The Perfect PU Foam Gasket
Published on : Sunday 01-01-2023
How to ensure high-quality and efficient automated production with dynamicLine.
Polyurethane (PU) gaskets protect component interiors from moisture, dirt and other environmental influences.
For example, they seal control cabinets, their housings, and doors, or the lights and speakers in cars. They are also used in the filtration and packaging industries. PU foam gaskets can be inserted manually. However, an automated solution offers significantly higher process reliability. The seal adheres firmly and permanently to the component. There are no coupling points or open notches. Thanks to a controlled overlap, the start and end points of the foam bead merge. A nozzle-closure system ensures seamless closure of the sealing bead. It prevents dripping at the nozzle opening, which could otherwise create an untidy sealing bead or make the component or belt system dirty. PU gaskets can also be produced much faster and in higher volumes by means of the FIPFG process (formed-in-place foam gasket).
PU gaskets are made from reactive polymer materials. In general, two components are processed with a dynamic mixing system. Metering and mixing are carried out precisely and with consistently high quality. With the use of a linear robot, the gaskets can be applied directly onto the component automatically. It is also possible to position the component beneath a permanently installed mixing head with the aid of an industrial robot and start with the geometry of the foam bead. The result is a soft foam seal that hardens at room temperature. To compensate for different ambient temperatures, the temperature of the mixing chamber as well as that of the material containers and hoses can be controlled. The control unit can store several metering and positioning programs. For example, it is possible to switch between different components or material formulations. Furthermore, different discharge capacities with varying seal widths or heights can be selected.
High flexibility: applications for bonding and potting
Dopag dynamicLine offers solutions for the dynamic mixing and automated metering of adhesives and potting compounds. The dynamic mixing head is suitable for a wide range of materials, from extremely liquid to highly thixotropic. The use of linear or industrial robots makes automation possible that meets the exact requirements of the application.
With the FIPFG process (formed-in-place foam gasket), reactive polymeric materials are metered, mixed and then applied using a dynamic mixing system such as dynamicLine. This involves an A-component (polyol) and a B-component, as well as the hardener (MDI isocyanate). The A-component has molecule chains of different lengths. They determine how soft or hard the foam is after hardening. The longer the molecule chains, the softer and more flexible is the foam. Mixing the A and B components in the mixing system starts the reaction. The molecule chains connect with one another and a polymer is formed. This produces carbon dioxide as a fission product. The technology used by DOPAG, the low-pressure process, is responsible for foaming the material and then hardening it at room temperature.
Benefits of automated production compared to manually inserted seals
i. They are automatically fixed in position and can stick without any additional adhesive tape.
ii. Thanks to the precise coordination of metering volume and robot speed, the start and end points of the foam bead come together perfectly, so there are no undesired coupling points or open joints or notches.
iii. Considerably lower costs for a seal
iv. Higher-quality seal
v. Short cycle times enable efficient, automated production.
vi. Practically no waste compared to punched or cut seals, and
vii. System is rinsed with water, solvent-free.
Producing PU gaskets in just seconds
A fully automated system like the one DOPAG developed for Gealan Formteile GmbH and Foster is ideal for high-quantity series production. The system developed by DOPAG had to meet high quality assurance standards.
Production in the automotive industry involves high-quantity orders, where reproducibility, process reliability and quality assurance play a crucial role. DOPAG developed a system that meets these requirements exactly, to be used by Gealan Formteile (developer and manufacturer of technical plastic parts and components) and Foster (sound system manufacturer) for applying PU gaskets to speaker modules. The system features a flexible overall design so that PU gaskets can be applied to multiple different components at multiple points.
The dynamic mixing head is part of the dynamicLine and the beating heart of the machine. It processes the highly reactive multi-component polyurethane. Three robots were integrated in the system to handle the components while the individual work steps are carried out. Before the robots spring into action, components are first placed in the system manually and sent off to a robot via two conveyor belts. A plasma pretreatment nozzle is positioned in the centre. The plasma ‘activates’ the surface so that the gasket bonds to the component. The robot takes the component from the conveyor belt to the left or right of the nozzle, guides it to the nozzle and traces what will be the contour of the future gasket. The robot then puts the component in a workpiece carrier. The workpiece carriers have an important secondary function: they help with ionisation. The components are statically charged and the surfaces are neutralised for the subsequent application of material. The workpiece carriers can be replaced within just a few minutes if necessary. The different metering and application processes are stored in the system in advance so that they can be selected via the touch panel quickly and easily. This preprogramming gives the user maximum flexibility in series production. The user can respond quickly to different needs and manufacture variable quantities of different components.
Dynamic mixing of material
The other two robots then alternate as they take the components from the workpiece carriers and hold them under the nozzle so the gasket can be applied. The polyurethane is metered and mixed in the dynamic mixing head, which is mounted on a travelling axis. The mixing head can move to the two positions on the left and right in order to apply the material. The mixing head then remains still as the robot on the left or right moves the component accordingly so that the material is applied along the intended contour. This approach has the decisive advantage over a linear robot in that a gasket can be applied to a component on multiple sides in just one work step.
The dynamic mixing head is suitable for processing highly reactive materials. In addition to gasketing, it can also handle adhesives and potting compounds. Thanks to the programmed controlled overlap, the start and end point of the foam bead merge into one another, producing an optimal coupling point. The nozzle-closing system (NCS) is an additional feature that ensures seamless closure of the sealing bead. It prevents dripping at the nozzle opening, which could otherwise create an untidy sealing bead or make the component or belt system dirty.
Once the material is applied, the robots place the components on a specially designed conveyor belt, where the PU gasket hardens at room temperature. The conveyor belt has been designed and synchronised to cover the entire time needed by the gasket to harden, so that by the time a component reaches the end of the belt, the gasket has fully hardened and the component can be removed and further processed.
High process reliability in series production
Extensive process reliability systems were installed to meet all of the requirements of the automotive industry and ensure consistently high quality. Right from the start, as soon as a component is manually placed in the system, camera sensors verify the component type against the programmed preset. Components that do not match the preset type or cannot be identified are rejected. Each time the system is restarted, the grippers and the nozzle of the mixing head are checked for damage. If no damage is detected, the system starts in regular production mode and the material is metered, mixed and applied.
Material supply
The material is supplied via two material pressure tanks for the A and B components, in which additional functions are integrated, such as a controlled air supply to the A component or fine filtering of the B component. High-precision DOPAG gear pumps meter the material, aided by a refilling station that ensures continuous, automatic filling and uninterrupted production. A temperature control unit is also installed. The temperatures of the material pressure tanks, hose lines and mixing chambers are controlled using a heat transfer medium, so that the material is always at the right processing temperature. With this feature, the system covers all considerations, ensuring the clean, reliable and high-quality completion of PU gaskets in series production.
References
1. https://www.dopag.com/news-portal/exact-customer-magazine/
2. https://www.dopag.com/applications/application-cases/gealan-foster-series-production-of-gaskets/
3. https://www.dopag.in/applications/application-cases/series-production-of-pu-foam-gaskets-1/
4. https://www.dopag.com/news-portal/exact-customer-magazine/
