knife temperature in woodworking

Cutting heat mainly occurs in the area of plastic deformation of the workpiece in front of the cutting edge, the area of friction between the front knife surface and the chip, the back knife surface and the workpiece. For wood processing, the cutting temperature generally refers to the knife temperature.

There are two results caused by the increase of knife temperature, one is that the rise of the cutting edge temperature will accelerate the wear of the knife, and the other is that the uneven temperature distribution of the knife body will make the knife lose its original stability. The former is due to the hardness of the knife material at high temperature, or thermal deterioration; The latter is related to the thermal expansion and thermal stress of the knife itself.

When the knife temperature rises, the friction on the surface of the knife is the main source of heat generation, and when the wood is cut, because the thermal conductivity of the wood is much smaller than that of the metal, so the heat transmitted to the knife is much larger than that of the metal cutting.

Measurement of knife temperature:

Since the cutting speed of wood is very high, and the parts where the temperature rises significantly only occur in the very small area of the cutting edge of the knife, and the dry wood is an insulator, the commonly used methods to measure the temperature of the knife and the cutting contact surface in metal cutting, such as tool-work thermocouple method, are used to determine the temperature of the knife and the cutting contact surface. It can not be used in wood cutting, so it is difficult to directly determine the temperature of a certain point of the wood cutting knife, especially the cutting edge temperature.

knife temperature measurement is generally the thermocouple or thermal resistance sensor pasted or welded on the prop, but the measurement must stop the movement of the knife, because the temperature field generated by the element hot melt mess and the impact of the response lag, to accurately determine the temperature of the knife and the blade is also difficult, unless it is with a very fine thermocouple, is to minimize the heat capacity of the element, High response measurement can also be achieved under the condition that the temperature field is not chaotic.

Or use the heat emitted by the object to determine the temperature of the object with the radiation thermometer, can not disturb the temperature field, in a non-contact way to determine the temperature of the knife, such as far infrared temperature measuring instrument, can obtain very sensitive and accurate measurement results.

The hardness of the blade is obtained by quenching and tempering, with a higher tempering temperature (carbon steel 150-200 degrees, alloy knife steel 100-500 degrees, high-speed knife steel 550 degrees), heating and cooling of the knife material, the hardness of the knife will be significantly reduced, the higher the heating temperature, the more obvious the hardness reduction.

Factors affecting knife temperature,

The biggest factor affecting the knife temperature is the heat output per unit time of the cutting system, and the heat output is proportional to the cutting power. That is, the greater the cutting force and cutting speed, the higher the temperature of the knife, but even if the cutting force is the same, according to the cutting Angle, back Angle, cutting type, the wear state of the knife and other conditions, the contact state of the knife and the chip and the easy processing is different, the temperature distribution near the blade is different.

The factors that affect the temperature rise of the knife are in the aspect of the knife itself, mainly the thermal physical properties of the knife material, the shape of the blade or conductor and the shape of the contact surface with the workpiece. In general, the greater the thermal conductivity of the knife material, the lower the surface temperature of the knife, and the gentler the temperature gradient inside the knife in a stable state. Therefore, the surface temperature of the cemented carbide knife is lower than that of the high-speed steel knife. Related to the shape of the knife, the heat capacity of the knife material and the surface area, the smaller the blade wedge Angle, the faster the temperature rise, and the faster the cooling.

The heat lost from the knife surface to the surrounding air heat conduction and radiation also affects the temperature of the knife itself, the faster the airflow speed, the greater the heat conduction coefficient, the more heat lost by the knife.

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