GB2332738A

GB2332738A - Ice-making process

Info

Publication number: GB2332738A
Application number: GB9726910A
Authority: GB
Inventors: Robin Boon
Original assignee: ICE WORK Ltd
Current assignee: ICE WORK Ltd
Priority date: 1997-12-19
Filing date: 1997-12-19
Publication date: 1999-06-30
Also published as: GB9726910D0

Abstract

A process for forming a moulded object of ice in which the water is agitated as the ice forms by means of a movable paddle (30) to promote inward growth and clearer ice formation. A controller may be provided to move the paddle automatically as the ice sets. Cooling preferably comprises immersing a mould (20) in a tank of brine. The mould may comprise an outer casing (22a,b), and a flexible silicone rubber inner mould lining (24).

Description

ICE-MAKING PROCESS The present invention relates to the manufacture of ice and more particularly to the manufacture of decorative moulded or sculpted objects from ice.

Ice is, of course, in general terms produced simply by freezing water.

However, to produce decorative sculptures, it is desirable for the ice to have particular properties. In particular, the ice should be as clear as possible, without the frosting which typically occurs if water is simply frozen in a conventional freezer. In addition, for complex and delicate shapes, the ice should have a relatively uniform crystal structure to minimise the occurrence of points of weakness.

It is generally known that the structure of the ice is dependent on factors such as the rate of cooling of the water and the temperature at which the ice is formed.

It is found that if air is forced through the water as the water is freezing or if a submerged fluid pump is provided in the water to circulate the water as it begins to freeze, clearer ice may be formed.

The inventor has proposed that articles be formed by a moulding process in which water is frozen into a mould. With intricate mould shapes, however problems can arise and uneven freezing may result even when circulation is effected by means of pumps or air, leading to imperfections in the finished product, therefore spoiling its appearance or rendering it more liable to fracture.

The inventor has devised a process by which, at least in preferred embodiments, high quality near perfectly transparent intricate decorative moulded articles may be produced from ice. The inventor has found that the process can provide consistently good results.

In one aspect, the invention provides a process for forming a moulded object of ice, the process comprising: providing a mould; filling the mould with water; cooling the outside of at least a portion of the exterior of the mould; and circulating water within the mould interior by means of a movable paddle element so that ice grows predominantly from the periphery of the mould inwards.

The process is particularly suited to the moulding of irregular articles, or articles including constrictions. The process is preferably performed so that ice commences growing predominantly from a pre-determined region of the mould, preferably adjacent the bottom of the mould. The process is useful for forming substantially transparent, clear ice (colouring may optionally be added), which is substantially free of visible defects, such as air bubbles, cracks or frost.

Use of a movable paddle element has been found by the inventor to offer surprising advantages; it allows effective circulation of the water in a desired flow path to be established and maintained throughout the majority of the mould, and the flow may be more controllable. In particular, a paddle element may provide more effective circulation around desired portions of a mould, particularly at the extremities thereof while producing less unwanted turbulence (and heat) than an air lance or submerged pump.

Preferably, the paddle is rotated and is mounted on an elongate shaft driven by a remotely disposed drive means, preferably an electric motor. This enables the position of the paddle element to be adjusted with minimal constraint within the interior of a mould of intricate shape. In addition, the "dead" volume (i.e. that which is neither directly moved nor available to be frozen while the moving element is in place) may be reduced, thereby enabling a more efficient cooling protocol to be adopted.

Most preferably, the process further comprises moving the effective position of the paddle element relative to the mould while ice is growing within the mould. This enables the ice growth rate to be carefully controlled throughout the freezing process. It is to be understood that references to movinf the element while ice is growing are intended to be construed in the context of the process as a whole and imply that ice growth continues after movement of the paddle element; temporarily suspending ice growth at the time of actual movement of the paddle element is not excluded. Preferably, the paddle element is immersed deep into the mould to provide effective circulation at the lower extremities of the mould at the outset of the freezing process, effective cooling being applied to the mould to initiate freezing adjacent the bottom of the mould, and the paddle element withdrawn in at least one stage, preferably in several stages or substantially continuously as ice grows within the mould. The paddle element may be moved manually, for example by adjusting the position at which the housing of the drive means is supported relative to the mould. In an advantageous development, the movement is effected by a movable member controlled by a control means. In a simple, but nonetheless effective version of this development, the control means may simply be arranged to withdraw the moveable member along a path (for example in a generally straight line) over a period of time. In a more complex, but advantageous, development, the control means in arranged to move the paddle member based on a measure of the progress of ice formation within the mould.

The measure of ice formation may be obtained based on any one or more of measurements of mould temperature, density of fluid within the mould, volume of fluid within the mould, or sensors obtaining a measure of the position of an ice front (whether optical, acoustic or mechanical sensors). Altematively, a measure of ice growth may be obtained by manual inspection.

Preferably also, the properties of the paddle means may be altered during the ice forming process. For example the pitch and/or diameter of the paddle may be altered (either by use of an adjustable paddle or by substituting one paddle for another paddle) or the excitation (for example rotation speed) applied to the paddle means may be varied.

Cooling preferably comprises immersing the mould in a fluid maintained at a temperature below the freezing point of water. The inventor has found that most preferably the fluid is maintained at a temperature of between -5eC and 12"C, most preferably at between about -8"C and -10 C; for reasons which are not fully understood, but are believed to be due to the rate of crystal growth, a temperature of -8 to -10 C is found to produce consistently good quality (clear and defect free) ice in a variety of moulds and under a variety of excitation conditions. The fluid is preferably brine; this is relatively inexpensive, has a similar density to that of the water within the mould, and has sufficient thermal conductivity and also heat capacity to provide effective cooling around the exterior of a large mould.

Preferably, the ice is formed over a period of at least 1 day, more preferably at least about 2 days to about 4 or 5 days, advantageously about 3 days. This, relatively slow, rate of formation of the ice is found to contribute to consistent even formation of ice, whilst being relatively efficient in terms of energy and time consumed.

The mould is preferably supported, at least initially, with at least a portion (preferably an upper portion) of the mould, and the water therein, exposed to air, preferably at a higher temperature (for example ambient air) than the temperature of the cooled portion of the mould. In this way, heat can be admitted into the water, and the location(s) of preferential formation of the ice can be controlled so that ice crystals grow preferentially from the sides of the mould exposed to cooling rather than throughout the water in the mould. Heat may be positively admitted, for example by means of a (relatively low power) heating element, but this will usually be unnecessary and wasteful of energy.

In addition to controlling the distribution of ice formation, the rate of formation of the crystals can advantageously be controlled by adjusting the relative proportions of the mould exposed to cooling and those exposed to external air; if the mould is deeply immersed into the cooling fluid, freezing will proceed more rapidly than if a significant proportion of the mould is exposed to warmer air. At a certain point, equilibrium will be reached. Thus, by altering the cooling parameters of the mould and the rate of circulation of fluid an optimum freezing rate (preferably within the range mentioned above) can be achieved.

The rate of freezing (for example measured in terms of kilograms of water frozen per hour) need not be, and in most cases will not be, constant throughout the duration of the ice formation process. For example, a relatively low rate of freezing may be employed around delicate regions and around constrictions within the object, and a higher rate of freezing employed to freeze less complex portions of the object.

Preferably, the mould comprises a relatively flexible inner mould layer and a relatively rigid outer casing. With such a construction, the shape of the finished object can be well defined, but separation of the mould from the complex object may be facilitated. The inventor has found that materials such a silicone rubber are particularly useful for the mould interior, and fibreglass is advantageous for the casing; both of these materials have the advantage that they can be moulded themselves relatively easily. In an independent aspect, the invention provides a mould for use in the formation of a moulded ice object comprising an inner mould member formed of flexible material; preferably silicone rubber, the interior shape of the inner member defining the exterior shape of the moulded article; and a relatively rigid outer mould member, preferably formed from fibreglass, serving to support the inner mould member during formation of the moulded article. At least the outer mould member has walls which are preferably relatively thin (for example less than 1cm thick, to enhance the thermal conductivity of the mould. Preferably, particularly where the mould is intended to form an article having a neck or constriction, the mould inner member includes a gusset, the inner member being configured so that in use, located inside the outer mould member, the gusset is substantially closed but on removal of the outer mould member, the gusset can be opened to facilitate extraction of the moulded article from the mould interior.

The casing may be discontinuous, for example in the form of bands or a frame, but preferably substantially encases the inner mould member; this may lead to greater stability during moulding.

The method and apparatus are preferably applied to moulding of articles of at least about 1/4kg, more preferably at least about 10kg in mass, and may be used for objects weighing of the order of 100kg or more. The mould preferably has a minimal internal diameter of at least 5cm, preferably at least 10cm over a major portion thereof (ie excluding any extremities). Particularly where the article to be moulded has a mass in the range of about 1/4 kg (or less) to 5kg (or possibly 10kg or more), a mould having a plurality of similar cavities is preferably employed for moulding multiple articles in a single operation.

For greater rigidity and ease of production, the mould (particularly a mould for multiple articles) may be formed from aluminium (or other rigid, preferably metal or other good thermal conductor) castings or mouldings, preferably with a relatively non-stick lining (such as silicone, or possibly PTFE) to ease separation of the moulded article from the mould. Advantageously, the mould has means for heating the mould adjacent the surface of a major portion of the article (for example means for passing heated fluid such as water through the mould) to promote melting of the surface of the article and facilitate separation from the mould. The mould preferably comprises two (or more) mating portions, preferably with sealing means (preferably elastomeric, for example rubber) provided on mating surfaces. Preferably such a mould is passed through a cooling fluid bath in a continuous or semi-continuous process, the mould entering a portion of the bath, remaining in the bath as the ice grows within the mould and being removed from the bath after a pre-determined time; this may be achieved by means of a relatively slow-moving conveyor system on which one mould (or preferably a plurality of moulds) is disposed. As in the above aspects, the mould is preferably provided with means for stirring the water within the mould as ice grows, most preferably a paddle element.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic diagram of apparatus for use in the method; Fig. 2 is an enlarged view of a portion of an inner mould member showing detail of the gussett; Fig. 3 is a schematic diagram depicting positioning of the paddle member at various stages in the freezing process of a single article; and Fig. 4 is a corss-sectional diagram of a mould incorporating a gusset and insulation to inhibit freezing of a portion of the water.

Referring to Fig. 1, the apparatus comprises a cooled fluid bath 10, which in this embodiment is formed by a commercial chest freezer 12 which has been lined with a waterproof lining 14 and is filled with a brine solution of sufficient concentration to inhibit freezing at temperatures down to below at least -8 C. The thermostat (not shown) on the freezer 12 is preferably set to maintain the brine solution temperature at about -8"C. Not shown for clarity in Fig. 1, the apparatus preferably includes insulating slabs, for example preferably formed from expanded polystyrene or the like, covering portions of the exposed cooling bath, to reduce energy consumption due to heat ingress into the cooling bath from the ambient air; as will be appreciated, the designa nd configuration of these is not critical, but the better the insulation provided, the lower will be the wastage of cooling power.

Positioned within the cooling fluid is a mould 20 comprising an outer mould casing 22a,b, formed in several separable (here two) parts and an inner mould lining 24 formed from flexible silicone rubber. The two outer mould members 22a, 22b are held together by a plurality of fixings, typically stainless steel wing nuts and bolts, passing through protruding lugs or ears 23, one of which can be seen in Fig. 1. To facilitate separation of the mould from the moulded article, a gussett 26, more details of which can be seen in Fig. 2, is provided. The inner mould member defines a mould cavity 28 of shape corresponding to the desired shape of the moulded article.

Referring to Fig. 2, the walls of an inner mould member having a cavity of nominal diameter about 20cm may be nominally about 4 to 10 mm thick or more (this thickness may vary considerably at different portions of the mould), and one or more gussetts 26 extending through a major portion of the wall may be provided to facilitate opening of the mould to remove the moulded article.

Preferably, an extension of the outer mould casing is formed by outer mould casing members 22c and 22d as shown in Fig. 2. In the area of the gusset 26, the two layers of the inner mould member forming the gusset may be held or pressed together by the outer mould casing members 22c, d. Additionally, a screw, clamp or similar may be provided near or at the outer ends of outer mould casing members Zc and 22d to ensure improved holding or pressing together of the inner mould member forming the gusset.

However, it is also possible to omit the extension of the outer mould casing formed by outer mould casing members 22c and 22d. In this case the gusset 26 may simply extend through a slot or similar formed between points 22 e and 22 f by outer mould casing members 22a and 22b. The two layers of the inner mould member forming the gusset are in this case held or pressed together by the outer mould casing members 22a and 22b between points 22 e and 22 f. A suitable clamp or similar may be provided as well.

The precise size and shape and number of gussetts 26 may be selected according to the shape of the article; a mould for an article having a thin neck or constriction preferably has more or larger gussetts 26, to enable an enlarged portion of the article to be drawn more easily through the neck portion of the mould.

Whenever interior openings are required in the article, for example when forming handles, rings or other generally annular structures, the outer mould casing may comprise annular outer mould casing members. Since this annular member needs to be openable so that the article can be unwrapped, the annular member comprises at least two semi-annular members between which a corresponding part of the article can be formed. This structure bears the risk that water (or brine, if the inner portion were exposed to the outside of the mould) could seep through one or more gaps between the two or more parts of the annular member. In the case of water seeping through a gap, a thin plate of ice could build up at the radially inner side of the annular structure.

After unwrapping of the article, removing of this unwanted built-up of ice could damage the article.

To this end, the mould may comprise thickened (and hence more insulating) portions of the mould lining, preferably having inserts 40 of lower thermal conductivity as shown in Fig. 4. These inserts 40 may, for example, be made of foam rubber. The inserts 40 reduce the cooling of water in the centre of the cavity, thereby inhibiting part of the water in the mould from freezing1 in the example shown in Fig. 4 the middle region situated substantially between the inserts 40. Therefore, the article will be formed with an annular member of ice with some water in the radially inner area. When unwrapping the article after freezing for sufficient time to freeze desired portions of the mould interior, the water will pour away. The duration of cooling needs to be chosen carefully in this embodiment so as to prevent the annular structure from freezing in the radially inner region as well.

The inserts 40 may be wholly enclosed by the inner mould lining 24 (integrally moulded therein), as shown in Fig. 4. Alternatively, the inserts 40 may be situated between the outer mould casing and the inner mould lining.

It is to be understood that for the purpose of this specification references to generally annular are intended to impiy any shape that comprises any kind of internal opening (not necessarily circular).

In place of a gussett, the inner mould member may have a slit which extends through the wall so that the mould can simply be unwrapped; however, this may give rise to problems with sealing, since the water must remain in the mould for a prolonged period of time, leading to possible mixing of the brine and water in the mould, or loss of water from the mould. Although the problems are alleviated by the relatively rapid freezing of water which begins to seep from the mould, ingress of brine may lead to melting of this ice, and the use of a gussett which ensures reliable containment of the water in the mould is greatly preferred.

To produce a moulded article, water (preferably reasonably pure, for example purified mains water [most preferably purified by means of a reverse osmosis process, although distillation or ion exchange may be used], optionally containing colouring or fluorescent agents) is poured into the mould cavity 28.

The upper portion of the mould is preferably left open and exposed to ambient air, the lower portion being immersed in the chilled brine; in this way ice growth can be initiated in a controlled manner predominantly from a predetermined region of the mould, typically adjacent the bottom.

A paddle member 30 driven via a elongate shaft 32 by an electric motor 34 mounted on a movable arm 36 is provided to stir the water as the ice crystals form so that the formation rate can be controlled.

In the embodiment depicted, the position of the arm may be manually adjusted, by loosening the knurled locking nut 38, adjusting the arm, and tightening it again. This will typically be performed in the morning and in the evening over the 3 days during which the ice is growing.

In a preferred development, a controller (not shown) is provided to move the paddle means automatically as the ice sets.

In its simplest automated form, the controller and movable member may simply comprise a device which moves over a (relatively long) period of time, for example based on a simple clockwork mechanism. For example, a clockwork mechanism on which a rope is wound, the rope being arranged to lift the arm 36 by means of a suitably positioned pulley can readily be arranged to give satisfactory results.

Typical movement of the paddle 30 as the ice 50 grows within the mould 20 can be seen in Fig. 3. Note that, in addition to moving the paddle 30, the configuration of the paddle can be changed; in the embodiment depicted, a relatively small paddle is employed initially (Figs. 3a and 3b), and a larger paddle is used at a later stage (Fig. 3c). In intricate moulds, it may not be possible or convenient to dispose a paddle element in close proximity to the extremities of the mould cavity; in such a case, a large paddle element arranged to cause sufficient turbulence to ensure that water at the extremities is agitated may be employed at the outset, with a smaller paddle element (or slower excitation) as the ice grows.

More preferably, the controller comprises a programmable controller (for example incorporating a micro-controller or integrated with a personal computer) which allows the rate of movement of the paddle member to be adjusted depending on the mould used. The controller may receive inputs from sensors giving a measure of the temperature of the water or of the position of the ice front, and may also be provided with further outputs to control, for example the motor speed and/or direction and optionally to control a mechanism for switching the paddle for a different paddle or for adjusting the pitch of vanes of the paddle member.

The controller may additionally have means for controlling the temperature of the fluid in the cooling bath. Where the controller is formed by a micro controller or computer-based controller, a single controller may control several different mould-forming processes, each of which may preferably have different parameters optimised for the mould in question. Several moulds may be disposed in a common cooling bath.

The cooling bath may include means (for example a pump) for circulating fluid within the cooling bath, which may assist in maintaining a more uniform temperature within the cooling bath.

As an alternative to use of a liquid, chilled air (or other gas) may be circulated around the exterior of mould. However, since air has a lower volumetric heat capacity and thermal conductivity, a relatively rapid air circulation is required to maintain an equivalent rate of cooling, and also to maintain an even temperature around the exterior of the mould. An additional drawback with the use of air-based cooling is that the air does not provide support for the mould (an advantage of using a fluid of similar density to water is that the fluid will support the mould and the mass of water within it (which may be of the order of 100kg or more). Thus, the walls of the mould outer casing may have to be stronger, for example thicker or of more rigid material when air or other gas based cooling is employed. In such a case, since thicker walls will have a lower thermal conductivity, it may be preferable for the material of the walls to be more thermally conductive (for example metal, preferably aluminum). Despite the above limitations, an advantage of the air(or gas)-cooled arrangement is that the overall weight of the apparatus may be significantly less, and the time required to cool the apparatus initially may also be less, so apparatus suited for portable, discontinuous may be provided in this way.

Although the apparatus is preferably employed for freezing water into pre-shaped moulded articles, the apparatus may be employed to form simpler articles, such as blocks, suitable for later sculpting or finishing. The apparatus may also be employed for freezing liquids other than water where the freezing conditions must be carefully and consistently controlled, and similar considerations apply.

Claims

CLAIMS: 1. A process for forming a moulded object of ice, the process comprising: providing a mould; filling the mould with water; cooling the outside of at least a portion of the exterior of the mould; and circulating water within the mould interior by means of a movable paddle element so that ice grows predominantly from the periphery of the mould inwards.
2. A process according to Claim 1, wherein the initial position of the mould, cooling conditions and circulation conditions are selected so that ice commences growing predominantly from a predetermined region of the mould interior, preferably adjacent the bottom of the mould.
3. A process according to Claim 1 or Claim 2, wherein the paddle element is mounted on an elongate shaft driven by a remotely disposed drive means.
4. A process according to any preceding claim further comprising moving the effective position of the paddle element relative to the mould while ice is growing within the mould.
5. A process according to Claim 4, wherein the effective position of the paddle element is moved through a plurality of discrete positions as the ice grows.
6. A process according to Claim 4, wherein the effective position of the paddle element is moved substantially continuously as the ice grows.
7. A process according to any of Claims 4 to 6, wherein the paddle element is moved in dependence on the elapsed time since commencement of the freezing process.
8. A process according to any of Claims 4 to 7, wherein the paddle element is moved in dependence on a measure of the progress of ice formation within the mould.
9. A process according to any preceding claim wherein the excitation applied to the paddle element is adjusted as the ice grows.
10. A process according to any preceding claim wherein the configuration of the paddle element is altered as the ice grows.
11. A process according to Claim 10, wherein the paddle element is substituted by another paddle element to adjust the configuration.
12. A process according to any preceding claim wherein the exterior of the mould is cooled to a temperature of about -5C or lower.
13. A process according to any preceding claim wherein the exterior of the mould is cooled to a temperature of about -18 C or higher.
14. A process according to Claim 12 and Claim 13, wherein the exterior of the mould is cooled to a temperature of between -8 C and -10 C.
15. A process according to any preceding claim, wherein the exterior of the mould is cooled by immersing the mould in a fluid, preferably brine.
16. A process according to any preceding claim, wherein ice is grown over a period of at least about 1 day.
17. A process according to Claim 16, wherein ice is grown over about 3 days.
18. A process according to any preceding claim wherein the mould is initially supported with at least a portion exposed to air.
19. A process according to Claim 18, wherein the mould is lowered further into the brine as the ice grows.
20. A process according to any preceding claim wherein the rate of freezing is controlled by varying the relative proportions of the mould cooled and exposed to air.
21. A process according to any preceding claim wherein the mould includes a relatively flexible inner mould member and a relatively rigid outer casing, the process further comprising separating the casing from the inner mould member or dismantling the casing and separating the mould from a moulded object by deforming the inner mould member.
22. A process according to Claim 21, wherein the inner mould member includes a gusset, separating the inner mould member from a moulded object comprising opening the gussett.
23. A process according to Claim 21 or 22, wherein the inner mould member is formed from silicone rubber.
24. A process according to any preceding claim wherein at least lkg of water is frozen within the mould.
25. A mould for use in the process of any preceding claim comprising a relatively flexible inner mould member and a relatively rigid outer casing, the inner mould member including an openable gussett to facilitate separation of the mould and a moulded object, the outer casing being arranged to maintain the gussett substantially closed for moulding.
26. A mould according to Claim 25, wherein the inner mould member is formed of silicone rubber.
27. A mould according to Claim 25 or 26 wherein the outer casing is formed of fibreglass.
28. A mould according to any of Claims 25 to 27 wherein the outer casing substantially encases the inner mould member.
29. A mould according to any of Claims 25 to 28 wherein the outer casing comprises a plurality of separable components.
30. A process for forming a moulded object of substantially transparent ice, the process comprising: providing a mould comprising a relatively flexible inner mould member and a relatively rigid outer casing; immersing at least a portion of the exterior of the mould in a cooling fluid; filling the mould with water; circulating water within the mould interior by means of a paddle element mounted on an elongate shaft driven by a remotely disposed drive means for at least about a day while the cooling fluid is maintained below the freezing point of said water, preferably at between about -8 C and about -10 C, the rate of freezing being such that ice grows predominantly from the periphery of the mould inwards; moving the effective position of the paddle element relative to the mould during the ice formation process; on completion of freezing, separating the mould from the moulded object by deforming the inner mould member.
31. A process according to any of Claims 1 to 24 or 30, wherein heat is admimed into the circulating water within the mould to promote ice growth from the predetermined region and inhibit spontaneous ice formation throughout the body of the mould.
32. A process according to Claim 31 wherein the heat is supplied from air to which a portion of the mould, or the water within the mould, is exposed.
33. A process substantially as herein described, with reference to the accompanying drawings.
34. A mould substantially as herein described, with reference to the accompanying drawings.