Key points of safety supervision and control of th

Control points for safety supervision of tower crane

torque limiter

1 It is analyzed that many tower falling accidents are mainly caused by overload. The reason for overload is that the weight of the heavy object exceeds the regulations and the horizontal distance of the heavy object exceeds the operating radius. After installing the torque limiter, when the weight is overweight or the operating radius is too large, which leads to the torque exceeding the technical performance of the tower crane, it will automatically cut off the lifting or luffing power source and send an alarm signal to prevent accidents

2. At present, there are two kinds of torque limiters: one is electronic and the other is mechanical. The electronic type can read the torque, operation radius and weight data at the same time on the display. When it is close to the allowable torque of the tower crane, the plastic granulator has an early warning signal and is easy to use, but it is greatly affected by the operation conditions, with poor reliability, easy damage and inconvenient maintenance; The mechanical type has no display device and no early warning signal, but it works reliably, which is relatively suitable for on-site construction and operation conditions, with simple structure and low damage rate

3. The torque limiter must be adjusted when the tower crane is reassembled at the transfer site, the magnification is changed, and the length of the jib is changed. The electronic overload alarm point must also be recalibrated with the actual working radius and the actual weight of the trial crane. For the tower crane with trolley luffing, the mechanical torque limiter must be adapted to the tower crane (the same factory type should be selected)

4. The jib luffing tower crane equipped with mechanical moment limiter must adjust the tonnage of overload limit in time according to the allowable load of operation radius after each luffing

5. During the safety inspection, if the reliability of the torque limiter is unconditionally tested, the test run records of the machine after installation can be checked to confirm that the test results of the machine on the torque limit at that time meet the requirements, and the comprehensive accuracy of the torque limiter system meets the provisions of ± 5%

6. Overload limiter (lifting load limiter). According to the regulations, some tower crane models are also equipped with overload limiters. When the load reaches 90% of the rated lifting capacity, an alarm signal will be sent; When the lifting capacity exceeds the rated lifting capacity, the power supply in the upward direction shall be cut off, and the mechanism can move in the downward direction. During safety inspection, test confirmation shall be carried out at the same time

limiter

1 The limiter is exceeded. It is also known as the upper upgrade limit position limiter, that is, when the tower crane hook rises to the limit position, the lifting power of the lifting mechanism is automatically cut off, and the mechanism can make a downward movement. Action test verification should be done during safety inspection

2. Luffing limiter. Including trolley luffing and boom luffing. Test verification shall be carried out during safety inspection

(1) trolley luffing. The tower crane adopts a horizontal boom, and the lifting weight is suspended on the lifting trolley. The utilization ratio of degradable green packaging materials by the trolley will be increased to 50%, and the luffing will be realized by moving horizontally on the boom. The trolley luffing limiter uses two travel switches and buffer devices installed at the head and root of the boom to limit the running position of the trolley

(2) boom luffing. Changing the working radius (amplitude) of the tower crane depends on changing the elevation angle of the jib. Through the change of the device contact, the light signal is transmitted to the indicator panel in the cab. And indicate the elevation degree. When the elevation angle of the control boom reaches the upper and lower limit respectively, press the lower limit switch to cut off the power supply, so as to prevent the tower crane from instability caused by exceeding the elevation angle

when doing action verification on site, experienced personnel should be responsible for supervision and command to prevent accidents

3. Travel stop. There is no derailment accident when controlling the operation of the rail tower crane. During the safety inspection, the traveling action test of the tower crane shall be carried out, and the reliability of the collision limiter shall be verified

safety device

1 Hook safety device. It is mainly used to prevent the hook off accident caused by the hook still falling when the heavy object is blocked when the tower crane is working. This device refers to the parts and components that clamp and tighten the test piece, are installed on the testing machine and are used for strength test. A spring gland is installed at the opening of the hook. The gland cannot be opened upward but can only be pressed downward to prevent the sling from falling out of the opening

2. Drum safety device. It mainly prevents the steel wire rope from being able to be arranged in sequence on the drum when the transmission mechanism fails, so as to cross the flange at the end of the drum and cause rope biting and other accidents

3. Ladder retainer

(1) when the access height of the ladder is greater than 5m, set the retainer from 2m above the platform. The retainer shall be kept in good condition, and there shall be no excessive deformation, few rings, open welding and other phenomena

(2) when the ladder is set inside the structure, if the distance between the ladder and the structure is less than 1.2m, it may not be set with a retainer

wall attachment device and rail clamping pliers

1 The free height of the jack up tower shall comply with the requirements of the instructions. When it exceeds the provisions, it shall be attached to the building to ensure the stability of the tower crane

2. Wall attachment device

(1) when attached to the building, its stress strength must meet the design requirements

(2) when attaching, the verticality of the tower body shall be checked with a theodolite and adjusted. The arrangement, spacing and vertical distance of the brace of each wall attachment device shall be in accordance with the instructions

(3) when the length and angle of the attachment rod need to be changed due to the particularity of the project, the strength, stiffness and stability of the attachment device should be checked to ensure that it is not lower than the safety of the original design

(4) when the track type crane is used as an attachment type, the bearing capacity of the track foundation must be improved and the power supply of the traveling mechanism must be cut off

3. Rail clamping pliers. When the rail crane is used in the open air, wind proof rail clamping pliers should be installed

4. The rail clamp device must ensure the braking effect after clamping. When the driver needs to leave the tower crane at lunch, after work and during temporary parking, he must clamp all the rail clamp of the tower crane as required before leaving. Stainless steel welding rod

installation and disassembly

1 The installation and disassembly of tower cranes is a complex and dangerous work. In addition, there are many types of tower cranes, different working environments, and different degrees of familiarity of the installation team. Therefore, it is required to formulate a detailed construction plan according to the type and characteristics of tower cranes, the requirements of the instructions, and combined with the operating conditions before work, including: operating procedures, the number of personnel and working positions The type of lifting machinery to cooperate with the operation and the position of the work, whether in the regional market or entering the global market, the laying of ground anchors, the preparation of rigging and the protection of the on-site operation environment. For the jacking work of the jack up tower, there must be specific requirements for the boom and balance arm to maintain a balanced state, as well as the jacking steps in the jacking process and reliable measures to prohibit slewing operations

2. The installation and disassembly of tower cranes must be carried out by professional teams and personnel with qualification certificates issued by relevant municipal departments. And assign special personnel to command

tower crane command

1 The tower crane driver is a special operator, who should be formally trained and assessed and obtain a certificate of qualification. The content of certificate or training assessment must be consistent with the type of crane driven by the driver

2. The signal commander of the tower crane shall be formally trained and assessed and obtain a certificate of qualification. Its signal shall comply with the provisions of the national standard GB "hoisting command signal"

3. When the on-site multi tower operation interferes with each other, or the driver of high tower operation cannot clearly hear the flute sound and see the gesture of the signal commander, he should use semaphore or interphone to command according to the actual situation on site

subgrade and track

1 The subgrade and track of the tower crane must be paved in strict accordance with the instructions. Generally, the bearing capacity of subgrade soil: medium-sized tower (3~15t) 0.12~0.16mpa; Heavy tower (above 15t) ＞ 0.2MPa. It shall be repaired, leveled and compacted, and paved with sand and ballast stones, with drainage measures

2. Timber, reinforced concrete or steel sleepers can be used as sleeper materials, and their cross-sectional dimensions shall be in accordance with the specifications (such as 16 × 240、180 × 260, etc.), the sleeper length should be at least 1200mm larger than the gauge size. When one long sleeper and two short sleepers are used for arrangement, a channel steel tie rod shall be added every 6m or so to ensure the gauge. Sleeper spacing is 600mm. When the finalized subgrade box is used, it shall be checked and accepted to confirm that it meets the requirements before use

3. Both sides of the track shall be nailed (or pressed) with dowels on each sleeper, and shall not be missing or loose. The joints of the track shall be staggered, and the joints shall be erected on the sleeper, and the height difference at both ends shall not be greater than 2mm. The joint plywood shall be matched with the track, and the bolts shall be fully filled and fastened

4. The horizontal deviation of the track shall not be greater than 1/1000 in the vertical and horizontal directions. (use a level meter to measure the average value of the period when it is not at three points on the two tracks within 10m)

5. A limit position stopper (stopper) shall be set 1m away from the rail terminal, and its height shall be greater than the radius of the walking wheel to prevent the tower crane sliding after power failure from derailing

6. The foundation construction of the fixed tower crane shall be carried out according to the design drawings, and its design calculation and construction details shall be included in one of the special construction organization design contents of the tower crane. After construction, it shall be accepted and recorded

electrical safety

1 The cable of the tower crane is not allowed to walk on the ground. The cable drum with tensioning device should be installed, and the cable will be wound automatically with the drum of the tower crane to prevent the cable from rubbing with the sleeper or being entangled by sundries on the track

2. The safety distance between the overhead line and the tower crane at the construction site shall be in accordance with the temporary electricity Code: "the minimum horizontal distance of the overhead line sideline below 10kV at any position of the rotating jib crane or the edge of the lifted object shall not be less than 2m." When it is less than this distance, protective frames shall be erected as required. 36V color bulbs (or red bulbs) shall be provided for night construction. When the crane operation radius passes above the overhead line, protective measures shall also be provided above the line

3. When TT system is adopted on site, the tower crane shall be grounded, and its resistance value shall not be greater than 4 Ω; When TN system is adopted, in addition to protective neutral connection, it shall also be repeatedly grounded according to the regulations of temporary electricity specification, and its resistance value shall not be greater than 10 Ω

4. For the repeated grounding of the tower crane, a group shall be set at both ends of the track. For the longer track, another group of grounding devices shall be added every 30m. Steel bars or flat iron shall be used for circular electrical connection between the two tracks, and conductor bridging shall be used at the joint of tracks to form electrical connection

5. The protective neutral and grounding wires of the tower crane must be separated. The power line can be sent to the distribution box at the rail end of the tower crane, and the PE line from this box is connected with the repeated grounding wire of the rail, that is, the equivalent PE line is connected with the equipment shell through the rail wheel

multi tower operation

1 When two or more tower cranes are working on adjacent tracks or on the same track, the minimum distance between the two cranes shall be maintained

(1) mobile tower crane. The distance between any parts (including lifting objects) shall not be less than 5m. The vertical distance between the tower hook and the lower tower shall not be less than 2m

2. When the construction cannot meet the requirements due to the limitations of site operation conditions, two measures should be taken at the same time

(1) organizational measures. The operation and traveling route of tower crane shall be regulated and supervised by specially designated supervisors

(2) technical measures. Limiting devices shall be set to shorten the boom, raise (lower) the tower body and other measures to prevent the tower crane from exceeding the specified operation range and causing collision accidents due to misoperation

installation acceptance

1 Commissioning of tower crane and