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What’s the Difference – Hot roll forming and cold roll forming.

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cold roll orming machine

The Benefits of Cold Roll Forming vs Hot Roll Forming

Roll Formed MetalsWhile different projects call for different materials, different processes produce steel that is best suited for different applications, and choosing the right option can make a difference in performance.

Hot Roll Forming

Hot-rolled steel means that the steel is rolled after being heated to above its recrystallization temperature, generally in excess of one thousand degrees Fahrenheit. The heated steel is malleable at this temperature, can be formed into the necessary shape, and then cooled to room temperature. This avoids certain types of stresses on the steel while it’s being shaped and hardened. However, as the steel cools, it shrinks. Because this shrinking cannot be precisely controlled, there are often variations in the overall size, shape, and finish of hot roll-formed steel. Further, hot-rolled steel has a scaly surface finish that requires an additional process to remove.

Hot forming is a combination of extruding and rolling using molten steel under extremely high temperatures. Some structural shapes, such as those used in holding up and reinforcing buildings, really cannot be made any other way than hot forming.

A classic example is having a large “plunger” that is filled with hot steel, which extrudes a shape used for an I-beam in structural applications. It then goes through a series of rollers that fine-tune the shape and squeeze it down into the tolerances required for that particular shape.

It doesn’t make sense to take a bar of steel and try to cold form it into something like an “I” shape. Coiled steel sheets down to a certain thickness (0.60”) can also be produced with hot forming.

Cold Roll Forming

Two applications of cold roll forming

Cold roll forming of metal profile

Roll Forming Machine
Cold Roll Forming Machine

Cold roll forming is the process of gradually bending a flat strip or coil of metal into a longitudinal, uniform profile. the cold roll forming process uses a continuous bending operation where long metal strips, typically coiled steel, are passed through consecutive sets of rolls at room temperature. Each set of rolls performs incremental parts of the bend to produce the desired cross-section profile. Cold roll forming is a cold-forming process that doesn’t require heating up the metal. High-temperature, specialized equipment isn’t necessary to produce cold-rolled shapes.

Cold-rolled steel

True-ish to its name, cold forming involves making shapes at room temperature or slightly above room temperature.

If precision, a smooth finish, and strength are important to your product, then cold-rolled steel is the way to go. Cold roll-formed steel is run through a series of rollers at room temperature and so requires no cooling. This allows the steel to be rolled to precise dimensions, creates a clean finish, and allows for precision in other in-line processes such as hole-punching and cut-off. Further, cold-rolled steel is stronger than hot-rolled products and does not have the added costs of time and materials to heat and cool the product.

3 differences between the hot roll forming and the cold roll forming

There are uses for both hot and cold forming. The properties of certain metal grades sometimes dictate whether you should have them hot or cold-formed. So, what are the big differences between hot-rolled steel and cold-formed steel?

Run Speed & Quality

With hot steel, it might take 50 rolls to thin a workpiece out, while that same piece may require 100 passes with cold roll forming, it takes more force to manipulate the metal.

With more rolls, can also get tighter tolerances on the piece and a higher-quality end product. This can increase the costs because of the additional machinery and labor time required, but it may be worth it to your customer.

Application

Structural shapes like I-beams are usually hot rolled. The formula of steel used for I beams is different than used in cold forming. It’s less ductile and harder, which makes it tougher to bend cold, hence the use for structural shapes that carry a lot of weight!

Cold roll forming has many commercial and industrial uses. They include:

  • Signposts & guard rails
  • Solar
  • Refrigeration
  • Escalators & elevators

Strength

For similar grades, cold-rolled metal can be stronger than hot-rolled metal because of what’s called work hardening. When you put a piece through 100 vs. 50 passes, the strain you put on the material actually hardens it and makes it stronger.

If the hot-rolled sheet is specified for a part that will be roll-formed, you’ll still get some added strength. But it won’t match the strength you would have received if you started with standard cold-rolled material.

Size Limits

As we mentioned, the steel sheet is only hot rolled up to a certain thickness.

Since roll-formed parts are usually produced from coiled material, product length is limited only by the amount of material in the coil and the handling of the finished part. Hot rolled shapes are also only limited by equipment capability.