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Alloy & Heat Treatment Suggestions for Bending Rolls/Dies

Alloy & Heat Treatment Suggestions for Bending Rolls/Dies

Alloy & Heat Treatment Suggestions for Bending Rolls/Dies

(OP)
I work for a company who bends/forms large heavy structural steel members (HSS Tubing, WF Beams, Channels, Angles, etc.) on 3 roll section benders often referred to as angle rolls. Most if not all of these machines are Mfg'd in Europe. Link

These machines use large cylindrical dies turned/cut from forgings as their primary tooling which are often referred to as bending rolls. When purchased, the machines come with minimal tooling from the Mfg. And obtaining tooling from overseas is expensive and requires extensive lead times. So for years we have been cutting and hardening our own bending rolls from 4140 and case hardening to a depth of 1-1.5mm @ 58-60 HRC. This works and has worked for a long time but we have to send these rolls/dies made in house out to get re-cut/cleaned up and re-hardened every few years. While the original tooling/dies that came from the machine Mfg, never have had to be sent out to get cleaned up nor re-hardened. This has caused us to question our alloy selection of 4140 and reconsidering our heat treatment on these rolls/tooling. In asking the Mfg about what alloy is used for their bending rolls, they are pretty hush/hush about it as they consider it proprietary information. But we did just purchased a new plate roll (Different type of bending machine dedicated to forming steel plate into cylinders) in which the Mfg specified that the top roll was made from 34CrNiMo6, which is equivalent to 4340. These two types of machines are slightly different in that the top roll of a plate roll is not typically changed out and there is no shaft that the bending roll fits/slides over, the top roll of a plate roll is the rotating shaft and the bending roll all in one. Where as the 3 roll section bender's tooling/rolls slide over a keyway'd shaft and are stacked up on top of one another to create the tooling setup for the machine.

In speaking to a few guys in the industry some have recommended 4340 or 4150 in stead of 4140, also I have heard that 60HRC could be too hard and possibly aiming for 50HRC could be beneficial.

Besides 4340 and 4140 are there any other alloys that stick out that we should be considering? And any thoughts on 50HRC vs 60HRC?

With respect to the 60HRC 4140 dies we are making in house, see attached photo of some quality issues we have been seeing when rolling HSS A500B/C Rectangular and square tubing. The tooling setup is stacked in a way to enclose the member being bent so as to prevent cross sectional distortion, i.e. tube growth/shrinkage/concavity and often sandwiches the structural steel member rather tight/snugly. Were not 100% sure what is happening here but it doesnt appear that the tooling is degrading, it appears the tooling is so hard that as the member being bent distorts within the tooling/grows at the inside face of the bend due to compressive forces, the tooling shears some of the tubes outside most material as it passes through the bending dies and gets trapped between the tooling and the member being bent and get impregnated back into the member being worked and as the rolls turn to pull the member through the machine, the material that has been sheared from the edge of the HSS tube gets swirled/galled back into the HSS Tube creating large unsightly scratches and deeper gouges. We use wax/lubricant to assist in preventing this but this issue seems to be persistent. Our machine operators blame the tooling we have made and tell us that the dies that came with the machine from the MFG do not cause this problem.

Many thanks for your consideration/input!



RE: Alloy & Heat Treatment Suggestions for Bending Rolls/Dies

Too many questions in a single post.

A few answers from the material aspect.

1. Carry out the material analysis of the original. This could be PMI but chemical analysis is preferred.

2. Cut some portion of the original and make tensile and impact samples. Carry out those mechanical tests and get the result. Also take hardness.

Match 1 & 2 above with ASTM standards to identify the original material used. Also, identify the heat treatment carried out to the original using hardness values.

Prepare quotation, purchase order for the same and look for new vendors.

DHURJATI SEN
Kolkata, India


RE: Alloy & Heat Treatment Suggestions for Bending Rolls/Dies

You need to at least grind a spot on the side of a good one and have someone use OES to get a real chemistry.
And check hardness on the working face as well as neat the hub to see if they are surface hardened.
My hunch would be a tool steel.
The need hardness, wear resistance, and toughness.
Which tool steel depends on the size, and how much money you want to spend.

Your tooling picks up metal on the surface because it is wearing and forming rough spots.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Alloy & Heat Treatment Suggestions for Bending Rolls/Dies

the 4140 parent material will core harden to 50 Hrc hardness, with carburize the surface will be 60 Min Hrc after carburize, will reduce slightly if to much grind stock is removed. there will be a benefit for using 4340 steel, however it is more expensive but more stable and tougher than 4140. however look into use A2 tool steel , very little distortion after heat treat may be a good candidate. but as suggested by above take one of the smaller cheaper rolls and do a destructive test and do a spectral analysis for the material. hardness test is sufficient for hardness requirements of the rolls. but have them do a section to verify the core and surface.

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