Electric heating – Metal heating – Of cylinders
Patent
1989-12-26
1991-06-11
Leung, Philip H.
Electric heating
Metal heating
Of cylinders
219 1075, 219 1071, 219 1079, H05B 610
Patent
active
050234196
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to methods and devices for magnetically heating a workpiece consisting at least partly of metal More specifically, the invention is concerned with the preheating of moulding or press tools, the separation of metal from a polymer, the production of composite materials, and the hardening of adhesive between two metal members.
For the preheating of press tools, which is necessary before the tool is operated, use is made at present of hot-air furnaces in which the tool is heated to about 450.degree.. This takes about 10 hours, which is far too long for an efficient production. Furthermore, it is difficult in a furnace, to heat the press tool to a uniform temperature across the entire tool cross-section.
Hitherto, a number of techniques have been utilised to separate polymeric materials, such as rubber and plastic from metal. One technique involved burning-off of the polymer, which has caused emissions hazardous to the environment, and structural changes and stress in the metal. DE 2,900,655 indicates a different technique involving the use of an induction coil. An object, for example a vehicle tire, is positioned within the induction coil which is activated by a high-frequency voltage to generate a magnetic field heating the metal in the vehicle tire to such an extent that the polymer can be detached from the metal. Generating high-frequency voltage is expensive and cannot be utilised for all types of objects. If the object has projecting metal parts, a so-called point effect is obtained which means that the projecting metal part is heated to red heat. Furthermore, the high-frequency technique is restricted to relatively thin objects since the penetration depth in metal is slight when use is made of high frequency, for example 1 to 16 kHz.
A first object of the invention is to achieve rapid and uniform heating of a workpiece, without having to rely on the shape and thickness of the object for the desired result. PG,3
A second object of the invention is to provide an inexpensive and uncomplicated heating device adapted to utilise the existing electric mains.
A third object is to provide a device which, upon separation, gives clean and faultless final products, i.e. metal parts which are clean from polymeric material and which have not been affected by structural changes and stress, as well as polymeric material which is not heated to temperatures at which it is destroyed, the final products being reusable.
A fourth object of the invention is to provide an energy-saving heating method by which the losses are restricted to the heat developed in the coils, and to losses in the core.
These objects are achieved by devices and methods having the features defined in the characterising clauses of the appended claims.
Embodiments of the invention will be described in the more detail below, reference being had to the accompanying drawings.
FIG. 1 shows a first embodiment of the invention, in which a movable core pole is displaced upwardly to produce an air gap adapted to accommodate a workpiece.
FIG. 2 shows a second embodiment in which the workpiece is a secondary winding of the circuit.
FIG. 3 shows a third embodiment adapted to separate polymeric material from a metal container or the like.
FIG. 1 illustrates a core 1 of transformer sheet steel. The core has a stationary pole 2 and a movable pole 3. The pole 3 is movable into engagement with the pole 2 to form a short-circuited core. In the embodiment shown in FIG. 1, the movable pole 3 is displaced upwardly to form an air gap between itself and the stationary core 2. A first coil 4 is positioned around the movable pole and a second coil 5 is positioned around the stationary pole. A third coil 6 is positioned around the air gap between the first and the second coil. The coils 4, 5 and 6 are connected in series via lines 9, 10, 11 and 12 and connected to an alternating voltage source 7 which is a single-phase source utilizing the zero conductor of the electric mains and gives, for example, 220 V at 50 Hz. Naturally, also two or three phase
REFERENCES:
patent: 1725465 (1929-08-01), Manson
patent: 3187155 (1965-06-01), Beckert et al.
patent: 3467806 (1969-09-01), Dixon
patent: 3472941 (1969-10-01), Floymayr
patent: 4311896 (1982-01-01), Junya
patent: 4775772 (1988-10-01), Chaboseau
patent: 4828227 (1989-05-01), Georges et al.
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