A Frame Crane Design – Trolley, Lifting Mechanism, Supporting Legs

Today, let's talk about A frame crane design! As we konw, A frame crane is a kind of gantry crane, the metal frame of A frame gantry crane looks like a door frame, two supporting legs are installed under the bearing main girder, which can directly run along the rail truck on the ground, what’s, more, there are cantilever girders (extension of main girder) on both end of the main girder, A frame gantry crane thus named. The supporting legs on both ends of main girder are usually rigid legs; when the span is more than 30m, one side is usually rigid leg, the other side is a flexible leg connected by ball joints and bridge, in order to make the gantry frame to be a statically determinate system, which not only can prevent the additional stress caused by lateral trust under the external load, but also compensate the longitudinal deformation of crane bridge, which will case the wind area of A frame gantry crane be larger. In order to prevent the decline or overturn under the strong wind, TICO designs each of A frame gantry crane with wind detecting instrument and rail clamp device interlock with running mechanism. Bridge frame can be designed without cantilevers on both ends, or with cantilevers on only one end or both ends, in order to extend the operation range. Semi A frame gantry crane has leg on only one side, the other side is designed without leg, directly runs on the rail track.

As A frame gantry crane belongs to gantry crane, there are many general characters,  it also composed of three major components: mechanical transmission, metal structure and electrical equipment, which are also the three main working mechanism of gantry crane. Mechanical transmission composed of the lifting mechanism, lifting trolley and so on. They a working area to achieve the going up and down, horizontal transportation and longitudinal transportation when lifting the goods.
Any production machinery is made up of prime mover, driving device, working mechanism and control equipment. If the motor is used as the prime mover to drag the production machinery of the working body, then its drive device and transmission device is usually referred to as the electric drive system. Electric motor, controlling and steering part, electric circuit, electrical devices, and so on in this system used to collectively referred to as electrical equipment.

Electrical equipment parts are mainly composed of the motor, electrical components and electrical circuits, etc. The electrical equipment part of A frame gantry crane can change the electric energy in power network to mechanism energy, to achieve the purpose of A frame gantry crane during working, at the same time, control each working mechanism according to the requirements of operation.

The function of electric equipment mainly includes: changing the electric energy to mechanism by the motor, dragging the working mechanism through driving device, with the help of various of controlling device and electric components to control the crane so that the motor can complete variety of actions according to the requirements of working mechanism.

Single Girder A Frame Crane Design Drawing from TICO

main technical parameters of A frame gantry crane design

The main technical parameters of A frame gantry crane includes lifting capacity, lifting height, span, length, speed and type of work, etc. We design A frame gantry crane with three indicators, namely the rated lifting capacity, lifting weight, weight under the hook. The lifting weight of A frame gantry crane we design is 32t. At present, the minimum span of gantry crane is 15m, the maximum is more than 60m, mostly is within the range of 25~35m. the working distance of crane is generally not more than 10m.
In this A frame gantry crane design, we design the span is 25m, cantilever on both ends are 5.5m. the speed parameter of A frame gantry crane includes lifting speed, running speed of trolley. With the continuous development of economy and technical level, the speed requirements for gantry crane are also getting higher and higher. There are three types of A frame gantry crane, which is different according to the difference of crane application and lifting weight. The running speed of trolley is generally not more than 50m/min. in thin design, the running speed of running bridge is 37.9m/min, running speed of trolley is 38.5m/min.

Running mechanism of trolley

The running mechanism for trolley of gantry crane can be divided into double girder running mechanism and single main girder running mechanism, in this design we adopts double girder running mechanism.

Common forms of trolley for A frame gantry crane includes the flowing:

• Lifting trolley for single girder gantry crane, there are three running wheels under the trolley frame, one of which is driving wheel, and the other two are driven wheels.
• Lifting trolley for double girder A frame gantry crane, which is mainly composed of trolley frame, lifting mechanism, and the trolley running mechanism. The lifting mechanism is installed on the platform of trolley. Running mechanism of trolley is composed of motor, gear coupling with brake wheel, reducer, transmission shaft, wheel set, and so on. The driving form of the trolley traveling mechanism is generally centralized drive, which is a motor, a brake, a speed reducer and a walking wheel.

The transmission process: the motor – gear coupling – reducer – gear – coupling – transmission – wheel set.

Working principle: Start lifting trolley walking mechanism, power up the motor, brake release, input power to reducer through coupling, which can change the high running speed and low torque to low running speed and large torque. Thus , the reducer can not only play a role in slowing down, but also can play a role in increasing the torque. Reducer low speed shaft output torque through the drive shaft, drive the wheel set on the track to roll, so as to achieve the horizontal movement of lifting trolley in the trolley track.

Supporting legs design of A frame gantry crane

The supporting legs are mainly subjected to the full load of the crane, including the self weight of the main girder and weight of the trolley.