GB2329968A

GB2329968A - Device for testing the strength of an adhesive connection

Info

Publication number: GB2329968A
Application number: GB9720707A
Authority: GB
Inventors: Robert Tonolla; Raphael Stolz
Original assignee: Gurit Essex AG
Current assignee: Dow Automotive AG
Priority date: 1997-09-29
Filing date: 1997-10-01
Publication date: 1999-04-07
Also published as: GB9720707D0; FR2769367A3; FR2769367B3; DE29717278U1

Abstract

The device comprises a first area 7 (Fig.4) coated with a glue 16 and a second area 8 that has a perforated area 9. In operation, the device is Z-folded about axes 13,14 to press the second area and the perforated area into contact with the glue to form an adhesive connection. The size of the perforated area ensures that its strength is lower than a defined minimum strength of the connection. The connection is tested by pulling both ends of the device in the direction of arrows 19,20 (Fig.5). On pulling, if the connection has hardened sufficiently, the connection tears open the perforated area so that the second area adheres to the glue and an imprint "GO" 10 (Fig.7) on the rear of the second area becomes visible. Once this imprint is visible, a user knows that the connection has reached the defined strength and it can be put under a load. The device may be used when fitting car windscreens.

Description

Device for Testing a Defined Minimum Strength of an Adhesive Connection The novelty relates to a device for testing a defined minimum strength of an adhesive connection according to Claim 1.

When parts are joined by means of an adhesive, it is hardly possible for the user to determine if and when the glue connection has arrived at a desired strength. This, however, is desirable in many application cases.

For example, a motor vehicle the windscreen or rear window of which has been replaced, should be returned into operation only when the adhesive connection between glass and body has arrived at a specified minimum strength. This is so because the windscreen or rear window as a supporting element is important for the rigidity of the entire vehicle. To meet defined crash-test norms, for example US Norm FMVSS 212, it is then indispensable that the mentioned adhesive connection between window and body has a defined minimum strength. Up to now, however, there is no reliable method which indicates to the vehicle owner or garage owner if, after replacement of windscreen or rear window, the adhesion offers a defined minimum strength which allows the vehicle to be returned into operation without doubt. Furthermore, premature loading of an adhesive connection can detrimentally affect its quality. On the other hand, it will also be desirable to return the vehicle into operation as quickly as possible. However, the adhesive connection can harden substantially quicker under favourable edge conditions than under unfavourable conditions; therefore, returning a vehicle into operation after gluing in a glass had to wait as long as the adhesive connection requires to arrive at a required strength under most unfavourable conditions. It is understood, however, that it is desirable to return the vehicle into operation as quickly as possible after gluing in the glass.

It is, therefore, an object of the novelty to offer a simple, costeffective device by means of which it can be checked if an adhesive connection has arrived at a defined minimum strength.

This object can be achieved by means of a device comprising the features of Claim 1.

The basic idea of the novelty lies in creating a device which is provided with a nominal fracture point which tears open or is torn open under load only when the adhesive connection has arrived at a defined minimum strength.

Preferred forms of embodiment of the novelty are defined in Subclaims 2 to 17.

In a preferred form of embodiment are then provided optical means which allow the user to determine whether hardening is sufficient or insufficient.

Preferably suitable for the above are in particular means which indicate to the user by way of a colour and/or a written message that a prescribed minimum strength of the adhesive connection has been arrived at and that the adhesion can be loaded.

An exemplary embodiment of the novelty will now be described based on the drawings. The drawings show, in Fig. 1: the essential individual components of the device; Fig. 2: the finished device in a top view; Fig. 3: the device as in Fig. 2 in a longitudinal cross-section along the line A-A in Fig. 2; Fig. 4: the device after application of the adhesive in an instantaneous illustration whilst being folded; Fig. 5: the device in its folded state; Fig. 6: the device after use with insufficiently hardened adhesive; and Fig. 7: the device after use with sufficiently hardened adhesive.

Fig. 1 illustrates the four essential individual parts 1, 2, 3, 4, which are preferably made of cardboard and of which the device is composed. Parts denoted 1 and 2 are provided to form the top, and parts denoted 3 and 4 are provided to form the bottom of the device.

The individual parts are all of rectangular shape, and the respective upper left 1 and lower right part 4 as well as the upper right 2 and the lower left part 3 are of identical dimension. The four individual parts 1, 2, 3, 4 are glued together to form the device.

The two upper parts 1, 2 are provided with a respective circular opening 6, 7, and the upper right part 2 is additionally provided with a circular area 8 which is defined by incisions 9a in such a manner that a nominal breaking area 9 in the form of a perforation is established.

The gluing between both parts 2 and 4 is recessed within the second area 8 so that area 8 can be removed once the nominal breaking area 9 has broken open.

Onto the back of the second area 8 is printed the word 10 "GO" to indicate to the user that the nominal breaking area has broken open.

Onto the left part of the two parts 3, 4 which form the bottom is printed the word 11 "STOP". The imprint 11 "STOP" is placed in such a manner that it corresponds with cutout 6 of left upper part 1 when upper part 1 is leftsidedly glued onto lower part 3.

Fig. 2 shows the finished device in a top view and Fig. 3 in a longitudinal cross-section along line A-A of Fig. 2. The length of the device in the form of a stripshaped section corresponds with multiples of the width. Both parts 1, 2 form the upper layer 20, and both parts 3, 4 form the lower layer 21 of the device. Fig. 2 shows that imprint 11 "STOP" corresponds with opening 6 in such a manner that the imprint can be seen through opening 6. As both the top and the bottom of the device are formed by two respective parts 1, 2; 3, 4, the device is cross-sectionally weakened in two places 13, 14 so that folding axes 13, 14, around which the device can be folded, are established between the ends of adjacent parts 1, 2; 3, 4. Folding axes 13, 14 extend transversely to the longitudinal axis of the device, and the second folding axis 14 is arranged in such a manner that area 8 lies on area 7 when the device is folded together. Through cutout 7 in the upper righthand part 2, the device has a recess 12 which serves to accommodate glue to be tested.

The operation of the device will be described in more detail based on Figs. 4 to 7. After recess 12 has been filled with glue 16, the device is folded like a Z as illustrated in Fig. 4 along both folding axes 13, 14, and the perforated area 8 is pushed onto glue 16 which causes the second perforated area 8 to make contact with the glue and the device takes up the form illustrated in Fig. 5. There is now an adhesive connection between perforated area 8 and gluing point 12.

Then, a specified period of time is allowed to elapse for the glue to harden. Both ends of the device are pulled in the direction of arrows 19, 20 in order to check if the glue has hardened sufficiently for breaking open the nominal breaking area under the effect of a load carried by the glue. The applied pulling strength now acts via the folding axes, now serving as rotary hinges, on the adhesive connection in that the latter is tensile loaded. If the adhesive connection has not yet hardened sufficiently, then the adhesion gives in under the effective load and breaks open without breaking open the nominal breaking area. Fig. 6 illustrates the device after use, and applied glue 16 had hardened insufficiently for braking open the nominal breaking area. In this case, glue 16 continues to adhere on both the second area 8 and the point of application 7, thus showing the user that the strength of glue 16 is still insufficient.

When the adhesive connection has hardened sufficiently, then its strength is sufficient to tear open the nominal breaking line in such a manner that the second area 8 adheres to the glue and the imprint "GO" on the rear of the second area becomes visible to the user. As soon as imprint "GO" is visible, the user knows that the strength of the adhesive connection has arrived at a defined minimum strength and that it can be put under load.

To further stress that the strength of the adhesive connection has arrived at a defined minimum strength, individual areas can in addition to a respective imprint or in lieu of the latter be underlaid by colours. The area provided with imprint "STOP" is preferably coloured red, whereas area 8a of the lower layer 21 (Fig. 3) located under the separated area is coloured yellow and the back of the second area 8 is coloured green. A colour scheme of this type shows the user by means of a kind of traffic-light effect that the strength of the adhesive connection after red and yellow is now within the green area and that it can now be loaded. Fig. 7 shows the device after use with sufficiently hardened glue.

Based on the example of gluing in a car screen, initially the car screen should be glued in and only thereafter should the glue be applied to the device. This procedure ensures that hardening of the glue between glass and vehicle has at least not progressed more than hardening of the glue applied to the device, thus allowing inclusion of a defined additional safety margin.

The described device offers a simple aid by means of which an adhesive connection can be tested for a defined minimum strength.

Furthermore, a device of this type makes it possible to take into account different edge conditions in that the adhesive connection of the device hardens under the same conditions - temperature, air humidity - as the glue by means of which said parts are to be joined.

Furthermore, this also allows testing whether the adhesive connection can reach sufficient strength at all, for example based on the age and/or storage conditions of the glue.

It is also feasible, for example, to provide two glue areas per device.

Should a test of the first glue area show that its strength is still insufficient, then the actual strength can be tested again after a specified period of time by means of the second glue area.

It is understood that the nominal breaking area can be dimensioned to meet respective requirements. There are possibilities of affecting the breaking force of the nominal breaking area in that different materials of different thickness can be used to produce the part which is provided with the nominal breaking area. Equally, the breaking force can be altered by way of the number and size of the incisions 9a. Naturally, a desired safety factor can be calculated when dimensioning the nominal breaking area.

Claims

Patent Claims 1: Device for testing a defined minimum strength of an adhesive connection, comprising a first area (7) for application of a glue (16), a second area (8) to be put in contact with the glue (16) for producing an adhesive connection, and a nominal breaking area (9) the strength of which is less than the defined minimum strength of the adhesive connection.

2: Device according to Claim 1, characterised in that optical means (10) are provided which indicate to the user of the device when the nominal breaking area (9) has broken open.

3: Device according to Claim 1 or 2, characterised in that the second area (8), which is to be put in contact with the glue (16), is designed as a nominal breaking area (9).

4: Device according to Claim 3, characterised in that the second area (8) is defined by circularly arranged incisions (9a) for forming the nominal breaking area (9).

5: Device according to one of the above claims, characterised in that the device has the shape of a stripshaped part.

6: Device according to Claim 5, characterised in that at least one folding axis (13, 14) is provided for folding the device, and the first area (7) is arranged on the one side of the folding axis (14) and the second area (8) on the other side of the folding axis (14), and both areas (7, 8) are arranged mirror-symmetrically to the folding axis (14).

7: Device according to Claim 5 or 6, characterised in that two folding axes (13, 14) are provided which allow Z-shaped folding of the device, and between both folding axes (13, 14) is provided an area (5) on which the one area (8) is arranged.

8: Device according to one of Claims 5 to 7, characterised in that the device for forming a folding axis (13, 14) is cross-sectionally reduced.

9: Device according to one of Claims 5 to 8, characterised in that the device is essentially of rectangular design, and the length in its unfolded state corresponds with a multiple of the width, and the folding axis/axes (13, 14) extend(s) transversely to the longitudinal axis.

10: Device according to one of the above claims, characterised in that the predominant portion of the device is, cross-sectionally seen, formed by two stacked and glued together layers (20, 21).

11: Device according to Claim 10, as far as referred to Claim 4, characterised in that the circularly arranged incisions (9a) which define the second area (8) are inserted into the one layer (20).

12: Device according to Claim 10 or 11, characterised in that the gluing is recessed within the second area (8).

13: Device according to one of Claims 10 to 12, as far as referred to Claims 4 to 9, characterised in that the device in arranged to be single layered in the area of the folding axis/axes (13, 14).

14: Device according to one of Claims 10 to 13, characterised in that into the one layer (20) is inserted a circular opening (12) for accommodating the glue.

15: Device according to one of Claims 3 to 14, characterised in that the rear of the second area (B) is coloured and/or provided with an imprint (10).

16: Device according to one of Claims 10 to 15, characterised in that the bottom layer (21) is coloured and/or imprinted in the surface area adjacent to the second area (8) of the top layer (20).

17: Device according to one of Claims 10 to 16, characterised in that the device is composed of four individual parts (1, 2, 3, 4) which are glued together, and two parts (1, 2) form the top and two parts (3, 4) the bottom, and a folding axis (13, 14) is established in the area of the adjacent ends of the parts (1, 2; 3,

4).