The Following information relating to perf blades/applications used in the manufacturer of continuous stationary in the business form industry has been personally acquired over many years of manufacturing and customer relations in several countries.

On continuous forms perforations are cut using perf wheels for vertical perfs and cross-perf blades for horizontal perfs.

Blade Description

Carbon steel is the material of choice and is hardened and tempered to Rockwell Hardness of approximately 50 - 55 RC depending on the application. The most common thickness of a cross-perf blade is 0.028" and commonly referred to as 2pt (2 points). A point is a form of measurement used in the printing industry that is 0.14". We could tell you that the most common height of a perf blade is 0.918" but there are many other heights used from 0.250 high to .938 high. The cutting bevel profile is available as a center bevel(CB) or side bevel (SB). It is machined onto the strip steel either by grinding wheels or by a shaving process and the most common bevel is 60deg inclusive. There are basically two types of perforating blades that are used in the business form industry.

• Standard Perforating - up to approximately 20tpi - CB or SB. Various tie sizes from approximately 0.020" to approximately 0.125". The depth of the tie varies slightly but on the average is 3/32".
• Micro Perforating - up to 100tpi normally CB. Various tie sizes from approximately 0.005" to approximately 0.015". The depth of the tie varies slightly but on the average 0.25" to 0.30".

Blade Height Tolerance

Obviously this tolerance can have an impact on the relative production process. Here are some facts worthy of note. One of the most common problems is inconsistent height of the blade over a given length which can cause bad perfing. All perf blades are manufactured to set tolerances. Ground edge rule is normally made to + or - 0.001" and shaved edge rule is normally made to + or - 0.0005". Since there are different tolerances its safe to say that a shaved edgerule would be more accurate and less likely to cause problems.

Blade Edge Quality

A cutting edge on a piece of rule can be produced either by a grinding or shaving process, visually the edges look identical except for the machining marks. Under a microscope a ground rule appears to have a saw tooth edge, unlike a shaved rule edge. Over the years we have learned that a shaved edge rule will run longer than a ground edge rule of the same hardness. Reason being, that the grinding causes a lot of heat to the edge of the rule and annealing may occur which cannot normally be seen and causes premature edge failure.