Method for enhancing surface smoothness of ball valve stem

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to manufacturing methods of ball valves, and more particularly, to a method for enhancing surface smoothness of a ball valve stem.

2. Description of Related Art

A traditional ball valve assembly is depicted in FIG. 1. The ball valve assembly employs a stem 1 to rotate a ball 2 for predetermined angles so as to open or close a vent. The ball 2 is settled in an inner chamber the ball valve assembly. The stem 1 extending inside a housing 3 of the ball valve assembly has one end connected with the call 2 and an opposite end hutting out the housing 3 to be coupled with a tool (not shown) so that the stem 1 can be rotated by the tool. The stem 1 is rotatably positioned in a channel formed in the housing by at least one retainer 5. At least one annular packing member 4 fixed in the channel allows the stem 1 to pass therethrough while keeping close contact with the stem 1 so as to prevent a liquid in the inner chamber from leaking out through the channel. The packing member 4 may be made of Teflon or graphite but not traditional elastic rubber material. However, repeated rotation of the stem 1 means constant friction against the packing member 4 and when the packing member 4 finally gets worn, it will lose close contact with the stem.

In the aforementioned ball valve, the durability of the packing member 4 is subject to the surface smoothness of the stem 1. In other words, the rougher the stem surface is, the sooner the packing member 4 gets worn. It is known that the tool marks formed on the surface of the stem 1 during the manufacturing process can shorten the service life of the packing member 4. Conventionally, a mechanical burnishing or polishing procedure may follow the manufacturing process in order to eliminate the foresaid tool marks. However, the mechanical burnishing or polishing procedure forms some finer and oriented impressions on the stem surface and thus fails to be a successful approach to improving the service life of the packing member. Besides, if the burnishing or polishing procedure is not performed properly, the stem may be made undersized or not round enough, and thus fail to closely contact the packing member.

SUMMARY OF THE INVENTION

One primary objective of the present invention is to improve the surface smoothness of a ball valve stem so as to reduce friction against a packing member of a ball assembly, thereby improving the service life of the packing member.

Another primary objective of the present invention is to ensure the accuracy of the stem in diameter and roundness, thereby ensuring close contact between the stem and the packing member.

According to the present invention, a method for enhancing surface smoothness of a ball valve stem comprises:

positioning the ball valve stem at a predetermined position while allowing the ball valve stem to axially rotate;

contacting a surface of the ball valve stem with at least one axially rotatable pressing roller and driving the pressing roller to axially rotate; and

pressing the rotating pressing roller against the surface of the ball valve stem to even and smoothen the surface of the ball valve stem.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention as well as a preferred mode of use, further objectives and advantages thereof will be best understood by reference to the following detailed description of illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a partial sectional view of a traditional ball valve assembly;

FIG. 2 is a perspective view of a first pressing roller, a second pressing roller of the present invention and a ball valve stem;

FIG. 3 is a schematic drawing illustrating the first pressing roller, the second pressing roller, and other components of the present invention and the ball valve stem;

FIG. 4 is a sectional view of the first pressing roller, the second pressing roller of the present invention and the ball valve stem taken along Line 4-4 of FIG. 2;

FIG. 5 is a partially enlarged sectional view of the ball valve stem showing tool marks on surface thereof;

FIG. 6 is another partially enlarged sectional view of the ball valve stem after the tool marks are pressed to even;

FIG. 7 is a schematic drawing showing the first pressing roller pressing the ball valve stem; and

FIG. 8 is a schematic drawing showing the first pressing roller evening the tool marks on the ball valve stem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While a preferred embodiment is provided herein for illustrating the concept of the present invention as described above, it is to be understood that the components in these drawings are made for better explanation and need not to be made in scale. Moreover, in the following description, resemble components are indicated by the same numerals.

Referring to FIGS. 2 and 3, the present invention proposes a method for enhancing surface smoothness of a ball valve stem. To realize the method, an apparatus implemented comprises a supporting device 11, a first pressing roller 21, a second pressing roller 25, and a pressing device 32.

The supporting device 11 serves to position a ball valve stem 10 at a predetermined position while allowing the ball valve stem 10 to axially rotate. The supporting device 11 may be any known mechanism, such as a supporter 111 settled below the ball valve stem 10 as shown in FIG. 3.

The first pressing roller 21 is to be driven by a power source 20. The first pressing roller 21 has an axis (indicated by Line 22) parallel to an axis (indicated by Line 14) of the ball valve stem 10. The first pressing roller 21 also has a periphery 23 linearly contacting a surface 101 of the ball valve stem 10. The first pressing roller 21 is made of a rigid metal and has a periphery 23 formed as a wear-resisting smooth surface.

The second pressing roller 25 is set as rotatable and has an axis (indicated by Line 26) parallel to the axis (indicated by Line 14) of the ball valve stem 10. The second pressing roller 25 also has a periphery 27 linearly contacting a surface 101 of the ball valve stem 10. The second pressing roller 25 is made of a rigid metal and has a periphery 27 formed as a wear-resisting smooth surface.

The pressing device 32 exerts a pressing force to press the ball valve stem 10 toward the first pressing roller 21. In the present embodiment, the pressing device 32 is a power cylinder 321, which has a driving shaft 322 connected to a brace 33 for holding the first pressing roller 21 so that the driving shaft 322 serves to exert the pressing force as indicated by Arrow A in FIG. 3 to press the first pressing roller 21 toward the ball valve stem 10.

As illustrated in FIG. 4, the pressing force (as indicated by Arrow A) keeps close linear contact between the first pressing roller 21, the second pressing roller 25 and the ball valve stem 10. The power source 20 drives the first pressing roller 21 to rotate and in turn makes the ball valve stem 10 and the second pressing roller 25 rotate. Since the pressing force (as indicated by Arrow A) is applied to first pressing roller 21 in a single direction, the first pressing roller 21 and the second pressing roller 25 cause a rigid pressing effect against the ball valve stem 10 so as to even the tool marks formed on the surface of ball valve stem 10 during the manufacturing process thereof.

FIGS. 5 and 6 depict how the tool marks on the surface of ball valve stem 10 get evened. In FIG. 5, the saw-toothed contour 50 represents the tool marks and the vertical broken line 51 running abreast the saw-toothed contour 50 represents the surface of the ball valve stem 10. At this time, the ball valve stem 10 has not been pressed and the tool marks can be seen at the surface of the ball valve stem 10. In FIG. 6, the ball valve stem 10 has received treatment of the apparatus of the present invention, and the saw-toothed contour 50 is evened to become level with the vertical broken line 51. In other words, the tool marks have been eliminated, and the surface of the ball valve stem 10 thus presents excellent smoothness.

In FIG. 7, the surface of the ball valve stem 10 is rotating and pressing by the first pressing roller 21. Therein, the curved line 53 represents the tool marks on the surface of the ball valve stem 10 and the curved line 54 represents the surface of the ball valve stem 10 while arrows 55, 56 represent rotation directions of the first pressing roller 21 and the ball valve stem 10, respectively. The aforementioned rigid pressing effect happens at a point P where the first pressing roller 21 and the ball valve stem 10 contact with each other. Due to the rotation of the pressing roller 21 and the valve stem 10, the point P actually extends and develops along the periphery of the ball valve stem 10. Consequently, the tool marks get pressed and evened down to the curved line 54 to form the smooth surface of the ball valve stem 10 as shown in FIG. 8.

In a ball valve assembly, the ball valve stem 10 with enhanced surface smoothness helps to reduce friction against a packing member of the ball valve assembly, thereby improving the durability of the packing member. Moreover, while improving the surfacing smoothness of the ball valve stem 10, the present ensures the accuracy of the stem in diameter and roundness, thereby ensuring close contact between the stem and the packing member.

The present invention has been described with reference to the preferred embodiment and it is understood that the embodiment is not intended to limit the scope of the present invention. Moreover, as the contents disclosed herein should be readily understood and can be implemented by a person skilled in the art, all equivalent changes or modifications which do not depart from the concept of the present invention should be encompassed by the appended claims.

Method for enhancing surface smoothness of ball valve stem

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