Frictional catastrophe behaviors and mechanisms of brake shoe for mine hoisters during repetitious emergency brakings

Abstract

Purpose -In order to improve the braking safety of mine hoisters, this paper aims to focus on the continuous repetitious emergency braking conditions to investigate an abnormal frictional phenomena called "Frictional catastrophe (FC)" and its mechanisms. Design/methodology/approach -The non-asbestos brake shoe of a mine hoister was selected as frictional material and its paring material is 16Mn steel. The tribological properties of the brake shoe were tested on the pad-on-disc friction tester by the simulation of continuous emergency braking conditions. The thermal analysis experiments, the temperature field simulations and the SEM analysis of the brake shoe were accomplished to reveal the mechanisms of the FC. Findings -It was found that the friction coefficient of the brake shoe sometimes falls suddenly during braking. This abnormal frictional phenomena is called "Frictional catastrophe (FC)". It is considered that the friction heat, which is accumulated rapidly by the braking on the surface of the brake shoe, makes the surface layer material qualitatively change from the solid state to a mixed state composed of gases, liquids and solid. The frictional modality of the braking changes accordingly from dry friction to lubrication with gases and liquids. The sudden lubrication makes the friction coefficient fall suddenly and induces the FC phenomena. Originality/value -An abnormal tribological phenomena called "Frictional catastrophe (FC)" was found in this paper. The investigations about the behaviors and mechanisms of the FC are considered helpful for improving the braking safety of mine hoisters and other machines.

Review on the friction and wear of brake materials

“…It has been proved that an abnormal tribological phenomenon called friction catastrophe (FC) is directly related to the lubrication film generated in emergency braking. [26][27][28] Friction and wear behaviors and mechanisms of brake's friction materials…”

Characterization and experiments on the friction catastrophe behaviors of brake material during emergency braking

“…2. Curves of the friction coefficient and surface temperature during ten times continuous emergency braking tests [11].…”

“…In order to reveal the mechanisms of the FC, the authors had carried out many investigations on the micro-structure, micro-composition, thermo-physical properties and temperature field of the friction material [17][18][19][20]. To sum up, the mechanism of the FC can be expressed as follows [11]. In continuous repeated brakings, the friction heat which is cumulated rapidly on the friction interface makes the surface friction material change qualitatively from solid state to a mixture state with gas, liquid and solid.…”

“…Obviously, once the abnormal tribological phenomenon is appearing in an emergency braking, the braking torque will decrease suddenly, which results easily in a terrible catastrophe. Therefore, the sudden falling phenomenon of friction coefficient in emergency braking was then called by the authors as Friction Catastrophe (FC) [11][12][13].…”

“…Presently, it is found that fractal geometry, chaos theory, wavelet principle and other modern nonlinear scientific theory have been applied to study tribological problems [9,10]. Earlier, the authors had found an abnormal tribological phenomenon and named it ''Friction Catastrophe, (FC)'', that is, the friction coefficient of brake material may drop sharply if it is subjected to an extreme braking condition with high speed, heavy load and high temperature [11]. Moreover the catastrophe theory was introduced to establish theoretical models for describing the FC [12,13].…”