Posts

CDA Bars & Rails

Cold Drawn – a Process Not a Material 

Cold Roll or Cold Drawn bar is often requested from a supplier as if the term indicated a grade of steel. Those terms refer to production methods not chemistry or grade. I point this out not to be stuffy, but to try to eliminate potential safety problems in the field.

Cold Roll, Cold Drawn, or Cold Finished bars may be made from 1018, 1020, 1045, 8620, 4140, etc. While most often they would be annealed (soft), there is the chance a cold drawn bar could be supplied in a hardened condition. The real problem is somewhat related to geography. In certain parts of the country, Cold Roll (Cole-roll), is most often produced as 1018 or 1020. Elsewhere, in other mills, the preponderance of production might lean toward 1045. The 1045 grade is hardenable; 1018 and 1020 are not. Expecting a material to be ductile in all circumstances could lead to significant problems should that steel turn out to be brittle.

Cold Drawn or Hot Rolled – When?
Cold Drawn steel materials may be used for various types of rails in heavy industrial applications. Hot Rolled Hardened wear bars may also be used for types of rails. If smooth and accurate travel along a rail is a concern, or if a finished cam/wheel is riding on it, you will probably want Cold Drawn, Cold Rolled, or Cold Finished (all the same) bars. If the application is “Big & Ugly”, let’s say a large heavy tank car is rolling over the rails and the rails eventually fail due to gouging, deforming, weight and wear, think Hot Rolled and Hardened. (Q&T).

Basically, a flat bar (cold drawn or hot rolled) is referred to as a rail when it has undergone some machining, and/or, hardening, or is used in an application where something is conveyed along it, or guided by it. A roller cam or trolley may ride along any surface of the flat bar, whether the bar is lying down flat, or is positioned up on end. Product may simply be slid along one surface of a flat, with no cam to assist movement. In the case of sliding, you will want to review “galling”.

If the application is “Big and Ugly”, such as moving bins of molten metal in a steel mill, the rail may be just hardened hot rolled bar stock. Pay close attention to the “out-of-square” allowable tolerance on hot rolled hardened mill bars. It is much more open than the tolerance of cold drawn bar.

WEAR BARS OR HOT ROLLED FLATS AS RAIL
Where the configuration is not sensitive to smooth uninterrupted movement (such as is required in an automation facility), hot rolled hardened bars may be used. These could be sizes like 3/8” x 2 ½”, or 5” x 8” depending on the weight of what is travelling the rail.

Generally, these types of rails will be welded or bolted to a substrate. Even Big and Ugly rails may require precise hole locations on the bars for alignment to pre-drilled holes in the substrate. When this is a requirement it is important to measure the holes centered on the length of the rail. So, you would not measure from the outside length dimension of the flat bar. You would find the center of the bar length and index the holes from that point radiating out in both directions. Otherwise, if the length was a bit oversize or undersize, the holes would not line up. The same goes for the width of the flat bar.

Our next post will focus on fabricating finished “Rails”; specifically impediments to fabrication and subsequent service-life. The third, and final post on CD bars will be an introduction to the trade-name rails produced and marketed by Associated Steel.

-Howard Thomas, May 9th, 2022

/0 Comments/by

When Hot Rolled Steel? – When Cold Finished Steel?

Whoever said; “Cuts like butter, or, Machines like butter”, may not have meant that was a good thing. Visualize butter; not cryogenic butter. The thing is, you need a little hardness (read as strength) if you are expecting decent cutting and machining.

Generally, cold finished steel; which takes into consideration both Cold Rolled and Cold Drawn, provides higher hardness and higher strength than Hot Rolled Steel. Hot Rolled Steel here, means Hot Rolled Annealed (softened) Steel. Hot Rolled Q&T (Hardened) Steel, on the other hand, is most often harder than Cold Finished Steel. A ball park assessment of the comparable hardness would be something like this;

Cold Drawn/Cold Rolled = 20RC          Hot Rolled Annealed = 18RC     Hot Rolled Q&T = 30RC

If you want a rough idea of the relative strength of each, convert RC roughly to Brinell (BHN) hardness (RC times 10), and divide by two. So, 20RC = 200bhn = 100,000psi Tensile. 30RC = 300 bhn = 150,000psi Tensile, and so on. Now, don’t be using this for engineering. It is simply a rough comparison for reference sake.

Cold finished steels are worked at room temp. Hot finished steels are worked hot, almost 2000°F. “Cold Rolled” typically refers to flat bar, sheet, and plate. “Cold drawn” generally refers to bar shapes. Cold working steel strain or “work” hardens it. The higher hardness elevates the strength. But, since it is not a thermally hardened material, the cold working process also imparts stress. That stress is retained in the steel. It may cause movement during subsequent machining or grinding. Q&T Hot Rolled Steels respond to thermal treatment, so, they may be stress relieved at some point of their production. That process relieves stress that may have been retained from processing.

With all of the changes that are happening in the world of steel availability, the question may soon be, which one is available in the size you need. More and more hot rolled shapes, that were once considered staples of the industry, are disappearing. There is a far greater variety of bar shapes available in cold finished product that in hot rolled product; especially hot rolled Q&T.

Also, cold finished bars are provided in much more accurate cross sections and closer tolerances than hot rolled. So, Cold Finished bars are more available, better surface condition, greater aesthetics, stronger, and offer greater opportunity to obtain the size and shape you need. That is why Cold rolled squares and rectangles (flats) are ubiquitously used as rails for automation. They are often machined to accept custom wheels, cams, and mounting hardware. Cold finished alloy bars may be surface hardened to minimize greatly extend wear resistance and service life.

Hot Rolled Annealed steels are more malleable. They tend to retain less stress which translates to less movement. Hot Rolled Q&T steels, especially Alloy steels, offer much higher strength, but, they are somewhat less available than the great variety of sizes available in Cold Finished products, have less cross sectional accuracy, and generally are used where accuracy is not critical and/or a portion of the surface will be removed.

High grade cold finished alloy bars are clean and strong. Better service centers will employ subsequent straightening, even with bars from their general stock. They will also provide fabrication services to prep the mill bars for specific automation rail applications. This may involve; further straightening, drilling and countersinking, surface hardening (multiple or single surface), and custom end preparation.

-Howard Thomas, August 19th 2019

 

/0 Comments/by

What is Brake Die Steel?

Let’s begin this post with two of my favorite words; Ubiquitous; (everywhere, like raindrops during a storm), and, Esoteric; (known by a select small group of people).

What do these mean? Brake Die, Gun Barrel or Rifle Stock, Pump Shaft Straightness, Boat Shaft, Food Service Grade Stainless, Cold Roll, “Ultrasonic Inspect to 388, (and even FDA approved). While they may have a specific meaning to someone (esoteric), they do not have a defined meaning to everyone (ubiquitous in certain industries). In reality these are generic descriptions without reference to defined requirements and properties, at best they are like answering someone’s question regarding the location of your pending vacation by responding; “Up North.”

From my experience, and from a supplier’s point of view, the only real commonality they have is the suggestion of liability. You cannot hope to avoid potential mishap if you really do not have more information on the chemical and physical requirements of the steel the person is discussing.

Brake Die Steel – Generally, a high quality carbon or alloy, appropriate for dies, that may be, or is, hardened. Often an alloy from the 4000 series. Is it pre-machined? Not necessarily. Is it pre-hardened? Not necessarily. Is it oversized square and shiny? Not necessarily.

Food Service Grade Stainless – Generally means it does not contaminate food with residue from the steel and it maintains a clean finish. Most often some grade of stainless. More information is needed.

Gun Barrel and Rifle Stock – Generally a 4000 series high integrity hardened alloy. But, not a specific grade.

Boat Shaft – You really have no information from that term. Could be anything, carbon, alloy, stainless, monel, bronze, etc. Most customers will require specific properties that conform to some sort of Marine Agency such as ABS, etc.

Cold Roll – Not a steel grade but a production method. Need more information.

FDA Approved – A misnomer. FDA does not grant approvals for metals.

Pump Shaft Straightness – The specifics are different for everyone. There are ASTM specifications but many large companies have their own “esoteric” specifications. You need to know more.

Ultrasonic Test 388 – An ASTM test method to determine the internal integrity of steel. Requires more detail such as acceptability and reject-ability levels.

-Howard Thomas, April 22nd 2019

/2 Comments/by

Ten Points to Eliminate Mistakes on Finish Size – Bar Clean Up, For Steel Bars

We have talked about round bar grinding in the past. The following posts will look deeper into the communicating skills that will help you minimize disappointments in this area. Unfortunately, more people than not have purchased a bar of steel and found that it won’t make their part because there was not sufficient stock allowance to “clean-up”. That need not be the case. Most often, communication is again the culprit. We are speaking of ROUND STEEL BARS.

  1. Diameter size relative to length will be important.
  2. Subsequent machining or grinding method will be important.
  3. Mill finish and mill tolerance will be important. This often varies by mill.
  4. You should share “end use” with your supplier.
  5. Also, share any subsequent operations you will be doing on the bar.
  6. If the finished shaft involves substantial step downs, or, if only a small portion of the bar needs to finish…share that information.
  7. Remember, your supplier cannot be made responsible for a third party’s work, and/or, mistakes.
  8. If liability on the shaft is considerable, consider parking it in another party’s driveway.
  9. Try to “Talk the Talk” phrases like, “a stick of steel”, or, “cold roll”, or, “a length of steel”, will get you in trouble.
  10. Share important ancillary facts with your supplier; have you received steel in the past that has not been straight enough, hasn’t cleaned up, or was inappropriate in another way?

Each one of the above should solicit further discussion. That is going to come under the header of; TO BE DISCUSSED (TBD). I will try to do just that over the next several weeks. So, stay tuned.

-Howard Thomas, February 26th 2019

 

/0 Comments/by