significantly changed within the last decade. Driven by the growing demand on high VI-base stocks for automotive oils, the capacity for group I oils is shrinking in many parts of the world as several production sites were closed. On the other hand, huge base oil facilities for group II and group III came on stream in the US, Europe and Asia.
Group I to III base oils are produced from petroleum crude oil by refining processes. Due to the higher quality and severity of the refining, the content of sulfur, aromates and unsaturates declines with the higher group and the viscosity index increases. The lower concentration of aromatic and other unsaturated compounds however results in a much lower solvency towards many types of lubricant additives. The solubility of many polar additives in group II or group III base oils is often not sufficient enough to achieve a concentration which meets the requirements of a certain lubricant application or metalworking process. This includes extreme pressure (EP-) additives based on sulfurized esters and triglycerides, anti-wear (AW-) additives, corrosion inhibitors and antioxidants. The addition of solubilisers can help to increase the solvency of low polar base oils but may also show negative effects like poor thermal or oxidative stability or insufficient elastomer compatibility.
The development of new lubricant additives with specifically adapted chemical structures makes it possible to formulate industrial lubricants or metalworking fluids based on low polar group II or group III base oils and even based on polyalphaolefin, without any lack of performance.
The formulation of soluble oils or semi-synthetic water-miscible MWF with group II – IV base oils requires an adaption of the emulsifier system.
as toxic to aquatic organisms, carcinogenic to rats and mice and possibly carcinogenic to humans. Hence, they were already banned and eliminated from metalworking fluid formulations in Europe and other regions. Medium chain chlorinated paraffins (chain-length C14 – C17) are supposed to be banned as well in many countries within the next years because of their risks to the ecosystem and to human health.
In most literature it is reported that the chlorinated paraffins act in a way that they coat the metal surface with a metal chloride film under the influence of high pressure. FeCl2 melts at 672°C and has low shear strength when compared with steel, thus it is able to prevent cold welding between metal surfaces. New research regarding the working mechanism of chlorinated paraffin molecules towards metal surfaces indicates that their outstanding lubricity is primarily a result of their physical adsorption properties. The ability of forming pressure stable adsorption layers is depending on the presence of charge centers in the additive molecule, in case of CLPs caused by chlorine atoms. Increased machining speeds, however, also induce higher temperatures of the metalworking process. Under these conditions CLPs still provide good lubricating properties but tremendous chemical wear. In practice, chlorinated paraffins with ~40 to 70 wt% chlorine are used as additives in metalworking applications; however, they are sensitive to moisture and light and can easily evolve into hydrogen chloride which can cause severe corrosion of metal surfaces. The following field tests were carried out to demonstrate the possibility to replace chlorinated paraffins in heavy duty metalworking processes.
Hobbing
In a hobbing field test, the influence of the cutting speed on the performance of a chlorinated paraffin was analyzed and compared to a special sulfur containing EP additive based on olefin and ester as well as to a phosphorous and sulfur containing anti-wear additive. At low cutting speed it was found that the chlorinated paraffin formed an adsorptive layer that effectively protected the hobbing tool from wear. The special sulfur carrier which was also used for the field test, showed a clearly lower performance. Only by a combination of the sulfur carrier with a metal free anti-wear additive it was possible to outperform the CLP. By increasing the cutting speed, the temperature of the process also increased which led to an increased tool wear when using the chlorinated paraffin. This effect can be explained by the thermal decomposition of the CLP followed by the formation of hydrogen chloride. In contrast to the CLP, the sulfur containing EP-additive gained outstanding tool life with increasing machining speed (figure 2).
Figure 1. EP-additives based on sulfurized triglycerides, solubility in group III oil. Left side conventional chemical structure, right side modified chemical structure with improved solubility
Replacement of chlorinated paraffins Chlorinated paraffins (CLPs) were one of the earliest EP- and AW-additives used in lubricants. They are still widely used as additives in metalworking fluids for a broad variety of manufacturing processes, especially for heavy duty processes like broaching or fine blanking of stainless steels.
Short chain chlorinated paraffins (chain-length C10 – C13) are classified as having a high potential for bioaccumulation if found to be present in the environment. Furthermore they are classified
Figure 2. Results of the hobbing field test Continued on page 8
LUBE MAGAZINE NO.139 JUNE 2017
7
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 |
Page 69 |
Page 70 |
Page 71 |
Page 72