Conveyor Noise Specification and Control

Large, outdoor Belt Conveyor Systems for bulk materials are major sources of industrial noise and frequently become an environmental emissions issue for many existing and proposed plants. Deficiencies in the industry’s understanding of the complex, underlying conveyor noise generating mechanisms has meant there are relatively few practical and cost-effective noise management strategies. On the other hand, pressure from regulators and the community generally has frequently led to unachievable conveyor noise specifications. This paper presents the results of an innovative programme of research and testing of conveyors and conveyor components. Conveyor noise is shown to be a composite of noise generating mechanisms, the most dominant of which is the dynamic interaction at the belt/idler roll interface. The Idler Roll surface profile is shown to be a major input to excitation of vibration and noise radiation for most conveyors. An idler roll surface profile measurement parameter is proposed the Maximum Instantaneous Slope, (MIS) which can be used to evaluate and assess the operating condition and noise generation potential of existing equipment, as well as to provide a practical basis for specification of new conveyor systems. Introduction Large, outdoor Belt Conveyor Systems for bulk materials (refer Figure 1) are major sources of industrial noise and frequently become an environmental compliance issue for many existing and proposed plants. Figure 1. Typical Large Conveyor Belt System. Measured Sound Power Levels of conventional belt conveyors range from 113 dBA to 119 dBA per 100 m for typical 10,000 TPH 5 m/s coal conveyors. This paper presents results for standard and alternative idler roll designs, referred to as “low noise” and “super low noise” conveyors. Such conveyors produce sound power levels of 107 dBA and 101 dBA per 100 m respectively, while almost identical in all other respects. A infor with Hors conv roll/ sour idler poss O appl som idler (TIR D com mec and othe gene unac ∗ TIR rol on ma gau min To pat bet dep In a inte literature survey revealed very little published mation implying a general lack of understanding respect to conveyor noise generation mechanisms. tmeir [4], as far back as 1980 presents results of eyor noise investigations which identifies the idler belt interaction and structure-borne noise as major ces. Horstmeir concludes that improvement of the roll surface as well as damping treatments were ible noise reduction strategies. ther studies have shown little or no benefit from the ication of idler roll damping treatments, whereas e conveyor component suppliers were suggesting that rolls with low, total indicator run-out values, )∗, produced quiet conveyors. eficiencies in the industry’s understanding of the plex, underlying conveyor noise generating hanisms has meant there are relatively few practical cost-effective noise management strategies. On the r hand, pressure from regulators and the community rally has often led to the unsuccessful application of hievable conveyor noise specifications. is a measure of the gross "out of roundness" of the roller. As the ler surface is rotated past the head of a contact dial gauge, resting that surface, the TIR is measured as difference between the ximum contact gauge deflection versus the minimum contact ge deflection (ie effectively the maximum radius versus the imum radius). use the analogy of the earth’s surface, for a nominally circular h flown around the earth the TIR would measure the difference ween the altitude of the highest mountain on the path versus the th of the deepest point on the ocean on that same path. ny event TIR correlates poorly with noise level due to roller belt raction. The development of an effective method of conveyor noise specification for new plant also presented a significant challenge. To date, attempts to specify conveyor noise levels had been unsuccessful due in part to the complex interaction of all conveyor components, which are typically sourced from a variety of suppliers. Specifications which set out global conveyor sound pressure or sound power levels were clearly inadequate as respective component suppliers had no control over interacting components. Furthermore noise emission limits placed on individual components were also impractical as separate components would generally comply with such limits when tested in isolation. Once installed in the completed conveyor it was often impossible to separate the individual component contributions, even though the composite noise level may have been well over such limits. This paper presents the results of an extensive programme of research and testing of conveyors and conveyor components. Conveyor noise is shown to be a composite of noise generating mechanisms, the most dominant of which is the dynamic interaction at the belt/idler roll interface. The Idler Roll surface profile is shown to be a major input to excitation of vibration and noise radiation for most conveyors. An idler roll surface profile measurement parameter is proposed the Maximum Instantaneous Slope, (MIS) which can be used to evaluate and assess the operating condition and noise generation potential of existing equipment, as well as to provide a practical basis for specification of new conveyor systems. The current research has not include detailed investigation of the conveyor belt surface characteristics, however it is likely that the belt surface profile is every bit as important as the idler roll surface profile and could probably be assessed and specified in a similar manner if required. The belt surface profiles of the conveyors reported here were apparently sufficiently smooth so as not to control the belt/idler roll interaction, and hence could be ignored. This may of course not always be the case. It is not the intention of this paper to address conveyor noise issues due to wear of components. Preliminary Conveyor Noise Tests Early investigations included the measurement and analysis of farfield conveyor noise. Noise emanating from typical sections of 8000 TPH and 10000 TPH conveyors was recorded and analysed to produce narrowband and time domain plots. Figure 2 shows a sample time history of conveyor noise while Figure 3 shows a sample narrow band noise spectrum at 5 m from such a conveyor, (8000 TPH 5m/s). The strong appearance of harmonic activity, (Figure 3), spaced at the idler rotational speed supported the obvious amplitude modulation, (Figure 2). T char to a nois impu T som majo -0. -0. -0. -0. 0. 0. 0. 0. 0. 0. 0.