Process for producing an adhesive bond in a folder joint

A process for achieving an adhesive bond in a folded joint between a first component (1) and a second component (2), preferably of sheet metal. The components (1,2) have essentially flat edge areas (3,4), and the second component (2) has a bent-up flange (5) to be bent down about the edge area (3) of the first component (1). The process comprises application of an adhesive string (8) along the surface of the second component (2), which is to lie in contact with the first component (1). The adhesive string (8) is applied a short distance from the edge flange (5), and the amount of adhesive in the adhesive string (8) is adjusted so that the adhesive, when the components (1,2) are pressed together, is forced past the edge of the first component (1) and covers the same. Furthermore, a second adhesive string (10) is applied along the surface of the first component (1), against which the edge flange (5) is bent down. The second adhesive string is placed a short distance from the edge of the first component (1) and the amount of adhesive is adjusted so that the adhesive, when the edge flange (5) is bent down, is, on the hand, pressed into contact with the adhesive in the first adhesive string (8), and, on the other hand, is made to cover the edge of the edge flange (5).

The invention relates to a process for producing an adhesive bond in a 
folded joint between an inner component and an outer component, preferably 
of sheet metal. The inner component has an essentially flat edge area and 
the outer component has an essentially flat edge area with a bent-up edge 
flange for bending about the edge area of the inner component. The process 
includes the application of an adhesive string along the surface of the 
edge area of the one component which is intended to lie in contact with 
the edge area of the other component. 
Folded joints are often used to join an inner component to an outer 
component of e.g. a hood, a door or the like in a motor vehicle. The inner 
component and the outer component are designed to be joined to each other 
by bending the edge flange of the outer component about the edge of the 
inner component. It is, however, difficult to make such a folded joint 
stable without some other bond between the components. In folded joints 
for motor vehicle body parts and the like an adhesive bond is often made 
between the inner component and the outer component. This adhesive bond 
has in addition to its bonding function a corrosion protection function, 
both in the folded joint itself and at the free edges of the inner 
component and the outer component. 
In a previously known process for achieving an adhesive bond in a folded 
joint between an inner component and an outer component, a string of 
adhesive, usually cold epoxy adhesive, is applied to the surface of the 
edge area of the outer component, which surface is to be in contact with 
the edge area of the inner component. The outer component and the inner 
component are then placed together and the folding of the joint is 
completed. The adhesive string is laid out and pressed around the edge of 
the inner component, so that the edge is protected. It is, however, not 
possible to make the adhesive cover the entire folded-over edge flange. In 
order to protect the folded joint and particularly the edges of the 
flanges, a folded joint seal is applied, usually of a PVC-material, over 
the edge of the folded-over edge flange. The material also adheres to the 
edge area of the inner component. This gives rise, however, to an air gap 
enclosed in the folded joint. In the subsequent processing of the part, 
e.g. curing of paint or other surface treatment, the air in the enclosed 
space will expand and give rise to blisters and pores in the sealing 
material. This is very difficult to detect and the blisters and pores will 
make it possible for moisture to penetrate into the folded joint, thus 
decreasing the resistance to corrosion. 
The purpose of the present invention is to provide a process which avoids 
the difficulties described above and achieves a completely satisfactory 
adhesive bond in a folded joint between an inner component and an outer 
component.

FIGS. 1-3 show a first component 1 and a second component 2, which are 
designed to be joined by a folded joint, with an adhesive bond according 
to the invention provided between the first component 1 and the second 
component 2. 
The first component 1 has an edge area 3, which is essentially flat and is 
designed to be applied against an edge area 4, also essentially flat, of 
the second component 2. The second component 2 also has a bent up edge 
flange 5, which is designed to be bent in over the flat edge area 3 of the 
first component to achieve a folded joint between the first component 1 
and the second component 2. The first component 1 also has a contact area 
6 for contact with another portion of the second component 2. Between the 
second component 2 and the contact area 6 a string 7 of adhesive sealing 
material is laid, in a manner known per se, to prevent the components 1 
and 2 from contacting each other. 
To achieve a seal in the folded joint between the first component 1 and the 
second component 2, an adhesive joint is made according to the invention 
in the folded joint. A first adhesive string 8 is applied on the side of 
the edge area 4 of the second component 2 which is facing the edge area 3 
of the first component 1. As an alternative, the first adhesive string can 
be applied to the surface of the edge area 3 of the first component 1, 
which faces the edge area 4 of the second component 2. This placement is 
indicated at 8a in FIG. 1. 
The first adhesive string 8 has, when used together with a first component 
1 and a second component 2 of sheet metal, e.g. for car body parts, a 
width a of 5-15 mm and a thickness b of 1-3 mm, and is spaced a distance c 
from the edge flange 5 of 1-5 mm. The material in the first adhesive 
string 8 consists of a rubber based material, hot-melt epoxy or another 
equivalent material for application in a hot state, preferably at a 
temperature of 60 -100.degree. C. 
Then the first component 1 is placed against the second component 2, i.e. 
the two components are placed in the position shown in FIG. 2. The first 
adhesive string 8 is pressed out between the edge area 3 of the first 
component 1 and the edge area 4 of the second component 2. By suitable 
selection of the dimensions a, b and c, the first adhesive string 8 is 
pressed out in such a manner that, on the one hand, a portion of the 
adhesive is pressed up around the edge of the edge area 3 of the first 
component 1 to protect the edge and, on the other hand, a portion of the 
adhesive is forced out and forms a bead 9 at the inner portion of the edge 
areas 3 and 4 to prevent penetration of foreign material between the edge 
areas. 
Prior to placing the components 1 and 2 together, a second adhesive string 
10 is applied to the surface of the edge area 3 of the first component 1, 
against which area the edge flange 5 is to be bent. The second adhesive 
string 10 has a width d of 5-15 mm and a thickness e of 1-3 mm. The 
placement of the second adhesive string 10 is selected so that a portion 
of the adhesive string extends out past the portion of the edge area 3 of 
the first component 1, which will be covered by the edge flange 5 of the 
second component 2 after folding the edge flange 5 in. The projecting 
portion of the second adhesive string 10 is suitably selected with a width 
of 1-3 mm. After folding in the edge flange 5, the second adhesive string 
10 will have been pressed out, firstly into contact with the first 
adhesive string 8, without enclosing any air whatsoever, and secondly into 
a second bead 11 which covers the edge of the edge flange 5 and protects 
the same. By virtue of the fact that the second adhesive string 10 is 
partially outside the edge of the edge flange 5, the material pressed out 
during the folding operation itself is thereby blocked. The material in 
the string will then move upwards and place itself as a protection against 
corrosion against the unprotected, cut edge of the edge flange 5. This 
position is shown in FIG. 3. 
A nozzle 12, shown schematically in FIGS. 4 and 5, is used to apply the 
adhesive strings 8 and 10. The nozzle 12 has an opening which is adapted 
to the width of the respective adhesive string 8 or 10, and it is kept at 
a distance f from the underlying surface, i.e. the first component 1 or 
the second component 2, of 1-2 mm. The nozzle 12 is moved in one direction 
over the underlying surface, see the arrow 13 in FIG. 4, and is held at an 
angle a of 70.degree.-80.degree. to the already applied portion of the 
adhesive string. With this design and orientation of the nozzle 12, the 
material in the adhesive string 8 or 10 is pressed against the underlying 
surface, thus achieving the best possible wetting of the underlying 
surface, i.e. adhesion to the same. 
With the process according to the invention, a folded joint is achieved 
which is completely protected from corrosion. No foreign matter can 
penetrate into the joint, and there are no blisters or pores in the joint. 
This means that later treatment of the components, e.g. different types of 
surface treatment, can not give rise to any problems in the folded joint. 
The invention is not limited to the examples described above, rather 
variations are possible within the scope of the following claims.