Moulding of articles

Abstract

A method of forming a molded article includes preparing a fiber suspension by liquidizing fibrous material in a suspending liquid using at least one high shear mixer. The fiber suspension is fed to the molding surface of a porous mold. The suspending liquid is removed via the pores of the porous mold to deposit suspended fibers on the mold surface as a molded article. Removing the suspending liquid is achieved by pressing a bladder formed of a flexible impermeable membrane against the article using pressure applied behind the membrane. The molded article is removed from the porous mold dried using microwave radiation generated using at least one magnetron. A molding apparatus is use in the method and a molded article is produced by the method.

Claims

1. A method of forming a moulded article comprising: preparing a fiber suspension by liquidising fibrous material in a suspending liquid using at least one high shear mixer, wherein the fibrous material is selected from the group consisting of: virgin paper fiber, recycled paper fiber, bamboo fiber and flax fiber, wherein suspended fibers have a length of 0.75 mm to 1.8 mm, and wherein the high shear mixer(s) comprises one or more rotors rotating at 1000-4000 rpm; feeding the fiber suspension to a moulding surface of a porous mould, the porous mold having pores with a diameter of 0.3 mm to 0.6 mm; removing said suspending liquid via pores of said porous mould to deposit the suspended fibers on said mould surface as a moulded article, the step of removing said suspending liquid comprising pressing a bladder formed of a resilient flexible impermeable membrane against the article using pressure applied behind the membrane; removing the moulded article from the porous mould; and drying the moulded article using microwave radiation generated using at least one magnetron.

2. A method as claimed in claim 1, wherein the moulded article is a three-dimensional hollow form.

3. A method of forming a moulded article as claimed in claim 1, wherein the at least one magnetron operates at a power rating of less than 5 kW.

4. A method as claimed in claim 1, comprising using a plurality of magnetrons arranged in an array.

5. A method as claimed in claim 4, wherein the plurality of magnetrons have individually controllable power outputs.

6. A method as claimed in claim 1, wherein the microwave radiation is transmitted from the magnetron(s) to the moulded article, and wherein the magnetron is free of a waveguide.

7. A method as claimed in claim 1, wherein the bladder is used to transport the moulded article from the porous mould for drying.

8. A method as claimed claim 1, comprising drying the moulded article free of use of hot air or infrared radiation.

9. A method as claimed in claim 1 wherein no drying takes place in the porous mould.

10. A method as claimed in claim 1, wherein the fiber suspension is prepared in two stages using a first high shear mixer followed by a second high shear mixer.

11. A method as claimed in claim 1, wherein the at least one or more rotors rotate at about 3000 rpm.

12. A method as claimed in claim 1, wherein the high shear mixer(s) further comprises a stator, and the rotors rotate within the stator.

13. A method as claimed in claim 1, wherein the porous mould is formed of bonded particles and/or is formed using an additive manufacturing technique.

14. A method as claimed in claim 1, wherein the fibrous material comprises paper.

15. The method as claimed in claim 10, wherein the first high shear mixer and the second high shear mixer are combined in a unit having a length of 0.5-1.0 meter.

Description

(1) The invention will be further described and illustrated with reference to the accompanying drawings in which:

(2) FIG. 1 shows a plan view of the moulding apparatus of a preferred embodiment of the invention.

(3) FIG. 2 shows a side view of the moulding apparatus of FIG. 1.

(4) FIG. 3 shows a cross-sectional view of the part of the moulding apparatus of FIG. 1 used to prepare the fibre suspension.

(5) FIG. 4 shows a cross-sectional view of the mould parts of the apparatus of FIG. 1.

(6) FIG. 5 shows a cross-sectional view of the part of the moulding apparatus of FIG. 1 used to charge the mould.

(7) FIG. 6 shows cross-sectional schematic views of the mould during various steps of the process using the moulding apparatus of FIG. 1: FIG. 6(a) shows the steps of feeding the fibre suspension to the moulding surface of the mould and removing the suspending liquid via the pores of the mould to deposit suspended fibres as a moulded article; FIG. 6(b) shows the step of removing suspending liquid by pressing a bladder against the article; FIG. 6(c) shows removing the moulded article from the mould.

(8) FIG. 7 shows a plan view of a turntable of the moulding apparatus of FIG. 1 provided with multiple mould blocks, each mould block being at a different stage of the process.

(9) FIG. 8 shows a cross-sectional view of the microwave drying chamber of the moulding apparatus of FIG. 1.

(10) FIG. 9 shows details of the arrangement of magnetrons in the microwave drying chamber of FIG. 8: FIG. 9(a) shows a plan view of the microwave drying chamber including the magnetron array; FIG. 9(b) shows a cross section through the microwave drying chamber on line A-A in FIG. 9(a).

(11) FIG. 10 is a graph of magnetron power vs. position in the microwave drying chamber (as measured by the length of time a moulded article has spent in the microwave drying chamber before it reaches the magnetron position) of FIG. 9, showing power levels for different magnetrons of the array for two different product weights.

(12) FIG. 11 shows the results (graph of force in N against displacement in mm) of vertical compression tests carried out on (a) 5 moulded bottles formed using the process of the preferred embodiment of the invention and (b) 5 plastics bottles for comparison.

(13) FIG. 12 shows the moulded bottles (a) and plastics bottles (b) of FIG. 11 after the vertical compression tests.

OVERVIEW OF MACHINE ARCHITECTURE

(14) The moulding apparatus (FIGS. 1 and 2) is fully automated to carry out the following steps shown in FIGS. 3-8: high shear mixing of water and recycled paper (1) second stage mixing of feedstock (2) filling of moulds with feedstock (4) dewatering/forming of moulded articles (5) demoulding of moulded articles (6) mould preparation (7) drying of moulded articles (8)

(15) Water-fibre suspension (feedstock) is prepared from water and recycled paper as explained in detail below (FIG. 3). The feedstock 22 supplies an automated multiple mould block 26 mounted on a turntable 28 (step 4 in FIGS. 6(a) and 7). There are four work stations (not shown), situated at 90 degree intervals around the turntable. A mould block 26 is situated at each work station. There are 4 moulds in a row per mould block 26, and each mould block 26 is formed in two symmetrical parts 30 (FIG. 6(c)) enabling it to automatically open and close as required to extract the moulded article 32. Once the feedstock 22 has been deposited in the moulds 26 (step 4 in FIGS. 6(a) and 7), the turntable 28 rotates 90 degrees, presenting the moulds 26 to the next workstation, at which point inflatable bladders 34 are introduced into the moulds 26 (step 5 in FIGS. 6(b) and 7). The bladders 34 are then inflated. The moulds 26 are opened and the articles 32 are transported on the bladders 34 as the turntable 28 rotates another 90 degrees (step 6 in FIGS. 6(c) and 7). The pressurising fluid is then removed from the bladders 34 and the moulded articles 32 are removed and transferred to a conveyor belt 36 (FIG. 8). The turntable 28 then rotates a fourth time to the point where mould preparation (step 7 in FIG. 3) is performed, ready for the next batch. The conveyor belt 36 enters the microwave drying chamber 38 (FIG. 8) for drying to produce the finished moulded articles 32. The process is controlled via control means 11 which includes a programmable logic controller.

(16) Preparation of Feedstock (Steps 1 and 2)

(17) The feedstock is prepared from recycled paper 12 (the fibrous material) and water 14 (the suspending liquid) (FIGS. 1-3) which are introduced separately into the first high shear mixer 16. This feeds a smaller second-stage high shear mixer 18 to further pulp the material.

(18) The process employs commercially available (e.g. from Maelstrom or Silverson) compact high shear mixer/homogenisers 16, 18 each having a rotor/stator arrangement (not shown). Silverson BE450™ (operating at 3000 rpm) is suitable. A high shear liquidisation head is used which avoids blocking. This converts the shredded paper fibre into a low concentration suspension (1-3 wt %) of paper fibre in water.

(19) The feedstock 22 is fed under pressure by the second mixer 18 to a storage tank 20. The feedstock 22 is then delivered under pressure by a pneumatic diaphragm pump to a header tank 24 on demand to supply the mould block 26 as explained in detail below.

(20) Introduction of Feedstock into Mould (Step 4)

(21) Each mould block 26 is made as a porous filter constructed of bonded particles. Such moulds are commercially available for example from from Aegis Advanced Materials (porous sintered bronze), www.sintermesh.com and www.porvairfiltration.com (Sinterflo™ P sintered porous bronze). As explained above, each mould block 26 is formed of two separable parts 30 (FIG. 4) which together form 5 cavities each defining the outside surface of one moulded article 32 in the form of a bottle with a neck. The feedstock 22 is introduced into each cavity of the mould block 26 (FIG. 6(a)) using fill control 25 which is in the form of a plug valve controlled by a rod (FIG. 5). Positive head pressure is used to charge the moulds 26, with water being drawn through pores 44 of the mould 26 using suction, depositing a layer of paper pulp 46 uniformly on the inside (FIGS. 6(a),(b)). During this process water is removed leaving a moulded article (bottle) 32 formed of the layer of paper pulp 46 and containing around 75% water by weight. The water may be recycled via a micromesh inline filter.

(22) Dewatering of the Product Using a Bladder (Step 5)

(23) A profiled bladder 34 of polychloroprene rubber BS2752 C2 45 IRHD (thickness 0.65-1.0 mm) (also referred to herein as a “resilient flexible impermeable membrane”) is introduced inside the mould 26 and is then inflated pneumatically (i.e. pressure is applied behind the membrane) using compressed air 35 at a pressure of 1-10 bar (100 kPa-1 MPa) gauge for 15-30 seconds (FIG. 6(b)). Suction is applied at the same time. This presses the bottle 32 against the mould 26 so that water is expressed from the bottle 32 through the pores 44 and the internal surface of the bottle 32 is smoothed.

(24) Demoulding (Step 6)

(25) The mould block 26 is automatically opened by separating the two mould parts 30 and the bottle 32 is removed, remaining supported on the bladder 34 (FIG. 6(c)). The bottle 32 at this stage is very fragile so that the bladder pressure has to be carefully controlled to achieve mould release without distortion or damage. An internal bladder pressure of 1.1 bar (1.11 kPa) gauge has been found to be suitable. The bottle 32 is then transferred using the bladder 34 to a conveyor belt 36 (FIG. 8) and released from the bladder 34 to be passed to the drying stage. The pressurising fluid is evacuated causing the bladder 34 to deflate allowing for its removal from the bottle 32.

(26) Microwave Drying (Step 8)

(27) The bottle 32 is then conveyed on the conveyor belt 36 through a microwave drying chamber 38 in the form of a tunnel (FIG. 8). The conveyor belt 36 is in the form of a permeable lattice to assist water evaporation. The bottles 32 are exposed to multiple direct microwave sources (magnetrons) 48 to achieve efficient drying as described in more detail below. Airflow is maintained through the microwave drying chamber 38 in order to extract evaporated water vapour, and to ensure that the magnetrons 48 are kept suitably cool.

(28) The microwave drying chamber 38 includes entrance and exit airlocks 40, 42, each including a pair of doors A, B operated in synchronisation so that they are not open at the same time. This allows continuous operation while ensuring no leakage of microwave energy outside the chamber. The entrance/loading airlock 40 is activated and signals conveyor belt 36 to advance and the bottles 32 are transported into the airlock chamber. A signal stops the conveyor belt 36 and reverses the action of the airlock 40. This procedure is repeated at the exit to the drying chamber 38, with activation of the exit/unloading airlock 42 allowing the bottles to exit the microwave drying chamber 38.

(29) As will be appreciated, microwave energy is focused upon the water contained in the bottles 32 and is therefore not wasted in heating the surrounding air or equipment. An array 50 of multiple domestic grade magnetrons 48 (power rating 1 kW) mounted to the upper wall of the microwave drying chamber 38 is used (FIG. 9). As shown in FIG. 9(a), a rectangular 5 (in direction of travel)×4 (widthwise) grid arrangement of evenly spaced magnetrons 48 is used as the array 50 in this preferred embodiment. The magnetron antennae 54 are used to direct the radiation field into the microwave drying chamber 38 without conventional wave guides.

(30) Each magnetron 48 of the array 50 is fitted with an individual power control (not shown) such that the power output can be controlled and switched on/off for individual magnetrons 48 or for the array 50 as a whole. This allows for power profiling along the microwave drying chamber 38 (FIG. 10) which can be adjusted to suit different products. Automatic control is used.

(31) The bottles 32 are arranged upright in an array 52 (shown in plan view in FIG. 9(a) and in section in FIGS. 8 and 9(b)) which is complementary to the array 50 of magnetrons 48. A rectangular 5×5 grid arrangement of evenly spaced bottles 32 having the same centre-to-centre spacing as the magnetrons 48 is used such that bottles 32 and magnetrons 48 alternate across the width of the chamber (FIG. 9(a)). Bottles 32 are passed through the microwave drying chamber 38 in batches.

(32) As examples, power profiles 56, 58 for bottles 32 weighing 120 g and 200 g respectively are shown in FIG. 10 (capacities 100 mL and 750 mL respectively). As bottles 32 pass along the microwave drying chamber 38 over a 10 minute period in FIG. 10, they will pass different magnetrons 48 within the array 50, operating at different powers.

(33) This final stage reduces the water content of the bottle to below 10%.

(34) Test Results

(35) Compression tests were carried out on vertically orientated 200 mL paper bottles (i.e. moulded articles of the preferred embodiment of the invention) and 200 mL PET plastic bottles at a compression rate of 10 mm/minute.

(36) Force displacement plots are shown in FIG. 11 and pictures of the bottles after testing are shown in FIG. 12. In general, the paper bottles required a higher force to yield (400-900 N rather than 100-250 N). The paper bottles yielded by inversion of the neck into the body of the bottle, whereas the plastics bottles yielded by crumpling of the body. As deformation of the paper bottles continued, the load increased as inversion continued until the neck was level with the main body (FIG. 12).

Advantages of Preferred Embodiment

(37) In addition to the advantages mentioned above, these include: environmentally friendly paper packaging products are produced using post-consumer recyclable materials. The process is optimised for energy conservation by eliminating or reducing the three main elements which contribute to excessive use of energy normally required with conventional pulp moulding processes. These are (a) the use of a hydropulper (eliminated), (b) vacuum (reduced), and (c) drying ovens (eliminated). the products can be manufactured to a high degree of precision and complexity that is difficult to achieve with existing techniques. the process can produce a high volume of product throughput whilst retaining portable, miniaturized and operationally flexible plant machinery. For example, a machine with a foot print of 10 square metres has a production capacity of 8 million bottles per year. the product bottle has a high crush strength, higher than PET.

(38) These design elements result in a significant saving on equipment cost as well as a high energy delivery efficiency. Apparatus of the general type of the preferred embodiment can be used to make well-formed containers of widely different shapes tailor-made to the customer's requirements.

(39) Although the invention has been described with reference to the preferred embodiment shown in the figures, the skilled person will understand that various modifications are possible within the scope of the invention.