ITRM20120461A1 - PLATE FOR PIANO. - Google Patents

Description

PLATE FOR PIANO

DESCRIPTION

Technical field of invention

The present invention relates to an innovative piano plate and to a piano including it.

Background

The piano is a wonderful engineering machine.

The modern piano has six main elements:

â– the â € œcaseâ € or the container made of a wood that plays a role in the resonance characteristics of the instrument;

â– the â € œframeâ € or harp or plate, made of gray lamellar cast iron to support the load of the strings; the plate of a small-tailed piano can weigh about 180 kg; a modern piano can have up to 230 strings with a tension of 15 to 30 tons;

â € œsoundboardâ € or soundboard, which is made of beech wood and serves to amplify the vibration of the strings which transmit the vibration to the soundboard with the pressure on two bridges of harder wood fixed to the soundboard itself ;

â– the â € œactionâ € or the mechanics, which is the series of levers that allow to transmit the action of the finger, when the fret is lowered, to the hammer that strikes the string.

In 1725, the German Daniel Faber built the first unbound clavichord, that is, having a fret for each string.

Many essential characteristics of the modern piano are inherited from the clavichord. This instrument had in fact metal strings, a percussion device to put the strings in vibration, a damping mechanism and an independent soundboard. The latter, placed at the bottom of the mobile "case" of the piano, was in fact not used like the frame, to keep the strings in tension.

Although the intensity of the sound produced was not high, the instrument expressed a good dynamics: that is, it allowed the execution of more or less intense notes.

Around the same time another precursor to the modern piano was developing: the harpsichord, invented by the Viennese Hermann Poll (1370-1401). It was essentially characterized by the introduction of longer strings and a soundboard of greater surface with the result of the production of more intense notes.

In the seventeenth century the most important builders of this instrument (such as Hans Ruchers, Portalupi, Rigoli, Taskin Kirchmanne Hildebrant) built harpsichords with many important innovations that have come down to the modern piano, such as the wing-shaped case, then typical of a coda, more than one string per note to increase the volume of the sound.

A remedy for these defects was devised by the Italian harpsichord maker Bartolomeo Cristofori, who in 1709 called this original instrument "gravecembalo col piano et forte", meaning that it could be played at both low and high volume. and the mechanics of the piano were greatly perfected.

However, these instruments could not vibrate heavy strings and the cases were not very strong to withstand the tension of the strings.

Only in 1825 Alpheus Babcock patented in Boston the first fusion frame for piano, made of cast iron.

The development of the cast iron frame - and particularly of the part of the frame known as the plate, which serves to hold the strings inside the piano - gave the piano sound much greater brilliance and power.

The modern frame is made up of a single piece of cast iron that bears all the tension of the strings. For example, in a large concert grand piano the frame weighs around 200 kg and is subjected to a tension of over 30 tons.

The frame of a piano must have specific properties that may appear contrasting with each other, in particular:

â ’its structure must be rigid but it must also maintain a certain flexibility;

∠’must have sufficient mass to favor the low frequencies, but must not hinder the high ones;

∠’must be built with a material with a low coefficient of thermal expansion, to minimize the changes in tension of the strings and therefore of the vibration frequencies with the temperature;

∠’must have a shape that leaves room for the various components of the mechanics; And

∠’must be built in such a way that no resonant frequency can interfere with the frequency range of the instrument.

Traditionally, the frame of the piano is produced with a process of so-called â € œfondery in the groundâ €, well known for a person skilled in the art. It involves a casting made using the method of compressed wet sand inside a stirrup. The cavity created by the removal of the Model is then poured.

However, the use of this method has some drawbacks.

The temperature difference between the molten metal and the wet sand weakens the resulting structure, creating residual internal stresses.

Measurement accuracy, particularly at the contours of the cavity, is compromised.

The surface is rough, making the plate, which is normally in plain sight, unsightly to the point that a series of grouting is required to make it pleasant.

Furthermore, any hot decorations applied during the casting process are imperfect.

Technology has eliminated many of these drawbacks by modifying the process, and in particular by applying a certain level of vacuum. In this case, a shape is first built, using the vacuum principle to firmly hold the very fine dry sand. The merger is then done. The resulting product has a uniform and smooth surface.

This variant of the method is very expensive so as to induce many foundries to give up production.

Summary of the invention

The technical problem posed and solved by the present invention is therefore that of providing a plate for piano which allows to obviate the drawbacks mentioned above with reference to the known art, and in particular a light plate with optimal mechanical and damping properties which can be achieved by means of innovative technologies. .

This problem is solved by a piano plate according to claim 1.

Preferred features of the present invention are the subject of the dependent claims.

The invention proposes to make the piano plate in a composite material reinforced with carbon fiber.

Replacing the cast iron plate with a carbon fiber reinforced composite plate has significant advantages.

First of all, the weight is extremely low. Indeed:

∠’the average density of the cast iron is 7.8 g / cm <3>, while the density of the composite material is generally included in a range of 1.5-1.8 g / cm <3>);

∠'for a cast iron plate, of a generic small grand piano, with a thickness varying from 5 to 6 cm, the weight would be around 180 kg, while the weight of a plate made of composite material of the same size becomes 39.2 kg considering the density of the new material of 1.7 g / cm <3>, with the same performance.

Furthermore, cast iron is more brittle than composite material. The latter has better resistance characteristics than cast iron.

Furthermore, a composite plate has, for the same performance, a lower thickness than that which cast iron must necessarily have and therefore an even lower weight which has a positive effect on the total weight of the frame and therefore on the cost.

Another advantage is the hygroscopicity: the composite material does not absorb the humidity of the environment.

Other advantages, characteristics and methods of use of the present invention will become evident from the following detailed description of some embodiments, presented by way of non-limiting example.

Detailed description of preferred embodiments

The piano plate according to the invention is made of composite material reinforced with carbon fibers.

Materials used

Preferably, the composite material reinforced with carbon fibers used â– Peek carbon fiber, also known as polyether-ether-ketone, ie Peek reinforced with carbon fibers.

â– Prepreg, also known as prepreg, or composite material (epoxy resin or Peek) reinforced with unidirectional, multiaxial or fabric carbon fiber.

Peek, unidirectional or random carbon fiber reinforced polyether ether ketone, is a semicrystalline thermoplastic polymer which, for the realization of the plate according to the invention, is supplied in sheets.

It has the following properties and advantages:

∠’has excellent strength, rigidity and dimensional stability even in the presence of high temperatures and in difficult work environments;

∠’It is easy to transform, it has a lower density than materials such as steel, aluminum and titanium;

∠’has a low coefficient of friction and high wear resistance without the need for lubrication;

∠’It is chemically resistant and insoluble in all major common solvents including acids, salts and oils;

∠’has low gas emissions, low particle generation and intrinsic purity;

∠’has mechanical traction and compression characteristics comparable to those of cast iron;

â ’can be processed using injection presses and molds;

∠’can be transformed by extrusion compression sintering.

As for the prepreg or prepreg, prepreg materials are unidirectional, multiaxial or woven carbon fiber reinforced composites.

The types of prepregs today for advanced use are made of modified thermosetting epoxy resin or semi-crystalline thermoplastic peek.

The fibers (or reinforcement) represent the structurally active part and the matrix (the resins) has no mechanical resistance tasks, but must guarantee cohesion between the various fiber layers.

The union of the resin or polymer to the reinforcement (whether it consists of unidirectional, multiaxial fibers or fabrics) is carried out in a phase prior to the execution of the piece itself in special ovens where the material is partially polymerized at of polymerization which oscillates between 45 ° and 180 ° C. This operation provides the product with the necessary compactness, totally eliminating residual air bubbles and guaranteeing subsequent workability without altering its characteristics.

Resin systems in these materials react very slowly at room temperature, guaranteeing very long processing times (days or even months). Resins for prepregs can only fully catalyze if cooked with the pre-set cooking cycles. They are characterized by having:

- excellent fiber-resin (or fiber-polymer) adhesion,

- high mechanical resistance and flexibility,

- resistance to creep and fatigue phenomena,

- chemical resistance,

- good electrical properties.

Since the methods of making prepreg materials are well known to a person skilled in the art, we will not dwell further on this aspect.

Plate forming technology

Which plate forming technology can be envisaged:

- a 3D technology - CaD, or

â ’mechanical processing starting from a composite sheet.

As for the 3D-CaD technology with prepreg material, this technology derives from the technology developed for the production of aeronautical, aerospace or vehicle chassis parts.

In the case of the plate of the invention, the design is developed in prepreg, considering long fiber composite materials suitably oriented and dispersed in the polymeric matrix (epoxy resin or peek) studied in order to have damping characteristics.

The resulting structure must have characteristics of non-deformability, even over time, and inert to any environmental condition, have characteristics of robustness, mechanical resistance, to withstand the loads of the ropes, dimensional stability both in the initial phase and over time and anigroscopicity.

In the manufacturing technology considered here, the entire process underlying the construction of the composite plate is controlled by computer tools, both in the design phase (cad) and in the construction phase (cam). In particular, the phases and design criteria described below are envisaged.

- We start from the 3D modeling of a gray lamellar cast iron plate, now used in all pianos; in the realization of the prototype, since the plate will be mounted on a traditional piano it is necessary to consider the plate of a commercial piano.

- The aluminum thermoforming mold is designed, taking into account that the new carbon fiber composite plate must have the conventional external shape to fit the shape of a traditional piano.

- The cut material is printed in the reference shape (mold) with a curing cycle at controlled temperature and pressure obtained through an autoclave containing the mold material assembly. The cure cycle can be carried out at a temperature between 0 and 150 ° C.

- In a plate of a piano made of cast iron there are load-bearing bars that serve to lighten the structure and to withstand the heavy load of the strings (15 or 20 tons in total). Since there are about 200 strings, each one has a tuning load of about 10 kg. The plate of the invention does not necessarily have to have the same design as that of the known cast iron plates (without prejudice to the external dimensions), but it can be modified during construction by adapting to the characteristics of the new material.

- The cast iron plate requires the insertion of â € œpinsâ € (ie the grips of the strings) by simply beating the plate. These are inserted easily and angled against the pull of the strings. The insertion of the pins in the prepreg constitutes a design reason and preventive tests. In particular, the pins can be inserted on a metal plate and the latter embedded entirely in the body of the prepeg. Preliminarily to this drowning, one possibility of realization foresees that the plate + pins together are superimposed, and in particular wrapped on them, fabrics - for example similar to socks - pre-impregnated with carbon fibers. In this way it is possible to guarantee the continuity of the fiber through all the junction points and therefore it is possible to transfer loads to the composite not only for shear stresses, but above all for shape constraints that make the fibers work in traction.

- The functional prototype is created which is used to be subjected to tests and to simulate the conditions of use of the finished object, in the specific case to calculate the resistance to the stress of the ropes and make the appropriate interventions and to improve the local mechanical resistance and consider the designer's variations from the original plate without prejudice to the external shape. For series production, once the plate has been optimized, the application of the so-called â € œReverse Modelingâ € process allows you to obtain a digital report of the project.

- The finished piece is installed in the chosen piano, the strings and other accessories are assembled in a qualified laboratory and the tensions and the resonance charge of the soundboard are checked. A spectrographic examination of the sound curve is performed before and after assembly.

- The tests are performed with different voltage loads from 430Hz to 444Hz bearing in mind that 440Hz correspond to 20 Tons of voltage.

As regards the production of a piano plate with the technology with mechanical processing starting from a composite plate, in the present embodiment the composite material Peek carbon fiber with unidirectional or prepreg randon fiber is used.

The Peek plates are mechanically worked to take the shape of the piano plate, so suitably shaped and equipped they are assembled with the strings, rehearsed on a traditional piano deprived of the harp.

The present invention has been described heretofore with reference to preferred embodiments. It is to be understood that other embodiments may exist which pertain to the same inventive nucleus, as defined by the protection scope of the claims reported below.

Claims (9)

CLAIMS 1. Piano plate, characterized in that it is made of a composite material comprising reinforcing carbon fibers. Piano plate according to claim 1, wherein said composite material is selected from a group comprising: Peek carbon fibers (polyether-ether-ketone) and pre-impregnated materials (e.g. epoxy resins and Peek). Piano plate according to the preceding claim, wherein said pre-impregnated material comprises Peek or a modified thermosetting epoxy resin reinforced with unidirectional, multiaxial or woven carbon fiber. 4. Piano plate according to any one of the preceding claims, in which said carbon fibers have a unidirectional orientation. 5. Piano plate according to any one of the preceding claims, in which said carbon fibers have a random orientation. 6. Piano plate according to any one of the preceding claims, in which said carbon fibers have a fabric or multiaxial orientation. 7. Piano frame, comprising a plate according to any one of the preceding claims. Piano frame according to the preceding claim, wherein only the plate is made of a composite material comprising carbon fibers. Piano comprising a plate according to any one of claims 1 to 5 and / or a frame according to claim 6 or 7.