GB2586650A

GB2586650A - Wet press mould filter and filter assembly

Info

Publication number: GB2586650A
Application number: GB1912566.5A
Authority: GB
Inventors: Newbury Peter; Green Barrie
Original assignee: Thomas Haimes & Co Ltd
Current assignee: Thomas Haimes & Co Ltd
Priority date: 2019-09-02
Filing date: 2019-09-02
Publication date: 2021-03-03
Also published as: GB201912566D0

Abstract

Wet press mould filter 200 with inner sorbent layer 204 between first 202 and second 206 outer fabric layers. The inner layer may be a nonwoven fabric. The first outer fabric layer comprises yarns or the second outer fabric layer comprises yarns arranged in a pattern. The yarns may be arranged in a knit pattern. The first or second outer fabric layer may have a greater weight per unit area than the inner layer. The outer fabric layers may be permeable and less sorbent then the inner layer. The first outer layer may be attached to a first face of the inner layer and the second outer layer may be attached to a second face of the inner layer. The layers may comprise thermoplastic material. The peripheral edges of the filter may be heat sealed. The layers may comprise polyethylene. The filter may be flexible. A filter assembly may include the filter and a filter former.

Description

WET PRESS MOULD FILTER AND FILTER ASSEMBLY

FIELD OF THE INVENTION

Embodiments of the present invention relate to a wet press mould filter. In particular, they relate to a wet concrete press mould filter, a filter assembly, and the wet press.

BACKGROUND TO THE INVENTION

A known wet press design is used to form concrete products via the application of compressive force. A wet cementitious workpiece is inserted into a mould in a viscous or semi-dry state, and pressed to form a product.

The cementitious workpiece comprises cement and may comprise the constituent materials of concrete, such as water, sand, aggregates, and any other additives.

The workpiece is pressed in the mould between platens (die heads) to form a desired shape, such as a paving slab or kerb, for example.

While the compressive force is applied, excess water is squeezed out of the workpiece. The excess water is conducted away from the mould under the assistance of a vacuum.

Normal practice is to place a filter in the path of the excess water conducted by the vacuum. Particulate material (finings) of the workpiece are trapped by the filter and prevented from entering press mould ducts along with extracted water.

If the filter is placed on the platen at the base of the mould to separate the workpiece from the platen, the finished concrete product will have a better surface finish and the platen will be on the clean side of the filter to reduce platen cleaning. However, this arrangement puts the filter in direct contact with the workpiece, and the filter will be subject to considerable and unevenly distributed compression forces and vacuum forces.

Various filter designs have been proposed. Paper filters are commonly used.

However, they are discarded after every use which is slow and environmentally unfriendly. Another filter design relies on a manufactured fabric fastened to a filter former to create a filter assembly. However, the fabric may be permanently attached to the filter former, making the fabric difficult to clean. The entire filter assembly including the filter former needs to be discarded after a few hundred pressings.

It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

BRIEF DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

According to various, but not necessarily all, embodiments of the invention there is provided a wet press mould filter comprising: an inner layer comprising sorbent (e.g. absorbent) material; a first outer fabric layer; and a second outer fabric layer, wherein the inner layer is between the first outer fabric layer and the second outer fabric layer.

An advantage is improved all-round performance, defined as the balance of filter durability, water dissipation, and finings filtration. The inner layer better dissipates water around the filter, while being encapsulated and protected by other more durable fabric layers of the permeable filter. Durability may be assessed based on a number of pressings before layer delamination, for example.

In some, but not necessarily all examples the sorbent material of the inner layer comprises nonwoven fabric. In some, but not necessarily all examples the first outer fabric layer comprises yarns and/or wherein the second outer fabric layer comprises yarns arranged in a pattern (e.g. knit or woven). An advantage is improved durability because the knit/woven layers protect the sensitive nonwoven layer from damage and clogging.

In some, but not necessarily all examples the yarns are arranged in a knit pattern. An advantage is more durability than a woven pattern, due to omnidirectional stretchability, and improved water transport due to the openness of knit loops.

In some, but not necessarily all examples the first outer fabric layer has a greater weight per unit area than the inner layer and/or wherein the second outer fabric layer has a greater weight per unit area than the inner layer. An advantage is improved all-round performance, with greater resistance to delamination and improved filtration.

In some, but not necessarily all examples the first outer fabric layer has a weight of more than 240 grams per square metre, and/or wherein the second outer fabric layer has a weight of more than 240 grams per square metre, and/or wherein the inner layer has a weight of less than 240 grams per square metre. An advantage is improved all-round performance, wherein examples tested within these limits have survived over a thousand pressings before delamination.

In some, but not necessarily all examples the first outer fabric layer is permeable but relatively less sorbent than the sorbent material of the inner layer, and/or wherein the second outer fabric layer is permeable but relatively less sorbent than the sorbent material of the inner layer. An advantage is that the filter is easier to clean.

In some, but not necessarily all examples the filter defines a filtration surface area having a value from the range approximately a hundred centimetres squared to approximately four metres squared. An advantage is suitability for paving slabs and kerbs.

In some, but not necessarily all examples the first outer fabric layer is attached to a first face of the inner layer facing the first outer fabric layer and/or wherein the second outer fabric layer is attached to a second face of the inner layer facing the second outer fabric layer. An advantage of this three-layer design, without additional intermediate layers, is improved all-round performance with less chance of delamination.

In some, but not necessarily all examples the filter comprises permeable adhesive attaching the first outer fabric layer to the first face of the inner layer and/or attaching the second outer fabric layer to the second face of the inner layer. An advantage is improved durability because the layers can be attached/glued along their continuous internal surfaces and not only at the edges, improving resistance to delamination at the centre of the filter.

In some, but not necessarily all examples the first and second outer fabric layers comprise thermoplastic material and/or wherein the material of the inner layer is thermoplastic material. In some, but not necessarily all examples peripheral edges of the filter are heat sealed. An advantage is ease of precise manufacture, and reduced chance of fraying or delamination at the edges.

In some, but not necessarily all examples the first outer fabric layer comprises polyethylene and/or wherein the second outer fabric layer comprises polyethylene and/or wherein the material of the inner layer is polyethylene. An advantage is that highly engineered materials are not required.

In some, but not necessarily all examples the filter is flexible. An advantage is 30 improved ease of use, because the filter can be peeled from the workpiece/platen.

According to various, but not necessarily all, embodiments of the invention there is provided a filter assembly comprising the filter and a filter former. An advantage is improved filtration because the former shapes the less-rigid filter assembly to fill the entire required space, without gaps.

In some, but not necessarily all examples the filter former comprises channels for enabling liquid (e.g. water) expelled from a cementitious workpiece during wet pressing to pass through the filter assembly. An advantage is improved filtration as the liquid has an efficient path.

In some, but not necessarily all examples the channels are formed by perforations in the filter former. An advantage is an improved vacuum at the workpiece compared with having no perforations or other conduits.

In some, but not necessarily all examples the filter former is relatively rigid compared to the filter. An advantage is improved filtration because the solid (non-fabric) filter former holds the filter in the desired shape in use.

In some, but not necessarily all examples the filter former and the filter are removably attached to one another. An advantage is improved durability and reduced material use because the filter can be removed for washing/cleaning, and the filter former can be re-used with a fresh filter when the original filter eventually fails.

In some, but not necessarily all examples the filter former and the filter are removably attached to one another by permeable adhesive. An advantage is improved durability and filtration.

According to various, but not necessarily all, embodiments of the invention 30 there is provided a wet press configured to form concrete products, the wet press comprising a mould for receiving a wet cementitious mixture, and comprising the filter or the filter assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of various examples of embodiments of the present 5 invention reference will now be made by way of example only to the accompanying drawings in which: Fig 1 illustrates a side view of an example wet press; Fig 2 illustrates a side view of an example wet press mould filter; Fig 3 illustrates a side view of an example filter assembly; and Fig 4 illustrates a top view of an example filter former for a filter assembly.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

Fig 1 illustrates a side view of a wet press 100 with which the filter assembly 106 is configured to be used. The wet press 100 comprises upper and lower platens 102, one or both of which is movable to compress a wet cementitious workpiece 108 placed therebetween.

A mould is formed between side walls (not shown) and the lower platen 102, so that upon compression the workpiece 108 is deformed to fill the mould. The shape of the mould depends on the type of product to be formed, for example a paving slab or a kerbstone.

As shown, one or both of the platens 102 may comprise water channels 104, 104' (liquid channels) configured to enable excess water to be squeezed out of the mould. The excess water is released from the cementitious workpiece 108 during compression. Removal of excess water via the water channels 104, 104' of the platens 102 may be assisted by a vacuum.

Prior to inserting/pouring the cementitious workpiece 108 into the mould, a filter assembly 106 according to at least one example of the present invention is placed into the mould and on the surface of a platen 102. As shown, filter assemblies may optionally be provided for each of the upper and lower platens 102. The filter assembly 106 is configured to permit the passage of moisture (e.g. water) therethrough but to prohibit the passage of particulate material (finings).

Figs 2-4 illustrate the filter assembly 106 in more detail. Fig 2 shows the filter 200 of the filter assembly 106 in detail. Fig 3 shows the filter 200 attached to an example filter former 300 for the filter assembly 106. Fig 4 is a top view of the filter former 300.

Dimensions of the filter 200 are not shown and depend on the size of the mould. Typically, wet presses for concrete products have a mould area from the range approximately a hundred centimetres squared to approximately four metres 15 squared.

As illustrated, the filter 200 itself comprises: an inner (interior) layer 204 comprising sorbent (e.g. absorbent) material; a first outer (exterior) fabric layer 202; and a second outer (exterior) fabric layer 206. The inner layer 204 is between the first outer fabric layer 202 and the second outer fabric layer 206.

The faces of the inner sorbent layer 204 are therefore encapsulated between two relatively durable fabric layers, protecting the faces of the inner sorbent layer 204.

The inner layer 204 will now be described in more detail. The sorbent material of the inner layer 204 is configured to dissipate the excess water around the filter 200, to improve evenness of water removal. The sorbent material absorbs moisture, such as water.

In some, but not necessarily all examples the sorbent material of the inner layer 204 comprises nonwoven fabric. A nonwoven fabric is neither woven nor knitted from yarns, and is instead made from fibres bonded together by chemical, mechanical, heat or solvent treatment. This is better than a foam/sponge material at least because the layers are easier to integrate to create a single strong multi-layer fabric.

The sorbent material of the inner layer 204 may comprise polymeric fibres or natural fibres. In a specific example, the sorbent material may comprise polymeric fibres for increased durability. The selected polymer may be a thermoplastic. The thermoplastic may comprise polyester (PE) such as polyethylene (PET) in an implementation. However, other thermoplastics/fibres could be used in other examples.

The sorbent material of the inner layer 204 may have a fabric weight of less than 240 grams per square metre (gsm). An optimum range is 90-220gsm, centred around well-performing specimens at approximately 140gsm. A fabric weight which is too high may impede removal of excess water due to an overly thick filter. A fabric weight which is too low will not dissipate excess water well.

If the sorbent material is nonwoven, the nonwoven fabric may be airlaid, spun bonded, spun laced, cross lapped, or needle-punched, etc. However, needle-punching provides useful internal conduits for transporting water through the inner layer 204.

The individual fibres for the sorbent nonwoven material may be round, trilobal or irregular, and may or may not be hollow. Trilobal fibres advantageously provide a high water permeability.

The outer layers 202, 206 will now be described in more detail. The outer layers 202, 206 are configured to protect the sorbent material of the inner layer 204. This increases durability and enable greater freedom of selection of materials for the sorbent material of the inner layer 204. In various examples, the outer layers 202, 206 are also configured to provide, in large part, the function of filtering out finings from the excess water. The outer layers 202, 206 are for contact with the wet cementitious work piece / the platen 102 / other parts of the filter assembly 106.

The outer layers 202, 206 are relatively less sorbent than the inner layer 204. 5 For example, a nonwoven inner layer 204 comprises more voids.

Each outer layer 202, 206 extends over a face of the inner layer 204. An outer layer 202, 206 may extend over the whole face of the inner layer 204 as illustrated in Fig 2, or at least a substantial portion thereof such as at least 80% of the face area of the inner layer 204. The outer layer 202, 206 keeps the inner layer 204 out of contact with the wet cementitious workpiece 108 / the platen 102 / other parts of the filter assembly 106.

The outer layers 202, 206 may comprise yarns arranged in a pattern. The pattern may be knit or woven. In a specific implementation, the outer layers 202, 206 are warp knit. An advantage of warp knitting compared to weft knitting is faster production, more design freedom, increased dimensional stability and a fabric less prone to runs.

The outer layers 202, 206 may comprise polymeric or natural yarns. The selected polymer may be a thermoplastic, such as polyethylene. Other thermoplastics/fibres could be used in other examples.

Each of the first and second outer layers 202, 206 may be identical in construction to each other, enabling the filter 200 to be positioned either side up. Alternatively, the outer layer on one side of the filter 200 may have a different construction from the outer layer on the other side of the filter 200.

At least the outer surfaces of the outer layers 202, 206 may be hydrophilic or hydrophobic, due to the natural material properties of the yarns or subsequent treatment. For example, polyester yarn/fibre is naturally hydrophobic.

The fabric for the outer layers 202, 206 may have a weight of more than 240gsm, as lower weights (thinner yarns/fewer needles per inch) can accelerate layer delamination. Results were found to improve above 300gsm, with the best performing specimens having the highest tested weight of 370gsm. The thickness of the finished fabric may be less than 5mm or less than 10mm.

The fabric for the outer layers 202, 206, if knit, comprises at least two bars. The term 'layer' as referred to herein does not refer to a single bar but refers to a finished fabric with the required number of bars. Bar 1 faces the inner layer 204 and bar 2 faces outwards (towards platen 102 or workpiece 108). At least a third middle bar could be provided in some examples.

The denier weight of the fabric for the outer layers 202, 206 may be at least 15 300den, expressed as the sum of the denier weights of each bar.

The denier weight-per-bar for outer bars 1 and 2 may be from the range approximately 100den to approximately 200den, for optimum durability and water dissipation. A very low denier yarn can snap easily, whereas a very high yarn weight may be too rigid and the holes for water permeation may be too small. In a specific example, both bars 1 and 2 are 167den. The denier weights for bars 1 and 2 may be the same or different.

If at least one middle bar is provided, the sum of denier weights may still be at least 300den, but with a lower denier weight-per-bar than the above two-bar example. The middle bar yarn can afford a lower denier weight than the outer bars 1 and 2 while maintaining durability, because the middle bar is just a control bar that controls stability. The deniers of the outer bars 1 and 2 may differ for ease of knitting. In an example, the outer bars 1 and 2 are 100den and 150den, and the third middle bar is 50den.

In some, but not necessarily all examples the bars may have different float lengths. Bar 2 may have a longer float than bar 1. This is because a shorter float for bar 1 helps to hold the layers together well, and a longer float for bar 2 provides a smoother surface, giving the pressed concrete product an improved surface finish.

Example tricot warp knit lapping patterns for bar 1 include: 1-0/1-2 repeat or 10/1-0 repeat. Example tricot warp knit lapping patterns for bar 2 include 1-0/45 repeat; 1-0/3-4 repeat; 3-4/1-2 repeat; 2-3/1-2 repeat. If the fabric comprises a middle bar, an example tricot warp knit lapping pattern for the middle bar is 0-1/1-0 repeat.

The float length giving the best results was found for bar 2=1-0/3A or 1-0/4-5. This is because as float length increases from an ideal of 3-4, plucking may start to occur, likely due to finings from the cementitious workpiece.

These lapping patterns, or similar, are configured to provide good filtration and elastic strength in all directions, as well as different floats for the reasons given above. The pattern notation depends on the machine used and the required 20 finish.

The tricot gauge for the fabric for the outer layers 202, 206 may be a value from the range approximately 18 to approximately 24 needles per inch.

The wales per inch (WPI) of the finished fabric for the outer layers 202, 206 may be a value from the range approximately 20 WPI to approximately 26 WPI.

The courses per inch (CPI) of the finished fabric for the outer layers 202, 206 may be from the range approximately 50 WPI to approximately 80 WPI. In other 30 examples, WPI may be greater than CPI.

The gauge, WPI and CPI, affect filtration capability. Values which are too low impede filtering whereas values which are too high are too tight to let sufficient excess water through.

In order to finish the fabric, the warp knit fabric may be heated at temperatures of over 100 Celsius, for example from the range approximately 100 to approximately 200 Celsius, depending on the thermal characteristics of the filter materials. In an implementation, the fabric may be processed using a high temperature jet dyeing machine to heat and finish the fabric, regardless of whether dye is actually applied.

Fig 3 shows how the inner and outer layers 202, 204, 206 of the filter 200 may be attached to each other, and how the filter 200 may be attached to a filter former 300. The filter former 300 is any body that shapes the filter 200, which is a flexible fabric, to fill the required space (mould cavity). Figs 3-4 show that the filter former 300 may be rigid, compared to the filter 200. For example, the filter former 300 may comprise moulded (non-fabric) plastic, or metal. If the filter former material is not moisture permeable, water channels 302, 302' may be provided through the filter former 300 as shown, to enable water to pass through the filter assembly 106, to the water channels 104, 104' of the platen 102. In Figs 3-4, the channels 302, 302' through the filter former 300 are perforations devoid of material. The number and pattern of perforations is implementation dependent. It would be appreciated that in other implementations, the channels 302, 302' may comprise conduits of permeable material rather than empty perforations.

Attachment of the inner and outer layers 202, 204, 206 of the filter 200 to each other will be discussed first. The attachment should be permanent and should resist delamination.

In various implementations of the present design, including Fig 3, the layers of the filter 200 are attached to each other along their continuous internal surfaces rather than just at the peripheral edges, increasing resistance to delamination from the centre.

As illustrated by adhesive layers 208, 210 in Fig 3, the first outer layer 202 may be attached to a first face 204a of the inner layer 204 using permeable adhesive 208. The second outer layer 206 may be attached to a second face 204b of the inner layer 204 using permeable adhesive 210.

An example permeable adhesive is a hot melt adhesive such as a urethane adhesive (e.g. polyurethane adhesive), permeable to water to avoid filter blockage. Urethane adhesives cure at lower temperatures than other hot melts and require few steps to apply.

A glue roller or other applicator may be used to apply adhesive with a continuous coverage over substantially 100% or at least 50% of the layer-to-layer contact area. Alternatively, the permeable adhesive may be arranged in a pattern of beads of adhesive, including beads running nonparallel to the edges and towards/through the centre, to resist centre delamination.

The adhesive may also be applied to the peripheral edges of the filter 200 which are sensitive to delamination. The peripheral edges of the filter 200 may then be sealed, which further increases resistance to delamination. The edges may be heat sealed. The heat sealing may at least partially melt the thermoplastic yarns of the inner and outer layers 202, 204, 206, and the permeable adhesive.

The temperature may be at least 100 Celsius. A hot knife may be used for combined cutting and heat sealing. Alternatively, a laser or other technique may be used.

In some, but not necessarily all examples, staples and/or stitches may also be applied to further connect the layers of the filter 200 to improve delamination resistance. For example, a line(s) of staples/stitches may run in close proximity (e.g. 1-4 centimetres) to a peripheral edge(s) of the filter 200. However, adhesive may still be used because peripheral staples/stitches provide limited resistance to delamination from the centre of the filter 200, away from the staples/stitches.

Attachment of the filter 200 to the filter former 300 will now be discussed. It would be advantageous to use a different, lower tack adhesive layer 304 here. The lower adhesion facilitates easy removal and periodic cleaning of the filter 200 from the filter former 300, without damaging the filter 200 or filter former 300 during peeling of the filter 200 away from the filter former 300. The filter 200 can therefore be cleaned, and the filter former 300 does not have to be discarded when the filter 200 reaches the end of its life.

An example adhesive for removably attaching the filter 200 to the filter former 300 is a contact adhesive. An example contact adhesive uses rubber or synthetic rubber as a chemical base, and may be applied as an aerosol or using another appropriate technique. A suitable example is Smart Tack (RTM), which is an aerosol contact adhesive, with a synthetic rubber/resin chemical base, and a density of 0.9-0.99g/cm3, that dries after a few minutes. The adhesive strength should not be so high that yarns are broken during removal of the filter 200 from the filter former 300. It would be appreciated that there are various other products easily found on the market which provide similar properties.

As an alternative to Fig 3, the peripheral edges of the filter could wrap around the filter former 300 and onto an upper surface of the filter former 300. The filter may be attached to the upper surface of the filter former 300. In some examples, double-sided sticky tape could be used for the upper surface attachment, or permeable adhesive. Further, the wraparound filter may also be attached to the lower surface of the filter former 300 as shown in Fig 3, for example by permeable adhesive.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example the filter may be usable with wet presses for non-cementitious workpieces.

All values given are nominal unless stated otherwise.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

I/we claim:

Claims

CLAIMS1. A wet press mould filter comprising: an inner layer comprising sorbent material; a first outer fabric layer; and a second outer fabric layer, wherein the inner layer is between the first outer fabric layer and the second outer fabric layer.
2. The filter of claim 1, wherein the sorbent material of the inner layer comprises nonwoven fabric.
3. The filter of claim 1 or 2, wherein the first outer fabric layer comprises yarns and/or wherein the second outer fabric layer comprises yarns arranged in a pattern.
4. The filter of claim 3, wherein the yarns are arranged in a knit pattern.
5. The filter of any preceding claim, wherein the first outer fabric layer has a greater weight per unit area than the inner layer.
6. The filter of claim 5, wherein the first outer fabric layer has a weight of more than 240 grams per square metre, and/or wherein the inner layer has a weight of less than 240 grams per square metre.
7. The filter of any preceding claim, wherein the second outer fabric layer has a greater weight per unit area than the inner layer.
8. The filter of any preceding claim, wherein the first outer fabric layer is permeable but relatively less sorbent than the sorbent material of the inner layer, and/or wherein the second outer fabric layer is permeable but relatively less sorbent than the sorbent material of the inner layer.
9. The filter of any preceding claim, wherein the filter defines a filtration surface area having a value from the range approximately a hundred centimetres squared to approximately four metres squared.
10. The filter of any preceding claim, wherein the first outer fabric layer is attached to a first face of the inner layer facing the first outer fabric layer and/or wherein the second outer fabric layer is attached to a second face of the inner layer facing the second outer fabric layer.
11. The filter of claim 10, comprising permeable adhesive attaching the first outer fabric layer to the first face of the inner layer and/or attaching the second outer fabric layer to the second face of the inner layer.
12. The filter of any preceding claim, wherein the first and second outer fabric layers comprise thermoplastic material and/or wherein the material of the inner layer is thermoplastic material.
13. The filter of any preceding claim, wherein peripheral edges of the filter are heat sealed.
14. The filter of claim 12 or 13, wherein the first outer fabric layer comprises polyethylene and/or wherein the second outer fabric layer comprises polyethylene and/or wherein the material of the inner layer is polyethylene.
15. The filter of any preceding claim, wherein the filter is flexible.
16. A filter assembly comprising the filter of any preceding claim and a filter former.
17. The filter assembly of claim 16, wherein the filter former comprises channels for enabling liquid expelled from a cementitious workpiece during wet pressing to pass through the filter assembly.
18. The filter assembly of claim 17, wherein the channels are formed by perforations in the filter former.
19. The filter assembly of claim 16, 17 or 18, wherein the filter former is relatively rigid compared to the filter.
20. The filter assembly of any one of claims 16 to 19, wherein the filter former and the filter are removably attached to one another.
21. The filter assembly of any one of claims 16 to 20, wherein the filter former and the filter are removably attached to one another by permeable adhesive.
22. A wet press configured to form concrete products, the wet press comprising a mould for receiving a wet cementitious mixture, and comprising the filter of any one of claims 1 to 15 or the filter assembly of any one of claims 16 to 21.