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Tool speed range study
There is a distinct difference in the cutting mechanism between high-speed and low-speed operations. When the cutting speed of the tool exceeds 5 m/s, both the maximum cutting force and the corresponding cutting resistance begin to decline. This trend suggests that when the cutting tool mills soil with a reduced thickness at speeds above 10 m/s, the maximum cutting force of the Roots reciprocating pump unit will be lower. At the same time, the dynamic cutting specific resistance becomes more consistent and remains relatively stable regardless of variations in chip thickness.
When the cutting speed is above 7 m/s and the cutting distance is less than 60 mm, the dynamic cutting resistance increases with the rotation angle H, which corresponds to the cutting thickness C. This relationship shows a linear rise throughout the entire speed range. The underlying mechanism involves the drum rotating at high speed, causing the cutter to move from the bottom of the soil layer to its surface. As a result, the cutting process transitions from a confined area surrounded by soil into a more open region. When the cutting distance is short, the tool advances along the path to the maximum thickness of the soil debris—essentially, the soil above the section is close to the Roots water jet unit. In this case, the soil is removed quickly without being constrained by the overlying material, reducing the impact on the tool. Therefore, at high speeds, the maximum cutting resistance increases significantly, and the variation in cutting specific resistance gradually stabilizes, becoming nearly constant.
The maximum cutting force and its corresponding resistance reach their peak within a working speed range around 5 m/s. This speed range lies between low-speed and high-speed cutting, acting as a turning point for both the maximum cutting force and the maximum specific resistance. During this phase, the tool starts cutting from the thinnest part of the chip at the bottom. As it progresses, the soil exerts an impact on the tool, leading to continuous impact cutting until the maximum chip thickness is reached. This results in a sharp increase in both the maximum cutting force and the specific resistance. Once the cutting speed surpasses this range, the cutting mechanism begins to shift toward either high-speed or low-speed behavior, causing the maximum cutting force and its corresponding resistance to decrease accordingly.