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Industry Applications - Packaging, Paper & Converting

IR Sensors in Paper Coating
Infrared Temperature Measurement in Paper and Converting Processing

Noncontact infrared thermometers are used in many applications for paper production and processing paper into finished products. From processing the pulp to converting the paper into labels, lottery tickets and coated papers, the temperature of the product is critical to improve the quality, insure proper drying and reduce production costs.

Listed below are just a few examples of how Ircon IR sensors are used in several common applications. For additional applications and product recommendations,  please contact our application engineers.

Paper Pulp Processing

To produce paper, the pulp wood is placed in a digester to dissolve the cellulose and produce the wood fibers. The byproduct of the process is black liquor, which has to be recycled into green liquor. The black liquor is sprayed into a black liquor recovery boiler and burned. The bed temperature has to be carefully monitored to insure complete burning of the cellulous and produce green liquor. If the liquor is too wet, it will cause a “black out” condition; if there is a lack of combustible material then a starving condition occurs. The bed temperature has to be maintained at about 1900ºF (1037ºC) to keep it burning. By using 4 two color thermometers, one in each of the 4 corners of the boiler, the low temperature can be detected and additional fuel is added to complete the combustion. In addition, the gas temperature in the boiler tube area has to be hot enough to prevent the fly ash from building up on the water tubes. Instruments like the Ircon® Infrarail will measure the hot gases and provide a linear output for alarms and controlling.

The green liquor is then placed into a rotary kiln, along with other chemicals, and heated to about 2100ºF (1150ºC). The end product temperature is critical to insure complete recycling of the green liquor and preparing the material to be reused in the digester. Often the entire kiln shell temperature is monitored with a linescanner to detect hot spots in the kiln or excessive wear of the refractory.

Recommended products: Modline® 5R for the bed temperature and kiln lime monitoring and InfraRail type S for the gas temperature.

Paper Converting

Paper becomes the basic material for hundreds of products, such as labels, catalogs, lottery tickets, boxes for food and lamination with plastic films. The process of converting requires the drying of inks or coatings in a hot air oven, which has many zones, and the temperature of the product in each zone has to be carefully controlled to insure proper drying. If the product is not dried correctly, the coating can be blistered, remain wet or overheated, which changes the color of the inks and often destroys the product. A common practice to insure proper drying is to slightly overheat the product. With the use of infrared thermometers, the correct product temperature is established and the fuel savings can be easily achieved.

The paper converting temperatures can be controlled using an 8-14 micron thermometer, like the Modline® 74 series. It is suggested that an air purge accessory be attached to the sensor to insure that none of the solvents adhere to the lens and cause low temperature indications.

Paper Drying

In a paper mill, the paper leaves the fourdrinier and proceeds to wind over several steam heated rolls to dry it before it is rolled up. If the drying is not complete, there will be streaks of water on the paper, which need to be detected. A linescanner with a high scan rate will scan the paper and indicate cold spots and streaks. These cold spots indicate the presence of excess moisture. The ScanIR®3 Linescanner and Thermal Imaging System provides a 2D image of the defects and alarms to indicate their presence.

Cardboard Production

Single layer linerboard or cardboard consists of an outer ply, a corrugated core and another outer ply. All of this is glued together in a machine called a corrugator. The glue is cured as the board passes over a steam heated roll. The temperature is controlled by how much the board is wrapped around the roll and the tension on the board. Temperature measurement is required at the center and both edges to insure proper bonding and flatness of the board. Uneven heating can cause the board to warp. Heavier boxes can consist of multiple layers of single ply and corrugated board. Each layer has to be dried to insure good bonding and to insure the product remains flat.

Cardboard production temperatures can be measured and controlled with the Modline 74 series.

Every step in the paper manufacturing and converting process can benefit from the use of Ircon infrared thermometers. These benefits include:

  • Increased product quality and uniformity
  • Reduced production costs and faster startups
  • Eliminated excess fuel usage
  • Automated process control
  • Reduced scrap

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