Part 2 of 3
a. if you start with cold rolled or cold drawn material remember that the manufacturing process for that product generally contributes to a noticeable amount of “retained stress”. That stress will tend to be released by temperature, and/or, vibration; meaning, while you are making the rail, or when the rail is in service.
b. if you start with a hot rolled bar, you must allow more stock removal, not only for potential decarb on the surface, but also distortion in shape (out-of-square, etc.). The mill allowance for out of square with hot rolled bars is significantly more than it is for cold drawn material. Often, a final grind is needed after processing.
So, there will be limits of what you can do to that piece of steel. Many variables will have to be taken into consideration. When we say, “Our steels machine better, weld better, or wear longer”, you must understand that is within a certain context. The statements we make are relative to other high strength steels used for maintenance applications (apples to apples). We are not saying they machine better than free-machining steel, or mild steel, or copper, or plastic.
A round bar that has been supplied as hardened from the mill, may not want to be straightened to a very tight T.I.R. To achieve a specific T.I.R. the straightener will have to overcome many factors. Consideration will have to be given to size vs length, the bar’s propensity to retain stress, etc. The operator will have to know something about the specific material’s “memory” properties and be familiar with all the potential conditions that might prohibit the required end result.
Conditions that might prohibit achieving that, are present in different forms for all fabrication jobs. They may relate to; number of pieces, grade, hardness, length, configuration, tolerance, surface finish, service temperature, etc. In addition, there are a limited number of companies offering value added services who are comfortable dealing with maintenance steels.
Metals fabrication shops only work with “serious” experienced companies, or the people they trust at those companies. They can easily lose faith in a job if you don’t have all the information needed. They can back away from a job if you keep feeding them additional or changing information every couple of days. Maintenance jobs cannot afford delays.
Metals fabrication is serious business. It is not a training ground for eager novices. Some words of wisdom you might want to tattoo somewhere on your person are: “Fabrication may be late, wrong, and dangerous.”, “Wear Plate is big and ugly!” and,” If you can’t stand the heat, stay out of that kitchen.”
Steels for maintenance and tooling need to be hard and tough. They need to resist abrasive wear, or gouging, or bending, or fatigue failure, or all of those issues.
Once you have made the base metal hard and tough, you have made a material that does not want to be messed with.
Making finished hardened and machined custom wear rail is not for the faint of heart. Anyone who has done so knows there is truth in that statement. If you are familiar with Murphy’s Law, when rail is being discussed, think of it as “Murphy’s Rail”.
-Howard Thomas, June 21st 2022