Ballscrews are one of the most critical components of a CNC machine. It is essential to keep the ballscrew in a good condition to maintain the accuracy in the machine. Some of the most common ways a ballscrew loses its accuracy are
1. Excessive heating of Ballscew
2. Insufficient lubrication
3. Running over the suggested rpm
Whenever there is an excessive heating of ballscrew the material tend to expand due to thermal expansion because of which the ballscrew may start to loose its original accuracy. In order to prevent this type of thermal expansion, PMI has developed 2 special types of ballscrews to prevent excessive heating up of ballscrew.
The hollow cooling system designed by PMI uses a coolant pipe through the hollow hole of Ballscrew. The hollow hole is through all of the Ballscrew, and one end is clogged with the oil seal by PMI patent. The coolant is pumped into the coolant pipe and flows to the end of the coolant pipe. The coolant then flows reversely along the hollow hole back into the coolant collector. It can cool down the Ballscrew.
The features of this are:
1. Well and effectively control thermal expansion
2. Simple design and structure to save cost
The above we saw was a screw cooling type of ballscrew, now we will see the similar as nut cooling. There are tubes passing through the nut which can carry the cooling fluid through the nut body and can cool the system continuously.
There are 2 models in nut cooling as shown below:
In this type of nut cooling the coolant is circulated through connected tubes on the Nut OD. There is an inlet and an outlet on the flange of the ball nut to ensure the circulation of coolant effectively.
In this type of nut cooling the coolant is forced through all the tubes at once. There is an inlet at one end and outlet at the other end of the nut.
If we compare the effeciency of both this types of nut, we can see that the direct passing type is more effective in reducing the temperature rise of the ballscrew.
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