Pneuma-Tool Inc.
Impact of Heat
Scorched seals, burnt pistons, heat fractured vanes, black carbonized parts.

These are all indications of the tremendous heat buildup within percussive mining equipment. The color chart on the left side panel enables mechanics to estimate the temperature to which the parts they are replacing or repairing have been subjected. It is not uncommon for parts to turn blue after a hard service period, which indicates that they have been exposed to temperatures in the range of 550 - 575F.

Too bad that the conventional rock drill oil that you're using fails at just over 425F.

And don't look for help by switching to liquid rock drill greases. The photo below shows an overbased calcium sulfonate grease after a brief exposure to 300F. The liquid grease has separated into two phases. The center glob is the calcium component, and surrounding it is the mineral oil phase. Once the calcium component is repeatedly exposed to high temperatures, it can form hard deposits that can block lubricant flow, potentially resulting in premature equipment failure.
Source: http://www.pneuma-tool.com/Impact_of_Heat.html
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