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Common rolls for rolling mill flaw detection methods in roll workshops


The cost of the roll workshop in a modern steel rolling mill directly determines the cost of the rolling mill. The surface quality of the roll directly determines the quality of the rolled products, and the internal quality of the roll determines the service life of the roll. How to reduce costs (roll consumption) and improve product quality (rolls that meet the requirements of the steel rolling production line) has become an urgent problem that needs to be solved in the rolling mill rolls workshop. The application of reasonable roll flaw detection methods (mainly non-destructive testing) in production practice has become a faster and more effective way to solve this problem.

steel work rolls

Common flaw detection methods

Common roll flaw detection methods The main roll flaw detection methods include the following: magnetic particle flaw detection, penetrant coloring flaw detection, eddy current flaw detection, and ultrasonic flaw detection. They are introduced one by one below.

The roll shop mainly relies on grinder eddy current flaw detection equipment, operator observation and roll managers to use magnetic particle testing or ultrasonic flaw detection instruments to monitor the presence of cracks in the rolls. Nowadays, automatic eddy current flaw detection and manual ultrasonic testing are generally used, which further reduces the chance of the impact of roll defects. This provides a guarantee for grinding qualified rolls.

1. Magnetic particle inspection

Magnetic particle inspection technology is mainly used to detect cracks on the surface of the roll body and fatigue cracks in the roll neck area, excessive cyclic loading or subsequent normal corrosion.

Principle of magnetic particle inspection: principle of electromagnetism, the magnetizing current passes through the surface of the ferromagnetic workpiece to form an electromagnetic field. The existence of defects will cut off the magnetic lines of force, form a leakage magnetic field and attract magnetic particles. The magnetic particles accumulate to form magnetic traces. The existence of defects can be judged by observing the magnetic traces (magnetic traces are essentially magnified defects).

Advantages of magnetic particle inspection technology:

(1) Determine surface and subsurface linear discontinuity defects;

(2) Operation and explanation are relatively simple.

Disadvantages of magnetic particle inspection technology:

(1) Can only be used on ferromagnetic materials;

(2) Flaw detection limited to surface defects.

2. Penetrant coloring flaw detection

Penetrant coloring flaw detection is widely used for roller surface crack inspection due to its simplicity of use. The most common is red dye, which can be applied by spray. Provides clear contrast compared to the white base.

Advantages of penetrant coloring flaw detection:

(1) No power supply required;

(2) Can detect complex shapes and point out the shape and size of defects;

(3) Able to display few and dense defects;

(4) Able to detect ferrous and non-ferrous metals.

Disadvantages of penetrant coloring flaw detection:

(1) Unable to detect subsurface defects;

(2) The surface must be clean, oil-free and dry.

3. Eddy current flaw detection

Eddy current flaw detection began to be used in the 1970s. This method was the first crack detection system developed and automated. It gives the grinder a clear and correct signal when surface cracks are present. It can also pinpoint the location of defects and the level of cracks. Eddy current testing is mainly used to identify surface cracks.

Eddy current testing principle: Eddy current testing is a non-destructive testing method based on the principle of electromagnetic induction. It is suitable for conductive materials. When a conductor is placed in an alternating magnetic field, an induced current exists in the conductor, that is, an eddy current is generated. Due to changes in various factors of the conductor itself (such as conductivity, magnetic permeability, shape, size and defects, etc.), changes in eddy currents will occur. The detection method that uses this phenomenon to determine the properties and status of the conductor is called eddy current testing.

Advantages of eddy current flaw detection:

1. During detection, the coil does not need to contact the workpiece and no coupling medium is required, so the detection speed is fast.

2. It has high detection sensitivity for defects on the surface or near the surface of the workpiece, and has good linear indication within a certain range, and can be used for quality management and control.

3. It can measure the thickness of metal covering layer or non-metallic coating.

4. Non-metallic materials that can induce eddy currents, such as graphite, can be inspected.

5. The detection signal is an electrical signal and can be processed digitally to facilitate storage, reproduction, data comparison and processing.

Disadvantages of eddy current testing:

(1) Flaw detection can only be done on conductor materials;

(2) Shallow penetration depth;

(3) Many factors such as material geometry and permeability affect the signal. in some situations

In case of magnetic particle inspection, residual magnetism or other signal sources will cause erroneous readings;

(4)The eddy current flaw detection device has a certain blind area (generally at the beginning and end of the detection area)

4. Ultrasonic flaw detection

In recent years, roll ultrasonic flaw detection systems have become popular and as mentioned above they have been combined and used with eddy current flaw detection. Its main advantage is the detection of sub-surface defects and the ability to detect defects at the joints of composite cast rolls. Generally speaking, coupled crystal column probes are used to detect subsurface flaws. In order to effectively transmit sound waves into the roller, water (oil) is used as a coupling agent. Surface wave and shear wave synthetic probes have been further developed and may replace eddy current flaw detection.

Principle of ultrasonic flaw detection: Ultrasonic flaw detection is a flaw detection method that uses physical properties such as propagation, reflection and attenuation of ultrasonic waves in materials to find defects. Ultrasonic flaw detection has the advantages of high sensitivity, fast detection speed, low cost, easy operation, large detection thickness, harmless to the human body and the environment, and is especially sensitive to dangerous defects such as cracks and lack of fusion. However, there are also disadvantages related to the operator’s level and experience. In flaw detection, it is often used in conjunction with other flaw detection methods to improve the reliability of flaw detection results.

Advantages of ultrasonic flaw detection

(1) Can penetrate into many materials to a considerable depth;

(2) Ability to detect flaw on sub-surface;

(3) Able to detect very small cracks;

(4) Relatively accurate in determining crack size and depth;

(5) Portable batteries can provide energy for operation;

(6) Ability to detect changes in internal defects.

Disadvantages of ultrasonic flaw detection

(1) A good coupling agent is needed;

(2) Requires trained and experienced operators;

(3) Operators must have extensive knowledge of defects.

Composition of ultrasonic flaw detection: Standard ultrasonic cleaning equipment consists of three parts: ultrasonic generator (also called ultrasonic power supply), transducer and other auxiliary equipment.

Ultrasonic generator: what we often call a flaw detector, converts low-frequency electricity into high-frequency electrical signals above 28KHZ, which are connected to the transducer through a link line.

Ultrasonic transducer: commonly known as probe, is a high-efficiency transducer element that can convert electrical energy into powerful ultrasonic vibration. When ultrasonic vibration is generated, it looks like a small piston with a very small amplitude, about only a few microns. This is what we usually call ultrasound. Auxiliary equipment: link wire, coupling agent, test block.

rolling mill rolls manufacturers

Commonly used probes:

2M surface wave probe: used to detect roll surface cracks

2 megapixel dual element probe: used to detect the thickness of the working layer of the roll

2M straight probe: used to detect internal defects of the roll

2 trillion 45 degree angle probe: used to detect crack depth

Possible problems in ultrasonic flaw detection

1. Because ultrasonic waves will be affected by the unevenness of the measured object, reflection angle and multiple reflections, it may increase the measurement data error.

2. Since ultrasonic waves have the inherent characteristics of measurement blind spots, if the measurement position changes but the received data remains unchanged during close measurement, it means that the measurement blind spots have been entered.

3. When ultrasonic waves are measuring distant objects, if no measurement data is returned, it may be that the measurement range is exceeded or the measurement angle is wrong. The measurement angle can be adjusted appropriately.

Advantages of reasonable roll flaw detection technology

1. Cost savings

(1) Rolling mills that do not use roll flaw detection generally use open-loop grinding or turning when repairing rolls. Generally speaking, this means removing a standard depth of the roll surface. If the defect is small, unnecessary waste is caused; if the defect is large, it may not be removed cleanly. After using the roll detection device, the minimum removal amount can be ensured, which is only 1/3 to 1/2 of the original amount under normal circumstances, thus avoiding unnecessary losses and ensuring the grinding quality of the roll.

(2) It can reduce the downtime of the rolling mill, increase the service life of the rolls, reduce the amount of scrap steel, and reduce product quality due to crack expansion under normal operating conditions. After applying reasonable roll flaw detection, it can basically ensure that each roll is used to the guaranteed minimum size before being scrapped. This can solve the problem that in the past, many rolls could not be inspected due to internal defects, causing the defects to expand, and eventually many roll breakages or other accidents that seriously affected production occurred.

2. Improve quality

The use of a roll flaw detection device means that defects on the roll can be removed while ensuring the integrity of the roll’s mechanical properties and surface finish. This ensures that the quality of the product will not be reduced due to these reasons.

Although there are many methods for flaw detection of rolls, generally speaking, they are all intended to remove various defects on the rolls to ensure the surface quality and internal quality of the rolling line rolls are qualified. In order to achieve this goal, roll flaw detection is now developing in the direction of automation (installed on roll grinders), comprehensive (several flaw detection methods are used in combination), and specialization (professional flaw detection personnel are set up). Our current flaw detection level needs to be improved, and we strive to learn and master more advanced flaw detection technology and experience.

Rolling mill rolls

Generally it is 5-10 days if the goods are in stock. or it is 15-20 days if the goods are not in stock, it is according to quantity.

A: Payment<=1000USD, 100% in advance. Payment>=1000USD, 30% T/T in advance ,balance before shippment.

Always a pre-production sample before mass production;
Always final Inspection before shipment;
During the epidemic, provide remote detection technical support

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Rolling mill rolls product

Classification by roll material:

Cast iron mill rolls

  • Alloy indefinite chilled cast iron rolls
  • Alloy chilled cast iron rolls
  • Alloy SG ductile cast iron roll
  • Pearlitic ductile cast iron roll
  • Bainite ductile cast iron roll
  • Centrifugal cast iron roll

Cast steel mill rolls   

  • Alloy cast steel rolls
  • Semi-steel roller
  • Graphite steel rolls
  • High-chromium steel roll
  • High-speed steel roll

Forging mill rolls

Sort by position on the rolling mill:

Work rolls
backup rolls

Intermediate roll

Product advantage

The world No. 1 in crude steel production steel plant, over 70% of the HSS for bar and wire are from us.

LMM high-speed steel rolls have higher steel passing per groove (times) due to their good wear resistance, which saves roll changing time, improves rolling mill operation rate, reduces roll consumption, and improve the overall efficiency of the factory.
Generally, the amount of steel passing in a single groove (times) is 3 to 5 times that of cast iron rolls.

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