Patent Application
20110057365
The invention relates to an apparatus for bracing sheet-metal joints in a high-temperature annealing furnace having at least one carrier, which frontally receives a sheet-metal joint and has a central axial passage opening, and on which a support pipe, which axially penetrates the sheet-metal joint, having a carrier for receiving a further sheet-metal joint can be placed in a load-bearing manner.
Transformer plates made of steel having a silicon proportion of 0.5-3.5 wt.-% are typically subjected to a high-temperature treatment in a hood furnace for technological reasons. The annealed material is heated up to 1200° C., essentially by radiant heat. The intrinsic strength of the annealed material decreases greatly at these high temperatures, so that the sheet-metal joints, which comprise coiled steel strips having a strip width of 1000 mm at a strip thickness of 0.3 mm, for example, are each supported on carriers. These carriers are formed by thick-walled disc bodies having a central, axial passage opening, if two sheet-metal joints are stacked one on top of another, the disc-shaped carrier for the upper sheet-metal joint being supported on the carrier for the lower sheet-metal joint, which typically rests on an annealing pedestal, in a load-bearing manner via a support pipe which penetrates the lower sheet-metal joint. While the radiant heat can be supplied largely unobstructed to the sheet-metal joints in the area of the upper front side and the outer turns, heating of the sheet-metal joints in the area of their lower front side is essentially only possible via the disc bodies of the carriers, which not only requires additional power for heating the disc bodies, whose weight can be up to one-third of the joint weight, but rather also results in uneven joint heating. In this context, it is to be considered that because of a minimum distance between the individual turns, the heat introduction results are better in the axial direction than in the radial direction, so that the outer turns are heated significantly more rapidly than the inner turns of the sheet-metal joints, with the result that the strip width and the diameter of the outer turns increases more rapidly as a result of the thermal expansion caused by the higher temperatures. Because of the temperature difference between the disc bodies receiving the sheet-metal joints and the strip turns, in particular in the outer diameter area, deformations of the turns in the contact area and, as a result thereof, welds may occur as a result of the decreased intrinsic strength of the sheet-metal joints. In order to provide a remedy here, the disc bodies of the carriers form conical surfaces which drop off outward, on which the sheet-metal joints rest, but only partial relief can be provided by this measure. The heat introduction into the sheet-metal joints in the area of their lower front side via the disc-shaped carriers additionally causes thermal tensions inside the disc bodies, which are accompanied by the danger of cracking and thus a loss of the load capacity of the carriers.
In order to be able to heat sheet-metal joints from the frontal contact surface with the aid of a heated gas stream, providing essentially radially running flow channels in the carriers, which receive the sheet-metal joints and have a central passage opening, which are permeated from the outside to the inside in order to withdraw the hot gas through the central axial passage opening of these carriers, is known (GB 918 356 A). For this purpose, ring-disc-shaped carriers are provided, which have radially running ribs on their upper and/or lower sides, between which the flow channels result. In order to avoid damage of the contacting front sides of the sheet-metal joints, the ribs widen radially outward in triangular form. Because the annealing material is almost exclusively heated by radiant heat in modern hood annealing furnaces, however, these known ring-disc-shaped carriers having flow channels between axially protruding ribs cannot provide a decisive improvement with respect to the heating of the sheet-metal joints.
Finally, providing ring-disc-shaped carriers having a support made of high-temperature-resistant bulk material for the careful support of sheet-metal joints to be subjected to a high-temperature treatment is known (DE 100 16 096 A1), so that differing thermal expansions of the sheet-metal joints may be readily absorbed via the loose bulk material. However, hardly any improvements are to be expected with respect to the uniform heating of the sheet-metal joints through this measure.
The invention is thus based on the object of implementing an apparatus of the type described at the beginning for bracing sheet-metal joints in a high-temperature annealing furnace in such a manner that the sheet-metal joints may be heated more uniformly to shorten the annealing times, the power required for heating the carriers of the sheet-metal joints is reduced, and the unavoidable tensions due to the heating of the carriers are kept within permissible limits, in order to be able to extensively prevent cracking.
The invention achieves the stated object in that the carrier has a ring body, which forms the passage opening, having radially protruding carrier arms distributed around the circumference.
Because of the radially protruding carrier arms distributed around the circumference of the ring body, space remains between these carrier arms for direct engagement of the radiant heat on the sheet-metal joints, so that the sheet-metal joints may also advantageously be heated from the lower front side. Because of the distribution of the carrier arms around the circumference of the ring body, the uniform bracing of the sheet-metal joints via their lower front side is not impaired. The more uniform and thus significantly more rapid heating of the sheet-metal joints is thus ensured without disadvantageous effect on the joint bracing. In contrast, the occurring thermal tensions are reduced and thus a danger of cracking is largely prevented by the radial carrier arms, which allow more uniform heating of the carriers. In addition, the weight of the carriers is reduced, which results in a corresponding reduction of the energy expenditure required for the carrier heating. It has thus been shown that with the aid of the proposed carrier, not only is more rapid heating of the annealing material to the required treatment temperature ensured with reduced energy introduction, but rather also the strain of the carriers due to thermal tensions is reduced and the load capacity of the carrier can thus be increased.
A particularly advantageous constructive design of the carriers results if the radial carrier arms form an I-profile in cross-section, which allows the adaptation to the particular loading conditions of these carriers through a corresponding web height, in order to be able to ensure a sufficient resistance torque for the load bearing.
The contact surfaces of the carrier arms which receive the sheet-metal joints may lie in a way known per se on a conical surface which drops off radially outward, in order to consider more rapid heating of the outer joint turns with respect to the axial and radial thermal expansions in spite of the proposed measures.
If the carrier is implemented as symmetrical to an axis-normal central plane, such a carrier can be used to receive sheet-metal joints on both front sides, which lengthens the lifetime of such carriers, if the contact surface for the sheet-metal joints no longer meets the requirements on one side, so that frontal joint damage may also be prevented over longer periods of use.
The object of the invention is shown for exemplary purposes in the drawing. In the figures:
As can be inferred from
As is immediately obvious from the drawing, the free spaces between the carrier arms 8 of the carriers 2 ensure direct heat supply to the lower front side of the sheet-metal joints 1, which allows more uniform and thus more rapid heating of the sheet-metal joints 1 to the high treatment temperature. In addition, a more uniform thermal strain results for the carriers 2 because of the radial carrier arms 8, which largely prevents thermal tensions resulting in cracks, so that greater joint weights may be received or carriers 2 having smaller dimensions may be used.
| Number | Date | Country | Kind |
|---|---|---|---|
| A 2065/2007 | Dec 2007 | AT | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/AT2008/000396 | 11/4/2008 | WO | 00 | 6/15/2010 |
