Magnetic-Abrasive Surface Modification: example of magnetic-abrasive machining of small diameter tubes

Problem Relevance

Mechanical methods, chemical etching or electrochemical polishing are usually used for surface finishing of the critical parts of machines and devices. These technologies are labor-intensive and environmentally unfriendly, poorly mechanized and automated, and they not always meet modern production requirements.

One of the technological challenges is the surface finishing treatment of long small diameter tubes, rods and wires.

Innovative technology –
Magnetic-Abrasive Machining (surface modification)

Magnetic-Abrasive Machining method: description, features and benefits

The Magnetic-Abrasive Machining (MAM) method is performed by ferro-abrasive powder-tool that is compressed under the magnetic field influence, pressed against the treated surface and polishes it. More about Magnetic-Abrasive Machining (MAM)

Technology and equipment for MAM of pipes and rods

The challenging MAM method application area is surface finishing treatment (modification) of zirconium tubes – the nuclear fuel element cladding.

The efficient operation of nuclear reactors and their safety are directly dependent on the manufacturing quality of zirconium fuel assembly components including fuel elements. The nuclear fuel elements operate in water coolant at high temperature and pressure, which leads to corrosion and hydrogen absorption of their shells. As consequence, it limits the service life of these elements.

The surface finishing of nuclear fuel cladding plays extremely important role in their performance properties – resistance to corrosion, abrasion, thermal and mechanical failure.

The accident at the Japanese "Fukushima" nuclear reactor in 2011, occurred due to a sudden coolant loss. This accident made clear the necessity of a significant increase in corrosion resistance and durability of fuel element cladding. Currently the shells finishing treatment is performed by traditional methods (abrasive belts grinding, etching in hydrofluoric solutions), which exhausted their technological resources.

The Magnetic-Abrasive Modification technology is an alternative to traditional fuel cladding treatment. It forms a modified surface layer of parts with high performance specifications.

Equipment for Magnetic-Abrasive Surface Modification
Figure 1 – The development samples of equipment for Magnetic-Abrasive Modification

The research of the MAM of zirconium fuel cladding, completed by the scientists of POLIMAG and the Institute of Industrial Nuclear Technologies of the National Research Nuclear University “MEPhI” (Moscow), found promising industrial application in nuclear engineering. They have developped the technology fundamentals of the modification of the outer and inner shells surfaces. Furthermore, they have designed some equipment samples (Figure 1).

The developmental prototype of the T15 model (Figure 2) provides the process of Magnetic-Abrasive Modification with the magnetic induction in the working area up to 1 Tesla.

There are active magnetoplastic, magnetoelectric and magnetostrictive effects. Other physical and chemical processes of energy and mass transfer at the atomic and molecular level are activated in the presence of special process fluids. These effects balance the treated material structure and "heal" many structural defects. As a result, the polished surface nanorelief with a minimum of structural defects in the surface layer is formed.

The results of 150-days corrosion tests of fuel-element cladding samples demonstrate the increase in corrosion resistance of the modified samples by 25% compared with the initial.

Equipment for Magnetic-Abrasive Surface Modification
Figure 2 - The development sample of the T15 model

One of Rosatom's enterprises (Russia) successfully caried out several industrial tests of the technology of magnetic-abrasive modification.

T19 model

In 2019 Polimag designed the T19 model for automatic implementation of the MAP process on the outer and inner surfaces of small-diameter pipes. T19 tests will be completed in 2021.

Tecnnical characteristics of T15 and T19 models
T15 model T19 model
Diameter of polished parts, mm 6 - 15
Length of processed pipe, m 0.7 - 5.0
Ra (polished surface nanorelief parameter), μm 0.2 - 0.4
Dimensional metal removal, μm 10 - 30 10 - 40
Polishing performance, m/min 0.5 - 1.5 0.5 - 2.0
Automatic operation of the unit no yes
Power consumption, kW 2.5 4.0
Overall dimensions L x B x H, m 11.5 x 0.6 x 1.3 13.0 x 0.7 x 1.5
Weight, kg 200 360