Plate for piano

Abstract

 A piano comprising a plate made of a composite material including, or not, unidirectional, multiaxial or woven-material like carbon fiber, in particular preimpregnated materials (resin or Peek).

Description

Technical Field of the Invention

[0001] The present invention relates to an innovative plate for piano and to a piano including it.

Background

[0002] The piano is a wonderful engineering machine.

[0003] The modern piano has six main elements:

■ the "case" or the container made of a wood which plays a role in the instrument's resonance features;

■ the "frame" or harp or plate, made of lamellar grey cast iron to support the load of the chords; the plate of a baby grand piano can weigh about 180 kg; a modern piano can have up to 230 chords with a a tension from 15 to 30 tons;

■ the "soundboard", or harmonic board, which is made of fir (or red fir) wood and it is used to amplify the vibration of the chords which transmit the vibration to the harmonic board with the pressure on two bridges made of heavier-wood fastened to the harmonic board itself;

■ the "action" or the mechanisms which is the series of levers allowing to transmit the action of the finger, when a key is lowered, to the hammer hitting the chord.

Piano History

[0004] The modern piano derives from harpsichord. Under the term harpsichord a family of stringed musical instruments, equipped with keyboard, is designated. These instruments generate the sound by plucking the chord by means of a psaltery which has indeed the function of plucking the chords.

[0005] The harpsichord, invented by the Viennese Hermann Poll (1370-1401), mainly characterized by the introduction of longer chords and an harmonic board with larger surface with the result of producing more intense notes.

[0006] In XVII^th century the most important manufacturers of this instrument (such as Hans Ruchers, Portalupi, Rigoli, Taskin Kirchmanne Hildebrant) built hapsichors with many important innovations which have arrived up to the modern piano, such as the wing-shaped case, typical then of grand pianos, more than a chord per note to increase the sound volume.

[0007] In 1688 the first piano model was implemented by Bartolomeo Cristofori, of Padua, at the Florentine court of Cosimo Terzo de' Medici. Precisely, it was a "gravicembalo col piano e forte", towards the end of '700 called under the name of "fortepiano". The novelty was the application of a hammer mechanism to the harpsichord.

[0008] Cristofori's idea was to create a harpsichord with dynamic possibilities which could be controlled by the performer; in the harpsichord, in fact, the plucked chords do not allow controlling the dynamics (even for this reason, piano and harpsichord do not belong to the same subfamily).

[0009] In order to increase the sound volume thereof, the chords needed to have a larger thickness and a more robust supporting structure so as to support great inner tensions which had created.

[0010] The piano frame, commonly made of wood, became thicker and heavy and it was reinforced with crossed supports.

[0011] In 1808 Broadwood (who in 1783 had already patented the pedals of the "piano" and of the "forte") for the first time adopted metallic reinforcements on the frame and in 1820, Thomas Allen started using metallic tubes to keep the chords in tension. The use of metal was becoming more and more predominant.

[0012] In 1825 Alpheus Babcock patented the first metallic plank, made of cast iron (obtained by melting). The development of the cast-iron frame - and in particular of the frame portion known as plate, which is used to keep the chords inside the piano - conferred on the piano sound definitely better brilliance and power.

[0013] Later, in 1843, the American Jonas Chickering started manufacturing the pianos with the whole periphery made of metal, feature of the modern grand pianos.

[0014] Grand pianos started to be mass-produced in 1850, with the factories of John Broadwood & Sons, Jonas Chickering, Julius Blüthner, Ignaz Bosendorfer, Friedrich Bechstein, Henry Steinway, e Sebastien Erard, these companies wholly developed the bases of modern mechanisms of grand piano.

[0015] The modern frame is constituted by a single cast-iron piece supporting the whole tension of chords. For example, in a big concert grand piano the frame weighs about 200 kg and it is subjected to a tension higher than 30 tons.

[0016] The frame of a piano must have specific properties which can appear to be contrasting therebetween, in particular:

• the structure thereof must be rigid, but it must even keep a certain flexibility;
• it must have sufficient mass to favour low frequencies, but it must not obstruct high ones;
• it must be constructed with a material having a low thermal expansion coefficient, to minimize the changes in tension of chords and therefore vibration frequencies with temperature;
• it must have a shape leaving space to the various components of the mechanisms; and
• it must be constructed so that no resonance frequency can interfere with the instrument frequency range.

[0017] Traditionally, the piano frame is produced with a process of so-called "inland foundry", well known to the person skilled of art. It involves a melting performed by using the method of wet sand compressed within a stirrup. The cavity created by the Mould removal is then cast.

[0018] However, the use of this method has some drawbacks.

[0019] In particular, the temperature difference between melt metal and wet sand weakens the resulting structure, by creating inner residual tensions.

[0020] Furthermore, the measuring precision, in particular at the cavity outlines, is compromised.

[0021] Still, the surface results to be wrinkled, by making the plate, which usually is clearly visible, so antiaesthetic that a series of fillings is needed to make it nice-looking.

[0022] At last, any hot decoration applied during the melting process results to be imperfect.

[0023] The technology has removed many of these drawbacks by modifying the process, and in particular by applying a certain void level. In such case, first of all a shape is constructed, by using the void principle to keep firmly the very fine dry sand. Subsequently melting is performed. The resulting product has a uniform and smooth surface.

[0024] However, this method variant is very expensive so as to induce many foundries to renounce to production.

Summary of the Invention

[0025] The technical problem placed and solved by the present invention is then to provide a plate for piano allowing to obviate the drawbacks mentioned above by referring to the known art and in particular a light plate with optimal mechanical and dampening properties which can be implemented by means of new technologies.

[0026] Such problem is solved by a piano plate according to claim 1.

[0027] Preferred features of the present invention are subject of the depending claims.

[0028] The invention proposes implementing the piano plate in a single piece - that is as monolithic structure - made of a composite material reinforced with carbon fiber.

[0029] The replacement of the cast iron plate with the one made of composite reinforced with carbon fiber involves considerable advantages.

[0030] First of all, the weight results to be extremely reduced. In fact:

• the cast iron average density is 7.8 g/cm³, whereas the composite material density is generally comprised in a range of 1.5-1,8 g/cm³;
• for a cast iron plate of a general baby grand piano, with a thickness variable from 5 to 6 cm, the weight would be about 5 out of 180 kg, whereas the weight of a plate made of composite material of same sizes becomes 39.2 kg by considering the density of the new material of 1.7 g/cm³, performances being equal.

[0031] Furthermore, cast iron is more fragile than composite material. The latter has better resistance features than cast iron.

[0032] Still, a plate made of composite, the performances being equal, has a smaller thickness than the one which cast iron necessarily must have and therefore a much lower weight reflecting positively on the frame whole weight and then on costs.

[0033] Another advantage is anhygroscopicity: the composite material does not absorb humidity in the environment.

[0034] Other advantages, features and application modes of the present invention will result to be evident from the following detailed description of some embodiments, shown by way of example and not for limitative purposes.

Detailed description of preferred embodiment

[0035] The plate for piano according to the invention is implemented in one single piece, made of a composite material reinforced with carbon fibers.

Used materials

[0036] Preferably, the used composite material reinforced with carbon fibers is:

■ Peek carbon fiber, even known as polyether-ether-ketone, that is Peek reinforced with carbon fibers;

■ pre-impregnated resin (Prepreg), that is a composite material made of thermosetting resins (Phenolic, Epoxy) or thermoplastic (polyester) or Peek reinforced with unidirectional, multiaxial or braided woven (thin or large wefts or hybrids) carbon fiber;

■ resin added to the dry tissue.

[0037] Peek, polyether-ether-ketone reinforced with unidirectional or random carbon fiber is a thermoplastic semi-crystalline polymer, it has the following properties and advantages:

• it has excellent resistance, stiffness and size stability even in presence of high temperatures and in difficult working contexts;
• easy to transform, it has lower density than materials such as steel, aluminium and titanium;
• it has low friction coefficient and high wear-resistance without lubrication needing;
• it is chemically resistant and insoluble in all main common solvents, including acids, salts and oils;
• it has low emissions of gas, low generation of particles and an intrinsic purity;
• it has tensile and compression mechanical features which can be compared to those from cast iron;
• it can be processed by using injection presses and moulds;
• it can be transformed by extrusion, compression, sintering.

[0038] As far as resin-fiber composite is concerned, these materials are no more than composite materials reinforced with unidirectional, multi-axial or braided woven carbon fibers, as explained above (page 5, lines 15-20). The prepreg types nowadays for advanced use are formed by modified thermosetting epoxy resin or by semicrystalline thermoplastic peek.

[0039] The fibers (or reinforcement) represent the structurally active portion and the matrix (the resins) has no tasks of mechanical resistance, but it has to guarantee the cohesion between the several fiber layers.

[0040] The union of resin or polymer to the reinforcement (whether it is constituted by unidirectional, multi-axial or woven fibers) is made in a phase preceding the implementation of the piece itself in suitable ovens wherein the material is partially polymerised with polymerisation temperature ranging between 45° and 180°C. This procedure provides to the product the necessary compactness, by wholly removing residual air bubbles and by guaranteeing the subsequent workability without altering the features thereof.

[0041] The resin systems in these materials react very slowly at room temperature, by guaranteeing very long working time (days or even months). The resins for preimpregnated materials may catalyse completely only if baked with the preestablished baking cycles. They are characterized in having:

• optimum fiber-resin (or fiber-polymer) adhesion,
• high mechanical resistance and flexibility,
• resistance to creep and fatigue phenomena,
• chemical resistance,
• good electric properties.

[0042] Since implementation modes of preimpregnated materials or dry tissues are well known to a person skilled in the art, one will not dwell upon this aspect.

Plate formation technology

[0043] Possible plate formation technologies:

➢ 3D - CAM technology, which processes the detail geometry for implementing the prototypal model until forming the plate rolling equipment. Once processed the piece geometry the plate can be implemented with three possible technologies.

(a) manual rolling of preimpregnated tissue with epoxy/phenolic resin on suitable mould: it is the most common solution for components with complex geometry assuming the use of tissue containing resin on moulds specifically created, then cured in autoclave and at last trimmed; this method, however, is suitable for simple geometries, provided that there are limited productive volumes;

(b) forming of thermoplastic tissue: a tissue made of carbon fiber is used wherein the epoxy resin is replaced by a thermoplastic polymer and the wished shaped is given thereto thanks to a classical heated mould of matrix-punch type inside a press; it is particularly suitable for producing simple components with high volumes;

(c) RTM ("Resin Transfer Moulding"): a hybrid method between the previous ones, wherein dry tissues are used arranged in a mould which, once rolling has ended, is closed sealingly to receive the resin injection; it is suitable for components with intermediate complexity and with good productive volumes.

➢ Mechanical processing starting from composite sheet.

[0044] As far as the implementation of a piano plate with the technology with mechanical processing starting from composite sheet is concerned, in the present embodiment the composite material Peek carbon fiber with unidirectional random fiber, or prepreg provided in sheets, is used.

[0045] The Peek sheets are processed mechanically to assume the shape of the piano plate.

Description of the preferred implementation process

[0046] In case of the invention plate, planning is developed by considering a hybrid process among the described ones. Composite materials are used with long fiber properly oriented and dispersed in the polymeric matrix (epoxy resin or peek) devised so as to have dampening features.

[0047] The resulting structure must have properties of non-deformability, even in time, and inert to any environmental condition, it must have features of stiffness, mechanical resistance, to resist to chords' loads, size stability both in the initial phase and in time and anhygroscopicity. The structure has to be monolithic.

[0048] In the here considered manufacturing technology, the whole process implying the implementation of the composite plate is controlled by computing tools, both in design phase (CAD), and in the manufacturing phase (CAM).

[0049] In particular, the phases and the design criteria described hereinafter are provided.

(I) - Geometrical Analysis

[0050] The original component is implemented by means of cast iron melting, it appears like a monolithic body without junctions and it has all geometrical devices needed to guarantee the production thereof with the above-mentioned process: in fact, shapeless elements and unions typical for this technology are numerous and evident, but not necessary for the component functionality and resistance.

[0051] It is necessary doing a geometry depuration, aimed at defining the unavoidable and essential design constraints thereof which should be kept on the new structure made of composite material:

1. overall dimensions: the component should be able to be installed on the remaining piano structure without having to make modifications on the same;

2. assembly holes: the position of the assembly holes will have to be kept, so that each adjacent component, as well the supporting structure, could be correctly coupled to the component;

3. holes of chords: the position of the chords' installation holes is essential for the component functionality;

4. resting surfaces: the surfaces with specific functionality, such as resting of chords and pre-tensioning of structure, are different, which will have to be identically reproduced in the new manufacturing.

[0052] At this point it is necessary re-engineering the component in the optic of an implementation with composite materials.

[0053] By disassembling the geometry, indicatively plane different members, with constant thickness, can be obtained: in Figure 1 the different sections can be seen which can be easily implemented separately and joined subsequently by means of connections of structural type to form a monolithic block.

[0054] It is necessary explaining that the re-union of pieces does not be equal to an assembly by gluing or by structural junction to finished piece as these operations usually are made before re-arranging the final piece in autoclave and with the material (fiber-polymer), as already explained above, partially polymerized so that the material finishes polymerizing, thus creating a single monolithic structure.

(II) - Materials and processes

[0055] The composition of the different sections is mainly linked to two constraints:

1. vibrations' attenuation: in order to allow the chords to emit a clean sound, not polluted by parasite frequencies, it is absolutely necessary that each section is constituted by tissue only, by excluding each possible sandwich-like configuration with fillers and by limiting as much as possible the introduction of metallic inserts drowned in rolling (however these will be indispensable in the areas in contact with other elements wherein local high pressures develop, such as for example the pre-tensioning basement shown in blue);

2. structure resistance: since the plate is subjected to not unimportant tensions (15 or 20 tons in total, with a tuning load on each one of 10Kg, the chords being about 200), the minimum thicknesses of the different sections will be established by means of simulation with finished members, suitable to the above-described functional needs, thus optimized from the production point of view and in case corrected according to the global aesthetic impact.

[0056] In the light of all this, it is necessary using a qualitative rolling of this type, by proceeding from outwards towards inwards of the different sections:

1. the most external skin, at sight, will be made of braided woven material made of carbon fiber with small weft, to favour the aesthetic aspect;

2. where necessary (for example in the beams or on the area for inserting pins or other devices for grasping the chords) one or more layers of high-performance unidirectional tissue will be introduced, to increase the property of flexural and torsional stiffness of sections and to increase the resistance thereof;

3. the introduction of pins constitutes design motif and resistance preventive tests; other solutions can provide to drown a metallic plate whereon the pins, preliminarily wound in layers of unidirectional tissue, are inserted;

4. the most internal skins will be constituted by woven materials made of carbon fiber with rougher weft, equipped with larger thickness.

[0057] As one can easily imagine, the composite implementation of the different plane sections (apart from some functional and aesthetical detail therefor there are some simple solutions), there are mainly right prisms which can be obtained as extrusions of plane profiles.

[0058] Among all possible technologies, one has chosen the manual rolling based upon the following observations:

• the productive volume, especially for the prototypes, is quite reduced or at least not sufficient to amortize the charges of dedicated moulds which can be adopted in a second production;
• dedicated moulds are not necessary, as each component is obtained from a simple plane sheet;
• it is the most flexible process and it allows easily in-progress modifications.

[0059] The sequence of operations will be then as follows:

1. Creation of the templates for cutting the skins;

2. Rollings of the different sections with minimum material waste;

3. Curing cycle in autoclave to obtain the composite raw materials of the various sections;

4. Contouring and milling of the various sections in CNC mill with 5 axes;

5. Assembly of the sections on suitable precision mask;

6. Structural gluing of the different sections in the previously specified terms;

7. Curing cycle for consolidating gluing;

8. Size control of the assembled product;

9. Drilling in CNC mill with 5 axes;

10. Manual finishing;

11. Complete size control of the finished product.

[0060] In the processing phase the functional prototype is created which is useful to be subjected to tests and for simulating the use conditions of the finished object, in the specific case for calculating the sealing to the chords' stress and making the suitable interventions and for improving the local mechanical resistance and considering the design variations from the original plate, the outer shape remaining the same.

[0061] For the series production, once optimized the plate, the application of the so-called "Reverse Modeling" process allows obtaining a digital print-out of the design.

[0062] The finished piece is installed in the chosen piano, the chords and other accessories are mounted at a qualified laboratory and tensions of the harmonic board resonance charge are checked. Tests are performed with different tension charges from 430Hz to 444Hz, by considering that 440Hz correspond to 20 tons of tensions.

[0063] A spectrographic examination of the sound curve on the piano with the cast iron plate and on the piano with the carbon fiber composite plate is performed.

[0064] The invention plate not necessarily must have a design equal to the one of the known cast iron plates (the outer sizes remaining the same), but it can be modified during manufacturing by adapting to the features of the new material.

[0065] The present invention has been sofar described by referring to preferred embodiments. It is to be meant that other embodiments belonging to the same inventive core may exist, as defined by the protection scope of the here below reported claims.

Claims

1. A piano plate, characterized in that it is made as single monolithic structure and it is made of a composite material comprising reinforcing carbon fibers.

2. The piano plate according to claim 1, wherein said composite material is selected in a group comprising: Peek (polyetheretherketone) carbon fibers and pre-impregnated materials (for example epoxy resins and Peek).

3. The piano plate according to the preceding claim, wherein said material comprises Peek or a pre-impregnated resin (Prepreg), that is a composite material in thermosetting (Phenolic, Epoxy) or thermoplastic (polyesther) resins or Peek, reinforced with unidirectional, multiaxial or braided woven (thin or large wefts or hybrids) carbon fibers.

4. The piano plate according to anyone of the preceding claims, wherein said carbon fibers have an unidirectional orientation.

5. The piano plate according to anyone of the preceding claims, wherein said carbon fibers have a random orientation.

6. The piano plate according to anyone of the preceding claims, wherein said carbon fibers have woven-material like or multiaxial orientation.

7. A piano frame, comprising a plate according to anyone of the preceding claims.

8. The piano frame according to the previous claim, wherein the plate only is made of a composite material comprising carbon fibers.

9. A piano comprising a plate according to anyone of claims 1 to 6 and/or a frame according to claim 7 or 8.

10. A method for implementing a plate for piano according to anyone of claims 1 to 6, comprising one of the following alternative processings:

- manual rolling of pre-impregnated material with epoxy/phenolic resin on suitable mould;

- forming of thermoplastic material;

- RTM ("Resin Transfer Moulding"), that is a hybrid method wherein dry materials are used arranged into a mould;

- mechanical processing starting from a composite sheet for the Peek CF.

11. The method according to the previous claim, wherein said manual rolling comprises the following steps:

- creation of the templates for cutting skins;

- rollings of different sections;

- curing cycle in autoclave to obtain the composite raw materials of the various sections;

- contouring and milling of the various sections, preferably in CNC mill with 5 axes;

- assembling the sections on suitable precision mask;

- structural gluing of the different sections under the previously specified terms;

- curing cycle for consolidating gluing;

- size control of the assembled product;

- drilling, preferably in CNC mill with 5 axes;

- manual finishing;

- completing size control of the finished product.

Drawing