NZ744141A - Screw - Google Patents

Abstract

A screw (3) includes a shank (31), a head (32) and a drilling portion (33) respectively formed at two ends of the shank, and spiral threads (34). The threads (34) extend spirally from the shank (31) to the drilling portion (33) to define a first, a second and a third threaded section (S1, S2, S3) which extend spirally in sequence to construct a continuous threaded portion. The threaded sections (S1, S2, S3) are respectively formed in a single spiral arrangement where each thread (34) of the first threaded section (S1) is continuously disposed a revolution around the shank (31) and each thread (34) of the third threaded section (S3) is continuously disposed a revolution around the drilling portion (33). Any two adjacent threads (34) of the first and the second threaded section (S1, S2) expose a shank segment (311) which increases progressively towards the drilling portion (33). The drilling portion (33) is tapered to form a terminal end (331), and the third threaded section (S3) is connected to the terminal end (331). Spaced apart recesses (35) are formed on the threads (34) of the second threaded section (S2) and inclinedly open with respect to a central axis (R) of the shank (31). The progressively increasing shank segment (311) supports the threads (34) to resist the twisting force and pulling-out force and prevent the shank (31) and threads (34) from being broken, and the recesses (35) also help cut, receive and remove debris, thereby cutting quickly, attaining an anti-loosening effect and increasing a fastening and positioning effect.

Description

SCREW BACKGROUND OF THIS INVENTION 1. Field of this invention This invention relates to a screw and relates particularly to a screw capable of resisting the pulling-out force and attaining an anti-loosening effect. 2. Description of the Related Art Referring to Figs.1 to 3, the U.S. Patent Application Publication No. 2005/0186048 discloses a thread-forming screw 1 having a shank 11, a head 12 and the drilling tip 13 disposed at two ends of the shank 11, and a plurality of threads 14 spirally disposed on the shank 11. Each thread 14 includes a plurality of connective troughs 141 open by a trough angle 146 and has an upper surface 142 and a lower surface 143 opposite to the upper surface 142. The two surfaces 142, 143 converge on a crest 145. During the drilling operation, the cutting efficiency of the threads 14 depends on the trough angle 146. For example, if the trough angle 146 is too small, fibers provided with the elastic property may not enter the troughs 141 easily, which renders the troughs 141 unable to assist the thread 14 in cutting fibers. In contrast, if the trough angle 146 is too large, the threads 14 may become thinner. The thinner structure may be easily broken because it is not strong enough to bear the twisting force and resistance caused by the drilling action. Regarding the crest 145 with an included angle B, if a larger turning power or driving torque is required for drilling the screw into a hardwood, the resistance of the drilling operation is relatively large. Thus, the thread 14 with the included angle B smaller than a common crest angle may not be strong enough to fight against the resistance, and the threads 14 get broken easily. In contrast, the threads 14 may bear the twisting force and resistance during the drilling operation when the included angle B is larger than the common crest angle. However, the cutting effect of the larger included angle B is worse than that of the smaller included angle B. Therefore, the screw 1 still needs improvement.

SUMMARY OF THIS INVENTION The object of this invention is to provide a screw capable of resisting the pulling-out force, increasing the cutting efficiency, and attaining an anti-loosening effect and a speedy drilling and stable fastening effect.

The screw of this invention includes a shank with a plurality of threads spirally disposed thereon, and a head and a drilling portion respectively disposed two ends of the shank. The plurality of threads include threads which are spirally disposed around the shank to define a first threaded section, threads following the first threaded section and extending spirally toward the drilling portion to define a second threaded section, and threads following the second threaded section and spirally disposed around the drilling portion to define a third threaded section. Each of the threads has an upper flank facing the head and a lower flank facing the drilling portion. The upper flank and the lower flank converge on a crest. The shank is formed with shank segments. Any two adjacent threads of the first threaded section and any two adjacent threads of the second threaded section are spaced apart to expose the shank segment which has a base part and an extension part extending outwards from the base part. The extension part is connected to the upper flank to allow the shank segment to increase progressively in the direction of the drilling portion. There are spaced apart recesses mainly formed on the threads of the second threaded section, each of which includes two slanting cutting walls.

Accordingly, the third threaded section located within the drilling portion and the recesses formed on the threads of the second threaded section cooperate to assist the screw in drilling into a workpiece smoothly during the drilling operation. This attains a speedy drilling effect and facilitates the removal of debris, thereby reducing the driving resistance and saving labor and working time. The shank segment widening gradually because of the extension part also cooperates with the first threaded section and the second threaded section to resist the twisting force and the pulling-out force during the drilling operation, thereby attaining an anti-loosening effect and increasing the fastening and positioning effect.

Preferably, the extension part can be inclined to the base part by 5 to 10 degrees so that each shank segment which widens gradually to extend to the upper flank of the thread is formed like a truncated cone. Further, the drilling portion can be tapered to form a terminal end so that the third threaded section may be connected to the terminal end to help the initial drilling action.

Preferably, each of the threads may be of an asymmetric shape.

In particular, the thread defines a line which passes through the crest and is perpendicular to a central axis of the shank. A first angle defined between the upper flank and the line is smaller than a second angle defined between the lower flank and the line.

Preferably, the shank can have ribs formed between the first threaded section and the head and inclined to the central axis. Also, a thread-free section extends axially between the first threaded section and the head. In one preferred embodiment, the thread-free section is located between the ribs and the head.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing the screw of the U.S. application publication no. 2005/0186048; Fig. 2 is a top plan view taken on line I-I in Fig. 1; Fig. 3 is a cross-sectional view taken on line II-II in Fig. 2; Fig. 4 is a perspective view showing a preferred embodiment of this invention; Fig. 5 is a front elevational view showing the preferred embodiment of this invention; Fig. 6 is a schematic view showing a partial portion of the preferred embodiment of this invention; Fig. 7 is a top plan view taken on line III-III in Fig. 6; Fig. 8 is a cross-sectional view showing the preferred embodiment of this invention; and Fig. 9 is an enlarged view of Fig. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figs. 4 and 5, a screw 3 of a preferred embodiment of this invention includes a shank 31, a head 32 disposed at one end of the shank 31, a drilling portion 33 disposed at another end of the shank 31, and a threaded portion spirally disposed around the shank 31. The threaded portion is formed with a plurality of threads 34, and threaded sections S1, S2, S3 extending from the shank 31 to the drilling portion 33 are sequentially defined according to the distribution of the threads 34. Specifically, the threaded portion includes a first threaded section S1 spirally disposed on the shank 31, a second threaded section S2 following the first threaded section S1 and spirally extending toward the drilling portion 33, and a third threaded section S3 following the second threaded section S2 and spirally disposed around the drilling portion 33. In other words, regarding the threads 34 of the threaded portion in the preferred embodiment include at least one convolution of thread 34 spirally disposed around the drilling portion 33 to define the third threaded section S3, a number of threads 34 following the third threaded section S3 and continuing extending spirally onto the outer periphery of the shank 31 to define the second threaded section S2, and a number of threads 34 following the second threaded section S2 and continuing extending spirally around the shank 31 in the direction of the head 32 to define the first threaded section S1. Thus, the combination of the three threaded section S1, S2, S3 construct the continuous threaded portion with spiral threads 34, of which the first threaded section S1 extends around the outer periphery of the shank 31, the third threaded section S3 extends within the drilling portion 33, and the second threaded section S2 extends between the first threaded section S1 and the third threaded section S3. All or most of threads 34 of the second threaded section S2 are spirally disposed around the shank 31. It is possible that at least one convolution of thread 34 of the second threaded section S2 is still located within the drilling portion 33, as shown in Figs. 4-5.

The length of the spiral extension of the aforementioned threaded sections can be adjusted according to demand. In the preferred embodiment, as shown in Figs. 4 and 5, it is taken as an example that the first threaded section S1 does not run to the bottom of the head 32, and thus between the first threaded section S1 and the head 32 are formed ribs 36 which are inclined to a central axis R of the shank 31 and a thread-free section 37. Specifically, the ribs 36 are located adjacent to the first threaded section S1 and are inclined by an angle different from a spiral angle of the threads 34, and the thread-free section 37 extends axially between the ribs 36 and the head 32. Thus, the above arrangement benefits the accommodation of debris, helps the anti-loosening ability and attains a stable fastening effect.

As shown in Figs. 5, 6 and 8, each of the threads 34 has an upper flank 341 facing the head 32 and a lower flank 342 facing the drilling portion 33. The upper flank 341 and the lower flank 342 converge on a crest 343. The upper flank 341 and the lower flank 342 extend radially from the shank 31 and connect with each other to form the crest 343.

Further, each thread 34 defines a line L passing through the crest 343. The line L is perpendicular to the central axis R of the shank 31. A first angle a1 is defined between the upper flank 341 and the line L, and a second angle a2 is defined between the lower flank 342 and the line L. The first angle a1 may be equal to the second angle a2 (not shown). Alternatively, the first angle a1 may be smaller than the second angle a2 (shown in Fig. 8) so that the thread 34 can be of an asymmetric shape. The asymmetric thread is adopted in the preferred embodiment. The number of the first angle a1 and the second angle a2 can be adjusted according to demand. For example, the first angle a1 can be set from 0 to 5 degrees and the second angle a2 can be set from 35 to 45 degrees.

Referring to Fig. 5, the threads 34 of the threaded sections are spaced apart. The shank 31 is formed with a plurality of shank segments 311, each of which is exposed between any two adjacent threads 34 of the first threaded section S1 and the second threaded section S2.

As shown in Figs. 6 and 9, the shank segment 311 has a base part 3111 and an extension part 3112 extending outwards from the base part 3111.

The extension part 3112 is inclined to the base part 3111 by an angle a3 and flares gradually from the base part 3111 to the upper flank 341. This shows that the extension part 3112 reaches and connects with the upper flank 341. Thus, the shank segment 311 increases progressively toward the drilling portion 33, namely the shank segment 311 widens gradually to be formed like a truncated cone. The angle a3 formed by the extension section 3112 can be adjusted according to demand. For example, the angle a3 can be set from 5 to 10 degrees.

This truncated cone structure assists the shank 31 in suffering the cumulative resistance caused by turning the screw 3 during the drilling operation and prevents the shank 31 from being broken because of insufficient suffering strength.

Referring to Figs. 6 and 7, there are spaced apart recesses 35 formed on the threads 34 of the second threaded section S2, each of which includes two slanting cutting walls 351 so that the recess 35 is open in the direction inclined to the central axis R of the shank 31. In the preferred embodiment, the threads 34 of the first threaded section S1 and the third threaded section S3 can be in a complete thread form, namely they are formed without the recesses 35 as shown in Figs. 4-5.

Thus, the recesses 35 are only formed on part of threads 34 for the full threaded portion. Further, the drilling portion 33 may be tapered to form a sharp terminal end 331, and the third threaded section S3 is connected to the terminal end 331, as shown in Figs. 4 and 5. Further as an alternative, the drilling portion 33 may be a drill tip with a slot or slots (not shown). Herein, the sharp terminal end 331 is shown as an example.

When a driving tool (not shown) is engaged with the head 32 and a driving torque is added to the screw 3, the drilling portion 33 and the third threaded section S3 start drilling into a workpiece without a pilot hole. The workpiece (not shown) can be a hardwood or other suitable materials. Because the third threaded section S3 is spirally disposed around the drilling portion 33 and connected to the terminal end 331, the threads 34 of the third threaded section S3 cut fibers of the workpiece into debris immediately when the drilling portion 33 pierces the workpiece so that the drilling portion 33 can enter the workpiece directly and move gradually under the assistance of the third threaded section S3. Also, the cut debris moves upward to the second threaded section S2 along the threads 34 of the third threaded section S3 to prevent the accumulation of excessive debris and prevent the drilling portion 33 from getting entangled with the fibers. Then, the recesses 35 and the second threaded section S2 keep cutting the unbroken fibers. In other words, the cutting walls 351 of the recesses 35 sever the remaining fibers to cut them into small debris. This helps reduce the drilling resistance to a great degree for cutting speedily and save labor and time. Part of the cut debris is received in the recesses 35 and redundant debris moves to the first threaded section S1 along the spiral second threaded section S2. The first threaded section S1 then provides an auxiliary cutting effect and helps the gradual removal of the cut debris to prevent the improper accumulation of the redundant debris. Because the threads 34 of the first threaded section S1 are formed without the recesses 35, part of the cut debris can be received between the threads 34 of the first threaded section S1 to increase the fastening effect and allow the screw to be stably fastened. Thus, the whole threaded portion constructed by the threaded sections S1, S2, S3 not only increases the cutting efficiency to save labor and time and fasten stably but also prevent the undue accumulation of cut debris to solve the problem that the workpiece gets cracked because of the improper accumulation and push of debris impacting on the workpiece.

After the threads 34 complete the cutting operation, the ribs 36 which are located between the first threaded section S1 and the head 32 and are in angular orientation different from the spiral angle of the first threaded section S1 (as shown in Figs. 4-5) can interfere with the removal of some cut debris come from the first threaded section S1 and press the debris inwards. Thus, the ribs 36 can engage with the workpiece firmly to prevent the screw 3 from loosening and allowing the screw 3 to be stably fastened to the workpiece. The debris can also be accommodated within the thread-free section 37 to attain the stable fastening effect and the anti-loosening effect.

Furthermore, each shank segment 311, widening gradually because of the extension part 3112, provides an auxiliary support so that the screw 3 can resist the gradually increasing resistance of the drilling operation. In other words, the thread segment 311 formed like a truncated cone increases the strength of screw 3 to fight against the twisting force and the pulling-out force during the drilling action, thereby providing the screw 3 with a better suffering ability and an increase in the drilling strength to prevent the shank 31 and the threads 34 from being deformed or broken by improper driving torque. In addition, the lower flank 342 with the large angle a2 has a steeper slope. This slope cooperates with the shank segment 311 described above to drill the shank 31 into the workpiece in a vertical or approximately vertical condition. Such condition helps reduce contact area between the threads 34 and the workpiece and benefits a speedy drilling action. Concurrently, the shank segment 311 also provides the auxiliary support to increase the drilling strength of the screw 3, as described above. Therefore, the screw 3 increases the cutting efficiency and attains an anti-loosening effect and a quick and stable fastening effect.

To sum up, this invention provides the threads including the plurality of threaded sections, and spaced apart recesses formed on part of the threads, namely on the second threaded section, for increasing the cutting efficiency. Each shank segment of the shank also forms an extension part which increases progressively toward the drilling portion, thereby providing an auxiliary support and increasing the strength to resist the twisting force and pulling-out force during the drilling operation. Accordingly, the shank and threads are not easily broken. The recesses formed on the second threaded section also help cut fibers into debris and facilitates the accommodation and removal of debris. Thus, the screw cuts efficiently, provides an anti-loosening effect and attains a stable fastening and positioning effect.

While the embodiment of this invention is shown and described, it is understood that further variations and modifications may be made without departing from the scope of this invention.

Claims (4)

WHAT IS CLAIMED IS:

1. A screw comprising a shank, a head disposed at one end of said shank, a drilling portion disposed at another end of said shank, and a plurality of threads spirally disposed around said shank; 5 wherein said plurality of threads extend spirally from said shank to said drilling portion for constructing a continuous threaded portion and include threads spirally disposed around said shank to define a first threaded section, threads extending spirally from said first threaded section in the direction of said drilling portion to 10 define a second threaded section, and threads extending spirally from said second threaded section to said drilling portion to define a third threaded section, each thread of said first threaded section is continuously disposed a revolution around said shank and each thread of said third threaded section is continuously disposed a 15 revolution around said drilling portion, wherein each of said plurality of threads of said first and said second threaded section having a single upper flank facing said head and a single lower flank facing said drilling portion, said upper flank and said lower flank converging on a single crest, said shank 20 being formed with a plurality of shank segments each being exposed between any two adjacent threads of said first threaded section and said second threaded section, each of said shank segments having a base part and an extension part extending outwards from said base part, said extension part being connected to said upper flank and being inclined to said base part by 5 to 10 degrees to allow said shank segment to increase progressively toward said drilling portion, a plurality of spaced apart recesses being cut into each of said 5 threads of said second threaded section, each of said recesses being enclosed by two cutting walls, said cutting walls slanting relative to a central axis of said shank and extending from said upper flank of said thread of said second threaded section to said lower flank of said thread of said second threaded section directly in order that 10 each of said recesses is inclinedly open with respect to the central axis and goes through from said upper flank to said lower flank, said drilling portion being tapered to form a terminal end, said third threaded section being connected to said terminal end.

2. The screw as claimed in claim 1, wherein each of said threads defines 15 a line which passes through said crest and is perpendicular to a central axis of said shank, a first angle defined between said upper flank and said line being smaller than a second angle defined between said lower flank and said line.

3. The screw as claimed in any of claims 1 to 2, wherein said shank 20 includes a plurality of ribs formed between said first threaded section and said head, said ribs being inclined to a central axis of said shank.

4. The screw as claimed in any of claims 1 to 3, wherein a thread-free section extends axially between said first threaded section and said head. (PRIOR ART) (PRIOR ART) (PRIOR ART) 3111 3112 3111 3112 a2 341 3111 3112 FIG. 8