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Electro-Friction Plating

#3945


Investigation and Development of the Method of Electro-Friction Plating of Machine-Parts’, Tool’s and Other Items’ Surface with the Purpose of Improvement of their Working Capacity

Tech Area / Field

  • MAT-COM/Composites/Materials
  • MAN-MAT/Engineering Materials/Manufacturing Technology

Status
3 Approved without Funding

Registration date
29.01.2009

Leading Institute
MISIS (Steel and Alloys), Russia, Moscow

Supporting institutes

  • State Enterprise Krasnaya Zvezda, Russia, Moscow

Collaborators

  • SMS-Siemag, Germany, Hichenbach-Dahlbruch\n"Hatch" Corp., Canada, ON, Mississauga

Project summary

Relevance of work. Global problems of the third millennium are economy of metals, resource saving and ecology. The main role here belongs to the surface and superficial layers of metallic products, which can be considered as the original composites possessing special complex of physical and mechanical properties. The superficial layer appreciably defines durability, tribological behavior and corrosion properties of products.

One of effective ways of metal products service properties improvement is application of protective coating possessing high corrosion stability, hardness, wear resistance and other properties. The big influence on working capacity of products exerts strain hardening of superficial layer. In some cases processes of coating application and strain hardening can be combined. It seems to be expedient to create materials with essentially new properties in superficial layers or to put in advance prepared composite material on product’s surface in the form of coating.

As a result of analysis and generalization of available works and our own investigations, it is developed the new promising direction in materials science in the field of protection, hardening and modification of metal surface, namely, plastic deformation of superficial layer combined with application of coating by the flexible tool. The coating material (CM) in the form of rod, tape, etc. has been pressed under certain force to the flexible tool i.e. rotating metal brush (RMB). In the zone of contact of CM with RMB, it is warmed up to a high temperature. CM particles are captured by the ends of RMB fibers and transferred onto the surface under processing. Thus simultaneously, there is carried out stripping of product’s surfaces, its heating and combined plastic deformation of the superficial layer and CM particles that promotes their strong adhesion with the basis. Various metallic and ceramic materials or specially created composites can be used as CMs. It enables to form superficial layers with essentially new complexes of properties. The considered method of surface hardening combined with application of coatings has been named friction plating (FP). Its comparison to traditional methods of protection, hardening and modification of metal surfaces shows that in the certain conditions FP method possesses a number of advantages such as lower metal and power consumption, elimination of operations of preliminary preparation of surfaces, which are usually complicated and harmful to the attendants, high efficiency and productivity of processing and its ecological safety.

Practical application of FP method in various areas of engineering has enabled to reveal a number of its limitations and to draw up the ways of its further development and improvement.

It is recognized necessary to raise essentially productivity of FP, thickness and quality applied coatings and, as the main thing, to expand technological potentials of FP method, namely, to obtain possibilities to put on the product’s surface refractory and hard materials, to process surfaces of complex shape such as cogwheels, spline surfaces, welded seams, etc. Our preliminary estimations and experiments have shown that solution of these problems is possible due to intensification of FP process by electric current supply to zones of contact CM-RMB and RMB-product under processing.

Combination of deformation by the flexible tool and high-speed electrical heating of superficial layer of a product under processing enables to raise essentially efficiency of application of various coatings, surface hardenings and restoration.

The essence of such combined process, which can be called electrofriction plating (EFP), consists in the following. Heavy current passes through zones of contact CM-RMB and RMB-product under processing during processing by FP method causing in addition to friction allocation of heat and leading to high-speed heating of contact zones. While high-speed electrical heating in superficial layer, there take place absolutely other processes than at slow enough rise in temperature of superficial layer as a result of friction i.e. local heating accompanied action of significant pressure, short-term (parts of seconds) thermal cycles, high speed of cooling due to intensive heat removal inside the detail under processing. All this causes obtaining of special fine and hard structure of superficial layer possessing high physical, mechanical and service properties.

The heat caused by passage of electric current, which defines behavior of high-speed process, has the greatest significance.

The basic advantages of ÅFP process are:

  1. Intensive heating in zones contact RMB-product under processing caused by action of two sources of heat i.e. external (heat caused by friction) and internal (heat caused by passing current). The important feature of the second source is that heat caused by it is created simultaneously and instantly in all superficial layer.
  2. Deeper warming up of superficial layer of the product under processing caused by superficial effect of current passage through the conductor that promotes accelerated passage of diffusion processes between coating material and the basis. It provides stronger adhesion of CM with the basis, improves quality of coating and increases productivity of the process.
  3. Considerably higher temperature in the zone of contact CM-RMB caused by electric current enables to use refractory materials and alloys for plating.
  4. Simplicity of heating temperature control in zones of contact by changing electric power input depending on physical and mechanical properties of CM and the basis.

It is possible to use for ÅFP both alternate and direct current. Pulse current can be also used.

The preliminary analysis has shown that pulse current for transfer to zones of contact of the energy necessary for maintenance of high-speed heating is energetically and economically expedient. The capacity evolved in elementary volume by each impulse is known to be considerably higher than that with contact and continuous supply of energy as discharge voltage by tens times more than that with constant contact. It is necessary to notice, that pulse generators of big capacity are rather expensive; that is why expediency of their use for ÅFP demands experimental checks. Besides in some cases, it is possible to generate impulses of electric current not only from pulse generator, but also by means of mechanical devices.

The choice of the scheme of heating of contact zones by electric current is defined by various factors, namely, type and dimensions of the product under processing, properties of coating material, etc.

Finally, it is necessary to note that ÅFP method using flexible tool is one of ways of modification and alloying of the surfaces, which enables to obtain products with high service characteristics and essentially new properties. ÅFP method is almost not studied and represents a "niche" for scientific researches. All mentioned above indicate the urgency of carrying out the complex work on theoretical and experimental investigation of ÅFP method.


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