Part one of three –
I thought we would sneak into 2021 by looking at a steel shaft that is often misunderstood; Chromed Steel Shafts (Rods).
Chromed steel shafts are referred to as “Rods”, or “Cylinder Rods”. Not all are used for Cylinder applications. The manufacturing and automation industry is a prolific user of this type of product. The default term Rod, is simply “jargon of the trade”. The base metal may be mild steel (soft), carbon steel, alloy steel, or stainless steel; it may be soft or hard, through-hard, or skin (surface) hard. Communicate with your vendor to understand what you are getting. The tolerance, type of chrome, and thickness of coating varies by supplier, so you will need to pay attention to that if you intend to compare brands, etc.
The base metal shafts are usually precision ground and precision straightened. Straightness is critical where telescoping is involved (such as with cylinder applications).
Diameter tolerance and surface finish are also critical. More about that later.
Persons working in industries other than heavy industry will still encounter Hydraulic Rods and Pneumatic Rods in their daily life. The door closer on a screen door, the shiny bars visible on a piece of landscaping equipment, are types of cylinder and shaft assemblies. Even a BB gun operates on the same principle.
Descriptive terms esoteric to chromed rods may be CP (Chrome Plated), IHCP (induction hardened chrome plated), HCP (Hard Chrome Plated), pneumatic rods, cylinder rods, hydraulic rods, etc. Typically, the differences identify the application.
Chrome plating generally begins as a powder. It may be considered “Hard Chrome”, or “Chrome). In some cases, it may be applied as a weld overlay. Chrome coating has its own hardness, intrinsic to the weld or powder. It then takes on the hardness of the sub-straight. If the shaft it is applied to is soft, it will be soft.
A bit of clarification is required here; The medium itself has its own hardness, important for initial sliding abrasion. The resistance to an impact or gouging event will come from the hardness of the sub-straight (the underlying shaft material), as will ductility. Think of a soft cream topping on a gingersnap cookie, or a hard chocolate coating on a marshmallow or strawberry. Each of those is subject to different adversities. A chocolate covered cherry may have a hard-coat, but most of us have put our thumb through it.
Next postings will look at; explanation of terms, cutting & drilling, how to order lengths (end-condition), failures, and how surface finish affects lubrication.
-Howard Thomas, March 3rd 2021
