GB2298032A

GB2298032A - A drying roller for drying tables

Info

Publication number: GB2298032A
Application number: GB9503108A
Authority: GB
Inventors: Robert Briggs; Thomas Michael Sangster
Original assignee: Dalgety Spillers Foods Ltd
Current assignee: Nestle Purina Petcare UK Ltd
Priority date: 1995-02-17
Filing date: 1995-02-17
Publication date: 1996-08-21
Anticipated expiration: 2015-02-17
Also published as: GB9503108D0; GB2298032B

Abstract

The invention provides a drying roller 1 for a drying table, the drying roller having an outer layer formed from a tough polymeric closed-cell foam such as crosslinked ethylene vinyl acetate copolymer. The invention also provides annular discs of the foam, from which the drying roller can be formed.

Description

IMPROVEMENTS IN AND RELATING TO DRYING TABLES This invention relates to drying rollers and discs for drying rollers of the type found on drying tables for drying among other things washed vegetable and fruit produce such as potatoes, apples, oranges, etc.

As is commonly known, potatoes and other vegetable and fruit produce are graded and washed before packaging for shipment to retail outlets such as supermarkets. Following the washing stage the produce is conventionally dried on a drying table prior to packing. Drying tables in general use at present consist of a series of rollers covered in an absorbent material, usually an open-cell natural rubber foam material. The foam covered rollers are compressed against underlying steel rollers which are rotated by a suitable drive mechanism, and rotation of the steel rollers serves to rotate the foam covered rollers. The rotating foam covered rollers convey the items of vegetable or fruit produce across the table, and water from the surface of the produce is absorbed by the foam as the produce travels across the table.An item of vegetable or fruit arrives at the downstream end of the table still slightly damp but with the excess surface water removed. Water is squeezed out of the foam covered rollers by means of the compressing action of the underlying steel rollers.

The foam covering the rollers typically takes the form of either an array of foam discs, or a spirally wound foam sheath. In the United Kingdom at least, foam discs have been considered somewhat expensive to manufacture and as a consequence spirally wound foam sheaths have become widely used.

The foam covering conventionally employed is of an open-cell foam type and typically is formed from natural rubber. Foam materials of this type have, to our knowledge, been in use for at least 25 years.

A severe problem encountered with the foam coverings used hitherto, and described above, has been a tendency for the foam to break up and crumble after only a relatively short period (e.g. 6-12 weeks) of use. Not only is this undesirable from an economic standpoint, but perhaps more importantly the crumbs or foam fragments are deposited onto, and thus contaminate, the food articles. This has proved to be a major source of concern within the food packaging industry.

Thus, at present, there exists a need for an alternative material which retains the drying properties of the existing foams, but which is more durable and long lasting and does not break up into fragments or crumbs which contaminate the food items.

Accordingly, in a first aspect, the invention provides a drying roller for a drying table, the drying roller having an outer layer formed from a tough polymeric closedcell foam.

In a further aspect, the invention provides a drying roller for a drying table, the drying roller having an outer layer comprising a plurality of annular discs formed from a tough polymeric closed-cell foam.

The invention also provides an annular disc for use on a drying roller of a drying table, the annular disc being formed from a tough polymeric closed-cell foam.

In a still further aspect, the invention provides a method of drying an item of vegetable or fruit produce which comprises conveying the said item over a drying table comprising a plurality of rotating rollers having an outer layer formed from a tough polymeric closed-cell foam.

The tough polymeric closed-cell foam used in accordance with the present invention is preferably a crosslinked polymeric foam.

By tough is meant that the foam has the ability to withstand the rigours of use without crumbling or breaking up for at least four months, preferably at least six months and more preferably at least a year or more.

The polymeric closed-cell foam may have a density of at least 40 kg/m3 and preferably below 100 kg/m3, more preferably a density in the range 40-75 kg/m3, for example in the range 45-65 kg/m3, and in particular approximately 50 kg/m3.

The foam preferably has a tear strength, as defined by ISO 8067 (1991), of at least 1000 N/m, preferably at least 1200 N/m, for example 1300 N/m or more.

The tensile strength of the polymeric foam, as defined by ISO 1798 (1985) is preferably at least 800 kPa, more preferably at least 850 kPa and particularly at least 900 kPa.

The permeability of the foam to water, as defined by ISO 1663 (1981), for a 25mm thick layer of the foam may advantageously be between 0.75 and 0.90 ng/Pa/s/m.

The water vapour transmission may, for example, be at least 150 pg/m2/sec, e.g. 175 pg/m2/sec or more, e.g. 190 pg/m2/sec.

With a closed cell foam, in contrast to an open cell foam, water is only absorbed in any quantities by the surface of the foam where the cells have been cut open during the forming process. In the open cell foams conventionally used, water is absorbed throughout the foam layer.

A particularly preferred foam is crosslinked ethylene vinyl acetate (EVA) copolymer foam, sold under the trade name "EVAZOTE" by Zote Foams Ltd, Croydon, United Kingdom.

A particularly preferred grade of foam is the "EVAZOTE" 50 grade which has the following characteristics.

Density - 50 kg/m3 Tear strength - 1300 N/m Tensile strength - 930 kPa Water permeability (25mm thick sample) - 0.82 ng/Pa/s/m The above characteristics are defined in accordance with the ISO Standards referred to above.

The invention will now be illustrated by reference to a particular embodiment as shown in Figures 1 to 3 in which: Figure 1 is a schematic side elevation of a part of a drying table in accordance with the invention; Figure 2 is a schematic sectional elevation along line I-I through the drying table shown in Figure 1; and Figure 3 is a view from one side of a polymeric foam disc according to the invention.

Referring now to the Figures it can be seen that a drying table comprises a plurality of foam covered rollers 1 each of which has an associated driving roller 2 formed from a suitable grade of steel. Rollers 1 may be linked to a common arm (not shown) which enables the rollers to be raised and lowered with respect to the steel rollers 2. In this way, the rollers 1 may be compressed against steel rollers 2, firstly to enable the steel rollers 2 to drive the foam covered rollers 1 and secondly to provide a means of squeezing excess water from the foam layer.

Steel rollers 2 are driven by an appropriate driving mechanism, for example a chain mechanism (not shown).

A sectional elevation through a roller is shown in Figure 2 from which it can be seen that each roller has a central metal shaft 4 on which are mounted a plurality of polymeric foam discs 5 having a central hole to accommodate a shaft 4. An end flange 6, which is secured to the shaft 4 by means of screws 7 serves to retain the foam discs in place. A central spindle 8, about which the shaft 4 rotates, passes along the centre of shaft 4.

A drying table of the type illustrated will form part of a vegetable/fruit produce processing line and, for example, may be connected to a potato washing station.

Washed potatoes P are tumbled on to the upstream end of the drying table and are conveyed across the table in the direction D by the rotation of the rollers 1, which are driven by the rollers 2. Water from the surface of the potatoes P is absorbed by the surface of the foam layer such that the potatoes are progressively dried as they pass across the table. At the downstream end of the table, the potatoes are slightly moist, a condition which is considered desirable to enable them to be efficiently packaged, but excess surface water has been removed.

As the rollers 1 rotate, water is squeezed out of the surface of roller 1 by the steel roller 2 and means may be provided on the underside of the table for collecting and removing the residual water.

The foam annular discs 5 in this embodiment are formed from the EV 50 grade of "EVAZOTE", the characteristics of which are described above. Trials have been carried out using rollers formed from "EVAZOTE" EV 50 discs and it has been demonstrated that even after fourteen months of routine use, the rollers show no significant signs of wear and no tendency to crumble or otherwise break up. This is in marked contrast to the open-cell foam discs and roller coverings used conventionally which tend to break up after only six to twelve weeks.

Although the foam material of the present invention could be formed as a spirally wound sheath, it is preferred that the foam be in the form of annular discs. Such discs can be made cheaply and simply by die-stamping from a sheet of the foam material. A particular advantage of the use of the discs is that in the event that one disc becomes damaged, it is a simple matter to replace the disc and it is not necessary to replace the whole roller, as is currently the case with spirally wound foam sheaths.

It will readily be appreciated that numerous modifications and alterations could be made to the arrangements illustrated in the Figures without departing from the principles underlying the invention, and all such modifications and alterations are intended to be embraced by this Application.

Claims

1. A drying roller for a drying table, the drying roller having an outer layer formed from a tough polymeric closed-cell foam.

2. A drying roller for a drying table, the drying roller having an outer layer formed from a tough polymeric closed-cell foam, said foam having an absorbent surface constituted by cut-open cells.

3. A drying roller according to claim 1 or claim 2 wherein the outer layer comprises a plurality of annular discs formed from the said closed-cell foam.

4. A drying roller according to any one of the preceding claims wherein the closed-cell foam is a cross-linked foam.

5. A drying roller according to any one of the preceding claims wherein the closed-cell foam has a density of at least 40 kg/m3.

6. A drying roller according to claim 5 wherein the density is below 100 kg/m3.

7. A drying roller according to claim 6 wherein the density is in the range 40-75kg/m3.

8. A drying roller according to claim 7 wherein the density is in the range 45-65 kg/m3.

9. A drying roller according to any one of the preceding claims wherein the closed-cell foam has a tear strength of at least 1000 N/m.

10. A drying roller according to claim 9 wherein the tear strength is at least 1200 N/m.

11. A drying roller according to claim 10 wherein the tear strength is 1300 N/m or more.

12. A drying roller according to any one of the preceding claims wherein the tensile strength of the closed-cell foam is at least 800 kPa.

13. A drying roller according to claim 12 wherein the tensile strength is at least 850 kPa.

14. A drying roller according to claim 13 wherein the tensile strength is at least 900kPa.

15. A drying roller according to any one of the preceding claims wherein the closed-cell foam is a cross-linked ethylene vinyl acetate copolymer foam.

16. A drying roller according to claim 15 wherein the ethylene vinyl acetate copolymer foam has a density of 50 kg/m3, a tear strength of 1300 N/m, a tensile strength of 930 kPa and a water permeability (for a 25mm thick sample) of 0.82ng/Pa/s/m.

17. An annular disc for use on a drying roller of a drying table, the annual disc being formed from a tough polymeric closed-cell foam as defined in any one of the preceding claims.

18. An annular disc according to claim 17, said disc having been die-stamped from a sheet of the closed cell foam.

19. A method of drying an item of vegetable or fruit produce which comprises conveying the said item over a drying table comprising a plurality of rotating drying rollers as defined in any one of claims 1 to 16.

20. A method of preparing an annular disc for a drying roller as defined in any one of claims 1 to 16, which method comprises die-stamping the annular disc from a sheet of the closed-cell foam material.

21. A drying roller substantially as described herewith with reference to the accompanying drawings.

22. An annular disc for a drying roller substantially as described herein with reference to Figures 2 and 3 of the accompanying drawings.

23. A method of drying an item of vegetable or fruit produce substantially as described herein with reference to the accompanying drawings.