The rational use of milling tools for cold milling machines on road surfaces

Motion analysis of milling characteristics

The rotational motion of the milling cutter loads (through the machine weight and the forward movement of the machine) onto the material of the milled road surface, generating a very high contact stress at the point between the milling cutter and the material of the milled road surface. When this contact stress reaches its limit, the road surface material is crushed and falls off. As the movement proceeds (the rotational motion of the cutter and the linear motion of the machine), the crushing and falling off of the road surface object alternate continuously. Thus, milling is formed (as shown in Figure 1).

As shown in Figure 1, when the milling drum is performing milling, the speed of the tool tip is composed of two parts: the rotational speed (milling speed) ω and the traveling speed (feed speed) v. The cutting path of the tool tip is the wheel line, and the equation is described as:

x = vt + rsinωt

y = r (1-cosωt)

In the formula: ω - angular velocity, ω=2πn/60, n - milling rotational speed, r - milling radius

For each full rotation of the milling drum, the milling space of the tool in the axial projection area of the milling drum is the region formed by the wheel line and the road surface (as shown in Figure 2). In the horizontal direction, the distance between any two adjacent points on the rotary wheel line is W=1000vt/60(mm), where hi is the milling depth. The tool milled from the bottom up, and the milled thickness gradually increased.

2. Tool structure and failure factors

1). The cutting tool consists of four parts (as shown in Figure 3) : a. hard alloy head, b. tool body, C. Protective ring, d. elastic sleeve.

The hard alloy head is brazed onto the tool body and directly participates in the milling of the road surface. The guard ring separates the knife body from the knife seat, preventing it from direct contact with the knife seat and protecting the knife seat from wear. The tool is installed in the tool holder. Through the elastic sleeve, the tool is tightly fitted into the installation hole of the tool holder, and the tool body can rotate within the elastic sleeve to ensure uniform wear of the tool during the milling process (as shown in Figure 4).

2). Failure factors (as shown in Figure 5)

a. The milling tools were not selected based on the hardness of the milled road surface, which led to abnormal wear of the tools.

b. Insufficient cooling water volume causes thermal corrosion of the hard alloy head of the cutting tool.

c. The mismatch between the milling speed and the milling depth causes interference and wear of the tool holder.

d. The tool body and the elastic sleeve are stuck by sand particles. During milling, the tool body cannot rotate within the elastic sleeve, resulting in uneven wear of the tool.

The rational use of cutting tools

In view of the above four failure factors of cutting tools, measures for the reasonable use of cutting tools are proposed:

a). To prevent excessive tool wear caused by tool holder interference wear, the following table corresponding milling speed and milling depth is recommended:

As can be seen from Figure 2, the greater the milling depth, the longer the contact time between the tool and the material, and the more frictional heat is generated. To prevent thermal corrosion of the hard alloy head of the tool, the amount of water sprayed to cool the tool head needs to be increased. When the milling depth is relatively shallow (less than 5cm), the amount of water sprayed to cool the tool head should be reduced to facilitate the ejection of the material, decrease the contact probability between the tool and the milled material, and reduce the wear of the tool.

c). Select the cutting tools based on the power of the milling machine and the hardness of the milled road surface

The following table lists the selection of Wirtgen tools and Knnametal tools under different construction conditions

d). Every 6 to 8 hours of operation, check the rotation and wear of the cutting tools to ensure that the installed tools can rotate freely in the tool holder holes. Tools that are severely worn should be replaced in a timely manner. The overhang length of the cutting tools has a significant impact on the construction quality. When changing the cutting tools, try to ensure that their overhang lengths are consistent. If half of the milling cutter is severely worn and needs to be replaced, it is recommended to replace the entire set of tools. Recombining used but not severely worn cutting tools into a set and continuing to use them can not only ensure the quality of road surface construction but also extend the service life of the cutting tools and reduce construction costs.

4. Conclusion

Through the above analysis and summary, the rational use of tools during the construction process is crucial to the construction quality, construction efficiency and construction

Cost is of great significance.