A Better Fogless Coolant System Design Improving On The Fogbuster Mist & No Fog Free Coolant Spraye
One major issue with the Fogbuster and other similar fogless coolant applicators that use air pressure is that they can have issues with the consistency of the coolant flow rate. If the coolant flow rate could be either measured or controlled, then the application would be much more reliable.
The coolant volume that's being applied to the tool/cut only needs to be about 1 drop per 2 seconds (30 drops per minute). 1 drop of water equals 0.05ml. 1ml = 20 drops. So the pump needs to have a flow rate as low as 1.5 ml per minute. This is a very small flow rate, and there are few pumps capable of delivering such low flow rates.
Peristaltic Pumps
Peristaltic pumps are ideal flow rate metering pumps for relatively low flows. Using a stepper motor to drive the pump allows for fine-tuned control and very low flow rates. The solution being pumped never comes into contact with the mechanical systems of the pump, so it's a low-maintenance system. The downside to peristaltic pumps is that they have a pulsation on the output. This is caused by the stretching and contracting of the tubing. For applications were volume metering is the important factor, the pulsing is not an issue. But for constant, low-flow rate applications like this, the pulsing becomes an issue because it results in periods of time where there's no flow. The solution is to add more rollers to the pump head and decrease the diameter of the tubing such that the pump can be run at a higher rpm.
Peristaltic Pumps
Peristaltic Pump Tubing
1x3.2mm BPT tubing - https://a.co/d/13lGX7n
0.8x4mm BPT tubing - https://a.co/d/7sRS1RA
1x3mm Silicone tubing - https://a.co/d/7XlfjKW
1x3mm Silicone tubing - https://a.co/d/ag7ZY2X
1x3mm Silicone tubing - https://a.co/d/c9nf3SK
Micro Gear Pumps
Gear pumps are generally used in high-pressure, low-volumetric flow rate applications, such as hydraulic systems. They are therefore well suited for very low flow rate applications. They do not have pulsation issues. Microgear pumps are generally more expensive than peristaltic pumps, and the pump is exposed to the fluid (which in the case of metal cutting coolant is probably not an issue because it has lubricants and rust preventatives in it, so it's similar to running oil through the pumps).
This inexpensive micro gear pump has a flow rate of 0.8ml/revolution. To achieve a 1.5ml per minute flow rate, the pump would need to be turned at about 2 RPM, which is easy to achieve using a stepper motor.
The downside is that this pump is designed for a minimum RPM of 1000 RPM, and a volumetric efficiency of 88%. That means that 12% of the liquid will slip past the space around the gear and gear teeth. Since the pump relays on continuous rotation to build pressure, there maybe too much loss at 2 RPM for a consistent flow.
WHERE TO BUY
Specification
Name: Hydraulic Pump-1A-0.8
Sputum volume: 0.8ml/r
Preset pressure: 21MPa (3045 psi)
Rated speed:1800rpm
Maximum speed: 4300 rpm
Minimum speed: 1000 rpm
Volumetric efficiency:88%
Mechanical efficiency: 85%
Flange mounting method: SAE standard
Input shaft connection form: Flat key
Inlet and outlet connection type: Thread
Oil inlet: PT3/8”
Oil outlet: PT3/8”
Product Weight: 0.95KG
Product size: 10.1*8.12*6.75cm
The gear pump will need to be driven by a stepper motor. Since the force is low, it can be direct drive. A flex coupler will be needed to connect the shafts between the stepper and pump shaft, and an interface part to connect the servo motor housing to the pump housing.
This interface part can be 3D printed.
