SAWING WIRE SPOOL WITH TWO CONCENTRIC DRUMS AS CORE Field of the invention.

The present invention relates to a spool on which a fine metal wire is wound. More specifically, the present invention relates to a spool made of thick metal sheet for a fine metal wire, such as a wire for a wire saw

(hereinafter referred to as "saw wire") or a wire to reinforce a rubber hose (hereinafter referred to as "host wire"), to wind thereon.

Background of the invention. A conventional spool 10, as shown in FIG 1 , has a core 12, and two flanges 14. The two flanges 14 are welded to the both ends of core 12. The core 12 and the two flanges 14 are made of thick metal sheets such as carbon steel for machine structural use.

A fine metal wire to be wound on the above-mentioned spool is, for example, a fine metal wire having a diameter of 0.12 to 0.16mm or less and serving as a saw wire, or a fine metal wire having a diameter of about 0.20 to 0.80mm and serving as a hose wire. Another application is a fine metal wire having a diameter of about 0.12 to 0.40mm and serving as a wire for a twisted steel cord to reinforce rubber products.

In the case where the above-mentioned fine metal wire is wound on the spool under a predetermined tension (for example, a tension of 4 to 15 Newton), the winding tension causes a high tightening tension to the core, thus resulting in applying to the flanges a big force pushing them apart. And this force for pushing apart (hereinafter referred to as "side pressure") causes the flanges at both ends to be pushed away in a direction that they separate from each other.

In a typical application, a saw wire is used to cut silicon for microchips.

To eliminate material waste and to maintain a high productivity, the customers are asking a spool winding with a fine wire with diameter of 0.12mm and length of 800km. As the diameter of the metal wire becomes smaller, or as the winding tension becomes larger, or as the

reciprocating number of turns of the wire becomes larger, the side pressure generated becomes larger.

To provide sufficient strength and rigidity to withstand such side pressure, the conventional spool 10 utilizes the thick metal sheet with a thickness of about 20mm to 50mm. Accordingly, the conventional spool is so heavy that the operability thereof becomes very poor, and that the spool suffers from the high cost of transportation. Also, the conventional spool suffers from the high cost of materials and treatments.

Besides, since the side pressure is excessively large, even this mechanically strong spool can not avoid plastic deformation of the flanges and the drum. After repeated use of several times, the deformation of the spool is proceeding, or the spool is broken to become unusable. That is, the conventional spool has a disadvantage that it fails to ensure durability appropriate to the high costs.

Therefore, it is an aim of the present invention to provide a spool for an extra fine metal wire having sufficient mechanical strength and repetitive usability, while achieving reduction in weight and cost, and a method of manufacturing same.

Summary of the invention.

The present invention relates to a spool made of thick metal sheet for a fine metal wire. The spool comprises a core and two flanges coupled to the drum. The core further comprises two concentric drums: an inner drum with inner diameter d, and an outer drum with outer diameter D. The present invention changes the load distribution of side pressure and further improves the structural rigidity of spool to against deformation.

Brief description of the drawings.

The invention will now be described into more detail with reference to the accompanying drawings wherein

FIGURE 1 is a cross-sectional view of a conventional spool; - FIGURE 2 is a A-A cross-sectional view of a spool incorporating the present invention;

FIGURE 3 is a schematic diagram showing the load distribution of side pressure on the flanges with a conventional spool;

FIGURE 4 is a schematic diagram showing the load distribution of side pressure on the flanges with a spool incorporating the present invention;

FIGURE 5 is the side view of a spool incorporating the present invention;

FIGURE 6 is the detail drawing of the weld between the outer periphery of the inner drum and the inner periphery of the center hole on the flanges;

FIGURE 7 is the detail drawing of the weld between the inner periphery of the outer drum and the evenly distributed slots on the flanges; - FIGURE 8 is the detail drawing of the weld between the outer periphery of the outer drum and the surface of the flanges;

Item 10 is a conventional spool.

Item 12 is the core of a conventional spool. Item 14 is the flange of a conventional spool.

Item 20 is a spool incorporating the present invention.

Item 22 is the core of a spool incorporating the present invention.

Item 24 is the flange of a spool incorporating the present invention.

Item 26 is the inner drum of a spool incorporating the present invention. Item 28 is the outer drum of a spool incorporating the present invention.

Item 30 is the center hole on the flange of a spool incorporating the present invention;

Item 32 is the evenly distributed slot on the flange of a spool incorporating the present invention;

d is the inner diameter of the inner drum 26. D is the outer diameter of the outer drum 28. φ is the outer diameter of the flange 24.

H is the height of the outer drum 28.

F2 is the side pressure, on the flange 14.

F4 is the side pressure, on the flange 24

Description of the preferred embodiments of the invention.

In FIGURE 1 , there is shown in cross section view of a conventional spool. The spool 10 has a core 12 and two flanges 14 coupled to the drum 12.

In FIGURE 2, there is shown in A-A cross-sectional view of a spool incorporating the present invention. The spool 20 has a core 22 and two flanges 24 coupled to the core 22, while the core 22 comprises two concentric drums, an inner drum 26 with inner diameter d, and an outer drum 28 with outer diameter D.

As shown in FIG 3, the flanges 14 are under the side pressure F2 generated from the tension of fine metal wire. The load distribution on a slice of the flange 14 can be simplified as a beam supported at one end with evenly distributed side pressure F2. While as shown in FIG 4, the flanges 24 are under the side pressure F4 generated from the tension of fine metal wire. The load distribution on a slice of the flange 24 can be simplified as a beam supported both at one end and at the middle with evenly distributed side pressure F4. This double supported beam is structural stronger than the beam supported at one end.

Besides, we find out:

1 , the more layers of fine metal wire winded on the core, the higher the pressure on the core, because more metal wires exert tension on the core; 2, the more layers of fine metal wire winded on the core, the higher the side pressure on the flanges, because more metal wires exert tension on the flanges;

Therefore, increasing the outer diameter D of the outer drum helps to reduce the layers of fine metal wire winded on the drum, and further helps to reduce the pressure on the core and side pressure on the flanges. Additionally, when φ and D are increased, the rotational speed of the spool during the winding and un-winding process decreases, this will make the positioning of the wire near the flanges more controlled and thus less problematic. But there is always a limit for the expansion of the outer diameter of the outer drum and the outer diameter of the flange, because the spool should fit with the space on the saw machines. Hence, the outer diameter D is between 1.3 and 2.1 times of the inner diameter d, while the outer diameter φ of the flange is between 2.2 and 2.8 times of the inner diameter d.

A further improvement is to extend the height H of the spool to further reduce the layers of fine metal wire on the drum. Since the spool should fit with the space on the saw machines, there is a limit for the extension of the height H of the spool. Therefore, the height H of the spool, i.e. the height H of the outer drum, is between 2.0 and 3.0 times of the inner diameter d.

The following comparison between a conventional spool, spool 0 and spools, spool 1 and spool 2, incorporating present invention can further illustrate the improvements and benefits. A conventional spool, as shown in FIGURE 1 , has the following specifications: d = 150mm;

φ = 315mm;

H = 315mm;

While spools incorporating present invention, as shown in FIGURE 2, has the following specifications:

If the spools, a conventional spool, spool 0, and two spools, spool 1 & spool 2, incorporating present invention, are to wind the same volume of fine metal wire, the pressure on the core, and the side pressure on the flanges of spools incorporating present invention decrease dramatically, while the structural rigidity increases drastically, compared with those of a conventional spool.

With the improvements on the load distribution on the core and flanges, and the improvements on the structural rigidity of the spool, present invention can use thinner metal sheet with thickness between 2.5mm and 7.0mm, and preferably between 3.0mm and 5.0mm to make spools compared with conventional ones.

The following table illustrates the improvements and benefits of the spools incorporating present invention.

The above comparison test further discloses that the ratio φ/D is also critical for this double drum spool. The smaller the ratio φ/D, the smaller the deformation of the spool after use, and therefore the more times reuse of the spool. But there should be some limits for ratio φ/D. On one hand, the lower limit for ratio φ/D should be greater than 1.0 because the outer diameter of the flange φ should be greater than the outer diameter D of the outer drum to make the spool workable. On the other hand, the upper limit for ratio φ/D should be no more than 2.0 because the higher the flange exceeds the outer drum the bigger the deformation of the spool after use. Therefore, the ratio φ/D is between

1.0 and 2.0, and more preferably, between 1.3 and 1.6.

As shown In FIGURE 5, the flange 24 has one center hole 30 and evenly distributed slots 32 around the center hole. As shown in FIGURE 6, there is a weld between the outer periphery of the inner drum 26 and the inner periphery of the center hole 30 on the flanges 24. As shown in FIGURE 7, there is a weld between the inner periphery of the outer drum 28 and the evenly distributed slots 32 on the flanges 24. The above arrangement has following advantages: 1 , improves the connection between the inner drum and the flanges;

2, improves the connection between the outer drum and the flanges;

3, guarantees the concentric between the inner drum and the outer drum;

4, limits the deformation of flanges because of the limited weld between the outer drum and the flanges;

5, easy to manufacture because of the simplified structure;

As shown in FIGURE 8, there is a weld between the outer periphery of the outer drum 28 and the surface of the flanges 24. This weld further improves the connection between the outer drum and the flanges, and improves the structural rigidity of the spool.

The method of manufacturing a spool incorporating present invention includes:

1 , the flange 24 is manufactured by press working of the thick metal sheet, and the outer periphery of the flange 24 is generally reinforced by a folding procedure. The center hole 30 and the evenly distributed slots 32 are manufactured by the press working.

2, the inner drum 26 and the outer drum 28 are formed by bending a metal sheet into a cylindrical shape.

3, the outer periphery of the inner drum 26 is welded to the inner periphery of the center hole 30 on the flanges 24;

4, the inner periphery of the outer drum 28 is welded to the evenly distributed slots 32 on the flange 24;

5, the outer periphery of the outer drum 28 is welded to the surface of the flanges 24. 6, both the ends of the inner drum 26 can have a chamfer angle to facilitate the mounting the spool on the machines; 7, the weld between the outer periphery of the outer drum 28 and the surface of the flanges 24 can be cut and rounded to facilitate smooth winding and re-winding process.

Another improvement to present invention is to weld some support plates 34 between the outer periphery of the inner drum 26 and the inner periphery of the outer drum 28 as shown in Figure 9. The support plates 34 improve the strength of outer drum 28 against deformation, and make sure the inner drum 26 and outer drum 28 are concentric.

A further improvement to present invention is to make the chamfer angle around the center hole 30 on the flanges 24 as shown in Figure 10, and to weld the ends of the outer drum 28 to the surface of the flanges 24. Therefore, it is not needed to weld between the ends of the inner drum 26 and the surface of the flanges 24 because the ends of the inner drum 28 are under a pressure against the surface of the flanges 24 when the spool is loaded with fine wire.