Disassembly and assembly of Equipment Repair

Prepare before disassembly any mechanical equipment is composed of many parts.

—Disassembly and assembly are important links in mechanical Equipment Repair. Failed parts can only be repaired or replaced after disassembly. The purpose of disassembling mechanical parts is to facilitate inspection and maintenance. Due to the characteristics of the structure of each mechanical equipment, there are differences in weight, structure, precision, etc. If the disassembly is improper, the parts will be damaged or even irreparable. In order to ensure the quality of Equipment Repair, careful planning must be made before the mechanical equipment is dismantled, and the possible problems must be fully estimated and disassembled step by step.
—The structure and principle must be clear before disassembly and custom parts
There are many types of mechanical equipment with different structures. Before disassembly, the structural characteristics, working principles, performance and assembly relationship must be clarified, so as to have a clear mind and not be careless or blindly disassemble. For unclear structures, the drawings and materials should be consulted to clarify the assembly relationship and matching properties, especially the position and withdrawal direction of the fasteners. In addition, it is necessary to analyze and judge while trying to disassemble, and sometimes it is necessary to design appropriate disassembly fixtures and tools.
—Select the disassembly site and formulate protective measures and get custom parts ready
Before disassembly for Equipment Repair, a good site should be selected to meet the disassembly requirements. For example, if the lifting equipment is fully prepared, a lifting personnel with operating ability and qualifications must be arranged; there must be enough space to ensure that the equipment is easy to enter and exit; the disassembly site must be clean: have the corresponding disassembly construction power source
Before disassembling the equipment, the power supply of the equipment must be cut off first, the hydraulic transmission equipment must be emptied of the power oil, and after the electrical equipment and control system are disassembled, they must be well protected and the connection marks of each control unit, component, and wire must be made; prevent parts from rusting; protect the hydraulic system and components: safety measures at the disassembly site, establish obvious safety warning signs. Protect parts that are prone to rust.
–Be familiar with the equipment structure, prepare tools and technical information
Be familiar with the transmission mechanism, the matching relationship of parts: Be familiar with the relationship between mechanical mechanism, hydraulic system and electrical control, including the corresponding relationship between the object of hydraulic control and the mechanical mechanism, and the relationship between hydraulic control and electrical signals: For the electrical and control parts, make wiring marks for the control circuit and draw wiring records.
—Various disassembly tools for Equipment Repair, and custom parts in advance if needed, including some special disassembly tools made in advance. Prepare various maintenance materials, equipment manuals, Equipment Repair atlases, power underground pipeline network diagrams, equipment disassembly processes, corresponding quality standards, and inspection procedures.

General principles of disassembly
—Choose reasonable disassembly steps
The order of disassembly of mechanical equipment is generally from the whole to the assembly, from the assembly to the components, and from the components to the parts: or from the accessories to the main machine, from the outside to the inside. When disassembling more complex parts, it is necessary to analyze the principles of the assembly drawing, be familiar with the assembly structure, and pay special attention to the parts with high precision. Make the disassembly and Equipment Repair orderly and lay the foundation for repair and assembly.
—Reasonable disassembly
In repair and disassembly, we should adhere to the principle of not disassembling what can be disassembled as much as possible, and must disassemble what needs to be disassembled. If the parts meet the requirements without disassembly, they do not need to be disassembled, which can reduce the disassembly workload and avoid damaging the matching properties, and can also extend the service life. For parts that can still ensure the performance of use, after necessary tests or diagnosis, it is not necessary to disassemble them if there are no hidden defects. If you are not sure about the internal technical status, you must disassemble and inspect to ensure the quality of Equipment Repair.
—Proper use of disassembly tools and equipment, and prepare correct custom parts
After understanding the steps of disassembling equipment parts, it is important to use disassembly tools and equipment reasonably. When disassembling, you should try to choose special or suitable tools and equipment, avoid hitting the equipment at will, and prevent damage or deformation of parts. If there are no corresponding tools, you can only use objects made of softer materials to hit harder parts, including hammers, wooden sticks, and copper sticks. For example, when disassembling sleeves, rolling bearings, gears, etc., use a press or puller. When disassembling large nuts, use the corresponding wrench.
—Main points for attention in disassembly
(1) Check and mark the disassembled parts
There are many matching components and parts in the equipment, which have requirements for accuracy, installation position and direction, especially including any custom parts, and no mistakes can be made: the circuit connection and direction of the equipment gas and control parts must be very clear, and the connection between electrical cabinets, between electrical cabinets and equipment, and between electrical cabinets and actuators must not be wrong; the model of the sensor, the wiring of the sensor, etc., must not be wrong; many components of the hydraulic system have the same appearance but different models, and must be marked.
(2) Classify and store parts
Parts of the same assembly or the same component should be placed together as much as possible, and stored separately according to the size and accuracy of the parts. Parts that should not be interchangeable should be stored in groups: Precision parts should be stored separately to prevent contamination and damage: Rubber parts that are afraid of oil should not be stored together with parts with oil; small standard parts or custom parts that are easy to lose, such as washers and nuts, can be strung together with iron wire and stored in a container.
(3) Protect the machining surface of the disassembled parts
During the disassembly process, be sure not to damage the machining surface of the disassembled parts, otherwise it will bring difficulties to the repair and may cause the technical performance and accuracy of the equipment to decline.

(4) Disassembly should create conditions for assembly
If the technical data is incomplete, the disassembly process must be recorded so that it can be reassembled according to the principle of “disassembly before installation” during installation. When disassembling precision parts or parts with complex structures, an assembly sketch should be drawn or marked during disassembly to avoid misassemble. After disassembly, the parts should be thoroughly cleaned, oiled to prevent rust, and the processed surface should be protected to avoid loss and damage. Slender parts such as long shafts should be hung and not placed horizontally to prevent bending and deformation.
(5) Mutual cooperation and professional division of labor
The control system and hydraulic system are independent systems in the equipment. They are independent of each other based on their respective professional characteristics, but they are also connected. The hydraulic system is the controlled object of the electrical control system. The equipment consists of mechanical, electrical control and hydraulic systems. The major repair of the equipment must be carried out by corresponding professional technicians, with division of labor and cooperation to complete the repair work.
Common disassembly methods
1. Impact unloading method
The impact energy generated by a hammer or other heavy object when knocking or hitting the parts is used to remove the parts. Note that this method should not damage or injure the surface of the parts.
2. Pulling method
For parts with high precision that are not allowed to be knocked or cannot be disassembled by knocking and unloading, the pulling method should be used, and a special puller should be used for disassembly.
3. Pressing method
Use tools and equipment such as spiral C-type chucks, mechanical presses, hydraulic presses or jacks for disassembly. The pressing method is suitable for interference fit parts with simple shapes.
4. Temperature difference method
This method can be used when the disassembly size is large, the interference amount of the fit is large, or it cannot be disassembled by knocking and pressing, or to make the fit parts with large interference and high precision easy to disassemble. The temperature difference method uses the thermal expansion and contraction properties of the material to heat the containing parts so that the fit parts lose the interference amount under the temperature difference conditions and achieve disassembly.

5. Destruction method
If it is necessary to disassemble fixed connectors such as welding and riveting, or the shaft and sleeve are bitten each other, or the auxiliary parts are destroyed to save the main parts, destructive disassembly can be carried out by turning, sawing, chiseling, drilling, cutting, etc.

Disassembly of typical connectors when Equipment Repair
—Threaded connectors
Threaded connections are widely used, simple, easy to adjust, and can be disassembled and assembled multiple times. Although disassembly is relatively easy, it is sometimes damaged due to improper tool selection and incorrect disassembly methods, and special attention should be paid.
1) General disassembly method. First identify the direction of thread rotation, and then select appropriate tools. Try to use a flat wrench or screwdriver, a special wrench for stud bolts, etc. When disassembling, the force should be uniform. Only special threads with high force are allowed to use extension rods.

2) Disassembly of broken head screws. The screw head in mechanical equipment is sometimes broken. When the broken head screw is below the surface of the machine body, you can drill a hole in the center of the broken head end, tap the reverse thread, screw in the reverse screw and unscrew it, as shown in Figure 3-1a. When the broken head nail is above the surface of the machine body, you can drill a hole in the screw, drive in a multi-angle hardened steel rod, and then screw the nail out, as shown in Figure 3-1b. You can also saw a groove on the broken head and screw it out with a flat screwdriver; or use a tool to process a flat head or square head on the broken head and screw it out with a wrench; or add a bent rod to the broken head to screw it out; or weld a nut to the broken head to screw it out, as shown in Figure 3-1c. If the screw is thick, you can use a flat chisel to pick it out along the circumference.

3）Removal of slipping hexagon socket screws. When the hexagon socket is rounded and slipping, you can use a hexagonal nut with a hole diameter slightly smaller than the outer diameter of the screw head, put it on the hexagon socket screw head, weld the nut and the screw into one, and use a wrench to tighten the nut to remove the screw, as shown in Figure 3-2

4) Removal of rusted threads. After the threads are rusted, you can turn the screw in the tightening direction, then loosen it, repeat this process, and gradually screw it out; use a hammer to hit the screw head, nut and surrounding areas, and screw it out after the rust layer is loosened; pour some kerosene or diesel on the edge of the thread, soak it for about 20 minutes, and gradually screw it out after the rust layer softens. If the above methods are not feasible, and the parts allow it, you can quickly heat the containing parts to expand them, and the softened rust layer can also be screwed out: you can also use chisels, saws, drills and other methods to destroy the threads.

—Removal of grouped threaded connections. The disassembly sequence is generally four weeks first and then the middle, alternating in the diagonal direction. Loosen a little or half a week first, and then screw it down in sequence to avoid stress concentration on the last screw, damaging the parts or deforming the combined parts, causing difficulties in disassembly. Pay attention to removing the threaded parts in the difficult-to-remove parts first

—Interference connectors
To remove interference parts, choose appropriate disassembly tools and methods according to the matching size of the parts and the size of the interference. Depending on the tightness from loose to tight, use a mallet, copper rod, hammer or sledgehammer, puller, mechanical press, hydraulic press, water press, etc. to disassemble. If the interference is too large or to protect the mating surface, the containing part can be heated or the contained part can be cooled before being quickly pressed out.
Regardless of the method used for disassembly, check for additional fixing or positioning devices such as locating pins and screws. If there are any, they must be removed first. The force should be applied to the correct location, uniform and in the correct direction.
When disassembling larger bearings or other interference fits, in order to prevent the bearings and shafts from being damaged, heating can be used for disassembly. Figure 3-3 shows a method for heating the inner ring of the bearing to disassemble the bearing. Before heating, isolate the part close to the bearing with asbestos, then put a ring on the wheel to insulate the parts, and then grab the inner ring of the bearing with the hook of the disassembly tool. Quickly pour hot oil at about 100°C on the inner ring of the bearing to heat the inner ring of the bearing, and then start to remove the bearing from the bearing during Equipment Repair.

—Disassembly of rolling bearings
When disassembling rolling bearings, in addition to following the disassembly points of interference fit connectors, you should also pay attention to not using rolling elements to transmit force as much as possible. When disassembling the bearing at the end of the shaft, you can use a copper rod or soft metal or wooden rod that is smaller than the inner diameter of the bearing to support the end of the shaft, place a washer under the bearing, and then hit it with a hammer.
—Disassembly of non-detachable connections
Usually, the disassembly of welded parts can be done by sawing, flat chiseling, drilling a row of holes with a small drill bit and then chiseling or sawing, and gas cutting; the disassembly of riveted parts can be done by chiseling off, sawing off, gas cutting the rivet heads, or drilling off the rivets with a drill bit. Disassembly mainly refers to the disassembly of connectors. In addition to complying with the above rules, you should also master the disassembly methods.