Screw comprising through holes

TECHNICAL FIELD The invention relates to a screw comprising a cylindrical unit and an outer flange. The cylindrical unit comprises a threaded outer casing, and the flange comprises a matching-fit section designed with a cross section in a radial direction that is suitable for the insertion of a tool that is intended to rotate the cylindrical unit.

BACKGROUND ART

It is known to use screws to fasten parts together during construction of houses, furniture, toys etc. The screw comprises a head in form of an outer flange and a cylindrical unit with a threaded outer casing.

The head is designed with a matching-fit section in form of a depression or projection in the axial direction. The matching-fit section is designed with a cross section in a radial direction that is suitable for the insertion of a tool, and can consist, for example, of a triangular, four-sided, five-sided, hexagonal or other suitable shape that provides a good engagement between the tool and the matching-fit section. The screw is adapted to be screwed through a first portion and be fastened to a second portion, to create a fixing between the first portion and the second portion. The head of the screw is adapted to contact the first portion, and there is often a wish to have the head countersunk into the first portion. In the prior art, this is performed by removing the part of the first portion where the head shall be countersunk, before screwing in the screw. Two steps are consequently necessary to countersink the head of the screw. According to an alternative method, the under side of the head is used to compress and scrape away material of the first portion in order to countersink the head. The first alternative generates unattractive edges because the compressed material projects at the sides of the head, and requires subsequent machining like grinding and possibly

filling. The last alternative generates splintering and ragged edges around the head, which requires subsequent machining like grinding and possibly filling etc.

There is consequently a well known problem by countersinking of screws according to above, and hence it has been recognised for a long time that there is a need for an improved device and an improved method for countersinking screw heads.

DISCLOSURE OF INVENTION

The present invention is intended to solve the problems described above, by means of a screw comprising a cylindrical unit with an at least partially threaded outer casing, and a head in form of an outer flange comprising a first end face, which projects radially outside of the outer casing. The outer flange comprises an edge part, which limits the outer flange radially. The head comprises a matching-fit section comprising one or more depressions or projections adapted to match with a tool when the screw shall be screwed/rotated into or out from a workpiece.

The invention is characterized in that the outer flange comprises a machining surface having an extent from the edge part to the outer casing, the machining surface being arranged at an angle φ relative to a normal to the outer casing. The outer flange comprises through holes extending from the first end face through the outer flange to the machining surface The first end face comprising first openings for the respective holes, and wherein the machining surface comprises corresponding second openings. Each second opening being delimited by a front edge and a rear edge comprising a cutting edge arranged to machine a surface of a workpiece into which the casing is intended to be screwed, wherein the hole is arranged to evacuate material machined by the cutting edge away from the workpiece.

An advantage of the invention is that the machining surface according to the invention generates a depression in the workpiece without appearance of splintering, which reduces the risk of a wrongly adjusted screw, as well as a nicer depression without preparatory work. The above mentioned workpiece can be any type of constructional workpiece, but the workpiece can for example be a frame for a door, or a frame to a window, whereby the invention simplifies the installation of doors and windows, because the machining surface generates an optimal depression without edge splintering and consequently reduced risk of deviation. The screw can in this example be a frame screw comprising a bore that that passes right through, but in other constructional workpieces can the screw be solid, can be of any required size, and additionally be manufactured in any material as long as the depression can be generated according to the invention.

The first end face has a spread in the radial direction which exceeds the spread of the outer casing in the radial direction. The difference should be of such an extent that the holes in the outer flange have space without weakening the flange such that it can collapse during the countersink process.

The machining surface can be symmetrically, and/or asymmetrically conical around the centre of rotation axially, and/or symmetrically or asymmetrically convex, and/or symmetrically or asymmetrically concave. In addition, the machining surface can have different radii along its axial spread.

The holes are each arranged in the outer flange at an angle φ\ and φl relative to a normal N to the first end face, wherein the angles φ\ and φl being substantially perpendicular to each other. The angle φ\ is measured substantially in the direction of rotation, or in a tangent to the direction of rotation, and φl substantially in radial extension, i.e. in a direction from a centre axis of the casing toward the edge part of the outer flange. With

"centre axis" an axis of rotation with axial extension is intended, substantially perpendicular against radial extension.

According to an aspect, the machining surface comprises recesses arranged with an extent substantially in a rotational direction of the casing. Each recess extending in the rotational direction from the front edge of the second opening to a position before the rear edge of the next second opening, i.e. the cutting edge. The recesses extend sufficiently far towards the holes that the front edge is lower than the rear edge. The difference enables the cutting edge to machine the material of the workpiece, especially when the angle φ equals, or is close to zero.

The edge part has a thickness which allows the edge part to resist bending when the screw is screwed into the workpiece in such a way that the edge part comes into contact with the workpiece. The edge part consequently being able to bear against the workpiece and machine the workpiece when the screw is screwed into the workpiece. The fact that the edge part is part of the countersink process is of advantage since this further reduces the risk of edge splintering. When the holes transport the machining material away from below the machining surface can the edge part compress the material in the workpiece to an even and circular depression.

Given below is an example of a screw in shape of a steel frame screw according to the invention, which empirically has performed well in practice:

The frame screw comprises a sleeve comprising a bore that passes through.

The sleeve comprises the partly threaded outer casing and the outer flange.

The sleeve is adapted to be secured in a frame (door or window) and a fixing device, for example in shape of a screw, is adapted to fit inside the bore to create a joint between the frame screw/frame and a constructional body into which the frame shall be secured.

The diameter of the outer flange is 28 mm.

The outer flange comprises 8 holes each with a diameter of 5 mm and an angle φ\ of 0-10 degree and an angle φl . The holes are not radially displaced. The machining surface lacks recess.

The angel φ is about 30 degrees.

The machining surface is formed as a symmetrical cone.

The material thickness between the edge part and the holes is 1 - 2 mm.

The diameter if the outer casing is about 14 mm. The total length of the sleeve is 28 mm.

The length of the outer casing is 24 mm.

The threads have a length of 15 mm.

The threads have a diameter of about 17 mm.

There are about 5 threads per cm. The threads start about 5 mm from the edge of the outer casing.

The edge of the outer casing is bevelled for guiding the sleeve in the workpiece.

The length of the outer flange = the total length of the sleeve minus the length of the outer casing. With length is meant axial direction, and with diameter is meant radial direction.

The frame screw can be formed in metal, plastic, composite material, or other suitable material, which is harder than the surface to be machined.

A regular constructional screw according to the invention lacks normally such a bore which exists in the frame screw, and the outer casing can have a diameter of less than 1 mm, or greater than 1 mm, or substantially greater than 1 mm, depending on the constructional object. The outer flange has a diameter and thickness which are adapted to the size of the outer casing and the workpiece material.

DESCRIPTION OF DRAWINGS

The invention will be described below in association with a number of drawings, in which:

Figure 1 shows schematically a side view of a screw according to the present invention;

Figure 2 shows schematically a cross section along the line A-A in figure 1 according to a first example of the invention;

Figure 2a shows schematically a cross section along the line A-A in figure 1 of a casing of a screw according to a second example of the invention; Figure 2b shows schematically a cross section along the line A-A in figure 1 of a casing of a screw according to a third example of the invention;

Figure 2c shows schematically a side view according to an embodiment of a screw according to any of the figures 1-2b;

Figure 2d shows schematically a side view of figure 2c seen from the other side of the casing;

Figure 2e shows schematically a side view according to an embodiment of a screw according to any of the figures 1-2b;

Figure 2f shows schematically a side view according to an embodiment of a screw according to any of the figures 1-2b; Figure 2g shows schematically a side view according to an embodiment of a screw according to any of the figures 1-2b, and where;

Figure 3 shows schematically a screw comprising a cutting edge according to the present invention.

MODES FOR CARRYING OUT THE INVENTION

Figure 1 shows schematically a side view of a screw 1 according to the present invention. The screw 1 comprises a cylindrical unit 3 comprising an outer casing 4a and an outer flange 4b. The outer flange 4b comprises a first end face 12a, which delimits the screw in the axial direction. The first end face 12a is delimited in the radial direction R of an edge part 12b. The outer flange 4b comprises a machining surface 12c between the cylindrical unit 3

and the edge part 12b. The screw 1 is consequently divided in the longitudinal extension, that is in the axial direction X, by means of the outer casing 4a, and the outer flange 4b. In the axial direction, the outer casing 4a comprises at least partially threads 4 such that the screw can be screwed into a workpiece 17 comprising a hole 21. The workpiece 17 can be made of wood, metal, or polymeric materials, for example plastic. The shape of the threads, that is, pitch, height, width, and threaded share of the length of the outer casing, can be varied depending on the material in which the screw shall be used.

The outer flange 4b designed with a depression 5 in the axial direction X at the first end face 12a around the centre of rotation. The depression 5 comprises a matching-fit section 10 designed with a cross section in a radial direction R that is suitable for the insertion of a tool, and can consist, for example, of a triangular, four-sided, five-sided, hexagonal or other suitable shape that provides a good engagement between the tool and the matching- fit section. The matching-fit section 10 is designed to receive a tool (not shown) with a corresponding shape as the matching-fit section 10, for example triangular, four-sided, five-sided, hexagonal or other suitable shape that provides a good engagement between the tool and the matching-fit section 10. After the matching-fit section 10, in direction towards the first end face 12a, the bore 5 can comprise a third section 11 , which is designed to facilitate the insertion of a tool to be fitted into the second section 10. The third section 11 can be omitted, in which case the matching-fit section 10 extends from the bottom of the depression 5 to the first end face 12a. The matching-fit section comprises according to another example (not shown) a projection in the first end face in the axial direction. The projection replaces here the depression, and the matching-fit section is designed to be gripped by a tool. The matching-fit section/projection can just like the depression comprise a section with specially formed geometry which fits the tool.

The screw 1 is arranged to be screwed into the above mentioned workpiece by means of the tool in the matching-fit section 10, whereby the screw 1 is arranged to rotate in a direction of rotation R1 around a central axis C1 , which extends in the axial direction X. In the figure, the direction of rotation R1 is defined as a clockwise rotation because the cylindrical unit 3 is right- threaded. The direction of rotation R1 is consequently anticlockwise with a left-threaded cylindrical unit 3.

The outer flange 4b comprises the first end face 12a, which is radially limited by an edge part 12b. The first end face 12a has a spread in the radial direction R greater than the spread in radial direction R of the outer casing 4a. The machining surface 12c has an extension from the edge part 12b to the outer casing 4a. The machining surface 12c being arranged at an angle φ relative to a normal N ₂ to the outer casing 4a, which depends on a number of factors, which will be described below. The machining surface 12c can be conical, that is comprising straight lines, or can be convex, that is comprising bent lines (see figure 2a). An advantage having a conical surface compared with a convex is that the amount of material which must be evacuated when the machining surface 12c operates on a workpiece is minimal.

Figure 1 shows that the outer flange 4b comprises through holes 31 , which extend from the first end face 12a through the outer flange 4b to the machining surface 12c. First openings 32 for respective holes 31 are thus located in the first end face 12a, and corresponding second openings 33 are located in the machining surface 12c. The holes 31 are each arranged in the outer flange 4b at an angle φ\ and φl (shown in figure 2b) relative to a normal N to the first end face 12a. The angle φ\ is measured to the normal N substantially in the direction of rotation, that is, in a direction that substantially coincide with a normal to radius of the first end face 12a. The angle φl is measured to the normal N substantially in the radial direction R, that is, in a direction which substantially coincides with the radius of the first end face

12a. The angles φ\ and φl consequently being substantially perpendicular to each other in the plane of the first end face 12a.

In figure 1 is showed that the machining surface 12c comprises recesses 34 arranged with an extension substantially in direction of rotation R1 of the screw 1. Each recess 34 extend in the direction of rotation R1 from the front edge 35a of the second opening 34 to a position before the rear edge 35b of the next second opening 34. The length of the recess and its geometrical form depends on a number of factors, namely the angles φ\ , φl and φ, and the material of the workpiece, on which the screw 1 shall be used.

The angle φ\ depends on the material of the workpiece and can vary between 0° to 70°. The angle depends among other things on the material of the screw, since the edge part 12b is not allowed to bend due to excessive weakening of the material when the holes 31 are produced. Experiments have shown good results for wood when φ\ is 0°- 45°, and particularly good results when φ\ is 5°- 10°.

The angle φl depends on the material of the workpiece and can vary from 0° to about ±30°. The angle depends among other things on the material of the screw, since the edge part 12b is not allowed to bend due to excessive weakening of the material when the holes 31 are produced. Experiments have shown very good results for wood when φl is about 0°.

The angle φ depends on the amount of material to be evacuated. The smaller the angle, the less material to evacuate. The angle φ depends also the ability of the cutting edge 35 to operate. The bigger the angle, the better can the cutting edge 35 operate. Both these factors depend on the material of the workpiece 17. A soft material give the possibility of a big angle φ since the large amount of material to be evacuated via the holes 31 easily can be machined by the cutting edge. A hard material give wish of evacuation of as

little material as possible, that is, a small angle, but the cutting edge 35 must then be able to operate sharply. The angle φ shall consequently be optimised depending on choice of workpiece 17 material. The angle φ shall also be optimised with respect to the pitch angle of the threads 4, that is, number of threads per length unit, since the pressure of the machining surface 12c on the material of the workpiece 17 depends on the relationship between pitch angle and the angle φ, and the amount of material to be evacuated. The screw 1 moves a longer distance in the axial direction with a high pitch angle than with a low pitch angle. With a high pitch angle, more material must consequently be transported per time unit through the holes 31 in order to avoid too high pressure, such that the screw 1 can no longer be screwed in. Here is a wish that as little material as possible should be evacuated and the keeping the angle φ small. The amount of material which can be evacuated though the holes 31 depends also on the diameter of the holes 31 , and the angles φ\ and φ2. The angles φ\ and φ2 determines the ability of the cutting edge 35 to machine the material, since the angles φ\ and φl define the angle of action of the cutting edge 35 on the material in the workpiece 17. The ability to machine the material depends also on the form of the recesses 34, that is, depth and length, and the angle between the recesses 34 and the other openings 33. Experiments have shown very good results for wood when φ is about 10°- 50°, and particularly good results when φ is about 25°- 35°. Having these angles of φ, it has shown that the machining surface produces good results without the occurrence of the above mentioned recesses 34 in the machining surface 12c.

The rear edge 35b forms a cutting edge (hereinafter called the cutting edge 35b), which is intended to machine, for example by means of cutting, reaming, scraping, or other suitable method of machining, the workpiece 17 on which the screw 1 is used. The screw 1 is during installation in the workpiece 17 arranged to be screwed into the hole 21 , such that the machining surface 12c machine the workpiece 21 , wherein the cutting edge

35b machine the material of the workpiece such that material come loose from the workpiece and being transported out via the holes 31.

In one example of the invention, each recess 34 extends so far towards the corresponding hole 31 that the front edge 35a is located lower than the rear edge 35b. The second opening 33 lies consequently not in one plane, but has a surrounding edge with varying height in the axial direction, and where the rear edge 35b is higher than the front edge 35a. The recesses 34 provide an improved characteristic of the machining surface at small angles φ, and is necessary when φ=0 such that the rear edge 35b can form a cutting edge. The recesses are not necessary when the angle φ is about 20°- 45°, but the rear edge 35b of the second opening 33 forms despite this a cutting edge, because the machining surface 12c operates in spiral-formed movement when the screw is screwed into the workpiece. The spiral-formed movement 17 appears due to the threads 4 in the outer casing 4a.

The difference between the radial extension of the first end face 12a and the radial extension of the outer casing 4a depends on a number of factors: namely the number of holes 31 ; the size of the holes 31 , the angles φ\ , φl and φ, and the material of the workpiece, on which the screw 1 shall be used; and the choice of the material thickness between the edge part 12b and the holes 31. In figure 1 has the edge part 12b an extension in the axial direction X, that is, a thickness, but the machining surface 12c can be arranged to meet the first end face 12a without any edge part 12b, that is, the thickness of the edge part 12b is zero, or at least a very thin edge part. The edge part must however have a thickness which allows the edge part 12b to resist bending when the screw 1 is screwed into the workpiece 17 and the edge part contacts the workpiece. The choice of material for the screw 1 and the material of the workpiece 17 are consequently decisive for the thickness of the edge part 12b. The edge part 12b is circular in figure 1 , which has shown being advantageous when the screw 1 is screwed into the workpiece

17, such that the edge part 12b lies against the workpiece 17 and machines the workpiece 17, because the material does not splinter, at least when using wood. When the holes evacuate material from below the machining surface, can the edge part 12b compress the material of the workpiece 17 to an even and circular depression. The circular edge part 12b together with the distance between the holes 31 is a parameter to take in consideration to achieve a depression without splintering.

Figure 1 shows with a broken line 36 in the workpiece 17 that the workpiece 17 comprises a recess 37. The recess is a result of the screw having been screwed into the hole 21 in the workpiece 17, wherein the machining surface 12c has machined away material from the workpiece 17 by means of the cutting edges, which material was subsequently evacuated from the workpiece 17 via the holes 31.

In figure 1 is shown that the outer flange 4b comprises seven holes 31 , but the outer flange can comprise less as well as more holes 31 , for example one hole, or 14 holes in total, depending on the material in the outer flange 4b, the sizes of the holes 31 , the sizes of the recesses 34, φ\ , φl and φ, and the material of the workpiece 17, on which the screw 1 shall be used. A compromise might be needed with respect to the number of holes, but the aim is to provide favourable machining ability and material evacuation away from the workpiece 17, and the strength of the outer flange 4b, which allows machining without bending of the outer flange. The holes do not have to be round, but can be oval or of any other suitable geometry.

Figure 1 shows that the screw 1 comprises a tip 39 comprising a second end face 40 and a shell surface 41 whose circumference decreases in direction from the cylindrical unit 3 toward the second end face 40. The tip 39 can be conical or bulged, and can be pointed or blunt. With blunt is meant that the second end face is flat or bulging. The first end face 12a and the second end

face delimit the screw in the axial direction X, that is they are located on opposite sides of the screw.

In those cases where the workpiece is predrilled, the shell surface 41 can be substantially omitted, whereby the second end face 40 form the end of the cylindrical unit.

Figure 2 shows schematically a cross section along the line A-A in figure 1 of a screw according to first example of the invention.

In figure 2 is shown that the machining surface 2c has a substantially conical geometry, that is, straight cross-sectional profiles.

Figure 2 shows that, after the matching-fit section 10, the bore 5 comprises a third section 11 with an essentially circular cross section. Figure 2 shows that L1 = the length of the guiding section 9 in an axial direction; and L2 = the distance between the guiding section 9 and the first end face 12a of the cylindrical unit 3. L2 comprises the length L1 of the guiding section. D1 = the diameter of the guiding section 9.

Figure 2a shows schematically a cross section along the line A-A in figure 1 of a screw according to second example of the invention. In figure 2 is shown that the machining surface 2c has a substantially convex geometry, that is, bent cross-sectional profiles. The machining surface 2c can also be convex, or a mixture of the convex, concave and conical geometry.

Figure 2b shows schematically a cross section along the line A-A in figure 1 of a screw according to third example of the invention. The angle φ2 is measured to the normal N substantially in the radial direction R, that is, in a direction which substantially coincides with the radius of the first end face 12a. The angle φ2 depends on the material of the workpiece and can vary

from 0° to about ±30°. The angle depends among other things on the material of the screw, since the edge part 12b is not allowed to bend due to excessive weakening of the material when the holes 31 are produced. Experiments have shown very good results for wood when φl is about 0°. In figure 2b, the angle φl is positive and about 25°, but the angle can vary as previously mentioned.

Figure 2c shows schematically a side view according to an embodiment of a screw according to any of the figures 1-2b. The above mentioned description should be applied on the figures 2c-2f. The angle φ\ is positive in figure 2c as in figure 1 , and the angle φl equals zero.

Figure 2d shows schematically a side view of figure 2c seen from the other side of the casing.

Figure 2e shows schematically a side view according to an example of a screw according to any of the figures 1-2b. The angle φ\ in figure 2e equals zero, and the angle φl equals zero.

Figure 2f shows schematically a side view according to an example of a screw according to any of the figures 1-2b. The angle φ\ in figure 2f equals zero, and the angle φl equals zero. In figure 2 is shown that the machining surface 2c lacks recesses 34, but this is only possible when the angle φ is greater than zero. The machining surface 2c can lack recesses 34 in all the embodiments described in connection to figures 1-2e provided that the angle φ is greater than zero. The holes 31 are displaced in the radial direction R in figure 2f. The holes 31 can be displaced in the radial direction R in all embodiments described in connection to figures 1-2e.

Figure 2g shows schematically a side view according to an example of a screw according to any of the figures 1-2b. The angle φ\ in figure 2f equals

zero, and the angle φl equals zero. In figure 2f is shown that parts 38 of the edge part 12b have been removed in connection to the holes 31.

Figure 3 shows schematically a side view of a screw according to the present invention comprising a cutting tip 39. The tip 39 comprises a cutting edge 42 for producing a hole in the workpiece 17 when rotating the screw 1.

The screw can comprise a bore passing though the screw for evacuation of material from the tip 39 to the first end face 12a.