Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
concentration below 20 mg/L. By default, a low TDS will result in low calcium, magnesium, and anion levels. High TDS, above 5,500 microsiemens (μS) can result in fluid instability. In figures 2A and 2B, the water phase is considered inert and non-conductive. When the water phase becomes highly conductive with high TDS, then the charges on the emulsion droplet are less effective.
Caution
A water softener that regenerates with sodium chloride can reduce hardness by substituting calcium and magnesium ions for sodium ions but will not reduce the anions. A poorly adjusted softener can increase the chloride levels if the backwash cycle of the softener is not set properly.
Water that is used as replenishment processed by RO or DI can lead to foaming since calcium and magnesium ions can act as a defoamer. Tool life may decline since calcium soaps offer a level of boundary lubrication. Metal soaps such as iron and aluminium can also aid in boundary lubrication.
3. Effects of extraneous oils (tramp oils). Simply stated, tramp oil is not just “oil” from one oil source. Tramp oils can be hydraulic, way, gear, and spindle oils. Hydraulic oils can contain anti-wear components such as zinc dialkyldithiophosphate (ZDDP), dispersants, demulsifiers, viscosity index improvers, and emulsifiers. Gear oil can contain sulphur compounds which are ideal food for microorganisms. The oil in various tramp oils can be paraffin-based whereas the base oil in the metal removal fluid can be naphthenic-based.
There are at least three tramp oil failure mechanisms: a. Sharing of the emulsifier and upsetting the hydrophilic, lipophilic balance (HLB).
b. Reactivity of the ZDDP molecule. Recall that ZDDP has zinc (Zn++
), sulphur, and phosphorus.
c. Dispersants and demulsifiers in the hydraulic oil also upset the HLB.
Figure 3: Failure Mechanism #3 - Tramp Oil.
Control plan for tramp oil: Fix the leaks. This is the most effective plan, but it is not simple. Leaks can be ubiquitous and usually require stopping production to access the leaking components.
Use a lower additive level of hydraulic oil (if that is the source). Anti-wear and rust and oxidation- rated hydraulic oils are typically present in premium hydraulic oils. Rust and oxidation-rated hydraulic oil may be sufficient for lower-pressure hydraulic systems (less than 40 BAR).
Remove the tramp oil within 48 hours of their entrance into the fluid. This will require some type of continuous tramp oil separators such as decanting tanks or a centrifuge. Once the tramp oil is thoroughly combined into the metal removal fluid, removing the tramp oil by centrifuging will remove a portion of the metal removal fluid since the two fluids are homogeneous.
Caution There have been some advocates that support the practice of intentionally emulsifying the tramp oil into the metal removal fluid. This is not an acceptable control plan since sulphur, phosphorus, and tackifiers can be present in the tramp oils. Machine lubricants are typically paraffin-based oils and may not be comparable with the naphthenic oils used in the base
LUBE MAGAZINE NO.174 APRIL 2023 35
No.145 page 4
Figure 3 demonstrates various reactants involving tramp oil.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
