Electric heating – Inductive heating – With workpiece support
Reexamination Certificate
1999-12-21
2001-01-23
Walberg, Teresa (Department: 3742)
Electric heating
Inductive heating
With workpiece support
C426S406000, C426S234000, C219S620000
Reexamination Certificate
active
06177662
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for the heating of canned products. More particularly the invention relates to such a process and device that utilises induction heating from an induction coil to heat the contents of the can by induction heating the metal can.
BACKGROUND ART
It is well know that many canned goods such as canned food. canned pet food, and the like require to be sterilised after canning to prevent the growth of toxic bacteria in the can. This is a relatively energetic process and considerable efforts have been made to improve the energy efficiency of processes for the heat sterilising of canned goods. A further requirement of such processes is that, at least in the case of foods for human consumption, it is important to retain the flavour, texture and nutrient status of the contents of the can. Typically this requires the minimum heating possible consistent with the proper sterilisation of the food. A difficulty that then arises is that the rate at which heat can be transmitted to the canned product will affect the total heating time for the food. Many foods also have a tendency to burn onto the inside of the can if heated too quickly. The canner must then heat the can slowly to the sterilisation temperature which results in the contents of the can being maintained at all elevated temperature for considerably longer than is desirable for optimum taste, texture and nutrient status.
It has been proposed in U.S. Pat. No. 3,961,150 to heat canned goods by the application of heat to the can by the use of induction coils. The cans are described as being rotated in a reciprocating fashion beneath a flat induction coil. This arrangement was found in practice to be unsatisfactory. The time at which the contents of the can were maintained at an elevated temperature was excessive due to the problems of heat transfer rates, despite the reciprocating rotation of the cans.
French patent specification 2 501 631 describes an alternative arrangement in which cans are passed through the lumen of each of a plurality of helically wound induction coils. The cans are described as being rotated about their own axes between successive induction coils to allow homogenisation of the temperature of the contents of the cans. It is believed by the present inventors that in this design, where the cans are not rotated while they are actually being heated that either the rate of heating would have to be very low or there would be unacceptable burning of the contents against the can wall during the heating steps.
U.S. Pat. No. 4,256,922 describes the heating of loose foodstuffs on a rotating metallic tube surrounded by a helically wound coil. In this case the beat transfer problems are rather different due to the fact that the food is free to tumble and rotate relative to the tube unconstrained by a surrounding can.
The present invention is directed to an alternative method of heating canned product which offers an alternative to the known processes described above.
DISCLOSURE OF INVENTION
The present invention relates to a method for the heating of a convective material contained within a metallic can, the method including the steps of passing the can longitudinally through the lumen of a helically wound induction coil, while simultaneously rotating or oscillating the can. The present further relates to apparatus for the heating of a convective material contained within a metallic can, the device including a helically wound induction coil adapted to induce heating in the wall of the can, means to pass cans longitudinally through the lumen of the coil, and means to cause the cans to rotate about their own axes as they are passed through the coil.
The cans are preferably continuously rotated about a longitudinal axis. It is, however, within the ambit of the invention to oscillate or rotate the cans about any axis or randomly by tumbling the can.
The present inventors have found that by passing the cans through the lumen of a coil it is possible, at least using preferred embodiments of the invention, to effectively heat the can at a high rate with increased energy efficiency. They have also found that if the cans are simultaneously rotated at an appropriate rate it is possible with many canned products to heat the product very rapidly while avoiding the problems traditionally experienced with high heating rates.
It is preferred that the cans contain products that are liquid or are disposed in a liquid. This allows the product to move reasonably readily relative to the surface of the can as it is rotated about its axis. Such products are called convective products. Suitable convective products include canned pasta in a sauce, canned vegetables in liquid, and some canned pet foods.
The canned products are preferably rotated at least 50 rpm., more preferably at least 80 rpm, and even more preferably 120 rpm. In particularly preferred embodiments of the invention the cans are rotated at speeds of from 150 rpm to 200 rpm, preferably 180 rpm.
The calls for use in the process of the present invention must be metallic or there will be no electromagnetic currents generated in the call. Typically the cans will be formed of steel sheet coated with a protective metal such as tin. Any container in the walls of which heating may be induced by an oscillating electric current passing through the coil may be used in the present invention are for the purposes of the present invention regarded as being metallic cans.
The induction coil is, or coils are, driven at a frequency of from 1 to 500 kHz, preferably from 20 to 250 kHz. and more preferably from 50 to 200 kHz. In particularly preferred embodiments of the invention the frequency if from 60 to 180 kHz. The lower frequencies are cheaper to generate but suffer from the disadvantage that they heat more slowly. In any particular case there will be a trade off as between the cost of the process and the advantage to be obtained from more rapid processing of the canned product.
In a particularly preferred embodiment of the present invention the cans are passed through the lumen of an induction coil in a non metallic tube. The calls may be pushed through the tube or conveyed through it in any other suitable way. The cans may be rotated at any desired speed simply by rotating the tube at that speed. While this is a strongly preferred mode of carrying out the present invention it is recognised that there are many other ways of carrying out the present invention.
If the canned product is a non-acid convective food it is essential that it be heated at a temperature in excess of 100° C. if it is to be properly sterilised. Heating to this temperature may cause the contents to boil. The steam pressure from this boiling could cause the calls to distort or even rupture during heating. In order to avoid the possibility of this distortion it is preferred that the heating of such products be conducted in an atmosphere which is maintained at a super-atmospheric pressure. The cans may be pre heated to, say, 90° C. at atmospheric pressure and then passed through a pressure lock into an atmosphere at an elevated pressure and the heating completed. The heating step is most preferably carried out such that the contents of the can are heated at a rate of about 1° C. per second.
The heating is preferably carried out at the maximum rate possible until the can wall is at or above the maximum desired temperature. The can and its contents are then preferably allowed to rest for a period to allow equilibration of the contents of the can before further heating occurs. The can is most preferably rotated continuously throughout this resting period. If desired the rate of heating may be varied as the can is passed through the lumen of the coil in order to provide a complete or partial rest period. Alternatively there may be a plurality of coils in spaced apart array with a rest period between each coil.
Obviously in order to reduce the total time during which the contents of the can are elevated it is important to both raise and lower the temperature of the
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
Pwu Jeffrey C
Walberg Teresa
LandOfFree
Inductive heating method and apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Inductive heating method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Inductive heating method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2555236