Hearth rolls structure optimization and cost control (3)

3. Optimization of the structure of hearth rolls:                                 Link above
(1). Diameter of outstretched shaft affect the mechanical properties of the hearth rolls. In Figure 3 shows the results 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.  In Figure 4 below shows he results. When changes in the thickness of the ring plate of hearth roll (t = 50mmt = 100mm), Impact strength and stiffness of the hearth roll 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.

The effect of elongate shaft diameter d on the static performance of the hearth rolls
The effect of elongate shaft diameter d on the static performance of the hearth roll——-Fig









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Hearth roller structure optimization and cost control(2)

Link above

-Hearth roller structure diagram  show Fig 1

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 and even more simplify some the original structure appropriately:

hearth roller
hearth roller structure diagram  Fig 1

(1). Ignored the effects of various friction.
(2). Almost all position welding are ideal for welding.
At first according to the requirements of the calculation accuracy the finite element model subdivided into a grid chart. As a result the part of thin-walled made of the shell elements. Similarly 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.

First ao all in the analysis process, except angular displacement of the x-direction on surface of the hearth roller ends is free. While other linear displacement and angular displacement are restrictions. Likewise symmetry constraints are imposed on symmetry boundary of finite element model. Above all can 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. Therefore this may explain the reason that weld fracture is the main failure mode in a way. Therefore they are possible to optimize the design through construction to improve stress distribution. Similarly to minimize the stress at the weld cone body.

ANSYS analysis of bottom rollers
ANSYS analysis of bottom rollers  Fig 2







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Hearth roller structure optimization and cost control(1)


Hearth roller is a typical centrifugal casting pipe fittings. It is one of the important components in support of metallurgical equipment and transport slabs. As a result it has wide application in Continuous casting- rolling production line. In the rolling process first of all to heat the steel slab to 1050 ~ 1150 rolling temperature in the furnace continuously and stably. Furthermore 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 directl the tapered section. Similarly 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. Consequently the 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. Which ensure the smooth delivery of high-temperature slab.

"<yoastmarkRequirements: hearth roller shaft not deformed. And external roller ring heat-resistant, wear-resistant. Research shows that the hearth roller is use of large in the metallurgical industry. almost it has high manufacturing costs. Similarly has a long-term high temperature overload working conditions. Consequently prone to failure damage.

Several major forms of roller hearth failure:

1 Weld fracture.

2 Shaft neck fracture.

3 Connect the fracture.

The main reason include:

  1. 1. Welding performance of high temperature nickel-base alloy is poor. Prone to weld cracking and other defects.
  2. 2. Welds to withstand pull – push alternating stress loads. Prone to fatigue fracture.
  3. 3. Weld is cold-hot junctional zone, exists of large temperature gradient cause thermal stress, thermal stress will accelerate fracture.
  4. Above all there are much attempts to improve hearth roll on material and welding workmanship. However the life of a hearth roller has not achieved significant results. Therefore to improve the performance of  hearth roll
  5. and improve its life by structural optimization is very important. Consequently it may improve the quality of the product. It is a effective way to enhance the competitiveness of products.

to be continue

Hearth roll of continuous annealing furnace

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 materialhearth rolls 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. Furthermore two end shaft welded in the roll end. The thin-walled rollers to give axial thermal resistance. The 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 hearth roll body
The hearth roll body

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.

The furnace hearth roll commonlu use spiral roller bearings or spherical bearings . 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.