Paper Trim Removal
CFW provides fans, blowers, valves and ducting suitable for paper trim removal applications. We supply both standard and custom fans and components. We also provide cyclones, dust collectors, and temperature and humidity control systems. CFW has decades of experience with air technology systems. To ensure that your pneumatic conveying system operates reliably and efficiently, contact our sales engineers.
During the manufacture of paper, the roll winding and finishing processes produce “trim”, a form of paper broke. Trim also results from printing and packaging operations. It can build up and cause problems in production lines, necessitating the use of trim removal (also known as trim extraction) systems. The importance of adequate trim handling systems and their effect on profits often goes unrealised. Trim removal prevents trim blockages at production lines, thus increasing production up-times and permitting machinery to run faster. The trim can be recovered, stored in hoppers and eventually transported to a repulper to reduce costs resulting from material loss.
The paper grade, market demand and type of manufacturing process determine the amount of trim, which is typically 3%-5% of total production. This figure is not usually constant and can increase to 12% or more at times. The precise requirements of a manufacturer regarding sizing can only be determined by factoring in considerations gained from experience.
It is vital to select the right equipment to deal with paper trim. While various trim systems are in use (eductor tubes, choppers, cyclone separators), vacuum, or negative pressure, pneumatic conveying systems are becoming the norm because of their low noise output and energy efficiency. Variable-speed fans or variable-speed drives are often recommended for better control and cost reductions. Venturi eductors are also common, since they avoid the problem of trim hitting moving parts. Many factors need to be taken into account when considering the best system for a particular application, including line speed, trim stiffness and width, number of machines (such as winders), energy costs, and conveying distance.
Cyclones, a more conventional solution, are very big. Their size generally requires outside installation, where efficiency may be influenced by environmental conditions, and additional pipes are usually necessary for conveying. They use a great deal of energy and tend to concentrate dust unless filters are used. Accessing the hopper in which the scrap is collected while a cyclone separator is working also causes scrap and dust to blow around and exit the hopper.
A well-functioning vacuum pneumatic conveying system for trim removal has many benefits.
- Production efficiency: Costs are reduced by automating the trim collection process rather than relying on labour, and production uptime is increased.
- Energy efficiency: Vacuum pneumatic conveying systems sometimes have a higher capital cost, but can save money on electricity use. There is no chopping operation, simplifying the process. A high-efficiency fan does the work of moving trim continuously through the system.
- Space: Pneumatic conveying systems are compact and do not require allowing for the floor clutter present in non-automated production processes. This improves layout flexibility and reduces the risk of accidents.
- Low noise: The conveying system is enclosed and air velocities can be closely controlled to reduce noise pollution.
- Fewer dust control problems: A properly constructed pneumatic conveying system releases very little dust because the lines are enclosed, resulting in a clean and healthy space.
- No air discharge problems: Large amounts of air do not enter the pulper.
- Flexible: The lack of excess air makes for flexible and narrow ducting across longer distances. It is possible to have more choices about trim chute configuration and blower placement.
- Reliable: Maintenance on valves and other parts can be lower because air velocities and pressure differentials are low. There are no moving parts in the air stream, eliminating the hazards of sparking and reducing material degradation, dust generation and part abrasion. Greater control over air velocity also means a more consistently high-quality product.
- High capacity: The system can be connected to many winders at once and can allow trimming at the full speed of which modern winders are capable. It can also handle very wide trims.
Very heavy grades of paper must be chopped or shredded as they cannot be conveyed to the repulper unbroken. For these types of paper, positive pressure trim handling systems are preferable. However, these pneumatic conveying systems still have many of the same advantages, including the reduction of noise and dust.
In some cases, the upgrading of older technology is required. In these cases, a specially designed trim handler can be used. This might be
- A shredder fan: This solution incorporates a negative pressure system with an integrated chopper fan. The replaceable blades cut the trim in pieces and, at the same time, the fan blows them into a separator for recovery.
- An ejector vacuum system: The negative pressure is produced by ejectors instead of more conventional kinds of air mover. Trim is continuously conveyed, almost always to a repulper.
- A hybrid system with a chopper. If the trim speed is low and the paper is very tough, a chopper can be used before the trim is transported by one of the pneumatic conveyor systems mentioned above.
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