EP2443625B1 - Method for producing a metal sound musical instrument - Google Patents

Description

The invention relates to a method for producing a metal sound musical instrument, in particular a so-called Hang®. The term Hang® is protected as a registered trademark in several countries.

The Hang® is a lenticular musical instrument that belongs to the idiophons. It consists of two connected shells made of treated sheet steel. Both halves are tuned into a harmonious whole by hammering similar to the Steelpan Trinidads. On the upper half shell are clay fields, which are incorporated with hammers in the sheet metal.

The playing possibilities of the Hang® are very versatile. The builders have tuned it so that it can develop its fullness on the player's lap. It is played with the fingers and hands, which gave the name: Hang is Bern German for hand. The instrument was developed in 2000 by two Swiss instrument makers.

The body of the Hang® has in particular a diameter of about 53 cm and a height of about 24 cm. On the one upper side, seven sound fields are arranged in a circle around a sound field lying in the middle, the thing. Opposite, in the middle of the lower half-shell, is the Gu, a hand-sized, round resonance opening with an inwardly drawn neck. But other dimensions and training are possible.

The upper half shell of the Hang® is also referred to as the Ding side, the lower half as the Gu side.

Until 2007, the Hang® was offered in a variety of sound models. They differ in the pitch of the thing (between D3 and B3), the number of tone fields in the tone circle (seven or eight) and the tuned tone scale (between Ges3 and F5). Since 2008, only one model, the integral Hang®, has been built.

More information about the Hang® can be found in the Internet Dictionary Wikipedia, from which most of the above information comes from.

When playing the Hang®, surprisingly well-sounding, gong-like sounds with high dynamics are generated. However, it is desirable to achieve a more balanced sound and to refine the multi-dimensionality of the sound. It was found that the sound quality of the Hang® is closely related to the internal structure of the material used and its strength, which in principle is already familiar to players of brass instruments. The object of the invention is therefore to expand the sonority of the instrument.

From the Swiss patent no. 693319 (Panart Steelpan-Manufaktur AG), as well as from the document " History, Development and Tuning of the Hang ", ISMA 2007, pages 1-8, by Felix Rohner et al, a method for the production of Blechklang musical instruments is known in which after some mechanical preliminary work, starting from a steel sheet, a hardening of this sheet is made. As the hardening method, the patent mentions gas nitriding, nitrocarburizing in gas at 550 to 650 ° C, nitrocarburizing in the bath at 560 to 620 ° C and plasma nitriding at 400 to 600 ° C.

It is in the o.g. These documents describe that in these nitrations a surface hardening of the deep-drawn sheet metal cutout used as starting material is achieved, and that a soft ferritic inner layer remains between the two hardened surface layers.

Surprisingly, it has now been found that exhaustive nitration, ie nitration also of the inner ferritic layer, gives the desired new sound quality; Furthermore, it is surprising and could not be expected that even the rather soft sound dynamics is not lost when playing the instrument properly, but is even increased.

Such continuous nitration increases the intrinsic and energy storage capacity of the material, allowing for a smooth, harmonious sound quality even when the instrument is played with bare hands.

Continuous nitriding increases the strength, elasticity and stiffness of the material, which means more design options for the instrument maker, such as more opportunities for residual stress and tuning.

Accordingly, the inventive method is defined in the first independent claim. Particular or preferred embodiments form the subject of dependent claims. Furthermore, the present invention also includes the metal sound musical instrument obtained by the new method.

The method according to the invention is characterized by a complete nitration of the material of which the metal-tone instrument consists, as will be explained in detail below. The nitriding of steel has long been known for the purpose of improving its mechanical properties. There are many different nitration processes, some of which differ only slightly from each other. An overview of steel nitriding can be found in Hardening Manual, chapter Nitriertechniken, Rübig u. Ipsen, EFD hardening workshop, EVS archive 2006 ,

Nitration can be done in a variety of ways. The success of the process according to the invention does not depend on the type of nitriding process. Nitration may be carried out as gas nitriding using nitrogen donating compounds such as ammonia, hydrazine, etc., by nitrocarburizing (less preferred), by plasma nitriding, by vacuum nitriding, etc. These methods are known to the person skilled in the art.

Generally, nitration occurs at elevated temperatures. The nitration in the gas phase using ammonia proceeds at a Temperature from 380 to 600 ° C from; For (non-preferred) nitrocarburizing, temperatures between 550 and 620 ° C are recommended. The nitriding must be continued until the sheet is completely nitrated; Nitration times of more than 100 hours may be required, which of course depends on the thickness of the sheet used. The present process generally uses sheets having a thickness of 0.75 to 1.25 mm, usually those having a thickness of 0.9 or 1 mm. Of course, there is a relationship between duration, concentration of nitrating agent, temperature and workpiece thickness; ideal conditions can be easily determined by simple experiments.

The nitriding according to the invention is carried out in such a way that the starting sheet metal part is "exhaustively" nitrided, as it were. the nitriding is carried out under conditions under which a soft inner layer, generally a ferritic layer, remaining in the prior art is also nitrided. The conditions of such exhaustive nitration are generally stricter conditions with respect to conventional surface nitriding, for example longer nitriding times (more than 100 hours), higher gas density in gas nitriding, higher temperatures (there being an upper limit which should not be exceeded since then the nitrides formed begin to disintegrate again), choice of thinner plates for the instrument, choice of suitable alloyed steels, etc. The through-nitriding can also be faster, but it has been found that the acoustic quality of the material is much higher if the Durchnitrierung slower is carried out. This is due to the increased anisotropy and uniform distribution of the nitride needles formed thereby as well as the increased uniformity of the lengths of these needles. As the nitride needles form more slowly, they can also grow through grain boundaries of the material (e.g., steel), thus causing a fundamental change in the physical properties of the material.

The nitrided metal also allows better control of the machining boundary conditions as well as increased solidification capability. This is important if the metal is tempered after and / or during processing or tuning.

Whether the chosen conditions lead to complete nitration can easily be determined by an analysis, for example by creating a micrograph which is then suitably dotted or deep etched. The analysis is completed by observing the micrograph under the microscope.

As is known, during nitriding, for example during gas nitriding in an ammonia atmosphere, first of all a so-called bonding layer is formed on the two surfaces, in which a lot of iron as ε-nitride (Fe ₂ N • Fe ₃ N) and γ-nitride (Fe ₄ N )). Inwardly, the so-called diffusion zone or precipitation layer closes, in which needle-shaped nitrides are precipitated and embedded in an iron matrix. The basic structure present in a partial nitration according to the invention is not present here because of the continuous nitration.

For the success of the process according to the invention, it is important that the acicular iron nitrides be found throughout the structure of the nitrided sheet (with the exception of the two tie layers); this is proof that continuous nitration has taken place. In particular, the aim is to achieve a certain density of the precipitated crystal needles; it has been found that the best sound characteristics are produced in a certain density range, which will be specified below.

und wenn die Fläche F in m² und die Länge L in m ausgedrückt wird, hat D_L die Dimension m^-1.Since it is very difficult to determine the number of needles of iron nitrides (and also the nitrides of the accompanying elements, such as manganese) in a unit volume, the needle density is detected and specified according to a proposal by the inventor as so-called linear density. In this case, a micrograph of a cut of the material is produced and suitably etched to make the needles visible. Suitable etchant is an alcoholic solution of nitric acid ("Nital"). Subsequently, the needles are counted in a certain surface area (where a number N is obtained) and their average length L determined. Finally, the product of average length L and the number N is divided by the area F under consideration. The linear needle density DL is thus defined as $${\mathrm{D}}_{\mathrm{L}}=\mathrm{N}\times \mathrm{L}/\mathrm{F}.$$

and when the area F is expressed in m ² and the length L in m, D _{L has} the dimension m ^-1 .

Another possibility for relating the generated sound image of the finished instrument to the continuous nitration procedure is to determine the area fraction of the precipitated iron nitride crystals on the total area of a sectional image. For this it is of course necessary to determine not only the length L of the individual crystal needles, but also their (average) width.

An image serving this purpose can be obtained, for example, by the use of the SEM (SEM = Scanning Electron Microscopy) technique. For this purpose, a SEM image is created on a section of the material, and the area fraction of the crystal needles is obtained either by electronic processing of the gray values of the image (the precipitated crystals appear brighter than the iron matrix) or by color analysis of a stained sectional image.

The test methods mentioned are executed quickly and give good indications of the final properties to be achieved. An estimation of the accuracy of both analysis methods yields about ± 10%, which is quite sufficient in practice. It is easily possible to refine the methods to obtain more accurate values, but this is usually not necessary and only leads to higher costs.

Investigations on several steel samples have shown that the preferred properties of the finished instrument according to the invention, which are based on the Durchnitrierung, with density values of 40 • 10 ³ m ^-1 to 80 • 10 ³ m ^-1 and with surface fractions of iron nitrides of 10 to 50% be achieved.

The finished nitrided steel sheets can be blued before, during and after further processing for the purpose of preventing corrosion as well as beautifying the appearance. That's what you do

Workpiece or instrument in a bluing bath. Such a bath consists, for example, of 3500 ml of water, 1700 g of NaOH, 105 g of NaNO ₂ and 450 g of NaNO ₃ . The workpiece is placed in the bath (25 ° C) and taken out once the desired blueness has occurred.

The invention will now be further explained by a method example. It should be noted that this example does not limit the invention, neither in terms of the choice of materials and aids, nor in terms of the process conditions used.

example

The mechanical conditions and process steps largely correspond to the example which is described in the patent CH-693 319 is specified. For details, reference is made to this document.

A circular deep-drawn sheet with a diameter of 80 cm and a thickness of 0.9 mm was deep-drawn over a steel dome with a diameter of 600 mm and a height of about 215 mm. The material of the sheet was DC04 steel (0.08% C max, 0.03% P max, 0.03% S max, 0.04% Mn max, balance C, Rm 270-350 N / mm ² , Re 210 N / mm ² , elongation 38% min.). Two steel shells were made in a completely identical way.

The two obtained deep-drawn steel shells were cut to form a foldable edge, which was folded up. After thorough cleaning, the workpieces were then placed in a gas nitriding furnace where they were nitrided at a temperature between 570 ° C. and 585 ° C. for 145 hours in an ammonia atmosphere (pressure 2.8 bar).

After slow cooling to room temperature, the one shell according to the example of the patent CH-693 319 processed into the finished Hang®. The instrument was characterized by a full sound with a strongly metallic, almost blaring timbre, which could be slightly reduced and amplified while playing.

The second steel shell was cut diametrically and small samples were prepared by conventional techniques for micrographs. The linear density of the precipitated iron nitride crystals was determined to be 58,500 m ^-1 and the area ratio of the crystals to 21%. The precipitated crystals were distributed almost uniformly over the entire cross section of the sheet, with the exception of the two surface layers, which represent the connecting layer and had an average thickness of 22 .mu.m. These layers were detected by spotting with a 12% aqueous solution of cupric ammonium chloride ((NH ₄ ) ₂ [CuCl _4] .2 • H ₂ O) at 25 ° C.

The invention can be further perfected and modified, and these changes, which are made by those skilled in the art, are within the scope of protection. In particular, all the nitriding methods described in the above-discussed patent CH-693 319 described and / or claimed, are also applied in the inventive method after appropriate adjustment.

Claims (13)

1. Method for production of a metallic-sounding musical instrument, which has a vibration-producing sheet metal membrane, in the method (a) a steel sheet blank being deep-drawn, forming a sheet metal membrane, (b) the sheet metal membrane obtained being hardened by nitriding and (c) the hardened sheet metal membrane being joined to a second piece of shaped sheet metal to form a hollow instrument body, characterised in that the nitriding mentioned in step (b) is carried out under conditions which result in a thorough nitriding throughout of the sheet metal membrane.
2. Method according to claim 1, characterised in that the nitriding is carried out with treatment periods of over 100 hours.
3. Method according to claim 1 or 2, characterised in that the nitriding takes place by gas nitriding in an ammonia atmosphere.
4. Method according to claim 1 or 2, characterised in that the nitriding is carried out by plasma nitriding at 400°C to 600°C.
5. Method according to one of the preceding claims, characterised in that nitriding is carried out to a linear density of precipitated needle-shaped iron nitride crystals in the range of 40000 to 80000 m^-1.
6. Method according to one of the claims 1 to 4, characterised in that nitriding is carried out to an area proportion of precipitated needle-shaped iron nitride crystals in the range of 10% to 50%.
7. Method according to one of the preceding claims, characterised in that the complete nitriding throughout is determined by measurement of precipitated iron nitride crystals on polished micrograph sections of the nitrided workpieces.
8. Method according to one of the preceding claims, characterised in that the nitrided workpiece is subjected to a surface bluing procedure.
9. Metallic-sounding musical instrument, which has a vibration-producing sheet metal membrane, the sheet metal membrane being hardened by nitriding, and the hardened sheet metal membrane being joined to a second piece of shaped sheet metal to form a hollow instrument body, characterised in that the sheet metal membrane is thoroughly nitrided throughout.
10. Metallic-sounding musical instrument according to claim 9, the sheet metal membrane being nitrided to a linear density of precipitated needle-shaped iron nitride crystals in the range of 40000 to 80000 m^-1.
11. Metallic-sounding musical instrument according to claim 9, the sheet metal membrane being nitrided to an area proportion of precipitated needle-shaped iron nitride crystals in the range of 10% to 50%.
12. Metallic-sounding musical instrument according to one of the claims 9 to 11, the sheet metal membrane being surface blued.
13. Metallic-sounding musical instrument according to one of the claims 9 to 12, the musical instrument being lens-shaped.