The majority of defects encountered in steel bars in our shops are found on the surface. Internal defects can also be encountered, and we posted about central burst (chevron) defects here. This post describes Pipe Steel. Definition: A central cavity formed by contraction of the metal during solidification is called pipe.
When this cavity is found in wrought or cast products, this is also called pipe.
In the days of ingot casting, the location of the shrinkage cavity was controlled by ingot mold design and the addition of hot tops to assure that after cropping the material containing the void off, there would remain sufficient sound material to roll into product.
Today with modern computer controlled billet and bloom casting processes, pipe steel and center porosity is very seldom encountered.
Recently a question was asked about centerline defects on cast billets in one of my LinkedIn Groups.
“hello can any one tell us why some times whe have holes along the center of the billets just casted thanks”
Despite a lack of specifics about grade, deoxidation, and many other factors, we can make some comments based on the fact that this is continuously cast billets according to question.
Here are my comments addressing the continuous billet casting process and how it can be implicated in the creation of centerline voids (pipe steel defects). The three key parameters in the casting process that are most likely to result in centerline pipe are
Electromagnetic Stirring. EMS amperage and frequency (Together they drive intensity.)
1. Casting Speed– Incorrect casting speed can result in pipe/ centerline looseness/ porosity. This can be aggravated by issues with mold level control. Slow down your casting speed to get sufficient solidification.
2. Superheat is critical to maintaining the proper fluidity and solidification dynamics in the mold. Liquid metal shrinks in three steps; 1) volume decreases the liquid cools goes from the pouring temperature to the freezing temperature; 2) volume decreases as the metal solidifies. This is reinforced by the driving out of dissolved gases as the metal freezes; 3) the metal shrinks as it cools from solidification temperature to ambient temperature.
3. Electromagnetic Stirring (EMS)– If you macroetch transverse sections of the billets and still see columnar rather than equiaxed grain structure in the cast billet, it is a sign that the EMS is ineffective.
There are a host of other operating parameters as well as chemistry and processes that can contribute to porous centers or central cavity pipe steel defects. Here is a list of questions to help address these: Do you have adequate cooling water through the molds? Are you running EMS? What is the metallurgical distance on this caster? What is the mold level control? Evidence of turbulence into the mold? Meters per minute for casting speed? Shrouding status on nozzles? What was superheat? What was water flow? Do you have chemistry in control, steel deoxidized, so that the large void is a result of solidification shrinkage, not divorce of gas from the liquid steel? What is grade? What was deoxidizer? Continuous casting of steel is a complex process with a large number of operating parameters and processes that need to be in close control. Understanding how these parameters can impact the final product is critical to eliminating defects that result from lack of control.
The Precision Machining Industry continues to show solid sales in 2014. The PMPA Business Trends Index for July 2014 rose 3 points over last month (~2.5%) from 120 to 123. Up 8 points over July 2013. According to the Fed, Industrial Production (IP) for July was up 0.4% and Factory Output was up 1%. Our index out-performed these Fed Benchmarks.
Automotive is a market heavily served by our industry, and the Fed reported Auto Production to be up 10.1% in July. We believe our industry’s strong sales performance was a result of the surge in auto production in July.
Forward looking sentiment of respondents for next three months rose for Profitability; leveled off for Sales; while Lead Time and Employment declined.
The July Industry sales was right at the average of industry sales for the year to date.
July garnered a strong report.
See the July 2014 PMPA Business Trends Report here.
If a tool gets too hot to hold while grinding, you have already ruined it. You knew that, right?
By the time the heat gets to your hands and is too hot to hold, you have already lost the temper on the edge being ground. If you then put it in water to cool it down, depending on the material grade, the water quench is likely to help form untempered martensite, a very brittle microstructure. The tool will lose properties, and fail in very short order. Often with catastrophic consequences.
The point of grinding is to take very small amounts of removal by abrasion, not to create lots of heat by hogging the material off.
Heat treated tools are actually very sophisticated system involving the interaction of material chemistry, microstructure, mechanical properties (including hardness) and design. Out of control grinding practices can destroy this system with a single temperature excursion above the tool’s last tempering temperature and formation of untempered martensite by water quenching. Thanks to John Detterbeck at Lester Detterbeck Enterprises Ltd for sharing the above cartoon and confirming the failure mode.
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 burrsso that you can safely hold the part for grinding. Or use leather finger cots to grip the part for grinding.
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
If there is a worse combination than grinders and gloves, I don’t know what it is, except perhaps for gloves and a drill.
We posted a really cool video on our career blog about making a light saber sword here. But we were shocked to see the guys in the video wearing heavy leather gloves while working with grinders.
By “grinders,” we mean abrasive belt grinders, bench grinders, pedestal grinders, surface grinders, and also abrasive cutoff machines.
Sanders, polishers, and buffers that involve rotating wheels or transversing motion are also included in this classification for the purposes of hazard analysis. Here are 6 reasons to not wear/not permit the wearing of gloves while working with Grinders or Grinding Machines
In a resounding victory for actual manufacturers- the people that make things- the OMB reported today that the proposal to create a “Factoryless Goods Producer’ classification for the NAICS 2017 has been withdrawn.
PMPA has been on the forefront of challenging the classification which would have created a class of phantom manufactures that did not actually manufacture goods, but rather purchased finished goods for resale, and possibly from foreign sources. August 1 2012 link,March 17, 2014 link,July 16, 2014 link
On May 22, 2014, the Administration announced the U.S. Census Bureau was considering a proposal to count a business as a manufacturer even if they outsource all of the transformation steps traditionally considered production activities, or manufacturing. The proposal would have counted some activities outsourced overseas as U.S. manufacturing and included financiers and others as manufacturers even though they never visit a shop floor.
Among PMPA’s objections to the scheme were the following:
NAICS is based on the primary activity of an establishment.In the absence of actual production processes, the primary activity of the so-called “Factoryless Goods Producers” is Wholesale activity. “Factoryless Goods Producers” produce no goods, and employ no manufacturing processes. They do not “produce goods.” They employ actual manufacturers who utilize recognized transformative processes to manufacture goods. This makes the proposed FGPs best classified by their “process” as Wholesale trade.
NAICS is for classifying domestic activities only. In many cases, the outsourcing of the “Factoryless Goods Producer’s” actual manufacturing occurs overseas. The NAICS System is for classifying North American operations only. Classifying as a “manufacturer of record” any entity that outsources actual manufacturing operations to off shore / overseas companies allows the distortion of statistics based on said classification. Federal regulations are replete with rules regarding the origin and labeling of production. Yet the proposed change to recognize “FGP’s” as “Manufacturers” would foster the type of inaccuracy and mischaracterization that these labeling rules are expressly designed to prevent. An NAICS classification should not mislead the public that manufacturing occurred in a U.S. establishment when in fact the manufacturing took place in a faraway land that, perhaps, does not provide the same types of wages, working conditions and environmental protections as U.S. manufacturers.
PMPA commented that by definition, a business must manufacture or alter the physical content of a product to fall under NAICS 31-33. Further, these production activities must occur within North America, or they undermine the very purpose of a North American Industry Classification System. If manufacturing processes are not actually required for a “manufacturing” classification, the statistics produced by such a distorted definition are virtually useless.
“This is an important victory for U.S. businesses and we applaud the Administration for recognizing the flawed thinking behind this proposal,” said Mike Kobylka, Executive Director of PMPA. “This proposal would have created a class of phantom manufacturers. The NAICS classification system has never and should never take into account foreign sourced production processes.” August 8 Federal Register Notice withdrawing FGP Proposal for NAICS 2017.
Baby-boomer demographics continue to shape industry and employment.
According to Peter Coy with Bloomberg,”…older workers’ share of the workforce briefly dipped below 12 percent in the early 1990s but has risen steeply ever since. The population bulge of the baby boom is the big factor, of course. The peak birth year of the baby boom was 1957. Those peak boomers, no longer babies, reached age 55 in 2012—the first year older workers’ share of employment hit 21 percent.” As managers we need to
Understand that this cadre of talent has (is!) our tribal knowledge;
Find ways to help them share and preserve this knowledge;
Find new talent to learn from them;
One more item to think about- many baby-boomers will not be taking traditional retirements for various reasons-
They enjoy their jobs,
They are still too fit to “retire,”
They can’t afford to,
They decide to keep working to assure that they won’t run out of money when they finally do retire.
We remain optimistic for the outlook for manufacturing for the next three months based on the latest ISM PMI and PMPA Business Trends Indicators. The latest Institute for Supply Management PMI (Purchasing Managers Index) increased 1.8 points to 57.1 for July. The July value was the 14th consecutive month of manufacturing expansion; the 62nd consecutive month of expansion in the broad economy, and the highest value since April 2011.
Using the July reading, this value indicates an expansion in manufacturing, but if annualized, is also consistent with a 4.6% rate of increase of real GDP according to ISM.
If the January through July data is annualized, the corresponding GDP growth would be about 3.7%.
PMPA’s June 2014 Business Trends Report showed a seasonal decline in shipments for the month of June, but the average for the year to date is 123, up 6 points (~5.1%) from last year’s 117 year end average.
PMPA’s Business Trends Indicator for Sales/ Shipments sentiment was strongly positive in June, with ~88% of respondents expecting sales to remain the same or increase over the next three months. and 89% of respondents expecting lead times to increase or remain the same for the next three months. July ISM PMI GRAPH courtesy St Louis Fed July 2014 ISM PMI Report for Manufacturing