Technical Field

This invention relates to sinkers for use with fishing lines, and/or to methods of manufacturing same.

Background Art

Fishing line sinkers are almost universally made of lead, because of its ready availability, high density, low melting point and its relative ease of moulding. When fishing, sinkers are frequently snagged on underwater obstacles, and then are lost when the fishing line breaks. Due to the toxicity of lead, lead sinkers that have been lost have caused widespread poisoning in birds, particularly ducks, swans and other waterfowl, and also to mammals via the food chain. Lead is also toxic to humans. It can be absorbed through the skin if the metal is handled, and lead fumes can be inhaled during smelting.

Steps are being taken to reduce unnecessary lead use and replace lead sinkers with less toxic alternatives. For example, other heavy metals such as bismuth and tungsten are now being used to make sinkers, however these metals are much more expensive than lead, so they have not been commercially successful. Other alternative sinkers are made of stone, however these are generally brittle and can easily break if dropped. Some sinkers have been made from iron, however these require a covering or coating to prevent corrosion of the sinker, and rust stains on fishing equipment. The density of any lead substitute must also be considered as the sinker needs to be of a sufficient density to be acceptable to a wide spectrum of potential users and applications.

Another drawback of conventional fishing line sinkers is that when they are attached to a fishing line but not in use, and are subject to movement for example from a vehicle or boat, the weight of the sinker may cause the line to detach from its fixed position and the sinker and any fish hooks attached to the fishing line may swing dangerously to and fro with the movement of the vehicle or boat.

There is therefore a need for an improved sinker which overcomes at least some of the above mentioned disadvantages. Object of the Invention

The present invention provides an improved sinker for use with fishing lines and/or a method of manufacturing same, which offers advantages over the prior art or which will at least provide the public with a useful choice. All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinence of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein; this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the tenn 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process. Summary of the Invention

In a first aspect, the invention broadly resides in a fishing line sinker, comprising a moulded cement matrix, wherein said cement matrix is formed from a composition of:

(i) ferrous-ferric oxide in an amount of from about 40% to 85% by dry weight, and

(ii) hydraulic cement in an amount of from about 2% to 25% by dry weight. Preferably the cement matrix has magnetic properties.

Preferably the ferrous-ferric oxide component (i) is magnetite. Magnetite is preferred because of its high density and its significant magnetic properties. Preferably the magnetite is included in an amount of from about 50% to 80% by dry weight.

Preferably the hydraulic cement component (ii) is high-alumina cement or Portland cement.

Preferably, the high-alumina cement or Portland cement is included in an amount of from about 15% to 25% by dry weight. Preferably, the cement matrix composition further comprises from about 2% to 15% by dry weight of amorphous silicon dioxide or reactive pozzolan.

The cement matrix composition may further comprise from about 4% to 15% by dry weight of iron (II) oxide.

Preferably, the cement matrix composition further comprises one or more additives and/or excipients selected from the group comprising super-plasticisers, plasticisers, binding agents, cement retarders, cement dispersants, cement accelerants, pigments, colouring agents, and micro fibre or flammable fibre materials.

Preferably the cement matrix composition is pressure moulded to form the fishing sinker.

Preferably, the fishing sinker is made absorbent or porous by sintering, firing or autoclaving the cured cement matrix composition.

Preferably, the fishing sinker is sufficiently absorbent or porous to absorb one or more liquid substances selected from the group comprising flavours, oils, scents and fish attractants.

In a second aspect, the invention broadly resides in a fishing line sinker comprising a pressure moulded cement matrix having magnetic properties, wherein said cement matrix is formed from a composition of:

(i) from about 50% to 80% by dry weight of magnetite,

(ii) from about 15% to 25% by dry weight of high-alumina cement or Portland cement.

Preferably the composition further comprises from about 2% to 15% by dry weight of amorphous silicon dioxide or reactive pozzolan. Preferably the composition further comprises from about 4% to 10% by dry weight of iron (II) oxide.

Preferably, the cement matrix composition further comprises one or more additives and/or excipients selected from the group comprising super-plasticisers, plasticisers, binding agents, cement retarders, cement dispersants, cement accelerants, pigments, colouring agents, and micro fibre or flammable fibre materials.

Preferably, the fishing sinker is made absorbent or porous by sintering, firing or autoclaving the cured cement matrix composition.

Preferably, the fishing sinker is sufficiently absorbent or porous to absorb one or more liquid substances selected from the group comprising flavours, oils, scents and fish attractants.

In a further aspect, the invention broadly resides in a fishing lure or a fishing jig comprising a moulded cement matrix as described herein, together with one or more fishing hooks embedded therein or attached thereto.

In a further aspect, the invention broadly resides in a method of manufacturing a fishing line sinker comprising a moulded cement matrix, said method comprising the steps of:

(a) screening and/or milling ferrous-ferric oxide,

(b) mixing the ferrous-ferric oxide with hydraulic cement and water and optionally other additives and/or excipients to form a dough or a paste,

(c) pressure moulding the dough or paste in a moulding means to form a moulded cement matrix,

(d) allowing the moulded cement matrix to cure.

Preferably the moulded cement matrix of the fishing line sinker comprises a composition of from about 40% to 85% by dry weight of ferrous-ferric oxide, and from about 2% to 25% by dry weight of hydraulic cement. Preferably the ferrous-ferric oxide component is magnetite. Preferably the magnetite is included in an amount of from about 50% to 80% by dry weight. Preferably the fishing line sinker has magnetic properties.

Preferably the hydraulic cement component is high-alumina cement or Portland cement. Preferably, the high-alumina cement or Portland cement is included in an amount of from about 15% to 25% by dry weight. Preferably, the screening step involves passing the ferrous-ferric oxide through a coarse mesh screen of approximately 100 mesh.

Preferably, the milling step involves milling between 15 - 50% of the screened ferrous-ferric oxide to reduce the particle size of the ferrous-ferric oxide to fit through a finer mesh screen of approximately 270 mesh. Preferably the method comprises both screening and milling steps.

Preferably, step (b) further comprises combining iron (II) oxide, and/or amorphous silicon dioxide or reactive pozzolan with the ferrous-ferric oxide and the hydraulic cement.

Preferably, the amorphous silicon dioxide or reactive pozzolan comprises from about 2% to 15% by dry weight of the moulded cement matrix composition. Preferably, the iron (II) oxide comprises from about 4% to 15% by dry weight of the moulded cement matrix composition.

Preferably step (b) further comprises combining one or more selected additives and/or excipients with the ferrous-ferric oxide and the hydraulic cement.

Preferably, the additives and/or excipients are selected from the group comprising super- plasticisers, plasticisers, binding agents, cement retarders, cement dispersants, cement accelerants, pigments, colouring agents, and micro fibre or flammable fibre materials.

Preferably the moulding means (step (c)) is adapted to allow one or more channels or holes to be formed through the moulded cement matrix, sufficient to accommodate a fishing line or one or more fixed attachment means, or one or more hooks or swivels or other types of fishing equipment. Preferably the curing step (step (d)) comprises placing the moulded cement matrix in a humid enclosed environment.

Preferably the manufacturing method further comprises the step of making the finished sinker absorbent or porous. This may be accomplished by sintering the moulded cement matrix or by firing or autoclaving the moulded cement matrix.

Preferably the sintering process involves firing the cured cement matrix in a kiln at a temperature and for a duration sufficient to sinter said cement matrix.

Preferably the firing process involves firing the cured cement matrix in a kiln at a temperature and for a duration sufficient to make the cement matrix porous. Preferably the autoclaving process involves autoclaving the cured cement matrix in an autoclaving apparatus at a temperature and for a duration sufficient to make said cement matrix porous.

Preferably the absorbent or porous sinkers are contacted with an absorbent amount of one or more liquid substances selected from the group comprising flavours, oils, scents and fish attractants.

These and other features of the invention as well as advantages which characterise the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.

Brief Description of the Drawings

FIG. 1 is a flow chart depicting a method of manufacturing a fishing line sinker in accordance with an embodiment of the present invention.

FIG. 2 is a block diagram of a pressure moulding apparatus used for performing the method of manufacturing a fishing line sinker in accordance with an embodiment of the present invention. FIG. 3 is a side view of a fishing line sinker in accordance with a preferred embodiment of the present invention. FIG. 4 is a bottom view of a fishing line sinker in accordance with a preferred embodiment of the present invention.

FIG. 5 is a side view of a fishing lure or fishing jig in accordance with a preferred embodiment of the present invention. FIG. 6 is a perspective view of a fishing line sinker and a "U" shaped attachment means in accordance with a preferred embodiment of the present invention.

Description of the Invention

The invention relates generally to a fishing line sinker which is formed by pressure moulding a cement matrix composition comprising at least ferrous-ferric oxide and hydraulic cement. A preferred sinker composition comprises ferrous-ferric oxide in an amount of from about 40% to 85% by dry weight (preferably from about 50% - 80% by dry weight), and hydraulic cement in an amount of from about 2% to 25% by dry weight (preferably from about 15%» to 25% by dry weight). These components are mixed together with water and optionally with additional components, as well as carefully selected additives and/or excipients, to form a dough or paste, and the dough or paste is then moulded (preferably by pressure moulding) into any desired shape and size and weight to form a fishing sinker. The fishing line sinker preferably has magnetic properties. The magnetic properties of the finished sinker have the advantage of allowing the sinker to be secured in a restrained position using magnetism as the securing force, to prevent unwanted movement of the fishing line (with attached fish hooks and sinkers) when it is not in use (for example, when it is in storage, or when it is on a moving vehicle or boat). The sinker could be secured by some type of magnetic device such as a permanent magnet or electro-magnetic device present on a rod or reel or boat. Another advantage of the magnetic properties of the sinker is that they may also act as an attractant to some species of fish. The ferrous-ferric oxide component of the composition is preferably magnetite (also known as ironsand). Magnetite is preferred because of its high density and its significant magnetic properties. Magnetite with significant magnetic properties can be sourced for example, from the North Island of New Zealand, or from the Philippines. Suppliers include Industrial Sands Ltd in Auckland and NZ Steel Glenbrook in South Auckland. Because magnetite has a high density, it is preferable to include as much magnetite as possible in the composition, as this will increase the density of the finished fishing sinker. In order to further increase the density of the finished fishing sinker, some (between about 15 - 50%) of the magnetite sand can be milled into a smaller particle size before being mixed with the hydraulic cement. These smaller particles fill voids between the larger magnetite particles thereby increasing the density of the sinker beyond that which would result from using only unrefined or unmilled magnetite sand.

The hydraulic cement is preferably calcium aluminate cement (also known as high-alumina cement) or Portland cement. Although Portland cement is suitable for use in the invention, it has been found that sinkers made of high-alumina cement are more durable and have more resistance to salt water.

The fishing sinker composition may further comprise iron (II) oxide in an amount in the range of from about 4% to 15% (preferably from about 4% to 10%) by dry weight of the composition. The iron (II) oxide is used as a pigment to darken the colour of the sinkers, while maintaining the magnetic properties of the sinkers. Iron (II) oxide is commercially available as a powder from most cement suppliers or builders merchants.

The fishing sinker composition preferably further comprises amorphous silicon dioxide or reactive pozzolan (also known as silica fume or micro silica) in an amount in the range of from about 2% to 15% by dry weight of the composition. This component is used in the cement matrix in order to increase the strength of the cement matrix. It also provides a cement matrix with low porosity which is very useful for producing non-porous or non- absorbent sinkers. Sinkers comprising amorphous silicon dioxide can be made absorbent or porous again by sintering, firing or autoclaving as discussed further below.

Amorphous silicon dioxide with a very fine particle size is preferred. An example of a suitable micro silica is MICRO SILICA 600 available from Firth Industries, Auckland, New Zealand. This is a highly reactive pozzolan. Another suitable silica fume is that available from Shanghai Topken Silica Fume Co., Ltd., China. It has an average particle size of 0.15- 0.20 micron in diameter, and a specific surface area in the range of from 15, 000 to 20, 000 m2/kg. Other examples of suitable amorphous silicon dioxides or reactive pozzolans include ORISIL from India and SIKACRETE 950DP from the USA. The cement composition used to make the fishing sinker may further comprise additional components, namely additives and/or excipients for various purposes. Some examples of possible additives and/or excipients are now described.

Plasticisers and/or super-plasticisers such as acrylic or styrene copolymers may be used in the composition in order to reduce the water content of the cement and to improve the physical and chemical performance of the cement matrix. The properties improved include tensile and flexural strengths, abrasion and impact resistance. Waterproofing styrene acrylic is a styrene/acrylic copolymer emulsion, specially designed to improve the flexibility of cement, and to provide waterproofing and weather resistance. An example of a suitable acrylic polymer is BOND-R which is commercially available from Fraser Brown & Stratmore Ltd, New Zealand. Approximately 2 - 10 ml of this component may be added per 100 ml of water when the water is added to the combined ferrous-ferric oxide and hydraulic cement during mixing of the composition.

A cement setting retarder such as DARAMENE R may be added to the composition in order to lengthen the workable handling time of the cement matrix. As warm temperatures accelerate the curing time of the cement matrix, this component can be added in situations with warmer temperatures in order to slow the setting time between mixing and moulding. This component can be added in an amount in the range of from about 200 - 500 ml per 100 kg of cement, depending on the workable handling time required. Where a considerable increase in set retardation is required, higher amounts of a cement setting retarder can be used.

Binding agents may also be included in the composition in order to hold the mixture together after moulding and while curing takes place, as well as to strengthen and improve the impact resistance of the finished sinkers. An example of a suitable binding agent is calcium silicate (also known as Wollastonite) which is commercially available from most pottery clay suppliers. Another example of a possible binding agent is polyvinylacetate such as polyvinyl alcohol (for example, Febbond PVA). This has been found to increase the aggregate-paste bond strength which is particularly useful when attaching fixed attachment means and other fishing equipment to the finished sinkers. It also improves the physical and chemical performance of the cement matrix such as its tensile and flexural strength, abrasion and impact resistance. Approximately 5 - 25 ml of this component may be added per 100 ml of water when the water is added to the combined ferrous-ferric oxide and hydraulic cement during mixing of the composition.

Binding agents are likely to make up approximately 0.5% to 25% of the overall composition, but higher rates of binding agent may be used if necessary. A micro fibre or other flammable fibre material may be added to the cement compositions of sinkers which are to be made absorbent or porous. This material is added to the dry components of the cement composition before moulding, and will be incinerated during the firing or sintering process which increases the porosity or absorbency of the sinker even further. Such materials are preferably included in an amount in the range of about 0.1 - 1% dry weight.

It should be appreciated that further additives and/or excipients other than those discussed above may be added to the composition in order to modify the characteristics of the wet cement mix or set cement matrix as required. For example, cement accelerators may be used in order to accelerate curing time (for example in low temperatures), cement dispersants may be used in order to reduce the viscosity of the wet cement mix and to improve fluid flow characteristics which may be required for the moulding process. Other pigments or colouring agents (instead of or in addition to iron (II) oxide) may be added to the composition to create sinkers with certain colour characteristics.

Referring now to FIG. 1, a flow chart is depicted which generally outlines the steps involved in the method of manufacturing a fishing line sinker in accordance with a preferred embodiment of the invention. As can be seen from the flow chart, the method comprises four essential steps, namely a screening or milling step (1), a mixing step (2), a moulding step (3) and a curing step (4). An optional step of making the sinker absorbent or porous is also possible (step 5). The screening and/or milling step (1) involves the processing of the ferrous-ferric oxide component to a desired particle size range. It is preferred that there is a range of particle sizes present in the ferrous-ferric oxide sand, as this improves the density of the finished sinker as the smaller sand particles fill voids between the larger sand particles. A preferred method involves a two stage process of both screening and milling. As a first step, the ferrous-ferric oxide may be passed over a coarse mesh screen, for example, a 100 mesh screen, to remove any large particles. Then as a second step, between about 15 - 50% of the resulting screened material can be milled using conventional milling techniques (for example, a ball mill, a hammer mill, a grinding mill) to reduce the particle size even further. Preferably the particle size is reduced sufficiently to enable the resulting material to pass through a finer mesh screen, for example, a 270 mesh screen. '

The mixing step (2) involves combining the resulting screened and/or milled ferrous-ferric oxide component with the hydraulic cement component and water to produce a cement mix or paste. Preferably the mixing is done in a mixing apparatus (for example, a commercial dough mixing machine). Other dry components, such as iron (ii) oxide and/or amorphous silicon dioxide or reactive pozzolan and/or any other additives and/or excipients that are in dry form may also be added to the ferrous-ferric oxide and hydraulic cement before water is added. If a micro fibre or flammable fibre material is to be included in the composition, it is added at this stage of the process and mixed with the other dry components until uniformly blended before any liquid is added to the composition. If WoUastonite is used in the composition, because it is a crystalline powder, it is preferably mixed first with a liquid (for example, a plasticiser, super-plasticiser and/or a small amount of water) to form a dispersion or suspension before being added to the composition. Other dry or liquid additives or excipients may also be pre-mixed in this manner if necessary depending on their physical or chemical characteristics (such as solubility etc). Water is then added to the dry mixture in stages in order to produce a cement mix or paste. Preferably, only a small amount of water in total is added to the composition, as the higher the water content the less strength the cement mix will have. Also, any surplus water added above 4% of the total weight of the mixture must be removed during the moulding process, so the less water added the better. Preferably, the amount of water added to the composition is between about 10% to 14% of the total combined weight of the dry and liquid ingredients in the composition. Super-plasticisers are preferably used in the composition to reduce the amount of water needed to be added to the cement mix. Any other liquid additives and/or excipients can also be added to the composition at this stage of the process.

Preferably only about 90% of the water is added initially (including any water that is used to formulate solutions, dispersions or suspensions of additives or excipients). The composition is then thoroughly mixed to form a dough or a stiff paste. The mixture can then be visually assessed for mouldability, and further water may be carefully added as needed until the mixture forms a dough or paste which can be held together when handled in a firm ball.

The composition is then transferred to a moulding means for the moulding step (3). Preferably the moulding step involves a pressure moulding process in which the cement mixture is pressed under pressure to exclude any surplus water in the mixture (that is, any water above 4% of the weight of the composition). The main advantage of pressure moulding is that the finished sinker will have a higher density than sinkers which have been manufactured using other moulding or casting processes, as most of the water and air in the cement mix is expelled during the pressure moulding process. Another advantage of pressure moulding is that the finished sinker will be very strong because the cement mix has been compressed under pressure. A further advantage of pressure moulding is that the finished sinker can be handled immediately after moulding as it is hard and strong enough to be handled immediately. Conventional techniques for manufacturing sinkers (such as casting and rolling) generally produce sinkers which require very long drying times before they can be handled which is very inconvenient.

Pressure moulding can be carried out by any known pressure moulding techniques such as pneumatic pressing, mechanical pressing, hydraulic compression, injection moulding and the like.

A hydraulic compression moulding apparatus such as that depicted in FIG. 2 may be used to mould the cement composition to form one or more moulded fishing sinkers. In any moulding process, if desired, the moulds may be prepared for the introduction of the cement paste by spraying a thin film of a mould releasing agent onto the contacting surfaces of the moulds to enable the finished sinkers to be easily removed from the moulds (suitable products include for example Dafacote MRA1 made by Grace (USA); Cemix RELEASE WB which has good form release properties and provides a good finish to moulded products; Repel made by Berryessa (Australia); and Betopro).

Referring to FIG. 2, a moulding apparatus for pressure moulding the sinker compositions of the invention is shown. The moulding apparatus has a female cylinder mould with two open ends (101, 102), having identical openings. These openings (101, 102) are adapted to receive two piston like compression rams with concave ends (103, 104). The lower compression ram (104) is mounted in a fixed position, while the upper compression ram (103) moves up and down on a hydraulic ram (105). Two further hydraulic rams (106, 107) are connected to a horizontal bar (108) which holds the female mould (109) in position. In use, downward pressure is exerted on the two hydraulic rams (106, 107) and this forces the female mould (109) down to a position over the lower compression ram (104) just sufficiently to seal the bottom opening of the female mould (102).

The pre-mixed cement composition is portioned and injected into the opening of the female mould at the point 110, and the upper compression ram (103) is then brought into contact with the remaining open end of the female mould (101) then a rod of stainless steel or other material (111), long enough to pass through two holes located one in either end of the male piston moulds, enters the hole (112) in the lower compression ram and passes through the paste to be compressed (113) in the female mould, then continues on to locate in the hole (118) in the upper compression ram. The upper compression ram (103) then enters its compression stroke of at least 1600psi and squeezes the paste hydraulically using the ram (105) which moves the upper compression ram (103) down, forcing air and liquid from the matrix of the paste (113), through the contacting surfaces, there being sufficient tolerance between the male compression rams and female parts of the mould that liquid can be expressed to the outer mould joints (this liquid is blown aside with compressed air, away from the mould joints and into a drainage tray below the moulding apparatus, as the appearance of the sinker surface is spoilt by contact with this liquid until after pressing is complete). The hydraulic ram (105) maintains pressure long enough to lower the water content to around 4% in the sinker composition. The central rod (111) which was inserted through the hole in the lower compression ram (112) is then withdrawn, leaving a formed hole through the centre of the moulded cement matrix (see FIG. 4, 120).

The upper compression ram (103) is then retracted upwards ready to repeat the process. The compressed cement matrix is then removed from the female mould (109) by the following procedure: both compression rams (103, 104) remain stationery; downward pressure is exerted on the two hydraulic rams (106, 107) which forces the female mould (109) down over the lower compression ram (104) until the compressed cement matrix appears above the level of the horizontal bar (108) which has descended. The descending movement and the following accent of the horizontal bar (108) is guided in a steady position by the guide rods (114, 115) which connect the base plate (116) and the top plate (117) that hold all the moving parts in place. It will be appreciated that the moulding apparatus can be modified to produce sinkers of any desired shape and/or size and/or weight.

It will also be appreciated that the moulding apparatus can be modified to produce sinkers iwith one or more channels or inserts in them, sufficient to accommodate a fishing line or one or more fixed attachment means or one or more hooks or swivels or other types of fishing equipment. The moulding process may even be modified so that the attachment means or hooks are integrally moulded or embedded into the cement matrix.

After the moulding step (3), the moulded cement matrix is set aside for curing (step 4, of FIG. 1). Preferably, the sinkers are placed in a humid enclosed environment for curing, for example, on a curing rack in a high humidity temporary storage area. This is to avoid rapid drying of the cement matrix, as rapid drying may result in incomplete curing.

The moulded sinkers can be left to cure for any amount of time between about 12 hours to 28 days. Generally the sinkers will be sufficiently cured for use within 2 - 4 days.

FIG. 3 shows a cylindrical shaped sinker made in accordance with the above method. After curing, one or more fixed attachment means may be added to the sinker as shown in FIG. 3 (121). The fixed attachment means enables the sinker to be attached to a fishing line or other piece of fishing equipment, rather than being a free running sinker. If a fixed attachment means is desired, the sinker may be further processed in order to attach or cement a crimped wire loop (see FIG. 6, 123) or other type of attachment means through the central channel (124) of the sinker. This can be accomplished as follows: the sinker is first immersed in water for several minutes (the reason for this being that the rapid absorption of water during the injection process of a dry sinker causes the injection material to solidify before complete filling of the tube can be achieved); after draining, the sinker it is left to stand for a few minutes until any remaining surface moisture is absorbed by the sinker; then a "U" shaped pre- formed stainless-steel wire of around 1 mm diameter with zig-zag legs (see FIG. 6, 123), is pushed legs first into the central tube (124) of the sinker.

The wire legs may be glued into the hole or tube of the sinker (124) by injecting the same cement mixture as is used to make the body of the sinker, but preferably with the addition of a concrete pumping aid (for example, SKA PUMP) to improve the viscosity of the mixture so that it is easier to inject into the sinker hole.

One or more swivels and/or hooks and/or other items of fishing equipment may also be attached to the sinker. This can be done by threading the item(s) onto the "U" shaped wire before insertion into the hole of the sinker. Such an embodiment is shown in FIG. 5 where a swivel (122) is attached to one end of the sinker in order to enable the sinker to rotate, without causing undue twisting of the line, and a hook (125) is attached to the other end of the sinker. This embodiment is an example of how the sinker can be modified to create a fishing lure or fishing jig. For running fishing line sinkers the central channel of the sinker is left clear but may be lined or painted with low friction material such as superglue or an insert of smooth hard wearing material, in order to reduce abrasion on a fishing line where it enters the tube and is subject to the sharp angle of entry that the line may encounter during use.

It has been found that by making the cement matrix sinkers of the invention absorbent or porous, they have improved durability, salt water resistance, and other advantages such as the ability to absorb liquid substances that may attract fish. In order to produce absorbent or porous sinkers (refer optional step 5 of FIG. 1), the cement matrix sinker can be sintered or fired after curing. Sintering is carried out on sinker compositions which contain high- alumina cement, whereas firing is carried out on sinker compositions which contain Portland cement. Sintered sinkers comprising high-alumina cement have been found to be of better quality than fired sinkers comprising Portland cement, as they are more durable and have better salt water resistance.

Sintering can be accomplished by firing the cured sinker in a kiln at a temperature and for a duration sufficient to sinter the sinker. Sinkers comprising high-alumina cement should be cured for about 24 hours at a temperature below 20°C, before being placed in a kiln where the temperature is raised in stages to a final temperature of at least 800°C. This temperature is maintained for about three hours in order to sinter the sinker. Sintering results in the expulsion of water from the sinker, leaving open pores within the cement matrix of the sinker, thus making the sinker absorbent or porous. Sinkers comprising Portland cement can be similarly processed, however they should be fired at a lower temperature (around 600°C) for a duration suitable to make the sinker porous.

Other methods of making the cement matrix sinkers absorbent or porous are possible. One example is by way of autoclaving. If this method is used, the sinker is preferably left to cure for at least 12 hours, preferably overnight, then placed in an autoclaving apparatus at a temperature (about 120°C) and for a duration (about eight hours) suitable to make the sinker porous.

Fixed attachment means and other items of fishing equipment can be incorporated in or attached to these absorbent or porous sinkers by the same method as described above, but the method is carried out after the firing, sintering or autoclaving process takes place.

Absorbent or porous sinkers can be soaked in or contacted with a liquid such as a fish oil or other type of oil, scent, flavour or fish attractant, in order for the sinker to absorb some of the liquid, so that the oil, scent, flavour or fish attractant will slowly be released when the sinker is used in water, thereby helping to attract fish to the bait. Some examples of suitable liquids for absorbing into the sinkers include Berkley Gulp alive, Crave Gravy (a catfish attractant), Berkley Powerbait, BioEdge Wand Fish Attractants, Kick 'n Bass Saltwater from Scientific Bass Products (for gamefish). A 4 oz sinker will generally absorb over 5 ml of liquid. The sinkers of the invention may be made in various weights, shapes (ball shaped, cylinder shaped etc), sizes and colours. The sinkers may be coloured by adding a pigment or colouring agent to the cement mixture during mixing, or they may be painted in any desired colour after moulding or curing. For example, pigments such as titanium dioxide rutile (white pigment) may be applied to the sinker while the sinker is still moist after the moulding process and before curing. Such pigments have a strong chemical reaction with the hydraulic cement and chemically bond to the surface. Therefore, the pigments could be used to inscribe written details on the sinker such as specifying the weight of the sinker and/or brand name etc. Pigments could also be used to colour or mark the sinker in other ways. For example, it is envisaged that the cement matrix composition of the invention could be modified to form a fishing lure or a fishing jig. These lures or jigs could have one or more hooks embedded therein or attached thereto (see FIG. 5, 125), and could be coloured or painted with different patterns or markings to attract fish.

Example Compositions

Some non-limiting examples of fishing sinker cement matrix compositions in accordance with the invention will now be described.

Example 1

Example 3

Microfibre (Grace) 0.5

Water to activate the mixture Added at a ratio of about 10 - 14% of total combined weight of dry and liquid ingredients

Example 6

Component Amount (% weight)

Ferrous-Ferric Oxide (magnetite sand) 79.975

Hydraulic cement (high-alumina cement) 12.75

Amorphous silicon dioxide or pozzolan 5.0

Calcium silicate (Wollastonite) 1.75

Super-plasticiser (Daracem 100) 0.025

Acrylic Polymer (Bond R) 0.5

Water to activate the mixture Added at a ratio of about 10 - 14% of total combined weight of dry and liquid ingredients

Example 7

Component Amount (% weight)

Ferrous-Ferric Oxide (magnetite sand) 40.00

Hydraulic cement (Portland cement) 22.95

Amorphous silicon dioxide or pozzolan 8.75

Iron (II) oxide 9.04

Calcium silicate (Wollastonite) 18.725

Super-plasticiser (Daracem 100) 0.035

Acrylic polymer (Bond R) 0.5

Water to activate the mixture Added at a ratio of about 10 - 14% of total combined weight of dry and liquid ingredients Example 8

Advantages

The fishing line sinkers of the invention have one or more of the following potentially realisable advantages:

• They are non-toxic or have very low toxicity therefore they are not harmful to the environment;

• They do not rust;

• They do not require coating in any other medium or encapsulation in any waterproof medium;

• They have high impact resistance and durability;

• They are strong and have good density for many applications;

• They have magnetic properties so that when they not in use they can be stored or restrained in a fixed position ready for use, either by a permanent magnet or electro-magnetic device, for example on a rod or reel or boat;

• They are suitable for use in both fresh and salt water;

• They can be handled immediately after moulding as the moulds do not require a lengthy drying and/or setting time;

• They can be made to be absorbent or porous to improve their quality, and also to absorb a fish attractant substance. Variations

It is to be understood that even though numerous characteristics and advantages of the various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functioning of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail so long as the functioning of the invention is not adversely affected. For example the particular elements of the fishing sinker may vary dependent on the particular application for which it is intended to be used, without variation in the spirit and scope of the present invention.

In addition, although the preferred embodiments described herein are directed to a fishing sinker for use with fishing lines, it will be appreciated by those skilled in the art that variations and modifications are possible within the scope of the appended claims, for example, by modifying the invention to produce a fishing lure or fishing jig.