Guest post by James Pryor
We like to make parts. That is the nature of our business. When we think of workplace safety we generally think in terms of accidents related to the fabrication of machined parts such as hand and eye injuries.
However, the most frequently cited threat (Current OSHA data) safety violation for machine shops is the Control of Hazardous Energy (Lockout/ Tagout). – OSHA 10/09 -09/2010.

I prefer a padlock myself...

 Lockout / Tagout OSHA standard 29 CFR 1910.147 requires all employers to provide protection for employees performing maintenance and servicing on equipment or machines from the accidental start up or release of energy which could result in an employee being injured.

  • When was the last time you reviewed your control of hazardous energy procedures?
  • When was the last time you performed an audit to assure they are being followed?
  • Does someone review the requirements for control of hazardous energy whenever there is a change in your systems such as the introduction of new equipment?

 Training on these changes is a federal requirement.
The following review  questions are provided to help you assure that your control of hazardous energy covers all the bases.

  • Do you have a written company policy on the control of hazardous energy? Is the role of management clearly defined?
  • Have supervisors been trained in lockout/tagout procedures?
  • Have authorized employees been trained in lockout/tagout procedures?
  • Have affected employees been trained in lockout/tagout procedures?
  • Have other employees been trained in lockout/tagout procedures?
  • Are the approved locks and tags in place and in use?
  • Is there a written lockout / tagout procedure and have employees been trained?
  • Does this plan include warnings, testing and positioning of equipment and procedures for restoring machines and/ or equipment to normal production operations?
  • Does the plan include procedures for more than one person?
  • Does the plan include shift changes?
  • Does the plan include an annual audit of authorized employees?
  • Does the plan include procedures for multiple energy source equipment?
  • Does the plan include minor tool changes and adjustments?
  • Does the plan include emergency lock removal procedures.?
  • Does the plan include provisions for qualified employees?
  •  Does your company enforce the plan and document enforcement?
  • Does the plan allow for re-training?
  • Does the plan clearly define roles and responsibilities?

Control of hazardous energy is the most cited failure in our industry, we hope that these review questions will help you keep your workers safe and your program in compliance.

Hardness of Quench and Tempered alloy steels is a function of the tempering temperature. The higher the tempering temperature, the lower the hardness.
This is called an inverse relationship.
And it’s why some people call tempering “drawing.”
The temper “draws the hardness out of the steel.”

Normalized at 1600F, Quenched in oil 1550 F, Tempered 2 hours

 These curves are a rough approximation of the as tempered brinell hardness for the grades shown. For example, I have other data for 4340 that shows 440 BHN at 800F; 410 at 900F; 380 at 1000F; 340 at 1100F, and 310 at 1200F temper temperature.
Fire! Can't do a blog on heat treat without a picture of fire.

Your mileage may vary, in other words, but this graph is close enough for ‘considered judgement.’
Additional 4140 data that I have from my notes suggests 397 BHN at 800F; 367 at 900F; 335 at 1000F; 305 at 1100F and 256 at 1200F.
If you have better data from your process – USE IT.
Better yet, if you have time, send a sample to your heat treater for a pilot study.
In the absence of data from your process, the above figure and data will give you “a place to stand” in understanding what is possible when heat treating .40 carbon alloy steels- the steels most commonly encountered in our precision machining shops for Automotive, Aerospace, Agricultural and general applications.
Here is a video from PMPA member company Nevada Heat Treating to give you an inside look at what goes on at a heat treat service provider.