A Tech Bite from Greener Technical Service Specialist Chris Stawasz
When you install a new knife on your flow wrappers and rotary vertical baggers, do you always install a new anvil? This Greener Tech Bite explains why reusing the old anvil when you install a new knife will cause cutting and sealing problems, delay production, and increase spare parts costs.
Why Anvils Don’t Get Replaced
The old, used anvil is often retained with good intent; when a knife fails, there is great pressure to minimize downtime. A new knife may be installed without a new anvil with the hope to save time and resume production as quickly as possible or to reduce spare parts costs.
Why You Should Replace the Anvil When Installing a New Knife
The expenses of a new anvil and the time it takes to install it are minimal compared to the costs of increased scrap rates and downtime caused by failing to replace the anvil.
Problems Caused by Not Replacing the Anvil
A new knife must be over adjusted to cut across the impression in the old anvil made by the previous knife.
When knives are over adjusted you can hear the heavy impact as they strike the anvil and feel the vibration when you put your hand on the machine. This condition causes multiple problems:
Premature Knife Failure
Over adjusted knives wear prematurely and must be replaced more often, increasing both downtime and spare parts costs.
Premature Failure of Critical Components
The heavy impact of the knife against the anvil also causes the premature failure of sealing jaws, springs, bearings, shafts, and other critical components.
Poor Seal Quality
When an over adjusted knife strikes the anvil with excess force, the trailing sealing faces of the jaws ”bounce” apart, reducing the transfer of pressure and heat to the leading seal of the next package and causing poor seal quality.
The missing serration imprints on this carbon impression clearly illustrate the bounce from an over adjusted knife.
Problems Caused By Compensatory Adjustments
Machine adjustments made to compensate for poor seal quality caused by an over adjusted knife often create additional problems.
Sealing Jaw Temperature
If temperature settings are raised in an attempt to restore seal quality, the additional heat expands the sealing jaws, knife, and anvil, making the knife over adjustment more severe and creating excessive pressure between the leading sealing faces of the jaws that can crush or split the trailing package seal.
Spring Pressure
Increasing spring pressure to compensate for an over adjusted knife can cause the knife to wear out even faster. And just as with higher temperatures, excess sealing pressure can split and damage the seals.
Clearance
Never adjust the clearance between the upper and lower sealing jaws to address cutting issues. Clearance should be set when the sealing jaws are installed and generally left unchanged.
Install New Anvils When Replacing Knives
Once you consider the problems caused by reusing anvils, you will better understand why installing a new anvil every time you replace a knife is the lowest cost, most productive practice for optimizing performance on flow wrappers and rotary vertical baggers.
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