**4. Development of the system of increasing thermal conductivity of cemented carbide**

 It is known that the contact area in all friction pairs is determined not by the nominal and by the actual contact area, which is the total area of the contacting asperities of microroughness of friction pair and which comprises some percentages of the nominal contact area [8]. The air areas (pockets) are formed in places with absence of contact. The thermal conductivity of air is 3500 times lower than that of metals used in composite cutters. Therefore, the border between the contact surfaces of cutting insert and tool holder has high thermal resistance, and that greatly deteriorates the conditions of heat transfer into the tool.

Reduction of the thermal resistance in the narrow area of contact supporting surfaces is proposed by use of thermally-conductive interface with increased thermal conductivity. The specified interface formed by special thermally-conductive paste which thin layer is located between the contacting surfaces of tool holder and carbide cutting insert (**Figure 9**). Paste AlSink-3 on the basis of a mixture of oxides of aluminum and zinc together with a silicon organic solvent.

To ensure normal heat transfer, all air should be eliminated from gaps by special elastic thermally conductive composition with much higher thermal conductivity. However, in any case, the thermal properties of the best thermally conductive

#### **Figure 9.**

*Example of supporting surfaces of the cutting insert and tool holder [2]: 1—air gap clearance, 2—thermally conductive paste, 3—supporting surfaces of the carbide inserts and tool holder, and 4—heat flow.* 

pastes are lower than that of metals, and therefore, the quality of the mating surfaces and the thickness of the layer of thermally conductive paste are critical.

 The thickness of paste at the point of contact shall not exceed the value of roughness on the mating components; and the paste should be applied with even layer to the degreased surface and smeared for guaranteed filling of all surface irregularities.

One of the main advantages of the presented method to reduce thermal stress in the cutting zone through removing heat from the cutting insert to the tool holder is its low cost and no need to use complicated equipment. In the process of the tool operation, the thermally conductive interface does not require frequent replacement, since it is sufficient to form it for the whole lifetime of cutting insert, and it should be replaced only with the dismantling and replacement of worn-out cutting insert. However, prior to the formation of a new layer of thermally conductive interface, the old paste should be removed with a detergent, and the surfaces should be completely degreased and dried. The above shows the great technological effectiveness of use of thermally conductive paste in production environment [2]. The studies have shown that the use of thermally conductive paste in composite cutter improves heat transfer from the cutting zone and reduces the thermal stress of tool cutting wedge. This greatly increases the efficiency of the cutting tool during wheel turning.
