Invisible connection for faced parts, in particular for furniture

An invisible connection for faced parts, in particular for furniture. The adhesive for the connection is hermetically enclosed in a sheath consisting of flexible or easily breakable material. The sheath of adhesive is introduced as an independent component into the borehole of the connection, the sheath being destructible on driving-in or pressing-in the connecting member.

BACKGROUND OF THE INVENTION 
The present invention relates to an invisible connection for faced parts, 
in particular for furniture of wood or chipboard, involving use of 
adhesive and a connecting member. In such a connection the adhesive is 
introduced in fluid form or in the form of a paste into cylindrical 
boreholes in the parts to be connected and the connecting member is driven 
or pressed at each of its two ends into the boreholes. The connecting 
member has a form which is symmetrical about its axial mid-point and is 
provided with one or more longitudinally extending grooves and annular 
notches and/or other profiling on the outside of the member and each of 
the two end faces of the connecting member is formed so as to extend to a 
point or each has a point. The term "invisible connection" as used herein 
refers to a connection which is not apparent to the eye, at least when the 
joined-together parts are viewed. 
For the invisible connection of faced parts in furniture, for example for 
the right-angled connection of a side wall of the body of an article of 
furniture to the floor of the article, a multiplicity of connecting 
members are known. These connecting members are introduced into prepared 
cylindrical bores in the parts to be connected. For improving the 
rigidity, a fluid or pasty material with gluing or adhering and/or foaming 
up properties is introduced into the cylindrical bore before the 
introduction of the connecting member. This introduction of the adhesive 
is time consuming and requires a high degree of care. Soiling of the 
surfaces of the faced parts cannot be avoided. An exact dosage of the 
quantity of the adhesive required for each borehole is necessary, but this 
cannot be brought about without waste. The adhesive introduced into the 
borehole is forced principally against the end wall of the borehole and in 
part into the chipboard by the connecting member when it is introduced. A 
uniform distribution of the adhesive over the length of the connecting 
member does not take place. After the introduction of the adhesive the 
making of the connection must take place in a relatively short time, since 
otherwise a hardening of the adhesive will occur. 
The preparation of this connection requires knowledge in a special field. 
Therefore, in the case of later assembled furniture parts, for example 
after transport of the furniture parts on pallets in order to save space, 
connection of the faced parts is not carried out by use of an adhesive in 
combination with connecting members introduced into the cylindrical 
boreholes, but in general a problem free screw connection is used. This 
screw connection is adequate enough from the technical point of view but 
not however from the aesthetic point of view, since it remains visible and 
is thereby prejudicial to the appearance of the furniture. 
In order to achieve an interference fit, the diameter of the connecting 
member is slightly greater than the diameter of the borehole. The 
connecting member must be driven or pressed into the borehole in each case 
in order to produce a secure and fully close connection between the parts. 
In this it cannot be excluded that a forcing out of adhesive material may 
occur at the outer edge of the borehole. 
It is an object of the present invention to provide an invisible connection 
of the kind described above, in which the adhesive is introduced into the 
boreholes in the precise dosage required with little waste and without 
danger of soiling the surfaces of the parts to be connected, and in which 
the making of the connection is not tied in time to the introduction of 
the adhesive, a uniform distribution of the adhesive over the length of 
the connecting member being achieved and the connecting means being formed 
so that no press tool or driving tool is necessary for its introduction 
into the borehole in achieving an extremely rapid and secure connection 
between the parts. 
SUMMARY OF THE INVENTION 
According to the invention, there is provided an invisible connection for 
faced parts, in particular for articles of furniture of wood or material 
similar to wood, involving the use of adhesive and a connecting member. In 
this connection the adhesive is introduced in fluid form or in the form of 
a paste into cylindrical boreholes in the parts to be connected and the 
connecting member is driven or pressed at each of its two ends into the 
boreholes, the connecting member has a form which is symmetrical about the 
axial mid-point of the member, one or more longitudinally extending 
grooves and annular notches and/or other profiling are provided on the 
outside of the member and each of the two end faces of the connecting 
member is formed so as to extend to a point or each has a point. The 
adhesive is hermetically enclosed in a sheath and the sheath with the 
enclosed adhesive is formed to be introduced as an independent component 
into the borehole, the sheath being destructible on driving in or pressing 
in of the connecting member. The connecting member may consist of a 
cylindrical blank of wood or another material which is statically stable 
and is able to swell up, the blank being compressed to a predetermined 
degree and having a diameter which is smaller than the diameter of the 
borehole. In carrying out the invention, the sheath may be formed from a 
flexible material or from a breakable material, preferably glass. 
The adhesive hermetically enclosed in a sheath may advantageously be 
pressed or blown into the cylindrical borehole immediately after the 
production of the borehole. Since the outer diameter of the flexible 
sheath is slightly greater than the diameter of the borehole, the flexible 
sheath jams after its introduction into the borehole. In this way it is 
possible to introduce the adhesive independently in time from the making 
of the actual connection between the faced parts. One or more clamping 
elements may be provided on the exterior of the sheet for clamping the 
sheath in the borehole. The clamping element may be flexible and extend 
uniformly over the periphery of the sheath in an evenly distributed manner 
about the periphery. The sheath may have a substantially cylindrical form 
with a covering on an end face. The covering may be connected to the 
cylindrical wall of the sheath by welding. This cylindrical wall may have 
a peripheral angled-out part and the covering, which may be of foil, may 
project over the cylindrical wall of the sheath to form a clamping 
element. The covering may then be sealed flush with the peripheral 
angled-out part of the wall. 
The assembly of the individual parts with use of an adhesive enclosed in a 
sheath in combination with connecting members may also be carried out in 
an extremely clean manner by unskilled people, for example, in 
do-it-yourself. The volume of adhesive enclosed in the sheath may be 
measured out for the particular use in each case. It has a storage life 
over quite a long period of time, which may amount to years. The sheath 
itself is destroyed on introduction of the connecting member into the 
cylindrical borehole and the adhesive is thereby released. Where the 
sheath is of glass, it may have one or more peripheral constrictions on 
the glass sheath, a cylindrical nozzle being provided on the outer surface 
of the sphere. The nozzle may be closed to the outside by melting, by 
means of an elastic body or plug or by a cap. 
The longitudinal grooves provided on the outside of the connecting member 
preferably continue to the end faces of the member. The outer surface may 
also be destroyed at a number of places by cutting-in so that the 
cross-grain is exposed. This destruction may be carried out in the end 
regions of the connecting member, for example, by one or more annular 
millings or cuts. By exposing the cross-grained wood of the cylindrical 
connecting member, this cross-grained wood being known to have poor 
resistance to penetrating moisture, the ability of the wood or of the 
material which is similar to wood to swell up is substantially improved 
and the connecting effect is also therefore substantially improved. Also, 
moisture contained in the adhesive is taken up significantly quicker and 
thus the period of time for the establishment of a rigid joint is 
shortened. As a result of the ability of the connecting member to swell up 
speedily, no vibration occurs in the joining of the individual parts. The 
occurrence of so-called hair cracks is therefore excluded. The joining 
effect is substantially accelerated and increased to a still further 
extent by the chipboard or wood sheet of the body of the article of 
furniture also taking up a part of the moisture of the adhesive and 
thereby swelling up, having regard to the possibilities available to it to 
do so. In this way, the sheet expands into the annular contours and forms 
so-called tongues. This tongue and groove connection is able to transfer 
quite large forces, and may be formed after hardening of the adhesive 
between the connecting member and a chipboard panel of the body of an 
article of furniture. The tongue is formed by the chipboard panel as a 
result of take-up moisture from the adhesive and conforms to the annular 
milling on the connecting member. 
In the manufacture of a connecting member for the connection according to 
the invention, a cylindrical blank for the member may be compressed to a 
predetermined degree and during this, profiling is simultaneously 
pressed-in or cut-in on the outer surface of the member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 1, an adhesive 11 located in a flexible sheath 8 is 
pressed in or blown in as an independent component into a cylindrical 
borehole 9 located in a sidewall 10 of the body of an article of 
furniture. Since the diameter of the flexible sheath 8 is somewhat greater 
than the diameter of cylindrical borehole 9, flexible sheet 8 with 
adhesive 11 is held securely in borehole 9, as hereinafter described. For 
this flexible sheath 8 can have any suitable form. The quantity of 
adhesive 11 heremetically enclosed in flexible sheath 8 is exactly 
measured out for the particular use. 
The connecting member is formed as a unit and consists of a base portion 1 
and a connecting portion 2, each of which has the same length. On the 
outer surface of the connecting member, annular notches 3 are arranged, 
which are directed towards each other and have identical diameters, their 
widths being of different magnitudes. The connecting member can be 
produced from any suitable material, for example, from wood, plastic, cast 
iron or a combination of different materials. 
Between base portion 1 and connection portion 2, a central cylinder portion 
6 is provided. For receiving the forcing out of the material at the outer 
edge of borehole 9 which occurs on the introduction of the connecting 
member into the cylindrical borehole 9, annular grooves 5 are provided 
between the cylinder portion 6 and the base portion 1 and the connecting 
portion 2 respectively. There is a point 7 on each of the two end faces, 
which serves to destroy the flexible sheath 8 for adhesive 11 and thereby 
facilitates the release of the adhesive. At the same time an additional 
anchoring of the connecting member in the end wall of the borehole 9 is 
thereby achieved. As clearly seen in FIG. 5, the fractured sheath 8a and 
distributed adhesive 11a are distributed in borehole 9. 
On the outside of the connecting member, grooves 4 are provided which are 
arranged to extend longitudinally in the region of the base portion 1 and 
the connecting portion 2. The outer surface of the cylinder portion 6 has 
very fine fluting 4', which can extend in any suitable manner. 
As shown in FIG. 2, flexible sheath 8 may be made of plastic and has a 
substantially cylindrical form, with a covering 12 on its end face, this 
covering 12 being welded (e.g., ultrasonically welded) to a peripheral 
angled out part 13 of sheath 8, so that adhesive 11 is hermetically 
enclosed. Covering 12 on the end face consists of a foil and projects over 
the peripheral angled-out part 13. It serves simultaneously as a flexible 
clamping element for flexible sheath 8 introduced into borehole 9, as 
clearly seen in FIG. 1. The periphery of covering 12 extending beyond 
sheath 8 engages with the wall of borehole 9 when sheath 8 has been 
pressed thereinto since the diameter of covering 12 is slightly greater 
than the diameter of borehole 9. This engagement of covering 12 with the 
wall of borehole 9 results from the flexure of covering 12 and serves to 
secure sheath 8 within borehole 9. By the provision of one or more 
clamping elements, it is possible to use sheaths 8 of similar size for 
each of a number of different diameters of borehole and in spite of that 
to achieve an excellent clamping of sheath 8 in borehole 9. The clamping 
effect in borehole 9 is in this embodiment of flexible sheath 8 not 
therefore now achieved directly by sheath 8, but by means of the flexible 
clamping elements disposed on the outer side of the sheath. By this, the 
introduction of the flexible sheath 8 filled with an adhesive 11 into the 
cylindrical borehole 9 is also facilitated, since it is not now sheath 8 
itself which must be compressed but rather only the flexible clamping 
elements. 
The form of flexible sheath 8 as shown in FIG. 2 facilitates forming by the 
deep drawing with heating method, preferably from a flat sheet. The 
covering 12 for the front face is welded on after filling of the adhesive 
into the cylindrically formed sheath 8 and subsequently the flat sheet is 
divided by burning or by stamping into the individual sheaths 8 which are 
now hermetically sealed. 
The spherical-form sheath 14 of FIG. 3 consists of an easily breakable 
material, for which glass is particularly suited, and is filled with 
adhesive. A cylindrical nozzle 15 is provided on the wall of sheath 14, 
this nozzle being hermetically closed off against the outside by means of 
an elastic body 16. 
In the case of a sheath 14 consisting of glass, the individual glass 
splinters of destroyed sheaths 14 are pressed into the walls of the 
cylindrical borehole 9 by the pressure of the connecting member and in 
part are also pressed into the connecting member itself which consists of 
wood, the glass fragments thereby providing an additional connection 
between the connecting member and the walls of the boreholes 9 of the 
parts to be connected. 
The connecting member shown in FIG. 4 consists of wood or an equivalent 
material and has a smaller diameter than the diameter of borehole 9. The 
blank for the connecting member is compressed to a predetermined degree 
and thereby at the same time the annular notches 3, the longitudinally 
extending grooves 4, the very fine fluting 4' and the annular contouring 
17 are pressed in and/or cut out on the outer surface. 
In a preferred embodiment, borehole 9 has a diameter of 8 mm. The diameter 
of the blank for the connecting member has an initial diameter of 8.7 mm 
and is compressed to a diameter of 7.9 mm. As a result of taking up the 
content of bound water, the connecting member swells to a diameter of more 
than 8.2 mm, in general to a diameter of 8.8 mm, so that a strong 
interference fit of the connecting member introduced into the borehole 9 
is thereby achieved. 
By means of annular contouring 17, the cross-grain of the cylindrical 
connecting member is uncovered, by which its ability to swell up is still 
further improved with a simultaneous shortening in the time to establish 
the joining effect. Both the connecting member and the chipboard or wood 
panel 10 of the body of the article of furniture take up moisture from 
adhesive 11 and thereby swell up. In this way chipboard panel 10 expands 
into annular contourings 17 of the connecting member and forms the keys 
18, as clearly seen in FIG. 5. 
It is understood that the foregoing general and detailed descriptions are 
explanatory of the present invention and are not intended to be 
restrictive of the scope of the following claims.