US3303825A - Ball point writing instruments - Google Patents

Description

Feb. 14, 1967 R. c. SHUMAN ETAL 3,303,325

BALL POINT WRITING INSTRUMENTS Original Filed April 29, 1957 FIG.4

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PER CENT LAND PER CENT LAND M m mU wzw m m C W 0 DH mamas JOHN MEINHARDT BY Patented Feb. 14, 1967 3,303,825 BALL POINT WRITING INSTRUMENTS Robert Cowan Shuman, Janesville, and Francis John Meinhardt, Edgerton, Wis., assignors to The Parker Pen Company, Janesville, Wis., a corporation of Wisconsin Continuation of application Ser. No. 655,623, Apr. 29, 1957. This application Sept. 21, 1961, Ser. No. 140,973 12 Claims. (Cl. 12042.4)

The present invention generally relates to writing balls of the type used in ball point Writing instruments and it more particularly relates to writing balls of the type having a roughened or non-smooth surface. This application is a continuation of application Serial No. 655,623 filed April 29, 1957, now abandoned.

In the past, the balls used in ball point pens and the like have had a substantially smooth surface, such balls usually being made of steel, sapphire or ruby. Smooth surfaced balls have always been used, since it is most important that the ball rotate freely in its socket, and for that reason every effort has been made to make the balls extremely smooth. On the other hand it has been known for many years that smooth writing balls do not write well over slick or greasy surfaces because the friction between the ball and such surfaces is less than the friction between the ball and its socket. This failure of a ball point writing instrument to write over such surfaces is usually referred to as skipping or sliding. The term skipping" being used because the ink line skips over the greasy spots on the writing surface, and the term sliding" being used since the ball slides rather than rolls over the greasy spots.

There are many suggestions in the prior art that the problem of skipping can be overcome by increasing the friction between the ball and the Writing surface by roughening the surface of the ball. No solution is offered, however, to the new problems which the suggested roughening of the ball surface would create. A rough surface is more abrasive than a smooth surface so that if a ball is simply roughened as suggested by the prior art, the ball-seat wear is increased thereby reducing the useful lift of the ball-seat assembly. Moreover, by merely roughening the surface of the ball the wear of the ball itself as it rolls over the writing surface would be increased. Accordingly, the mere provision of a ball having a roughened surface is not a satisfactory solution to the problem of ball pen skip. Nevertheless, a solution to this problem is desirable and, undoubtedly, would quickly be adopted by the ball pen industry if a feasible solution could be determined.

Therefore, an object of the present invention is to provide a new and improved writing ball for use in a ball point writing instrument.

Another object of the present invention is to provide a new and improved writing ball which has the ability to write over slick or greasy surfaces.

Still another object of the present invention is to provide a new and improved writing ball and socket combination wherein the friction between the ball and a slick or greasy writing surface is greater than the friction between the ball and its seat.

A further object of the present invention is to provide a new and improved writing ball and seat combination wherein the ball composition and surface configuration of the ball provides improved writing surface gripping qualities while not appreciably increasing the wear of the ballseat combination.

A still further object of the present invention is to provide a new and improved method of making a writing ball for use in a ball point writing instrument.

Briefly, the above and further objects of the present invention may be realized by providing a cemented carbide ball preferably formed of a plurality of carbide particles cemented into a unitary mass in a sintering operation and which is then suitably ground to provide a homogeneous texture throughout the surface area of the ball. The texture is formed by randomly distributed land areas and pits which are controllably related to one another statistically. The land areas are formed by the carbide particles and the pits are disposed between such lands. The sphericity of the ball must also be accurately controlled as more fully described hereinafter or excessive seat wear or other performance malfunctions will result.

Further objects and advantages and a better understanding of the present invention will be had from a reading of the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is an elevational view, partly in section, of a ball and a ball housing portion of a ball point writing instru ment, the ball housing being shown in section, the ball being stippled to schematically show that the surface thereof is textured;

FIG. 2 is a schematic representation of a greatly enlarged view of a portion of the spherical surface of the ball shown in FIG. 1; the stippled portion representing the pits and the portions shown as smooth surfaces representing the lands;

FIG. 3 is a graph in which the curve represents the relationship between the surface texture of the ball, expressed as the percentage of the entire land area surface of the ball, and the ability of the ball to write over greasy surfaces; and

FIG. 4 represents the relationship between this same surface texture factor and the wearing of the ball seat by the ball.

Referring now to the drawings and particularly to FIG. 1 thereof, there is shown the writing tip for a ball point pen comprising a tip housing 6 having a centrally arranged feed duct 7 extending therethrough for feeding ink from a rearwardly disposed reservoir, not shown, into a forwardly disposed socket having a base or rear seat portion 8 having seating sections generally conforming to the spherical surface of a writing ball 10. A plurality of feed grooves or channels 8 branch outwardly from the feed duct 7 and divide the seat portion 8 into the plurality of separate seating surfaces. Ink is thus fed from the bore 7 through the grooves 8' to the generally annular space which is disposed around the ball forwardly of the seat portion 8 and rearwardly of the lip portion 9 which engages the ball 10 forwardly of its equator and holds it in place within the socket. The lip portion 9 additionally provides a metering area which controls the transfer of ink from the socket to the ball during rotation of the ball 10 during writing.

The housing 6 may be formed of any suitable material such, for example, as brass, bronze or steel to permit its formation by the usual drilling and spinning operations although other materials may also be used.

In accordance with an important feature of this invention, the surface of the writing ball 10 is very finely and uniformly textured throughout, being formed by a plurality of land areas between which are located pits or channels. The ball 10 thus has a roughened surface and means must be provided to minimize ball wear caused by friction between the ball and the writing surface as well as to minimize wear of the ball seat.

The most common writing surface is paper and the sizing normally used therein is silicon dioxide which is an extremely hard substance, having a hardness of about MHO-S. Consequently, if a writing ball is not to be worn away by the abrading action of the sizing, it should have great hardness. It is known that the carbides, such as tungsten carbide and titanium carbide have a hardness comparable to and greater than that of silicon dioxide and it has been found that balls made from these are adequate to withstand this abrasion. There are, of course, other materials having substantially this same degree of hardness, such, for example, as other carbides, borides, nitrides, silicides and oxides such as sapphire and ruby.

However, the sphericity of a ball is extremely critical in order to minimze ball-seat wear and friction and to insure acceptable performance otherwise, and. therefore, the composition and structure of the ball must be compatible with present day techniques for grinding or finishing balls. It has been found that with these presently well-known techniques the necessary degree of sphericity cannot be obtained practicably with single crystalline structures, such as sapphire or ruby, for the reason that these structures have crystallographic planes along which they prefercir tially grind or finish. In accordance with the present invention. the ball is made from a multiplicity of sep arate, randomly oriented, crystalline particles of tungsten carbide or the like which, after grinding, form the lands at the surface of the ball. Preferential grinding is thus avoided, since each carbide particle is extremely small and because of the random orientation of such particles, no alignment of the crystallographic planes of the separate particles occurs. Consequently, a ball having the necessary degree of sphericity can be ground.

Another important feature of the present invention is that the ball 10 has a textured surface formed of land I areas and pits. The land areas obviously may not appear to be completely smooth, at high magnification as on the order of 4000 but they are, nevertheless, not sharp peaked surface protuberances, such as commonly characterize roughened surfaces" and such as are, for example, typical of pitted sapphire or ruby ball surfaces. While these latter types of balls may write over slick or greasy surfaces, the ball-seat wear is so great as to preclude their use with practical ball seat materials.

The ball 10 is thus a cemented carbide or similar ball which is made by powder metallurgy methods. Fine particles of the tungsten or titanium carbide are compacted together with cobalt or nickel or some other metallic binder and are then sintered to provide an integral structure composed of tungsten or titanium carbide, the binder metal itself, and intermediates of the carbide and the binder metal. This resulting unit is finished by grinding, to obtain a ball of the desired size, sphericity and surface character to provide sufiicient sphericity to perform well, a land surface configuration which does not cause undue seat wear, and a cumulative percentage land area which is homogeneously and randomly distributed throughout the ball surface for proper cooperation with the writing surface. Moreover, the percentage land area is within the range of land areas which results in satisfactory writeability without providing undue seat wear.

Referring to FIG. 2, there is shown in greatly magnified form, a portion of the surface of the ball 10. As there is shown, the land areas 11 are formed by the carbide particles 11a and the pits 12 are formed by the spaces between the land areas.

As more fully described hereafter, the ball is formed from carbide particles, precoatcd with a binder metal, and in the final ball each carbide particle is surrounded beneath the surface with a portion b constituting an inter face of carbide and the binder metal and an outer portion comprising substantially the pure binder metal itself.

During grinding, the major portion of the interface and the binder metal is removed from the surface of the ball, whereby the land surfaces 11 are mainly carbide and the surface of the pits 12 include a greater amount of the binder metal. In the particular ball which is shown in FIG. 2, the pits 12 are substantially all interconnected to provide channels which generally surround the land surfaces, the cumulative land area percentage being approximately 50 percent.

Referring now to FIG. 3, there is shown a curve illustrating the relationship between the percentage cumulative land area and the ability of the ball to write over slick or greasy surfaces.

It will be understood that the ability to write over a slick or greasy surface epends upon many factors, and although therefore, the curve shown in H6. 3 will be somewhat displaced, depending upon these other factors, its general shape is substantially the same for all materials and shows the critical nature of the percentage land area on the surface of the ball. The curve in FIG. 3 represents the ability of a ball to write over typical greasy surfaces, as are encountered during the normal use of a ball point pen.

In accordance with an important feature of the present invention, it has been determined to be extremely important that the percentage of the cumulative land area of the apparent total surface area of the ball be maintained within predetermined limits in order to provide a ball having acceptable writing characteristics which does not unduly wear away the seat.

Referring to FIG. 4, there is shown a curve illustrating the relationship between the percentage cumulative land area and the wear of a bronze seat resulting from the relative rotation between a cemented tungsten carbide bail and the seat. A study of the curves of FIGS. 3 and 4 shows that there is a range of percentage land areas which gives satisfactory writcability over greasy surfaces, without causing excessive seat wear. The writeability curve of FIG. 3 shows that when the percentage of cumulative land area of over-all surface area is 50 percent or less, the ability of the ball to write over a greasy surface does not vary with variation in the percentage land area. Above 60 percent, the ability of the ball to write over a greasy surface decreases rapidly. At about percent land area, the curve has a very sharp knee and beyond about percent land area, the ability to write over slick surfaces is at its poorest and essentially no better than prior art steel or other smooth balls, and does not vary with variation in the percentage land area.

The degree of writeability of a ball which is acceptable in any particular instance necessarily varies, but to provide a general purpose ball point pen which can be used for most purposes without undue sliding or skipping, it has been found, as shown in FIG. 3, that land area percentages exceeding 85 percent are no more satisfactory than steel or other smooth balls of the prior art. Moreover, it will be readily understood by those skilled in the art that on a quantity production basis each and every ball will not have exactly the same percentage land area and, therefore, in order to minimize the number of balls which are manufactured with a surface area greater than 85 percent, it is preferable to employ a manufacturing process wherein the average ball has a percentage land area well below 85 percent, the value at the knee of the curve, and, therefore, it is preferable to adjust the parameters of the manufacturing process so that most of the balls made will have a percentage land area well below 85 percent and preferably around or below 70 percent.

Reference to FIG. 4 shows that the combination of a cemented tungsten carbide ball and a bronze seat results in a seat wear curve which has a knee when the total land area measures about 40 percent of the total apparent surface area of the ball. When the cumulative land area exceeds 40 percent, there is acceptably low wear, such low seat wear decreasing slowly as the percentage land area is increased above 40 percent. However, with cumulative land areas less than 40 percent, the wear increases rapidly with decreases in the percentage land areas. It will be apparent to those skilled in the art that the position of this knee along the abscissa of FIG. 4 is dependent upon the hardness of the seat material, and that as the hardness of the seat material is increased, the corresponding minimum acceptable percentage land area decreases. It is clear that the percentage land area has an important bearing on the seat wear and must be maintained above some predetermined limit which depends upon the particular material from which the seat is made. Where a bronze seat is used, a percentage land area below 30 percent is objectionable for a marketable ball point pen, since the ball seat assembly will wear out before a reasonable quantity of ink will have been written out. Where quantity production techniques are to be employed in manufacturing the ball, it is preferable that the percentage land area be maintained above the knee of the curve and, therefore, above 40 percent.

Referring to the curves shown in FIGS. 3 and 4, it will, therefore, be apparent that if the percentage land area of the ball is maintained within the range of 30 percent to 85 percent there will be produced balls which will write over greasy surfaces and which will not unduly wear the ball seat.

In order to minimize seat wear and to provide satisfactory writeability of the ball over slick or greasy surfaces, the entire surface of the ball should preferably be textured to the same degree, that is, the surface texture should be homogeneous throughout and to this end the sizes of the individual land areas should be controlled.

The sizes of the land areas depend upon the size of the carbide particles which are used in making the ball, although the particular grinding techniques which are used and the sintering techniques which are followed, will have some bearing upon these values. Consequently, it has been found advantageous to sinter the ball from carbide particles having a diameter of 5 microns or less on the average.

In order to prevent a prohibitive fiatting effect, which would decrease the effective sphericity of the ball and deleteriously affect writing, the individual pit sizes must not exceed a particular limit. For best results the average chordal distance across pits should not exceed 32 microns for the usual 1 mm. diameter ball, or a proportional distance, for other sizes. An occasional accidental pit may have a distance across equal to about A the ball radius.

In order to form a ball having the characteristics set forth hereinbefore, a powder metallurgy process can readily be employed. In one such process, cobalt coated tungsten carbide particles having a diameter of the average of less than microns are compacted with a suitable binder metal, such as cobalt or nickel into a mass which is then sintered to cement or otherwise join together the carbide particles. If tungsten carbide par ticles of sufficiently large size are used, the result is a porous mass of particles of tungsten carbide joined together by cobalt and compositions of tungsten carbide and cobalt. However, if tungsten carbide particles having an average size of the order of 5 microns or less in diameter are used, then the resulting ball is substantially solid throughout. The sintered compact is thereafter finished by surface grinding to an adequate sphericity. The grinding operation provides relatively smooth land surfaces substantially free of the binder metal or interfaces thereof, which gives to the ball of required hardness, a surface of the required spherical shape and percentage land area.

The percentage land areas may be observed and measured in any suitable way, such as visually by means of a light microscope, as a reference to FIG. 2 will indicate. Such measurement may, however, be facilitated by attaching a cross-hatched Whipple eyepiece to the microscope through which the ball surface is observed, thus simplifying the measurement of the land and pit areas.

While the present invention has been described in connection with a particular embodiment thereof, it will be understood that those skilled in the art may make many changes and modifications without departing from the true spirit and scope of the invention and, therefore, it is intended by the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.

We claim:

1. In a ball point writing instrument, a writing ball comprising a plurality of carbide particles sintered together to form a cemented carbide compact, said ball having a substantially true spherical surface except for pits which interrupt land areas on the ball surface, said surface having a substantially homogeneous texture formed by randomly distributed lands and pits, said lands being formed by carbide particles and said pits being the spaces between said lands.

2. The writing ball set forth in claim 1 wherein said ball is formed by a sintering process followed by a grinding operation.

3. The writing ball set forth in claim 1 wherein said particles are tungsten carbide and are cemented together by a binder metal selected from the group of cobalt and nickel.

4. The writing ball set forth in claim 1 wherein said carbide is tungsten carbide and the particles of tungsten carbide from which the ball is made are about 5 microns or less in diameter on the average.

5. For a ball point writing instrument, a writing ball formed of a plurality of randomly oriented tungsten carbide particles cemented together in a compact mass, the surface of said ball being composed of land areas and pits homogeneously and randomly distributed throughout said surface, said land areas being formed of tungsten carbide particles and cumulatively occupying between 30 and percent of the apparent surface area of the ball.

6. A tip for a ball point writing instrument comprising a socket formed of a metal having about the same degree of hardness as bronze, and the writing ball set forth in claim 5.

7. A ball for a writing instrument comprising a cemented carbide compact having a homogeneously and randomly distributed texture formed by lands and pits, wherein the average distance across pits does not exceed 32 microns, and the land areas cumulatively occupy between 30 and 85 percent of the apparent surface area of the hall.

8. The method of making a writing ball for a ball point writing instrument, comprising forming a sintercd compact of randomly oriented carbide particles and a binder metal, said particles having an average diameter of 5 microns or less, and thereafter grinding said compact into a sphere wherein the land areas cumulatively occupy between 30 and 85 percent of the apparent surface area of the ball.

9. The method of making a writing ball for a ball point writing instrument, comprising forming a sintered compact of randomly oriented carbide particles and a binder metal, said particles having an average diameter of 5 microns or less, and thereafter grinding said compact into a sphere wherein the average distance across pits is no greater than 32 microns, and the cumulative land area occupies between 30 and 85 percent of the total apparent surface of the ball.

10. A Writing ball for a ball point writing instrument comprising a spherical compact of carbide particles and a cobalt binder, said compact having a homogeneously textured surface formed of land areas and intermediate pits, said land areas being formed of carbide and being substantially free of cobalt, said pits having a surface which is substantially cobalt, and said land areas cumulatively occupying between 30 and 85 percent of the total apparent surface of the ball.

11. A writing ball for a ball point writing instrument comprising a spherical compact of carbide particles and a nickel binder, said compact having a homogeneously textured surface formed of land areas and intermediate 7 pits, said land areas being formed of carbide and being substantially free of nickel, said pits having a surface which is substantially nickel, and said land areas cumulatively occupying between 30 and 85 percent of the total apparent surface of the ball.

12. For a ball point writing instrument, a writing ball formed of a plurality of randomly oriented tungsten carbide particles cemented together in a compact mass, the surface of said ball being composed of land areas and pits homogeneously and randomly distributed throughout said surface, said land areas being formed of tungsten carbide particles and occupying between 40 to 70 percent of the apparent surface area of the ball.

References Cited by the Examiner UNITED STATES PATENTS 2,630,383 3/1953 Schwartz et a1 75204 X 2,798,005 7/1957 Love. 2,847,751 8/1958 Reed.

FOREIGN PATENTS 894,857 3/1944 France. 1,009,193 3/ 1952 France.

LAWRENCE CHARLES, Primary Examiner.

JEROME SCHNALL, E. HOROWITZ,

Assistant Examiners.

Disclaimer 3,303,825.-[Z0bert Oowan Shaman, Janesville, and F rancis J 07m M einhardt,

Edgerton, Vis. BALL POINT WRITING INSTRUMENTS. Patent dated Feb. 14, 1967. Disclaimer filed July 17, 1969, by the assignee, The Parker Pen Company. Hereby enters this disclaimer to claims 5, 6, 7, 8, 9, 10, 11 and 12 of said patent.

[Ojfieial Gazette September 2, 1.969.]

Claims (1)

1. IN A BALL POINT WRITING INSTRUMENT, A WRITING BALL COMPRISING A PLURALITY OF CARBIDE PARTICLES SINTERED TOGETHER TO FORM A CEMENTED CARBIDE COMPACT, SAID BALL HAVING A SUBSTANTIALLY TRUE SPHERTICAL SURFACE EXCEPT FOR PITS WHICH INTERUPT LAND AREAS ON THE BALL SURFACE, AND SURFACE HAVING A SUBSTANTIALLY HOMOGENEOUS TEXTURE FORMED BY RANDOMLY DISTRIBUTED LANDS AND PITS, SAID LANDS BEING FORMED BY CARBIDE PARTICLES AND SAID PITS BEING THE SPACES BETWEEN SAID LANDS.

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