"EQUAL SPEED" COOLANT DELIVERY
"Equal Speed" Grinding fluid of Coolant Supply
Grinding fluid (or coolant) nozzles convey the grinding fluid to the grinding zone via a pump in the filtration tank. Flexibility is of utmost importance in toolmaking – or any other job shop situation - as different workpieces have to be ground in small quantities. For this reason, "Loc-Line" nozzles [1] are well suited, as they can be brought into position by hand and immediately adapted to new workpiece geometries. Loc-Line nozzles are made of plastics, which, unfortunately, are easily damaged. There are also stainless steel alternatives (g-Flex metal joint system from Grindaix) [2].
Fig. 1: Adjustable joint system for KKS hoses
The flexibility of the adjustable nozzle system comes at a price. Each of the links in the articulated system creates a certain amount of turbulence, which affects the overall efficiency of the KKS delivery system as the turbulence picks up air when the coolant exits the nozzle. In addition, the delivery position can easily be shifted in the wrong direction. For these reasons, solid steel or copper nozzles are usually used in high-performance grinding to supply the right location constantly. Today, additive 3D machining offers innovative ways to produce nozzles with ideal internal flow profiles.
Figure 2: 3D-printed nozzle (source Reishauer)
As shown in Figure 3, a flow-optimized 3D-printed nozzle has a lower flow resistance at the same flow rate than a standard nozzle.
Figure 3: Standard nozzle compared to a 3D-printed nozzle (Source Reishauer)
In some applications, the nozzles even have their own NC axis to account for the reduction in the grinding wheel size due to dressing and to correct the nozzle position accordingly.
The coolant jet should be used at the same speed as the grinding wheel features on its circumference. H.W. Ott, a Swiss grinding pioneer, developed the concept of "equal speed" in the early 1980s [4]. In 2022 (!), Karpuschewski et al. proved that Ott was right, see Figure 4. In this case, the gear profile grinding method was used. It was shown that the same speed of the coolant results in high specific chip volume v'w. (The specific chip volume refers to the amount of material removal possible until a grinding wheel needs to be dressed again). Interestingly, a lower speed than the "equal speed" speed proved to be more efficient than a higher speed than the "equal speed." The author assumes this is due to the coolant jet bouncing off the wheel's periphery if it is too fast.
Fig. 4: Related chip volume at different jet velocities
领英推荐
To achieve "equal speed," the grinding nozzle is arranged above the grinding wheel centerline. The coolant jet should hit tangentially on the grinding wheel circumference, as shown in Figure 5.
Figure 5: Synchronous lubrication
If the grinding fluid jet's speed corresponds to the grinding wheel's peripheral speed, the fluid jet adheres to the grinding wheel and ensures that it transports the coolant into the grinding zone. While in sophisticated grinding systems, such as those used in the ball bearing and automotive industries, the coolant jet velocity matches the process parameters, the reality in toolmaking is different. Nevertheless, it is possible to achieve satisfactory results even in toolmaking environments. The nozzle position should also be as described in Figure 5. The flow of the coolant jet can be adjusted with the valve of the coolant feed nozzle on the machine. The workpiece must first be removed from the grinding wheel; the nozzle is moved to the position described, and the grinding wheel is run up to operating speed. The coolant valve is then opened continuously until the coolant jet adheres to the grinding wheel (See Fig. 6)
Figure 6: Synchronized lubrication
?
Literatur:
[3] Ott, H.W.: Wichtige Merkpunkte der Schleiftechnik, 1976 – 2005, Eigenpublikation,
H.W. Ott & Co, Schleiftechnik, Pf?ffikon-Z
[4] Karpuschewski, Bernard:?Effizienzsteigerung der Kühlschmierstoffversorgung beim Schleifen, Universit?t Bremen, Fachbereich Produktionstechnik, Fachgebiet Fertigungsverfahren, 2022
Walter Graf ?, May 2023, The Philosopher’s Grindstone
GrindCraft Operations
1 年Hello Walter, What are typical PSI values for coolant delivery? After reading this article it seems that it suggested to adjust pressure until you have achieved "equal speed". I have a system that is outputting ~5 PSI from what I have read to achieve proper chip evacuation pressures should be in the ~30 PSI range. I understand that there are a lot of other parameters that come into play (such as nozzle design). Thank you for writing these articles, I have often referenced them.
General Manager - Bharuch Operations
1 年Please send me more details