FIELD OF THE INVENTION

The present disclosure relates to electro-mechanical horns and particularly relates to an apparatus, a system, and a method for improving oxidation and wear resistance of tungsten electrical contact in an electro-mechanical horn.

BACKGROUND

Recent developments in products of automotive sector technology have increased the customer requirements concerning the quality and its working life in end products. A vehicle horn is one such product, which is a sound-making device for motor vehicles. The vehicle horn is used to warn others on the road of any approaching vehicle or of its presence or to point out some hazard. Vehicle horn is a kind of a transducer that converts electrical energy into sound energy. Broadly disc, fanfare and compressor trumpet type horns are available in market. Disc type horns are usually further classified into two categories which include electro-mechanical horns and electronic horns.

The electro-mechanical horns include electrical contacts which are one of the key components in functioning of the electromechanical horn. The electrical contacts are present in a live circuit of the electromechanical horn and are adapted to be made and broken for proper functioning of the electromechanical horn. As is generally known, during the make and break function of contacts in live circuit of an electromechanical horn, an arc is often generated between the electrical contact pairs which remains until they are separated by a certain gap.

During the generation of the arc, the arc temperature can reach a very high temperature (4000K–40000K) within a very short time of 1–100 msec. Though higher temperature exposes the surface of contact for a very short time, during the repeated cycling, surface temperature of tungsten electrical contact surface reaches up to the melting temperature of tungsten. This high temperature exposure of the tungsten electrical contact surface leads to oxidation. A thickened oxide layer is consequently formed on the surface of the tungsten electrical cycle with repeated cycles. The oxide layer being not very conductive can lead to the connectivity breakage in the live circuit leading to horn failure.

In other circumstances, if oxides grow thicker, they can chip off easily due to the impact during make and break cycles. The repetitive surface contact in comparison to the bare tungsten surface leads to high wear rate of the tungsten electrical contacts. The extent of tungsten contact degradation would vary depending on the oxidation and mechanical forces exerted by a particular contact.

Therefore, there is a need of prolonging life of electromechanical horn by reducing high temperature oxidation, abrasion, erosion, and wear of tungsten electrical contacts in electromechanical horns.

SUMMARY

This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended for determining the scope of the invention.

The present disclosure relates to a method for development of a master alloy coating on a tungsten substrate. The method includes mixing of a predetermined amount of a master alloy with a predetermined amount of an activator and a predetermined amount of a filler material in a container. The mixing is done for a predetermined mixing time in the range of 0 to 10 hours to obtain a pack mixture. The tungsten substrate is then immersed into the pack mixture. The container with the pack mixture and the tungsten substrate is placed inside the tube furnace containing an atmosphere comprising at least one of an inert gas and a reducing gas. The container with the pack mixture and the tungsten substrate is then subjected to heating in a tube furnace at a predetermined temperature for a predetermined heating time to obtain the master alloy coating deposition on the tungsten substrate.

. Coating the tungsten electrical contact provides oxidation protection to the tungsten electrical contacts and is a viable option for high temperature applications. The coating helps in tackling high temperature oxidation along with wear and tear of tungsten contact surface. Further, the coating helps in enhancing life of an electromechanical horn by protecting the high temperature oxidation resistance coating on tungsten electrical contacts which also improves abrasion, erosion & wear property of contacts. The surface of the tungsten electrical contacts is modified by aluminizing and chromizing of the tungsten material through pack Cementation method. Aluminizing and Chromizing coatings have been selected based on the comparison of melting point and hardness of tungsten oxide (WO3) to the other coatings such as chromic oxide (Cr2O3), aluminum oxide (Al2O3), titanium oxide (TiO2) and silicon oxide (SiO2) to consideration of melting point property. Aluminizing and chromizing the tungsten electrical contacts ensures high temperature stability. Further, aluminizing and chromizing enhances hardness of the tungsten electrical contacts, thereby ensuring the improvement in wear and tear performance of contact surface.

To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 illustrates a diagram of the electromechanical horn, in accordance with an embodiment of the present disclosure;
Figure 2 illustrates a schematic line diagram of a circuit in the electromechanical horn, in accordance with an embodiment of the present disclosure;
Figure 3 illustrates a schematic line diagram of an apparatus for conducting pack cementation process, in accordance with an embodiment of the present disclosure;
Figure 4a illustrates a cross sectional Scanning Electron Micrograph of (a) aluminized and (c) chromized tungsten contact and elemental analysis data from surface of coating to tungsten of (a) aluminized and (c) chromized contact by Energy Dispersive Spectrum data, in accordance with an embodiment of the present disclosure;
Figure 4b illustrates a cross sectional optical image micrograph of (a) aluminized and (b) chromized tungsten contact showing indents made for Vicker’s hardness measurement, in accordance with an embodiment of the present disclosure; and
Figure 5 illustrates a schematic diagram of typical cross section of material after pack cementation process, in accordance with an embodiment of the present disclosure.

Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION OF FIGURES

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

For example, the term “some” as used herein may be understood as “none” or “one” or “more than one” or “all.” Therefore, the terms “none,” “one,” “more than one,” “more than one, but not all” or “all” would fall under the definition of “some.” It should be appreciated by a person skilled in the art that the terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and therefore, should not be construed to limit, restrict or reduce the spirit and scope of the present disclosure in any way.

For example, any terms used herein such as, “includes,” “comprises,” “has,” “consists,” and similar grammatical variants do not specify an exact limitation or restriction, and certainly do not exclude the possible addition of one or more features or elements, unless otherwise stated. Further, such terms must not be taken to exclude the possible removal of one or more of the listed features and elements, unless otherwise stated, for example, by using the limiting language including, but not limited to, “must comprise” or “needs to include.”

Whether or not a certain feature or element was limited to being used only once, it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element.” Furthermore, the use of the terms “one or more” or “at least one” feature or element do not preclude there being none of that feature or element, unless otherwise specified by limiting language including, but not limited to, “there needs to be one or more…” or “one or more elements is required.”

Unless otherwise defined, all terms and especially any technical and/or scientific terms, used herein may be taken to have the same meaning as commonly understood by a person ordinarily skilled in the art.

Reference is made herein to some “embodiments.” It should be understood that an embodiment is an example of a possible implementation of any features and/or elements of the present disclosure. Some embodiments have been described for the purpose of explaining one or more of the potential ways in which the specific features and/or elements of the proposed disclosure fulfil the requirements of uniqueness, utility, and non-obviousness.

Use of the phrases and/or terms including, but not limited to, “a first embodiment,” “a further embodiment,” “an alternate embodiment,” “one embodiment,” “an embodiment,” “multiple embodiments,” “some embodiments,” “other embodiments,” “further embodiment”, “furthermore embodiment”, “additional embodiment” or other variants thereof do not necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or in the context of more than one embodiment, or in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

Any particular and all details set forth herein are used in the context of some embodiments and therefore should not necessarily be taken as limiting factors to the proposed disclosure.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

For the sake of clarity, the first digit of a reference numeral of each component of the present disclosure is indicative of the Figure number, in which the corresponding component is shown. For example, reference numerals starting with digit “1” are shown at least in Figure 1. Similarly, reference numerals starting with digit “2” are shown at least in Figure 2.

Embodiments of the present disclosure will be described below in detail with reference to the accompanying figures.

The present disclosure is focused on enhancing life of electromechanical horn by reducing high temperature oxidation, abrasion, erosion, and wear of tungsten electrical contacts inside the electromechanical horn. The surface of the tungsten contacts is modified by Aluminizing / Chromizing of tungsten material through Halide activated pack cementation process. The pack cementation process is a batch process which includes a chemical vapor deposition technique for imparting corrosion resistance to ferrous alloys. The pack cementation process is used for producing corrosion free and wear resistant coatings on various substrates. Aluminizing / Chromizing process is a diffusion-based process, through which at surface metal atoms of Al/Cr gets diffused having tendency to form oxide layer Al2O3/Cr2O3 faster than tungsten oxide (WO3) and restricts further diffusion of oxygen.

Figures 1 and 2 illustrate working principal of an electromechanical horn 100. Specifically, Figure 1 illustrates a diagram of the electromechanical horn 100, while Figure 2 illustrates a schematic line diagram of a live circuit in the electromechanical horn 100. The electromechanical horn 100 includes a flexible diaphragm 118, a coil 102 of wire that forms an electromagnet, a pair of tungsten electric contacts 105 which act as switch, a fixed nucleus 116, a mobile nucleus 117, a housing 121, and a resonator (not shown). The diaphragm 118, the resonator and other accessories are connected with the mobile nucleus 117 and are collectively known as a diaphragm assembly. The fixed nucleus 116 remains steady creating a gap between the fixed nucleus 116 and the mobile nucleus 117.

When a user presses the switch 101 to blow the horn 100, current passes through the coil 102 from the tungsten electric contacts 105 which generates electromagnetic field, thereby energizing the fixed nucleus 116 and attracts the mobile nucleus 117 towards the coil 102. A back movement of the diaphragm 118 is caused., thereby attracting an armature 104 towards the coil 102 causing inward movement of a flexible diaphragm 118. This inward movement of the armature 104 forces the electrical contacts 105 to open-up, breaking the contact between the electrical contacts 105 and collapsing the electromagnetic field, while the diaphragm 118 moves back to its original position. Thus, it again makes contact between contact points 105 and the whole process repeats until the switch 101 is pressed. This drive mechanism in the electromechanical horn 100 rapidly flexes the diaphragm 118 back and forth at very high frequency, which may range from ?300 to 500 Hz, pushing the air in front of the diaphragm 118 and creating sound waves.

The electrical contacts 105 are generally made up of tungsten, due to its high melting and boiling temperature as well as very high hardness at room and elevated temperatures. Thus, tungsten material provides good abrasion and wear resistance. However, it has poor oxidation resistance above 500 °C. To protect the tungsten electrical contacts 105 from oxidation, the electrical contacts 105 are coated with a master alloy (Aluminium/Chromium) using pack cementation process which may be done by aluminizing (Pack Aluminizing Process) or chromizing (Pack Chromizing Process). The master alloy coating protects the tungsten electrical contacts 105 reduces high temperature oxidation, abrasion, erosion, and wear of tungsten electrical contacts 105 in the electromechanical horn 100. The pack cementation process is conducted in an apparatus as depicted in Figure 3. Specifically, Figure 3 illustrates a schematic line diagram of an apparatus 200 used for conducting the pack cementation process. The apparatus 200 includes a tube furnace 219, a container 211. The tube furnace further includes an Inconel tube 212 which includes an inlet 113 and an outlet 216.

The pack cementation process in the present disclosure is used for development of a master alloy coating on a tungsten substrate, which in the present disclosure are the tungsten electrical contacts 105 for the electromechanical horn 100. The pack cementation process includes mixing of a predetermined amount of a master alloy with a predetermined amount of an activator and a predetermined amount of a filler material in the container 211 to obtain a pack mixture. The mixing of the master alloy, the activator and the filler material is done in the container 211 for a predetermined mixing time, which may range from 0 to 10 hours. This range of the predetermined mixing time helps in obtaining uniform distribution of the pack constituents, i.e., the master alloy, the activator and the filler material, thereby enhancing uniformity and composition of coating thickness. In one embodiment, the activator is a halide-based activator, and may include ammonium iodide or ammonium chloride, while the filler material may be a powder aluminum oxide or silicon dioxide.

In one example, the master alloy may be a powder of Aluminum. The powder of Aluminum is used as the master alloy in a case where the tungsten substrate is to be coated by Pack Aluminizing Process. In such a case, the predetermined amount of the powder of Aluminum may be taken in a range of 15 percent to 40 percent by weight. The predetermined amount of the activator may be taken in a range of 2 percent to 5 percent by weight, while the predetermined amount of the filler material may be taken in a range of 55 percent to 83 percent by weight. Further, the predetermined temperature may be in a range of 750°C to 1100°C, and the predetermined heating time may be in the range of 5 hours to 15 hours.

In another example, the master alloy may be a powder of Chromium. The powder of Chromium is used as the master alloy in a case where the tungsten substrate is to be coated by Pack Chromizing Process. In such a case, the predetermined amount of the powder of Chromium is in the range of 30 percent to 40 percent by weight. The predetermined amount of the activator is in the range of 2 percent to 5 percent by weight, while the predetermined amount of the filler material is in the range of 55 percent to 68 percent by weight. Further, the predetermined temperature is in the range of 900°C to 1200°C, and the predetermined time is in the range of 18 hours to 24 hours.

The tungsten substrate is then immersed into the pack mixture in the container 211. The immersed pair of tungsten substrates (tungsten electrical contacts 105) are spaced apart inside the container 211, and do not make a contact with each other. The container 211 with the pack mixture and the tungsten substrate is placed inside the Inconel tube 212 of the tube furnace 219. In one embodiment, the container 211 is a retort capable of being subjected to heating at high temperatures in the tube furnace 219. The tube furnace 219 contains an atmosphere including an inert gas and a reducing gas. In one embodiment, the inert gas may include 90 percent to 95 percent Argon (Ar) and the reducing gas may include 10 percent to 15 percent Hydrogen (H2). In another embodiment, the inert gas and the reducing gas may be selected based on the application, availability and requirement.

The container 211 with the pack mixture and the tungsten substrate is then subjected to heating in the Inconel tube 212 of the tube furnace 219 at a predetermined temperature for a predetermined heating time to obtain the master alloy coating deposition on the tungsten substrate. The inert gas and the reducing gas may be filled into the Inconel tube 212 through the inlet 113 and may be released from the outlet 216. Heat is supplied to a heating element (not shown) of the tube furnace (219) until the predetermined temperature is reached. While supplying heat to the heating element, two temperature zones are formed in the tube furnace 219 namely, cold zones 210, 214 and a constant temperature zone 209. The temperature at the constant temperature zone 209 is maintained by employing a K-type thermocouple (not shown). The constant temperature zone helps in achieving an efficient coating in terms of thickness uniformity and chemical composition. At the elevated temperature, the master alloy reacts with the activator to produce volatile metal halides which diffuse through the gas phase of the porous pack to deposit into the substrate. The following equation represents the reaction taking place between the master alloy and the activator:

Me (alloy) + AX (S or L)= MeXx (V) + A(L or V)
where,
Me is Cr, Al, or Si,
A is Na, NH4, etc.,
X is F, Cl, or Br, and
S, L and V stand for Solid, Liquid and Vapour states respectively.

Multiple vapor species (V) may be formed for each element, e.g., Al, AIX, AIX2, AIX3, and Cr, CrX2, CrX3, and Si, SiX2, SiX3, and SiX4. Because of unique metallurgical characteristics, each alloy requires a specific pack chemistry to obtain the optimum coating composition. An ideal coating contains sufficient concentrations of the two elements for safe steady-state oxidation/corrosion resistance, without excessive contents which could lead to brittleness, unwanted phase changes and oxidant penetration in service.

Figures 4a and 4b depict initial characterization of the Aluminized/ chromized tungsten substrate 105. Specifically, Figure 4a illustrates a cross sectional Scanning Electron Micrograph of (a) aluminized and (c) chromized tungsten contact, and elemental analysis data from surface of coating to tungsten of (a) aluminized and (c) chromized contact by Energy Dispersive Spectrum data. Specifically, Figure 4b illustrates a cross sectional optical image micrograph of (a) aluminized and (b) chromized tungsten contact showing indents made for Vicker’s hardness measurement.

The coating thickness obtained in an aluminized tungsten substrate may be in a range of 15-30 µm. An average coating hardness of the aluminized tungsten substrate may be 660 HV0.05. Further, the bare tungsten hardness in case of aluminized tungsten substrate may be 570 HV0.05. Further, the coating thickness in a chromized tungsten substrate may be in a range of 25-45 µm. An average coating hardness of the chromized tungsten substrate may be 700 HV0.05. Further, the bare tungsten hardness in case of chromized tungsten substrate may be 570 HV0.05.

The tungsten substrate is coated with a corrosion/wear resistant coating after the pack aluminizing/chromizing process, as depicted in Figure 5. Specifically, Figure 5 illustrates a schematic diagram of typical cross section of the tungsten substrate 105 after pack aluminizing / chromizing. The tungsten substrate 105 has been depicted in which a diffusion layer 108 is formed. The diffusion of metal atoms forms a protective oxide layer 107 on the tungsten substrate 106. The diffusion layer 108 acts as reservoir of Aluminium (Al)/ Chromium (Cr) and forms the oxide layer 107 even if existing oxide layer 107 erodes until there is sufficient availability of Al and Cr in diffusion layer 108.

. Coating the tungsten electrical contact 105 provides oxidation protection to the tungsten electrical contacts 105 and is a viable option for high temperature applications. The coating helps in tackling high temperature oxidation along with wear and tear of tungsten contact surface of the electrical contacts 105. Further, the coating helps in enhancing life of the electromechanical horn 100 by protecting the high temperature oxidation resistance coating on tungsten electrical contacts 105 which also improves abrasion, erosion & wear property of the electrical contacts 105. The surface of the tungsten electrical contacts 105 is modified by aluminizing and chromizing of the tungsten material through pack cementation method. Aluminizing and Chromizing coatings have been selected based on the comparison of melting point and hardness of tungsten oxide (WO3) to the other coatings such as chromic oxide (Cr2O3), aluminum oxide (Al2O3), titanium oxide (TiO2) and silicon oxide (SiO2) to consideration of melting point property. Aluminizing and chromizing the tungsten electrical contacts 105 further ensures high temperature stability. Furthermore, aluminizing and chromizing enhances hardness of the tungsten electrical contacts 105, thereby ensuring the improvement in wear and tear performance of contact surface of the tungsten electrical contacts 105.

While specific language has been used to describe the present disclosure, any limitations arising on account thereto, are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein. The drawings and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. ,CLAIMS:1. A method for development of a master alloy coating on a tungsten substrate (105), the method comprising:
mixing a predetermined amount of a master alloy with a predetermined amount of an activator and a predetermined amount of a filler material in a container (211) for a predetermined mixing time in the range of 0 to 10 hours to obtain a pack mixture;
immersing the tungsten substrate (105) into the pack mixture;
placing the container (211) with the pack mixture and the tungsten substrate (105) inside a tube furnace (219) containing an atmosphere comprising at least one of an inert gas and a reducing gas ; and
subjecting the container (211) with the pack mixture and the tungsten substrate (105) to heating in the tube furnace (219) at a predetermined temperature for a predetermined heating time to obtain the master alloy coating deposition on the tungsten substrate (105).

2. The method as claimed in claim 1, wherein tungsten substrate (105) is a pair of electrical contacts and the pair of electrical contacts do not make a contact with each other.

3. The method as claimed in claim 1, wherein the container (211) is a retort capable of being subjected to the heating in the tube furnace (219).

4. The method as claimed in claim 1, wherein the inert gas atmosphere is composed of 90 percent to 95 percent Argon and the reducing gas atmosphere is composed of 10 percent to 15 percent Hydrogen.

5. The method as claimed in claim 1, wherein the master alloy is one of a powder of Aluminum and a powder of Chromium.

6. The method as claimed in claim 5, wherein the master alloy is the powder of Aluminum and:
the predetermined amount of the powder of Aluminum is in the range of 15 percent to 40 percent by weight,
the predetermined amount of the activator is in the range of 2 percent to 5 percent by weight; and
the predetermined amount of the filler material is in the range of 55 percent to 83 percent by weight.
the predetermined temperature is in the range of 750°C to 1100°C, and
the predetermined heating time is in the range of 5 hours to 15 hours.

7. The method as claimed in claim 5, wherein the master alloy is the powder of Chromium, and:
the predetermined amount of the powder of Chromium is in the range of 30 percent to 40 percent by weight,
the predetermined amount of the activator is in the range of 2 percent to 5 percent by weight; and
the predetermined amount of the filler material is in the range of 55 percent to 68 percent by weight.
the predetermined temperature is in the range of 900°C to 1200°C, and
the predetermined time is in the range of 18 hours to 24 hours.

8. The method as claimed in claim 1, wherein the activator is a halide-based activator.

9. The method as claimed in claim 6, wherein the halide-based activator includes one of sodium fluoride, and ammonium fluoride.

10. The method as claimed in claim 7, wherein the halide-based activator includes one of ammonium iodide, and ammonium chloride.

11. The method as claimed in claim 1, wherein the filler material is one of a powder aluminum oxide and a powder of silicon dioxide.

12. A vehicle horn (100) comprising a tungsten electrical contact (105), the tungsten electrical contact (105) coated with a master alloy, using a method (200) as claimed in claim 1.