Why Blade Holders Are Essential To The Doctoring Process?

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Read expert's view over the use of blade holders for smoother doctoring process in paper mills.

 Why Blade Holders Are Essential To The Doctoring Process?

For better understanding, the role blade holders play in the doctoring and roll cleaning process, Read the interview of Mr.Scott, Product Line Manager – Doctoring for Kadant Solutions Division. Scott has worked for Kadant Solutions for 18 years and provides doctoring and roll cleaning support to the organization’s sales team.

What is a blade holder?

Blade holders are an essential part of the doctoring or roll cleaning system. The blade holder is mounted or integrated into the doctor or roll cleaning structure. Its main purpose is to hold the blade in place. The blade is the working portion of the system that engages the roll surface to perform the function of cleaning and removing water or contaminants or the sheet from the roll surface. 

What makes the blade holder an essential part of the doctoring or roll cleaning process?

Blade holders are each designed to provide the best doctoring or roll cleaning results for a given application. There are many types of blade holders available from rigid to flexible to self-profiling. Each type of blade holder has different functionality. Selection of the appropriate blade holder is critical to the success of proper doctoring or roll cleaning for a given application.

How can you determine the best blade holder for a process?

The first step is understanding the functions the blade must perform. Some questions to ask include:

• Is the blade removing water, fiber, contaminants, product, sheet, or something else?

• What is the blade holder environment?

• What is the temperature?

• Is it dry or wet?

• What level of roll cleaning is needed?

• What is the roll material?

Often a new doctoring or roll cleaning system is specified, but sometimes a blade holder to mount on an existing doctor structure is supplied.  If the latter is the case, it’s important to understand how the doctor blade is engaging to the roll. Is the holder providing blade loading to roll or is the entire doctor system rotating the blade into the roll? This will help determine the holder selection. Does the process require a rigid holder or a flexible holder? Not all rolls have a flat profile due to design or wear. Also, some rolls will change shape when the machine is in operation due to the application. For these scenarios, a flexible or self-profiling holder may be more beneficial than a rigid holder. 

Earlier you mentioned blade loading. What are typical blade load requirements?

Blade holders are designed to handle different blade load requirements. Understanding the environment is important for holder construction options. Some holders can be supplied with metallic components, but options for composite holders and blends of composites and metal are available. Temperature and duty are important in the selection of specific holder sub-components like top plates and loading tube materials.

What is one interesting thing you have learned about blade holders during your tenure at Kadant?

I have learned a lot about blade holder history going back more than 50 years. A year doesn’t go by that I don’t receive an inquiry for a blade holder I don’t recognize. Usually, I discover it’s a very old holder from a previous Kadant acquired business. Gathering information about these types of requests has helped me understand the development of blade holder technology over the last 50-60 years. Understanding the history of holder technology is important to integrating past successes to a new holder design. 

Have you experienced any unusual situations with blade holders?

I have experienced some unusual situations with blade holders installed on process equipment.   Several times I have rushed to a mill site due to poor holder performance on critical applications.  Often the performance is so bad that the doctor blade could not shed the sheet from the roll causing the roll to wrap which leads to downtime and even the mill purchasing new felts. After investigating the holder in each application, we often discover that either the holder was recently rebuilt and assembled improperly or without all the parts! 


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