Sealing automotive batteries in e-mobility

Sealing automotive batteries for use in electric vehicles is an important step in the production process. Precise application of the sealant protects both the interior of the battery pack from environmental influences and the occupants from gases or other toxic substances that can escape if the battery pack is defective. The butyl-based sealants used to seal car battery covers not only seal out air and gas, but are also highly resistant to environmental influences such as salt, stone chipping and even freezing temperatures. Sealant viscosities of 1.5 – 3 million mPa*s are commonly encountered. When applying these high viscosity sealants, it is important to ensure a homogeneous application in a reproducible process in order to achieve a full surface seal. In addition, process and travel speeds of up to 400 mm/s must be achieved to meet the cycle times of the automotive industry.

In addition to protecting the battery from the environment and ageing, another important consideration is the protection of vehicle occupants in the event of a defect or accident. In order to give vehicle occupants sufficient time to evacuate in the event of an emergency or fire, batteries are required by law to have a fire retardant coating. This coating is achieved using mica shields, which are bonded to the outside of the battery pack using reactive adhesives. In the event of a battery fire, the flames can be prevented from spreading to the vehicle for up to 5 minutes. For this application, moisture-curing polyurethane-based hot melt adhesives are used, which do not melt even under high heat. Application is by a flat spray. A homogeneous layer of adhesive optimises material usage without compromising adhesion.

Based on initial applications in the area of battery pack sealing, SM Klebetechnik optimised its equipment engineering for the specific requirements in this field. The result is a usage-oriented application solution that satisfies the broad range of automotive battery sealing requirements.

SM Klebetechnik’s KP 81 pump application head with its gear pump built into the head has proven effective in applying butyl. The bead module makes it easy to change the application nozzle, thereby enabling different bead patterns. That means both round beads with diameters of up to 20 mm and also other bead geometries such as square or triangular beads are possible.

The integrated gear pump allows for a very short control system between nozzle discharge and pump. This, in turn, makes it possible to apply sealant precisely with minimal pressure fluctuations during application. Moreover, a front closing needle valve ensures clean start-stop action without stringing over the component.

Pump application head KP81

With the KF0170, SM Klebetechnik also offers a suitable application head for surface spraying. This fibre spray head uses heated compressed air to atomise the adhesive, producing a homogeneous application pattern. The maximum application width per head is 220 mm. Larger application widths can be achieved by modular arrangement of several application heads. With interchangeable masking plates, the application head is very low maintenance and can be customised to meet individual customer requirements.

Spray pattern – Fibre spray

 SM Klebetechnik offers a wide range of systems for melting and conveying the various adhesives and sealants.
To melt and pump high-viscosity sealants, drum melters for 20 or 200-litre packages are used in the most common applications. Along with the required melting capacity, the drum melter must also have a suitable ram force to achieve continuous mass flow and optimal pump inflow as well as filling level. Its screw spindle drive enables SM Klebetechnik’s GX 78 screw spindle drum melter to melt and pump these highly viscous materials in high discharge volumes.

Reactive hot melt adhesives are applied with pneumatic drum melters and special bag or tank melters. GR Series tank melters are equipped with an integral compressed air dryer to prevent cross-linking of adhesives within the unit. These units also have a reservoir that allows uninterrupted dispensing even when the adhesive is being refilled.

Tank melter GR22

Bag melter GR21

„The tests were conducted in the technical centre of SM Klebetechnik in Heinsberg, Germany. The company employs about 60 people and its size makes it a very flexible and active partner for us.

The 200-litre GX7882 screw spindle drum melter system was soon able to apply a perfect sealing seam without any problem. After adjusting the parameters, it also successfully applied sealant to a simulated section with a tight radius. By selecting various nozzles and fine-tuning further machine settings, the system essentially satisfied all requirements with regard to injection quantity, geometry, application rate, etc. This proves the overall suitability of the proposed system. SM Klebetechnik’s systems are already used in the automotive sector and we have agreed in principle to collaborate on future projects – to seal battery housing covers, for example.

We can also envision further collaboration on reactive hot-melt applications, such as gluing mica sheets to plastic battery housings.“