Foaming- Why Base Oil Differences Matter In Your Shop.

November 6, 2017

You don’t need a degree in Organic Chemistry to understand the differences in your shops’ metalcutting fluid base oils and what they mean to you.

Synthetic base oils clearly are less prone to foaming than mineral oil base stocks.

A recent discussion on PMPA’s member’s only Technical Listserve centered around the issue of foaming in our machines and its relation to the type of cutting oil selected for use in our CNC and Swiss machines.

John Wiley, Business Development Manager for PMPA Technical Member Qualichem, Inc. contributed a nice piece of sensemaking regarding the role that the selection of base oil plays in the foaming we encounter on the machine.

“In this picture you can clearly see the differences in a base oil’s tendency to foam.  These are pure base oils, nothing added.  Poly Alpha Olefin (PAO) and Gas To Liquid (GTL) synthetics are  identical, while the two mineral oils foam considerably more than the synthetic stocks.  If you are a shop that has yet to experiment with new cutting oil technology, now is the time.  The benefits are firmly within your budgets. If you are doing medical work, the GTL oils are ideal.  If you are running lights out operations, the GTL are ideal.  If you want a cleaner shop, cleaner machines and cleaner parts, GTL is ideal.”

John went on to describe the scenarios where PAO’s and GTL’s would be expected to be the best choice for certain operations (like high pressure pumps) and applications, as well as compared the economics of  PAO’s and GTL’s. Our members got actionable insight as to the effects of the base oil in their metalcutting fluids in terms of both performance and economics.

You may not know a lot about Organic Chemistry, but the photo above is worth a semester in class (as well as a thousand words!) to show us why now is the time to consider Synthetic base oils in our CNC and High Pressure coolant metalcutting operations.

Qualichem,Inc.

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Top Ten OSHA Violations in 2017

October 4, 2017

Deputy Director  of OSHA’s Directorate of Enforcement Programs Patrick Kapust presented the agency’s preliminary list at the National Safety Congress and Expo on September 26.

Powered Industrial trucks 1910.178 makes the TOP TEN again in 2017

Here are the Top Ten, along with the number of citations.

  1. Fall Protection – General Requirements (1926.501) – 6,072
  2. Hazard Communication (1910.1200) – 4,176
  3. Scaffolding (1926.451) – 3,288
  4. Respirator Protection (1910.134) – 3,097
  5. Lockout/Tagout (1910.147) – 2,877
  6. Ladders (1926.1053) – 2,241
  7. Powered Industrial Trucks (1910.178) – 2,162
  8. Machine Guarding (1910.212) – 1,933
  9. Fall Protection – Training Requirements (1926.503) – 1,523
  10. Electrical – Wiring Methods (1910.305) – 1,405

If you are just now reviewing your OSHA training  performance, these standards would be a great place to start.

The  items numbered 1910 are General Industry, those numbered 1926 are Construction.

Photo courtesy Staffing Talk


Employment Population Ratio- Good News

April 18, 2017

The BLS’s Employment Population Ratio was 60.1 in March 2017, its first time back over 60% since February 2009.

February 2009!

This indicator actually shows what it purports to, unlike the U-3 (headline) Unemployment rate.

Not since February 2009…

The U-3 Unemployment rate may actually fall if workers give up looking for work, as the labor market falters. As the labor market is recovering,  the U-3 unemployment rate can rise because more people are re- entering the labor force as they start to look for work again.

The Employment-Population ratio, because it is unaffected by voluntary changes in labor force participation, is a useful indicator of current labor market conditions. Lows in the employment-to- population ratio correspond with economic downturns. The employment-to-population ratio holds clear and discernible implications for the labor market, both among and between segments of the population.

The Employment-Population ratio is a useful indicator. And currently, a positive one.

BLS Employment Population Ratio


Thank You to My Readers

April 12, 2017

Actually, a million thank yous! Thanks to readers like you, SPEAKINGOFPRECISIONBLOG has over 1,000,000 views.

1,000,000 views!

Our first post  was from June 30, 2009 and remains as relevant to day as it did then: 5 Reasons to choose a Career in Precision Machining

We’ve come quite a way since that very first post!

What do you like? 

Our post on The Difference Between Accuracy and Precision Measurement in Your Machine Shop is our most popular with 44,445 views.

Hardness vs. Hardenability- There is a Difference is our second most popular post at 35,780 views.

5 Facts About Manganese in Steel, 7 Causes for Quench Cracking of Steel, and Why Manufacturing is the Right Career Choice- DATA! all came in between 21,000 and 30,000 views each.

Average number of times a post gets seen on PMPASPEAKINGOFPRECISIONBLOG: 1048 times.

1,000,000 is an aspirational number. How many of us get to measure anything that we do in quantities of millions?  (Actually, all of our shops do, they call it “normal production!”)

But as an individual, as someone sharing knowledge and experience- 1,000,000 views;  1,000,000 shares of information; 1,000,000 human to human connections- that is an unexpected and very satisfying validation.

Thank you for spending a small part of your day with me here at my blog.

Together, we’ll continue to make sense of the the issues that make a difference to all of us in North American Manufacturing.

Especially Precision Machining.

1,000,000 views!

Do I believe in the power of social media to help us connect and share?

You bet I do! 1,000,000 times YES!

Tooting Own Horn  photo credit.


Decarburization and Your Precision Machine Shop

March 17, 2017

Decarburization on surface layers can affect heat treatment and hardness attained on parts. Decarburization also provides evidence of where in a process a defect or imperfection occurred.

Most defects  in steel workpieces encountered in our precision machine shops are longitudinal in nature. While their presence alone is enough to concern us, for the purposes of corrective action, it becomes important to identify where in the process the longitudinal imperfection first occurred. Visual examination alone is not enough to confirm the source. Did it occur prior to rolling? During rolling? After rolling? Understanding decarburization and how it presents in a sample can help us to identify where and when  in the process the imperfection first occurred.

The question that we want to answer as part of our investigation is usually “When in the process did the defect first occur?” Looking at decarburization and any subscale present can help us answer that question with authority.

What is Decarburization?

The light area (ferrite) surrounding the dark intrusion is decarburization. note the lack of pearlite in this decarburized (lighter) zone. There is no evidence of scale, indicating that this defect was created during, rather than prior to rolling.

“Decarburization is the loss of carbon from a surface layer of a carbon containing alloy  due to reaction with one or more chemical substances in a medium that contacts the surface.”Metals Handbook Desk Edition

The carbon and alloy steels that we machine contain carbon. In the photo above, the carbon is contained in the pearlite (darker) grains. The white grains are ferrite. In an etched sample, decarburization surrounding a defect is identified as a layer of ferrite with very little, or none of the darker  pearlitic structure typically seen in the balance of the material. The black intrusion in the photo above is the mount material that has filled in the crevice of the seam defect.

What is Subscale?

The grey material adjacent to defect within the white decarburized area is subscale. This subscale is evidence that the crack was present on the bloom prior to reheat for rolling

Subscale is a reaction product of Oxygen from the atmosphere with various alloying elements as a result of time at high temperatures. The presence or absence of the subscale is the indicator that helps us to pinpoint the origin of the defect. For a subscale to be present,  the time at temperature must be sufficient for oxygen to diffuse  and react with the material within the defect. According to Felice and Repp, 2250 degrees F and fifteen minutes  is necessary to develop an identifiable subscale. Lower temperatures would require longer times. Typically rolling mill reheat cycles offer plenty of time to develop a subscale in a prior existing defect. However, for defects that are created during rolling, the limited time at temperature and the decreasing temperatures on cooling make formation of subscales unlikely.

Reading Decarb and Subscale to Understand the Defect

Decarburization is time and temperature dependent. This means that its relative depth and severity are clues as to time at temperature, though interpretation requires experience and understanding of the differences in appearance from grade to grade based on Carbon content.

Symmetrical Decarburization

If the decarburization is symmetrical this is an indication that the defect was present in billet or bloom prior to reheat and rolling. oxygen in the high temperature atmosphere of the reheat furnace depletes the carbon equally from both sides of the pre-existing defect.

Asymmetrical Decarburization

Decarburization that is obviously asymmetrical indicates that the defect is mechanical in nature and was induced some time  during the hot rolling process.

Ferrite Fingers

Unetched specimen of seam (top). Etched specimen showing “ferrite finger.” (Bottom)

Ferrite fingers are a surface quality problem that is associated with longitudinal bar defects. During reheat, a defect in the bllom or billet is exposed to high temperature atmosphere, forming decarburization and subscale  around the defect. Rolling partially closes or “welds shut” the crack. However, a trail of of subscale is entrained in a  formation of almost pure ferrite which has been depleted of pearlite, carbon and alloy by the reaction at elevated temperature.   This trapped scale remains a potential oxygen source, driving further internal oxidation and decarburization if temperatures remain high.

Continuous improvement requires  taking root cause corrective action. Obviously identifying the root cause is critical. When we encounter longitudinal linear defects in our steel products, using a micro to characterize the nature of the decarburization and presence or absence of sub scale or ferrite fingers are important evidence as to when, where, and how in the process the defect originated.

 

 

 


Stress Cracks in Steel Bar Products.

March 14, 2017

“Stress cracks are defined as transverse or near transverse open crevices created when concentration of residual stresses exceed the local yield strength at the temperature of crack formation. These stresses can be mechanically induced or can be attributable to extreme temperature differences and /or phase transformations. They can originate at almost any point in the manufacture of the steel.”AISI Manual Detection, Classification, and Elimination of Rod and Bar Surface Defects

Stress cracks are often found visually  at locations that experience bending or straightening. They are also referred to as “Cross Cracks” or “Transverse Cracks.” Originally they were identified in mill billet and bloom products, prior to rolling.

Micro examination can help determine crack origin by noting:

  • Orientation
  • Intergranular nature
  • Presence of scale
  • Presence of subscale

Additional microstructural characteristics can reveal the thermal history of heating and cooling at the crack location.

This photo shows stress cracks on a conditioned billet.

Causes and Corrective Action

  • Excessive load during straightening can exceed the local yield strength of the material causing it to crack; reduce load applied by machine, or consider tempering or stress relieving material prior to straightening or further cold work.
  • Cooling too quickly can also induce stress cracks. Critical cooling rates are highly dependent on steel chemistry. Crack sensitive chemistries (Medium carbon and high carbon steels; also medium and high carbon steels with straight chromium or straight manganese additions.) These steels should be slowly cooled through transformation temperatures to minimize the occurrence.
  • Design faults such as
    • Heavy sections adjacent to light sections and sharp corners 
    • Failure to fillet sharp corners
    • Use of fillets rather than tapers
    • Undercuts
    • Overloading the material during fabrication, processing, or application.

Detection of stress cracks  is problematic as their transverse orientation makes them difficult to detect on equipment set up to detect longitudinal defects.

Final caveat: The term stress crack is arbitrarily defined based on industrial usage in the market. It does not necessarily imply anything about the specific metallurgical nature of the crack, I know that a number of people use the term “stress crack” to describe longitudinal cracks on steel bar products as well, which the AISI calls “Strain Cracks.”

 

 


December ISM PMI Positive Bellwether for 2017

January 5, 2017

The Institute for Supply Management announced on Tuesday that its Purchasing Manager’s Index (PMI) for Manufacturing index rose 1.5 percentage points to 54.7 in December, its highest level in two years and up from 53.2 in November.

This is great news- let’s look at some details to find out why:

  • New Orders component– new orders rose 7.2 percentage points to 60.2 – their highest level since November 2014
  • Strength in Employment component– employment rose 0.8 percentage point to 53.1 – the highest since June 2015
  • And strength in the Production component-production improved to 60.3- very unusual outcomes for Manufacturing in December.

This is an unexpectedly solid report showing Manufacturing industry performance stronger in December than in November.

Highest in 2 years and up 1.5 points over November 2016

Highest in 2 years and up 1.5 points over November 2016

Here is why we see this as a bellwether for a great 2017 for our precision machining companies.

  • U.S. Light Vehicle (Auto) Sales set annual sales record according to the Wall Street Journal and reports we heard from online videos from AUTO NEWS. “A total of 17.55 million vehicles were sold in 2016, roughly 60% of which were classified as light trucks” according to the Wall Street Journal.
  • 2016 sales volume was up ~ 700,000 light vehicles, according to reports from Auto News
  • The average age of the U.S. Light Vehicle Fleet in 2016 was a record 11.6 years, According to Statista online, 

There is still plenty of reason to expect demand for light cars and trucks to be sustained based on the average age of the U.S. Fleet and the current low unemployment rate reported by the Federal government. Knowing that Automotive is the precision machining industry’s most heavily served market convinces us that these numbers reported by ISM, WSJ, Auto News and Statista bode well for our precision machining shops in 2017. I hope that you are preparing for success, not for hunkering down in 2017.

Happy New Year, indeed!

Auspicious!

Auspicious!

 

Link to ISM December 2016 report

Statista Age of Light Vehicles in U.S.

Calculated Risk December ISM Post and Chart