AU2018204643A1 - Improved Moulding Process for Manufacture of Multi-segment Plastic Components - Google Patents

Abstract

with FIG. 4 A method of injection moulding to form a wheel-like product having a thickness, a width, and a peripheral rim interrupted by a rim entry opening, the rim entry opening being a generally open segment of the product defined by adjacent spoke like radially extending walls, further circumferentially spaced radially extending walls defining further segments and the walls forming spokes that terminate at the rim and at a central bore, the central bore having a side entry in line with and communicating with the rim entry together forming a passage into the central bore, the method comprising: a. providing an injection moulding machine having at least a two part mould of the product defining a mould cavity between the two parts; b. the two part mould cavity or additional mould cavities in the case of multiple products having an entry passage(s) for moulding the product(s) with a molten plastics though the entry passage(s); c. injecting molten plastic into the cavity or cavities through the entry passage(s) over a molten plastics entry period; d. subsequently cooling the mould to cool the injected plastics for a cooling time; e. subsequently separating the mould(s) and ejecting the product(s). CC 1/5r r CN Cf) Ct) rar r

Description

TECHNICAL FIELD [0001] THIS INVENTION relates to an improved moulding process for manufacture of multi-segment plastic components and in particular but not limited to wheel like plastics products and to a product made according to that process.

BACKGROUND [0002] Multi-segment plastic components including many rotating devices such as rotors, impellers and plastics wheels and wheel-like products are made by injection moulding and are used in various environments. In the case of a wheel, the wheel may be placed under compression which tends to flatten the wheel or in other cases the wheel may be used as a vertical rolling spacer where it is under less load. Wheel sizes will vary according to the application as will specific design features.

[0003] Important commercial factors in production of plastics products mainly concern cycle time per unit and the amount of plastics used per unit. The cycle time is important because the more units that can be made reduces the basic cost in terms of fixed production costs. The amount of plastics wherever possible should be minimised while making a product that is sufficiently robust for the desired use.

[0004] Manufacture may be further complicated where the wheel-like product has moveable parts or parts that are required to flex or move to align with other parts of the product. The design and configuration of the product for its actual use is often a compromise between function and cost.

[0005] It is an object of the present invention to provide a multi-segment plastics product of generally known configuration using an improved process or a process that will at the very least provide the public with a useful alternative to present production methods.

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OUTLINE [0006] The following description relates to a wheel-like product but it will be appreciated that this covers any multi-segment plastics product of generally known configuration. In the example of course the specific configuration will influence the actual process as applied to the wheel like product and again more so to the specific examples afforded by the drawings.

[0007] In one aspect there is provided a method of injection moulding to form a wheel-like product having a thickness, a width, and a peripheral rim interrupted by a rim entry opening, the rim entry opening being a generally open segment of the product defined by adjacent spoke like radially extending walls, further circumferentially spaced radially extending walls defining further segments and the walls forming spokes that terminate at the rim and at a central bore, the central bore having a side entry in line with and communicating with the rim entry together forming a passage into the central bore. Preferably, the passage may be closed. The passage may be closed by a closure. The closure may be a separate part of or may be an integrally formed movable part or parts that may be used to close the entry or entries and ultimately closing the bore to trap an axial member in the bore.

[0008] In a preferred aspect there is provided a product by process, the product being in combination a case where there is a central bore and a co-axial rim, the bore is typically a closable ring, the ring being interrupted by a ring entry opening communicating with a rim entry opening via a radially extending passage and there being circumferentially spaced spoke-like formations bridging between the rim and central ring to retain the rim and ring in spaced configuration, the process comprising the steps of:

1. providing an injection moulding machine having a two part mould of the product;

2. the two part mould having a mould cavity or mould cavities for moulding the product with a molten plastics entry passage;

3. injecting molten plastic into the cavity or cavities through the entry passage over a molten plastics entry period;

4. subsequently cooling the mould to cool the injected plastics for a cooling time;

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5. subsequently separating the mould and ejecting the product(s).

[0009] In a preferred embodiment two products are formed in the mould and the mould cavities have the rim entry opening of each product set in opposition so that injected plastics first flows into the products in the region of the rim entry.

[0010] The injection moulding process is preferably accomplished using a moulding machine have a feed hopper, a barrel with an internal screw extruder having an injection nozzle and a mould tool including a mould cavity or cavities.

[0011] Preferably, pellets of a suitable mouldable polymer are provided. The pellets preferably comprising the mouldable polymer, and any desired lubricant or other additive (which may have already been added to the pellets during their production) are then placed into the hopper to be fed into the screw extruder.

[0012] The conditions under which the product is injection moulded are determined by the injection moulder employed, the configuration of the wheel-like product, and the composition of the mouldable polymer and optional additives.

[0013] In one preferred method, the mouldable polymer is first heated to between 80 to 100 degree C, preferably 85 to 95 degree C for pre drying, and is placed in the hopper to be gravity fed into a screw feed zone of the extruder. The barrel temperature of the screw extruder and injector is preferably from about 180 to 230 degree C., more preferably from about 185 to 210 degree C. The temperature of the mould is preferably from about 10 to 90 degree C, more preferably from about 10 to 30 degree C. Cycle time range is from 30 - 45 seconds.

[0014] The cycle time (the time from introducing the mixture into the screw extruder to opening the mould to remove the moulded product) will preferably range between 0.5 to 180 seconds, more preferably from about 5 to 60 seconds. The injection pressure will preferably range from about 690 to 6,900 kPa (100 to 1000 psi), more preferably from about 2070 to 4830 kPa (300 to 700 psi).

2018204643 26 Jun 2018 [0015] The injection mould cycle will depend upon the material composition and the wheel like product configuration. In one preferred embodiment, there will be a single insertion or shot of mixture of the polymeric material to mould the wheel-like product, including the rim, spokes and bore. In one example the method involves the use of a feedstock plastic being predominantly a recycled Polypropylene with a melt flow of 100°C and a shot weight of about 190 gms which provides a net part weight of 100 gms using this feedstock.

[0016] After injection moulding, the mould is rapidly cooled to solidify the mouldable polymer. Mould halves are then separated to allow removal of the product.

[0017] Preferably, an ejector assembly is provided on an opposite side of mould from the injection port to eject the solidified product from the mould.

[0018] In another preferred aspect there is provided a wheel like product made according to the present method and having an outer rim with an entry gap and a central bore, the rim being between 15 mm and 40 mm wide and between 3-10 mm thick in rim wall thickness, there being a passageway for entry of a bar radially into the product so that the entry gap is able to be resiliently widened so that the bar can pass through and locate in the bore. The wheel like product may adapted so that the passageway may be closed to the position. The passageway which comprises adjacent spokes may have a catch and tongue arrangement aligned to engage with the catch to secure the wheel like product in a closed position. The passageway typically comprises adjacent biassed apart connectable spokes to secure the wheel like product in a closed position, the bias being provided by curved sections opposite the said connectable spokes.

BRIEF DESCRIPTION OF THE DRAWINGS [0019] In order that the present improvements may be more readily understood and put into practical effect reference will now be made to the accompanying drawings which illustrate preferred embodiments of the invention and wherein:2018204643 26 Jun 2018

Figure 1 is a perspective drawing illustrating one embodiment of a wheel like product;

Figure 2 is a perspective drawing illustrating another embodiment of a wheel like product in this case being a closable product shown in its open state ;

Figure 3 is a side view of the wheel-like product of Figure 2 shown closed;

Figures 4-6 are drawings illustrating typical mould arrangements; Figure 7 is a drawing illustrating a typical moulding machine; and Figures 8A through 8E are dimensioned drawings illustrating a typical wheel like plastics product made according to the Example of paragraphs [0037] - [0039].

METHOD OF PERFORMANCE [0020] Referring to the drawings and initially to Figures 1 and 2 there is illustrated two wheel like plastic products 10 and 100, the wheel like plastic product is a heavy duty product whereas the wheel like product 100 is a lighter duty product and while each may be made using an injection moulding process they differ mechanically and they differ in terms of the amount of plastics employed but both provide basically the structure of an outer rim with an entry gap and a central bore, the two will be compared and contrasted in the following description. They have respective rims 11 and 101, the rim 11 is 30mm wide at 12 while the rim 101 is 20mm wide at 102 while the product 10 is 6mm thick in rim wall thickness at 13 while the product 100 is 3mm thick at 103, each is provided with a passageway 14 and 104 for entry of a bar radially into the product so that the entry 14, 104 is resiliently widened so that the bar can locate in the bore 15, 115. Unlike the wheel like product 10, the wheel like product 100 is adapted so that the passageway 104 may be closed to the position illustrated in Figure 3. Each of the wheel like products 10 and 100 include radially extending spokes 16, 106, while the product 10 includes an intermediate ring 17 which is not present in the product 100.

[0021] The spokes 106 define segments 107 while the rim 101 has circumferentially spaced axially extending rims 108 which serve to strengthen the rim 101.

[0022] The passage 104 comprises spokes 109 and 110 with the spoke 110 having a catch

2018204643 26 Jun 2018 arrangement 111 and the spoke 109 has a tongue 112 which is aligned to engage with the catch

111 to secure the wheel like product in the closed position as illustrated in Figure 3.

[0023] The range of movement between the opened and closed positions is facilitated by the radially opposite arrangement 113 which comprises a section of rim 114 with gaps 115 and 116 which close under bias when the catch is released and the product assumes the open position illustrated in Figure 2.

[0024] The bias comes about by the combined effect of the curved sections 117, 118 and 119 and so that the shoulders 120 and 121 tend to move apart while the shoulders 122 and 123 tend to move together. The combined effect is to bias the catch 111 and tongue 112 apart.

[0025] The wheel like product according to the invention is preferably injection moulded. The mould will contain a cavity or cavities which are the inverse of the desired product configuration. Thus the mould design must take into account the the size and configuration of the rim, the spokes, and the side entry as well as optimizing the cavity or cavities of the mould tool for multiple units. Referring to Figures 4 to 6 there is illustrated one section of tandem, triple and quad tools 124, 125 and 126 respectively. Each tool has a central screw 127 leading to symmetrical runner systems 128, 129 and 130 which in turn feed wheel like product cavities 131 from the rim passage entry side of the products.

[0026] A typical moulding machine is illustrated in Figure 7 with the machine and process being described below.

[0027] In terms of general arrangement the injection moulding machinery of Figure 7 is of sufficient capability in terms of power to provide sufficient clamping pressure to hold both halves 132, 133 of the tool 134 together whilst molten plastic material is injected into the cavity(s) (see Figure 4-6) of the tool 134.

[0028] The machine of Figure 7 is programmed to manage all pressures and speeds of the process to accommodate the outcome of a finished product as required. The tool comprises as

2018204643 26 Jun 2018 noted two separate halves one generally referred to as the fixed half 133 and the other as the moving half 132. The fixed half 133 when installed in the machine is bolted to a platen being the fixed platen 135 of the machine located at the forward position or nozzle end 136 of barrel 137 described below. The moving half 132 is bolted to the moving platen 138 so that it can be hydraulically moved to meet with the fixed half 133 to form the cavity(s) of the tool when in the closed position and moved to the open position when the part has been made.

[0029] Raw material plastic in the form of granular beads of plastic which can vary from almost any type of plastic including Polypropylene, Glass filled Polypropylene, Nylon with or without additives and Polystyrene etc can be used in the manufacturing process. These alternate materials can be in virgin form or recycled form. They can also have additional expandable graphite added to achieve high degree Coolum ratings for the product applications required in some concrete structures.

[0030] Primarily these selected granular materials are loaded to the hopper 139 situated on top of the machine, usually through an automatic vacuum loading process via entry 140, and the material is fed by gravity to the throat 141 of the moulding machine in a room temperature state. The throat 141 of the moulding machine leads to the barrel 137 of the machine. The barrel 137 has multiple heating elements 142 which are temperature controlled and set in accordance with the requirements that are applicable to ensure the granular material is melted and at sufficient temperature to enter the closed cavity and to easily flow through the sprue along any runners (temperature controlled or otherwise) into the cavity(s) under required controlled pressure.

[0031] Temperatures of the material in the barrel are generally in the region of 170° to 230° Centigrade depending on the material used and other existing conditions.

[0032] The injection process is achieved by an internal barrel screw within barrel 137 which is a spiral pusher (known as a screw) together with a check valve at its forward most nozzle end 136. In coordination with the operation of the machine the screw is hydraulically rotated so that the molten plastic is forced forward towards the tool cavity(s) injecting the molten plastic into the cavity(s) when clamping pressure on the moving half is at maximum. The screw, when it has

2018204643 26 Jun 2018 finished pushing the plastic into the cavity(s), will hold in its forward position using the check valve to stop any leakage back into the barrel 137 for a set predetermined time to ensure the molten plastic holds in the cavity(s) until the plastic solidifies sufficiently for it to form a manageable finished product.

[0033] The screw with its rotating action draws in more granular material from the hopper 139 through throat 141 and repeats the heating and pushing process. This rotating process creates a certain degree of friction generated heat which assists in maintaining the required material temperature prior to the injection step.

[0034] The process of cooling of the plastic material referred to above is managed by passing water through the water jackets on the tool at such temperatures and for such time as appropriate to allow the plastic material to cool so that the moulded part can be ejected from the tool in at least a semi-solid condition. This is achieved using an industrial water chiller set at a temperature less than the ambient temperature and sufficiently lower than the molten plastic to ensure the tool can cool the plastic in a reasonable amount of time.

[0035] The critical temperature is set by what is the maximum temperature the product can be ejected at whilst maintaining its required dimensional accuracy and planned integrity. The faster the cycle time will be a major function of the cost of the item so it is to efficient production advantage to hold the part the least amount of time in the tool. Ejecting the part too fast and hence less cooling time may allow too much shrinkage to occur or at worst the part may be deformed from its planned shape.

[0036] The process of ejecting the finished product from the tool and the machine to a conveying system 143 for packaging at 144 is once again a function of the machine in combination with the design of the tool. The design of the tool is such that the moulded finished product having filled both the fixed half cavity 133 and the moving half cavity 132, it will, when the tool is opened, remain in the moving half 132 of the tool rather than in the fixed half cavity 133 which is required.

2018204643 26 Jun 2018 [0037] If necessary it may be necessary to provide better friction points on the moving half cavity to ensure the finished product holds to the moving half rather than the fixed half. This can be achieved by providing catch points for the cooling plastic to temporarily engage within the cavity on the moving half 132 of the tool. Following the process of cooling mentioned above, based on the performance of this process, the ejection method is achieved by the machine opening the moving half 132 of the tool towards the rear of the machine to achieve a sufficient gap between the two halves of the tool and activating an ejector plate and ejector pins of the tool to push the finished product from the moving half cavity(s). Care is taken to achieve a clean ejection of the moulded products and this is achieved by allowing sufficient time for the product to cool enough so that the ejector pins do eject the products and not simply pierce non-solidified plastic which would possibly result in the part not being ejected.

EXAMPLE [0038] The injection molding machine used was a 180 ton Chende EM180-V single shot extruder with a toggle clamping system, a 598 gram barrel and a general purpose screw.

[0039] Moulding parameters varied for each example due to formulation changes, mould design, mould condition, screw condition, and barrel condition. Typical moulding parameters included: nozzle temperature 180°C., temperature at the front of the barrel (proximate the nozzle) 185°C-190°C, temperature at the rear of the barrel (proximate the hopper) 180°C screw rotation 150RPM, 9000 kPa injection pressure, 20mm cushion, and a 160mm shot distance or length. A complete cycle time on average was about 35 seconds per run producing two products in a twin cavity tool.

[0040] The Predominant feedstock plastic used is a recycled Polypropylene with a melt flow of 100°C. The shot weight is 193.5gms which provides a net part weight of 96.75gms using this feedstock. Utilizing further additives or differing feedstock may achieve enhanced strength results which may provide qualification for use under differing building standards.

[0041] A wheel like product made according to this Example is illustrated in dimensioned

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Figures 8A through 8E, the dimensions are included to provide the context of volume and weight of material used in the two cavity mould in the Example.

[0042] Whilst the above has been given by way of illustrative example many variations and modifications will be apparent to those skilled in the art without departing from the broad ambit and scope of the invention set out in the appended claims.

[0043] Please note the words comprising, having, including, and the like are all used in the non-exhaustive sense insofar as described and claimed only requires at least the integers or integers claimed but could include additional features.

Claims (13)

1. A method of injection moulding to form a wheel-like product having a thickness, a width, and a peripheral rim interrupted by a rim entry opening, the rim entry opening being a generally open segment of the product defined by adjacent spoke like radially extending walls, further circumferentially spaced radially extending walls defining further segments and the walls forming spokes that terminate at the rim and at a central bore, the central bore having a side entry in line with and communicating with the rim entry together forming a passage into the central bore, the method comprising:

a. providing an injection moulding machine having at least a two part mould of the product defining a mould cavity between the two parts;

b. the two part mould cavity or additional mould cavities in the case of multiple products having an entry passage(s) for moulding the product(s) with a molten plastics though the entry passage(s);

c. injecting molten plastic into the cavity or cavities through the entry passage(s) over a molten plastics entry period;

d. subsequently cooling the mould to cool the injected plastics for a cooling time;

e. subsequently separating the mould(s) and ejecting the product(s).

2. The method according to claim 1 wherein two products are formed in the mould in respective mould cavities, the cavities having the rim entry opening of each product set in opposition and the method further comprises injecting plastics so that injected plastics first flows into the products in the region of the rim entry.

3. The method according to claim 1 or claim 2 wherein the injection moulding process is accomplished using a moulding machine have a feed hopper, a barrel with an internal screw extruder having an injection nozzle and the mould is a mould tool including a mould cavity or cavities.

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4. The method according to any one of the preceding claims further comprising the use of a mouldable polymer first heated to between 80 to 100 degree C then fed into a screw injector at a temperature from 180 to 230 degree C the temperature of the mould being between 10 to 90 degree C, the dimensions of the wheel like product and the moulds being so made and arranged that cycle time range is from 30 - 45 seconds.

5. The method according to any one of the preceding claims further comprising the use of a mouldable polymer, the dimensions of the wheel like product and the moulds being so made and arranged that the cycle time ranges from 5 to 60 seconds with an injection pressure in the range of 690 to 6,900 kPa.

6. The method according to any one of the preceding claims further comprising the use of a mouldable polymer and a single insertion or shot of mixture of the polymer to mould the wheel-like product, including the rim, spokes and bore.

7. The method according to any one of the preceding claims further comprising the use of an injection molding machine having a single shot extruder with a toggle clamping system, a screw and operating substantially according to the following moulding parameters:

nozzle temperature 180°C., temperature at the front of the barrel (proximate the nozzle) 185°C-190°C, temperature at the rear of the barrel (proximate the hopper) 180°C, screw rotation about 150RPM,

9000 kPa injection pressure, 20mm cushion, and a 160mm shot distance or length. A complete cycle time on average was about 35 seconds per run producing two products in a twin cavity tool.

8. The method according to any one of the preceding claims further comprising the use of a feedstock plastic being predominantly a recycled Polypropylene with a melt flow of 100°C and a shot weight of about 190 gms which provides a net part weight of 100 gms using this feedstock.

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9. A wheel like product made according to any one of the preceding claims.

10. A wheel like product made according to any one of the preceding claims having an outer rim with an entry gap and a central bore, the rim being between 15 mm and 40 mm wide and between 3-10 mm thick in rim wall thickness, there being a passageway for entry of a bar radially into the product so that the entry gap is able to be resiliently widened so that the bar can pass through and locate in the bore.

11. A wheel like product made according to any one of the preceding claims having an outer rim with an entry gap and a central bore, the rim being between 15 mm and 40 mm wide and between 3-10 mm thick in rim wall thickness, there being a passageway for entry of a bar radially into the product so that the entry gap is able to be resiliently widened so that the bar can pass through and locate in the bore and further wherein the wheel like product is adapted so that the passageway may be closed to the position.

12. A wheel like product made according to any one of the preceding claims, there being a passageway which comprises adjacent spokes having a catch and tongue arrangement aligned to engage with the catch to secure the wheel like product in a closed position.

13. A wheel like product made according to any one of the preceding claims, there being a passageway which comprises adjacent biassed apart connectable spokes to secure the wheel like product in a closed position, the bias being provided by curved sections opposite the said connectable spokes.