Deck machinery is the special machinery equipment for ship outfitting, mainly including the anchor winch and ship crane installed on deck. Among them, the ship crane is mainly equipped with a series of characteristics, such as compact structure, convenient operation, large lifting weight, quick action, high efficiency and convenient maintenance, etc., in a large bulk cargo ship of 30,000-50,000-ton class, and plays an important role in modern ship deck machinery.
At present, the Marine crane has formed a series of production in China through the introduction and transformation of foreign technology in the past 20 years. Except the ordinary crane, the slimming crane, the double crane and the hose crane have also been produced in series. However, most ship cranes were imported from abroad before 2003, especially the slewing bearing in the rotary mechanism which connected the rotating tower body and fixed base column. As an extremely large ship crane kit, due to the particularity of the use environment, the selection and development design of the ship crane were still blank in China at that time. FRB Bearings work with a domestic Marine machinery factory to select and design slewing bearings.
1. Analysis of bearing selection
1.1 Installation site
Marine crane mainly consists of rotating tower body, lifting arm, fixed base column welded on deck, lifting, pitching and rotating mechanism, hydraulic power and pipeline system, electrical control system and other parts.
The bottom of the crane tower is installed with the turntable bearing for the ship crane. The bottom end face of the inner ring is connected with the fixed base column welded on the deck of the ship through bolts. The end face of the outer ring is connected with the crane tower body through bolts. When the ship crane works, the small rotary gear driven by the rotary mechanism meshes with the inner gear ring of the slewing bearing to realize the outer ring rotation, thus realizing the normal rotation of the ship crane.
1.2 mechanical characteristics and common bearing structures
The function of swing bearing is to support ship crane and transfer torque, mainly bearing axial force and overturning moment. In order to make the structure of the main engine compact, the bearing diameter and height are much smaller than the normal product, and the weight is not set, its overturning moment can reach 18 times the axial force, the ratio of the two is basically between 14.9 and l8. At present, the most commonly used structures are double row eccentric ball slewing bearing and three row cylinder roller combined slewing ring.
Due to the following characteristics of double row ball slewing bearing with different diameter, it can withstand a large overturning moment and is more suitable for crane operation. The ability to resist the roughness of the bottom plate is strong, which can make up the machining error of the joint. Radial dimensions are relatively small.
2. Selection of materials and sealing structures
2.1 Material
At present, both at home and abroad with 42CrMo alloy quenched and tempered steel as the material of bearing ring, on the normal bearing mechanics performance requirements, should also meet: (1) in a 20 ℃ when charpy V impact absorbing energy of three specimens shall be not less than the average of 42J, one of the sample should be not less than 27J; (2) the quality control hardness of the gear ring reaches 260-290HB. The material of steel ball is commonly used bearing steel, which is no different from that of general slewing bearing.
2.2 Bearing seal
Because Marine crane slewing bearing in the process of work are highly susceptible to erosion, sea water thereof so as to prevent the water of the sea into the lead to bearing failure in advance, sealing lips rubber sealing structure of the bearing, and stainless steel wire circle, tight, this structure can effectively prevent erosion of water, easy to replace, reliable sealing effect.
FRB BEARINGS has a Marine machinery companies supporting the nearly thousand sets of Marine crane slewing bearing, both by the hosts factory test, the earliest manufacture of Marine crane slewing bearing used for more than five years, product performance and various aspects index has reached the requirement of the host.
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