Month: August 2010

6 Reasons To Consider Rolled Threads

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Because the steel grain structure is cold forged, rather than cut, rolled threads are up to 30% stronger…

Sketch iluustrating grain flow lines due to cold work of rolling.

While the strength of a thread is a function of section thickness, a thread rolled rather than cut thread is usually superior in mechanical properties, all other things being equal- here are 6 reasons why:

  1. The flow of the material by cold work during rolling reinforces the shape.
  2. The cold working strain increases mechanical properties, Surface Hardness,Tensile Strength, Yield Strength, and the Yield Strength / Tensile Strength ratio.
  3. The surface finish of the thread flanks is usually smoother due to the burnishing action of the rolls.Smoother finish means better fatigue life and fewer opportunities for stress risers.
  4. There is more material (section thickness). This results in material savings*, since the diameter of the blank will be between the major and minor diameter of the thread, rather than greater than the major diameter for a cut thread.
  5. The compressive stresses on the threads resulting from rolling improves the fatigue life.
  6. The root of the thread has a smoother radius, improving fatigue life.

Schematic view of the thread rolling process.

Pictures courtesy PMPA member Ray Industries
Click here for a video of the thread rolling process in action from PMPA member Rolled Threads Unlimited LLC.
*I got my first “learnin” on rolled threads at my customer Keystone Threaded Products back when my hair was not silver and B.K. (Before Kids): “Why do you always buy funny sizes Jim?” I asked. That was a great first lesson on how engineering can add savings:
Blank diameter will be between major and minor diameter = $ Saved.

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Believe in Manufacturing

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Our colleague Ryan over at Change the Perception wrote a wonderful piece the other day, and it was just so powerful I wanted to help him share his thinking. Here  is  his statement of faith about Manufacturing:

Thanks for sharing!

  • It is my belief that creating tangible goods is the foundation for all economic growth.
  • I believe our society should value people that choose to work with their hands, because these are the people that possess the skills to grow our economy.
  • I believe government should only involve themselves with manufacturers insofar as they help them, support them, protect them and enable them to thrive.
  • Taxes on manufacturers should be minimal.
  • Manufacturing education should be integrated into ALL levels of education. It should never be cut from a school budget…ever!
  • I come from a family and/or community that depended on manufacturing, I saw how many good jobs were created through it, I intend to build our community/state/nation with this model in mind.

    • WOW! This is some thoughtful and passionate thinking.
    Ryan had one more point, and it was aimed at the politicos who go up to Washington D.C. to represent OUR interests but then succumb to the “agency problem”- that is, they do only what helps them stay in power. Here is Ryan’s last tip for elected officials who really care about a strong U.S. manufacturing capability:
    “I understand that I may have to make decisions that could be perceived as politically damaging to myself or my party, and threatening to my own reelection; but if my decisions help American manufacturer’s, I’m going to do it anyways.”
    Ryan, I would call that “statesmanship.” Something we haven’t seen for a long, long time.
    If you were running, Ryan, you’d have my vote!
    To see Ryan’s full post click here.
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    Do As We Say- NOT As We Do

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    Warning, this piece is loaded with facts, not our opinions!

    Just the facts.

    We have written at great length here, here, here, and here, about OSHA’s plans to enforce safety regulations and fine violators. The “new sheriff in town” is on a mission.
    So imagine what we felt when we found this report detailing 6,300 safety hazards just in Capital Hill Buildings.

    • 1058 fire hazards
    • 1742 electrical problems
    • 102 storage shelving violations
    • 70 machine guarding violations (In the last fiscal year, the machining industry had just  56 violations.  See the link here. Capital Hill machine guarding violations alone are equal to about 125% of the entire machining industry’s violations for the entire country in 2009)
    • 25% of hazards continue to be high risk to employees and visitors.

    6300 violations compared to 56 for the machining industry, thats 11,250% more violations than our machining industry.
    Library of Congress- 530 violations- not quite 10 times the violations of the entire machining industry..
    “Congress has one standard for itself and another for everyone else.“- Melanie Sloan, committee for Responsibility and Ethics in Washington.
    In other words “Do as we say, not as we do.”
    We could go on, but whats the point? You can read the report at this link.
    Here’s a wrap up quote from Senator Joseph Lieberman:
     “We are talking about the safety of real people…Congress’s failure to meet OSHA workplace safety standards means that it is putting the health- and possibly the lives- of its workers at risk…This state of affairs is not just bad public relations, it is bad government.“ (Page 16)
    So when you hear all that stuff about how the government is somehow more concerned about safety today- well, now you can see that they don’t practice what they enforce. That the push is for revenue not real safety.
    If it was really about safety, wouldn’t you think they’d make it safe to work for the government?
    That “new sheriff in town”  and this administration is merely trying to  enhance revenue collection from private manufacturers – shops like ours.
    If it was about safety, well, why wouldn’t they start on Capital Hill? Thats where 11250% of the violations are,  compared to machining.
     

    Thanks to Hypocrisy.com for the cartoon.

     
     
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    7 Causes For Quench Cracking Of Steel

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    Failures of steel parts in service or production occur very infrequently. However, when steel parts fail, the consequences are dire.

    Quench crack- this is not good!

    Here are 7 ways that steel can fail as a result of Quench Cracking from heat treatment.

    1. Overheating during the austenitizing portion of the heat treatment cycle can coarsen normally fine grained steels. coarse grained steels increase hardening depth and are more prone to quench cracking than fine grain steels. Avoid over heating and overly long dwell times while austenitizing.
    2. Improper quenchant. Yes, water, brine, or caustic will get the steel “harder.” If the steel is an oil hardening steel, the use of these overly aggressive quenchants will lead to cracking.
    3. Improper selection of steel for the process.
    4. Too much time between the quenching and the tempering of the heat treated parts.  A common misconception is that quench cracks can occur only while the piece is being quenched. This is not true. If the work is not tempered right away, quench cracks can (and will) occur.
    5. Improper design– Sharp changes of section, lack of radii, holes, sharp keyways, unbalanced sectional mass, and other stress risers.
    6. Improper entry of the part/ delivery of the quenchant to the part. Differences in cooling rates can be created, for example, if parts are massed together in a basket resulting in  the parts along the edges cooling faster than those in the mass  in the center. Part geometry can also interfere with quenchant delivery and effectiveness, especially on induction lines.
    7. Failure to take sufficient stock removal from the original part during machining. This can leave remnants of seams or other surface imperfections which can act as a nucleation site for a quench crack.

    Finally, materials that are heat treated to very high strength levels, even though they did not quench crack, may contain localized concentrations of high residual stresses. If these stresses are acting in the same direction as the load applied in service, an instantaneous failure can occur. This will be virtually indistinguishable from a quench crack during an examination, due to its brittle failure mode, lack of decarburization on surface of the fracture, or other forensic evidence of a process failure.
    When looking at quench cracking failures under the microscope, cracks and crack tributaries that follow the prior austenitic grain boundaries are a pretty good clue that grain coarsening and or its causes-  overheating or too long time at temperature- occurred. Temper scale on the fracture surface helps the metallurgist know that the crack was present before tempering. Decarburization may show that the crack was open prior to quenching.
    Photo1 Thanks to WIP SAMI over at British Blades for the photo.
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