Belt tongue, manufacturing method, and seat belt system

Abstract

The invention relates to a belt tongue (10) for a seat belt, the belt tongue (10) comprising a main body (11) made of metal, and the main body (11) comprising an insertion portion (12) and a belt fastening portion (13). The main body (11) has an enamel coating (14) at least in the insertion portion (12). The invention further relates to a method for manufacturing a belt tongue (10) and to a corresponding seat belt system (20) having a belt buckle (21).

Description

[0001] Belt tongue, manufacturing method and safety belt system

[0002] The present invention relates to a belt tongue for a safety belt in a vehicle according to the preamble of claim 1, a method for producing a belt tongue according to the preamble of claim 9 and a safety belt system according to the preamble of claim 15.

[0003] The tongues of seat belts are subjected to frequent insertion and removal processes during operation, placing considerable stress on the surface of the insertion section of the tongue, which is inserted and removed from the corresponding buckle. Therefore, high demands are placed on protecting the surfaces of the tongues or base bodies, especially the insertion sections, from scratches and abrasion. Accordingly, current belt tongues are typically coated with a nickel-chromium plating.

[0004] However, applying nickel-chromium coatings is highly energy-intensive and involves chemicals that are difficult to handle properly. Furthermore, recycling used belt tongues with nickel-chromium coatings is complex.

[0005] Furthermore, the base bodies of the belt tongue are usually made of hardenable steel, for example C60, in order to achieve, among other things, the required crash strength and sufficient wear resistance.

[0006] The object of the present invention is to provide a belt tongue and a safety belt system that are free of chromium-nickel coatings and offer sufficient durability at low cost. Furthermore, the object is to provide a method for producing such a belt tongue.

[0007] The problem is solved by the features of the independent claims. Further preferred developments can be found in the dependent claims, the figures, and the associated description. To solve the problem, a belt tongue for a safety belt is proposed, wherein the belt tongue has a base body made of metal, in particular steel, wherein the base body has an insertion section and a belt fastening section. It is proposed that the base body have an enamel coating at least in the insertion section.

[0008] An enamel coating, also known as vitreous enamel, is a glass-like coating that provides wear and abrasion resistance to the surface. The usual firing process for an enamel coating is carried out at temperatures at which steel is typically annealed, thus avoiding the application of an enamel coating to highly stressed steel parts in the prior art. Furthermore, an enamel coating typically does not achieve the surface hardness of nickel-chromium coatings, so enamel coatings are not considered for surfaces such as the insertion area of ​​a seat belt tongue, which are subject to very stringent requirements. Furthermore, the enamel coating can provide good corrosion protection for the base body of the seat belt tongue. In advantageous embodiments, the entire surface of the base body of the seat belt tongue has an enamel coating.With the enamel coating, a nickel-chrome coating on the belt tongue can be avoided, so that the belt tongue has a significantly higher environmental compatibility during production and recycling.

[0009] In addition, the enamel coating allows the belt tongue to be colored in a way that isn't possible with a nickel-chrome coating. The belt tongue, especially the insertion area, can therefore be any color, for example, black, blue, white, or orange. It is also possible for the belt tongue, especially the insertion area, to have a color with a shimmering or glass effect.

[0010] The insertion section of a belt tongue is essentially the part of a belt tongue that is designed to be inserted into a slot in a belt buckle and locked there. The belt attachment section is located outside the corresponding buckle when the belt tongue is inserted. A seat belt can be connected to the belt tongue at the belt attachment section, which can be achieved, for example, in a typical design, using an eyelet for the seat belt.

[0011] In a preferred embodiment, the base body has rounded edges, at least in the insertion section. The rounded edges preferably have a radius of at least 0.2 mm. This prevents unwanted chipping of the enamel coating at the edges during operation. Furthermore, a more uniform thickness of the enamel coating can be achieved.

[0012] According to a further development, it is proposed that the enamel coating be pre-stressed, preferably thermally, with residual stresses. The enamel coating is therefore preferably pre-stressed similarly to safety glass, so that increased compressive residual stresses are present in the enamel coating. The pre-stressed enamel coating can thus achieve increased wear resistance, largely compensating for the disadvantages in terms of hardness compared to a typical nickel-chromium coating.

[0013] In advantageous embodiments, the base body is made of hardened steel. The hardenable steel is preferably heat-treated steel, e.g., C60. This enables the required breaking load values ​​for the belt tongue to be achieved. In preferred embodiments, the strength of the hardened steel of the base body is not reduced by the enamel coating, so that the belt tongue achieves the required breaking load values ​​even with the applied enamel coating. Coating high-carbon steel is unusual, since the formation of carbon dioxide from the silicon dioxide of the enamel coating or the enamel slurry or paste and the carbon in the steel can lead to undesirable blistering in the enamel coating.

[0014] According to a further development, it is proposed that the base body have a bainite structure, at least on the surface beneath the enamel coating. This allows residual stresses in the base body to be reduced, particularly on the surface beneath the enamel coating. This allows for greater toughness to be achieved.

[0015] Bainite structure is also known as intermediate structure.

[0016] Preferably, the enamel coating has a thickness of less than 100 µm, more preferably less than 50 µm, for example 25 µm.

[0017] In other possible embodiments, the enamel coating contains friction-reducing additives. This can further increase the wear resistance of the enamel coating.

[0018] In advantageous embodiments, the belt fastening section of the base body is overmolded with a plastic body. In possible embodiments, an enamel coating is arranged between the plastic body and the insertion section. In alternative embodiments, there is no enamel coating between the plastic body and the insertion section.

[0019] Furthermore, to achieve the object of the invention, a method for producing a belt tongue with an enamel coating on a base body or one of claims 1 to 8 is proposed: a) Providing a base body of the belt tongue b) Applying enamel paste to the base body c) Heating the base body and the enamel paste d) Forming an enamel coating on the base body e) Quenching the base body with the formed enamel coating.

[0020] Before step a), the base body is preferably punched from sheet metal and then deburred. Deburring is preferably carried out such that the base body has rounded edges. Furthermore, it is possible for the edges of the base body to be machined to round them. The base body of the belt tongue is preferably made of hardenable steel and is further preferably provided in an unhardened state in step a). The enamel paste, which is, for example, a suspension containing glass particles, is applied at least to the insertion section of the base body. Enamel paste can also be applied to the belt fastening section.

[0021] The enamel paste on the base body is preferably dried. Drying can occur before and / or during the heating process in step c).

[0022] The heating in step c) can be carried out, for example, in an oven. In an advantageous process, the base body with the enamel paste is heated inductively, which allows for very fast and efficient heating.

[0023] Preferably, the heating in step c) takes place to more than 800°C, preferably 850°C. Furthermore, the heating in step c) preferably takes place to a temperature above the melting point of the enamel (glass) and above the austenitizing temperature of the steel.

[0024] Due to the temperature influence in step c), the enamel coating is formed from the enamel paste in step d). Preferably, the steel of the belt tongue is austenitized at the same time. This allows the necessary step for hardening the base body to occur simultaneously with the formation of the enamel coating on the base body. Thus, one heating process can be used for two different processes.

[0025] Furthermore, the belt tongue with the enamel coating is quenched in step e), so that the base body is preferably hardened. In advantageous embodiments, the formation of the enamel coating and the hardening of the base body can be carried out in a single operation, which allows the production of the belt tongue to be carried out in a particularly environmentally friendly and economical manner.

[0026] In a preferred embodiment, it is proposed that the quenching in step e) takes place in a bath with a temperature between 250°C and 400°C. According to a further development, it is proposed that the quenching in step e) takes place in a salt bath. Quenching to this temperature range enables hardening of the base body of the belt tongue, while at the same time preventing the enamel coating from flaking off the base body. Preferably, the enamel coating is thermally prestressed by quenching to this temperature range to such an extent that increased wear resistance of the surface of the belt tongues is achieved, at least in the insertion area. The thermal prestress increases the resistance of the enamel coating to cracks, thus increasing the longevity of the belt tongue. At the same time, an advantageous bainite structure can be achieved in the base body made of hardenable steel, e.g. C60.

[0027] Accordingly, during quenching in step e), the base body is preferably hardened, and furthermore, thermal prestressing of the enamel coating is preferably effected. Quenching the formed enamel coating from more than 800°C, preferably 850°C, to 250°C to 400°C, preferably in a salt bath, not only effects thermal prestressing of the enamel coating with the associated residual compressive stresses, but also particularly good adhesion to the base body.

[0028] According to a further development, it is proposed that the heating in step c) be carried out under a protective gas atmosphere. This prevents the formation of carbon dioxide on the base body, especially a base body made of a high-carbon, hardenable steel, which further suppresses the formation of bubbles in the enamel coating during its production. This allows the enamel coating to be applied to a belt tongue with a high carbon content, which is avoided due to the formation of carbon dioxide and possible bubbles in the enamel coating.

[0029] Furthermore, to achieve the object of the invention, a safety belt system with a belt tongue according to one of claims 1 to 8 and a belt buckle is proposed. The belt buckle has, at least in part in the contact area for the insertion section of a belt tongue, a wear layer with zinc particles in a plastic matrix with a thickness of at least 10 μm. This can further increase the longevity and closure strength of the safety belt system and the surface of the insertion area of ​​the belt tongue. The wear layer with zinc particles in a plastic matrix in the belt buckle is softer than the enamel coating of the belt tongue and wears away upon contact with the belt tongue. This can reduce wear on the belt tongue visible to a user.The increased thickness of the wear layer of zinc particles, preferably zinc flakes, in a plastic matrix, preferably epoxy, allows for an increase in the number of possible cycles until the wear layer wears out. This further compensates for the disadvantages of the enamel coating compared to a conventional nickel-chromium coating, in terms of its lower hardness. Contact between the enamel coating and the metal parts in the contact area of ​​the belt buckle can therefore be delayed significantly longer.

[0030] The invention will be explained below using preferred embodiments with reference to the attached figures.

[0031] Fig. 1 Belt tongue with an enamel coating;

[0032] Fig. 2 Belt tongue with an enamel coating and an overmolded belt fastening section;

[0033] Fig. 3 schematic representation of the process steps for the production of a belt tongue with enamel coating; and

[0034] Fig. 4 Safety belt system with an enamel-coated belt tongue and a belt buckle.

[0035] Figure 1 shows an advantageous embodiment of a belt tongue 10 with a base body 11 made of steel. In this advantageous embodiment, the base body 11 is made of hardenable steel. The base body 11 can, for example, be punched out of sheet metal. The base body 11 can be divided into two sections. First, an insertion section 12, which is intended to be inserted into a belt buckle 21 in order to lock the belt tongue 11 in the belt buckle 21. Adjacent to the insertion section 12 is a belt fastening section 13, which is intended to attach or guide a safety belt and is not covered by a belt buckle 21 when inserted. The edges 15 of the base body 11 are deburred and preferably rounded. This particularly applies to the insertion section 12, which is subject to high levels of wear due to the insertion process into a belt buckle 21.

[0036] This advantageous belt tongue 10 has an enamel coating 14 in the insertion section 12 and in the belt fastening section 13, whereby the surface of the belt tongue 10 in the insertion section 12 is wear-resistant. Therefore, a nickel-chromium coating can be omitted in the advantageous belt tongue 10. In alternative embodiments, the enamel coating 14 can also be applied only to the insertion section 12. The enamel coating 14 is preferably less than 50 μm thick, for example, 25 μm thick. Furthermore, the enamel coating 14 is black in this embodiment, but other colors of the enamel coating 14 are also possible.

[0037] The base body 11 of the belt tongue 10 is further preferably made of hardened steel so that the belt tongue 10 meets the requirements for the breaking load and the surface of the base body has a high hardness as a substrate for the enamel coating 14.

[0038] In a particularly advantageous embodiment, the base body 11 made of hardenable steel, for example C60, has a bainite structure, which is particularly advantageous for the wear resistance during the insertion and removal processes and for the toughness and strength in a retention case.

[0039] In an advantageous embodiment, the enamel coating 14 contains friction-reducing additives, which can further increase the wear resistance of the belt tongue 10. Figure 2 shows the embodiment of the belt tongue 10 provided with an enamel coating 14, wherein the insertion section 12 is overmolded with a plastic body 16. The enamel coating 14 of the belt fastening section 13 is covered by the plastic body 16 in this embodiment.

[0040] Figure 3 schematically illustrates the process sequence for manufacturing a belt tongue 10. In a first process step 30, the base body 11 of the belt tongue 10 is prepared from steel, preferably from a hardenable steel, for example, C60. The material of the base body 11 in process step 30 is unhardened in this advantageous embodiment. The edges 15 of the belt tongue 10 are deburred, particularly in the insertion section 12, and rounded in advantageous embodiments.

[0041] In the following process step 31, the enamel paste or enamel slurry is applied to the base body 11. The enamel paste is applied at least to the insertion section 12 of the belt tongue 10, but it can also be applied additionally to the belt fastening section 13.

[0042] In the following process step 32, the enamel paste is dried; for this purpose, the base body 11 is heated with the enamel paste. In this exemplary embodiment, the heating takes place to a temperature of 850°C and is preferably carried out in a protective gas atmosphere. Process step 32 proceeds to process step 33, wherein, due to the temperature influence, an enamel coating 14 forms from the enamel paste on the base body 11 of the belt tongue 10. Furthermore, in this advantageous exemplary embodiment, the steel of the base body 11 assumes an austenitic structure in process step 33.

[0043] In the subsequent process step 34, the base body 11 with the enamel coating 14 is quenched in a salt bath to a temperature between 250°C and 400°C. This thermally prestresses the enamel coating 14 and hardens the steel of the base body 11. Furthermore, the formation of a bainitic structure in the base body 11 can be achieved by quenching the belt tongue 10 to this temperature, which can also be referred to as intermediate hardening. The surface treatment of the belt tongue 10 is thus completed, so that the production of the enamel coating 14 and the hardening of the base body 11 can be completed in a single operation. Any process steps for coating with a nickel-chromium coating, such as low-hydrogen annealing, can therefore be omitted.

[0044] Figure 4 schematically shows an embodiment of a safety belt system 20 comprising a belt tongue 10 and an associated belt buckle 21. The belt buckle 21 has, in the contact area 22 for the insertion section 12 of the belt tongue 10, a wear layer 23 with zinc particles in a plastic matrix, which prevents direct contact between the enameled belt tongue 10 and the steel parts of the belt buckle 21, so that this wear layer 23 serves as wear protection for the insertion section 21 of the belt tongue 10. The wear layer 23 has a lower hardness than the enamel coating 14 and therefore wears more quickly when the two come into contact. To adapt to the enamel coating 14 of the belt tongue 10, which in principle has a lower hardness than conventional nickel-chromium coatings, the wear layer 23 is particularly thick, so that the durability of the wear layer 23 is significantly increased.

Claims

Claims:

1. Belt tongue (10) for a safety belt, wherein the belt tongue (10) has a base body (11) made of metal, in particular steel, wherein the base body (11) has an insertion section (12) and a belt fastening section (13), characterized in that the base body (11) has an enamel coating (14) at least in the insertion section (12).

2. Belt tongue (10) according to claim 1, characterized in that - the base body (11) has rounded edges (15) at least in the insertion section (12).

3. Belt tongue (10) according to claim 1 or 2, characterized in that - the enamel coating (14) is prestressed with residual stresses.

4. Belt tongue (10) according to one of the preceding claims, characterized in that - the base body (11) is made of hardened steel.

5. Belt tongue (10) according to one of the preceding claims, characterized in that - the base body (11) has a bainite structure at least on the surface below the enamel coating (14).

6. Belt tongue (10) according to one of the preceding claims, characterized in that - the enamel coating (14) has a thickness of less than 50 pm.

7. Belt tongue (10) according to one of the preceding claims, characterized in that the enamel coating (14) comprises friction-reducing additives 8. Belt tongue (10) according to one of the preceding claims, characterized in that the belt fastening section (13) of the base body (11) is overmolded with a plastic body (16).

9. A method for producing a belt tongue (10) according to one of the preceding claims, characterized by the steps: a) providing a base body (11) of the belt tongue (10); b) applying enamel paste to the base body (11); c) heating the base body (11) and the enamel paste; d) forming an enamel coating (14) on the base body (11); e) quenching the base body (11) with the formed enamel coating (14).

10. The method according to claim 9, characterized in that the heating in step c) takes place under a protective gas atmosphere.

11. The method according to claim 9 or 10, characterized in that the heating in step c) takes place to more than 800°C, preferably to 850°C.

12. Process according to one of claims 9 to 11, characterized in that the quenching in step e) takes place in a bath having a temperature between 250°C and 400°C.

13. A method according to any one of claims 9 to 12, characterized in that the quenching in step e) takes place in a salt bath.

14. Method according to one of claims 9 to 13, characterized in that during quenching in step e) a hardening of the base body (11) takes place and a thermal prestress is effected in the enamel coating (14).

15. Safety belt system (20) with a belt tongue (10) according to one of claims 1 to 8 and a belt buckle (21), characterized in that the belt buckle (21) in Contact area (22) for the insertion section (12) of a belt tongue (10) at least partially has a wear layer (23) with zinc particles in a plastic matrix with a thickness of at least 10 pm.

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