Our post on No Gloves When Working on Grinders has prompted a number of responses.
Here are some additional reasons why you should not even need gloves when working on grinders and grinding machines.
Issue: “There are sharp edges or burrs  that will cut me if I hold the part. The grinding will be to remove the burrs.”
Response: Use a file to knock down the burrs so that you can safely hold the part for grinding. Or use leather finger cots to grip the part for grinding.

We permitted these for use on belt grinders for holding small parts.
We permitted these for use on belt grinders for holding small parts.

Issue: “The part gets too hot to hold.”
Response: Then you are grinding wrong. Here is a list of some of the things that can go wrong  by letting the heat of grinding get out of control:

  • Remove the temper from Steel. Especially on tools, loss of temper means loss of tool hardness and edge life. A drop from Rc63 to about Rc48 for a couple of tenths (0.0002-0.0005) can contribute to side wear and edge failure.
  • Crazing or checking on Carbide can be caused by burning during grinding.
  • Work Hardening. Overly shiny surfaces are usually the clue that work hardening has occurred.
  • Creation of untempered martensite.

Untempered martensite can be formed in high carbon and alloy steels by getting high surface temperature from grinding- red heat- then quenching in water.

  • Untempered martensite is very brittle and reduces toughness.
  • Keeping the work cool  continuously while grinding is an important aspect of preventing damage to work, the wheel, and injury from occurring to the worker. Hogging off material and infrequently quenching is a great way to destroy a tool by grinding
  • Water needs to be plentiful to absorb the heat from grinding,  and frequently used to reduce heat buildup in the work.
  • Take multiple small passes  and cool in between in a large bath of water while grinding to minimize heat build up.

Of course, wearing the required PPE, making sure the grinding wheel is properly dressed, all guards are in place and properly adjusted are also key to safe grinding in our shops.
Bottom line: If the work is too hot for your fingers, it may be approaching the danger zone regarding loss of mechanical properties and function in end use.
Photo credit
 

Some built up edge (BUE) is normally encountered in machining

Built Up Edge (BUE) is the accumulation of workpiece material onto the rake face of the tool. This material welds under pressure, and is separate from the chip.
In school we were taught that this is because the first material to contact the tool workhardens, and we did hardness tests to confirm this.
Because BUE changes the effective geometry of the tool, it can have either positive or negative effects.
Positive effects

  • Less tool wear
  • Lower power requirements
  • Less contact of the workpiece with the tool (It contacts the BUE instead)
  • Better surface finish and improved process capability

These effects are only beneficial if the BUE is thin and stable. Machining additives such as sulfur combine with manganese to form manganese sulfides. Manganese sulfide helps to control BUE because of its anti weld properties. On resulfurized steels, BUE is usually stable and not a problem.
Negative effects

  • Poor tool life
  • Poor and variable surface finish ( As the BUE sloughs off the tool, it can weld to the workpiece)
  • Loss of statistical capability on dimensional control
  • Loss of uptime trying to troubleshoot the process

I have found that BUE is more likely on alloys that work harden.
In order to get BUE under control, the steps that you take depend on the tool material.
For Carbide

  • Decrease the feed. (Pressure welding  usually is the culprit)
  • Increase the speed
  • Increase the rake angle or “hook”
  • Get a better metalworking fluid (including get the fines out of your existing MWF!)
  • Get a different coating

For High Speed Steel (HSS)

  • Reduce speed

If the tool is High Speed Steel (HSS) you may think you are in oppositeland when you discover that slowing down the speed reduces the build up. I have found on HSS that as speed (heat increases) so does the tendency to form BUE.
Graphic.
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