Gorazd Bombek

Velocity measurements in a shotblasting machine

Abstract Abrasive shotblasting particles and a high concentration of dust within the closed testing chamber make particle velocity measurement in a shotblasting machine very difficult. The application of non-obstructive optical methods is usually impossible. Robust shields protecting the sensors from abrasion have to be used for contacting velocity measurements and make direct application of capacitive or electrodynamic sensors usually applied in the correlation-based velocity measurements methods not possible. An alternative electronic measurement system has been developed. It has a simple construction and uses low cost elements which can be replaced very quickly and, therefore, no robust shields are necessary. This enables very good mobility and positioning of the sensor along both axis in a cross-section plane of a particle stream. The system has been tested along with a robust mechanical measuring device. The development, operation and application of mechanical and electronic particle velocity measurement system are described in this paper. Experimental results are presented, discussed and both methods are compared.

Research into the possible causes of squealing brake-drums

This paper presents a problem-solving procedure regarding brake-drum noise issues performed by engineers within a short time period and additional measures to be taken for avoiding similar issues in the future. Cimos TAM Ai company is a member of Cimos Group, which is a component producer in the automotive industry. We have taken the production of the rear brake-drums during the phase of the car manufacturing (transfer of production). Soon after the instigation of this production, the customer reported squealing issues with the brake-drums. No detailed information was received about the issue except that it occurred on new cars during everyday operation. It was our goal to find the root cause, fix the issue and take some preventive actions. Research was based on comparing the Cimos brake-drum (B) with the brake-drum of previous supplier (A). The research was focused on resonant frequency of the brake-drum as the most likely parameter connected to the squealing. First the natural frequency of drums A and B was determined by impact-hammer test. Then a numerical simulation was carried out with the goal of detecting the most problematic surface of the drum for causing the squealing. A weakness was found in the brake-drum design where no thickness or tolerance was specified at the critical area, and large deviations existed between the finished brake-drums. The problem was solved by changing the machining parameters. Besides solving the noise problem, an in-depth investigation was conducted into the gray cast-iron modulus of elasticity, in order to find a representative value for those small deformations occurring in cases dealing with noise-emission issues. This value proved to be higher than in the case of larger deformations as considered during mechanical and temperature behavior simulations.