Piano hammer felt
United States Patent 11 1 1111 3,878,752 Yamada 1 Apr. 22, 1975 PIANO HAMMER FELT 364.496 6/1887 Dolgc 84/254 853.595 5/1907 P lissier... 84/254 [75] Inventor: Tsuguo Yamada Hamamatsu, Japan 884.597 4/1908 M arsonm. 84 254 x 912.860 2 1909 Laker 84/254 [73] Asslgneez Nippon Gakki Seizo Kabushiki, 1.365.340 1/1921 Pfldemer 84/254 Kaisha Shizurka, Japan 1.892.416 12/1932 Vltto 84/254 X [22] Filed. Feb 1973 3.487.429 12/1969 Johnson 85/254 [211 App, NO&#39;: 333704 Primury Eraminer-Richard B. Wilkinson Related U.S. Application Data Assistant E.\-aminerVit W. Miska [63] Continuation of Scr. No. 143.033. May 13. 1971. AHOY/1e).A8P&#39;1r-vrFirmHerbert Lerner abandoned.  
 [] Foreign Application Priority Data Aug. 28, 1970 Japan -85221 Aug. 28, 1970 Japan 45-85222 ABSTRACT 52 U.S. c1. 84/254 A Piano hammer constYuCfiO wherein 511 1m. 01 Gl0c 3/18 Plastic resin material is advamagewsly incorpmted [58] Field of Search 84/254 into Superimposed woolen layers to improve resistance to deformation of the hammer heads.  
 [56] References Cited UNITED STATES PATENTS 1.971 2/1841 Fobcs 84 254 3 Claims. 7 a ing Figures PIANO HAMMER FlELT This is a continuation, of application Ser. No. 143,033, filed May 13, 1971, now abandoned.  
  This invention relates to a hammer felt for pianos, and more particularly to an improved hammer felt which is sturdy in construction and free from deformation.  
  In the specific case of pianofortes, commonly termed pianos, and so named hereafter, tensioned strings are vibrated by percussive action of hammers in order to produce musical tones. The heads of the hammers which directly act on the strings are generally wrapped by a felt, and as a consequence the tone quality of the piano largely depends on and is seriously affected by the conditions of the felt material constituting the strinking surface of the hammer head, said conditions including tightness or hardness and shape-retaining characteristic of the felt structure.  
  It has heretofore been proposed to form a felt fabric for the piano hammer solely from wool fibres in such a manner that the felt fabric is softer or has lower density on the bass side of the piano while it is harder or has higher density on the treble side. A hammer head wrapped by such woolen felt is often found to be too soft to endure repeated hammering action, and therefore prone to deformation. In order to overcome this difficulty, more recent prior art proposes to blend the wool fibres with thermoplastic synthetic resin fibres. However, this entails various difficulties in the felting process and results in a hammer head which is too hard and produces objectionable noises at the time of hammering, rendering the tuning operation difficult.  
  It is accordingly an object of this invention to provide an improved hammer felt construction which will eliminate the above noted difficulties.  
  It is a further object of the invention to provide a hammer felt fabric which is simple in construction, easy to manufacture and which will contribute to improving the tone quality of the piano.  
  According to one feature of the invention, the improved hammer construction comprises high density inner felt layers each composed of a mixture of wool fibres and thermoplastic synthetic resin staples, and an outer felt layer forming hammering surface and composed solely from wool fibres.  
  A further feature of the invention resides in the hammer felt construction comprising multi-ply woolen felt layers containing thermoplastic synthetic resins, said felt layers and synthetic resins being cured together into a final shape on a tapering fore end portion of a hammer head.  
  These and other object and advantages of this invention which will become subsequently apparent reside in the detaills of construction as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:  
  FIG. 1 is a perspective view of a hammer felt base fabric or sheet formed according to the present invention;  
  FIG. 2 is a fragmentary section, on an enlarged scale, of the multiply base sheet shown in FIG. 1;  
  FIG. 3 is a perspective view of a hammer felt of the invention;  
  FIG. 4 is a sectional view showing the positioning of the hammer felt relative to the hammer head prior to gluing operation;  
  FIG. 5 is a sectional view showing the hammer felt glued around the fore end portion of the hammer head;  
  FIG. 6 is a sectional view showing a modified structure of the hammer felt according to the invention; and  
  FIG. 7 is a fragmentary sectional view of a multiplied base sheet for forming the hammer felt of FIG. 6.  
  Referring to the drawing, and first to FIGS. 1 through 5, there is firstly provided a multi-layer or multi-ply base sheet 10 of felt having inner felt layers or laps ll superimposed on each other and composed of wool fibres 12 blended with thermoplastic synthetic resin fibres 13 of relatively short lengths, such as polyethylene, polyvinyl-chloride and polypropylene fibres. The inner layers 11 are securely interposed between two outer felt layers 14 composed entirely of wool fibres. This composite base sheet structure may be obtained by fulling the outer and inner felt layers between two hot plates and through exercise of steam, pressure and friction as in the conventional felting process. A chemical compound as usually employed in the art for promoting the fulling operation may be utilized. The composite hammer felt base sheet 10 is formed such that its longitudinal cross-sectional area is tapered or reduced lengthwise as shown in FIG. 1. The base sheet 10 is longitudinally cut into elongated strips 10&#39; having alternate trapezoid and inversed-trapezoid end faces. As mentioned hereinbefore, the base sheet 10 has a longitudinally reduced cross-sectional area, and accordingly thickness of each strip 10 is gradually reduced from one end to the other, the longitudinal section of the strip 10&#39; presenting an angular shape. Each strip 10 is then transversely cut into individual hammer felt sizes, that is to say, into individual hammer felt pieces 15 having upper or smaller surface 15a and a lower or larger surface 15b. The number of hammer felt pieces 15 necessary for the whole hammer heads of a piano may be made out of a single strip 10&#39;, the thicker pieces being used for the hammers on the bass side of the piano while the thinner ones are used for the treble-sided hammers.  
  In order to attach the felt piece 15 to the hammer head 16, the tapering fore end portion 16a of the hammer head 16 is positioned substantially at the center of the upper or smaller surface of the felt piece 15 and then wrapped by the latter in a securely glued relation therewith in the manner as shown in FIG. 5. Under this condition, suitable pressure and heat are applied to the wrapping felt piece 15.  
  With the hammer felt construction of the first embodiment described above, the hammer head may have a relatively tight or hard inner layers 11 covered by a moderately soft outer layer 14 of a woolen felt, so that the head will not produce any noise as would be generated by a hammer head which contains synthetic resin fibres in its hammering surface. Furthermore, according to the invention, the head is free from deformation due to the thightness or hardness of the wool/synthetic resin inner layers 11. In other words, the synthetic resin fibres incorporated into the inner layers serves to impart a moderate hardness and shape-retaining characteristic to the head.  
  The base sheet 10 should preferably be cut into alternate trapezoid and inversed-trapezoid strips 10&#39; in order to avoid waste by cutting. The base sheet 10 may have the woolen felt layer 14 on one side thereof. However, where the base sheet is cut into alternate trapezoid and inversed-trapezoid strips 10, it is desirable to provide the woolen felt layer 14 on both sides of the base sheet, so that the cut apart strips invariably have the woolen outer layer 14 on the bottom or lower face b which is adapted to form the hammering surface of the hammer.  
  In the first embodiment of the invention, the individual hammer felt pieces are described as being attached directly to the tapering fore end portions of the hammer heads, however, an underfelt layer with suitable hardness may be interposed between the hammer heads and felt pieces, if desired. Further, instead of blending thermoplastic resin fibres with woolen fibres, the woolen fibres may be impregnated with thermoplastic resin solvent as described hereinafter with reference to the following modification.  
  FIG. 6 shows a modified structure of the hammer felt according to the invention. The modified hammer felt 15&#39; is formed from a base felt sheet 10 shown in FIG.  
 7. The base sheet 10 of FIG. 7 comprises woolen felt layers or laps ll superimposed on each other, each woolen felt layer containing a thermoplastic resin such as vinyl acetate resin. This base felt sheet 10 may be obtained by filling the woolen felt layers impregnated with fluidized thermoplastic resins under heat and pressure, and then curing them into a final hammer felt shape with desired thickness. The base felt sheet 10&#34; may, however, be soaked into, sprayed or brushed with a thermoplastic resin solvent after completion of the fulling operation of the base sheet. The thermoplastic resin preferably occupies l to percent of the composition of the base felt sheet 10. The thermoplastic resin may be contained uniformly in the entire crosssectional area of the base felt sheet 10&#34; but it may preferably be concentrated in the inside layer or layers 11 of the hammer felt, that is, the layer or layers adjacent to the fore end portion 16a of the hammer head 16, as shown in FIG. 6. Moreover, the distribution of the thermoplastic resin may be varied depending on the musical scale ranges. For example, 10 to 20 percent of the resin may be impregnated into the hammer felt base sheet in the treble tone range, 3 to 15 percent in the intermediate tone range, and l to 5 percent in the bass tone range. Similar to the foregoing embodiment, the base sheet 10&#34; is formed with its thickness gradually reduced from one end to the other and longitudinally cut into elongated strips having alternate trapezoid and inversed-trapezoid end faces. Each one of the elongated strips are cut into the individual hammer felt piece sizes and then attached to the hammer heads in the same manner as in the foregoing embodiment, and the resins contained in the felt pieces 15 are once fluidized by heating and then cooled and cured into the final hammer shape together with the woolen felt layers when the pieces 15 are mounted on the hammer heads. Each hammer felt piece 15 is formed into a final hammer shape by applying a temperature of about C. and a pressure of 4 metric tons for about 20 minutes.  
  The embodiment of FIG. 6 has advantages in that the fulling operation of the base felt sheet may be facilitated and that the woolen fibres are firmly held together with the resin material in such a manner as to retain the hammer head shape undeformed over repeated and extended use of the heads, and that the percentage of the thermoplastic resin occupied in the felt material can be greatly reduced, as the resin is impregnated&#39;into the woolen material in a liquid state.  
  The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.  
 What is claimed is:  
  1. In a piano hammer having a hammer head and a hammer member fixedly attached thereto, the hammer member comprising multi-ply mutually superimposed inner layers each composed of wool fibres blended with thermoplastic resin fibres of relatively short lengths, and two outer layers respectively smaller in thickness than said inner layers and between which said inner layers are disposed, said outer layers being composed solely of wool fibres and covering both sides of said mutually superimposed inner layers, said blend of wool fibres and thermoplastic resin fibres being harder and possessing greater shape-retaining characteristics than said outer layers, said layers forming a hammering surface of the hammer member.  
  2. The piano hammer as claimed in claim 1 wherein said hammer member includes 1 to 20 percent of thermoplastic resin. 3  
  3. The piano hammer as claimed in claim 1 wherein there are contained about 10 to 20 percent of thermoplastic resin in the treble tone region, about 3 to 15 percent in the intermediate tone region, and about I to 5 percent in the bass region.