Hearth roll apparatus for annealing furnace
A hearth roll apparatus for feeding a strip sheet in an annealing furnace is disclosed. The hearth roll apparatus includes a ceramic tube which is provided inside the annealing furnace to contactingly feed a strip sheet, a roll shaft which is coupled to a first end of the ceramic tube and extends across the annealing furnace through the ceramic tube, a tube fixing sleeve which is coupled to a second end of the ceramic tube and through which a portion of the roll shaft is inserted, and a tension generating unit which interlocks with the roll shaft and the tube fixing sleeve and supplies a tensile force for stretching the roll shaft in a longitudinal direction. Accordingly, thermal deformation like creep buy which the roll shaft is bent down is minimized, and a line speed of the strip sheet can be increased by high-speed rotation of the hearth roll.
1. A hearth roll apparatus for an annealing furnace comprising:
a ceramic tube which is provided inside the annealing furnace to contactingly feed a strip sheet;
a roll shaft which is coupled to a first end of the ceramic tube and extends across the annealing furnace through the ceramic tube;
a tube fixing sleeve which is coupled to a second end of the ceramic tube and through which a portion of the roll shaft is inserted; and
a tension generating unit which interlocks with the roll shaft and the tube fixing sleeve and supplies a tensile force for stretching the roll shaft in a longitudinal direction,
wherein the roll shaft is formed with multiple step portions in the longitudinal direction and the tube fixing sleeve is formed with multiple step portions in the longitudinal direction, the multiple step portions of the roll shaft being disposed inside thereof.
2. The hearth roll apparatus according to claim 1 , wherein ends of the roll shaft and the tube fixing sleeve are supported by bearing blocks mounted to brackets fixed to a wall of the annealing furnace so that the roll shaft, the ceramic tube and the tube fixing sleeve can rotate.
3. The hearth roll apparatus according to claim 1 , wherein the ceramic tube is formed with first coupling portions at both the first end and the second end, the roll shaft is formed with a second coupling portion protruding around an outer peripheral surface to closely contact the first coupling portion formed at the first end of the ceramic tube, and the tube fixing sleeve is formed with a third coupling portion protruding around an outer peripheral surface to closely contact the first coupling portion formed at the second end of the ceramic tube.
4. The hearth roll apparatus according to claim 3 , wherein the first coupling portions formed at the first end and the second end of the ceramic tube include recessed portions and protruding portions which are formed alternately in a peripheral direction, and the second coupling portion of the roll shaft and the third coupling portion of the tube fixing sleeve include recessed portions and protruding portions which are closely engaged with the recessed portions and the protruding portions of the first coupling portions.
5. The hearth roll apparatus according to claim 4 , wherein the protruding portions of the first coupling portion, the second coupling portion and the third coupling portion protrude while being tapered off from the recessed portions.
6. The hearth roll apparatus according to claim 4 , wherein the apparatus further comprises covers which surround a coupling area between the ceramic tube and the roll shaft and a coupling area between the ceramic tube and the tube fixing sleeve.
7. The hearth roll apparatus according to claim 1 , wherein the multiple step portions of the roll shaft include a first step portion, a second step portion stepped down from the first step portion in the longitudinal direction, and a third step portion stepped down from the second step portion in the longitudinal direction, and the multiple step portions of the tube fixing sleeve include a first step portion and a second step portion stepped down from the first step portion in the longitudinal direction, the second step portion of the roll shaft being disposed inside the first step portion of the tube fixing sleeve and the third step portion of the roll shaft being disposed inside the second step portion of the tube fixing sleeve.
8. The hearth roll apparatus according to claim 7 , wherein the first step portion of the roll shaft and the first step portion of the tube fixing sleeve are inserted into the ceramic tube by same lengths, a gap is formed between the second step portion of the roll shaft and the second step portion of the tube fixing sleeve, and a gap is formed between the third step portion of the roll shaft and an inner surface of the second step portion of the tube fixing sleeve.
9. The hearth roll apparatus according to claim 7 , wherein a sealing member is mounted between the third step portion of the roll shaft and the second step portion of the tube fixing sleeve.
10. The hearth roll apparatus according to claim 7 , wherein the tension generating unit includes an elastic member or a hydraulic/pneumatic part which interlocks with ends of the tube fixing sleeve and the roll shaft to apply the tensile force to the roll shaft.
11. The hearth roll apparatus according to claim 10 , wherein the elastic member is a coil spring, the coil spring having a front end supported by the second step portion of the tube fixing sleeve and a rear end supported by a fastening part which is coupled to the third step portion of the roll shaft passing through the coil spring, whereby the coil spring stretches the roll shaft in the longitudinal direction by an elastic force, and pressurizes the tube fixing sleeve.
12. The hearth roll apparatus according to claim 11 , wherein the fastening part includes a guide ring which is put around the third step portion of the roll shaft and at least one nut which is tightened to the third step portion of the roll shaft, and a protrusion extends integrally from the second step portion of the tube fixing sleeve to surround the elastic member and the guide ring.
13. The hearth roll apparatus according to claim 10 , wherein the hydraulic/pneumatic part includes a cylinder which is provided inside the tube fixing sleeve and horizontally mounted to a fixing plate coupled to a protrusion extending integrally from the second step portion of the tube fixing sleeve, and a piston rod which is provided inside the tube fixing sleeve and connected to the third step portion of the roll shaft, and wherein the protrusion is formed with a hole for discharging air or hydraulic oil leaked from the cylinder.
14. The hearth roll apparatus according to claim 10 , wherein the tension generating unit interlocking the tube fixing sleeve and the roll shaft is surrounded by a protective cover which sealingly contacts a bearing block connected to a wall of the annealing furnace, and wherein the protective cover is provided with a partition ring thereinside for storing grease with the bearing block to prevent inflow of external air into the annealing furnace, and formed with a hole for discharging leaked grease, air or hydraulic oil.