CA2225056C

CA2225056C - Screw

Info

Publication number: CA2225056C
Application number: CA002225056A
Authority: CA
Inventors: Sen-Yang Chen; Chao-Tai Cheng
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-11-25
Filing date: 1997-12-17
Publication date: 2001-10-16
Anticipated expiration: 2017-12-17
Also published as: AU689729B2; CA2225056A1; AU7170896A

Abstract

The shank portion of a screw has a surface formed with a screw thread throughout the length thereof and a lower section formed with a flute at the surface thereof. The flute extends from a tip of the shank portion and has a longitudinal length which is inclined with respect to a longitudinal axis of the shank portion. The flute is defined by a planar side wall, which is inclined relative to the longitudinal axis, and a curved bottom. The planar side wall has a surface with screw thread portions that are disposed in a staggered arrangement in a direction receding from a direction of screw advancing rotation. The flute has a depth which decreases gradually from the tip of the shank portion, and which has a maximum value equal to radius of the shank portion. The longitudinal length of the flute forms an angle ranging from 12° to 32.5° with the longitudinal axis. The screw further has a head portion with an annular skirt adjacent to the shank portion. The annular skirt has one side which is formed with an annular recess around the shank portion and a plurality of radial teeth in the annular recess.

Description

CA 0222~0~6 1997-12-17 .~ . . ~

SCREW
FIELD OF THE ll.v~..ION
This invention relates to a screw and particularly to a screw which can be quickly driven into a workpiece at a smaller driving force requirement, and which provides an enhanced binding force with the workpiece when driven through the latter.

In drawings which illustrate embodiments of the invention, Figure 1 is a perspective view of a conventional screw that is adapted for use with a fibrous board;
Figure 2 is a schematic view which illustrates the conventional screw when being driven into a fibrous board;
Figure 3 is a schematic view which illustrates a first preferred embodiment of a screw of the present invention when being driven into a fibrous board;
Figure 4 is a schematic view which illustrates a second preferred embodiment of a screw according to the present invention when being driven into a fibrous board;
Figure 5 is a schematic view which illustrates a third preferred embodiment of a screw according to the present invention; and Figure 6 is a schematic view which illustrates the third preferred embodiment when being driven through a CA 0222~0~6 1997-12-17 metal plate.
BACRGROUND OF THE l~V~ lON
Screws are used to fasten together two workpieces or to regulate the distance between two workpieces.
s Although all screws have the aforementioned functions, different types of screws exist due to differences in the materials of the workpieces. Figures 1 and 2 illustrate a conventional screw 1 that is adapted for use with a fibrous board 2. Prior to application of the screw 1, which is free of a drill bit portion, to the fibrous board 2, a small hole 21 is initially cut into the fibrous board 2. The screw 1 is then rotated so as to be driven into the fibrous board 2 at the hole 21.
When driving the screw 1, the resulting shavings must be discharged to prevent blocking of the screw thread 12 at the surface of the shank portion 11 of the screw 1 and to prevent disruption of the threaded engagement between the screw 1 and the fibrous board 2.
To achieve this goal, the surface of the lower section of the shank portion 11 of the screw 1 is formed with a flute 15 which extends from a flat tip of the shank portion 11 and which has a longitudinal length parallel to a longitudinal axis 14 of the shank portion 11. The flute 15 is defined by a side wall 151 parallel to the longitudinal axis 14, and a curved bottom 152.
Some of the drawbacks of the conventional screw 1 are as follows:

CA 0222~0~6 1997-12-17 1. The conventional screw 1 cannot be quickly driven into the fibrous board 2. As shown in Figure 2, the screw thread portions on the surface of the side wall 151 of the flute 15 are arranged along a straight line parallel to the longitudinal axis 14 and contact the fibrous board 2 at the same time, thereby resulting in a relatively large resistance between the shank portion 11 and the fibrous board 2. This large resistance retards the driving speed of the screw 1 and results in a larger driving force requirement and in a longer driving time.

2. As mentioned beforehand, the conventional screw 1 has a larger driving force requirement. Thus, when the conventional screw 1 is driven with the use of a mechanical driving tool (not shown), this large driving force requirement easily uses up the reserve power of a pressure source of the driving tool. Thus, the pressure source must be frequently replenished when driving the screw 1, thereby inconveniencing the operator.

3. In view of the large driving force requirement of the conventional screw 1, the application of an extremely large driving force usually occurs. This may lead to damage to the screw thread 12 on the screw 1 which, in turn, may adversely affect the binding force between the fibrous board 2 and the screw 1.

4. When the screw 1 is driven through a thin metal plate (not shown), the plate is bound to the screw 1 CA 0222~0~6 1997-12-17 via threaded engagement with a relatively short section of the screw thread 12 on the shank portion 11, thereby resulting in a relatively weak binding force between the screw 1 and the plate. In particular, when the screw 1 is advanced through the plate so that the latter is disposed adjacent to a head portion of the screw 1, the plate is in contact with an end section of the screw thread which is less than a full circumference of the shank portion 11. As such, threaded engagement between the screw 1 and the plate is weak, and idle rotation of the screw 1 relative to the plate usually occurs. Thus, the screw 1 is not suitable for use in fastening thin plates.
SUMMARY OF THE lNv~NlION
Therefore, the object of the present invention is to provide a screw which can be quickly driven into a workpiece at a smaller driving force requirement, and which provides an enhanced binding force with the workpiece when applied to the latter.
According to the present invention, a screw comprises a head portion and a shank portion which extends from the head portion. The shank portion has a surface that is formed with a screw thread throughout the length thereof. The shank portion further has a lower section that is formed with a flute at the surface of the shank portion. The flute extends from a tip of the shank portion and has a longitudinal length CA 0222~0~6 1997-12-17 which is inclined with respect to a longitudinal axis of the shank portion. The flute is defined by a planar side wall, which is inclined relative to the longitudinal axis, and a curved bottom. The planar side wall has a surface with screw thread portions that are disposed in a staggered arrangement in a direction receding from a direction of screw advancing rotation.
The flute has a depth which decreases gradually from the tip of the shank portion. The flute has a maximum depth equal to radius of the shank portion. The longitudinal length of the flute forms an angle ranging from 12~ to 32.5~ with the longitudinal axis. The head portion is formed with an annular skirt adjacent to the shank portion. The annular skirt has one side which is formed with an annular recess around the shank portion and which is formed with a plurality of radial teeth in the annular recess.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 3 illustrates the first preferred embodiment of a screw 4 according to the present invention when being driven into a fibrous board 5 at a small hole 51 in the latter. The screw 4 is free of a drill bit portion, and has a head portion 43 and a shank portion 41 which extends from the head portion 43. The shank portion 41 has a surface that is formed with a screw thread 42 throughout the length of the shank portion 41. The shank portion 41 further has a lower section CA 0222~0~6 1997-12-17 formed with a flute 45 at the surface thereof. The flute 45 extends from a tip of the shank portion 41 and permits the discharge of shavings which result when the screw 4 is driven into the fibrous board 5 so as to prevent blocking of the screw thread 42 on the shank portion 41 and so as to prevent disruption of the threaded engagement between the screw 4 and the fibrous board 5. The flute 45 has a longitudinal length which is inclined with respect to a longitudinal axis 44 of the shank portion 41, and is defined by a planar side wall 451 which is inclined relative to the longitudinal axis 44, and a curved bottom 452. The planar side wall 451 has a surface with screw thread portions that are disposed in a staggered arrangement in a direction receding from a direction of screw advancing rotation.
The depth of the flute 45 decreases gradually from the tip of the shank portion 41. The flute 45 has a maximum depth equal to the radius of the shank portion 41. In addition, the longitudinal length of the flute 45 forms an angle of less than 45~ with the longitudinal axis 44. The size of this angle depends upon the intended application of the screw 4 and ranges from 12~ to 32.5~.
The head portion 43 is formed with an annular skirt 431 which has a bottom side formed with an annular recess 432 around the shank portion 41. The bottom side of the annular skirt 431 is further formed with a CA 0222~0~6 1997-12-17 plurality of radial teeth 433 in the annular recess 432.
As shown, when the screw 4 is rotated, the screw thread portions (a), (b), (c), (d), (e) on the surface of the planar side wall 451 of the flute 45 contact the fibrous board S in sequence. The gradual contact between the screw thread portions (a), (b), (c), (d), (e) and the fibrous board 5 results in a smaller resistance between the shank portion 41 and the fibrous board 5, thereby resulting in a smaller driving force requirement and in a shorter driving time. Thus, the screw 4 can be quickly driven into the fibrous board 5 and is not easily damaged during the driving operation.
Two experiments were conducted to verify the improved effects of the screw 4 over the conventional screw 1 described beforehand. In a first experiment, a number of the screws 4, 1 were driven into a wooden board that is 40 mm thick under an axial load of 25 kg.
at a speed of 2500 RPM. The results indicate that it takes an average of 0.318 and 1.298 seconds, respectively, to drive the screw 4 and the conventional screw 1 into the wooden board. These results verify that the screw 4 can be quickly driven into the wooden board without causing damage to the screw 4. In addition, since the screw 4 can be driven into the wooden board within a shorter amount of time as compared to the conventional screw 1, one can conclude CA 0222~0~6 1997-12-17 that a smaller resistance is encountered by the screw 4 and that a smaller driving force is required by the same.
In a second experiment, a number of the screws 4, 1 were driven through a steel plate that is 1.5 mm thick under an axial load of 25 kg. at a speed of 2500 RPM.
The results indicate that it takes an average of 1.438 and 2.088 seconds, respectively, to drive the screw 4 and the conventional screw 1 through the steel plate.
These results verify that the screw 4 can be quickly driven through the steel plate without causing damage to the screw 4. In addition, since the screw 4 can be driven through the steel plate within a shorter amount of time as compared to the conventional screw 1, one can conclude that a smaller resistance is encountered by the screw 4 and that a smaller driving force is required by the same.
Figure 4 illustrates the second preferred embodiment of a screw 6 according to the present invention when being driven into a fibrous board 7. The screw 6 is generally similar to the screw 4 of the previous embodiment, the main difference residing in that the shank portion 61 of the screw 6 has a gradually tapering tip, whereas the shank portion 41 of the screw 4 has a flat tip. As with the previous embodiment, the screw 6 has a head portion 65 formed with an annular skirt 651, and a shank portion 61 which has a surface CA 0222~0~6 1997-12-17 that is formed with a screw thread 64 and a flute 63 which extends from the tip of the shank portion 61 and which has a longitudinal length that is inclined with respect to a longitudinal axis 62 of the shank portion 61. The annular skirt 651 of the head portion 65 has a bottom side formed with an annular recess 652 around the shank portion 61 and a plurality of radial teeth 653 in the annular recess 6S2.
Figure 5 illustrates the third preferred embodiment of a screw 8 according to the present invention. The screw 8 is generally similar to the screws 4, 6 of the previous embodiments, the main difference residing in that the tip of the shank portion 83 of the screw 8 has a drill bit section 82. As with the previous embodiments, the screw 8 has a head portion 81 formed with an annular skirt 84, and a shank portion 83 which has a surface that is formed with a screw thread 831 and a flute 830 which extends from the tip of the shank portion 83 and which has a longitudinal length that is inclined with respect to a longitudinal axis of the shank portion 83. The annular skirt 84 of the head portion 81 has a bottom side formed with an annular recess 841 around the shank portion 83 and a plurality of radial teeth 842 in the annular recess 841.
Referring to Figure 6, when the screw 8 is rotated for driving through a thin metal plate 69, a portion of the metal plate 69 that is located around the shank CA 0222~0~6 1997-12-17 portion 83 of the screw 8 tends to bulge slightly in a direction opposite to the advancing direction of the screw 8. After the shank portion 83 of the screw 8 is driven completely through the metal plate 69, the bulging portion of the metal plate 69 extends into the annular recess 841 to contact the annular skirt 84.
Under this condition, the metal plate 69 engages threadedly several turns of the screw thread 831 that is located within the annular recess 841. Idle rotation of the screw 8 relative to the metal plate 69 can be effectively avoided. In addition, the metal plate 69 engages frictionally the radial teeth 842 formed on the bottom side of the annular skirt 84. An enhanced binding force between the screw 8 and the metal plate 69 thus results. Since the bulging portion of the metal plate 69 extends into the annular recess 841 of the screw 8, the metal plate 69 has a flat exposed surface and a neat appearance.
The advantages and characterizing features of the screws 4, 6, 8 of the present invention are as follows:
1. The screw of the present invention can be quickly driven into a workpiece. Since the screw thread portions on the surface of the planar side wall of the flute are disposed in a staggered arrangement, simultaneous contact of the same with the workpiece can be avoided, thereby resulting in a smaller resistance between the shank portion of the screw and the CA 0222~0~6 1997-12-17 workpiece which, in turn, results in a faster driving speed, a smaller driving force requirement and in a shorter driving time.
2. Since the screw of this invention has a smaller driving force requirement, when the screw is driven with the use of a mechanical driving tool, the reserve power of a pressure source of the driving tool is not easily used up. This results in added convenience to the operator.
3. In view of the smaller driving force requirement of the screw, the application of large driving forces is not needed, thereby avoiding damage to the screw thread on the screw which, in turn, ensures that an effective binding force is present between the workpiece and the screw.
4. Since the screw thread formed on the screw of the present invention has several turns disposed in the annular recess that is formed in the bottom side of the annular skirt, a thin plate can engage threadedly and securely the screw when the screw is driven fully therethrough. Idle rotation of the screw relative to the metal plate can be avoided.

5. Since the bottom side of the annular skirt is formed with a plurality of radial teeth, friction between the head portion and the metal plate is enhanced for greater binding force between the screw and the thin plate.

CA 0222~0~6 l997- l2- l7 While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.

Claims

1. A screw comprising a head portion and a shank portion which extends from said head portion, said shank portion having a surface that is formed with a screw thread throughout the length of said shank portion, said shank portion further having a lower section formed with a flute at said surface of said shank portion, said flute extending from a tip of said shank portion and having a longitudinal length which is inclined with respect to a longitudinal axis of said shank portion, said flute being defined by a planar side wall which is inclined relative to said longitudinal axis, and a curved bottom, said planar side wall having a surface with screw thread portions that are disposed in a staggered arrangement in a direction receding from a direction of screw advancing rotation, said flute having a depth which decreases gradually from said tip of said shank portion, said flute having a maximum depth equal to radius of said shank portion, the longitudinal length of said flute forming an angle ranging from 12° to 32.5° with said longitudinal axis, said head portion being formed with an annular skirt adjacent to said shank portion, said annular skirt having one side formed with an annular recess around said shank portion, said one side of said annular skirt being further formed with a plurality of radial teeth in said annular recess.

2. The screw as claimed in Claim 1, wherein said tip of said shank portion is flat.

3. The screw as claimed in Claim 1, wherein said tip of said shank portion tapers gradually.

4. The screw as claimed in Claim 1, wherein said tip of said shank portion is provided with a drill bit section.