Many industries require processed sheet metal following guidelines and standards for their particular application. When a specific sector needs strips of metal coil cut to size in varying lengths, they turn to metal slitters. A metal slitter machine sits on the slitting line and cuts the width of large coils into narrower widths by passing the metal through a sheet metal slitter. Precision slitting can make the subsequent manufacturing process of metal products faster and more accurate.
The slitting machine has sharp, powerful circular blades (single edge knives) that cut through the metal as it leaves the master coil and uncoiler on its way to the recoiler. The blades are also known as “slitting knives” and are modified to produce various widths of sheet metal strips.
What is interesting is that the metal is not cut as you might imagine. The process of high-quality metal slitting can be described better as metal fracturing. Two rotating blades – one upper and one lower – begin the fracture when the coil passes through the slitter.
Adequate compressive pressures are needed to fracture material effectively. In addition, horizontal knife clearance, penetration depth, stripper ring size, material properties, and the slitting head are all aspects when making a slit coil. But to completely comprehend the slitting process, it is necessary to have a working knowledge of fracture mechanics.
Fracture mechanics is the science used for predicting and diagnosing the failure of materials from cracks or flaws. The existence of a fracture increases stress, which can lead to failure sooner than anticipated by typical strength-of-materials methods. In metal slitters, the same methodology helps engineers determine how to create a clean and predictable fracture with consistent squareness. This fracture occurs when compressive forces exceed the material’s ultimate tensile strength.
A Four-Part Process
Slitting has four parts: Rollover, burnish, fracture zone, and burr. When the knives first come into contact with the material, it is called the rollover. Next, a deformity in the metal occurs by knife contact, which causes the rollover. The burnish section of the slitting process can be referred to as the shear zone. The shear zone is the shiny part when looking at the strip’s edge.
The fracture zone is usually the largest zone within the slitting process, and it’s also the hardest to control. Depending on the material being slit, materials commonly fracture at 7 to 9 degrees.
If done correctly, the slit edge will have a bright shear zone, a dark fracture zone, and a distinct straight line dividing the two. The burr is the fourth component in the slitting process. The burr is a good indicator of whether your setup is accurate. Burr forms on the opposing side of the rollover and is caused in significant part by compressive displacement of the material. The more the compressive forces required to fracture the material the larger the burr. The burr will be negligible if your slitter knife setup is precise, and you have sharp knives. The knife setup and tooling are vital for the desired result of metal slitting. When the clearances are off, too tight, or too wide, a heavy burr is created, or a double fracture can occur. When your knives are sharp, tooling is on point, and clearances are properly in play, you can guarantee a burr-free stainless steel slit coil. These factors allow tighter tolerances on materials for the project, increase machine speed (FPM), and increase knife life and longevity.
Reading The Edge
Another facet of metal slitting is the operations themselves. The Slitters and shear operators must learn to “read the edge.” Knowing what to look for while looking at a slit edge will help you figure out if your setup is correct and, if it isn’t, what measures to take to fix the problem. Operators become experts at “fixing” the setup by understanding what they see and applying the science of fracture mechanics to each roll.
Knife clearance and compressive forces are all determined by the type and gauge of material being slit. It doesn’t matter if you’re slitting copper alloys, magnesium, aluminum, cold-rolled steel, heavy-gauge steel, stainless steel, carbon steel, brass, or a composite metal. The setup requires optimal clearance and knowledge of the material’s thickness and characteristics of each metal. The rule of thumb for many years was to set the clearance at 10% of the thickness of the metal. A 0.006-in thick metal would have a clearance set at 0.060-in thick. But as technology, equipment, and software have improved, and metal slitters expect demand for tight tolerances on slit material, this old rule has fallen out of favor.
Metal Slitting with Consolidated Metal Service Inc.
The more we know your expectations and end-use of the strip coil, the better we can perform to meet those standards.
Metal working and the practice of cutting steel are indeed a true testament to our technological progress. Consolidated Metal Service Inc. adds value by making specific modifications to our rotary slitters and delivering rolled steel in a variety of minimum and maximum slitting widths based on the needs of a specific industry or customer.
As an industry leader and expert in steel coil slitting, mild steel edging, and distribution, Consolidated Metal Service, Inc. provides coil steel slitting and edge conditioning in a wide variety of sizes, materials, and finishes to the following industries and products.
- Appliance and automotive parts
- Commercial builders & roofing suppliers
- Machine repairs and many more.
For over 35 years, Consolidated Metals Service, Inc. has been one of the industry pioneers in metal processing and slitting. As a result, you can be confident that operators and equipment will meet all your expectations and standards for any OEM and industrial needs. Contact us now to learn more about Consolidated Metals’ precision metal slitting services.