Center for Tribology Research

Solutions for Paper Friction Testing

Advanced Paper Tribometer (PDF version)

Models: APT-2MT, APT-2M, APT-2HT, APT-2H

Features

  • Studies the fundamentals of paper friction, macro and micro-mechanical properties
  • Precise measurements of friction force, coefficient of kinetic friction, static friction, 
    stick-slip motion, adhesion, tear resistance, rupture resistance, paper wear and paper fatigue
  • Accurately performs repeatable and reproducible paper-on-paper sliding, paper-on-roller sliding,
    pen on paper sliding, eraser on paper sliding, tensile strength testing and indentation testing, 
  • Forces and loads from 0.1g to 20kg, Velocities from 1 micron/sec to 2500 meters/min 

Description

It is well known within the paper industry that the understanding and control of friction is a key parameter that is critical to measure in paper development, manufacturing and quality assurance testing. The science of friction, wear and lubrication is called tribology. The methodology of precision repeatable and reproducible measurements of friction and wear is called tribometrology. Developed and produced by CETR's 40-people-strong team of technical staff and tribologists, the Advanced Paper Tribometer is the most advanced instrument available today to study paper in moving interfaces.

The Advanced Paper Tribometer is a highly precise instrument and can accommodate both ideal friction pairs per industry standards or other non-standard interfaces that may be required by researchers either studying the fundamentals of paper friction or wishing to simulate exact real-world conditions. 

The micro-tribometer can provide any rotational or linear motion, in both vertical and horizontal directions, and thus fully simulate all the dynamics involved in moving paper interfaces. Sliding velocity can be as low as 0.5 microns per second to over 40 meters per second. Loading is produced using a computer controlled close-loop servomechanism for stability and accuracy (far superior to a dead weight mechanism) for constant or linearly increasing loads from 1 mN (0.1 g) to as high as 200 N (20Kg). Options to control temperature, humidity and atmospheric pressure at the interface are also available. Friction force (Fx), normal load (Fz), friction torque (FT) wear depth (WD) and acoustic emission (AE) are measured using a sophisticated A/D conversion system for real-time viewing and logged into the computer system for post-test analysis. Electric contact resistance (ECR), electric capacitance (EC) and a near-field focus digital camera are also readily available.

Typical Applications

Computer controlled experiments. Repeatable and reproducible data.

Friction Coefficient of Paper Sliding on Paper as a Function of Load

The envelope of Coefficient of Friction (COF) performance can be quickly characterized for paper sliding on paper at various normal loads. In this experiment load (Fz) was decreased from 500 mN (50 grams) to 50 mN (5 grams). Measurements were conducted during unidirectional linear sliding at a speed of 1 mm/s for a total of 60 seconds at each load. The lower paper specimen was held stationary on the flat surface of the lower stage. The moving upper paper specimen was mounted on a self-leveling flat surface to keep the upper paper exactly parallel to the lower paper surface while in motion. It is quickly evident that COF increases with decreasing normal force, indicating involvement of both elastic and plastic deformation at the paper interface as well as a creeping mechanism.

 

Paper Sliding on Rotating Rubber Roller (Stick-Slip Motion)

The envelope of Coefficient of Friction (COF) performance can be quickly characterized for paper sliding on paper at various normal loads. In this experiment load (Fz) was decreased from 500 mN (50 grams) to 50 mN (5 grams). Measurements were conducted during unidirectional linear sliding at a speed of 1 mm/s for a total of 60 seconds at each load. The lower paper specimen was held stationary on the flat surface of the lower stage. The moving upper paper specimen was mounted on a self-leveling flat surface to keep the upper paper exactly parallel to the lower paper surface while in motion. It is quickly evident that COF increases with decreasing normal force, indicating involvement of both elastic and plastic deformation at the paper interface as well as a creeping mechanism.

Paper Micro-Tensile Strength and Creep Test

The Advanced Paper Tribometer is an extremely flexible instrument capable of performing a variety of micro-mechanical experiments. In this example, deformation of paper during Micro-Tensile testing was observed and measured as a function of pull-force from 0 to 60 N then back to 0 N. As evident in the load-displacement plot, the displacement during the relaxation phase of the experiment is smaller than during the tension phase of the experiment. This behavior suggests that plastic deformation and creep deformation (visco-plastic) occurred in the paper sample under tension. This observation is also in agreement with a previous observation of COF as a function of normal force for this paper. For soft papers, the displacement will be larger at a given pull-force. One can also study the creep deformation at various increasing and decreasing rates of the pull-force.

 

Paper Tear-Strength Resistance Test

This experiment is designed to evaluate paper's ability to resist damage that may be caused by strong normal loads onto a point contact (simulating harsh pen-on-paper writing conditions). Normal force was linearly increased from 0 to 200 mN onto a pin during slow rotation of the paper. Friction force is displayed on the graph in green, acoustic emission (indicative of Stick-Slip encountered immediately preceding tearing and during paper tearing) is displayed in blue and normal load is displayed in red. At the time of 10 seconds, corresponding to a normal force of about 50 mN, start of tearing was evident by a sudden increase in acoustic emission and simultaneous change in the slope of the friction force plot. The normal force during start of tearing can be defined as the critical load. Needless to say, the higher the critical load measured for a given paper, the better the resistance of the paper to tearing.

Linearly Reciprocating Pencil Eraser On Paper Test (Micro-Wear)

Here we show an example of a real-world paper wear test for pencil eraser reciprocating against paper in a simulation of eraser action. Coefficient of friction (COF) was measured under a normal load of 10 grams, with the eraser reciprocating at a 10mm stroke with a velocity of 5 mm/s. COF continually increased with time as the eraser moved against the paper surface. This behavior suggests that the contact area between the eraser and the paper increased significantly during the test as paper and eraser material worn off so that the two surfaces (the eraser and the paper) became more confirming. Using this method, the Advanced Paper Tribometer proves to be very capable of distinguishing performance and durability of paper in an eraser-paper moving interface.

 

Advanced Paper Tribometer Features


 

Delivery and Prices

Center for Tribology offers nearly immediate delivery for the Advanced Paper Tribometer. Upon shipment, our installation engineer will travel to your laboratory and spend two days setting up the instrument, training your personnel and assisting you in developing test methods specific to your research.

CETR offers several payment options, including lease-to-buy terms, making the Advanced Paper Tribometer extremely affordable even for smaller laboratories.  Please call 1-408-376-4040 for pricing quotations and for information about a CETR distributor or agent nearest you.

Customization

We are proud to have an unusually strong engineering team that is always happy to customize the Advanced Paper Tribometer to your exact specifications. CETR can also assist you in supplying easy-to-operate ruggedized paper testers for high volume quality control and for production control in your paper mills.
Numerous new options are constantly being added to the Advanced Paper Tribometer by request of scientists in universities, commercial research labs and by industry organizations. Customizations are easily accommodated and very reasonably priced. If you have a unique request, please do not hesitate to contact us.

Warranty and Technical Support

The Advanced Paper Tribometer is covered by a full one-year warranty on manufacturer’s defects, both parts and labor. An extended warranty is available to ensure uninterrupted service for years to come. Our technical support department is proud of continuously maintaining a 24-hour response time to user calls and 48-hour response time to requests for parts and quotes for modifications. The Advanced Paper Tribometer is designed around a modular concept and new options to expand test capability can be added anytime without requiring factory installation. Whenever you have a technical question or want to request modifications to your existing hardware or software, our engineers will always be ready to support you. 

Published Papers


Contact CETR to discuss your testing needs in detail, for more information and pricing or to set up an appointment to visit our lab in Northern California. You will surely be pleased with our wide expertise, unique equipment and friendly effective services.