This is the last of our three-part post on chromed shafts.
In order to extend service life, by resisting surface wear on the rod, the rod surface needs to be hard. It also needs to be relatively smooth, so as not to tear up the seals.
And the rod needs to be straight. In most cases, chrome is an ideal surface coat for Hydraulic Rods. Hard Chrome may be better. IHCP is better still.
The finish however, cannot be so bright that it will not attract and hold the lubricant. Inadequate lubrication is just one of many potential contributors to shaft failure, chromed or not. You might to consider the following information, for a broader scope on this topic:
Fatigue Failure and The Importance of Design;
I have always felt that approximately 80% of shaft failures in heavy industrial maintenance applications are related somehow to fatigue. The following article found in Machinery Lubrication magazine compliments that supposition.
In his article on cylinder rods, Brendan Casey states that it is recorded that approximately 25% of hydraulic rod failures are design related. In hydraulic cylinder applications, one in four shafts fails to provide adequate service life. Bent rods make up a considerable portion of failures. It is important to clarify the straightness tolerance your vendor is proposing to supply.
Rods that are of insufficient diameter and insufficient strength will often bend in service. Once the rod bends, excessive load is placed on the seal. That results in premature seal failure. If a rod is bent, and use of a larger diameter rod is not practical, then the tensile of the rod must be increased. Induction hardened material (IHCP) offers a significant boost in strength.
A NOTE ON BAR ENDS
When full bars are chromed, most mills hold the bars by the bar ends and vertically coat them. In those instances, the bars are not fully chromed the length of the mill random bar. Several inches on each end will be bare. This is generally not trimmed off when random bars are sold. It is recommended that you specify “trimmed ends” when you order random length chromed bars. Probably a good idea to specify this on even cut-to-length material, even though most vendors provide that service as a default.
This completes our post on chromed rods. If you want to pursue information gathering on this type of material, you may want to do some additional research on; Black Nitrided Rods. That process is showing improved service life in similar applications.
-Howard Thomas, June 11th 2021
Continuing from our last post, we are discussing chromed rods. When they are applied correctly, chromed Rods typically extend service life compared to standard carbon and alloy bars. Variables relative to those materials would be the steel type, actual hardness, and the type of hardness (surface or throughout). The benefits of chromed rods address sliding surface abrasion and corrosion.
In actual service, however, even sliding abrasion applications are not just limited to sliding abrasion. Small bits of debris (tramp elements) find their way onto the exposed rod and then get pulled through the seal (intended to keep tramp elements out), between the rod and the cylinder. The motion of the rod is often interrupted by impact causing shock and twisting or bending of the rod.
Deciding between IHCP and Hard Chrome HP & Too great of a surface finish has a downside.
Since chrome plating is most often applied to a rod surface very thin (thousandths), the importance of a surface hardened sub-straight should not escape consideration. Where severe impact and gouging may be experienced, a hardened sub-straight will resist damage. You would think that, to be on the safe side, everyone should always order the IHCP material. The problem is, surface hardened sub-straights may be furnished at a hardness of 60 to 62RC (approximately 600bhn). Not everyone has machinery sufficient to handle that hardness. Drilling, cutting, machining may be a problem.
The thin chrome “skin” covering the rod is easier to penetrate when the sub-straight is soft. Various fabrication processes are readily accomplished. Smaller shops will find fabrication processes easier.
It is also important to always remember that high hardness in steel (carbon or alloy surface or throughout) also affects ductility. Application consideration must be given to the propensity for fracture.
CHROME SURFACE FAILURE
Abrasive related chrome surface failures often damage seals. When chrome gets very thin due to wear, it cracks and peels, exhibiting a razorblade sharp projection that often curls up, like the bark on a Birch tree. This type of failure is often experienced where there the surface of the shaft is subjected to severe temperature change (furnace). That projection tears up seals. In applications were liquid may escape, such as sludge from a barge pump, the contamination could be catastrophic. Read as “expensive”. In those applications, some alternative (such as utilizing hardened stainless shafts) should be considered.
Our last post of this three-part series will cover, lubrication, bar cut-ends, and dent bars.
-Howard Thomas, May 6th 2021
You do not have to be a metallurgist or engineer to accurately order steel. But you don’t want to order steel plates and end up with dishes. Take some time to ensure your language will be understood by the vendor. I’m not speaking about dialects, but try to avoid esoteric terms that may just be what you use at your company. Avoid jargon. Take a moment to familiarize yourself with the terms the vendor uses. You will quickly learn there are common terms that will help to avoid misunderstandings.
In general steel suppliers and steel service centers are used to working with people that may need help drilling down to what they actually need. Mills on the other hand are a different animal all together. They don’t need calls from every person trying to fix air fryer. Still, they get calls that should never have been directed to them. As a result, and I’m just sayin’, they can get testy and come across a bit like a bear with a sore behind.
I remember a call I made early in my career. I was mumbling and stumbling around when the person kindly interrupted with; “Look kid, when you know what it is your looking for, give us a call.” It helps to get your ducks in a row before you make that call.
The first thing you are going to want to present is the “family” the steel belongs to; is it mild steel, carbon steel, alloy steel, stainless, tool steel, or a non-ferrous grade like brass or bronze. The general form the steel takes should be right here. Is it wire, coil, sheet, angle, bar, shapes, or some other form? They should ask what hardness, or what finish? Try to answer those questions with industry familiar language. “I don’t want it to be hard to machine.” Is not good, for all they know, you may be the worst machinist in the world. “I want to see a reflection but it shouldn’t stretch my head a lot.” No help there either.
Next advise the specific size shape length and quantity. Get this out of the way quickly. I have been in long conversations about applications and failures only to find out the customer was actually looking for wire or coil, or some other form that we didn’t handle.
If it is a repeat order, mention that upfront. It will save both of you a lot of time.
Caution on the length. Does it need to be an exact length (you will need a tolerance), or can you take a random bar length? See previous posts on random bar lengths. A common mistake is asking for a 36ft length because you’ve calculated your mults (finish lengths) to be optimal from that length. That results in a lot of no quotes. Advise your mults first. Then advise how many “finish length pieces” you will need.
When you are discussing quantities and descriptions, the following are universally accepted; Pieces, Bars, Sheets, Plates, Tons, Metric Tons, etc. If it is thin plate you can use the words sheet or plate; although sheet is understood to be thinner. Those items can be purchased in pieces, pounds, tons, hundred weight (cwt). Thick plate, maybe heavier than 3/16” thick, should always be plate.
Bars may be pieces, bars, or rods, even sticks will work. ”Bundles” should be avoided.
Food for thought; If every order you place is a “Rush-Breakdown”, you should know that after a while your urgent need won’t even be heard by your supplier.
A group of crows is a “Murder of Crows”. Just in case that ever comes up.
-Howard Thomas, April 5th 2021
Click here to add your own text
Associated Steel Corporation reserves the right to delete comments that contain vulgar language, personal attacks of any kind, or offensive comments that target or disparage any ethnic, racial, or religious group. Further Associated Steel Corporation also reserves the right to delete comments that are: spam, advocates illegal or unethical activity and infringes on copyrights or trademarks.
Click here to add your own text
Howard Thomas
Experience
Sr. Acct. Mgr. (US Southwest) / Metallurgical Consultant
Associated Steel Corporation
Jan 2017 – Present
Past Vice President / General Manager
Associated Steel Corporation
Apr 1998 – Jan 2017
Past Vice President / General Manager
Baldwin International
Apr 1974 – Mar 1997
Education
Cleveland State University
Kent State University
University of Denver
