Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
10. Poor cold-water mixing. 11. Freeze/thaw stability. 12. Poor initial mixing. 13. Poor grounding / stray direct currents / storage tank.
Any one of these Category 1 or 2 identified failure mechanisms can severely impact or even destroy the fluid stability and/or performance. When this happens, production rates decline, tool wear increases, residues build on machine surfaces, corrosion cells develop, foul odours increase, and worker health and safety may decline.
This paper will only address the five basic failure mechanisms and a control plan for each mechanism. Rarely will only one failure mechanism be present. It is more likely that three failure mechanisms will be present at any one time. The control plan must be implemented before the failure mechanism occurs. Once a metal removal fluid has failed, it is unlikely that it can be returned to an acceptable condition with sump-side additives. Refer to Figure 1.
Failure mechanisms and control plans
1a. Attack by positively charged contaminants: cut or ground metal surfaces Properly formulated metal removal fluids are a careful balance of interactive chemistries. If one of the key components is neutralised or removed, the fluid will deteriorate. Most modern fluids have common negatively charged (anionic) chemistries. These chemistries are common in emulsifiable oil, semi-synthetic, and true solution synthetic fluids. These negatively charged chemistries can be from soaps, fatty acids, and wetting agents.
When metal is cut, the exposed surface has a positive (cationic) charge. Iron has two or three positive charges, aluminium has three positive charges, magnesium has two positive charges and copper
No.145 page 2
has two positive charges. The freshly cut surface of the metal is highly active and reacts with the anionic chemistries in the metal removal fluid. This reaction of the cation metal surface and the anion chemistry forms an insoluble precipitate that binds to the metal chips, the metal part, or the machine surface. If the fluid is filtered, then this precipitate is removed from the metal removal fluid and it continues the failure process. Imagine links in a chain. Metal removal fluids are a balanced mixture of chemicals consisting of up to 25 raw materials. If one or two of these chemicals is partially or completely removed, then the chemical “chain” weakens or separates (i.e. fails).
It is important to note that this is a metal surface area reaction. Therefore, the more particles that are generated in the chip-making process, the more positive charges are generated because of the increased surface area. This reaction can be observed in the manufacturing environment. Single-point turning operations have a lesser effect than fine grinding or polishing operations, which have a more severe effect on fluid stability. Certain metals are more reactive than others. Grinding cast iron (a reactive metal) will generate very small particles with 2 or 3 positive charges. Single-point turning of ANSI 316 stainless steel will have a lesser effect per pound or kilogram of metal removed because less surface area is exposed in the chip-making process, and stainless steel is less reactive.
Refer to Figures 2A and 2B to understand how metal ions react with emulsions.
Figure 2a: Failure Mechanism #1 - Cation Attack.
LUBE MAGAZINE NO.174 APRIL 2023
33
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
