Adhesive Dispensing Systems

With adhesive connections it is possible to bond different materials permanently and with complete preservation of their properties. Besides the weight-saving in general, there are many other advantages:

• Due to their elasticity, adhesives can, for example, compensate for different thermal expansions of both joining partners, which means that thermal cycling stresses do not lead to local internal stresses. These stresses could loosen the joining connection or put such a high mechanical load on individual assemblies that they would be damaged.
• Bonding provides more flexibility in the component design, as there are usually sufficiently large areas available for secure bonding. Therefore, a more even distribution or transmission of force can be generated. When screwing or riveting, this often happens at very localized points. This would be used in the automotive industry, for example. A targeted bonding of the car body would result in a significantly higher crash resistance. This in turn ensures greater safety for the driver. By utilizing a much larger surface area, the adhesive bond can receive a great deal of the crash energy and absorb it. The situation is similar with other types of bonding.
• In the electronics sector, for example, adhesives are dispensed as encapsulation of sensitive components. This protects the electronic components from external influences and increases their service life.
• The dispensing of adhesive also ensures that there is no local weakening of the strength of the joining partners by screws or rivets.
• In contrast to welding or soldering, the application of the adhesive does not place the joining partners under high temperature stress. This too could lead to a local weakening of the strength due to the application of stresses.
• Depending on the type of adhesive that is dispensed, a combination of different properties is possible. This includes, for example, the electrical insulation of both joining partners or an electrical conduction through the bond and the adhesive can be thermally insulating or thermally conductive.
• On the one hand, so-called spacers in the bond can be used to generate the defined and perfect bonding gap, where the bond has the greatest strength, and at the same time the joining partners can be brought to a predefined distance.
• During the dispensing process of adhesive, it is possible to join and seal in one single step (keyword Form-In-Place Gaskets).

• Compliance with the mixing ratio of 2-component adhesives: Especially in the case of polyaddition curing reactions, which would result in insufficient adhesive properties, or even no curing at all would occur.
• Moisture-curing adhesives must not come into contact with moisture: As a precaution, we work with regular rinsing intervals as required or, if necessary, with sensor technology to monitor possible curing in the dispensing needle.
• Low-viscosity and filled adhesives must be homogenized before dispensing or kept homogeneous in a treatment system through circulation and stirring. If not, there is a risk of inadequate material properties.
• With UV-curing adhesives, any contact with light should of course be avoided until dispensing is complete.
• Thermosetting adhesives (e.g. epoxy or silicones) often have to be stored in a cool place and the dimensions of the dispensing system has to be adapted to the consumption quantity or dispensing time at the customer’s site. In the worst case, the adhesive could cure inside the complete system.
• Strongly exothermic adhesives can overheat if applied in excessive quantities. This must be taken into account when selecting the dispensing technology, especially at the time of mixing two-component adhesives. The right design is particularly important to guarantee a permanently stable dispensing process, especially for high-viscosity and highly abrasive adhesives. Errors in the design of the dispensing system with regard to pressure and material flow rate promote wear to the dispensing components and the dispensing system could block locally due to deposits of filler.
• The dispensing needle also has an influence on the achievable repeatability and the service life of the dispensing system, especially in the case of minimal dispensing quantities. It must be selected correctly and in accordance with the specific application. A diameter that is too small would, for example, result in a too high dispensing pressure and therefore dispensing inaccuracies due to back flow.
• Strong thixotropic adhesives must not be sheared too much during dispensing, as they would, in some cases, drip too much after application – this is particularly relevant for vertical or overhead dispensing.