WO2000058557A1

WO2000058557A1 - Pulp moulding process and related system

Info

Publication number: WO2000058557A1
Application number: PCT/ZA2000/000057
Authority: WO
Inventors: Johan Jacob Oosthuizen; Jonathan David Taljaard
Original assignee: Southern Pulp Machinery Pty Ltd
Current assignee: Southern Pulp Machinery Pty Ltd
Priority date: 1999-03-26
Filing date: 2000-03-24
Publication date: 2000-10-05
Anticipated expiration: 2001-09-26
Also published as: US6706151B1; AU3775900A; EP1165890A1

Abstract

A pulp moulding process including the steps of preparing pulp stock, forming wet products by means of a forming die (7), transferring the wet products from the forming die by means of a heated transferring die (13)-and-heated pressing tool (14) arrangement for in-mould pressing and drying of the wet product, and delivering the dried products to a down line facility (18). The invention extends to a pulp moulding system, specific pulp moulding apparatus and a pulp moulded product made by such a process, system and/or apparatus.

Description

PULP MOULDING PROCESS AND RELATED SYSTEM

TECHNICAL FIELD

This invention relates to a pulp moulding process. More particularly but not exclusively,

the invention relates to a pulp moulding process, a pulp moulding system, specific pulp

moulding apparatus and a pulp moulded product made by such a process, system and/or

apparatus.

BACKGROUND ART

The process of pulp moulding in which pulp, typically constituted by water and raw

materials such as paper, is moulded to produce products such as functional packaging

materials is well known. The process traditionally incorporates the steps of pulp stock

preparation, wet forming of products with forming dies, transferring of wet products

with transfer dies, drying and packing of the final dry products.

Known disadvantages of the traditional pulp moulding process include relatively high

capital costs, poor product quality, high energy costs and high space requirements as well

as relatively high manpower requirements. A known improvement of the traditional pulp moulding process is the so-catted "in-

mould drying" or "thermo-formed" process, the process endeavouring to achieve an

improved quality comparable with injection moulded, thermoformed plastic products.

The in-mould drying process comprises the traditional process, characterized in that it

substitutes the step of conveyor drying with an in-mould drying step wherein the wet or

so-called "in-mould" dried product is press dried between heated, opposed, closable

pressing tools, with steam resulting from the heating being scavenged under vacuum.

The incorporation of the in-mould drying step is aimed at improving poor produα finish

such as surface coarseness as well as dimensional inaccuracies and deformities. The poor

product finish is caused primarily during the drying process, where the wet produα is

subjected to high temperature, high velocity air flow. In a preferred form, the in-mould

drying process includes further in-mould drying in down line pressing stations. The

added advantage of additional pressing stations is the speeding up of the pressing portion

of the pressing and drying process.

Known disadvantages of the in-mould drying process however include relatively slower

cycle times and corresponding lower product output, relatively high down time due to

slower mould changing procedures, expensive tooling, an additionally required vacuum

system for steam scavenging and relatively larger sized moulders so as to provide for the

additional pressing stations and expensive pneumatic and/or hydraulic pressing system. It is accordingly an object of the invention to provide a pulp moulding process, a pulp

moulding system as well as products moulded from such a process and/ or system which

will overcome or at least reduce the above disadvantages, or at least to provide a novel

and/or relatively inexpensive, alternative pulp moulding process.

DISCLOSURE OF INVENTION

According to a first aspeα of the invention there is provided a pulp moulding process

including the steps of preparing pulp stock; forming wet products by means of a forming

die; transferring the wet produαs from the forming die by means of a heated transferring

die-and-heated pressing tool arrangement for in-mould pressing and drying of the wet

product; and delivering the dried products to a down line facility.

The process may include the step of using a heated fluid medium for providing heat in

the pressing and drying step, the medium being preferably steam.

the pressing and drying step, the medium being preferably thermal oil. The thermal oil

may be maintained at a negative gauge pressure. The process may include any one or both of the steps of forcing steam generated during

the pressing and drying step in one direction through the in-mould wet product; and

venting the generated steam to the atmosphere, alternatively scavenging the steam under

vacuum.

The method may include any one or both of the steps of forcing heated gas, such as air,

through the in-mould wet product at high pressure; and venting the steam generated

during the in-mould pressing and drying step to the atmosphere, alternatively scavenging

the steam under vacuum.

According to a second aspect of the invention there is provided a transfer die-and-heated

pressing tool arrangement for use in a pulp moulding process as hereinbefore defined,

the transfer die-and-pressing tool arrangement comprising a male part and a female part,

at least one part being provided with a primary fluid passage for receiving a heating fluid

therethrough and at least one part being provided with at least one vent so as to allow

steam generated during an in-mould pressing and drying step to escape therethrough to

the atmosphere, alternatively to a vacuum.

The heated transfer die-and-pressing tool arrangement may be charaαerized in that at

least one of the male pan and female pan may comprise a die element mounted on a plate including a plenum chamber incorporating the primary fluid passage. The heated

transfer die-and-pressing tool arrangement may be configured so as to allow the in-

mould pressing and drying step to take place with the plate being orientated substantially

vertically.

The heated transfer die-and-pressing tool arrangement may be charaαerized in being

provided with at least one secondary fluid passage for receiving pressurized gas, such as

air, therethrough, the secondary fluid passage being orientated so as to communicate

gaseously with the vent to force the pressurized gas and the steam generated during the

in-mould drying step in one direction through the in-mould wet produα via the vent

directly to the atmosphere, alternatively to a vacuum.

The heated transfer die-and-pressing tool arrangement preferably is provided with a set

of secondary fluid passages and a set of vents, the set of secondary fluid passages and the

set of vents being staggered relative to each other so as to enhance the substantially

uniform flow of pressurized gas through the wet product.

According to a third aspect of the invention there is provided press drying equipment for

an in-mould drying, pulp moulding system, the equipment including a heated transfer die

and a heated pressing tool, the heated transfer die and the heated pressing tool being operatively associated mechanically with each other so as to provide a heated, mechanical

press therebetween in a heated transfer die-and-heated pressing tool arrangement.

The heated transfer die-and-heated pressing tool arrangement may be rotary so as to

enable rotary transfer and drying of a wet produα between a forming die and a down line

facility.

According to a fourth aspect of the invention there is provided a method for in-mould

drying of a wet product in a pulp moulding process, the method including the step of

passing pre-heated gas, such as air, through an in-mould wet product so as to accelerate

the drying of the produα.

According to a fifth aspect of the invention there is provided a method of heating a

pressing tool in a pulp moulding process, the method including the step of flowing a

heating fluid through a fluid passage in a heated pressing tool.

According to a sixth aspect of the invention there is provided an in-mould drying, pulp

moulding system comprising means for preparing pulp stock; a wet forming section,

incorporating forming dies; and means for transferring wet product from the forming dies and press drying the wet product, the means including a heated transferring die-and-

pressing tool arrangement, the arrangement being substantially as hereinbefore defined.

The system may include a down line drying tunnel so as to complete drying, thus

enhancing the overall cycle of the system.

According to a seventh aspect of the invention, there is provided a pulp moulded

product, manufactured using pulp moulding process including the steps of preparing

pulp stock; forming wet products by means of a forming die; transferring the wet

products from the forming die by means of a heated transferring die-and-heated pressing

tool arrangement for in-mould pressing and drying of the wet product; and delivering the

dried produαs to a down line facility.

A preferred embodiment of the invention will now be described by means of a non-

limiting example only and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a diagrammatic layout of a traditional pulp moulding process; Figure 2 is a diagrammatic layout of an existing in-mould drying or so-called

"thermoformed" pulp moulding process;

Figure 3 is a diagrammatic layout of part of an in-mould drying, pulp

moulding process in accordance with the invention;

Figure 4 is a cross-section side view of existing in-mould drying equipment;

Figure 5 is a cross-section side-view of in-mould drying equipment in

accordance with the invention;

Figure 6 is a cross-sectional side view of an alternative design of in-mould

drying equipment in accordance with the invention; and

Figure 7 is a cross-sectional side view of a second alternative design of in-

mould drying equipment in accordance with the invention.

Please note that the same reference numerals are used to denote corresponding parts in

the accompanying drawings. MODES FOR CARRYING OUT THE INVENTION

A traditional pulp moulding process as illustrated in figure 1 typically includes a pulper

(1) in which weighed raw materials such as waste paper is loaded together with processed

water from a white water feed tank (2) in the required dry fibre-to-water ratio and

pulped. Once the required pulp is obtained, it is pumped to a stock container (3) from

where it is fed on demand to a moulder (6).

The moulder (6) includes a set of forming dies (7), consisting of perforated bases over

which fine mesh is fitted. During the process, vacuum is applied to the forming dies (7)

or moulds while they are submerged in the pulp. During this forming process, water in

the solution is drawn through the mesh, leaving behind matted fibres in the shape of the

product as formed by the forming dies (7). The forming dies (7) are then removed from

the pulp and engaged with transfer dies (8) or moulds. Vacuum is then applied to the

transfer dies (8) while positive pressure is simultaneously applied to the forming dies (7)

to transfer the product from the forming dies to the transfer dies.

The transfer dies (8) are then removed to a position (9) in which the vacuum is removed

and positive pressure is applied so as to eject the wet products therefrom. A conveyor belt (11) then transfers the wet products through a dryer (10) in which the wet produαs

are subjected to high velocity, high temperature air flow.

Once the dried products leave the dryer (10), they are stacked and/ or stored manually or

automatically as required. At this stage, the final product finish is coarse and dimensional

accuracy is poor as well as product deformation exists, primarily due to the application of

high velocity, high temperature air flow on the wet products during the drying process.

A secondary process or so-called "after pressing" process is often incorporated, during

which products are placed between two precisely machined heated moulds which are

brought together under pressure for a short period during which the produα is ironed

into shape (not shown) so as to improve product quality.

In an effoπ to overcome the disadvantages of poor surface finish, dimensional

inaccuracy and deformation, an in-mould drying or so-called "thermo-form" process was

developed.

The in-mould drying process with reference to figure 2 substituted the steps of conveyor

drying with an in-mould drying step wherein the wet product, once the forming die (7) is

removed from the moulder (6), is transferred by^τ means of the transfer die (8) to a series

of pressing stations (10), each pressing station having a set of heated, opposed, closable pressing tools (9) with means for scavenging steam resulting from heating under vacuum

from the wet product. Once the product has been dried to the required degree, the dried

product is ejected onto a conveyor (11) for transfer to down line facilities.

The process typically includes a facility (12) for cooling the steam scavenged under

vacuum from the wet products (9).

An in-mould drying, pulp moulding process in accordance with the invention and

partially as illustrated in figure 3 includes the steps of preparing pulp stock in a pulper

(not shown); forming wet products by means of forming dies (7) in a moulder (6);

transferring the wet produαs from the forming dies by means of a heated transferring

die (13)-and-heated pressing tool (14) arrangement for in-mould drying of the wet

products; and delivering the dried products to a conveyor belt (11) for conveyance to a

storage f ac ity (18) where the dried products are stacked by means of an automatic

stacker (15).

As in the traditional type moulding process (figure 1) and the existing in-mould drying,

pulp moulding process (figure 2), the in-mould drying, pulp moulding process in

accordance with the invention utilizes negative and positive air pressures to retain the products in the respective dies (7), (13) and to eject the products from the dies and/or

pressing moulds (14) when required.

The in-mould drying equipment in the form of the heated transfer die (13)-and-heated

pressing tool (14) arrangement is rotatable so as to enable the transfer and press drying

of the wet products from the forming die (7) to the conveyor (11) as dry produαs.

The heated transfer die (13) and the heated pressing tool (14) are operatively associated

mechanically with each other so as to provide a heated mechanical press therebetween,

thus defining the heated transfer die-and-heated pressing tool arrangement therewith.

Existing in-mould drying equipment as illustrated in figure 4 comprises a mould, having a

male pan (7) and a complementary female pan (8), each part being heated electrically by

means of electric elements (19) so as to ensure the drying of an in-mould wet product

(18). Male and female parts (7) and (8) are provided with air passages for scavenging

steam generated during the drying process from the wet product (18) under vacuum.

In-mould drying equipment in accordance with the invention and as illustrated in figure 5

comprises a male part (20) and a female part (21), each part being provided with a fluid

passage (22) for receiving a heated fluid therethrough for the drying of the in-mould wet

product (18). The male part (20) is further provided with a set of vents (23) so as to allow steam

generated during the in-mould drying step to escape from the wet product (18)

therethrough to the atmosphere. Alternatively, the steam generated may be scavenged

under vacuum.

Alternatively designed in-mould drying equipment in accordance with the invention and

as illustrated in figure 6 comprises a male part (24) and a female pan (25), each pan being

provided with a primary fluid passage (22) for receiving heating fluid therethrough so as

to dry the in-mould wet product (18) therebetween.

In a second, and preferred, alternative design for in-mould drying equipment, as

illustrated in figure 7, both the male pan (24) and the female pan (25) comprise a die

element (28) and (29) respectively, mounted to a plate (30) including a plenum chamber

(31) incorporating the primary fluid passage. The heated transfer die-and-pressing tool

arrangement is configured so as to allow the in-mould pressing and drying step to take

place with the plate (30) being orientated substantially venically.

The male pan (24) is further provided with a set of secondary fluid passages (27) and the

female pan (25) is funher provided with a set of vents (26), the set of secondary fluid

passages and the set of vents being staggered relative to each other so as to communicate gaseously to allow the introduction of pressurized gas to the wet produα through the

secondary fluid passages and the venting of the gas together with the steam generated

during the in -mould drying step in a singular direction through the wet product (18) via

the vents to the atmosphere, while enhancing the substantially uniform flow of the

pressurized gas through the wet product. Alternatively, the steam may be scavenged

under vacuum.

The in-mould drying, pulp moulding process and related system in accordance with the

invention thus provide a pulp moulded produα with relatively good quality finish and

high dimensional accuracy without deformation in a more energy efficient process in a

relatively small area, requiring relatively less manpower and relatively less tooling.

It will be appreciated that may variations in detail are possible without departing from the

scope and/or spirit of the invention as claimed in the claims hereafter.

Claims

1. A pulp moulding process including the steps of preparing pulp stock; forming

pulp products by means of a forming die; and delivering the pulp products to a

down-line facility, the process being characterized in that wet pulp produαs are

transferred from the forming die by means of a heated transferring die-and-heated

pressing tool arrangement for in-mould pressing and drying of the wet pulp

products such that pressed, dried pulp products are delivered to the down-line

facility.

2. A pulp moulding process according to claim 1, including the step of using a heated

fluid medium for providing heat in the pressing and drying step.

3. A pulp moulding process according to claim 2, wherein the heated fluid medium is

steam.

4. A pulp moulding process according to claim 2, wherein the heated fluid medium is

thermal oil.

5. A pulp moulding process according to claim 4, wherein the thermal oil is

maintained at a negative gauge pressure.

6. A pulp moulding process according to any of the preceding claims, including at

least one of the steps of forcing steam generated during the pressing and drying

step in one direction through the in-mould wet product; and venting the generated

steam to the atmosphere.

7. A pulp moulding process according to any of claims 1 - 4, including at least one

of the steps of forcing steam generated during the pressing and drying step in one

direction through the in-mould wet product; and scavenging the steam under

vacuum.

8. A pulp moulding process according to any of the preceding claims, including at

least one of the steps of forcing heated gas, such as air, through the in-mould wet

product at high pressure; and venting the steam generated during the in-mould

pressing and drying step to the atmosphere.

9. A pulp moulding process recording to any of claims 1 - 7, including at least one of

the steps of forcing heated gas, such as air, through the in-mould wet produα at

high pressure; and scavenging the steam generated during the in-mould pressing

and drying step under vacuum.

10. A transfer die-and-heated pressing tool arrangement for use in a pulp moulding

process including the steps of preparing pulp stock, forming wet produαs by

means of a forming die, transferring the wet products from the forming die by

means of a heated transferring die-and-heated pressing tool arrangement for in-

mould pressing and drying of the wet product, and delivering the dried produαs

to a down line facility; the transfer die-and-heated pressing tool arrangement being

characterised in having a male pan and a female pan, at least one pan being

provided with a primary fluid passage for receiving a heating fluid therethrough

and at least one pan being provided with at least one vent so as to allow steam

generated during an in-mould pressing and drying step to escape therethrough.

11. A heated transfer die-and-pressing tool arrangement as claimed in claim 10,

characterized in that at least one of the male pan and female pan comprises a die

element mounted on a plate, having a plenum chamber incorporating the primary

fluid passage.

12. A heated transfer die-and-pressing tool arrangement as claimed in 10 or 11,

characterized in being provided with at least one secondary fluid passage for

receiving pressurized gas, such as air, therethrough, the secondary fluid passage

being orientated so as to communicate gaseously with the vent to force the pressurized gas and the steam generated during the in-mould drying step in one

direction through the in-mould wet product.

13. A heated transfer die-and-pressing tool arrangement as claimed in any of claims 10

- 12, characterized by being provided with a set of secondary fluid passages and a

set of vents, the set of secondary fluid passages and the set of vents being

staggered relative to each other so as to enhance the substantially uniform flow of

pressurized gas through the wet produα.

14. Press drying equipment for an in-mould drying, pulp moulding system, the press

drying equipment being characterized by including a heated transfer die and a

heated pressing tool, the heated transfer die and the heated pressing tool being

operatively associated mechanically with each other so as to provide a heated,

mechanical press therebetween in a heated transfer die-and-heated pressing tool

arrangement.

15. Press drying equipment as claimed in claim 14, characterized by the heated

transfer die-and-heated pressing tool arrangement being rotary so as to enable

rotary transfer and drying of a wet product between a forming die and a down line

facility.

16. A method for in-mould drying of a wet product in a pulp moulding process, the

method characterized by including the step of passing pre-heated gas, such as air,

through an in-mould wet product so as to accelerate the drying of the produα.

17. A method of heating a pressing tool in a pulp moulding process, the method

characterized by including the step of flowing a heating fluid through a fluid

passage in a heated pressing tool.

18. An in-mould drying, pulp moulding system comprising means for preparing pulp

stock; a wet forming section, incorporating forming dies; and means for

transferring wet product from the forming dies and press drying the wet produα,

the means including a heated transferring die-and-pressing tool arrangement.

19. A pulp moulded product, characterised in being manufactured using a pulp

moulding process including the steps of preparing pulp stock; forming wet

products by means of a forming die; transferring the wet produαs from the

forming die by means of a heated transferring die-and-heated pressing tool

arrangement for in-mould pressing and drying of the wet product; and delivering

the dried produαs to a down line facility.