Extreme Pressure Additives

To avoid metal to metal bonding during an extreme pressure operation the use of sulphur, chlorine and phosphorus will stop build up on the tool. These three products when used in this situation are known as EP additives and should be considered when choosing a metal working fluid for your application. When used as EP additives chlorine & sulfur become active at higher temperatures to maintain a fluid’s lubricity where the tool meets the work piece. Chlorine is active from about 200°C to more than 500°C and sulfur from about 650°C to over 950°C.

When working in a job-shop type of environment, EP additives can aid machining in day-to-day activities, things change however, when we talk about aerospace machining and every manufacturer of metal working fluids offers a number of chlorine & sulfur-free coolants. The lack of these additives would traditionally mean a loss of lubricity and consequently, an increase in friction and heat at higher temperatures and pressures.

Using the correct coolant is especially important in the aerospace parts industry where they machine aerospace alloys such as titanium. This industry tends to stay away from coolants with chlorine as it can cause hydrogen embrittlement in titanium. This can cause the part to form microscopic fissures, weakening the material and causing it to crack. Metal working fluid manufacturers however, can replace these additives with partial boundary lubricants such as esters and fatty oils.

So, while EP additives can do many good things for general machine shops, please make sure you look at the application and material before picking a coolant to ensure maximum performance and no damage is being caused to your parts.

Hard Turning – To Cool or not to Cool, that is the question.

The application of coolant in hard-part turning is a widely debated topic. “Coolant use is not recommended for hard-part turning as it offers no benefit to tool life”, said (Sandvik product specialist, David) Andrews. “It can be used however, to keep parts cool for accurate measuring and to clear away chips from the workpiece.”

In hard turning most of the heat removed in the chip itself, however, some residual heat will be trapped in the workpiece and tooling. CBN tooling is designed to run at very high temperatures, which is why it is a good choice for hard part machining.

Some tooling manufacturers not only recommend the use of coolant, but recommend its application at high volumes and high pressures.

“We tell our customers to either use no coolant at all or use a lot of it. There is no in-between in hard-part turning.” explains Iscar Product manager, Steve Geisel.

Ultra-high pressure coolant can be in the 2,500 – 5,800 psi range.

“There are benefits to be gained from using high-pressure coolant, especially at the cutting edge. It’s all about chip control, tool life, and speed” said Geisel. “If you apply coolant with a high pressure coolant system, you can run two to three times faster, while at the same time getting longer tool life.”

Adapted in part from the article, Hard Turning. CIM Magazine. April 2011. www.cimindustry.com