DD203560A1 - METHOD FOR THE PRODUCTION OF ADHESIVE COMPOUNDS - Google Patents

Abstract

In particular, metallic materials with particularly high static and dynamic strength are to be filled by means of an adhesive bond. This manufacturing process has the goal to develop metal adhesive bonds for all organic adhesives by tasks gleichzeszige stress distribution in adhesive bonds by a defined multiple interrupted bond joint, regardless of the type and delivery form of the adhesive to be achieved. According to the invention, a small amount of from 0.1 to 2.5% of a liquid substance is added to the organic adhesive which, under conditions of extreme pressure such as pressure and / or temperature, leads to uniformly distributed micro-vacuole formation in the adhesive joint. Heavy-duty construction adhesive joints of this type are used mainly in mechanical engineering and metal lightweight construction u.ae. used.

Description

a- 231 868

Process for the production of adhesive bonds

Field of application of the invention

The invention relates to a method for producing adhesive bonds, preferably metallic materials, with particularly high static and dynamic strength, which is in the range of the base material strength.

Characteristic of the known technical solutions

It is known that metal adhesive bonds made with organic adhesives experience a large decrease in their mean tensile shear strength with increasing overlap length. The reason for this is the uneven distribution of stress over the length of the bondline with pronounced stress peaks at the overlap ends. In the case of static or dynamic loading of such adhesive bonds, a break in the adhesive bond occurs even at relatively low material elongation (-0.2%), starting from the overlap ends. Structural adhesive joints with bond strength in the area of the base material strength are therefore not achievable. It has already been proposed to dismantle the

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To achieve peak stresses at the overlap ends by using an adhesive combination that consists of a hard adhesive at the center of the joint and an elastic adhesive at the overlap ends. The required compatibility and the same curing characteristics of the two adhesives, as well as the associated technological effort, have hitherto not disclosed a practical application.

According to BG-Reg.üTr. 28 969 (1974) is proposed to achieve a more uniform stress distribution in adhesive bonds a multi-interrupted bond joint, which is produced by the fact that liquid adhesives are applied in strips or perforated adhesive films. However, an application of this method is severely limited by the fact that only a few adhesives are in film form and strip-applied liquid adhesives under the curing conditions (pressure, temperature) experience an indefinable change in the application image and thus the stress distribution in the bondline.

Object of the invention

It is an object of the invention to develop a process for the preparation of preferably metal adhesive bonds, which is applicable to all organic adhesives and ensures high-strength construction adhesive joints whose strength is in the range of the base material strength.

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The essence of the invention

The invention has for its object to achieve a uniform stress distribution in adhesive bonds by a defined multiple interrupted bond joint, regardless of the type and delivery form of the adhesive.

According to the invention, the object is achieved by adding to the organic adhesive a small amount, preferably 0.1 to 2.5%, of a liquid substance which under the curing conditions, such as pressure, temperature by evaporation leads to a uniformly distributed micro-vacuole formation in the adhesive joint ,

Suitable substances are e.g. Water or at the usual hardening temperatures boiling solvent u.a. in embossing.

In the case of hygroscopic adhesives, it is also possible to dispense with the addition of such substances if the adhesive film applied to the parts to be joined is conditioned within a certain open waiting time, i. is exposed to a room climate with defined humidity. The moisture absorbed from the air leads to subsequent hardening temperatures

> 100 ⁰ C also to the desired Yakuolenbildung in the Klebfuge.

Another possibility according to the invention for producing microvaculols in the adhesive joint is to add to a glue a filler having a low residual moisture content, preferably from 0.1 to 1 %, and then to cure at temperatures of> 100 ^° C.

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A further possibility is also given by the air conditioning of the parts to be joined before the application of adhesive, since the resulting on the surface water film at curing temperatures> 10O ⁰ C also leads to micro-vacuole formation in the joint.

The inventively produced micro-vacuole formation in the joint results in the adhesive joint a so-called sandwich structures similar Zeil structure with uniform stress distribution and thus high static and dynamic strength, which reaches the base material estigkeit with optimal overlap length or even exceeds.

embodiment

The invention will be explained in more detail below with reference to two embodiments. With a commercially available cold-curing adhesive based on epoxy resin, an average tensile shear strength according to TGL 14 910/02 of 17.8 N / mm ^{2 was} achieved with an overlap length of the adhesive bond of 10 mm for an Al Mg 3 alloy. When adding 30 % quartz powder with a residual moisture content of about 0.5% to the adhesive and an ultrasonic treatment of the bond line of 5 seconds, wherein the adhesive temperatures of about 120 ... 150 ⁰ C, it comes by evaporation of the barrel to the desired Micro-vacuole formation in the bondline and the tensile shear strength increased to 19.6 U / mm Considering that by the formation of vacuoles in the joint, the load-bearing adhesive cross-section

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is reduced by about 50 % , the actual increase in strength, based on the adhesive cross-section over 100%. With increasing overlap length increases in both cases (with or without US), the breaking load and decreases the average tensile shear strength, but a material fracture of the joining parts is only achieved in the US-treated specimens with an overlap length of 40 mm. ·

With another epoxy resin adhesive which already contained the filler, an average tensile shear strength of 23.6 H / mm was achieved for the same joining part material and an overlap length of 10 mm. When the applied adhesive is air-conditioned for 5 minutes at 75 % relative humidity and then thermally shock-cured for 15 minutes at 110 ° C., micro-vacuole formation also occurs in the bondline, and the tensile shear strength increases to 32.0 TT / mm. Based on the actual load-bearing adhesive cross section, this means an increase in strength of about 150%.

When the overlap length is increased to 30 mm, a material break occurs only with the adhesive joint with vacuole formation.

Claims (5)

invention claims 1. A process for the preparation of adhesive bonds, preferably metallic materials with organic adhesives, which have adhesion strengths in the area of the base material strength due to defined micro vacuoles in the adhesive joint, characterized in that the micro-vacuolation is achieved by an addition of substances to the adhesive, the Energy input during curing of the adhesive evaporate. 2. A process for the preparation of adhesive bonds according to item 1, characterized in that the substances to be added to the adhesive are preferably water or at the hardness temperatures boiling liquids and are used in amounts of preferably 0.1 to 2.5%. 3 · Process for the preparation of adhesive bonds according to item 1, characterized in that these substances are bound to the additives to be added to the adhesive, preferably fillers. 4. A process for the preparation of adhesive bonds according to item 1, characterized in that the hygroscopic adhesives, the introduction of Fasser in the adhesive film by air conditioning during the open waiting period. 5. A process for the preparation of adhesive bonds according to item 1, characterized in that the adherend surface is conditioned prior to the adhesive application.