A new concept referred to as progression-based prediction of remaining life (PPRL) is proposed in the present paper in order to solve the problem of accurately predicting the remaining bearing life. The basic concept behind PPRL is to apply different prediction methods to different bearing running stages. A new prediction procedure which predicts precisely the remaining bearing life is developed on the basis of variables characterizing the state of a deterioration mechanism which are determined from on-line measurements and the application of PPRL via a compound model of neural computation. The procedure consists of on-line modelling of the bearing running state via neural networks and logic rules and not only can solve the boundary problem of remaining life but also can automatically adapt to changes in environmental factors. In addition, multi-step prediction is possible. The proposed technique enhances the traditional prediction methods of remaining bearing life.
The tremendous acoustic signal exiting during the plasma arc cutting process includes a lot of information about this process and has a close relation with cut quality. To investigate the relationship between the plasma arc cutting acoustic and cut quality, a number of experiments have been carried out. In the present study, cut quality by plasma arc is described by top and bottom kerf widths, bevel angle, and attached dross state, and the relationship between the evaluation items for cut quality and the SPL (sound pressure level) of the cutting acoustic is investigated in detail. It is shown that the SPL reaches a maximum as the bottom kerf width equals the diameter of the plasma arc potential core. The attached dross and kerf widths in a state of free dross obviously affect the low and high frequency components of the plasma arc cutting acoustic, respectively. These results also suggest the possibility of designing an acoustic-based monitoring system for the plasma arc cutting process.
Oxygen plasma arc cutting characteristics and cut surface quality factors are discussed in this paper. It has been carried out to cut the SS400 workpieces with various plate thicknesses. Such measurements as top and bottom kerf widths, bevel angle, straightness, dross attached level and cut surface roughness are used to evaluate the cut surface quality. A new classification method of the dross attached level, by which the dross attached level is classified into three kinds of states, is put forward. Influence of cutting conditions on cut shape and cut surface state is investigated in detail. With the increase of cutting speed and the decrease of arc current, kerf width decreases, bevel angle increases, while straightness varies within a variation range of about 0.2 mm for the thicknesses of 3.2 to 8.0 mm. And compared with top kerf width, bottom kerf width more rapidly decreases. Moreover, with the increase of cutting speed, the cut surface roughness exhibits a slight drop regardless of arc current, and under the present conditions the smoother cuts of Rz less than about 40 gm are obtained. It is proved that the dross attached state bears relation to not only cutting heat input, but also arc current and plate thickness. There are two dross attached areas, respectively, occurring under low and high cutting heat inputs. The heat input range obtaining the dross free cut varies with plate thickness. The dross free area gets wider when cutting current increases. Furthermore, it has been made clear that kerf width and bevel angle are approximately in linear proportion to the logarithm of cutting heat input for a given thickness, respectively. A vertical cut can be available under high cutting heat input.
The sound emitted during plasma arc cutting is closely related to the cutting conditions including cutting speed, arc current, operating gas owrate, torch standoff height, nozzle shape, etc., and it therefore contains useful information for the evaluation of the plasma arc cutting process. The present work investigates the characteristics of the sound emitted during plasma arc cutting under various cutting conditions, using fast Fourier transformation and probability statistical analyses. An acoustic model of plasma arc cutting, having two jet sound sources, is proposed to interpret this sound. The sensitive frequency band of the cutting sound and the relationship between the cutting sound and the conditions are then revealed. It is shown that the cutting sound is a random signal readily affected by cutting conditions, and its energy is concentrated in the high frequency eld and originates mainly from the mixing region of the rst sound source and the mixing and transition regions of the second sound source. Experimental results also suggest the possibility of developing an acoustically based monitor system for this plasma arc process, and of reducing the acoustic exposure level, thereby improving working conditions. STWJ/369The authors are in the
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