CA2008383A1 - Breakable composite drill screw - Google Patents
Breakable composite drill screwInfo
- Publication number
- CA2008383A1 CA2008383A1 CA 2008383 CA2008383A CA2008383A1 CA 2008383 A1 CA2008383 A1 CA 2008383A1 CA 2008383 CA2008383 CA 2008383 CA 2008383 A CA2008383 A CA 2008383A CA 2008383 A1 CA2008383 A1 CA 2008383A1
- Authority
- CA
- Canada
- Prior art keywords
- shank
- screw
- thread
- drill bit
- break zone
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000002131 composite material Substances 0.000 title claims abstract description 11
- 238000003466 welding Methods 0.000 claims abstract description 15
- 239000002184 metal Substances 0.000 claims abstract description 9
- 238000005096 rolling process Methods 0.000 claims abstract description 9
- 238000010273 cold forging Methods 0.000 claims abstract description 5
- 229910000963 austenitic stainless steel Inorganic materials 0.000 claims description 5
- 229910001209 Low-carbon steel Inorganic materials 0.000 claims description 4
- 238000000034 method Methods 0.000 abstract description 12
- 238000010079 rubber tapping Methods 0.000 description 7
- 238000010791 quenching Methods 0.000 description 6
- 238000003754 machining Methods 0.000 description 4
- 238000005553 drilling Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000002344 surface layer Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 230000003796 beauty Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000005255 carburizing Methods 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
Landscapes
- Drilling Tools (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A breakable composite drill screw comprises a first shank made of a metal unsusceptible of hardening, a driving head extending from one end of the first shank and engageable with a screw driving tool, a second shank made of another metal susceptible of hardening, the second shank being fix-edly adjoined to the other end of the first shank to thereby provide a break zone at said other end, a drill bit formed by cold forging at an end of the second shank, a continuous thread formed by thread-rolling to extend around both outer cylindrical peripheries of the first and second shank wherein a portion extending from the break zone to the drill bit is hardened or quenched, and wherein said shanks are adjoined at their engaging surfaces to each other by projection-welding technique making use of a welding lug protruding from either engaging surface, said lug forming the break zone.
A breakable composite drill screw comprises a first shank made of a metal unsusceptible of hardening, a driving head extending from one end of the first shank and engageable with a screw driving tool, a second shank made of another metal susceptible of hardening, the second shank being fix-edly adjoined to the other end of the first shank to thereby provide a break zone at said other end, a drill bit formed by cold forging at an end of the second shank, a continuous thread formed by thread-rolling to extend around both outer cylindrical peripheries of the first and second shank wherein a portion extending from the break zone to the drill bit is hardened or quenched, and wherein said shanks are adjoined at their engaging surfaces to each other by projection-welding technique making use of a welding lug protruding from either engaging surface, said lug forming the break zone.
Description
BREAKABLE COMPOSITE DRILL S~REW
Z~ 33~3~
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a breakable composite drill screw which can be snapped in two in such a manner that a drill bit or chip and a superfluous threaded stem portion adjoined thereto are broken off to be removed from the drill screw after it has been turned tight.
Z~ 33~3~
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a breakable composite drill screw which can be snapped in two in such a manner that a drill bit or chip and a superfluous threaded stem portion adjoined thereto are broken off to be removed from the drill screw after it has been turned tight.
2. Description the Prior Art A so-called drill screw which has a drill bit formed at a tip end of a screw having a driv1ng head is advantageous in that the forming of holes in workpieces to be fastened, tapping of the holes and fastening of the workpieces with the screw can be carried out in one continuous operation.
Therefore, the range of its use 1s rapidly increasing.
As new and various uses are found for such drill screw, there arises a certain problem in some cases. For example, the drill bit and a superfluous portion of threaded stem - adjoining said drill bit protrude from a back surface of a structure after it has been fastened by the drill screw, 20~ thereby spoiling the beauty of the structure or building and further being;llkely to inflict an lnjury on a pFrson.
Thls has led to a serious demand for an improved drill screw which after fastening thereof permits its protruding super-: . :
fluous portions to be broken and removed from its main ~ portion.
' - ' : ~ . ,:.
, . . ,~ .:
In this regard, it is a common practice to form a groove at a point where a screw is to be broken to remove such protruding superfluous portions. However, such a common practice cannot be applied to aforementioned drill screws because they have previously been so hardened as to have sufficient hardness for the machining or cutting of their drill bits and also for the tapping of their threaded stems adjoining the drill bits. The thus hardened sur~ace makes it difficult to break the screw at such grooved portion thereof.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a drill screw which is formed with a drill bit and a threaded stem adjacent thereto wherein the drill bit and an end portion of the threaded stem which will protrude from a back surface of a structure fastened with the drill screw are easily broken and removed without failure.
The object is accomplished in the invention by employing in the drill screw a new composite structure comprising:
20 a first shank made of a metal unsusceptible of hardening;
a driving head extending from one end of the first shank so as to be engageable with a screw driving tool; a second :shank made of another metal susceptible of hardening~ the second shank being fixedly adjoined at a point to the other end oE the first shank in such a manner that a break zone is provided at the point; a drill bit formed by cold forging 2~3~3~
at an end of the second shank; a continuous thread formed by thread-rolling technique to extend around both outer cylindrical peripheries of the first and second shanks, wherein a portion extending from the break zone to the drill bit is hardened or quenched.
It is preferable to employ projection-welding technique in order to cause the first shank to fixedly adjoin the second shank by means of a welding lug protruding from one of contacting surfaces of the shanks.
It is also desirable that the continuous thread which is formed by the thread-rolling technique on a section of the second shank near the drill bit comprises at least one pitch of screw thread.
For practical purposes, it is advantageously effective to use an austenitic stainless steel as a material of the first shank and at the same time to use a low-carbon steel as a material of the second shank.
The drill screw which in accordance with the invention : has such a structure as described above enables easier and neater breaking or snapping and subsequent removal of the drill bit and superfluous threaded portion which will project from back surface o~ a fastened object.
: BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevation showing a first shank;
FIG. 2 is a ~ront elevation showing a second shank;
FIG~ 3 is a front:elevation of a blank;
. .
- . : . ,, '. ' ,' ' '" ', ' ~ '`' ~ `, ", " ' ' ' ` '~
.
2~ 3 FIG. 4 is a front elevation illustrating a process by which a drill bit is forrned; and FIG. 5 is a front elevation illustrating a drill screw provided by the present invention.
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the invention will now be described referring to the drawings in which FIG. 1 shows a first shank 11 constituting a drill screw according to the invention, and FIG. 2 shows a second shank 12 also con-stituting the drill screw.
The first shank 11 is made of austenitic stainless steel which is a metal unsusceptible of carburizing-and-quenching, and is of a predetermined diam~ter 'Dl suited to thread-rolling formation of screw thread as descrlbed hereinafter.
The first shank 1l has at its end a driving head 13 which is formed by header-machining technique to be of a shape engageable with a screw driving tool, whereas another end of said first shank 11 is machined to a flat surface 14.
The second shank 12 is made Oe a metal of another kind, for instance of a low-carbon steel which is susceptible of carburizing-and-quenching, the second shank 12 being of the same diameter lD' as that of the first shank 11, and having a welding lug 15 integral with and projecting from a central zone of an end surface o the second shank 12. The welding lug 15 which will form a break ~zone 16 as described later has usually a maximum diameter 'd' which ~: ~
, ~ . . f:,.
2~3~183~33 is predetermined to be included within a range from 0O5D
to 0.8D. Such a dimension is selected here in view of the fact that a drilling and tapping torque necessary for the drill bit and threaded stem portion adjoining it to dig a hole in a workpiece and to subsequently tap the hole is considerably low in general compared with a fastening torque for the turning tight of main portion of the threaded stem. The value of said drilling and tapping torque is equal to, for instance about one third (1/3) to two thirds ~2/3) of the fastening torque. Thus, said comparatively small diameter 'd' of the welding lug 15 can withstand well a force imparted thereto when drilling and tapping are simultaneously carried out by means of the drill bit and the threaded portion adjoining it, while at the same time a~lowing these portions to be broken off considerably easily from the main threaded portion.
FIGS. 3 to 5 illustrate a process for manufacturing the drill screw from the first shank 11 and second shank 12.
At first, the flat end surface 14 of the first shank 11 is caused, as shown in FIG. 3 by projection-welding method, to ixedly adjoin the welding lug 15 of the second shank 12 in order that the break zone 16 is formed at bonded portion between said shanks whereby a composite blank 20 is produced.
Next, a drill bit 21 is formed by cold forging of the second shank 12 in the blank 20, as shown in FIGo 4~ A
machining mold or die used for cold forging of the drill _5_ ~
'-' . ': ' ~ . - . . , , :
.
; . :
-' ' , ' ' . , .
' , ~ : ' . ' 38;~
bit 21 is not shown because it is well known in the industry.
Such machining will produce a scrap 22 along and projecting from an outer periphery of the drill bit 21.
Subsequently, a continuous screw thread 23 and 23a is formed as shown in FIG. 5 by thread-rolling method employing a known rolling die (not shown) so as to extend around both the outer cylindrical peripheries of the first shank 11 and the second shank 12. The scrap 22 referred to above is removed when the thread-rolling is conducted to form the thread, thereby finishing up the drill bit 21. The threaded portion 23a formed by thread-rolling on the second shank 12 desirably has to extend up to a close proximity of the drill bit 21 in a state that it comprises at least one pitch of screw thread which shall function as a tapping screw when tapping is done as described below.
A drill screw 25 which has been machined in a manner described above is then subjected to carburizing-and-quenching treatmPnt . This treatment causes carburizing of, i.e., diffusion of carbon into, surface layers of the drill bit 21 and threaded portion 23a which are formed on the second shank 12, to thereby impart a predetermined hardness to said surface layers. However, the threaded portion 23 formed on the first shank 11 is not carburized due to the unsusceptible nature of the metal of which said first shank is made. The break zone 16 located at the bonded or fixedly adjoined portions between the first and second shanks 11, 12 also is not hardened by carburizing-and-quenching since said zone is at an inner part of said shanks.
The drill screw 25 which is manufactured to obtain the abovedescribed structure will be used to fasten one object to the other (not shown). After a fastening operation is completed, the drill bit 21 and the threaded portion 23a which are likely to protrude from back surface of the other object are easily broken at the break zone 16 and separated from a remaining main part. A remaining main part 26 compxising the first shank 11 is highly corrosion-resistant by virtue of austenitic stainless steel of which said first shank 11 is made.
Although the first shank 11 and the second shank 12 are adjoined to each other by means of projection-welding method ~one of resistance welding methods) in the embodiment, they may be bonded or united to each other by any other suitable method such as pressure welding or by use of any suitable adhesive. If it is deemed appropriate for material of said second shank 12 and for character of fastened objects, any other usual hardening or quenching treatment may be utilized in place of the exemplified carbùrising-and-quenching in ;~ order to harden to a satisfactory degree the surfaces of drill bit 21 and threaded portion 23a which are formed from th second shank 12.
_, ~.
_7--' ~' ,
Therefore, the range of its use 1s rapidly increasing.
As new and various uses are found for such drill screw, there arises a certain problem in some cases. For example, the drill bit and a superfluous portion of threaded stem - adjoining said drill bit protrude from a back surface of a structure after it has been fastened by the drill screw, 20~ thereby spoiling the beauty of the structure or building and further being;llkely to inflict an lnjury on a pFrson.
Thls has led to a serious demand for an improved drill screw which after fastening thereof permits its protruding super-: . :
fluous portions to be broken and removed from its main ~ portion.
' - ' : ~ . ,:.
, . . ,~ .:
In this regard, it is a common practice to form a groove at a point where a screw is to be broken to remove such protruding superfluous portions. However, such a common practice cannot be applied to aforementioned drill screws because they have previously been so hardened as to have sufficient hardness for the machining or cutting of their drill bits and also for the tapping of their threaded stems adjoining the drill bits. The thus hardened sur~ace makes it difficult to break the screw at such grooved portion thereof.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a drill screw which is formed with a drill bit and a threaded stem adjacent thereto wherein the drill bit and an end portion of the threaded stem which will protrude from a back surface of a structure fastened with the drill screw are easily broken and removed without failure.
The object is accomplished in the invention by employing in the drill screw a new composite structure comprising:
20 a first shank made of a metal unsusceptible of hardening;
a driving head extending from one end of the first shank so as to be engageable with a screw driving tool; a second :shank made of another metal susceptible of hardening~ the second shank being fixedly adjoined at a point to the other end oE the first shank in such a manner that a break zone is provided at the point; a drill bit formed by cold forging 2~3~3~
at an end of the second shank; a continuous thread formed by thread-rolling technique to extend around both outer cylindrical peripheries of the first and second shanks, wherein a portion extending from the break zone to the drill bit is hardened or quenched.
It is preferable to employ projection-welding technique in order to cause the first shank to fixedly adjoin the second shank by means of a welding lug protruding from one of contacting surfaces of the shanks.
It is also desirable that the continuous thread which is formed by the thread-rolling technique on a section of the second shank near the drill bit comprises at least one pitch of screw thread.
For practical purposes, it is advantageously effective to use an austenitic stainless steel as a material of the first shank and at the same time to use a low-carbon steel as a material of the second shank.
The drill screw which in accordance with the invention : has such a structure as described above enables easier and neater breaking or snapping and subsequent removal of the drill bit and superfluous threaded portion which will project from back surface o~ a fastened object.
: BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevation showing a first shank;
FIG. 2 is a ~ront elevation showing a second shank;
FIG~ 3 is a front:elevation of a blank;
. .
- . : . ,, '. ' ,' ' '" ', ' ~ '`' ~ `, ", " ' ' ' ` '~
.
2~ 3 FIG. 4 is a front elevation illustrating a process by which a drill bit is forrned; and FIG. 5 is a front elevation illustrating a drill screw provided by the present invention.
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the invention will now be described referring to the drawings in which FIG. 1 shows a first shank 11 constituting a drill screw according to the invention, and FIG. 2 shows a second shank 12 also con-stituting the drill screw.
The first shank 11 is made of austenitic stainless steel which is a metal unsusceptible of carburizing-and-quenching, and is of a predetermined diam~ter 'Dl suited to thread-rolling formation of screw thread as descrlbed hereinafter.
The first shank 1l has at its end a driving head 13 which is formed by header-machining technique to be of a shape engageable with a screw driving tool, whereas another end of said first shank 11 is machined to a flat surface 14.
The second shank 12 is made Oe a metal of another kind, for instance of a low-carbon steel which is susceptible of carburizing-and-quenching, the second shank 12 being of the same diameter lD' as that of the first shank 11, and having a welding lug 15 integral with and projecting from a central zone of an end surface o the second shank 12. The welding lug 15 which will form a break ~zone 16 as described later has usually a maximum diameter 'd' which ~: ~
, ~ . . f:,.
2~3~183~33 is predetermined to be included within a range from 0O5D
to 0.8D. Such a dimension is selected here in view of the fact that a drilling and tapping torque necessary for the drill bit and threaded stem portion adjoining it to dig a hole in a workpiece and to subsequently tap the hole is considerably low in general compared with a fastening torque for the turning tight of main portion of the threaded stem. The value of said drilling and tapping torque is equal to, for instance about one third (1/3) to two thirds ~2/3) of the fastening torque. Thus, said comparatively small diameter 'd' of the welding lug 15 can withstand well a force imparted thereto when drilling and tapping are simultaneously carried out by means of the drill bit and the threaded portion adjoining it, while at the same time a~lowing these portions to be broken off considerably easily from the main threaded portion.
FIGS. 3 to 5 illustrate a process for manufacturing the drill screw from the first shank 11 and second shank 12.
At first, the flat end surface 14 of the first shank 11 is caused, as shown in FIG. 3 by projection-welding method, to ixedly adjoin the welding lug 15 of the second shank 12 in order that the break zone 16 is formed at bonded portion between said shanks whereby a composite blank 20 is produced.
Next, a drill bit 21 is formed by cold forging of the second shank 12 in the blank 20, as shown in FIGo 4~ A
machining mold or die used for cold forging of the drill _5_ ~
'-' . ': ' ~ . - . . , , :
.
; . :
-' ' , ' ' . , .
' , ~ : ' . ' 38;~
bit 21 is not shown because it is well known in the industry.
Such machining will produce a scrap 22 along and projecting from an outer periphery of the drill bit 21.
Subsequently, a continuous screw thread 23 and 23a is formed as shown in FIG. 5 by thread-rolling method employing a known rolling die (not shown) so as to extend around both the outer cylindrical peripheries of the first shank 11 and the second shank 12. The scrap 22 referred to above is removed when the thread-rolling is conducted to form the thread, thereby finishing up the drill bit 21. The threaded portion 23a formed by thread-rolling on the second shank 12 desirably has to extend up to a close proximity of the drill bit 21 in a state that it comprises at least one pitch of screw thread which shall function as a tapping screw when tapping is done as described below.
A drill screw 25 which has been machined in a manner described above is then subjected to carburizing-and-quenching treatmPnt . This treatment causes carburizing of, i.e., diffusion of carbon into, surface layers of the drill bit 21 and threaded portion 23a which are formed on the second shank 12, to thereby impart a predetermined hardness to said surface layers. However, the threaded portion 23 formed on the first shank 11 is not carburized due to the unsusceptible nature of the metal of which said first shank is made. The break zone 16 located at the bonded or fixedly adjoined portions between the first and second shanks 11, 12 also is not hardened by carburizing-and-quenching since said zone is at an inner part of said shanks.
The drill screw 25 which is manufactured to obtain the abovedescribed structure will be used to fasten one object to the other (not shown). After a fastening operation is completed, the drill bit 21 and the threaded portion 23a which are likely to protrude from back surface of the other object are easily broken at the break zone 16 and separated from a remaining main part. A remaining main part 26 compxising the first shank 11 is highly corrosion-resistant by virtue of austenitic stainless steel of which said first shank 11 is made.
Although the first shank 11 and the second shank 12 are adjoined to each other by means of projection-welding method ~one of resistance welding methods) in the embodiment, they may be bonded or united to each other by any other suitable method such as pressure welding or by use of any suitable adhesive. If it is deemed appropriate for material of said second shank 12 and for character of fastened objects, any other usual hardening or quenching treatment may be utilized in place of the exemplified carbùrising-and-quenching in ;~ order to harden to a satisfactory degree the surfaces of drill bit 21 and threaded portion 23a which are formed from th second shank 12.
_, ~.
_7--' ~' ,
Claims (5)
1. A breakable composite drill screw comprising: a first shank 11 made of a metal unsusceptible of hardening; a driving head 13 extending from an end of the first shank 11 and engageable with a screw driving tool; a second shank 12 made of another metal susceptible of hardening, the second shank 12 being fixedly adjoined to the other end of the first shank 11 to thereby provide a break zone 16 at said other end; a drill bit 21 formed by cold forging at an end of the second shank 12; a continuous thread 23 and 23a which is formed by thread-rolling so as to extend around both outer cylindrical peripheries of the first shank 11 and second shank 12 wherein a portion extending from the break zone 16 to the drill bit 21 is hardened or quenched.
2, A breakable composite drill screw according to claim 1, in which the first shank 11 and the second shank 12 are fixedly adjoined at their engaging surfaces to each other by projection-welding making use of a welding lug 15 pro-truding from either engaging surface whereby the welding lug 15 forms the break zone 16.
3. A breakable composite drill screw according to claim 1 or 2, in which a portion of the continuous thread 23a comprises at least one pitch of screw thread.
4. A breakable composite drill screw according to claim 1 or 2, in which the first shank 11 is made of an austenitic stainless steel and the second shank 12 is made of a low-carbon steel.
5. A breakable composite drill screw according to claim 1 or 2, in which a portion of the continuous thread 23a comprises at least one pitch of screw thread wherein the first shank 11 is made of an austenitic stainless steel and the second shank 12 is made of a low-carbon steel.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2008383 CA2008383A1 (en) | 1990-01-23 | 1990-01-23 | Breakable composite drill screw |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2008383 CA2008383A1 (en) | 1990-01-23 | 1990-01-23 | Breakable composite drill screw |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2008383A1 true CA2008383A1 (en) | 1991-07-23 |
Family
ID=4144104
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2008383 Abandoned CA2008383A1 (en) | 1990-01-23 | 1990-01-23 | Breakable composite drill screw |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2008383A1 (en) |
-
1990
- 1990-01-23 CA CA 2008383 patent/CA2008383A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |