Plastic tank for the storage and transport of bulk material

Abstract

The present invention relates to a plastic tank for the storage and transport of bulk materials, such as solids, liquids or semi-liquids, wherein said tank comprises a main body (1) with tapered sidewalls and a built-in pallet base (18) with four legs, a main rectangular lid (2), a secondary round lid (3) having a vent cap with a gas valve (4) and a bottom discharge opening (17). Said tanks are made of food grade HDPE of a special composition molded in one-piece using an injection molding process, and are nestable, when empty for shipment purposes and stackable, when full for storage purposes.

Claims

1. A plastic tank for the storage and transport of bulk materials, such as solids, liquids or semi-liquids comprising: a) a main body (1) having a rectangular base (18) with integrally built-in at least four legs (20), four sidewalls (11a, 11b, 12a, 12b) extending in trapezoid shape upwardly and outwardly from the base (18), and defining a rectangular top opening, which forms a body-rim (15) provided with a projecting edge (16) along the periphery of the body-rim (15), wherein said base (18) with said at least four legs (20) have a pallet type configuration, the bottom surface of the base (18) is externally reinforced with base ribs (19) molded in both directions, and said four sidewalls (11a, 11b, 12a, 12b) are provided with webbed ribs (13) molded across their external surface so as to provide great strength and stability to the main body (1); b) a main rectangular lid (2) having a top surface, a bottom surface, an eccentric round opening (30) for filling up the tank and a main-lid rim (31) with a main-lid groove (14) along the periphery of said main rectangular lid (2) and a main-lid rubber gasket (71) that fits in said main-lid groove (14), wherein said main lid (2) is attached to the open top of the main body (1) and is closed with safety-lock pins (8) secured along the body-rim (15) of said main lid (2) and the main-lid rim (31) of the main rectangular lid (2), said safety-lock pins (8) in conjunction with the main-lid rubber gasket (71) provide a watertight sealing to the tank, the bottom surface of the main lid (2) comprises webbed ribs (36) molded in both directions so as to control internal forces when the tank is loaded, the top surface of the main lid (2) comprises feet sockets (27) molded on the four corners so as to receive the feet of the upper tank during stacking, and the round opening (30) is provided with a round lid groove (34) around the its periphery to hold a round-lid rubber gasket (72) around the periphery of the secondary round lid (3) for a watertight seal when closed; and c) a secondary round lid (3) that fits in the eccentric round opening (30) of the main rectangular lid (2) comprising a vent hole (22) sealed with a vent cap with a gas extraction valve (4) to facilitate the outflow of the fermentation gases formed inside the tank, wherein said base (18) with the at least four legs (20) and the four sidewalls (11a, 11b, 12a, 12b) are made of plastic molded in one-piece, one of the sidewalls of the main body (1) adjacent to the base (18) of the main body (1) of the tank comprises a discharge opening (17) that can be equipped with a drainage valve (50) in order to empty the liquids inside the tank, and said at least four legs (20) of the base surface further comprise detachable and replaceable feet plugs (5) suitable to be plugged in said legs (20).

2. The tank according to claim 1, wherein said four sidewalls (11a,11b, 12a,12b) are reinforced with differentially dimensioned ribs (13) webbed symmetrically across the external surface of the sidewalls forming a turtle-shell-like design, in order to transfer pressure and weight forces from the top surface of said main rectangular lid (2) to the base (18) of said main body (1), when stacked, making said tank robust and durable.

3. The tank according to claim 1, wherein the at least four sidewalls at their corners are provided with particularly designed protruding corner-ribs (6), which extend from directly below the main body-rim (15) of the top opening, across its four corners, to the base (18), said protruding corner-ribs (6) providing the desired distance between the empty tanks, when nested to prevent jamming and minimize extraction effort.

4. The tank according to claim 2, wherein the discharge opening (17) on the lowest part of the front sidewall (11a) of the main body (1) is provided with a corresponding internal filter (9) for the containment of solids.

5. The tank according to claim 1, wherein said at least four legs (20) are shaped like caved pallet-feet so as to enable the use of a forklift on all four sides of the tank, and the detachable and replaceable feet plugs (5) are plugged in said legs (20) using specific safety feet-clips (21).

6. The tank according to claim 5, wherein two traverses (10) can be clipped onto the legs (20) of the base (18), each traverse (10) comprises three feet plugs (5) on a traverse base (53), two feet plugs (5) to be plugged in the legs (20) of the base (18) and a third middle traverse foot plug (54) to be plugged into the base (18) and secured with a middle foot clip (55).

7. The tank according to claim 1, wherein the bottom surface of the main rectangular lid (2) further comprises screen-ribs (37) that are elongated and differentially shaped than the webbed ribs (36).

8. The tank according to claim 1, wherein the main rectangular lid (2) further comprises a rainwater drain-off hole (29), and the main-lid rim (31) comprises main-lid ribs (33) molded on its top surface, which provide rigidness and strength.

9. The tank according to claim 1, wherein the secondary round lid (3) is manufactured from HDPE, comprising on its top surface six handles (40) with six security holes (41), its vent hole (22) comprises a vent-hole groove (42) wherein the vent-cap rubber gasket (73) is fitted, and six sealing ridges (23) on the bottom surface of the secondary round lid (3) secure it onto the main rectangular lid (2).

10. The tank according to claim 1, wherein said tank further comprises a rectangular retaining screen (60) placed under the main rectangular lid (2), said screen (60) has an eccentric round opening (61) corresponding to the round opening (30) of the main lid (2), wherein a small round screen (70) is placed

11. The tank according to claim 1, wherein the safety-lock pins (8) are manufactured of polyamide, and are inserted in key shaped holes (32) on the main-lid rim (31) of the main rectangular lid (2) and corresponding body-sockets (46) on the body-rim (15) of the main body (1).

12. The tank according to claim 5, wherein said vent cap with gas extraction valve (4) comprises a gas valve cover (56) with a safety cover-hole (57) and an internal gas discharge valve (58) comprising a specific elastic membrane (26) which automatically moves upwards and opens so as to enable the discharge of fermentation gases.

13. The tank according to claim 1, wherein the main-lid rubber gasket (71) fitted into the main-lid groove (14), the round-lid rubber gasket (72) fitted into the round-lid groove (34), and the vent-cap rubber gasket (73) fitted into the vent-cap groove (42) are all manufactured from food grade silicone material.

14. The tank according to claim 1, wherein the vent cap with gas extraction valve (4) is made from food grade HDPE and its elastic membrane (26) is made from food grade silicone material.

15. The tank according to claim 1, wherein the main body (1) of the plastic tank is manufactured from HDPE using a one-piece injection molding process.

16. The tank according to claim 1, wherein the main rectangular lid (2) of the plastic tank is manufactured from HDPE using a one-piece injection molding process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will become better understood with reference to the accompanying drawings, which show preferred embodiments in accordance with the present invention without limiting the scope or spirit of the invention

[0018] FIG. 1 shows a perspective view of the plastic tank and its various components according to the present invention.

[0019] FIG. 2 shows a perspective view of the main body of the plastic tank according to the present invention.

[0020] FIG. 3 shows a perspective view of the main lid of the plastic tank according to the present invention.

[0021] FIG. 4 shows a perspective view of the small round lid of the plastic tank according to the present invention.

[0022] FIG. 5 shows a detailed, perspective view of the feet plugs and the traverse of the feet of the plastic tank according to the present invention.

[0023] FIG. 6 shows a detailed view of the safety-lock pin and the vent cap with the gas valve of the plastic tank according to the present invention.

[0024] FIG. 7 shows a detailed view of the rectangular screen, the round screen and the filter of the plastic tank according to the present invention.

[0025] FIG. 8 is a perspective view of three plastic tanks according to the present invention stacked statically and dynamically the on top of the other.

[0026] FIG. 9 is a perspective view of the main body of the plastic tanks nested inside one another according to the present invention and the main rectangular lids stacked according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Referring to FIG. 1 of the drawings, the plastic tank for the storage and transport of bulk material according to the present invention comprises a main body (1), a main rectangular lid (2), a secondary round lid (3), a vent cap with gas extraction valve (4), four detachable and replaceable feet plugs (5). Said plastic tank, further comprises several safety-lock pins (8), an internal filter (9), two traverse (10) interconnecting said feet plugs, a rectangular retaining screen (60), a round screen (70), a main-lid rubber gasket (71), a round-lid rubber gasket (72) and a vent-cap rubber gasket (73).

[0028] Referring to FIG. 2, the main body (1) comprises a rectangular base (18) with at least four legs (20), four sidewalls (11a, 11b, 12a, 12b) extending in trapezoid shape upwardly and outwardly from the base (18) and defining a rectangular top opening formed as a body-rim (15). The four sidewalls form a first pair of equal opposite sidewalls (11a-11b) and a second pair of equal opposite sidewalls (12a-2b). The first pair of sidewalls is formed from the front and back sidewalls (11a, 11b). The top and bottom dimensions of the first pair of sidewalls (11a, 11b) are about 1000 mm and about 800 mm, respectively, while the top and bottom dimensions of the second pair of sidewalls (12a-12b) are about 800 mm and about 600 mm, respectively. These trapezoid shaped four sidewalls form the conical shape of the main body (1), said four sidewalls are provided with ribs (13) of different length and thickness, molded across their external surface, such as a turtle-shell like design, so as to provide great strength and stability to the main body and in order to make the main body (1) rigid and robust.

[0029] The ribs (13) extend symmetrically over all four sidewalls of the main body (1) of the plastic tank. Their length, number, thickness and placement has been standardized following a number of structural studies and tests with various types of plastic (construction analysis, flow mold analysis) to guarantee firmness and durability in stacking conditions.

[0030] The ribs (13) transform the main body (1) of the plastic tank into a safety cage. Pressure and weight forces are transferred across the ribs (13) from the main rectangular lid (2) (see FIGS. 1 and 3), to the base (18) of each plastic tank, enabling and securing the stacking of said plastic tanks. The specific structural and constructional design of the ribs (13) enables three-tanks to be stacked one on top of the other for storage purposes (static stacking) and two-tanks to be stacked one on top of the other for transportation purposes (dynamic stacking) as shown in FIG. 8.

[0031] The four sidewalls at their corners are provided with particularly designed corner-ribs (6), which extend from directly below the main body-rim (15) of the top opening, across its four corners, to the base (18). These protruding corner-ribs (6) provide the desired distance between the empty tanks, when nested (see FIG. 9), to prevent jamming and minimize extraction effort.

[0032] The body-rim (15) of the main body (1) is provided with a projecting edge (16) is along the periphery of said body-rim (15) corresponding to a main-lid groove (14) along the periphery of the main rectangular lid (2) (see FIG. 3), wherein a main-lid rubber gasket (71) fits to provide watertight seal to the plastic tank (FIG. 1). The main rectangular lid (2) is attached to the top opening of the main body (1) and it can be closed with several safety-lock pins (8), e.g. twenty two safety-lock pins, secured along the body-rim (15) of the main body (1) of the plastic tank, wherein there are corresponding sockets (46), e.g. twenty two sockets, to receive the safety-lock pins (8). The bottom of each socket is formed in a specific socket-angle (47), so that the safety-lock pins (8) can securely lock into place with a rightward half-turn motion. The pressure of the safety-lock pins (8) is transferred to the projecting edge (16) of the body-rim (15) and onto the main-lid rubber gasket (71) (FIG. 1). Thus, the plastic tank can be 100% watertight sealed, even throughout moving or stacking.

[0033] The front sidewall (11a) of the main body (1) at its lowest part adjacent to the base (18) of the plastic tank comprises a discharge opening (17) with a diameter such as a 2 inch, for the optional application of a plastic or metal external drainage valve (50) in order to empty the liquids inside the plastic tank.

[0034] The base (18) with the at least four legs (20) of the main body (1) has a pallet type configuration and its dimensions are about 800 mm600 mm190 mm. Said dimensions comply with international logistics standards and guarantee maximum stability during handling with the use of a forklift. The bottom of the base (18) is externally reinforced with symmetrical base ribs (19) in both directions, which provide strength and sturdiness during lifting. The base (18) can support the weight of at least two full tanks dynamically stacked (FIG. 8) by using forklifts. The at least four legs of the base (18) are shaped like caved pallet-feet, and said at least four legs (20) of the base (18) further comprise detachable and replaceable feet plugs (5) suitable to be plugged in said legs (20). The feet plugs (5) are detachable to provide the option of replacement in case of breakage or dirtiness, especially when the plastic tanks are stored outdoors, where it is highly possible for the feet plugs (5) to be damaged or soiled. Their being detachable and replaceable offers a cheap and easy solution to minimize contamination risk when tanks are moved from outside to the inside of the factory.

[0035] Alternatively, at least two one-piece traverses (10) (see FIGS. 1 and 5), can be plugged into the legs (20) of the base (18), to provide the option of 360o turnover of a fully loaded tank, maximizing steadiness. This option facilitates unloading, especially when the products inside the tank are solid. All four sidewalls (11a, 11b, 12a, 12b) are provided on their external surface with a labelling area (24) for traceability purposes. Labelling areas (24) have a granular surface design, so that labels can be removed easily leaving no paper residue. The inside surface of the body (1) is absolutely smoothened for a no-residue and easy-cleaning effect.

[0036] The plastic tank and all its components of the present invention are made of food grade High-density polyethylene (HDPE) and is molded in one-piece by using one-piece injection molding method, which provides a one-piece tank embodying the base (18) with the at least four legs (20), thus maximizing security and durability. The clamping force in the injection process for flowing HDPE is 5,000 tons. All parts of the tank can be made in one of 7 different colors or even transparent. Coloring and transparency is achieved by mixing additives with HDPE during injection process. The exact procedure as well as the materials and additives used are matters of disclosure. Generally, it is about mixing HDPE with additives and catalysts creating master-batches according to a disclosed polymer formula, to achieve the desired firmness, flexibility and durability of the tank.

[0037] The use of special polypropylene catalysts allows the tank to retain its physicochemical characteristics, standard dimensions and stacking stability in a temperature range of 20 Celsius up to 60 Celsius. This parameter of the present invention is critical for the food industry especially for products that are stored outdoors or require refrigeration. All interior surfaces of the body (1) have a smooth and round-cornered finish (25). On the inside lowest part of the front side (11a) there is a bottom discharge opening (17) of 2 inch for emptying liquids. Additionally, there is a filter socket (64) (FIG. 7) for placement of a detachable internal filter (9) to contain solids (e.g. olives, cherries etc.) when liquids have to be discharged separately.

[0038] Referring to FIG. 3, the main rectangular lid (2) comprises a top surface, a bottom surface, an eccentric round opening (30) for filling up the tank and the main-lid rim (31) along the periphery of said main rectangular lid (2). The top surface of the main rectangular lid (2) comprises feet sockets (27) on the four corners so as to receive the legs (20) of the upper tank during stacking, said feet sockets (27) are molded on the four corners of the top surface of the main lid (2). In these feet sockets (27) nest the legs (20) (FIG. 2) of the top tank during stacking, for maximum stability throughout transportation and storage. The feet sockets (27) have a sloping surface (28) that allows the tank on top to slide in and semi-automatically lock onto the bottom tank when elevated with a forklift, ensuring stable and secure stacking and transportation. Especially during loading tanks on transportation means (trucks or sea containers), these feet sockets (27) function as safety keys.

[0039] Further, on the top surface of the main rectangular lid (2), it is provided a rainwater drain-off hole (29) useful for outdoor storage conditions. Stagnant water on the main rectangular lid (2) could become contaminated with harmful organisms affecting the contents of the tank. The round opening (30) wherein a secondary round lid (3) (FIGS. 1 and 4) fits, protrudes from the top surface of the main rectangular lid (2) to prevent intrusion of water or undesirable particles (dust, dirt etc.) inside the tank. On the upper part of the opening (30) a specific round lid groove (34) is formed to hold a round-lid rubber gasket (72) around the periphery of the secondary round lid (3) (FIG. 1) for a watertight seal of the secondary round lid (3) (FIGS. 1 and 4).

[0040] The main-lid rim (31) comprises key-shaped holes (32) e.g. twenty two key-shaped holes, wherein the corresponding safety-lock pins (8) e.g. twenty two safety-lock pins, lock through. The main-lid rim (31) has main-lid ribs (33) molded on its top surface, which provide rigidness and strength, particularly when tanks are stacked one on top of the other.

[0041] The bottom surface of the main rectangular lid (2) is reinforced with webbed ribs (36) in both directions, which provide maximum sturdiness and stability, especially when the tanks are stacked. The webbed ribs (36) have a breakwater attribute, controlling internal forces when the tank is loaded with liquid products. The bottom surface of the main rectangular lid (2) further comprises screen-ribs (37) that are elongated and differentially shaped than the webbed ribs (36). Said screen-ribs (37) put downward pressure on the internal rectangular retaining screen (60) (FIGS. 1 and 7) which is used to eliminate levitation and keep solid products (olives, fruit, pickled foods etc.) inside liquid (brine or syrup) and remain intact during transportation. Along the periphery of the main rectangular lid (2), on its bottom surface, a main-lid groove (14) is especially designed for the main-lid rubber gasket (71) (FIG. 1) to be fitted in.

[0042] Referring to FIG. 4, the secondary round lid (3) socketed onto the main rectangular lid (2) comprises pin-storing sockets (38) which hold the safety-lock pins (8) when the tank is being returned empty, to prevent their misplacement or loss. A round-lid rim (39) of the second round lid (3) around its periphery comprises six handles (40) with little security holes (41) drilled on each handle and using plastic or metal fastening seal through one of the security holes (41) and the corresponding main-lid rainwater drain-off hole (29), the secondary round lid (3) can be secured when closed. The handles (40) open the secondary round lid (3) quickly and effortlessly, with a half-turn move. In the center of the secondary round lid (3) there is a vent hole (22) sealed with a vent cap with gas extraction valve (4) (FIGS. 1 and 6). Through said vent hole (22) the plastic tank of the present invention can be filled with liquid oe semi-liquid products without unsealing the main rectangular lid (2). The vent hole (22) can also be used as a quick access point for quality control. A vent-cap rubber gasket (73) nests in the corresponding vent-hole groove (42) provided right in the center of the secondary round lid (3), to secure the vent cap with the gas extraction valve (4) into place (FIGS. 1 and 6).

[0043] The bottom surface of the secondary round lid (3) is designed with a protruding bottom (44) to enter the main body (1) of the tank and press down upon the round screen (70), which keeps solids into liquids (e.g. pickled vegetables), despite levitation. Further, on the bottom surface of the secondary round lid (3), there are provided six sealing ridges (23) that secure it onto the main rectangular lid (2) (FIGS. 1 and 3). The diameter of the secondary round lid (3) is sufficient to allow easy access and control of the contents, liquid or solid.7The main-lid rubber gasket (71), as well as the round-lid rubber gasket (72) and the vent-cap rubber gasket (73) are all made of food grade silicone rubber material. The main rectangular lid (2), the secondary round lid (3) and the vent cap with gas valve (4) all fasten securely, make the plastic tank 100% watertight.

[0044] Referring to FIG. 5, the detachable and replaceable feet plugs (5) comprise safety feet clips (21) in order to secure the feet plugs into place, by clipping on the corresponding clip hole (48) on the legs (20) of the base (18). Alternatively, two traverses (10) can be clipped onto the legs (20) of the base (18), each traverse comprises three traverse feet plugs on the traverse base (53), two feet plugs are plugged in the legs (20) of the base (18) and the third middle traverse foot plug (54) is plugged into the base (18) and secured with a middle foot clip (55) through a corresponding middle clip hole (51). The one-piece traverse base (53) holds the main body (1), when a user flips over the tank to empty it, via forklift or mechanical dumper.

[0045] Referring to FIG. 6, the safety-lock pins (8) through their design guarantee absolutely secure sealing of the plastic tank. The safety-lock pins (8) are inserted in the key shaped holes (32) of the main rectangular lid (2) and the corresponding body-sockets (46). With a rightward, half-turn move, the safety-lock pins (8) are securely locked in a special socket-angle (47). The safety-lock pins (8) are preferably made of polyamide. The pinheads (49) are designed as common hexagonal, slotted screw heads with a 19 mm diameter. A common screwdriver or a combination wrench can be used for locking and unlocking the safety-lock pins (8).

[0046] Following various studies and tests, it has been found that in order to seal the tank 100% watertight, twenty two safety-lock pins (8) should be used pins, each locked in a key shaped holes (32) molded on every second main-lid rib (33) along the periphery of the main-lid rim (31). These safety-lock pins (8), made of polyamide for maximum durability, combined with the main-lid rubber gasket (71), which nests in the main lid groove (14), provide absolute and secure sealing even when tanks are stacked or moving. Moreover, the vent cap with the gas extraction valve (4) comprises a gas valve cover (56), to prevent entrance of undesired particles through the vent hole (22) and can also be secured against unauthorized access to the contents of the tank, with the use of a plastic or metal safety seal through its safety cover hole (57). Below the vent cap (4) an elastic membrane (26) on the gas-extraction valve (58) opens automatically to release fermentation gases formed inside the tank, especially in high temperature conditions. The function of the gas extraction valve (58) is triggered by interior pressure forces when said forces are more than about 37 psi. When the material of the tank are chemically inactive, the gas extraction valve (58) remains sealed. The vent cap with gas extraction valve (4) is screwed onto the secondary round lid (3) with a rightward half turn move. The sealing ridges (52) lock in the vent hole (22) of the secondary round lid (3) and is sealed with the vent-cap rubber gasket (73) fitted into the vent-hole groove (42).

[0047] Referring to FIG. 7, the plastic tank of the present invention may further comprises a rectangular retaining screen (60) comprising eight projecting flaps (59) that nest under the body-rim (15) to hold the screen (60) in place, and a round opening (61) eccentric located on the rectangular screen corresponding to the round opening (30) of the main rectangular lid (2) with a round screen (70) nesting in it. The round screen (70) comprises handle flaps (62) which function as grips to remove it when handling contents through the round opening (30), keeping the main rectangular lid (2) closed. Additionally, a small opening (63) in the center of the round screen (70), directly below the vent cap (4), enables content access through the vent-hole (22).8The plastic tank may also comprise an internal filter (9) with a filter flap (65) for easy removal, that sits on a specific filter-socket (64) on the inside of the tank at the discharge opening.

[0048] Referring to FIG. 8, three of the plastic tanks of the present invention are stacked one on top of the other. As depicted from FIGS. 1 and 3, the opening (30) of main rectangular lid (2) that corresponds to the secondary round lid (3), is formed eccentric and close to one side of the main rectangular lid (2). The stacked plastic tanks are separated with a stacking distance (66) of approximately 17 cm between each other. The secondary round lid (3) and the vent cap (4) can be screwed off and on with a rightward or leftward half-turn motion respectively. The stacking distance (66) is estimated and designed so as to enable a user to handle the contents of the plastic tank through its small round lid (3) or vent cap (4), without having to lift the tank stacked on top of it.

[0049] This feature enables the user to check, control and fill the tank with liquids or semi-liquids, without lifting the hole tank and opening the main rectangular lid (2), decreasing dramatically contamination risk, because the content of the tank doesn't have extended contact with outside air. The turtle-shell like design of the tank allows a three-tank static stacking (67) and a two-tank dynamic stacking (68).

[0050] Referring to FIG. 9, eleven main bodies (1) and thirty six main rectangular lids (2) of the plastic tank are nested inside one another, respectively. The maximum height (69) of said eleven main bodies (1) or said thirty six main rectangular lids (2), when nested, is about 2394 mm, which is the minimum standard height of trucks and sea containers. The plastic tank of the present invention is a conical, cuboid tank of 440 liters, made from HDPE using the method of high pressure injection molding, and is cost effective returnable and reusable.

[0051] The plastic tank is made watertight with two lids of different sizes, a main rectangular lid and a secondary round lid, which ensure quick and easy access for filling up, quality control and overall product safety. All parts of the tank are made from food grade HDPE and fully meet sanitation standards. The especially composed raw materials used in the production process, the manufacturing technology (high pressure injection molding) and the structural design of the tank (turtle-shell) make it stackable when full and enable steady transportation with no leakage. The conical design of the tank enables to be nested, so that empty tanks can be placed one inside the other and be safely returned to be reused. Furthermore, a drain valve facilitates liquid content removal. A vent cap with a one-way operating gas extraction valve enables the discharge of fermentation gases. As a result of manufacturing materials and production technology, the tank has an expected lifespan of 10 years and it can be efficiently reused. Due to its shape and construction, the tank can be handled effortlessly and securely using all current industrial transportation means (forklift, pallet dumper etc.).

[0052] The specifically calculated dimensions of the tank enable secure delivery with all standardized transportation means (trucks, sea containers).

[0053] While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made in the invention without departing from the spirit and scope thereof, as defined in the appended claims.