Bomlu kazı makinalarında kesici kafa tasarım parametrelerinin incelenmesi

Abstract

Bu çalışmada, bomlu kazı makinaları kesici kafa tasarım parametrelerinin kazı verimine ve makina dengesine etkisi incelenmiştir. Bomlu kazı makinaları kesici kafa tasarım parametreleriyle ilgili araştırmalardan yararlanarak kesici kafa kazı performansı analizi yapan bir bilgisayar programı geliştirilmiştir. Hazırlanan bilgisayar programı ile, bir bomlu kazı makinası kesici kafasının arma girme ve arını tarama modunda verilen kayaç için bom kuvvetleri, tork ve güç gereksinimleri hesaplanmaktadır. Ayrıca, her iki mod için, kesici kafanın bir dönüşü sırasında itme kuvveti, tarama kuvveti, tork. güç ve kayaçla kontak halindeki keski sayısına ait titreşimler de elde edilmektedir. Program yardımıyla, orijinal kesici kafa üzerinde yapılacak değişiklerin kesici kafa performansına ve dengesine etkisi gözlenebilmektedir. Programda, AM-75 bomlu kazı makinası kesici kafasının welded tuff lar için performans analizi yapılmıştır. Earth Mechanics Institute (EMI) / Colorado School of Mines (CSM) tarafından yapılan Yucca Mountain Projesi'ndeki AM-75 kesici kafası tasarım parametreleri ve welded tuff in lineer kesme deneyi verileri kullanılmıştır. AM-75 kesici kafasının EMİ / CSM analiz sonuçlarıyla hazırlanan programın analiz sonuçları yaklaşık aynı bulunmuştur. AM-75 kesici kafası analizi sonucu elde edilen titreşim grafikleri irdelenmiş ve titreşimin en önemli nedeninin, kesici kafa döndükçe, her bir segment için kayaçla kontak halindeki keski sayısının sabit olmamasından kaynaklandığı saptanmıştır. Titreşimi azaltabilmek için keskiler arası çevresel uzaklığın ve her bir keskiye gelen yükün eşit dağıtılması gerektiği görülmüştür.

In this study, roadheader cutting head desing parameters are researched that given Section 1-4. A computer programme was writen to analyse the performance of a roadheader cutting head. In Section 5, the programme design and results are given. Better cutting head design and analysis methods can lead to higher productivty of the roadheaders and improved pick utilization and pick life. Also, which means reduced vibration and bearing damage could be achived by proper design of cutting heads. Optimum cutting geometry is determined by rock cuttabilityand mechanical behavior. Therefore, the starting step in head design is the analiysis of rock type and cuttability. This parameter dictates the type of the tools to be used as well as the cutting geometry, or spacing and penetration. The tool type is mainly a choice of point attack or drag tools. Roadheader cutting head type is axial or transverse type. An axial cutting head is a single cutting head which is arranged axially to the cutter boom axis. Transverse cutting heads comprise two symmetrically positioned cutting head halves, the rotational axis of which is arranged perpendicular to the boom axis. The boom reaction in slewing and axial direction were calculated for both motions by Hekimoğlu. The results show that the direction and the magnitude of the resultant force are significantly affected by the cutting head design. The highest components of the result reaction force may then seen to be located on the plane perpendicular to the boom axis for the axial heads; whilst it is on the plane parallel to the boom axis for the transverse heads. With the axial cutting heads, the fact that the resultant force acts on the boom in a sideways fashion is disadvantegous and is likely to impair the machine stability. Therefore, adequate weight is necessary to match this relatively high sideways reaction. With transverse cutting heads the fact taht the highest components are on a plane parallel to the boom axis means that adequate force should be provided for lifting. xn After choosing the head type and proper spacing, one allocate the cutters on the head and define the head geometry based on the requirements of each type head. Allocation of cutters on the head is controlled by line spacing and circumferential spacing. Line spacing is the distance between the tracks of two neighboring cuts. Hurt and MacAndrew reported that the number of tools in a cutting line should not exceed half the number of cutting sequences. Line spacing must be maintained constant over the cutting profile It could be simply realized that spacing has projection in two planes, one for sumping profile and the other for slewing or arcing. From the spacing in each profile, the cutting area tool could be calculated for a nominal depth of sump. This value should be maintained more or less constant by controlling the tool spacing in each plane. In fact due to the 3-D geometry of the head and variable depth of sump, controlling the cutting area per tool distribution is very complicated. One should bear in mind that cutting area per tool also represents the cutting forces on the tools and uniform distribution of forces is an essential element in balancing. Circumferential spacing has an important effect on the load and force distribution on the head. The circumferantial spacing is the angular disposition of the tools viewed on a plane perpendicular to axis of cutting head rotation. It has an cirucial impact on the head balancing by defining the number of the tools in contact for each segment of cutter head as it rotates. In other words, while the heads is cutting rock (rotating), different segments of cutting head are exposed to the rock at any given time and they must have equal number of tools if possible. Variation in number of tools in contact cause variation in total cutting forces and torque which means vibration of the head. It is apparent that higher vibration caused by an uneven distribution of tools can adversely affect the production rate, tool life, and bearing life. With equally distributed circumferential spacing better balanced cutting heads can be achieved. Hekimoğlu (1991) has provided an extensive study of circumferential spacing by examinig the theoretical analysis, laboratory performance of heads (contolled environment), and field experience with different head designs. Number of starts can be determined by line and circumferential spacing between the tools and arrays. The sum of circumferential spacing (angles) between tools in an array defines the wrap angle. A wrap angle of 360° means each array is wrapped one full turn around the head (or starts and ends with one full rotation of the head). The wrap angles over 360° can produce the best result while they are easier to fabricate due to better block allocation and lower interference. According to his study, 3 start heads superior to 2 starts for the axial heads of medium duty roadheaders tested in his experiments. The nose area in the cutting head which has a very limited space and hence, xni limited number of blocks could be placed in this area. This limits the choice of locations for the tool blocks and their angle towards the face. Another factor to be considered is the restrictions in space of the nose are dictated by holes for installation bolts. There is not much freedom in positioning of these holes. Besides, nose tools in axial head should cut a confined area with tools turning within a short radius since this is the forefront of the cutting head during the sumping. As a result, cutting condition is very difficult and tools must take great loads. One solution could be putting more cutters in this area, but obviously it is not possible due to limited space available. Therefore, problem of tool allocation in nose area is more severe with axial heads. On the transverse heads, on contrary, the cutting area for nose tools is limited and these tools have the luxury of cutting towards a free face. This means lower loads and lower number of tools in this area. Lower number of tools are in contact in each mode of cutting since the tool path is cleared by proceeding tools. In addition, this prevents low cut spacing during the cutting in each action mode since the main portion of the face is already cut by more widely spaced tools. Higher efficiency and production rates is achievable by this arrangement since most of the production comes from tools that are optimally spaced. Low spacing, as already was mentioned, results in low efficiency and higher specific energy and should be avoided as much as possible. Number of tools to be placed on a head is a function of head size, tool spacing, and number of starts. Among the above parameters, the number of starts can be changed to find the optimum number of tools. Selection of number of starts and thus tool number has two effects on the head. One is that reduced number of tools increases the force and power available per cutter. The other factor is the head vibration which will increase ( the magnitude of force variation ) with decreased number of tools. The head vibration could be reduced by increasing the number of tools which result in more stable cutting head and prolonged tool and bearing life. This on one hand may increases productivity, but on the other hand may adversly effect and reduce it due to smaller depth of penetration due to lower forces available per tool. It is recommended that few different arrangements be stutied to find the optimum solution which is a compromise between these two effects. Tilt angle of tools on the head is an important factor regarding the cutting efficiency and tool life. Tool forces and tool duites become different wiht tilt angle. It is recommended to tilt the tools to the angle perpendicular to the cutting face. This means that each tool should be perpendicular to the cutting profile at its own position. Tilt angle is measured from the plane of rotation which is perpendicular to rotation axis. Tilt angle of zero means that tool is in the plane of rotation and perpendicular to head axis and 90° means that tool is parallel to the axis. On the axial head, the tilt angle varies xiv from 90° in the nose area to zero at the end if the head is dome shaped. Tools on the main face of axial heads are almost equal to the half angle of head cone. On transverse machines, this angle starts at about 70° and is reduced to zero and negative values in the back trimming area. Hekimoğlu reported that effective tool spacing and tool cutting position continuosly very with tilt angle. Corner cutting tool behaves as a gaugae tool after the value where the tilt angle is approximately equal to the breakout angle of the rock when cutting on a flat rock surface. The cutting head geometry is an important factor regarding the cutting efficinency and torgue and arcing force fluctuations. Hekimoğlu reported that conical cutting heads exhit lower torque and slewing force and their associated fluctuations, combine cuting heads with lower cone angles, however, emerge to be more advantageous in terms of respirable dust generation and tool durability. He compared axial and transverse cutting heads on dynamic and kinematic basis. The resultant boom force reaction act perpendicular axis for a axial head, whilst it tended to act paraleli the boom axis for a transverse head. The change in the magnitude of the resultant boom reaction are relatively high for the transverse heads during transitions from arcing to lifting. In this study, a computer programme is written to analyze the performans of a roadheader cutting head by using basis cutting head desing principles and method analysis of roadheader cutting head performance of Earth Mechanics Institues (EMI) / Colorado School of Mines (CSM). The computer programme is written in C ++ programme language. The program provides to analyze any cutter head in different modes of action. It allows monitoring the variations of cutting head parameters as the head rotates and enables user to simulate vibration on the cutting head. Using this feature, it is fairly easy to optimize the cutterhead geometry. Besides, for the head lacing of an existing machine, the maximum depth of sump within the capacities of the machine could be found. A rough performance prediction based on sumping depth and penetration per revolution for a given RPM can be obtained from this program. The performance analysis of AM-75 roadheader cutting heads for welded tuffs is carried out by the help of the computer programme. AM-75 roadheader cutting head design parameters and data for linear cutting experiments of welded tuffs are taken from Yucca Mountain Projects carried out by EMI / CSM. The result of the computer programme are compared with the EMI / CSM results and it is observed that both are very similar. Vibrating grafics are taken from the computer programme for AM-75 is examined. It is observed that number of tools for any segment is not xv constant. Variation in number of tools in contact cause variation in total cutting forces and torque which means vibration of the head. These types of the vibration can be reduced by keeping the circumferential spacing equal between the tools. Also the vibration can be reduced by distributing the force equally among the tools. For this, cutting depth of the tools and lateral spacing between the tools must be equal. Doing this especially for noise section of roadheader cutting heads is not easy. However. S/d ratio along the head should be equally. In order to tools to have equal maximum depth of cut, the cutting starts must be designed in equal along the head circumference. The experiments to obtain the relationships between the lateral spacing of tools and the cutting forces should be made and results should be added to the computer programme. In this way, the effect of the spacing between tools on the cutting head performance and vibration can be studied.