Hot Pressing
Presses and molding are often used to form high strength composites. It often consists of a rapidly cycling pressure chamber filled with a pressure transfer medium such as silicone that encloses a high pressure elastomeric vessel.
In a conventional hydraulic press there is a steel piston chamber that contains oil and as oil is pumped into the piston chamber, the piston is pushed out of the piston chamber into pressurized contact with a work piece. In an alternate, or hydro-forming press, high-pressure water is forced into a closed chamber against a metal sheet or tube and, as the pressure builds in the chamber, the sheet is pressed and stretched into a cavity behind it. Another press positions a work piece between a conventional movable forming die and an expandable bladder optionally filled with fluid under pressure. Still another press uses an enclosed inflatable container in communication with hydraulic fluid reservoirs to provide the pressure for the ram in the hydraulic press so the hydraulic fluid is never in direct contact with any of the structural mechanisms of the press.
In conventional press designs, the chamber is closed with a rubber gasket or a low pressure seal, or as is the case with a hot isostatic press (HIP) a simple screw type plug lock. In a conventional HIP press, the pressure transfer medium is a hot gas such as nitrogen or argon, or water, or oil or a rubber crumb, and heating and cooling is achieved by thermal transfer to the work piece through the gas or other transfer medium, or a by a heated mold.
Conventional high strength, low weight structural composites are made from materials such as fiberglass or graphite. The composite article is typically made of multiple layers of so-called pre-pregs (combination resin and fiber materials) which have been laid up over a mold or die and thereafter cured under selected temperature and pressure conditions. Curing of the pre-preg layup is conventionally accomplished in an autoclave and requires the use of a vacuum bag or other type of barrier to prevent the pressurized fluid or gas from penetrating the layers and ruining the composite article which is being fabricated. But autoclaves are expensive and limited in pressure range and vacuum bags have a tendency to leak, resulting in a comparatively high reject rate.
Recent US Patents
1/4/2011
7,862,323
Press and method for forming a composite article
Micarelli from Washington developed a press including a pressure chamber filled with a substantially incompressible medium that at least partially encloses an elastomeric vessel filled with a substantially incompressible fluid that is in fluid communication with a pressurized source of the same fluid. Method and systems employing the press are also disclosed. (RDC 7/13/2011)
11/2/2010
7,823,435
Die clamp mechanism for press machine
Bandou and Takano of Komatsu Ltd, Japan developed a die clamp mechanism with pluner for a press with moving bolster. (RDC 2/21/2011)
10/12/2010
7,811,407
Method for production of sandwich panel core from composites
Akishev et al, Russia manufactured cores for sandwich panels by impregnating a blank with a binder and hot pressing to form corrugated cores. (RDC 1/10/2011)
10/12/2010
7,811,498
Process for the production of a shaped article
Mokveld and Beugels of DSM, Netherlands has developed a process for producing an improved anti-ballistic material by compressing polyolefin fibers containing 0.02 to 25 wt% solvent. (RDC 1/7/2011)