Belt tongue, manufacturing method, and safety belt system
The enamel-coated steel belt tongue addresses the wear and environmental issues of nickel-chrome coatings by providing durable and recyclable safety belts with enhanced wear resistance and color options.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-02-26
- Publication Date
- 2026-04-10
AI Technical Summary
Existing belt tongues for vehicle safety belts are subjected to high stress and wear due to frequent insertion and removal, necessitating nickel-chrome coatings that are energy-intensive, environmentally harmful, and difficult to recycle.
A belt tongue with a steel body coated in enamel, which provides abrasion and corrosion resistance, eliminating the need for nickel-chrome coatings, and featuring a rounded edge and thermal pre-stressing to enhance durability.
The enamel-coated belt tongue achieves sufficient durability and wear resistance without the environmental drawbacks of nickel-chrome coatings, allowing for recyclability and color customization, while maintaining the required breaking load.
Smart Images
Figure 2026510706000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a belt tongue for a safety belt in a vehicle as described in the preamble of claim 1, a method for manufacturing the belt tongue as described in the preamble of claim 9, and a safety belt system as described in the preamble of claim 15.
Background Art
[0002] The belt tongue of a safety belt is subjected to frequent insertion and removal processes during operation, inserted into and removed from the corresponding buckle, resulting in large stresses on the surface of the insertion portion of the belt tongue. Therefore, there is a high demand for protecting the belt tongue or the body, particularly the surface of the insertion portion, from scratches and wear. Therefore, the belt tongues of the prior art are usually nickel-chrome coated.
[0003] However, the application of nickel-chrome coating is very energy-intensive and uses chemicals that are difficult to handle properly. Furthermore, recycling used belt tongues with nickel-chrome coating is complicated.
[0004] Furthermore, the body of the belt tongue is usually made of hardened steel such as C60 in order to achieve the required impact strength and sufficient wear resistance, etc.
Summary of the Invention
[0005] An object of the present invention is to provide a belt tongue and a safety belt system that have sufficient durability at low cost without a chromium-nickel coating. Furthermore, an object of the present invention is to provide a method for manufacturing such a belt tongue.
[0006] This object is achieved by the features of the independent claims. Further preferred developments can be obtained from the dependent claims, the figures, and the related description.
[0007] To achieve this objective, a belt tongue for safety belts is proposed, which has a metal, particularly steel, body, and which has an insertion portion and a belt fastening portion. It is proposed that the body has an enamel coating, at least on the insertion portion.
[0008] Enamel coatings, also known as vitreous enamel, are glass-like coatings that provide abrasion and wear resistance to surfaces. The typical firing process for enamel coatings is carried out at temperatures typically used for annealing steel, thus avoiding the application of enamel coatings to highly stressed steel components in the prior art. Furthermore, enamel coatings typically do not achieve the surface hardness of nickel-chromium coatings; therefore, enamel coatings are not considered for surfaces such as the insertion area of a belt tang where the requirements are extremely high. Additionally, enamel coatings can provide good corrosion protection to the body of the belt tang. In a preferred embodiment, the entire surface of the belt tang body is coated with enamel. Enamel coatings eliminate the need for nickel-chromium coatings on the belt tang, making the belt tang significantly more environmentally friendly during manufacturing and recycling.
[0009] Furthermore, enamel coating allows for coloring of the belt tang, which is not possible with nickel-chromium coating. Therefore, the belt tang, particularly the insertion area, can be any color, such as black, blue, white, or orange. This also makes it possible to give the belt tang, especially the insertion area, a color that has a shimmering or glassy effect.
[0010] The insertion portion of the belt tongue is, in principle, a part of the belt tongue intended to be inserted into a slot in the belt buckle and locked therein. When the belt tongue is inserted, the belt fastening portion is located outside its corresponding belt buckle. A safety belt can be connected to the belt tongue at the belt fastening portion, which in a typical design can be achieved, for example, using an eyelet for the safety belt.
[0011] In a preferred embodiment, the body has a rounded edge, at least on the insertion portion. Preferably, the rounded edge has a radius of at least 0.2 mm. This prevents undesirable chipping of the enamel coating at the edge during operation. Furthermore, a more uniform thickness of the enamel coating can be achieved.
[0012] In a further developmental form, it is proposed that the enamel coating is pre-stressed, preferably thermally, using residual stress. Therefore, the enamel coating is preferably pre-stressed, similar to safety glass, resulting in increased compressive residual stress being present in the enamel coating. Thus, a pre-stressed enamel coating can achieve improved wear resistance, and as a result, can significantly compensate for the hardness disadvantages compared to typical nickel-chromium coatings.
[0013] In a preferred embodiment, the body is made of hardened steel. The hardened steel is preferably a quenched and tempered steel such as C60. This allows the required breaking load value for the belt tang to be achieved. In a preferred embodiment, the strength of the hardened steel body is not reduced by the enamel coating, and as a result, the belt tang achieves the required breaking load value even when enamel coated. Coating high-carbon steel is not common because the formation of carbon dioxide from silicon dioxide in the enamel coating, enamel slurry, or enamel paste and carbon in the steel can lead to undesirable blistering in the enamel coating.
[0014] In a further developmental form, it is proposed that the main body has a bainite structure at least on the surface beneath the enamel coating. This makes it possible to reduce residual stress on the main body, particularly on the surface beneath the enamel coating. This makes it possible to achieve higher toughness. The bainite structure is also known as an intermediate structure.
[0015] Preferably, the enamel coating has a thickness of less than 100 μm, more preferably less than 50 μm, for example, 25 μm.
[0016] In other possible embodiments, the enamel coating contains friction-reducing additives, which can further enhance the wear resistance of the enamel coating.
[0017] In a preferred embodiment, the belt fastening portion of the main body is overmolded with a plastic body. In a possible embodiment, an enamel coating is placed between the plastic body and the insert portion. In an alternative embodiment, there is no enamel coating between the plastic body and the insert portion.
[0018] Furthermore, in order to achieve the objectives of the present invention, a method for manufacturing a belt tongue having an enamel coating on the main body or a belt tongue according to any one of claims 1 to 8 has been proposed, and this method is Step a) providing the body of the belt tongue, Step b) involves applying enamel paste to the main body, Step c) involves heating the main body and the enamel paste, Step d) forming an enamel coating on the main body, Step e) rapidly cools the body on which the enamel coating has been formed, Includes.
[0019] Prior to step a), the body is preferably punched out from sheet metal and then deburred. Deburring is preferably done so that the body has rounded edges. The edges of the body can also be machined to round them. The body of the belt tang is preferably made of hardenable steel and more preferably supplied in an unhardened state in step a).
[0020] The enamel paste is, for example, a suspension containing glass particles, and is applied to at least the insertion portion of the main body. The enamel paste can also be applied to the belt fastening portion.
[0021] The enamel paste on the main body is preferably dried. Drying can be done before and / or during step c) heating.
[0022] The heating step c) can be carried out, for example, in an oven. In a preferred method, the body is inductively heated together with the enamel paste, which allows for very rapid and efficient heating.
[0023] Preferably, step c) heating is performed at a temperature above 800°C, preferably up to 850°C. Furthermore, step c) heating is preferably performed at a temperature higher than the melting point of the enamel (glass) and higher than the austenitizing temperature of the steel.
[0024] As a result of the temperature effect in step c), an enamel coating is formed from the enamel paste in step d). Preferably, the steel of the belt tang is austenitized at the same time. This allows the steps necessary to harden the body to be performed simultaneously with the formation of the enamel coating on the body. This means that one heating operation can be used for two different processes.
[0025] Furthermore, the enamel-coated belt tongue is rapidly cooled in step e), and as a result, the body is suitably cured. In a preferred embodiment, the formation of the enamel coating and the curing of the body can be performed in a single operation, making the manufacture of the belt tongue particularly environmentally friendly and economical.
[0026] In a preferred embodiment, it is proposed that the quenching step e) is carried out in a bath at a temperature between 250°C and 400°C. According to a further development, it is proposed that the quenching step e) is carried out in a salt bath.
[0027] By quenching to this temperature range, the body of the belt tongue can be hardened, and at the same time, it is possible to prevent the enamel coating from peeling off from the body. Preferably, the enamel coating is thermally pre-stressed by quenching to this temperature range to such an extent that improvement in the wear resistance of the surface of the belt tongue is achieved, at least in the insertion region. Thermally pre-stressing increases the resistance of the enamel coating to cracking, and thus increases the durability of the belt tongue. At the same time, a suitable bainite structure can be achieved in a body made of hardenable steel such as C60.
[0028] Therefore, during the quenching step e), the body is preferably hardened, and more preferably, thermally pre-stressed in the enamel coating. By quenching the resulting enamel coating preferably in a salt bath from a temperature above 800°C, preferably above 850°C, to a temperature between 250°C and 400°C, not only is the enamel coating thermally pre-stressed with the associated residual compressive stress, but also particularly good adhesion to the body is ensured.
[0029] According to a further development, it is proposed that the heating step c) is carried out in a protective gas atmosphere. This makes it possible to prevent the formation of carbon dioxide on the body, particularly on a body made of high-carbon hardenable steel, thereby further suppressing the swelling in the enamel coating during its manufacture. This makes it possible to apply the enamel coating to a belt tongue with a high carbon content, which is avoided due to the formation of carbon dioxide and the possible swelling in the enamel coating.
[0030] Furthermore, in order to achieve the objectives of the present invention, a safety belt system having a belt tongue and a belt buckle according to any one of claims 1 to 8 is proposed. The belt buckle has, at least partially, an abrasion layer having zinc particles in a plastic matrix having a thickness of at least 10 μm in the contact area for the insertion portion of the belt tongue.
[0031] This further enhances the durability and abrasion resistance of the safety belt system and the surface of the belt tongue insertion area. The abrasion layer with zinc particles in the plastic matrix of the belt buckle is softer than the enamel coating of the belt tongue and abrades when in contact with the belt tongue. This reduces the wear of the belt tongue visible to the user. By increasing the thickness of the abrasion layer of zinc particles, preferably zinc flakes, in the plastic matrix, preferably epoxy matrix, it is possible to increase the number of potential cycles before the abrasion layer wears down. This further compensates for the disadvantage of enamel coatings, which are less hard than conventional nickel-chromium coatings. Therefore, contact between the enamel coating and metal parts in the buckle contact area can be delayed for a very long period of time. [Brief explanation of the drawing]
[0032] The present invention will be described below using preferred embodiments with reference to the attached drawings. The drawings are as follows. [Figure 1] Shows a belt tongue with an enamel coating. [Figure 2] The diagram shows a belt tongue having an enamel coating and an overmolded belt fastening section. [Figure 3] This is a schematic diagram of the steps in the manufacturing method of an enamel-coated belt tongue. [Figure 4] This shows a safety belt system with an enamel-coated belt tongue and belt buckle. [Modes for carrying out the invention]
[0033] Figure 1 shows a preferred exemplary embodiment of a belt tongue 10 having a steel body 11. In this preferred exemplary embodiment, the body 11 is made of hardenable steel. The body 11 can be punched out from, for example, sheet metal. The body 11 can be divided into two parts. Firstly, there is an insertion portion 12 intended to be inserted into a belt buckle 21 to lock the belt tongue 11 in the belt buckle 21. Adjacent to the insertion portion 12 is a belt fastening portion 13 provided for fastening or guiding the safety belt and not covered by the belt buckle 21 when inserted. The edges 15 of the body 11 are deburred and preferably rounded. This is particularly true for the insertion portion 12, which is subject to significant wear due to the insertion process into the belt buckle 21.
[0034] This preferred belt tongue 10 has an enamel coating 14 on the insertion portion 12 and the belt fastening portion 13, thereby making the surface of the belt tongue 10 on the insertion portion 12 wear-resistant. Therefore, the preferred belt tongue 10 does not require a nickel-chromium coating. In an alternative exemplary embodiment, the enamel coating 14 may be applied only to the insertion portion 12. The enamel coating 14 is preferably less than 50 μm thick, for example, 25 μm thick. Furthermore, although the enamel coating 14 is black in this exemplary embodiment, enamel coatings 14 of other colors are also possible.
[0035] The body 11 of the belt tongue 10 is preferably made of hardened steel, so that the belt tongue 10 meets the breaking load requirements and the surface of the body has high hardness as a base material for the enamel coating 14.
[0036] In a particularly preferred exemplary embodiment, the body 11, made of a hardenable steel such as C60, has a bainite structure which is particularly advantageous for wear resistance during insertion and removal processes, as well as for toughness and strength in restrained conditions.
[0037] In one preferred exemplary embodiment, the enamel coating 14 contains friction-reducing additives that can further enhance the wear resistance of the belt tang 10.
[0038] Figure 2 shows an exemplary embodiment of a belt tongue 10 with an enamel coating 14, where the insertion portion 12 is overmolded with a plastic body 16. In this exemplary embodiment, the enamel coating 14 is covered by the plastic body 16 from the belt fastening portion 13.
[0039] Figure 3 schematically shows the sequence of steps for manufacturing the belt tang 10. In the first step 30 of the method, the body 11 of the belt tang 10 is made of steel, preferably a hardenable steel such as C60. In this preferred exemplary embodiment, the material of the body 11 is not hardened in step 30 of the method. The edges 15 of the belt tang 10 are deburred, particularly at the insertion portion 12, and rounded in a preferred exemplary embodiment.
[0040] In the next step 31, enamel paste or enamel slurry is applied to the main body 11. The enamel paste is applied to at least the insertion portion 12 of the belt tongue 10, but may also be applied to the belt fastening portion 13.
[0041] In the next step 32 of the method, the enamel paste is dried. For this purpose, the body 11 is heated together with the enamel paste. In this exemplary embodiment, the heating is carried out at a temperature up to 850°C, preferably in a protective gas atmosphere. The method then proceeds to step 33, where, as a result of the effect of temperature, an enamel coating 14 is formed from the enamel paste onto the body 11 of the belt tang 10. Furthermore, in this preferred exemplary embodiment, in step 33, the steel of the body 11 takes on an austenitic structure.
[0042] In the next step 34, the body 11, which has been coated with enamel coating 14, is rapidly cooled in a salt bath to a temperature between 250°C and 400°C. This pre-stresses the enamel coating 14 thermally, hardening the steel of the body 11. Furthermore, the formation of a bainite structure in the body 11 can be achieved by rapidly cooling the belt tang 10 to this temperature, which can also be called intermediate hardening. In this way, the surface treatment of the belt tang 10 is completed, and the formation of the enamel coating 14 and the hardening of the body 11 can be completed in a single operation. Therefore, any step in the process for coating with a nickel-chromium coating, such as low-hydrogen annealing, can be omitted.
[0043] Figure 4 schematically shows an exemplary embodiment of a safety belt system 20 comprising a belt tongue 10 and an associated belt buckle 21. The belt buckle 21 has a wear layer 23 with zinc particles in the plastic matrix in the contact area 22 for the insertion portion 12 of the belt tongue 10, which prevents direct contact between the enameled belt tongue 10 and the steel component of the belt buckle 21, and as a result, this wear layer 23 functions as wear protection for the insertion portion 21 of the belt tongue 10. The wear layer 23 has a lower hardness than the enameled coating 14 and therefore wears faster when both are in contact. To match the enameled coating 14 of the belt tongue 10, which has a lower hardness in principle than conventional nickel-chromium coatings, the wear layer 23 is formed particularly thickly, significantly increasing the durability of the wear layer 23.
Claims
1. A belt tongue (10) for a safety belt, having a metal, particularly steel, body (11) having an insertion portion (12) and a belt fastening portion (13), wherein the body (11) is characterized in that at least the insertion portion (12) has an enamel coating (14).
2. The belt tongue (10) according to claim 1, characterized in that the main body (11) has a rounded edge (15) on at least the insertion portion (12).
3. The belt tongue (10) according to claim 1 or 2, characterized in that the enamel coating (14) is pre-stressed using residual stress.
4. The belt tongue (10) according to any one of claims 1 to 3, characterized in that the main body (11) is made of hardened steel.
5. The belt tongue (10) according to any one of claims 1 to 4, characterized in that the main body (11) has a bainite structure on at least the surface beneath the enamel coating (14).
6. The belt tongue (10) according to any one of claims 1 to 5, characterized in that the enamel coating (14) has a thickness of less than 50 μm.
7. The belt tongue (10) according to any one of claims 1 to 6, characterized in that the enamel coating (14) contains a friction-reducing additive.
8. The belt tongue (10) according to any one of claims 1 to 7, characterized in that the belt fastening portion (13) of the main body (11) is overmolded with a plastic body (16).
9. A method for manufacturing a belt tongue (10) according to any one of claims 1 to 8, a) The step of providing the main body (11) of the belt tongue (10), b) The step of applying enamel paste to the main body (11), c) A step of heating the main body (11) and the enamel paste, d) The step of forming an enamel coating (14) on the main body (11), e) A step of rapidly cooling the main body (11) on which the enamel coating (14) has been formed, A method that includes this.
10. The method according to claim 9, characterized in that the heating step c) is performed under a protective gas atmosphere.
11. The method according to claim 9 or 10, characterized in that the heating step c) is performed at a temperature greater than 800°C, preferably up to 850°C.
12. The method according to any one of claims 9 to 11, characterized in that the rapid cooling step e) is performed in a bath with a temperature between 250°C and 400°C.
13. The method according to any one of claims 9 to 12, characterized in that the step e) of rapid cooling is performed in a salt bath.
14. The method according to any one of claims 9 to 13, characterized in that during step e) of rapid cooling, the main body (11) is hardened and thermal stress is pre-applied to the enamel coating (14).
15. A belt tongue (10) according to any one of claims 1 to 8, Belt buckle (21) and, A safety belt system (20) comprising, The belt buckle (21) is characterized in that, at least partially in the contact area (22) for the insertion portion (12) of the belt tongue (10), it has a wear layer (23) having zinc particles in a plastic matrix having a thickness of at least 10 μm. Safety belt system (20).