Filter Bonding

Cost-effective production of quality filters is a challenge for manufacturers. From the high-volume automotive air or fuel filters to the high-end HEPA Filters, mixing and dispensing process is critical to the performance of filters in every environment. Twin Engineers has the expertise and equipment to automate PU filter foam, epoxy dispensing and paper joint sealing processes used in the manufacturing of various types of filters.

End-cap Gluing
The end cap bonding process involves use of thermosetting resin to bond filter media to metal or plastic end caps. The two-part epoxy resin is metered, mixed and dispensed in the cap on which the filter element is placed and bonded. The material cures to form a solid glue and hold the filter element. The process requires an accurate mixing ratio of the epoxy resins. The shot size is determined as per the mould and bonding strength required. Accurate shot size is critical to efficient use of the materials being mixed, and therefore achieved best through a meter mix machine.

PU Foam Dispensing
PU Foam dispensing involves mixing of two components, labelled ISO and POLYOL. Typically, the components are recommended to be stored in the temperature range of 18-25 deg Cel. ISO is a sensitive material which has a tendency to react with moisture and result in crystallising. Polyol components help in expanding the foam and typically have a low boiling point.

When mixed, ISO and Polyol form an exothermic reaction, and as the reaction progresses the viscosity of the mixture increases. With time, the mixed material forms a foaming process until the liquid completely turns to a polyurethane solid. To achieve the consistency of physical properties of the foam and adhesion, the temperature of the components have to be maintained at 20-25 deg cel. For lower temperatures, the material becomes thicker and difficult to blend and the foam yield from the reaction will be lesser. At higher temperatures, the reaction time for foaming will be faster which could make it difficult to ensure proper adhesion. Twin’s Machines come with Chillers to maintain an accurate temperature of the components.

Unlike Elastomeric PU, the materials in filter bonding are mixed in the presence of air. The process, termed as nucleation, allows the creation of tiny bubbles. The bubbles serve as the growth points for the foaming reaction and lead to improved cellular structure for the foam. The best quality PU foams in filters are produced through mixing and dispensing through a machine.

The polyurethane foam is poured into a mould which is treated with a release agent. The foam typically expands in volume by 10% after pouring. Twin Engineers offers various automation options for dispensing of foam (robots, extended arms) or holding the moulds (X-Y Tables Rotary Index Tables) as per the shape of the filter and production volumes.