3. Optimization of the structure of hearth rolls: Linkabove
（1）. Diameter of outstretched shaft affect the mechanical properties of the hearth rolls. The results are given in Figure 3 below we can see, with the increase of the diameter, the value of the torsion deformation resultant vector decreases. From 0.664E-3 down Low to 0.512E-3, to improve the Stiffness of hearth rolls. But when diameter of elongate shaft increases from 40mm to 60mm, the maximum stress values did not change significantly, diameter of outstretched shaft d generally selected about 60mm when designing.
(2) Effect of thickness of ring plate to mechanical properties of hearth roll. The results are given in Figure 4 below shows. When changes in the thickness of the ring plate of hearth roll (t = 50mmt = 100mm), Impact strength and stiffness of the hearth rolls more obvious. When the thickness of the ring plate is reduced, the strength and rigidity of it is weakened. Thereby increasing the possibility of damage of the hearth rolls under billet weight motor drive and furnace temperature interaction.
2. Finite element analysis of a hearth roll
1). Establish finite element model of the size of the actual structure of the hearth roller. Using software ANSYS of finite element analysis to analysis. In the modeling process of hearth roller finite element, simplify some the original structure appropriately：
(1). Ignored the effects of various friction.
(2). All position welding are considered ideal for welding.
According to the requirements of the calculation accuracy , the finite element model subdivided into a grid chart. The part of thin-walled made of the shell elements，part of collar plate are made of solid elements. Completion of the corresponding element real constants and materials parameters define the operating (Young’s modulus EX = 206, the thermal expansion coefficient of 0.45E-6, Poisson’s ratio of 0.28 and a density of 7800).
2). Determine the constraints condition.
In the analysis process, except angular displacement of the x-direction on surface of the hearth roller ends is free. Other linear displacement and angular displacement are restrictions. Symmetry constraints are imposed on symmetry boundary of finite element model, to ensure that the symmetry of deformation.
3). Solving and result processing, By analyzing the deformation and stress distribution of the hearth roll y-axis direction in the billet pressure, weight, torque, and the furnace temperature (1050 ℃) and other loads.
From the results shown in Figure 2
Hearth roller cone body weld stress maximum and lower weld strength here, this may explain the reason that weld fracture is the main failure mode in a way. Therefore, the need to optimize the design through construction to improve stress distribution, to minimize the stress at the weld cone body as possible.
Hearth roller is a typical centrifugal casting pipe fittings, is one of the important components in support of metallurgical equipment and transport slabs, widely used in Continuous casting- rolling production line, in the rolling process，first, the need to heat the steel slab to 1050 ~ 1150 ℃ rolling temperature in the furnace continuously and stably，Stable support of the slab through the hearth roller, to ensure a smooth and uniform delivery. Since intermediate section of the Hearth roller mounted on the billet calcining furnace directly , the furnace temperature is about 1150 ℃ during the process of production。Hearth roller usually was manufactured with ZG45Cr28Ni48W5Si2 and other high-temperature alloys.Meanwhile，since the intermediate section of the hearth roller mounted in furnace directly，The tapered section and the bearing support section are mounted inside the calcining furnace and outside the furnace respectively. The temperature gradient of hearth rolls is very large at different parts。So hearth roller welded together by the sleeve and cone and shaft generally。In order to reduce the burning of the inner surface of the cone, the inside of the cone have insulation board to ensure the smooth delivery of high-temperature slab.
Requirements hearth roller shaft not deformed, external roller ring heat-resistant, wear-resistant. Research shows that the hearth roller is use of large in the metallurgical industry, high manufacturing costs, long-term high temperature overload working conditions，prone to failure damage。
Several major forms of roller hearth failure:
2．Shaft neck fracture.
3． Connect the fracture.
Which mainly reason include: welding performance of high temperature nickel-base alloy is poor, prone to weld cracking and other defects; welds to withstand pull – push alternating stress loads, prone to fatigue fracture; weld is cold-hot junctional zone, exists of large temperature gradient cause thermal stress, thermal stress will accelerate fracture，Despite attempts to improve hearth roller on material and welding workmanship , but The life of a hearth roller has not achieved significant results. So by structural optimization to improve the performance of a hearth roller and increase their use life, may improve the quality of the product, an effective way to enhance the market competitiveness has important research value. Therefore, to improve the performance of hearth roller and improve its life by structural optimization, it may improve the quality of the product, effective way to enhance the competitiveness of products.
Hearth roll is one of the most important part of continuous annealing furnace. Its working condition is the decisive factor if annealing furnace can be normal production.
Work and structural features of a hearth roll
Structures and materials of hearth roll
Working at over 800 ℃in the furnace and rotation under load, meantime mechanical damage by charge , the hearth roll material must have high temperature strength and oxidation resistance. The structure shown that centrifugal casting roll is a hollow cylinder, two alloy roll end welded, then two end shaft welded in the roll end. The thin-walled rollers to give axial thermal resistance, insulation materials inserted from the roll barrel to roll end to reduce the temperature of the bearings.
Furnace hearth roll materials are ZG35Ni20Si or ZGCr25Ni35Nb, due to the high Ni alloy is expensive, domestic production of furnace hearth rollers using cheap ZG3Cr24Ni7SiNRe, this material has high temperature strength, endurance strength higher than ZGCr25Ni20Si2, after long-term use aging embrittlement tendency is small. Due to the addition of rare earth the oxidation resistance of the steel improved.
The diameter of the furnace hearth roll if possible use of smaller size at high temperature strength permitting to reduce the weight of the weight and save precious metal.
Spiral roller bearings or spherical bearings are used for furnace hearth roll. The bearing temperature is high so high-temperature grease lubrication is needed. The diameter of haft journal is usually smaller than the 0.1-0.25mm of bearing because of radial expansion.