HK1199423B - Corrosion-resistant screw, use of a screw of this type in a corrosive environment, and method for producing a screw of this type - Google Patents

Description

Corrosion-resistant bolt, use of such a bolt in a corrosive environment and method for producing such a bolt

Technical Field

The invention relates to a bolt and the use of such a bolt in combination with a corrosion-resistant component to be tightened in a corrosive environment and also to a method for producing such a bolt, which has a threaded shank, is made of a corrosion-resistant material suitable for a heat treatment for increasing the strength.

Such bolts are used in particular in so-called direct tightening, in which the bolt itself forms a thread into a nut part which, for receiving the bolt, usually has a corresponding through-hole or blind hole.

Background

It is known from the prior art to use bolts made of corrosion-resistant materials, such as stainless steel, in corrosive environments, as disclosed, for example, in DE 29706372U 1. However, the strength of such a screw is not sufficient for all applications, for example, when screwing directly into a plastic part or into a carbon fiber composite, a high strength is required.

EP 0948719B 1 discloses a screw that is screwed into plastic and that, due to its geometry, can be made of a material that has a lower strength than the materials conventionally used for screws that are screwed into plastic.

DE 19815670 a1 discloses a corrosion-resistant thread-rolled screw with partially hardened regions of reduced corrosion resistance, which form only a small part of the screw that is required for drilling and for forming the thread, but which are not hardened in the bearing region of the screw.

In principle, also bolts made of titanium are suitable, but the price is too high for screw connections in the field of mass production.

The DIN EN 10269 standard "steels and nickel alloys for fastening elements in use at high and/or low temperatures" specifies the requirements for the material of fastening elements made of unalloyed and alloyed (including stainless) steels and nickel alloys. Bolts made of said material are suitable for a heat treatment for increasing the strength, which material is corrosion resistant.

Disclosure of Invention

A first subject of the invention is a bolt with a threaded shank made of a corrosion-resistant material suitable for heat treatment for strength enhancement. The bolt has a first strength that is predefined by deformation prior to forming the thread, the strength being formed by a heat treatment. In order to form the thread, the threaded spindle having the thread lead, the thread ridge and the thread base is deformed, and the thread lead is increased in strength by the cold hardening occurring in this way relative to the region without deformation and has a second strength. Furthermore, the thread is formed in a self-tapping manner or in a thread rolling manner.

Such bolts have on the one hand sufficient strength and on the other hand sufficient corrosion resistance.

The material of the bolt may be particularly advantageous to overcome contact corrosion with carbon or carbon reinforced composites. Since carbon is detrimental to iron due to its electrochemical potential, it is particularly important for the continuous use of the bolt: furthermore, whether the surrounding environment is corrosive or not, such corrosion is not avoided without this concern.

The bolt can advantageously be made of a high-temperature-resistant material, in particular an austenitic material or a nickel-based alloy, according to EN 10269 or similar standards.

A particular embodiment relates to a bolt, wherein the pitch (P) has a ratio Q1= P/Da of 0.3 to 0.385 with respect to the outer diameter (Da), wherein each thread lead in the thread bottom between the thread ridges has a radius Rg, and wherein the radius Rg has a ratio Q2= Rg/P of 0.5 to 1.0, preferably 0.6 to 0.8, with respect to the pitch. Such a screw has proven to be suitable for screwing into plastic parts, in particular thermoplastic or thermosetting plastics with a high fiber content.

The transition from the thread root with the radius Rg to the thread ridge can advantageously be in the angular range 25 ° to 45 °, in particular in the angular range 28 ° to 38 °, and the thread engagement angle can be in the angular range 20 ° to 30 °. It has been shown that with such an angle, there is sufficient stability of the thread ridge on entering the nut component.

The screw may advantageously have a thread crest formed by the deformation and an undeformed region in the thread core, and the thread crest may be configured to have a second strength which is higher than the region of the first strength without deformation, wherein the second strength of the thread crest achieved by the deformation is at least 10%, preferably 30% and at most 55% higher than the first strength.

The bolt may advantageously have a self-tapping thread made of steel and made of a material that prevents corrosion in contact with stainless steel.

The invention also relates to the use of the screw connection according to the invention in corrosive environments, in which the components to be screwed are resistant to corrosion.

A further subject matter of the invention is a method for producing a bolt according to one of the preceding claims, which is made of a heat-treated material suitable for increasing the strength, wherein starting from the heat-treated blank, for increasing the strength, a deformation of the blank is carried out after the heat treatment of the blank in order to form the bolt geometry. No other treatment to significantly change the intensity is provided.

In order to remove particles which do not resist corrosion, for example from deformation of the bolt for reinforcement by heat treatment, pickling may advantageously be carried out. Such particles can be transferred from the thread rolling machine to the bolt, for example. The corrosion of iron impurity is avoided by pickling, in which the thin metal layer is removed.

In order to form a passivated protective layer, a so-called passivation of the surface can advantageously be carried out on the surface. In the passivation process, the material is not abraded, but rather the properties and the thickness of the passivation layer are specifically optimized.

Another subject of the invention is an assembly of a plurality of parts, said assembly having at least two parts made of different materials, wherein the parts are provided with a hole diameter depending on the respective material for receiving a bolt for providing a threaded connection. The material of the one part is a carbon fiber-reinforced composite material and the material of the other part is, in particular, NE metal cast material with a hard cast skin, a composite material (e.g., a fiber composite material), a durable composite material (e.g., a glass bead composite material) and mixtures thereof, wherein at least two parts made of different materials are connected to one another with one or more identical bolts according to the invention.

Heretofore, such assemblies have not been mass produced due to the lack of cost effective bolts.

Drawings

The method according to the invention is explained with reference to the drawing. The figures show:

FIG. 1 is a side view of a bolt according to the invention made of plastic for threaded connection;

FIG. 2 is a detail of the thread formation of the bolt of FIG. 1;

FIG. 3 is a side view of a metric threaded bolt with thread rolling in accordance with the present invention;

fig. 4 shows an assembly of a plurality of parts made of different materials in combination with a screw according to the invention.

Detailed Description

The screw 1 according to the invention, shown in a side view in fig. 1, for screwing into plastic has a shank 3 with a thread 2 and with an outer diameter Da and a core diameter Dk, wherein the shank 3 is made of a material suitable for a heat treatment for increasing the strength, which is corrosion-resistant. The head of the screw with the inner force application surface is likewise shown, but this is not essential to the invention.

The screw has a first strength which is predefined by a heat treatment due to deformation before the thread 2 is formed, and the shank 3 is additionally deformed for producing the thread 2 with a thread lead (gewinnerging) 4, a thread ridge 5 and a thread bottom 6, which thread ridge has a thread form angle phi.

The thread pitch 4 and in particular the thread ridge 5 are increased in strength by the cold hardening occurring during the deformation relative to the non-deformed region 7 of the screw 1, i.e. for example inside the threaded rod 3, wherein the thread 2 is formed in a thread-forming or thread-rolling manner.

Fig. 2 shows in detail the thread formation of the bolt in fig. 1. The pitch or thread lead P has a ratio Q1= P/Da of from 0.3 to 0.385 with respect to the outer diameter Da in such a bolt, which ratio is 0.37 in the illustrated case. Each thread lead 4 has a radius Rg in the thread bottom 6 between the thread ridges 5, wherein the radius Rg has a ratio Q2= Rg/P of from 0.5 to 1.0, preferably 0.55 to 0.8, in the case shown 0.62, with respect to the thread pitch P.

The thread angle phi of the thread 5 can lie in an angle range of 20 ° to 30 °, wherein in the case shown the angle phi is 25 °.

It can also be seen in the detail view that the transition from the thread root 6 with the radius Rg to the transition point 8 of the thread ridge 5 with the diameter D u has an angle alpha in the angular range from 25 ° to 45 °, in particular in the angular range from 28 ° to 38 ° and in the present case approximately 32 °.

The other two diameters min and max are not important for the description of the invention.

The screw 3, which has already had a first strength before the deformation for forming the thread 2 with the thread crests 9, has a non-deformed core region 10, so that the thread crests 9 are formed with a greater strength than the non-deformed core region 10, wherein the strength achieved by the deformation is increased by at least 10%, preferably by 30% and by at most 55%.

Fig. 3 shows a side view of a further screw 11 according to the invention with a self-tapping thread 12 made of steel. The thread 12 has a profiled region 13 which increases in diameter from the tip and which merges into a load-bearing thread region 14. The thread leads are fully formed in both regions 13, 14, so that the core diameter increases from the tip toward the loaded region 14.

The bolt 1, 11 can be used in a corrosive environment in combination with parts to be tightened that are resistant to corrosion relative to the environment.

Fig. 4 schematically shows an assembly 20 of a plurality of components 21, 22, 23 made of different materials, wherein each of the components 21, 22 has at least one bore, in this case a blind bore 24, 25 with a bore diameter d1, d2 depending on the respective material, for receiving a screw 26 for providing a threaded connection. The part 21 may be made of a carbon fibre reinforced composite material and the part 22 may be made of NE-metal cast material, in particular with a hard cast skin, or a composite material, such as a fibre composite, a durable composite material, such as a glass ball composite, and mixtures thereof. The parts 21-23 are connected to a respective one or more identical bolts 26 to form a single assembly 20.

In the production of threads by deformation, care must be taken that the temperature during the entire deformation is below the temperature for the purpose of eliminating the strength or toughness (fetigkeit) caused by the heat treatment. This is achieved by the following method: the bolt geometry is produced by rolling with a sufficiently large deformation length of the rolling tool.

Furthermore, suitable materials for using bolts may be: AL die casting, AlMg die casting, Mg die casting, carbon fiber or glass fiber reinforced plastics, such as unsaturated polyesters.

The bolt may be made of an austenitic corrosion resistant steel alloy with high strength and is suitable for use in cast or perforated core holes without contact corrosion with the material of the bolt screwed into the hole.

Claims (15)

1. A bolt having a threaded shank provided with a thread, made of a material suitable for a heat treatment for increasing the strength, which is corrosion-resistant, characterized in that the bolt has a first strength, which is predefined by deformation before the thread is formed, the first strength resulting from the heat treatment; the threaded rod is deformed in order to form a thread with a thread lead, a thread ridge and a thread base, and the thread lead is increased in strength by the cold hardening that occurs as a result relative to the non-deformed region and has a second strength, wherein the thread is formed in a self-tapping or thread rolling manner.

2. The bolt of claim 1 wherein said material prevents contact corrosion with carbon or carbon reinforced composites.

3. A bolt according to claim 1 or 2, wherein the bolt is made of a material which is resistant to high temperatures.

4. Bolt according to claim 1 or 2, characterized in that it is made of a material resistant to high temperatures according to EN 10269.

5. A bolt according to claim 1 or 2, wherein the bolt is made of an austenitic material.

6. A bolt according to claim 1 or 2, wherein the bolt is made of a nickel-based alloy.

7. Bolt according to claim 1 or 2, wherein the pitch P has a ratio Q1= P/Da of 0.3 to 0.385 with respect to the outer diameter Da, wherein each thread lead has a radius Rg in the thread bottom between the threads, and wherein the radius Rg has a ratio Q2= Rg/P of 0.5 to 1.0 with respect to the pitch.

8. The screw according to claim 7, wherein the transition region from the thread base to the thread ridge is in the angular range 25 ° to 45 ° and the thread form angle is in the angular range 20 ° to 30 °.

9. The screw according to claim 1 or 2, wherein the shank has a thread crest formed by deformation and an undeformed region in the thread core, and the thread crest has a second strength which is higher than the undeformed region having the first strength, wherein the second strength achieved by deformation is increased by at least 10% and by at most 55%.

10. A bolt according to claim 1 or 2, wherein the bolt has a self-tapping thread of a metric type and is made of a material which resists contact corrosion with stainless steel.

11. Use of a bolted joint according to any one of claims 1 to 10 for fastening components that are resistant to corrosion in relation to a corrosive environment.

12. Method for manufacturing a bolt according to any of the preceding claims 1 to 10, which bolt is made of a heat-treated material suitable for increasing the strength, characterized in that, on the basis of a heat-treated blank, after heat treatment of the blank, the blank is deformed to form the bolt geometry in order to increase the strength.

13. The method of claim 12, wherein pickling is performed to remove particles that are not corrosion resistant from the deformation of the bolt for strengthening by heat treatment.

14. The method according to claim 12 or 13, characterized in that the surface is so-called passivated in order to form a passivated protective layer on the surface.

15. Assembly of parts with at least two parts made of different materials, wherein the parts have a hole diameter depending on the respective material for receiving a bolt providing a threaded connection, characterized in that the material of the one part is a carbon fiber reinforced composite material and the material of the other part is an NE metal casting material or a composite material or a durable composite material or a hybrid thereof, wherein the parts are connected to one assembly with one or more respectively identical bolts according to any one of claims 1 to 10.