Technical Information - Airflex - #4

Airflex clutches and brakes are of the frictional type, that is, they rely upon a frictional force occurring between two surfaces to develop the required torque. The torque is called dynamic torque when slippage occurs be­tween the surfaces and static torque when no slippage occurs. Usually the two surfaces are of dissimilar materials. The combination of the two mate­rials used is referred to as a friction couple and their contacting surfaces as interfaces.

When the friction couple operates within a fluid, it is referred to as wet op­eration. Dry operation does not depend upon the presence of fluid.

Depending upon application, it may be desirable to have a large or small differential between the static and dynamic torques. For instance, when en­gagement is made at rest (no slippage between interfaces), as would occur for a clutch-coupling or a holding brake, the static torque should be more dominant. If the clutch or brake is required to slip continuously, as in a tensioning application, very little differential is desirable to avoid a stick-slip condition.

Standard linings - These are linings furnished as standard material on Airflex products which permits them to operate within their published capacities.

Lo-co linings - These are linings which have a coefficient of friction ap­proximately 65% of the standard linings. They are formulated for coefficient stability and wear characteristics and are used primarily for continuous slip applications.

Hi-co linings - These are linings which have a static coefficient of friction higher than the standard lining. They are used in applications requiring large locked-up torques with little or no slip between interfaces.

Two common types of hi-co linings furnished by Airflex are neoprene rub­ber and cork composite. The cork material is pressure sensitive. When this material is used, published torque ratings are increased by the factor ob­tained from the graph shown.

Friction material is a specially formulated composition intended to provide a specific stable coefficient of friction over a wide range of operating temper­ature. Beyond the operating range, the coefficient drops drastically, result­ing in loss of frictional force. This condition is referred to as lining fade.

Some desirable friction material properties are that they have good wear life, be non-aggressive to the surface they interface with, and have suffi­cient strength so they can be attached to other components. The material is basically a replaceable lining to which wear can be confined; hence, the de­scription friction lining.

The majority of Airflex products utilize organic linings. Their composition consists of three types of ingredients - fillers, fibers and binders. Fillers, in addition to providing bulk and assisting in material processing, are used as augmenting agents to affect the coefficient of friction. Fibers are used for reinforcement. Binders bond all the ingredients together.

Airflex magnetic and hydraulic products utilize sintered metal lining. This friction material is produced from a mixture of powdered metals and non-metals by pressure and fusion. Its primary advantage is being able to withstand high thermal stresses and operating pressures. To assist in heat dissipation, and because of its aggressiveness on its mating surface, it is intended for wet operation.

Friction linings offered by Airflex fall into three categories which are de­scriptive of their coefficient of friction. Due to the nature of the products and their suitability to specific applications, linings in each category are not available for all product lines or models. The three categories are:

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Copyright Eaton Corporation, 1995, All rights reserved.