Paper Machine Doctor Blade Components and Troubleshooting
Doctors are used on paper and board machines to remove excess water and contaminants from roll and cylinder surfaces, and to remove the sheet from these surfaces during sheet breaks and threading. Doctors must be properly installed and maintained to ensure their continued safe and efficient operation. It is important to examine worn blades and document wear patterns, and work with doctor and blade manufacturers to identify problems and improve doctoring operations. This course lists the potential causes and possible remedies for some well-known blade wear patterns. It also lists the steps necessary to properly install a doctor. [Discussion Points] Do you record doctor wear on your machine? Do you have a documented procedure for doctor installation for your machine?
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Learning Objectives
Identify the two main functions of paper and board machine doctors Identify the main components of a doctor and describe the purpose of each component Describe the two main types of doctor blade holders – rigid and self-conforming Identify common doctor blade materials List the key points involved in the proper installation of a doctor Identify the potential causes and possible remedies for some well-known blade wear patterns Describe safety hazards and considerations when working around paper machine doctors
Specs
| Course Level | Intermediate |
| Languages | English, French |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
What are the two basic types of paper machine doctor blade holders?
Rigid and self-conforming. Rigid holders are fitted to the roll initially and they do not automatically adjust. Self-conforming holders use one or two tubes to load the blade and they do automatically adjust to match the roll surface.
What are the three materials from which paper machine doctor blades are made?
Metals, composites (usually of resins and fibers), and plastics (usually a type of polyethylene).
What technique can be used to detect blade wear patterns that are more difficult to observe?
Lay the worn blade on the floor next to the straight back edge of another blade for comparison.
What could cause a blade edge to become feathered?
A feathered edge can be caused by a low blade angle, excessive blade loading pressure, or blade material that is too soft.
Why is it important to not increase a blade load after a blade has been used?
This can cause the tip of the blade to lift up (called “bird mouthing”), which can lead to debris getting trapped under the blade and sheet wrapping.
Sample Video Transcript
Once installed, to ensure the continued efficient operation of paper and board machine doctors examine doctored surfaces for cleanliness and lube showers for proper coverage on a daily basis. Also regularly check doctors for vibrations which can indicate bearing problems. Change all doctor blades on a regularly scheduled basis. This is important because as blades wear blade angles change which makes them less efficient. Inspect blade holders for damage and replace damaged holders immediately. Visually inspect loading mechanisms and oscillators and repair those that are not functioning properly, and visually inspect used blades and troubleshoot any unusual wear patterns. Doctor and blade manufacturers can help identify the causes and cures associated with many unusual blade wear patterns.
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