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Hot melt prepreg is a two-stage process. The common method of converting prepreg is by employing solvent and the fabric guided to dip in to the epoxy for wetting and then the web is directed through a drying tower to evaporate the volatile content. The heating tower is equipped with axial fan to create negative pressure to avoid accumulation of the volatile content in the chamber.
In the hot melt prepreg process, the fibre tow is impregnated with a hot melt resin film that is normally precoated on a paper or film carrier on a separate process called resin film casting machine.
The resin film which is cast on a carrier paper or laminated paper is transferred to the fibre using a combination of heat and pressure from the carrier paper into the spread fibre tow. Precision compaction rolls and heating plates are used in combination to achieve best results. The Compaction Rolls are set-up either in Nip arrangement or S-wrap arrangement.
Both Unidirectional (UD) Tape and woven fabric Prepreg can be produced in this machine depending on the customer requirement.
The Pathsfinder range offers Resin Film Casting Machines, Resin Film Casting and Sandwiching Machines, Prepreg Machines for Epoxy as well as Phenolic Resins. We offer Hot melt and prepreg machine in combination or as two separate machines according to the choice of the customer.
The coating unit is equipped with rollers that can be manually controlled to precise gap. The dial-gauge provided is to display the accurate position reading. The precision rollers are ground to 5 microns or lower depending on the customer demand. The coating rollers can be adjusted to coat epoxy as low as 20 gsm.
Creels can be programmed to have different levels of tension control. The specs can be from basic mechanical friction tension holdback or servo driven with load cell-controlled bobbin stations.
To achieve a good quality composite part, it is essential to have the back process with a dependable, high-quality prepreg conversion. Each fibre tow must be tensioned, guided and spread to achieve the target fibre areal weight (FAW) uniformly across the web. The machine is capable to manufacture multiple fibre areal weights from a variety of tow weights, with adjustable combs and fibre spreaders are incorporated into our systems for making UD prepreg.
It is essential to get precise fibre areal weight across the web, and hence the fibre spreading is arranged to get uniform fibre spreading. Our spreaders employ a series of fixed small-diameter spreader bars. Friction over these bars causes the tow to spread. Spreading can be optimized by changing the spacing between bars and the angle of the fibre as it passes over them.
Compaction is the heart of the hot melt prepreg process converting. Heat and pressure raise the temperature of the resin and transfer it from the carrier paper or film onto the spread fibre web. Resin flow from carrier to fibre is dependent on the heat transfer from the compaction rolls to the resin.
Our machine is equipped with compaction roll sets which can be used as S-Wrap or Nip modes. In S-Wrap mode, the web wraps 180 degrees around each compaction roll that increases the heat exposure of the web. The compaction process helps the web conversion with no voids or gaps.
Because of the viscoelastic characteristics of most resin systems, our prepreg machines typically incorporate multiple sets of compaction rolls. The gap between rolls is normally adjusted smaller on each progressive compaction roll set.
The machine is available to convert different width of UD Tapes like 300mm, 500mm, 650mm, and 1270mm.
In addition to the compaction rolls, the machine is also equipped with heating and cooling plates which is of aluminium and perfectly machined. Heat transfer is excellent with aluminium. The plates are curved to help the web to fully touch the full length of the surface.
Heating is can be achieved using hot oil, hot water or electric heaters. The thyristorised heating system ensures heating with a tolerance of 1 deg.C.
The unwind station is equipped with web alignment, edge sensors and Load Cells. The web alignment corrects if the edge moves away from the set web travelling set-up. Load Cell is to provide uniform web tension throughout the prepreg line. and rewind stations are
The use of composites in this field is expected to continue to grow as new materials and manufacturing techniques are developed, and as the industry seeks to improve efficiency and reduce environmental impact.
