Continuous casting operations run on data. But not all mold friction data represents the same thing.
Some systems infer friction from mold vibration and acceleration. Others determine the friction force acting during casting. That difference affects not only how the data is generated, but also how it is expressed and how confidently it can be used to understand mold/strand interaction.
Inferred friction is typically reported in acceleration units such as mm/sec² or as a percentage or index. Measured friction is expressed as a force, such as pounds (lb) or newtons (N).
Historically, many operations have relied on inferred friction because it was the information available from their mold oscillation monitoring systems. Changes in that signal could provide a general indication of changes in mold or casting stability. Today, measured friction provides a more direct way to understand what is happening at the mold/strand interface.
This guide explains the difference between inferred friction and measured friction, how each has been used in continuous casting, and why measured friction provides better information for evaluating mold/strand friction.
Key Takeaways:
- Inferred friction, or friction index, is derived from mold vibration and acceleration data rather than measured as a force.
- Inferred friction is typically expressed in acceleration units (mm/sec²) or as a percentage or index.
- Measured friction determines friction force and is expressed in pounds (lb) or newtons (N).
- Inferred friction has historically been used as a general indicator of changes in mold and casting stability when measured friction was not available.
- KT450 FieldSERVICE uses inferred friction as one part of a broader periodic oscillator diagnostic evaluation.
- KT500F provides continuous, real-time measured friction using either load cells or pressure measurements from the mold oscillation hydraulic system.
- Not all online mold oscillation monitoring systems provide measured friction. Some provide an inferred friction index instead.
What Is the Difference Between Inferred Friction and Measured Friction?
Inferred friction is derived from mold vibration and acceleration data.
Rather than measuring friction as a force, the system evaluates mold and oscillator behavior to infer changes associated with friction. The result may be expressed in acceleration units such as mm/sec² or converted into a percentage or friction index.
Measured friction determines the friction force acting during casting.
Because it is based on force measurement, the result is expressed in force units such as pounds (lb) or newtons (N).
The distinction is important.
An inferred friction index can indicate that mold or casting behavior may be changing, but the operator must infer what that change represents. The signal can also be influenced by mechanical behavior within the oscillation system.
Measured friction quantifies friction as a physical force, providing a more direct indication of mold/strand friction.
When friction information is being used to evaluate lubrication, oscillation settings, casting conditions, or mold/strand interaction, measured friction provides more definitive information.
Why Friction Data Matters for Casting Stability
Mold friction provides valuable information about conditions at the mold/strand interface. Operations and process teams can use friction information to:
- Evaluate lubrication performance. Friction trends can help determine whether mold flux or lubricant is performing consistently across heats and grades or whether mold conditions are changing.
- Evaluate oscillation parameters. Stroke, frequency, and negative strip all interact with mold/strand conditions. Friction information provides another way to evaluate those relationships.
- Identify developing mold/strand instability. Changes in friction behavior can provide an indication of sticking or other abnormal mold conditions that may contribute to breakout risk.
- Improve casting consistency. Comparing friction behavior across heats, grades, speeds, and operating practices can help teams identify stable casting conditions and investigate deviations.
For many years, operations without the ability to measure friction directly have used changes in an inferred friction signal to help identify these conditions.
But when friction information is being used to support process decisions, understanding whether the signal is inferred from oscillator behavior or determined from force measurement is important.
Inferred Friction: Useful as an Indicator, But Not a Measurement of Friction Force
Inferred friction is calculated from mold vibration and acceleration behavior rather than measured as a force.
Accelerometers mounted on the mold or oscillator capture the dynamic behavior of the system. Changes in that behavior are used to infer changes associated with mold friction.
Because the underlying signal is acceleration, inferred friction may be reported in mm/sec² or converted into a percentage or friction index. It does not quantify friction force in pounds or newtons.
Before measured friction was readily available, inferred friction was often the information available to teams trying to understand changes in mold behavior. Users could look for changes or trends in the friction index as a general indication of mold stability, lubrication changes, sticking conditions, or other changes in casting behavior.
That information can still provide an indication that conditions are changing. However, there is an important limitation: a change in inferred friction does not tell you how much friction force is actually acting between the mold and strand.
Mechanical conditions within the oscillator can also influence the vibration and acceleration data used to calculate the index. Bearing condition, linkage looseness, alignment, structural resonance, and other mechanical factors can affect the signal, making it difficult to separate changes in actual mold/strand friction from changes elsewhere in the mold oscillation system.
Kiss Technologies’ KT450 FieldSERVICE uses inferred friction as one part of a broader oscillator evaluation that also includes displacement, phase, vibration spectrum, negative strip, mold lead, and other measurements.
In this application, the friction index provides additional information that can help identify changes in mold or oscillator behavior and prioritize maintenance.
When the objective is to understand actual mold/strand friction, however, measured friction provides more meaningful information because it determines friction as a physical force rather than inferring it from acceleration behavior.
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Read more: Discover how teams use KT450 FieldSERVICE to prioritize maintenance ahead of planned outages. |
Measured Friction: Direct, Continuous Force Data
Measured friction determines the friction force associated with mold/strand interaction during casting and expresses the result in units of force.
Kiss Technologies’ KT500F Online Mold Oscillation Monitoring System provides continuous measured friction using one of two measurement methods, depending on the caster configuration:
- Load-cell measurement: Load cells measure the forces acting on the mold during oscillation.
- Hydraulic-pressure measurement: On hydraulically oscillated molds, KT500F can use pressure measurements from the oscillation hydraulic system to determine the forces acting on the mold.
In either configuration, KT500F accounts for the forces associated with accelerating the mold so that the friction component associated with mold/strand interaction can be determined.
The resulting measured friction is expressed in pounds (lb) or newtons (N) rather than in acceleration units, a percentage, or a friction index.
This gives operators:
- A quantified friction force. Instead of inferring friction from mold acceleration, operators can evaluate friction in actual units of force.
- Continuous process information. Friction is monitored throughout casting rather than during a periodic service evaluation.
- Heat-by-heat insight. Friction behavior can be evaluated by heat, grade, casting speed, lubrication practice, and other operating conditions.
- Better information for evaluating mold conditions. Changes in measured friction can help teams investigate lubrication performance, oscillation settings, mold/strand interaction, and developing casting instability.
- Long-term process data. Continuous measurement makes it possible to establish friction baselines and compare operating conditions over time.
For operations that want to understand mold/strand friction as part of day-to-day process monitoring, KT500F provides force-based information rather than requiring operators to interpret an acceleration-derived indicator.
Inferred Friction vs. Measured Friction: Side-by-Side Comparison
Inferred friction and measured friction are not simply two different ways of displaying the same measurement. They represent fundamentally different types of information.
Friction Index vs. Direct Friction Measurement |
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Feature/Metric |
Inferred Friction/Friction Index |
Measured Friction (KT500F) |
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Primary Data Source: |
Mold vibration and acceleration |
Load cells or hydraulic oscillation pressure |
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How Friction Is Determined: |
Inferred from mold and oscillator behavior |
Determined from measured force |
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Typical Output Units |
mm/sec² or percentage/index |
Lb or N |
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Measurement Type |
Inferred indicator |
Force-based measurement |
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Can be influenced by oscillator mechanical behavior |
Yes |
Significantly reduced |
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Can indicate general changes in mold behavior |
Yes |
Yes |
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Quantifies friction force |
No |
Yes |
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Suitable for continuous friction trending |
Limited to an inferred indicator |
Yes |
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Primary Use |
General indication and diagnostic evaluation |
Continuous mold/strand friction monitoring and process evaluation |
The most important difference is the physical quantity being reported.
A friction index uses acceleration behavior to infer friction.
Measured friction determines a friction force and reports it in force units.
Why the Type of Friction Data Matters for Casting Decisions
For many years, inferred friction was the information available to operators trying to identify changes in mold behavior. A rising, falling, or unstable friction index could be used as a general indication that casting conditions were changing and warranted further investigation.
The limitation is that the operator still has to infer what caused the change.
Because the signal is based on acceleration and vibration, it can be influenced by both mold/strand conditions and the mechanical behavior of the oscillation system.
Measured friction removes much of that uncertainty by determining friction as a physical force.
With KT500F, operators can see friction in pounds or newtons and compare that measured force with lubrication practices, casting speed, steel grade, oscillation settings, and other process variables. This provides a stronger foundation for understanding what is actually happening at the mold/strand interface.
That can be particularly valuable when teams are:
- Evaluating mold flux or lubrication performance
- Comparing casting practices across steel grades
- Optimizing oscillation settings
- Investigating abnormal mold/strand interaction
- Comparing friction behavior at different casting speeds
- Establishing normal operating ranges
- Investigating conditions associated with sticking or casting instability
Inferred friction can point to a change. Measured friction tells you the magnitude of the friction force associated with that change.
Choosing the Right Mold Monitoring Approach
The right approach depends on what your team needs to understand.
Preparing for a planned outage or evaluating oscillator mechanical condition?
KT450 FieldSERVICE combines inferred friction with displacement, phase, vibration spectrum, negative strip, mold lead, and other measurements to provide a broader evaluation of oscillator performance.
In this application, inferred friction is one piece of the diagnostic picture. Together with the other measurements collected during FieldSERVICE, it can help maintenance teams identify developing mechanical or control issues and prioritize work before planned downtime.
Monitoring mold/strand friction continuously during casting?
KT500F provides continuous measured friction in units of force.
Depending on the caster configuration, the system can determine mold forces using load cells or pressure measurements from the mold oscillation hydraulic system.
This allows operations and process teams to evaluate measured friction heat by heat and compare it with lubrication practices, oscillation settings, casting speed, steel grade, and other process variables.
If the primary objective is to understand friction at the mold/strand interface, measured friction provides substantially more useful information than an inferred friction index.
A Quick Decision Guide: Inferred Friction or Measured Friction? |
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|---|---|
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If you’re trying to… |
Recommended Approach |
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Get a general indication that mold or casting behavior has changed |
Inferred friction can provide an indicator |
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Evaluate oscillator mechanical condition as part of a periodic diagnostic |
KT450 FieldSERVICE |
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Diagnose developing oscillator mechanical or control issues |
KT450 FieldSERVICE |
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Quantify friction force during casting |
Measured Friction / KT500F |
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Monitor friction continuously during casting |
Measured Friction / KT500F |
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Evaluate lubrication performance heat by heat |
Measured Friction / KT500F |
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Investigate changes in mold/strand interaction |
Measured Friction / KT500F |
|
Compare friction across grades, speeds, or operating practices |
Measured Friction / KT500F |
|
Establish measured-friction baselines and operating ranges |
Measured Friction / KT500F |
Frequently Asked Questions
What is the difference between inferred friction and measured friction in continuous casting?
Inferred friction is derived from mold vibration and acceleration behavior rather than measured as a force. It may be expressed in acceleration units such as mm/sec² or as a percentage or friction index.
Measured friction determines friction force and reports the result in force units such as pounds (lb) or newtons (N).
An inferred friction index can indicate that mold behavior may be changing, but measured friction provides more definitive information by quantifying the friction force.
What is a friction index?
A friction index is an inferred indication of mold friction derived from mold vibration and acceleration data.
Because friction is not being measured as a force, the result may be expressed in acceleration units such as mm/sec² or converted to a percentage or index.
Historically, operators have used changes in friction index as a general indication of changes in mold or casting stability when measured friction was not available.
Is a friction index a measurement of friction force?
No. A friction index is an inferred friction value derived from mold vibration and acceleration behavior.
It is not a force measurement and therefore is not expressed in pounds or newtons.
This is an important distinction when comparing a friction index with a system designed to provide measured friction.
Is inferred friction useful for monitoring casting stability?
Inferred friction has historically been used as an indicator of general mold and casting stability, particularly when measured friction was not available.
Operators may look for changes or trends in a friction index as an indication of changing mold conditions, lubrication behavior, sticking, or other casting instability.
However, because the value is inferred from mold vibration and acceleration, it does not quantify the actual friction force and can also be influenced by mechanical conditions in the oscillation system.
Measured friction provides more definitive information. KT500F determines friction as a physical force in pounds or newtons, allowing operators to evaluate the magnitude and behavior of mold/strand friction rather than relying on an inferred indicator.
What is measured mold friction?
Measured mold friction is a force-based determination of the friction associated with mold/strand interaction during casting. Rather than inferring friction from mold vibration and acceleration, measured friction determines the forces acting on the mold and accounts for the forces associated with mold acceleration to determine the friction component.
The resulting friction measurement is expressed in units of force, such as pounds (lb) or newtons (N).
How does KT500F measure mold friction?
KT500F provides continuous measured mold friction using one of two methods, depending on the caster configuration. With load cells, the system measures the forces acting on the mold during oscillation.
On hydraulically oscillated molds, KT500F can use pressure measurements from the oscillation hydraulic system to determine the forces acting on the mold.
In either configuration, the system accounts for the forces associated with mold acceleration to determine the friction component associated with mold/strand interaction. The resulting measured friction is expressed in units of force, such as pounds (lb) or newtons (N).
Does KT500F require load cells to measure mold friction?
No. KT500F can provide measured friction using either load cells or pressure measurements from the mold oscillation hydraulic system.
The appropriate method depends on the design and configuration of the caster’s mold oscillation system. Both approaches allow KT500F to determine friction in units of force rather than infer friction from mold vibration and acceleration.
Do all online mold oscillation monitoring systems measure friction?
No. Not all online mold oscillation monitoring systems provide measured friction.
Some systems marketed as online mold oscillation monitoring systems provide inferred friction, using mold vibration and acceleration data to calculate a friction index. This type of friction information may be expressed in acceleration units such as mm/sec² or as a percentage or index. It is not a measurement of friction force.
Other systems, such as KT500F, provide measured friction. KT500F determines the forces acting on the mold using either load cells or pressure measurements from the mold oscillation hydraulic system. The resulting friction is expressed in units of force, such as pounds (lb) or newtons (N).
When comparing online mold oscillation monitoring systems, it is important to ask whether the system provides inferred friction or measured friction. The terms may sound similar, but the underlying measurements—and the information they provide—are fundamentally different.
What is the difference between KT450 friction index and KT500F measured friction?
KT450 FieldSERVICE provides inferred friction derived from mold vibration and acceleration data. The result is typically expressed in mm/sec² or as a percentage or friction index.
KT500F provides measured friction using either load cells or oscillation hydraulic pressure to determine mold forces. The resulting friction is expressed in pounds (lb) or newtons (N).
KT450’s friction index can provide a general indication of changes in mold or oscillator behavior and is useful as part of the broader FieldSERVICE diagnostic evaluation. KT500F goes further by determining friction as a physical force.
Does KT450 FieldSERVICE provide inferred or measured friction?
KT450 FieldSERVICE provides inferred friction based on mold vibration and acceleration data. It evaluates this information alongside other oscillator measurements to help diagnose mechanical and control conditions and prioritize maintenance.
Changes in inferred friction may also provide a general indication of changes in mold or casting behavior. It does not measure friction force in pounds or newtons.
How does mold friction affect casting stability?
Mold friction reflects the interaction between the mold and the solidifying strand and is influenced by lubrication, oscillation, casting speed, steel grade, and other process conditions.
Changes in friction behavior can help operations teams identify changes in mold conditions, evaluate lubrication performance, and investigate sticking or other instability that may contribute to quality problems or breakout risk.
Measured friction provides the advantage of quantifying those friction changes as a physical force rather than relying on an inferred indicator.
Is mold friction monitoring the same as mold oscillation monitoring?
No, although the two are closely related. Mold oscillation monitoring evaluates parameters such as displacement, frequency, phase, vibration, and negative strip behavior.
Friction monitoring adds information about mold/strand interaction. However, it is important to understand how a particular system obtains its friction information.
Some mold oscillation monitoring systems infer friction from vibration and acceleration data. Systems with measured-friction capability determine friction from force measurements and report the result in pounds or newtons.
The Difference Between Inferred and Measured Friction
For years, inferred friction has given continuous casting operations a way to look for changes in mold behavior when direct friction measurement was not available.
Changes in a friction index could point operators toward changes in mold stability, lubrication, sticking conditions, or other casting behavior.
But inferred friction remains exactly that: inferred.
It does not quantify the friction force acting between the mold and strand, and the signal can be influenced by mechanical behavior elsewhere in the oscillation system.
Measured friction provides a better way to understand mold/strand friction.
KT500F determines friction as a physical force and provides continuous friction data in pounds or newtons. Depending on the caster configuration, the required force measurement can be obtained using either load cells or pressure measurements from the mold oscillation hydraulic system.
For engineers evaluating an online mold oscillation monitoring system, the distinction is an important one.
Don’t just ask whether the system provides friction data. Ask whether that friction is inferred or measured.
Not sure which mold monitoring approach fits your operation?
Talk to a Kiss Technologies engineer about KT450 FieldSERVICE, KT500F, and the best approach for your caster.