Paper Machine Doctors
Doctors are used in all sections of paper and board machines to remove excess water and contaminants from roll surfaces. In some applications, they are also used to remove the sheet from roll surfaces on sheet breaks or during sheet threading. Doctors must be checked and inspected on a regular basis to ensure their continued, safe, efficient operation.
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Learning Objectives
• Identify the two main functions of paper machine doctors • Identify and describe the safety hazards associated with roll doctors and doctor blades • Identify the key components of a doctor • Identify the purpose of the doctor components • Differentiate between mechanically-adjusted and self-conforming blade holders • Identify typical locations for doctors on paper and board machines • Explain the importance of regular doctor and doctor blade inspections • Identify and describe key inspection points for doctors and doctor blades
Specs
| Course Level | Intermediate |
| Languages | English, Portuguese, French, Polish, Russian |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
Why are flexible, self-conforming doctor blade holders used on some rolls?
Flexible, self-conforming blade holders utilize two fluid-filled or air-filled tubes to load the blade against a roll surface. They maintain a uniform pressure on the blade across the machine and automatically compensate for changes to the roll surface, including roll deflection.
Why should you avoid increasing the load on a used doctor blade?
This can cause the blade tip to lift up, which greatly increases the risk of the sheet wrapping the roll.
Why are double doctors used on some suction rolls?
The first blade removes surface water and creates a vacuum pulse that pulls water out of the holes in the roll shell. This water is then removed by the second blade.
Where are air doctors used on paper and board machines?
Air doctors are used on drilled and grooved surfaces to prevent the type of damage that can be caused by contacting doctor blades.
Why is it important to change doctor blades on a regular basis?
This is important because as blades wear, blade angles change, which makes them less efficient.
Sample Video Transcript
Double doctors are often used on the suction couch roll to improve moisture profile and runnability, minimize rewet of the sheet, and keep the roll shell clean. The first blade removes surface water and creates a vacuum pulse that pulls water out of the roll holes. This water is then removed by the second blade. The center press roll double doctor is often accompanied by a roll shower to keep the roll surface clean. This doctor is often used to remove the sheet to a broke chute. And so the doctor back must be designed to withstand the additional force required.
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