DE29603866U1 - Screw for chipboard and plastics - Google Patents

Description

T2 - TAT

Screw for chipboard and plastics

The invention relates to a screw that is particularly suitable for wood chipboards and plastics, with a shaft arranged below the screw head, which has a head region, a cylindrical middle section and an end region along its length, in which at least the middle section and the end region are provided with a cutting and holding thread bead and the end region ends in a point. The aforementioned thread bead forms the thread on the shaft.

The aforementioned screw is essentially a wood screw or chipboard screw, as defined in DIN 95, 96 and 97, for example. The standardized screws are generally intended for use in heartwood. The standardized screws are less suitable, particularly for use in chipboard and plastic, as they have a relatively low pull-out strength in these materials, are relatively difficult to control at first, and screwing in and out often cannot be carried out perfectly. The known chipboard screws have the disadvantage that the thick core diameter creates a high resistance to screwing in during the screwing-in phase.

In addition, these screws do not have sufficient self-locking effect to prevent them from being unscrewed, especially when processed in plastics.

The task therefore arises of specifying a screw made of common materials, i.e. low-alloy steel or non-ferrous metals, that is particularly suitable for use with chipboard and plastics, where handling is easier and in particular the pull-out strength and unscrewing strength are increased with the aforementioned materials.

This task is solved by a screw of the

type mentioned above, which is characterized by 15

that the thread bead, seen in cross-section, has the shape of an acute-angled triangle in which the flank angle a , which the upper flank of the thread bead forms with the vertical on the shaft periphery, is smaller than the flank angle a , which the

2&Oacgr; ²

Lower flank of the thread bead with the vertical on the shaft periphery.

Preferably, the flank angle α should be 20° ± 2° and the flank angle α 15° ± 1.5°. It can be seen, for example, ^that

that with different designs of the flank pitch, in particular the larger flank angle of 20° for the screwing-in phase results in a reduced screwing-in torque. The smaller flank angle of 15° has a self-locking effect in the reverse phase, so that the screw can only be tightened with

can be unscrewed with great effort. The screw is therefore particularly suitable for use in plastics (polyethylene, PVC, polycarbonate) and for chipboard, including OSB boards.

Furthermore, the diameter of the shaft, also called core diameter, can vary over the middle section. It is therefore proposed to divide the middle section into a

upper middle section part with a core diameter D and a lower middle section part with a smaller core diameter D, whereby the thread

the same outer diameter over the entire middle section-5

knife and its outer diameter tapers towards the tip. The thinner core diameter in the lower middle section results in a reduced screwing-in torque during the screwing-in phase.

For example, the lengths from the upper to the lower section can be 5:1 to 3:1.

The core diameter D should be reduced by 5 to 20% compared to the core diameter D in order to achieve the specified 15

to achieve the effect mentioned.

The aim is to ensure that the transition from the core diameter D of the lower middle section to the core

diameter D of the upper middle section part soft *-

is rounded, preferably represents a clothoid line.

Furthermore, as an additional measure,

that the thread bead extends until shortly before the end 25

the tip so that the thread takes hold early when the screw is screwed in.

To speed up the screwing process and, if necessary,

To increase the extraction force, it is suggested that the 30

Screw with a second, essentially identical thread as the first, double-start.

Finally, it is proposed that in order to increase

the penetration speed the thread pitch h by 7 35

up to 10% compared to the known thread pitches for chipboard screws.

Embodiments of the invention are shown in the drawing. The figures of the drawing show:

Fig. 1 a screw in schematic

Depiction;

Fig. 2a and 2b the transition from the upper middle section

to the lower middle section with two screws, one of them with double thread ;

Fig. 3 shows a screw according to Fig. 1 in a clarifying representation.

Fig. 1 and 3 show a screw made of low-alloy steel and intended in particular for chipboard and plastics. However, it should not be ruled out that such a screw could also be made of non-ferrous metals, for example

Stainless steel is to be manufactured. The specialist must adhere to the relevant values.

The screw has a screw head 2, which is usually designed as a raised countersunk head, a countersunk head or as 25

Lens head is preferably designed with a Phillips slot, as known under the Pozidriv brand, or with a polygon socket, known under the TORX brand. The design of the screw head is not

Subject of the invention.
30

Below the screw head, the screw continues into a smooth head area 3. Then begins the cylindrical middle section 4, which is provided with a thread 10 and ends in a point 6. 35

furthermore, that the cylindrical central section 4 is divided into two parts, namely an upper central section part 14 and a lower central section part

» 15. The upper middle section part 14 has a shaft or core diameter D and the lower middle section part has a smaller core diameter D . In the present embodiment, the upper middle section part has about four times the length of the lower middle section part. The core diameter D is smaller than the core diameter

diameter D is reduced by about 17%.

The transition 9 can be designed in various ways. Preferably, a soft transition is chosen, as shown in Fig. 2a and Fig. 3. However, a truncated cone-like, more abrupt transition can also be chosen, as shown in Fig. 2b. The soft transition can preferably be designed in a clothoid curve, i.e. initially a slight gradient, which then becomes stronger towards the upper middle section.

A key feature of the drawing shown in the

The advantage of the screw provided is that the thread bead 7 forming the thread 10 has the shape of an acute-angled triangle in cross-section, in which the flank angle α that the upper flank 8 of the thread bead 7 makes with

the vertical on the shaft periphery 11 forms small-25

ner than the flank angle α which the lower flank of the thread bead forms with the vertical on the shaft periphery. In the embodiment according to Fig. 3, for α and α which the flanks of the thread bead form with the vertical on the shaft periphery, 15° and 25° respectively.

20°. The shape of the acute triangle is chosen to achieve a high cutting depth. The larger flank angle et of 20° causes the

The smaller flank angle α of 15° allows a certain self-locking

*■

in the reversing phase, so that the screw can only be unscrewed with increased effort. This makes it particularly suitable for a secure

Fastening in plastics.

The thread bead 7 continues until just before the end of the tip 6, but here with a tapered thread diameter d, so that the thread finds a hold early on when the screw is screwed in. The resistance is significantly reduced, so that the screw "grabs" immediately and can be screwed in without much effort at the beginning.

However, it should also be pointed out that a second, essentially identical thread 10' can be provided (see Fig. 2a), so that the screw is double-threaded.

Another special feature is that the screw can have a thread pitch h that is 7 to 10% higher than the thread pitches already set for chipboard screws. This measure

In the above-mentioned applications, a labor saving of 7 to 10% can be achieved when screwing in.

The double thread or the enlargement of the thread-25

Pitch is possible by the measures of shaft reduction and the special angles α and α . With a "normal" thread according to the above-mentioned DIN regulations, the screw would probably

tear off.
30

Claims (8)

Al (B:BIG23_A2.TAT) CLAIMS 1. Screw, especially for chipboard and Plastics, with a shaft (1) arranged below the screw head (2) and having along its length a head region (3), a cylindrical middle section (4) and an end region (5) in which at least the 10 The middle section and the end region are provided with a cutting and holding thread bead (7) and the end region ends in a point (6), characterized in that the thread bead (7) has the shape of an acute-angled triangle when viewed in cross section, in which the flank angle α that the upper flank (8) of the thread bead (7) forms with the vertical on the shaft periphery (11) is smaller than the flank angle α that the lower flank (14) of the thread bead forms with the vertical on the shaft periphery. 2. Screw according to claim 1, characterized in that the flank angle α is 20° + 2° and the flank angle α is 15° ±1.5°. 3. Screw according to claim 1 or 2, characterized characterized in that the middle section is divided into an upper middle section part (14) with a core diameter D^ and a lower middle section part (15) with a smaller core diameter D, wherein the ² Thread (10) has the same outer diameter over the entire middle section and tapers in its outer diameter towards the tip (6). 4. Screw according to claim 3, characterized characterized in that the lengths from the upper to the lower middle section part (14; 15) are in a ratio of 5:1 to 3:1. α2 5. Screw according to claim 3 or 4, characterized *" indicates that the core diameter D is reduced by 5 to 30% compared to the core diameter D . * 6. Screw according to one of the preceding claims, characterized in that the transition (9) from the core diameter D of the lower middle section part to the core diameter D of the upper middle section part ^&khgr; is softly rounded, preferably representing a clothoid line. 6. Screw according to one of the preceding claims, characterized in that the thread bead (7) continues until shortly before the end of the tip (6), so that when the screw is screwed in, the thread finds a hold early on. 7. Screw according to one of the previous Claims, characterized in that it is equipped with a second, essentially identical thread (10') as the first double-threaded one. 8. Screw according to one of the preceding claims, characterized in that the thread pitch h is increased by 7 to 10% compared to the thread pitches for wood screws specified in DIN 95, 96, 97.