Solid tires provided with means for indicating an excessive wear condition

Abstract

A solid tire (4; 8) is described that includes two or more radially overlapping circular layers. At least the outermost layer is made of a resilient material and comprises an outer portion or tread (16). The solid tire (4; 8) further includes at least one excessive wear indication layer (10) disposed at a predetermined position within the outer portion or tread (16). The excessive wear indication layer (10) is made of a color different from the color of the outer portion or tread (16). The excessive wear indication layer (10) is made of a specific material compound. This specific material compound makes the excessive wear indication layer (10) easy to see. This specific material compound also gives the solid tire (4; 8) lower hysteresis and, therefore, less susceptible to heat buildup compared to similar solid tires according to the prior art.

Description

[Technical field]

[0001] The present invention relates generally to solid tires, and more particularly to solid tires having means for providing an indication of excessive wear. Specifically, the present invention relates to solid tires having means for providing a visual indication of an excessive wear condition. [Background technology]

[0002] As is known, in industrial and commercial applications, tires are often used that are not inflated with air, but have a structure made of solid rubber and plastic composite materials. This structure, obtained by a molding operation, is particularly resistant to punctures and has improved load-bearing properties. By way of example, solid tires are used on various types of industrial vehicles and operating means. In particular, one of the most common applications of solid tires is on equipment for handling goods (forklifts).

[0003] The first type of solid tire is designated as the so-called superelastic tire or "resilient tire". Structurally, referring to FIG. 1, which shows a cross-section of a thickness of a prior art superelastic tire, this type of tire is formed by two or more circular layers of elastic material, radially overlapping, as generally indicated by the reference number 2. These layers form, from the center to the periphery of the superelastic tire 2, an inner portion called the bead 12, a middle portion simply called the intermediate portion 14, and an outer portion called the tread 16.

[0004] In particular, the beads 12 are the parts of the superelastic tire 2 that are mounted around the wheel rim, which is integrated with the axle on which the wheel rotates. The tread 16, on the other hand, is the structural part of the superelastic tire 2 that comes into contact with the ground on which the wheel rotates. The intermediate portion 14 is instead the structural part entrusted with the function of ensuring the elasticity of the superelastic tire 2. For the reasons mentioned above, the beads 12 and the tread 16 must be manufactured from a particularly resistant material.

[0005] More specifically, the structure of the superelastic tire 2 may be reinforced by a plurality of metal strands 18 in the beads 12, while the tread 16 may be smooth or may have grooves 20. The number, shape, and depth of the grooves 20 may vary depending on the application of the superelastic tire 2.

[0006] For superelastic tyres designed for use on low-speed vehicles (usually below 25 km / h), the functionality of the tread grooves is of little importance. In fact, the service life of this type of superelastic tyre does not depend on the wear of the tread grooves, but on the overall wear of the tread itself. In fact, the intermediate section, deprived of the coverage offered by a tread of sufficient thickness, cannot guarantee the suitable properties for the use of a superelastic tyre.

[0007] For this reason, and referring again to Figure 1, the superelastic tire 2 is provided with excessive wear indicators consisting of raised circular portions 22. Said circular portions 22 are located on the shoulders of the superelastic tire 2, i.e. on the sides of the superelastic tire 2, in particular on the sides of the contact area between the tread 16 and the intermediate portion 12. Each of these raised circular portions 22 has an excessive wear indication function and is called the "60J line". Summary of the Invention [Problem to be solved by the invention]

[0008] However, users of superelastic tires are often asked to replace them with new tires when the wear level reaches the bottom of the tread groove. Depending on the type of superelastic tire, i.e. the intended use, the bottom of the tread groove is reached long before the point of excessive wear of the superelastic tire is reached; that is, long before the "60J line" is reached. In some cases, the remaining thickness of the tread, which serves to protect the middle part and ensure the correct operation of the superelastic tire, can even be 20-40% of the initial thickness. As a result, users of this type of superelastic tire mistakenly complain that the actual service life does not match what is stated by the manufacturer. In view of the above, the solutions provided by the excessive wear indicators according to the prior art, and in particular the solution provided by the "60J line", do not meet the need to inform the user that the end of the service life of this superelastic tire has actually been reached.

[0009] Thus, a superelastic tire with means for visually indicating an excessive wear state has been achieved. These means for visually indicating an excessive wear state allow the user to utilize the superelastic tire to the limit of its potential, i.e., until the end of the actual useful life of the superelastic tire itself is reached. For example, document GB 2505034A filed by the same applicant discloses a superelastic tire with means for visually indicating an excessive wear state. These visual means have a color different from the color of the tread, in order to efficiently indicate that the end of the actual useful life of the superelastic tire has been reached, while at the same time providing the user with sufficient reassurance that an excessive wear state has not yet been reached.

[0010] A second type of solid tire is further known, known by the acronym POS ("Press On Steel") or POB ("Press On Band"). Structurally, with reference to FIG. 3, in which a POS / POB tire according to the prior art is shown in cross section through its thickness, this type of tire, generally designated by reference number 6, is always formed from two or more circular layers, overlapping radially. However, these layers are not all made of elastic material. Proceeding from the center towards the periphery of the POS / POB tire 6, it is in fact possible to distinguish: an inner part consisting of a metal ring 24, configured to simplify the mounting of the POS / POB tire 6 around the wheel rim, and a normal outer part or tread (16), made of elastic material and mounted around the metal ring 24.

[0011] The difference between POS / POB and superelastic tires lies in the fact that for POS / POB tires, the upper limit of tread wear has not been clearly and officially established. There is only one recommendation, from the European Tire and Rim Technical Organization (ETRTO), which identifies this wear limit at 1 / 3 of the tread thickness. However, a similar American association (TRA or "Tire and Rim Association") does not provide any recommendations for this type of solid tire.

[0012] It is therefore up to the manufacturer of the POS / POB tire to identify the wear limit of the tread of the POS / POB tire. For example, referring again to FIG. 3, the POS / POB tire 6 is provided with a so-called wear limit 26 at a predetermined position in the corresponding tread 16, which is designed to indicate a point of excessive wear of the tread 16 itself. That is, after degradation of the tread 16, the POS / POB tire 6 must be replaced when the wear limit 26 is reached.

[0013] For POS / POB tires, visual means for indicating an excessive wear state have been disclosed. These are shown, for example, in document WO2019 / 092756A1 filed by the same applicant. However, the applicant has discovered that these visual means, even when mounted on superelastic or POS / POB tires, can be produced in a particularly bright color and thus be easily visible when produced from a specific material compound. In addition to this, this specific material compound makes the visual means, and consequently the entire solid tire, low hysteresis and therefore less susceptible to heat generation.

[0014] The object of the present invention is therefore to produce a solid tyre which makes it possible to overcome the aforementioned drawbacks of the prior art in a very simple, inexpensive and particularly functional manner.

[0015] In particular, it is an object of the present invention to produce a solid tire with a visual indication of an excessive wear condition which is more easily visible than similar solid tires of known types.

[0016] Another object of the present invention is to produce a solid tire with a means for visually indicating an excessive wear condition that is more tolerable than similar solid tires of known types. [Means for solving the problem]

[0017] These and other objects according to the invention are achieved by producing a solid tyre as claimed in claim 1.

[0018] Further features of the invention are outlined in the dependent claims which form an integral part of the invention.

[0019] The characteristics and advantages of the solid tire according to the invention will emerge more clearly from the following description, which is given in an illustrative and non-limiting manner and which refers to the accompanying drawings, in which: [Brief description of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view of the thickness of a prior art superelastic tire. [Diagram 2] FIG. 1 is a cross-sectional view through the thickness of a first embodiment (superelastic tire) of a solid tire with a visual indication of an excessive wear condition according to the present invention. [Diagram 3] FIG. 1 is a thickness cross-sectional view of a POS / POB tire according to the prior art. [Figure 4] FIG. 2 is a cross-sectional view through the thickness of a second embodiment of a solid tire (POS / POB tire) with a visual indication of an excessive wear condition according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] With particular reference to Figures 2 and 4, there are shown two preferred embodiments of a solid tire according to the present invention. In particular, in Figure 2, the solid tire comprises a superelastic tire generally designated by the reference numeral 4. In Figure 4, the solid tire comprises a POS / POB tire generally designated by the reference numeral 8.

[0022] Both the superelastic tire 4 and the POS / POB tire 8 are manufactured from substantially the same components that form the prior art superelastic and POS / POB tires, respectively. Accordingly, the same reference numbers are used for these components as previously described. Thus, in general, the solid tire 4 or 8 comprises two or more radially overlapping circular layers, at least the outermost layer being made of an elastomeric material and comprising an outer portion or tread 16.

[0023] Additionally, the solid tire 4 or 8 includes at least one excessive wear indicating layer 10 disposed at a predetermined location on the inside of the outer portion or tread 16. For example, in a hyperelastic tire 4, the excessive wear indicating layer 10 may be disposed at a raised circular portion 22 ("60J line") on the outer portion or tread 16. In a POS / POB tire 8, the excessive wear indicating layer 10 may be disposed at a wear limit 26 on the outer portion or tread 16.

[0024] The excessive wear indication layer 10 is in any case made of a color that is clearly distinguishable from the color of the tread 16. In particular, the excessive wear indication layer 10 is made of a color that is different from the color of the tread 16. This allows for an immediate and easy visual indication if the wear of the tread 16 is such that the excessive wear indication layer 10 is exposed.

[0025] In accordance with the present invention, the layer for indicating excessive wear is manufactured using the following material compositions in the following weight percentages: -Rubber: 50% to 60%; -Silica: 20% to 30%; -One or more plasticizing additives: from 2% to 8%; -One or more compatibilizers between rubber and silica: 2% to 3%; -Pigments: 3% to 8%; -One or more protective agents: 1%; -One or more cross-linking agents: 3% to 8%.

[0026] The gums can be of both synthetic and natural types. A mineral binder is added to the pigment so that the mineral color results from the bond between the pigment and the mineral binder.

[0027] In particular, the protectants are of the so-called "non-staining" type, which contribute to keeping the mineral color brighter and thus at the same time avoiding the migration of coloring components to the surface of the compound. The protectants furthermore contribute to the reduction of the ageing effects of the rubber. A particular category of non-staining protectants usually used in compounds consists of the category of hindered phenols, known for example under the trade names "WingstayL" and "LowinoxGP45".

[0028] One of the main performance requirements for solid tires is resistance to heat build-up. During their use, solid tires are continually subjected to fatigue cycles due to the combination of rotational speed and the load placed on them. These fatigue cycles generate heat, which accumulates inside the solid tire. When the work cycles are long, each lasting more than eight hours a day, the solid tire does not have time to rest and cool down. When the inside temperature of a solid tire exceeds 130°C, aging accelerates and the solid tire becomes more susceptible to deterioration.

[0029] The silica and the compatibilizer between the rubber and the silica, which may be chosen, for example, from the category of silanes such as vinyltrimethoxysilane, form a specific compound that renders the solid tire 4 or 8 low hysteresis and therefore less susceptible to heat generation, compared to similar solid tires according to the prior art. In fact, the layer 10 for indicating excessive wear, comprising the aforementioned compound, gives the solid tire 4 or 8 discontinuities, reduces the accumulated heat and makes the solid tire 4 or 8 suitable for heavy work (2-3 consecutive shifts or 18-24 hour work cycles).

[0030] Thus, it has been found that the solid tire according to the present invention achieves the foregoing objects.

[0031] However, in the solid tire of the present invention thus conceived, many modifications and variations are possible, all of which are included in the same inventive concept. Moreover, all contents can be replaced with technically equivalent elements. In fact, the materials used, as well as the shapes and sizes, can be of any type according to technical needs.

[0032] Therefore, the scope of protection of the present invention is defined by the appended claims.

Claims

1. A solid tire (4; 8) for a forklift truck comprising two or more radially overlapping circular layers, At least the outermost layer is made of an elastic material and comprises an outer portion or tread (16); said solid tire (4; 8) further comprising at least one layer (10) for indicating excessive wear, located at a predetermined position inside said outer portion or tread (16); said at least one excessive wear indicating layer (10) being made of a color different from the color of said outer portion or tread (16); The at least one layer (10) for indicating excessive wear is made using a combination of the following materials in the following weight percentages: - rubber: 50% to 60%; - Silica: 20% to 30%; - one or more plasticizing additives: from 2% to 8%; - one or more compatibilizers between rubber and silica: 2% to 3%; - pigments: 3% to 8%; - one or more protective agents: 1%; - one or more crosslinkers: 3% to 8%, a mineral binder is added to the pigment such that a mineral color results from the combination of the pigment and the mineral binder; The solid tire (4; 8), characterized in that the protective agent is of the so-called "non-dyed" type, contributing to keeping the mineral color brighter and thus avoiding migration of coloring components to the surface of the compound.

2. A solid tire (4; 8) as described in claim 1, characterized in that the protective agent is selected from the category of hindered phenols.

3. A solid tire (4; 8) as described in claim 2, characterized in that the protective agent selected from the hindered phenol category is the product name "Wingstay L" or the product name "Lowinox GP45".

4. A solid tire (4; 8) according to any one of claims 1 to 3, characterized in that the compatibilizer between rubber and silica is selected from the category of silanes.

5. Solid tyre (4; 8) according to claim 1, characterized in that said rubber is of synthetic type.

6. Solid tyre (4; 8) according to claim 1, characterised in that the rubber is of the natural type.

7. 7. A solid tire (4; 8) according to any one of claims 1 to 6, characterized in that said solid tire (4; 8) consists of a superelastic tire (4) comprising a plurality of radially overlapping circular layers of elastic material, said layers forming, from the centre towards the periphery of the superelastic tire (4), an inner portion or bead (12), a central or intermediate portion (14) and said outer portion or tread 16.

8. 8. A solid tyre (4; 8) according to claim 7, characterized in that it further comprises raised circular portions (22) arranged on the shoulders of the superelastic tyre (4) at the sides of the contact area between said outer portion or tread (16) and said central or intermediate portion (14).

9. 9. A solid tyre (4; 8) according to claim 8, characterized in that said at least one layer (10) for indicating excessive wear is arranged in said outer portion or tread (16) in said raised circular portion (22).

10. A solid tyre (4; 8) according to claims 1 to 6, characterized in that the solid tyre (4; 8) comprises a POS / POB tyre (8) with an inner part consisting of a metal ring (24) and with the outer part or tread (16) mounted around said metal ring (24) from the centre towards the periphery of the POS / POB tyre (8).

11. 11. A solid tyre (4; 8) according to claim 10, characterized in that said solid tyre (4; 8) further comprises, at a predetermined position on the inside of said outer portion or tread (16), a wear limit (26) designed to indicate a point of excessive wear of said outer portion or tread (16).

12. 12. A solid tyre (4; 8) according to claim 11, characterized in that at least one layer (10) for indicating excessive wear is arranged in said outer portion or tread (16) at said wear limit (26).

Images