Experimental analysis of dynamic behaviors of cryogenic treated shafts

Rotating machinery systems play an important role in industry. These machinery systems are composed of various components, such as shafts, disks, and support bearings. The most used component is rotating shaft supported by rolling element bearing. Large amount of use of shafts indicate their vital contribution to the performance of rotating machinery. Due to necessity and vital contribution to most rotating machineries, the requirements on rotating shaft have become stricter everyday. These massive and flexible components dissipate energy through the system when corresponding to critical speeds in the system, and produce a unique pattern of a variety of response. Ignoring the occurrence of such dynamic behaviors may lead to catastrophic breakdown of the system. The demanding requirements placed on rotating machinery system have introduced a need for increasing reliability more than ever before. Rotating machineries must be designed to operate without excessive vibration throughout its range of operating speed. It is important to avoid vibrations in the system because excessive vibration can cause inefficiency and mechanical failure. The vibrations of a rotating machinery systems are influenced by number of parameters. One of parameters is rotating shaft material. Most of breakdowns in rotating machinery system are due to failure of the materials. The objective of this study is to show that the shaft materials properties have a significant influence on the efficiency of the rotating machinery systems. AISI 4140 steel material for shafts is chosen because of its widely used in the rotating shaft system such as automotive and machinery industry. It is used extensively in most industry for a wide range of applications such as; machinery parts and components, crankshafts, motor shafts, axle shafts, pump shafts, railway locomotive traction motor shaft. In this study; heat treated shafts were experimentally studied. In this study, ten categories of shafts were employed. The standart material (S) shaft was untreated. Conventional heat treated (CHT) shaft was firstly austenitized and tempered. After tempering, deep cryogenic treated (DCT) shaft was cooled to cryogenic temperature (- 140 °C) held at 12, 24, 36 and 48 hours for having four categories of the DCT shaft. After the DCT process Deep Cryogenic Treatment and Tempering (DCTT) shafts were tempered at 200 °C for 2 hours. The results obtained for experiments were presented and analyzed in detail. The results showed that the DCT36 and DCTT36 shafts dynamic behaviors were well and superior to the other shafts. Key words : Cryogenic treatment, Dynamic behavior, Roling element bearing, Shaft, Vibration analysis.