What’s the best Steel for your Crush & Shear knives?

Wednesday, 24 May 2017

Dave Rumson - Slitting Educator/Consultant 

The most common steels used today for both crush cutting and shear slitting knives are 52100, D2 and M2. Shear slitting also employs CPM-10V steel for top/male knives. 

But how did we get to these steels? Let's take a quick look at steel making history. 

The earliest known steel has been traced back to about 4,000 years ago from ironware excavated at an archaeological site in Anatolia (Kaman-Kalehoyuk)¹. Among other early societies, the Chinese Han Dynasty, circa 200 BC to 220 AD, began melting wrought and cast iron; creating a carbon-intermediate steel¹. 

Over the centuries important steel making improvements were developed. Among others, two stand out; 1776 - Englishman Industrialist John Wilkinson, developed a high volume air blowing mechanism that provided higher furnace temperature capability and was essentially a prototype of modern air compressors ... and ... circa 1856, Englishman Henry Bessemer purchased a Patent from American William Kelly for "a system of air blowing the carbon out of pig iron". From this Bessemer developed the "Bessemer Process" for faster making of higher grade steel; the basis for current steel making methods². 

Circa 1900 the demand for heavier load carrying capability helped initiate combining carbon and chromium steel for bearings. Some of these early steels closely resembled today's 52100 that was AISI defined in 1920 as a high load bearing steel³. 

52100 has very good compressive strength and is the most common steel for crush and shear cutting knives because of its ease to manufacture and relative low cost. It has excellent shock impact resistance, but consisting of 0.45% to 1.0% chromium, only reasonable wearing characteristics and poor corrosion resistance when compared to other knife metals. 

During and post WWII high speed production dies and gas turbine engines required much better metal-to-metal sliding friction capability⁴. D2 tool steel, consisting of high carbon and high chromium met this demand. With 12% chromium content, it has good wear characteristics – 3 to 4 times longer service life than 52100. Additionally, it has good corrosion resistance and a high compressive strength needed to handle high loads. But, with only a fair level of impact shock resistance D2 requires careful handling and operating care because of increased susceptibility to knife fracture. 

Within the past few years the cost of D2 steel has lowered to being close to that of 52100 steel. But keep in mind the cost to machine D2 is higher than 52100. 

Taking a short back step in time... because of a strong demand for increased machining production rates M2 steel was developed circa 1937⁵. M2 is a medium carbon, high molybdenum, high-speed, high operating temperature capable tool steel that has shown better cyclic fatigue and wear resistance than D2; 3 times more in both crush and shear slitting applications. But it does have poorer shock and corrosion resistance, and a higher cost than D2. 

CPM-10V tool steel is made from the powder and particle metal component making process that was patented in the late 1960's⁶. This process takes granulated metal alloys and using a high compressive force, "cold welds" them into a "hand-able" molded shape. The shapes are then sintered in a furnace that imparts strength and integrity. Then they're pre-finish machined, heat treated for hardness and durability ... then finish machined⁷. Having a near perfect alloy blend and uniform hardness level microstructure, CPM-10V provides high-speed, long run capability with minimum down time; a serious advantages over ingot steel. 

CPM-10V is the top-shelf top knife steel. It provides up to 6 times more life than D2 steel, [See Image 2]. CPM-10V is favored by paper mills and converters with high speed slitters. It has shown significant life running at speeds up to 12,000 fpm ... under controlled Laboratory conditions. 

Bottom/female shear knives are commonly made from 52100 and D2. The top-shelf bottom knives are made from C-13 tungsten-carbide; usually with narrow C-13 tungsten-carbide bands adhered to a more easily machined and less expensive steel ring. The best shear slitting knife metal combination is a tungsten-carbide bottom knife and a CPM-10V top knife. 

You might want to consider some in-house trials that may improve your slitting process. As always though ... do talk with suppliers about your web material and operating parameters. 

Who is Dave Runsom? 

Dave Rumson has 29 years of domestic and international sales/marketing management experience with slitting, unwind/rewind and roll/shaft-handling equipment and more than 26 years of experience developing and conducting technical presentations for CEMA, AIMCAL, TAPPI and employer sponsored seminars. 

Since 2009, he has been an independent slitting consultant, providing in-plant analysis/Slitting Educational Programs and lab slitting trials. Additionally Dave conducts “Web Slitting Technology”, an AIMCAL 2-Day Converting School Seminar. Dave also writes the “Cut Points” Q&A technical column for AIMCAL’s Converting Quarterly magazine and manages the 1,400 plus member Slitting Community Group on LinkedIn. He holds a B.S.B.A. degree from Westbrook College (Portland, ME).