"Which would be the best application of oil: an oil lifter (ring and collar) or oil circulation in a ventilator (large roller bearing with medium speed)?"
Oil application methods vary based on a number of variables such as speed, size, lubricant viscosity and ambient conditions. You must match the lubricant delivery mechanism with how the machine is expected to operate. Otherwise, large amounts of wear can be generated, causing downtime and potentially excess energy consumption.
It is important to understand the benefits and weaknesses of each method. Oil lifting devices are among the oldest lubricant delivery mechanisms. They utilize the machine's rotational movement to pick up oil and transport it to the component that needs to be lubricated.
The biggest difference between a ring oiler and a collar oiler is how it is affixed to the shaft. Ring oilers are not attached to the shaft but simply ride on it (sometimes in grooves) and lift the oil where it needs to go. Collar oilers are firmly attached to the shaft and rotate with it accordingly. Both ring oilers and collar oilers must operate at a defined shaft speed and be sized appropriately to lift the proper oil volume to lubricate the machine.
While these devices are simple and generally require little maintenance, there are some inherent drawbacks in their use. Perhaps the biggest potential problem involves insufficient oil levels. The oil level inside the machine must be continually inspected to ensure the lifting device can function properly. An oil level that is slightly too high or too low can greatly impact the effectiveness of these devices.
In cold conditions, there is also a risk of channeling, which means the lubricant viscosity is too high to be lifted. During startups and shutdowns, rings and collars may simply not lift enough oil to lubricate the machine. This can lead to boundary conditions and increased wear of the internal machine parts.
Circulating oil systems are common for large, complex equipment, but they can be adapted to work on most oil-filled housings. Machines operating with circulating oil tend to run cooler. The lubricant also tends to last longer in these systems.
Circulating oil systems typically have a larger volume of oil, and the additional piping and pumps allow you to better condition the oil with filters and heat exchangers built into the oil loop. Of course, there is added cost for these systems, and they must be monitored for leaks and to ensure the pump is working properly.
If feasible, it would be best to go with a circulating system, as its benefits far outweigh the negatives. While this will cost more, you can better lubricate your machine if the circulating system is installed correctly. To help prolong the life of the machine and potentially the lubricant, be sure to include filtration in this type of system. Over time, this may pay for the upgrade of the system.