3D Printable Screw Style Oil Skimmer for CNC Way Oil Removal From Coolant Includes Circulation For Better Oil Removal and Keeps Coolant Fresh
- 2 days ago
- 4 min read
Updated: 3 hours ago
There are many different designs for oil skimmers to remove way oil from coolant.
Belt
Tube
Disc
Most rely on the oil clinging to plastic or metal surfaces, while the coolant does not. The clinging oil is pulled up to a scraper, scraped off the belt (or tube, disc), and then runs down into a disposal container. The issue with these designs is that they also pick up a lot of coolant with the oil, as much as 50%, so a second oil separation unit is required to drain the excess coolant back into the coolant tank before diverting the oil to the used oil tank.
There are some interesting screw-style oil skimmers that claim to collect only about 7% of coolant, and therefore don't require a diverter. They use a long auger-style screw that passes inside an open-sided tube. The oil sticks to the auger-style screw and the wall of the open-sided tube and is moved upwards out of the coolant. Excess coolant drawn upwards drains out the opening of the tube. The auger-style screw has a low pitch, and therefore, the oil moves slowly upward, giving the coolant plenty of time to fall back down. In addition, there must be some mechanical action of the oil being pressed between the screw and the tube wall, which helps to separate the coolant.
Links to screw action oil skimmers:
Wear and Maintenance
Another advantage claimed of the screw-style oil skimmer is minimal maintenance compared to other skimmers. Since there are no scrapers, no parts are wearing out that will require replacement.
The screw threads will rub against the inside of the tube; however, that surface is also constantly lubricated by the oil being removed, so the wear between them should be insignificant.
Version 1
This is a quick concept for a 3D-printed design.
Using a DC gear motor (Bodine motor that I already have). Attached to a 3D printed motor mount plate (light blue), which attaches to the main body (grey).
The screw tube (light blue) is a standard 1.5in Sch40 PVC pipe. A slot is cut in the side of the tube to expose the screw to the coolant, so that the oil can stick to the screw.
The screw is 3D printed in several interlocking sections. The length of each section is limited by 3D printer Z-axis height. Multiple sections can be interlocked to form the long screw. The screw fits over a steel tube for strength (more details later).
At the base is a static stand that is attached to the end of the tube.
Inside the base is an impeller that is attached to the end of the screw. It draws coolant down towards the base of the screw. This circulates the coolant to increase oil in contact with the screw and aerates it, reducing biofilm buildup.
The top of the tube extends above a slanted drain area that surrounds the tube. The existing designs use a fin that swings around and scrapes the oil towards the drain hole. I think that's because of the way they are manufactured; it's easier to build with flat machined plates. This slanted design should work without an extra scraper.
The oil flows out and over the top edge of the tube and down towards the drain hole where additional plumbing can be used to direct it towards a waste oil container.
The top of the screw has a flange to prevent oil from being pushed up to the motor shaft.
The cross-section shows how the screw is made out of multiple parts. The outer screw body and thread is 3D printed. The inner part is a steel tube with an ID of 0.5 in, an OD of 0.75 in, and a 1/8 in wall. The tube has a split at the top that fits over the 0.5 in motor shaft. A shaft collar clamp serves a dual purpose: as a stop for the 3D printed screw sleeve and to clamp onto the motor shaft.
The shaft collar clamp has a keyway, which can be used to interlock with the tube, motor shaft and 3D printed screw sleeve, such that they won't slip on the motor shaft.
Cross-section of the whole assembly.
Cross-section of the impeller and impeller housing. The impeller fin designs are very basic, probably not efficient. But efficiency is not what's important here. As long as they circulate the coolant and if they create additional turbulence to aerate the water, that's a bonus.
Components:
The gear motor that we had on hand has the same body as this motor. This motor is expensive. A cheaper motor can probably be used. Not sure what speed to use, but starting with 150 rpm with a speed controller to test different speeds.
The existing products use induction motors (AC, brushless motors).
This is used in the internal part of the screw to strengthen the 3D print. It also conveniently has an ID the same as the OD of the motor shaft. Since it is a welded tube, it may require a 0.5 in. drill bit or reamer to clean out the weld bead on the inside of the tube.
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