Continued from page 7 Groove broaching
The negative performance of CLPs becomes even more apparent in more severe cutting processes like e.g. broaching. Particularly broaching tools can be very expensive. Regrinding and recoating of these tools due to excessive wear will not only lead to a down-time of the machine but will also add significant costs to the overall process. Therefore an improved tool life through optimal tool protection is the key factor for modern broaching processes. In the past broaching machines were operated at relative low speeds and chlorinated paraffin containing metalworking fluids worked just fine. With the demand for higher throughput, better surface quality of the work piece, lower production costs and improved worker’s and environment safety, there is a need to introduce new technologies to overcome the problems linked to chlorinated paraffins. Optimized formulations based on special light color low odor sulfurized products combined with anti-wear additives can cover a much wider range of cutting speed variations than oils based on chlorinated paraffins.
The broaching test was carried out with a cutting speed of 24m/minute using TiN coated tools and high alloyed steel work pieces. The most critical points of the broaching tool are the angles of the cutting edges where the mechanical and thermal stress is very high. Different broaching oil formulations were assessed in the field test. The first formulation which was containing a combination of chlorinated paraffin and sulfurized olefin showed very low angular wear at the beginning. After manufacturing some hundred parts the wear rose significantly. Again this effect can be explained by the formation of hydrogen chloride which corrodes the TiN coating of the broaching tool. The performance of the CLP containing formulation could be exceeded by a combination of sulferised olefin and inactive sulfurized ester which was tested afterwards. The best results in the groove broaching test were obtained by another broaching oil formulation which was combining a sulfurized olefin with a special sulferised EP-additive based on reaction products of hydrocarbons and triglycerides (figure 3). In conclusion the test results showed that a combination of sulfur containing EP-additives shows significant advantages regarding tool life in a groove broaching process when compared to a chlorinated paraffin containing broaching oil.
protection against adhesive wear chlorinated paraffins are still used there today. An example of such a severe forming operation is the fine blanking of stainless steel which is defined by the following parameters:
- Slow relative speed - Low process temperature -
Extremely high-pressure
- Large area of activated, fresh metal surface in direct contact with tools
- Boundary lubrication conditions
To simulate the fine blanking process the so called “Press-In- Test“ was used. In this test an oversized steel bolt of 30.1 mm diameter is pressed with a speed of 20 to 200 mm/min into a die with an inner diameter of 30.0 mm. The resulting radial pressure is approximately 180 MPa (approx. 26100 psi). The friction forces are recorded and used for the evaluation of the tested lubricants. Additionally the bolt and the die are examined after the test for wear, welding and material adhesion.
A suitable additive or additive combination which is able to replace chlorinated paraffin in this test has to show a similar affinity to metal surfaces to form pressure stable friction reducing molecular layers. Therefore polymeric sulfurized additives containing multiple polar centers and polar anti-wear additives were tested. By combining both additive types it was possible to reduce the friction force by approximately 30% in comparison to a sample containing 40% of chlorinated paraffin. A combination of a standard sulfurized ester and a polar anti-wear additive was not successful (figure 4).
Figure 4. Results of the Press-in-Test
Conclusion from the Field Test Results In many cases it is possible to replace chlorinated paraffins by alternative performance additives. An easy 1:1 substitution like x% chlorine = y% sulfur or phosphorous, is probably impossible due to the multi-functional properties of CLPs. However, by combining suitable lubricant additives it is possible to adjust the characteristics of the metalworking fluids to the specific demands of the metalworking processes and to even exceed the performance of CLP containing cutting and forming lubricants.
Figure 3. Results of the groove broaching test Press-In-Test
The substitution of chlorinated paraffins by suitable additive combinations is also possible for metal forming operations. Because a high performance forming oil has to give excellent
LINKS
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LUBE MAGAZINE NO.139 JUNE 2017
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