Heat exchange – Movable heating or cooling surface – Rotary drum
Patent
1991-09-20
1992-10-27
Ford, John K.
Heat exchange
Movable heating or cooling surface
Rotary drum
165 61, 165 64, 165168, 100 93P, 425143, 425407, 425DIG13, 219243, 219446, 219449, 219458, 1565831, 1565834, 156498, B29C 3302, B29C 3304, B30B 1506
Patent
active
051581329
DESCRIPTION:
BRIEF SUMMARY
The invention relates to high temperature electrical heater equipment for mounting on a rigid mechanical support, in particular the table or frame of a press for manufacturing products from plastic material and from composite materials, the equipment being of the type comprising:
a heat-distribution plate at a distance from said mechanical support;
thermal insulation means provided against said mechanical support and on the lateral margins of said equipment;
electrical heater means and cooling means disposed between said heat-distribution plate and said thermal insulation means; and
temperature regulation means for maintaining a uniform temperature over the entire area of said temperature distribution plate as a function of the manufacturing program.
Hot plates are already known using various different heating techniques such as steam, heat-conveying fluids, and electrical heater resistance elements.
Such hot plates are not suitable for adequately meeting the conditions specific to manufacturing composite material products, in particular local temperature regulation and accuracy in production tooling and molds.
Such a hot plate generally comprises a single block of steel perforated in various ways in order to allow a heat-conveying fluid to flow (e.g. oil flowing along a sinuous path or coil, or steam flowing through a "comb" of parallel paths). These dispositions limit the maximum size of such a plate to the maximum capacity of a drilling machine. Such hot plates may be fitted with cylindrical electrical heater resistances in the form of cartridge elements having a maximum length of 1 meter or placed end-to-end in facing pairs in order to obtain a maximum plate width of 2 meters. It is also possible to use rectilinear or circular metal-clad electrical resistance elements. These are difficult to extract. When extraction is necessary, it cannot be performed quickly and, in any case, such elements give rise to 5 mm to 60 mm wide cold zones at the margins of the plate whose effective size is thus reduced. Since these resistance elements are cylindrical in shape and since they are inserted in square-section holes, heat is poorly conducted because of the presence of air and because of the small contact area.
Use is also made of conventionally manufactured flat metal-clad resistances in the form of single heater elements offering a uniformly-distributed electrical load having a maximum length of 1.5 meters (m), which elements likewise suffer from the drawback of presenting cold end zones. For the purpose of partially compensating the heat losses at the margin of the plate, the electrical load may be concentrated at the ends. These resistance elements are defined and powered on the basis of theoretical calculations. The corresponding hot plates do not provide adequate heating accuracy where it is required, and as a result there are local anomalies in the manufacture of composite material products which may be prejudicial to their strength. In addition, the time required to manufacture such hot plates, and the time required for making products are both long. They do not make it possible to obtain the thermal and mechanical flexibility required particularly from a dimensional point of view, nor do they make it possible to obtain desirable energy efficiency, nor the speed of manufacture nor the temperature accuracies needed for uniform polymerization of composite structures which suffer from a high reject rate. In addition, the investment required is large compared with the unsatisfactory results obtained.
The U.S. Pat. No. 4,659,304 described heater equipment of the type mentioned above in which the heater means are constituted by resistances received in open grooves in one face of a metal hot plate. Patent WO-A-8,706,876 described heater equipment in which the metal hot plate likewise includes grooves for receiving electrical resistances, which grooves alternate with grooves provided for passing a cooling fluid. These heater equipments require special machining of the hot plate, thereby increasing the cost price o
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