For shears, wire cutters, scissors, secateurs, pruners, snips
The Need for Scissor Sharpness Measurement
CATRA has been involved in the testing of performance characteristics of scissors , shears and other blades for over 50 years. In particular the problems of evaluating the cutting ability have been studied using various manual and mechanical methods. This knowledge has enabled CATRA to design an automatic test machine that meets the requirements of test laboratories, manufacturers and retailers.
Such a cutting performance test will enable users:
• to compare objectively various brands, designs and types of scissors and determine which one is superior to another
• to monitor the consistency of quality of cutting performance against the norm of manufacturing, to be sure that the knives are within the standard values agreed upon
• To be used as a development tool to enable research into the optimum steel, heat treatment, surface coating, edge geometry and finishing operations to suit the application.
Measurement of sharpness of scissors, shears and other two blade sharing type cutters is best achieved by measuring the effort required to cut a standardised material under controlled and repeatable test conditions. The lower the cutting effort the sharper and therefore the better the performance of the product is. This is achieved in this machine by mounting the scissors onto the adjustable spigots, one through each bow. (On non-bowed products special leg clamps are available) One of these spigots is rigidly mounted to the machine frame. The other is mounted to an adjustable motor driven crank arm, such that the pivot of the scissors is inline with the centre of rotation of the crank arm. This spigot also has an adjustable bow side pressure applicator that can be set to simulate the side pressure often applied by the human hand when operating scissors or shears.
Within the crank arm is a high accuracy force sensor, which reacts to the effort applied by the arm to close the scissors when rotating through a predetermined arc at the programmable speed of the test.
The test media, can take a number of forms, but normally for scissors, special paper is used, which has controlled abrasive properties, as specified in ISO 8442.5 for measuring knife sharpness. The media is stored and fed from a tension controlled roller system which allows coordinated incremental amount of media to be passed into the open blades of the scissors.
The scissors are then closed under the control of the crank arm, during which the applied force to the moveable bow are fully recorded in real time.
The controlling and data recording computer analyses the force curve and selects the peak force as a measure of sharpness, alternatively the total energy for the whole cut can be recorded , calculated and used as the comparative factor.
By repeating the cuts many times, the changes in the closing force can be monitored which then gives a measurement of the wear resistance of the device under test.
The system is fully programmable, so that the user can choose the test parameters, for example, the total number of test cycles, how often force measurements are taken etc. The speed of scissors operation can be slowed down during the force measurement cycle to reduce vibration from scissors ensuring a very clear picture of the cutting forces and any variation in performance along the blade length.
The test analysis software is windows based and integrated with Microsoft Excel for data manipulation / graphical representation/ test reporting and Access for data storage, which then allows easy comparison with previous tests.
Specification Scissors Testing Machine Free standing with own frame and safety screen, which are constructed in anodised aluminium and black oxide treated steel.
Please discuss with us any specific applications you may have, as the machine design is very flexible, we may be able to make simple modifications to suit your requirements, in terms of hardware, control system,data analysis software and test materials.
CATRA can also supply a range of consistent calibrated test materials in various formats, please discuss you requirements with us.
We have a small video clip available, showing the machine in operation, please contact us for a copy.
We at CATRA can also offer independent and confidential testing services using equipment of this type
Available directly from the manufacturers
The Worlds Cutting Technology Organisation
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