Screw with filler-receiving head

A screw-type fastener having a threaded shank and a head integral therewith, and adapted to be driven into a structure by axial rotation about its longitudinal central axis in a driving direction such that the head is countersunk, is improved by forming the head with at least two ribs protruding from the surface thereof and extending radially outward from the central axis. The ribs define a corresponding number of sector-shaped cavities adapted to receive a filler material for engaging the ribs so as to prevent the fastener from axially rotating in a direction opposite the driving direction and to thereby secure the fastener against loosening.

BACKGROUND OF THE INVENTION 
The present invention relates to improvements in fasteners. More 
particularly, the invention is directed to an improved screw-type fastener 
having a threaded shank and a head integral therewith, and adapted to be 
driven into a structure by axial rotation about its longitudinal central 
axis in a driving direction such that the head is countersunk. 
Hithereto known screw-type fasteners suffer from a major drawback in that 
they undergo loosening after a certain period of time. Indeed, 
environmental conditions such temperature and/or humidity variations, 
vibrations, etc. cause such fasteners to axially rotate in a direction 
opposite the driving direction, resulting in loosening. This is especially 
true in the case of screws used for securing gyproc panels to a wooden 
structure, as well as screws used in watches, pressure gauges and 
compressors, for example, which are subject to vibrations. 
Although the art is abundant in screws of various kinds, some even of 
intricate designs, none of the screw-type fasteners proposed so far has 
solved the above problem. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to overcome the above-mentioned 
drawback and to provide a screw-type fastener which can be tightly locked 
in place and will not unscrew itself in time. 
It is a further object of the invention to provide a tool for driving such 
a screw-type fastener. 
According to one aspect of the invention, there is provided in a screw-type 
fastener having a threaded shank and a head integral therewith, and 
adapted to be driven into a structure by axial rotation about its 
longitudinal central axis in a driving direction such that the head is 
countersunk, the improvement wherein the head is formed with at least two 
ribs protruding from the surface thereof and extending radially outward 
from the central axis. The ribs define a corresponding number of 
sector-shaped cavities adapted to receive a filler material for engaging 
the ribs so as to prevent the fastener from axially rotating in a 
direction opposite the driving direction and to thereby secure the 
fastener against loosening. 
Thus, by providing the fastener head with ribs defining filler-receiving 
cavities, such cavities may be filled with filler material once the 
fastener is in place. Due to the ribs and the presence of filler material 
in the cavities, the fastener will be tightly locked in place and will not 
unscrew itself in time, as opposed to conventional screws which after a 
certain period of time will loosen. 
In a preferred embodiment of the invention, the head has a circular 
peripheral edge and each rib is rectangular in cross-section and extends 
radially to terminate flush with the peripheral edge. Preferably, the head 
is formed with four ribs which are disposed at 90.degree. relative to one 
another. 
According to another aspect of the invention, there is also provided a tool 
for driving a screw-type fastener as defined above. The tool of the 
invention comprises a shank member with a drive head at one end thereof. 
The drive head is formed with at least two sector-shaped protuberances 
arranged in spaced-apart relationship to define a corresponding number of 
channels adapted to receive the ribs of the head of the fastener with the 
sector-shaped protuberances fitting into the sector-shaped cavities of the 
fastener head so as to engage the ribs for driving the fastener. 
The drive head is preferably formed with an annular shoulder adjacent a 
peripheral edge thereof. This shoulder is adapted to abut the structure 
into which the fastener is driven, whereby to act as a stop to limit the 
countersinking of the fastener head into the structure. 
Where the structure into which the fastener is driven is made of metal, use 
is preferably made of a lock member instead of filler material for 
securing the fastener against loosening. Such a lock member may comprise a 
plate element having on a side thereof facing the structure at least two 
sector-shaped protuberances arranged in spaced-apart relationship to 
define a corresponding number of channels adapted to receive the ribs of 
the head of the fastener with the sector-shaped protuberances fitting into 
the sector-shaped cavities of the fastener head so as to engage the ribs 
for locking the fastener in place. A means for securing the plate element 
to the structure is also provided, such as a rivet.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring first to FIGS. 1 and 2, there is illustrated a screw which is 
generally designated by reference numeral 10 and seen driven into a gyproc 
panel 12 for securing same to a wooden structure 14. As best shown in FIG. 
2, the screw 10 has a threaded shank 16 and a head 18 integral therewith. 
The head 18 is formed with four ribs 20 protruding from the surface 
thereof and disposed at 90.degree. relative to one another. Each rib 20 is 
rectangular in cross-section and extends radially outward from the 
longitudinal central axis X of the screw to terminate flush with the 
circular peripheral edge of the head 18. The ribs 20 define a 
corresponding number of sector-shaped cavities 22 adapted to receive a 
filler material. 
Turning to FIGS. 3 and 4, the tool 24 used for driving the screw 10 
comprises a shank member 26 with a drive head 28. The drive head 28 is 
formed with four sector-shaped protuberances 30 arranged diametrically 
opposite one another in spaced-apart relation and defining a corresponding 
number of channels 32 disposed at 90.degree. to each other. The channels 
32 are adapted to receive the ribs 20 of the screw head 18 with the 
protuberances 30 fitting into the cavities 22 of the screw head so as to 
engage the ribs 20 for driving the screw 10. The screw is driven into the 
gyproc panel 12 and underlying wooden structure 14 by axially rotating the 
shank member 26 of the tool about its longitudinal central axis Y so as to 
correspondingly rotate the screw 10 in the driving direction such that the 
screw head 18 is countersunk. The drive head 28 of the tool 24 is 
conveniently formed with an annular shoulder 34 adjacent the peripheral 
edge thereof, the shoulder 34 being adapted to abut the surface 36 of the 
gyproc panel 12 whereby to act as a stop to limit the countersinking of 
the screw head 18 into the panel 12. As shown in FIG. 4, the ribs 20 of 
the countersunk head 18 lie flush with the surface 36. 
As seen in FIG. 4, the distance from the top 16a of the screw threads 16b 
to the substantially planar surface 22a of the head or base of the cavity 
22 is slightly less than one-half the distance from the screw threads to 
the top of the ribs 20a (i.e., the frustro-conical countersink head 18). 
In other words, each rib projects from the surface of the head a distance 
equal to at least one-half the thickness of the screw head. 
Once the screw 10 is in place, the cavities 22 are filled with a filler 
material 38 such as plaster which adheres to the inner peripheral wall of 
the screw bore while engaging the ribs 20 so as to prevent the screw from 
axially rotating in a direction opposite the driving direction, thereby 
securing the screw 10 against loosening, as shown in FIG. 1. 
FIG. 5 shows a lock member 40 for use in combination with the screw 10 
where the structure 42 into which the screw is driven is made of metal. As 
shown, the lock member 40 comprises a metal plate element 44 having on its 
side facing the structure 42 four sector-shaped protuberances 46 arranged 
diametrically opposite one another in spaced-apart relation and defining a 
corresponding number of channels 48 disposed at 90.degree. to each other. 
The channels 48 are adapted to receive the ribs 20 of the countersunk 
screw head 18 with the protuberances 46 fitting into the cavities 22 of 
the screw head so as to engage the ribs 20 for locking the screw 10 in 
place. The plate element 44 is riveted to the structure 42 by means of the 
rivet 50. Since the metal plate element 44 is slightly resilient, it can 
be bent in a direction away from the structure 42 and shifted laterally 
about the rivet 50 which thus constitutes a pivot, so as to gain access to 
the screw 10. The plate element 44 can thereafter be shifted back into 
place with the protuberances 46 being maintained in locking engagement 
with the ribs 20 of the screw head by the resilient force exerted by the 
plate element 44. 
It should be noted that in the case of the metallic structure 42, one can 
do without the lock member 40 and use instead a filler material such as 
LOCTITE (trade mark) to fill the cavities 22. 
Although the screw 10 illustrated comprises four ribs 20, it is apparent 
that such a screw may instead comprise only two ribs, in which case such 
ribs may be axially aligned along a common axis to define two 
hemi-circular cavities. Aleternatively, there may be three ribs 20 
disposed at 120.degree. to each other.