Importance of Mold Oscillation

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Importance of Mold OscillationM.O.M.S.* Technology to Ensure Good Lubrication

The Goal – Casting Lubrication

Mold oscillation was brought into continuous casting process as a way to eliminate sticking between the mold and the solidifying steel shell. Until the concept of mold oscillation was invented, the process of continuous casting of steel was not practical.

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The purpose of the mold oscillation is to put lubricant flux (fluxing powder or oil) into the space between the mold and the solidifying steel strand. The liquid lubricant fills the gap between the mold and the solidifying strand and provides a medium for heat transfer between the steel shell and mold. Without this, the heat transfer between the solidifying steel and the mold would be lower and not as stable preventing the proper formation of a solidified shell. See Figure Below.

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Figure 1 – Skin Formation.

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In the event of defects in the oscillation of the mold, liquid mold lubricant film may not be of uniform thickness on each mold face. This non-uniform thickness causes differences in heat transfer in time or in location in the mold.

These differences in heat transfer are the primary cause of longitudinal cracking but also can cause transverse and corner cracking too.

This uneven heat transfer can also contribute to rhomboidity in the cast product on square billets.

Additionally if the thickness of the mold flux film is small or non-existent, the solidifying shell may stick to the mold and cause a tear in it that can end up as a break out.

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Parameters to be Measured

For optimal lubrication control on the continuous casting process, it is important to measure/monitor events on the mold, mechanical and metallurgical.  The quality of the oscillation of the mold plays a critical role in assuring this result.

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The main mold oscillation parameters that can be measured and used to judge the quality of oscillation include Up/Down

Displacement, Left/Right and Front Back Displacement, Phase, and Negative Strip Time & Ratio. This is done with our MOMS technology that has as basis accelerometer readings on each corner of the mold table.

1- Up/Down Displacement

Each corner of the mold (or perimeter of the mold if casting rounds) should move the same distance peak-to-peak in the vertical direction. If this doesn´t occur, defects that can result include longitudinal and transverse cracking, corner cracking and the solidifying shell sticking in the mold which can lead to break-outs.

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2- Left/Right & Front/Back Displacement

The horizontal distance the mold moves through an oscillation cycle should also be minimized. If the horizontal displacement is greater than design the defects that can occur include longitudinal and transverse cracking, corner cracking, mold powder entrainment in the cast product, as well as rhomboidity in the case of square billets.

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Phase

Each corner of the mold should rise and fall with the same timing (all corners should reach the maximum/minimum Up/Down Displacement at the same time). This is most critical on slabs where it can happen longitudinal and transverse cracking, corner cracking and solidifying shell sticking in the mold which can lead to break-outs.

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4- Negative Strip Time & Ratio

The amount of time in the oscillation cycle where the mold travels past the strand is also very important. This parameter is set based on the type of casting machine and surface quality the cast product demands. Generally as the Negative Strip Time & Ratio are reduced the quality of the cast surface increases while the chance for sticking (and thus the chances for breakouts) also increases. The opposite is also true, where the Negative Strip Time & Ratio increases the quality of the cast surface decreases and the chances of sticking are reduced.

ConclusionChange in Practices

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For caster operators and maintenance personnel it is important to measure these parameters periodically (or continuously with an online system) to be assured that the mold oscillation mechanism is operating as designed for optimal product quality, productivity and lowest cost.

Online or programmed monitoring is essential to accurately portray the caster behavior, measure performance and evaluate causes.

To find out more feel free to contact us @ info@kti.cc or visit our website www.kisstechnologies.com

+1 616 394 1401

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