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What is Crush Strength for Paperboard Cores?

The crush strength of the core refers to the capacity of a material to withstand pressure. In the context of paperboard cores, crush strength indicates how much load the cylindrical structure can bear before collapsing or becoming compressed. This characteristic ensures the functionality of the core for specific applications and usage in the industry.

How is Crush Strength Measured?

Measuring crush strength is a meticulous process that involves applying steady pressure to the paperboard cores until they compress or collapse. This pressure is measured in pounds per square inch. Two common industry-standard tests are the Radial Crush Test and Flat Crush Test.

Radial Crush Test

The Radial Crush Test is a procedure where a paperboard core is subjected to pressure from all sides, simulating the forces it would face in usage. During the test, a core is placed into a machine equipped with a bladder. The bladder is then inflated, exerting uniform pressure around the circumference of the core until the material either collapses, creases, or compresses. Essentially, the Radial Crush Test measures the core’s resistance to inward crushing forces, reflecting its ability to retain structural integrity under stress.

Flat Crush Testing

The Flat Crush test is a measure of the strength of a core to withstand directional force.  This test is administered by placing a core between two plates that apply a downward force onto the core. When the instrument detects a variation in the core structure, it records the peak force.  This test identifies the maximum force that a core can withstand before it alters its original properties.

How Do You Know What Crush Strength is Needed?

Determining the crush strength required for a product is a nuanced process that depends on factors such as the weight and force of the anticipated product application.

The following are general criteria to be considered in determining the required crush strength set forth by the CCTI for industry standards:

  • Product Weight: The product weight will impact the core specifications needed for those applications.
  • Strength Preservation: The core must withstand the pressure of the wound material. Materials like film possess memory – when stretched, it strives to return to its original state.
  • Handling and Transportation: Paperboard cores must maintain their integrity when subjected to the rigors of moving and transporting.
  • Paperboard Attributes: The type of paperboard used, thickness, and the number of layers in the core influence the crush strength.

Crush strength isn’t just a technical parameter but a critical element in the design and manufacturing of paperboard cores. By understanding and testing for the correct crush strength, you can ensure that your paperboard cores will arrive with the specifications needed for your applications. This process can be determined and tested in collaboration with your Ox sales representative.