Introduction to technical inspection of cranes
Introduction to technical inspection of cranes

خانه Introduction to technical inspection of cranes

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Introduction to technical inspection of cranes

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Introduction to technical inspection of cranes

Introduction to Crane Inspection; The importance of using cranes in industry is very obvious. It has made it easier to install cranes, build buildings, unload and load ships, and so on. If these devices are not well maintained and regularly inspected and tested, they can cause major damage to devices, equipment and staff.

To prevent these injuries and accidents, cranes and lifting equipment should be regularly inspected and tested under a scheduled schedule to eliminate their defects and defects and be ready for safe operation.

Many accidents and losses have occurred due to negligence and lack of technical inspection and timely testing of cranes and lifting equipment, most of which were avoidable. In order to prevent damage caused by erosion and damage to parts, cranes and other lifting equipment, under the system and regulations of technical inspection published by the competent institutions and organizations, the components of each device should be fully inspected according to its function at the specified time. And tested and repaired if necessary.

Types of cranes

1- Overhead cranes (electric, pneumatic and manual)

These cranes are used to move loads in limited areas (halls, warehouses, workshops …), the driving force of these cranes is as follows:

Electric crane: Its driving force is electricity.

  • Pneumatic crane: The driving force is compressed air, which is mostly used in chemical industry industries and where there are gases an flammable materials.

  • Hand crane: It is performed by chains, pulleys and hand force, longitudinal, transverse and load lifting movements. These types of cranes are mostly used in pump houses and compressors to install devices and repair them that require slow movements.

2- Mobile ground cranes

It refers to cranes that are able to move on the ground with their allowable load and with their driving force (diesel engine). Their uses in various industries are very wide.

These cranes are generally divided into three categories:

2-1- Wheeled crane

22- Shoe crawler crane for heavy loads

2-3- Rotating or non-rotating cranes that are installed on the truck. These types of cranes are used to move loads quickly.

2-4- Offshore cranes: (especially for piers and docks), the driving force of most of this type of cranes is electric and moves on rails.

2-5- Tower cranes: These cranes are installed temporarily and in a fixed place and are used to build buildings and install devices.

Crane fixed column: secured by steel cable. These cranes often have no card during the industrial operation period and are mostly used during the construction of factories and buildings.

2-6- Floating cranes: This type of cranes is installed on ships and tugs and their driving force is the ship’s electricity or diesel engine.

2-7-Special cranes: As the name of these cranes shows, this type of cranes is installed on the railway wagon and their driving force is its own diesel engine. Application of these cranes in railway network networks for transportation And freight related to railways.

2-8- Wall cranes : They are used in workshops and are installed on steel columns by levers and beams. These types of cranes are manual or electric and usually do not have much load capacity. A number of this type of cranes are available in the central workshops of the complex. .

2-9- Pneumatic or electric elevators : These elevators are usually installed and restrained on the ground by winches, steel cables and hooks, and are used for repairs and relocation of devices at high altitudes. These cranes are used in the repair of large units. A lot is done.

3- Inspection and testing method of elevator accessories and equipment:

In this section, the important points that technical inspectors should consider in inspecting and testing important parts and accessories of cranes are described as follows:

3-1- Hooks: To control the opening of the hook opening during its life, before operation and testing the initial load, there is usually a sign on the hook opening that indicates the hook opening index. After performing the load test and in subsequent inspections, this mark is checked and if the hook opening is opened too much, the hook should be taken out of service, this size is approximately 8% of the hook opening diameter.

The points that should be considered in inspecting the hooks are:

Cracking, abrasion, fracture and fluidity of the ball bowl and its lubrication system. It is also necessary to have a safety fastener for hooks. The hook handle screw should be carefully inspected for looseness, wear and cracks. Cracks can be found and determined by non-destructive tests (penetrating paints or magnetic powder). The most wear on the hook floor is where the box wire Or boxed chains are created, this corrosion may be uniform and grooved and should not be more than ten percent of the hook thickness at the abrasion site. Hook connections, especially hooks that are connected directly to the steel cable by the weight, should be inspected for weight, corrosion and rust of the cable and connections. If possible, welding should not be done on the hook. If welding is required, the material of the hook metal should be specified first, and then the welding method and heat treatment should be applied according to the manufacturer’s instructions.

3-2- Steel cable:

Steel cable is a flexible rope made of several steel wires with high tensile strength and is used in industry for raising and lowering loads, drilling, pulling loads and so on. A steel cable is distinguished by its diameter, number of wires, number of strands, construction and placement, and type of layer (including core layer) and type of metal. Cables are made of different steels and their choice depends on their service, tensile strength and corrosion resistance. Regular inspection of steel cable is the best way to prevent accidents caused by cable rupture. For complete and longitudinal inspection of the cable, it must first be opened and cleaned from the machine.

To clean the cable, you should use a wire brush and compressed air and cloth, and avoid using materials such as gasoline, which decomposes the oil inside the cable and dissolves in it. Steel cables should be objectively inspected for corrosion, wear, tear and crushing. When replacing steel cables is always a problem for technical inspectors, because their replacement must always be done with regard to working conditions, safety and savings, if there is a sign of excessive corrosion, rupture, abrasion, etc. should be observed. Replaced it, according to the regulations and regulations of some industrialized countries regarding the standard of replacement of load-bearing steel cable, if the wires cut in length equal to ten times the diameter of the cable is more than five percent of the total number of strands or a sign of corrosion. If rupture, abrasion, etc. are observed, the cable should be replaced. If the cable is corroded quickly, the cause must be sought. The mismatch of the pulley dimensions with the cable diameter often causes rapid wear.

Some of the causes of steel cable failure are as follows:

* Wrong choice of cable in terms of size, construction and type.

* Lack of proper and timely lubrication.

* Passing the cable over the spool and cylinder is inappropriate and uneven.

* Cable coming out of the pulley and cylinder.

* Excessive stacking or twisting of the cable on the cylinder.

* Hard working conditions and severe load shocks on the cable.

* Work in the presence of high heat.

* Humid air and polluted gases.

* Use and install incorrect and non-standard connections at the end of the cable.

3-3- Steel cable pulleys and cylinders:

The pulleys must be inspected for cracks, fractures and abrasions in the groove for the passage and passage of the steel cable. If, due to heavy load or force, the pulley groove becomes worn, hollow, or scratched, it must be repaired or replaced with a new pulley, otherwise it will cause rapid damage to the steel cable. Care must be taken that the diameter of the pulley is not smaller than the design, otherwise it will cause a lot of bending and shorten the life of the cable. To be. Spools that have a ball and bearings must be careful that the ball is smooth and free and does not break and is well lubricated.

The grooves of the steel cable on the cylinders should also be inspected and repaired if they are worn, scratched or sharp. The edge of the cylinder should not be broken or should protrude beyond the cylinder. The cables should not be twisted and twisted too much at the edge of the cylinder. After installing the steel cable on the cylinder and bringing the hook to the lowest level where it is used, at least two rounds of rope must remain on the cylinder.

3-4- Brakes and connections:

The brakes should be opened from the brake bowl and their pads should be objectively inspected for wear, fracture or smoothness and lubrication. If they are defective, they should be replaced. If the brake pads are flat but have not yet reached the rivet, the pads can be cleaned with a wire brush and sandpaper. If the brake pads have reached the rivet, they should be replaced. If the pad is of the type attached to the shoe, it should be noted that the pad is fixed in place and is not detached from the shoe, the maximum wear of the pad should not be more than fifty percent of the original thickness.

Shoes and brake fittings such as rods and levers and brake mounting bolts should be inspected for breakage, abrasion and cracking and replaced if defective.

If the pads are disassembled and replaced, after re-installation, make sure that the rods are in place and secured by the toggle rod and fastened with screws. The toggle rod opening must be opened so that it vibrates during operation. It is not possible for them to leave.

Before using the crane, the brake pads must be weighed with the load so that they can hold the load steadily at any point.

If the brake pads are more than fifty percent of the original thickness, it should be replaced, burnt or uneven wear pads or riveted pads should be replaced.

The brake bowl, which has been scratched on the surface due to the contact of the pads and the protrusion of the rivets, must be smoothed and their defects removed by a lathe.

3-5- Load chains and connections:

Steel chains used to lift loads are usually made of low carbon steel by resistance welding.

To inspect the chain, it is better to disassemble it from the crane and place it on a clean surface. The decision is made whether or not to remove the chain from the machine with technical inspection. The inspection time of the chain depends on the working conditions and ambient temperature. In severe conditions and severe shocks and continuous work and high heat (such as smelting and casting of metals) the chains should be inspected once every six months, the inspection period of other chains is once a year.

Chain defects and chains generally include defective welds, cracks, fractures, abrasions, strains, twists, and knots and rust.

Weld cracks due to fatigue are mostly created on low-penetration and porous welds in the inner part of the chain rings that are exposed to friction and are mostly identified by the eye, so in each inspection, more attention should be paid to the inner parts of the chain.

In critical and sensitive services, cracking and breakage can be identified and found with the help of penetrating paints with magnetic powder. The breakage of the chain link is mostly due to the very cold working environment and the high hardness of the metal, especially in steel chains whose hardness is more than 375 Brinell or if it has become hard due to excessive work. To prevent breakage, these types of chains should be reduced to 300 to 350 Brinels in a workshop equipped with annealing oven.

The wear of the chain, which is mostly caused from inside and between the grains, should not exceed the specified amount specified by the manufacturer. The strength of the chain decreases, the load exceeds the capacity or the chain gets stuck under the load and high pressure causes the chain grains to stretch. This stretching and lengthening of hand cranes is important. In this type of crane, the chain grains are placed in their special place on the pulleys and rotate them. If the grains are pulled, this operation will not be done and the pulleys will not work and the chains must be replaced.

Partial tension due to wear along the chain up to approximately 12 mm by 300 mm is acceptable and safe.

The twisting, knotting and rusting of the chain can be seen with the naked eye. If it is noticeable, it must be replaced. Inspection of joints is exactly the same as inspection of chains.

3-6- Axes and bars:

The shafts and rods of pulleys, cylinders and wheels must be objectively inspected for wear, cracks and fractures. If the wear of the shafts and rods is more than 0.25 mm (0.01 inch) per 25 mm (1 inch) in diameter, they must be replaced. They showed.

The balance axis of pulleys, wheels and cylinders may crack due to the use of substandard steel in construction or due to severe impacts and continuous hard work or bending, these cracks are often in parts of the axis that have changed diameter and edges It is sharp or can be seen in the welding of the shaft and its surroundings. To determine the limits of cracks, penetrating paints or magnetic powder can be used.

The location of the grooves of the shafts that are connected to the wheel or gear should be checked for wear and looseness. The rods, especially in the case of the end of the steel cable, should be inspected for fluidity. It enters the cable wires where they are connected to the clamp and leads to the rupture of the cable. It should be noted that the two ends of the wheel axles are all in place and tightened. Inspect for openness to be well lubricated during operation.

3-7- Wheels, gears and gears:

Most overhead cranes are driven on steel rails by steel wheels. These wheels must be objectively inspected for wear, especially on the floor and edges, as well as for fractures, cracks and fluidity.

If the wheels have ball bearings, make sure that they are smooth and the ball bowl is not broken. If it is made of brass bush, it should not have much looseness. , Held the wheels up and inspected them.

All wheel and shaft gears and interface gears and the location of the gear shafts connected to the shaft and the coupling shaft to the electric motor must be objectively inspected for wear and tear (coupling), the gearbox valve must be opened and the gears in terms of Corrosion, rust, abrasion and breakage should be inspected. The gearbox valve should not be opened for inspection during gear rotation and operation. Also make sure that there is enough oil in the gearbox, the base screws of the gearbox to the crane body should all be in place and tightened.

3-8- Rails and connections:

Most rails are made of hard and medium or high carbon steel. Welding of this type of rails must be done according to the specific method and manufacturer’s instructions, otherwise the possibility of cracking on the weld and its surroundings that are affected by heat. , During welding and during operation.

During the initial inspections and during installation and periodicity, these welds should be objectively inspected and, if necessary, to be sure, they should be tested with penetrating paints or magnetic powder.

The alignment of the rails with the beam under the rails as well as the alignment and parallelism of the rails to each other should be measured during the initial installation and inspection and before and after the load test, and if necessary, be adjusted. It should be noted that the clamps of the rails (longitudinal and transverse movement) are all in place and tight.

3-9- Crane beams, cross connections, steel frame columns, bridges and carriages of cranes should be objectively inspected for bending, rust, fracture and cracking.

During the initial installation, the alignment of the load-bearing beams under the rails and the verticality and the amount of settlement of the columns, as well as the parallel and horizontal position of the rails relative to each other should be measured by a surveyor under the supervision of structural engineers and corrected if necessary. . The strength of the screws of the mentioned connections, if they are newly installed, should be checked by Torque Meter before and after the load test, it should be made sure that the screws are according to the manufacturer’s specifications.

In periodic inspections, screw joints should be inspected for strength, wear, breakage or rupture of the screw and, if necessary, the bolts should be bolted or replaced. Care should be taken to use a suitable and sloping washer under the bolts and nuts.

Welding joints, especially on-site welds, must be quality inspected and inspected.

If the ladder is designed and built for repair, service and inspection of the crane, it must be installed firmly and in such a way that the crane can be accessed without any problems or danger.

Crane railings, corridors, stairs, as well as corridor grilles should be objectively inspected for strength and adequate clamping.

In cranes used to carry ladles of molten material, for thermal protection, a strong metal sheet is installed under a special beam by the manufacturer, the presence of this sheet and its installation status should be checked.

Steel columns on the ground and where they are placed in the foundation concrete should be inspected for rust, corrosion, subsidence, cracking and fracture of cement foundations and, if necessary, with the inspector, concrete or soil around a part of the columns for skeletal load. Metal removed.

3-10- Deterrent devices and shock absorbers:

At both ends, at both ends of the load-bearing beam, the rails of the bridge and carriage of the overhead crane must be fitted with fixed restraining devices. The load-bearing beam of the rails is fastened by strong steel screws. During each inspection, care must be taken that all the screws are in place and tightened.

To neutralize the severe shocks caused by the longitudinal and transverse movements of the crane, shock absorbers are installed on the bridge and carriage and on both sides. Avoid cranes.

In terms of safety, oil shock absorbers should be secured to the crane body with a steel cable so that they do not fall down if the screws are cut. They ensure.

3-11- Magnet unit and connections:

All overhead cranes that hold and move loads by a magnet must usually be equipped with an emergency battery system so that in the event of a main power failure, the magnet can automatically suspend the load for at least 20 minutes, if this is the case. Cranes without an emergency battery system should be recommended considering the operating conditions and, if possible, the installation of a battery.

The magnet is supplied by a winding system inside the steel housing and is connected to the crane hook by chains with rings and fittings and is controlled by the driver. In each inspection, the magnets, chains, rings and fittings must be cracked. Fractures and abrasions should be inspected.

3-14- Safety keys:

To prevent the hooks from rising above the set limits, electric safety switches are installed on the crane that can stop the hooks after reaching the specified limits and prevent them from climbing beyond that limit.

Some cranes also have a secondary power switch fitted at a higher distance for added safety, in places where the driver is unable to see the load on the ground or below to prevent the hook from going too low. Automatic safety switch for moving down Is considered.

To ensure that the longitudinal and transverse motion of overhead cranes does not exceed a certain limit, if necessary, automatic safety switches are placed at both ends of the girder beams or on the bridge and carriage of the crane to prevent the crane from hitting the end of the rail and the surrounding steel frame. Oil switches can be used instead.

It should be noted that the purpose of installing these types of switches is to keep the devices safe and they should not be used to stop the crane or load.

In each inspection, this type of switches and the installation status of their pendant should be tested and adjusted if necessary.

3-15- Load test:

Before performing the load test, make an objective inspection of the rails, wheels, steel cables, hooks, brakes and fittings that are in place without defects and everything.

In the initial test of the crane, the crane bridge should be placed on the main columns as much as possible and the maximum vertical bending of the crane bridge should be measured. To obtain the maximum vertical bending, the crane should be tested with the allowable load. (Bridge or Span) and lift the allowable crane load slightly off the ground.

The amount of bending is measured according to the manufacturer’s instructions. If the instructions are not specified, the amount of bending can be measured with a plumb line that hangs from the middle of the bridge.

The maximum allowable bending under the load in the middle of the crane bridge should not exceed 1.750 of the span width. After measuring the bending, first the brake and then the longitudinal and transverse movements of the crane with the allowable load are tested. be .

If the above tests are satisfactory, the crane should be tested 25% more than the allowable load and all movements and brakes should work well. Overload testing should be performed on cranes with two or more hooks for each one separately.

After testing the load, the brakes are examined for overheating, the steel cable clamps for strength and other parts for bending, fracture, cracking and scaling of paint caused by load pressure, and the crane without load. To be moved.

3-16- Inspection of overhead cranes (electric and manual):

In general, overhead cranes are inspected in two stages:

A) Initial inspection and during installation:

All cranes and hoists should be inspected and tested by a technical inspector before initial operation. The following points should be considered in this inspection:

Prior to inspection and operation, all documents, drawings, specifications and certificates of manufacturers, equipment and parts of cranes and hoists should be checked and a summary of their technical specifications should be extracted by the technical inspector. In this inspection, the inspector gets acquainted with the design, construction, material, specifications and standards used in their construction to ensure that the parts are made in accordance with the design and specifications of the manufacturer and a certain standard and have a manufacturer’s certificate. In case of defects in the documents, the needs of technical inspection to complete or repair the test of the device are notified to the head of the unit.

A general inspection of all installed or under-installed parts, especially sensitive parts such as brakes, steel cables, hooks, magnets and safety switches, should then be carried out to ensure that they are properly installed and not damaged during transport. Their connections are without defects.

Objective inspection of metal structures, beams, columns and rails and ensuring the use of correct connections and control of screws and the integrity of welds are also the duties of the technical inspector. If the inspector deems it necessary, the structural engineers should check and calculate the load-bearing beams and columns for further assurance.

The alignment of the rails and the verticality of the columns must also be done by the surveyor, before and after the test under the load, and the necessary adjustments must be made.

The test under load is according to the instructions of the last stage of technical inspection, during which the amount of bending of the overhead crane rail is determined or the design criteria are compared.

– After the successful completion of the tests, the inspector must prepare an inspection report and, while reflecting the inspections performed, certify the health of the device for operation.

B) Periodic inspection:

After the operation of the cranes, in order to ensure their safety and to ensure the safety of their operation, it is necessary to periodically inspect them technically.

Periodic inspection time of electric overhead cranes located in workshops, warehouses, smelting and casting factories and other places that use the crane permanently is once a year, in case of continuous and 24-hour operation of the crane or near high temperature work. , The period of periodic inspections is shortened and is reduced to once every six months.

Author: persian / Date: 2017-10-26
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