angle of the plunger 42 reaches its maximum, the tip of the plunger 42 does not contact the injection cylinder 41.

[0079] Here, we envision the state where the plunger 42 has advanced the most and tilted the most. That is, we envision the following state: in the plunger 42, with one side having a first generatrix that is an arbitrary generatrix designated as one side, and the other side having a second generatrix that is the opposite side of the first generatrix designated as the other side, the plunger 42 advances as far as possible, with one side of the plunger 42 contacting the rear end of the sealing ring 51, and the other side of the plunger 42 contacting the front end of the sealing ring 51. Here, as... Figure 8 As shown, the explanation is based on a downwardly inclined plunger 42, with one side designated as the upper side and the other as the lower side. Furthermore, for illustrative purposes, sometimes... Figure 8 The dimensions of each part are exaggerated.

[0080] First, determine the tilt angle θ of plunger 42. For example... Figure 9As shown, let A be the width of the sealing ring 51, B be the length of the perpendicular line from the center of the cross-section of the inner hole 511 to the lower end of the inner hole 511, C be the distance between the center of the cross-section of the inner hole 511 and the lower front end of the inner hole 511, D be the length of the perpendicular line from the center of the cross-section of the inner hole 511 to the lower end of the plunger 42, θ1 be the angle between the diagonal of the cross-section of the inner hole 511 and the lower end of the inner hole 511, and θ2 be the angle between the diagonal of the cross-section of the inner hole 511 and the lower end of the plunger 42. Here, B is the value obtained by adding the second gap C2 to D, and is the value obtained by dividing the diameter of the inner hole 511 of the sealing ring 51 by 2. C is the value obtained by dividing the diagonal of the cross-section of the inner hole 511 by 2. D is the same as the radius of the plunger 42. Therefore, the following can be calculated:

[0081] θ = θ1 - θ2

[0082] ={tan -1 (2B / A)}-{sin -1 (D / C)}.

[0083] Next, determine the distance E between the lower front end of the inner hole 511 and the horizontal line passing through the lowest limit position of the plunger 42. When the top of the plunger 42 has a conical shape, there are cases where the apex of the plunger 42 is at the forward limit and cases where the upper end of the upper side of the plunger 42 is at the forward limit. Furthermore, the forward limit refers to the foremost position of the plunger 42 when it moves as far forward as possible.

[0084] First, let's begin with the case where the tip of plunger 42 is at its forward limit. Here, as... Figure 10 As shown, the distance between the lowest position of the plunger 42 and the perpendicular line passing through the front end of the sealing ring 51 is defined as F; the distance between the forward limit and the perpendicular line passing through the front end of the sealing ring 51 is defined as G; and the distance between the forward limit and the lowest position of the plunger 42 is defined as H. Furthermore, the size of the generatrix of the conical portion of the plunger 42 is defined as I; the angle between the generatrix of the conical portion of the plunger 42 and the horizontal line passing through the lowest position of the plunger 42 is defined as θ3; and the angle between the generatrix of the conical portion of the plunger 42 and the bottom surface is defined as θ4.

[0085] At this moment, becoming

[0086] E = F × tanθ

[0087] = (G - H) × tanθ

[0088] ={G-(I×cosθ3)}×tanθ

[0089] =[G-{I×cos(90°-θ-θ4)}]×tanθ.

[0090] Next, we will explain the case where the upper end of the upper side of the plunger 42 is at its forward limit. For example... Figure 11 As shown, F, G, H, θ3, and θ4 are similarly set. At this point, it becomes...

[0091] E = F × tanθ

[0092] = (G - H) × tanθ

[0093] =[G-{2D×cos(θ3+θ4)}]×tanθ

[0094] =[G-{2D×cos(90°-θ)}]×tanθ.

[0095] Furthermore, if the plunger 42 does not have a conical portion, then θ4 is considered to be 0°.

[0096] A suitable value for the first gap C1 is determined based on E, as calculated above. If the diameter of the inner hole 511 of the sealing ring 51 is set as J, then the first gap C1 is preferably greater than (E+B-D), i.e., (E+C2). In other words, the first gap C1 is preferably larger than the value described below, which is obtained by subtracting the radius of the plunger 42 from the distance between the central axis of the injection cylinder 41 and the lowermost position of the plunger 42 (i.e., the front end position of the lower side of the plunger 42). If the first gap C1 is this value, then theoretically even if the plunger 42 is tilted, it will not contact the inner side of the injection cylinder 41, thus further preventing contact between the plunger 42 and the injection cylinder 41. Furthermore, the larger the first gap C1 is, the greater the amount of molding material retained in the injection cylinder 41 or the greater the pressure loss during injection; therefore, the first gap C1 is preferably 500 μm or less.

[0097] When using a molding material comprising resin and filler, the sealing ring 51 preferably comprises a material that is resistant to sintering and wear-resistant to the filler. Specifically, the sealing ring 51 preferably comprises a material having a coefficient of friction with the filler of 0.6 or less and a Rockwell hardness (HRC) of 60 or higher. Furthermore, the coefficient of friction here is based on a value measured according to the Japanese Industrial Standards (JIS) R 1613 (2010) using a ball-on-disc method for wear testing. The sealing ring 51 comprising this material is less prone to adhesion to the filler and has a certain degree of hardness, thus it is less prone to wear and can be used for a long time. In this embodiment, for fillers containing stainless steel, the sealing ring 51 is constructed from Cermetal (registered trademark) CT510.

[0098] As illustrated in the accompanying drawings, this invention is not limited to the structure of the embodiments shown in the drawings, and various modifications or applications can be made without departing from the technical spirit of this invention.

Claims

1. An injection molding machine comprising: a plasticizing section to which a molding material containing at least a resin is supplied to plasticize the molding material; an injection section to which the molding material is supplied from the plasticizing section to measure and inject the molding material; a joint to connect the plasticizing section and the injection section; and a control device to control the plasticizing section and the injection section, the plasticizing section including: a plasticizing cylinder to which the molding material is supplied; and a screw rotatably provided in the plasticizing cylinder, the injection section including: an injection cylinder to which the molding material is supplied from the plasticizing cylinder; a plunger provided in the injection cylinder so as to be able to advance and retreat; and a seal ring provided at a rear end of the injection cylinder so as to be penetrated by the plunger, a first gap between the plunger and the injection cylinder when a center axis of the plunger coincides with a center axis of the injection cylinder is larger than a second gap between the plunger and the seal ring when the center axis of the plunger coincides with the center axis of the injection cylinder, the seal ring is configured so as to be able to cool, and a solidified / thickened material is formed by solidification or thickening of the molding material flowing between the plunger and the seal ring, and the solidified / thickened material seals between the plunger and the seal ring, the injection section further includes: a temperature adjustment block having a medium flow path through which a temperature adjustment medium is able to flow, and directly or indirectly abutting against the seal ring to cool the seal ring, the injection section further includes: a temperature sensor to detect a temperature of the seal ring; a pressure reducing valve to adjust the temperature adjustment medium to a desired pressure; an on-off valve to switch on / off of supply of the temperature adjustment medium to the medium flow path; and a flow rate valve to adjust the temperature adjustment medium to a desired flow rate, the control device controls the on-off valve so that the seal ring becomes a desired temperature based on a detection value of the temperature sensor, the temperature adjustment medium is compressed air, and the compressed air is discharged to the outside of the temperature adjustment block through the medium flow path after being adjusted to a desired pressure and a desired flow rate by the pressure reducing valve, the on-off valve, and the flow rate valve, the molding material contains the resin and a filler, the second gap is 5 μm or more and 100 μm or less, and the second gap is a value obtained by dividing a maximum diameter of the filler by 2.

2. The injection molding machine according to claim 1, wherein the first gap is larger than a value obtained by subtracting a radius of the plunger from a distance from the center axis of the injection cylinder to a front end position of the other side of the plunger when the plunger is advanced as much as possible with one side of the plunger having a first generatrix as an arbitrary generatrix and the other side of the plunger having a second generatrix as a generatrix opposite to the first generatrix, and the one side of the plunger is in contact with the rear end of the seal ring, and the other side of the plunger is in contact with a front end of the seal ring.

3. The injection molding machine according to claim 1, wherein the injection section further includes a holder to hold the seal ring and fix the seal ring to the injection cylinder. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 4. The injection molding machine according to claim 1, wherein the filler includes a metal.

5. The injection molding machine according to claim 1, wherein the seal ring includes a material having a friction coefficient of 0.6 or less and a Rockwell hardness HRC of 60 or more with the filler.

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