US 2273717 A
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Description (OCR text may contain errors)
Feb. 17, 1942. G. E. MILLARD ETAL 2,273,717
BRUSH Filed Jan. 14-, '193 s Sheets-Sheet 1 INVNTOR5 GLEN E-MILLARD WILLIAM G. HUGHES ATTORNEYS Feb. 17,1942. G. E. MILLARD am y 2,273,717
BRUSH Filed Jan. 14, 1938 3 Sheets-She et 2 7 INVENTOR$ GLEN E. MILLARD WILLIAM G. HueHEs ATTORN 5Y5 Patented Feb. 17, 1942 r jBRUSHY" GlenE'iMillardlalid WilliamG. HughesQSt. Paul,
Minnl, "assignorsfto Lactona Incorporated, St., l A
F Paul, Minn, a corporation of Minnesota Application january 14, 1938, Serial No. 184,982
s'ciaims. 01115-167) This invention relates to improvementsin brush construction by which 'the'servicelife of the bristles of the brush may be lengthened; Bristles of brushes'are subject to fatigue failurewhe'n repeatedly flexed beyond the endurance limit of the bristle material, with resultant shortening of the service life of the brush. This is particularly true of large diameter bristles,\"of brushes. containing bristles of various diameters because in the larger diameter bristles the stress within the'material may be increased beyond the endurance limit. It is also particularly true of bristles along the outside row of a brush because thesebristles are usually flexedto a greater extent than the average deflection of the brush. Although some grading of bristles is possible, most brusheshave bristles of varyingdiameters and the condition of breakage of large size bristles andboundary bristles is; therefore, commuously met with.
In brushes having bristles of varying diameters, 1
the amount of deflection of any bristledepends upon the average resisting" force "of adjacent bristles, and it frequently happens that the average deflection producedupon the large and small d ameter bristles alike is in excess of the deflection which the large diameter'bristles are able to stand? repeatedly, with the result that'the large diameter bristles fail after a comparatively few flexures. I
In the case of bristles along the trailing edge of the brush, both large and small diameter bristles are frequently deflected to. an extent "greater than'the average deflection of the bristles in'the brush generally; due to the fact that the outer trailing rowof bristles lacksthesupport afforded by adjacent rows. fBristle breakage due'to the fatigue stresses developed by repeated fiexures therefore frequently occurs to a greater extent along I the outer rows of l a brush than elsewhere in the brush. 1 l 1 We have discovered that fatigue failure ofbris tles'can be reducedto: a considerable extent by providing asupportingsurface adjacent the outer bristles of a bristle tuft, which surfaceis 'designed so as to lend support to such bristles when stresses within the bristle material approach the endurance limit. i f 1 It is therefore an object of the invention'to provide a brush construction in which the bristlesaresupported so as so that the life'of the bristles of the brush may be extended in service. i i i It, is a further object to provide a brushlconstruction in which the torelieve fatigue stresses bristle-supporting surface comprises a"rid"ge adjacent the outer rows of tufts of a brush which is shaped so as tos'upport said outer bristles, and in which the. bristlereceiving apertures are also shaped in accordance with such surface shape so as to relieve stress concentration in the bristles elsewhere thebrush.
It is alsoan'objectof the invention toprovide a construction in which strains are reduced and distributed in those sections of the bristles. adjacent the brush head, whereby the phenomenon within commonly known as notching of the bristles r with respect to tooth brush and breakage of the bristles is reduced.
It is a further object of the invention to provide amethod for forming thebristle supporting surface and bristle-receiving apertures'so as'to conform with a predetermined surface curvature, whereby undue stress concentration in the bristlesflmay be eliminated. I
It is also an object of the invention to provide a construction which may be easily cleaned. is applicable generally to brush construction, for example .to clothes brushes, fto'oth brushes, scrubbing brushes, brooms, rotary brushes, and others, ari'd'it is The present, inventlon therefore an objectof the invention to apply v the constructionto suchbrushesg v i The principlespf this invention are illustrated construction but this is not to beunderstood as limiting the scope of the invention.
In the description hereinafter given, reference is had to the accompanying drawings in which like characters represent corresponding parts in all views. V l Figure 1 is a plan View of a brush handle with the bristles removed;- I a Figure 2 is an elevation partly in section showing some of the bristles in place and some removed. 1 a 3 Figure 3 is a sectionalview along the lines 3-3 ofFigure 2. 4 g t Figure 4 is a fragmentary enlargement in section of the bristle receiving opening-of the brush, shown in-Figure 3. I i 1 Figure 5 isian enlarged view of one bristle and the bristle-supporting surface, showingthe derivation of the surface shape.
Figure 6 is an enlarged section of a modificationof the present invention.
Figure '7 is a fragmentary enlargement in sec-f fication shown in Figure -6.
Figure 8 is a fragmentary enlargement of the i selected for the bristle-receiving aperture of another modification of the invention.
Figure 9 is a fragmentary plan View of the bristle-receiving aperture of the brush modification illustrated in Figure 8.
In the construction illustrated in Figures 1 through 4 the brush consists of a head portion l and a handle 2 bywhich the brush is manipulated. The head 1 is elongated and is provided with a plurality of bristle-receiving apertures 3 which in this particular construction are ar- Each aperture ranged in two longitudinal rows. supports a bristle tuft 4 consisting of a plurality of individual bristles bent over staple 5 as shown in Figure 3.
6 of curved cross-section which serves as a support for the bristles of tufts 4 when the bristles are, deflected. In the construction shown in Figures 1 through 4, apertures 3 intersect ridge 6, although this is not an essential feature of the invention, as hereinafter pointed out.
The shape of the bristle-supporting surface 8 of'th'e'aperture 'andof that portion of the ridge 6 which is adjacent the aperture may be determined empirically or it may be derived mathematically. The numeral 8 in this application is used'to denote both'the bristle-supporting surface and the bristle deflection curve from which the surface shape is derived, as hereinafter pointed out. Y
. According to'the empirical method, a flexible bristle A is supported vertically, as shown in Figure 5, and then deflected by a force F applied at rightangles to the axis of the bristle until the bristle is deflected to the extent'commonly met within practice, which in the case of a tooth brush, is when a line drawn through the tip -T and base B'of the bristle, is in the neighborhood of forty-five degrees. This angularity, of course, depends upon the brush and the service to which it is subjected. Itis to be understood that the average bristles of the brush are stressed to about the endurance limit when deflected to this amount, and the supporting ridge is intended to be operative to lend support to the bristles if deflected beyond the 45 degree limit and to lend support to large bristles which are not average and which are stressed beyond the endurance limit when deflected to the forty-five degree limit. It is also 0 be understood that the bristle experimental determination is sufficiently thin and flexible that it will not be stressed beyond the elastic limit during test, that is tov say, it returns to a substantially upright position when released. The curve 8 of the deflected bristle is then determined photographically or by direct measurement and this curve is reproduced as the bristle-supporting surface 8 of the ridge 6. .The portions l of' the ridge between the bristle-receiving apertures donot ordinarily act as a bristle-supporting surface and hence may be of any desired cross-section, but are for convenience made of the same curvature as the portions of the ridge which are adjacent the apertures.
The mathematic method of determining the curve 8 of ridge 6 is based upon the following formula:
ex 3X iw 7 L Adjacent each of the rows isa ridge.
and depends upon the deflection to which the bristle is subjected. These applied in Figure 5.
It has been found that a portion of the curve expressed by the above equation may be approxvarious symbols are imated by a segment of a circle, the diameter and center of which'maybe determined either by known methods of graphic or mathematical Thus, when the bristle length S is 1i inch, the factor L has a value of .305 and the circle which approximates the curve mathematically expressed above, has a radius of inch about a center which is slightly above the face of thebrush head. The bristle-supporting surface'B, therefore, may be formed to this dimen- S1011.
The height of the ridge may be obtained from the following expression: H=LXK+C where H equals the height in inches of the ridge, L is as abovedefined. The factor X is applicable in a construction such as that shown in Figures 8 and 9, and. equals the value of X in the previously stated equation when Y equals -K, and K equals the extreme variation or tolerance in position of the bristle-receiving aperture with reference to the ridge. The factor C in this expression is a constant which depends upon a number of considerations, including the following:
(a) The support gained in case of excessive deformation.
(b) The position of the center of the bristlereceiving aperturewith reference to the curved surface.
(c). The effect of the height upon the sanitary features of the brush.
(d) The height required to prevent the spreading of the bristles of the tuft and the subsequent application of excessive forces or extreme pressures on a few remaining bristles in the tuft.
(e) The effect of the height upon the appearance of the brush.
Referring nowto Figure 4 it will be seen how the bristle deflectioncurve 8 is utilized in forming the bristle-receiving aperture and to that portion of the ridge 6 which is adjacent the aperture. The lower part of the aperture 3 from levelsHi to H2 is of circular cylindrical cross-section. From the leverI-Iz to Hz, the inner surface 8 of the aperture is a surface of revolution of the curve '8 about the center line of the aperture. Above level H3 and to the right of line la there is a portion 9 which forms the smoothly rounded entrance to the aperture from the surface ll of back I. To the left of line 1 and above level Ha, area 10 is a continuation of the surface of revolution of curve 8 where that surface intersects ridge'6.
The bristles'within the aperture are thus completely supported in every direction by the surface of revolution of curve 8 as high as level H3 and are additionally supported to level H5 by a continuation of this surface on the ridge side.
= It should beunderstood that the support given to outermost bristles of -thetufts; are transmitted to adjacent bristles within the tuft, thus protecting them against harmful deflection.
The brush back I and surfaces8, 9 and ID are preferably formed by molding, such as by injecting a hot viscous material intoa mold,'or by hot holding a'heat hardenable resinous material. Another method of forming the surface is by hot pressing a pre-cut blank of'Celluloid or other material capable of flowing under pressure at elevated temperatures. If desired the bristle-receiving apertures maybe-molded or pressed to form, for instance, surfaces 8, 9 and I0, and then drilled so as to form the circular cylindrical portion of the aperture. The "molded or hot pressed blank' with its completely formed surfaces 8, 9 and It] thus serves to assist-accurate drilling.
Figures 6 and 7 showamodification of the invention in which backli's provided with upstanding ridges l3 which-support the bristles. In this modification theridge [3 has an inner surface l4 which is parallel to the axis l 2 offthe tuft. When the tufts of the brush shown in Fig ure 6 are deflected beyond'th'e average endurance limit of the bristles, thejoutermost bristles are supported at the points I5 I and [6, the ridge height being such that these support points lie along the deflection curve 8 of a perfectly flexible bristle. These points, therefore, serve to distribute the deflection over a considerable length of the bristle and thus preventthe bristle from being deformed beyond its endurance limit at any point. It should be understood that the support given to any outermost bristle is transmitted to adjacent bristles, thus protecting them also from 2 undue deflection. v H ,7
The bristle-receiving apertures 3 of the brush, shown in Figure 6, is preferably formed, as shown in Figure 7, with a curved entrance similar to that shown to the right of the line Tin Figure 4, that is, with a section 8 between level Hz and H3 which is a surface of revolution of the bristle deflection curve 8 about centerline l2, and with a smoothly curved entrance section 9, between levels H3. and H4, joining with the aforesaid surface of revolution.
The modification shown in Figures 6 and '7 has the especial advantiagethat the bristle-receiving aperture can be formed by arevolving tool since the aperture shape does not intersect the adjacent ridge. Thus the holes can be drilled and then reamed with a cutter shaped to give the desired curvature to the aperture entrance. Of course, this form can also be obtained by molding orhot pressing if desiredyas with the form shown in Figures 1 through 4. v
A third modification of the invention is illustrated in Figures 8 and 9. In this form of the invention the bristle-receiving aperture is a circular cylinder from level H1 to level H2, and the same cylindrical shape is continued above level H3, to the left of vertical line 22 (see Figure 8). To the right of line 22, the aperture is shaped with surfaces 8 and 9, the same as for the corresponding surfaces of the modification shown in Figure 4. The ridge in this modification has a cross-sectional curve which conforms with the bristle deflection curve 8 ofa perfectly flexible bristle, derived as shown in Figure 5, and the intersection portion 23 is smoothly rounded so as to prevent undue stress concentration of a bristle bent over the intersection line.
It is recognized that in this modification, a defiected bristle in the position 24 of Figure 9 would be deflected about a shorter radius of curvature than at any place in Figure 8, but this is accepted as a design'compromise in order that a considerable number of bristles in areas 25-45 may receive the full benefits of the ridge curvature.
The advantage of the construction shownin Figure 8 is that the bristle apertures may be drilled. The curved off intersection as "between levels Hz and H4, and at 23 may be 'formed'bymolding or by any other desired process.
The dimension Kisthe tolerance permitted in the position of aperture 3 with respect to ridge 6 and is a factor (k) in the ridge height H=LXK+C. Thus in the'brush specifically illustrated in Figures '7' and 8, when the tolerance factor K equals .0096, C is .02 inch, and the bristle length is inch, the height'H of the ridge 6 Wi1lbe.065inch." 'If desired, bristle-supporting ridges of any of the brushes may have inwardly curved ends which partially enclose the end tufts of each row and thus lend-endwise supportto the endwise bristles of th'eend tufts, This is illustrated in the form of brush shown in Figures 1 through 4 in which the ridges 6 are curved in'wardly at l8 and shaped so as to support the outermost bristles of the end tufts. The inner curved ends l8 do not join each other and they therefore provide free passageways l9 and 2ll at each end of the brush, for the flow of liquid during cleaning of the brush, thereby preventing an accumulation of debris and toothpaste which might otherwise render the brush unserviceable. It has been found that the side ridges along the brush have the effect of concentrating thewater flow along the brush, thus assisting the cleaning action. In all modifications of the invention, the junction between the ridge and'the brush back is smoothlyfilleted to prevent. the lodging of debris, etc., thefillet curve being illustrated at 2| in Figures 4,6,7and8. n d w I It frequently happe s that brushes such as the toothbrushes illustrated contain bristles of varyingdiameters. If a bristleis of small diameter, or is freely elastic, deflection to, for instance the position of the curve 8 in Figures 3, 4, 5 and '7 would simply causethe bristle to assume a free position following the curve. However, when a stiffer bristle,,or one of larger diameter is similarly deflected itwould be excessively strained, or deformed, except that the bristle is forced to curve over. the ridge, vrl'iich accordingly distributes the stress and saves the bristle from concentr'ated stress and consequent breakage. The protective ridge of the brush, therefore, enables the brush to be used for a longer time than those made according to previous methods.
A tooth brush designed according to the present invention has had excellent lasting qualities even though the brush had only two rows of six tufts each, and even though mixed bundles of bristles of diameters from to inch were used.
We claim as our invention:
1. A bristle brush comprising a head, bristles mounted on said head to project from a face thereof, and means for supporting the outer of said bristles against outward deflection comprising a supporting ridge having a curved bristlesupporting surface rising from the plane of said face and from adjacent the outer sides of said outer bristles at said plane, said bristle-supporting surface being continuously curved away from the normal unflexed position of said bristles from said plane to substantially the top of the ridge, whereby said outer bristles will engage said supporting surface at. polntszpr'ogressively farther removed from th'eir normal unflexed positions, along their lengths from the said plane tothe top of the ridge, when said bristles are deflected in the direction of said supporting surface.
2. A tooth brush, comprising a head, a plurality of rows of bristles mounted on said head to project from a face thereof, ridges rising above said supporting surface at points progressively father removed from their normal unflexed positions, along their lengths from said plane to the top of the ridge, when said bristles are deflected in the direction of said supporting surface.
3. A bristle brush. comprising a substantially solid brush head, a shaped longitudinal ridge of curved cross-section along the head, said brush h'ead having a plurality of bristle-supporting sockets therein extending partially into said ridge at one side thereof, and a tuft of bristles in each of said sockets.
4. A'tooth brush having, a head, a plurality of rows of bristles projecting from said head, bristlesupporting ridges rising from the plane of said head and paralleling the outer rows adjacent the outer sides thereof, and each provided with inwardly directed portions at the row ends, said ridges being spaced at one end of the head, and said space being substantially free and unobstructed to provide a freedrain space-for liquid during cleaning of the brush.
5. A tooth brush comprising a brush back, a plurality of rows of bristle tufts mounted in sockets in said back,- bristle-supporting ridges adjacent the outer rows shaped soas to provide a smoothly curved surface for the support of the bristles when the bristlesare deflected, the entrance of each bristle socket being smoothly curved so as to prevent notching of the bristles, said bristle-supporting surfaces of the ridges being curved away from the bristles from the plane of the brush back surface in which the bristles are mounted to substantially the top of the ridge.
6. A tooth brush having a head, a plurality of rows of bristles mounted on saidhead to .pro-
ject from a face thereof, ridges rising above said face and paralleling the outer rows adjacent the outer sides thereof, and each provided with inwardly directed portions at the row ends, said ridges being spaced at one end of the head and said space being substantially free and unobstructed to provide a free drain space for liquid during cleaning of the brush, and said ridges each having a curved bristle-supporting surface rising from the plane of said face and from adjacent the outer and end bristles of one of said rows at said plane, said bristle-supporting surface being continuously curved away from the normal unflexed position of said outer and end bristles r from said plane to substantially the top of the ridge, whereby said outer and end bristles will engage said supporting surface at points progressively farther removed from their normal unflexed positions, along their lengths from said plane to the top of the ridge, when said bristles are deflected in the direction of said supporting surface.
7. A bristle brush comprising a head having a ristle-receiving aperture therein, a bristle-supporting member having a bristle-supporting surface adjacent to and intersected by said aperture, and a bristle knot or tuft in said aperture, the entrance curvature of the aperture and the said bristle-supporting surfac comprising a shaped surface which is curved in accordance with the curvature of a bristle used in the brush, when deflected.
8. A bristle brush comprising a head having a bristle-receiving aperture therein adjacent one edge thereof, a bristle tuft in said aperture, and a raised support between said tuft and said edge of the head, said support having a bristle-supporting surface facing said tuft, which surface lies closely adjacent said tuft where the latter emerges from said aperture and curves away from said tuft, substantially continuously from said head to the top of the ridge.
9. A tooth brush comprising a head, raised bristle-supporting means along each longitudinal edge of the head, bristles mounted on said head intermediate of said supporting means and normally substantially out of contact with said supporting means, said supporting means being adapted to support the outer bristles when outwardly flexed and being laterally spaced at one end of the head to facilitate ready flushing of the brush, the said lateral space being free and unobstructed.
GLEN E. MILLARD. WILLIAM G. HUGHES.