Inspection before dismantling
The pre-disassembly inspection is mainly to find out the degree of precision loss and functional damage of the equipment by checking the static and dynamic conditions of the mechanical equipment.
- The accuracy state of mechanical equipment mainly refers to the accuracy of the main geometric accuracy of the moving parts of the equipment. For metal cutting machine tools, it reflects the processing performance of the equipment. For equipment of mechanical operation nature, it mainly reflects the degree of wear of the parts.
- The functional state of mechanical equipment refers to the state in which the equipment can complete various functional actions. It mainly includes five items:
1）Whether the transmission system is running normally and the speed change is complete.
2）Whether the operation of the operating system is sensitive and reliable.
3) Whether the lubrication system is fully equipped, the pipeline is complete, and the oil passage is smooth.
4) Whether the electrical system is reliable and sensitive.
5) Whether the sliding parts are operating normally, and whether there are serious pulling, grinding, bruising and crack damage on each sliding part.
During the inspection, it should be determined whether each function of the mechanical equipment is severely damaged; or is generally damaged; whether it has major functions; or whether the equipment functions can meet the requirements of the production process; Specific existing problems and potential problems must be sorted out and registered.
The diagnosis operation is mainly to diagnose the key problems existing in the use of mechanical equipment through no-load operation and load operation. In the diagnosis, the fault diagnosis should be carried out in combination with the operator’s situation report, daily operation records, maintenance parts replacement table, accident analysis and daily maintenance files.
- No-load running diagnosis
Mainly by human senses through hearing, seeing, smelling and touching to diagnose equipment failures. Its main contents are as follows:
(1) Diagnose the abnormal noise of the transmission gear in the gear box of the equipment.
(2) Diagnose the cause of heating between the rotating parts of the bearing or sliding parts.
(3) Determine the main cause of equipment vibration.
- Load operation diagnosis
(1) Judging the wear of relevant parts of the machine tool, such as guide rails and bearings, and the cause of precision failures caused by improper assembly, by processing the workpiece.
- Experimental Operational Diagnostics
In the diagnosis operation, in order to accurately judge the location and main reason of the fault from many possible estimates of the fault, it is simple and easy to use the experimental method for diagnosis. In actual work, the commonly used experimental diagnosis methods are as follows.
1 isolation method; 2 replacement method; 3 comparison method; 4 tentative method; 5 measurement method; 6 comprehensive method.
Develop a modification plan
(1) According to fault diagnosis, fault analysis and wear of parts, determine the parts that need to be disassembled and the scope of repair, and determine the main parts that need to be replaced, especially castings, outsourced parts and outsourced parts.
(2) Formulate the repair process of the main parts that need to be repaired.
(3) Formulate assembly and adjustment process plans and requirements for parts and components.
(4) According to the status quo and repair conditions of the equipment, determine the quality standard for equipment repair.
Parts disassembly and cleaning
- Parts disassembly
- General principles for dismantling of equipment parts
(1) First of all, you must be familiar with the technical data and drawings of the equipment, understand the principle of mechanical transmission, master the structural characteristics of each component, the assembly relationship, and the positioning pin, bushing, spring collar, lock nut, lock screw and top Wire position and exit direction. Note: The source is Qianhui.com – machinery and equipment trading website.
(2) The disassembly procedure of mechanical equipment should adhere to the principle opposite to the assembly procedure. After cutting off the power supply, first disassemble the external accessories, then disassemble the whole machine into component assemblies, and finally disassemble all parts, and put them together according to the components.
(3) When disassembling the shaft hole assembly, you should generally adhere to the principle of disassembling with as much force as you use for assembly. If there is an abnormal situation, you should find out the cause to prevent the parts from being bruised, roughened, or even damaged during disassembly. Shrink-fit parts are disassembled by heating. For example, hot-loading bearings can be disassembled by heating the inner ring of the bearing with hot oil. When disassembling sliding parts, the suction force of the oil film between the sliding surfaces should be taken into consideration. In general, destructive disassembly is not allowed during the disassembly process.
(4) Adhere to the principle of prudence and safety when disassembling large parts. During disassembly, carefully check whether the locking screws and pressure plates are disassembled. When hanging, it is necessary to roughly estimate the position of the center of gravity of the part, and reasonably select a hanging rope with an appropriate diameter and a hanging stress point. Pay attention to the balance of force, prevent parts from swaying, and avoid accidents such as detachment and breakage of hanging ropes.
(5) Adhere to the principle that disassembly serves assembly. If the technical information of the equipment to be disassembled is incomplete, necessary records of the disassembly process must be kept during disassembly. In order to reassemble according to the principle of “disassembly first and then assembly” during installation. During disassembly, in order to prevent the assembly relationship and matching position of the key parts from being disturbed, and to avoid the reduction of accuracy during reassembly, the assembly parts should be clearly marked with a scratch needle. The disassembled shaft parts should be hung up to prevent bending deformation. Precision parts should be stored separately to avoid damage.
- Cleaning Parts Requirements
(1) In the cleaning solution, all disassembled parts should be cleaned.
(2) Attention must be paid to the cleaning of reused parts or new replacement parts, and the burrs generated during the use or processing of parts must be removed.
(3) After the parts are cleaned and dried, oil must be applied to prevent the parts from rusting. If the parts are cleaned with a chemical alkaline solution, they must be rinsed with hot water after washing to prevent surface corrosion of the parts. Precision parts and aluminum alloy parts should not be cleaned with alkaline solution.
(4) When cleaning all kinds of boxes of the equipment, the residual wear debris, paint flakes, gray sand, oil stains, etc. in the box must be removed. Check the lubricating filter for damage and leaks for repair or replacement. In addition to cleaning the surface of the oil mark, it is also necessary to carry out grinding and polishing to improve its transparency.
- Choice of cleaning solution
(1) Kerosene or light diesel oil is widely used in cleaning parts, and can remove general grease, regardless of castings, steel parts or non-ferrous metal parts. It is safer to use, but less volatile. For precision parts, it is best to use special gasoline containing additives for cleaning.
(2) At present, in order to save fuel, various metal cleaning agents for cleaning mechanical parts are being vigorously researched and promoted. It has good hydrophilic and lipophilic properties, excellent emulsification and diffusion. The market price is cheap, there is a good prospect of use, and the applicability is also very good.
- the cleaning method
(1) Manual cleaning:
(2) Spray washing with the cleaning box:
Replacement options for parts
- Principles for determining whether equipment parts need to be replaced
The general principles for determining whether equipment parts need to be replaced are as follows:
(1) Determine whether to replace the parts according to the influence of the worn parts on the accuracy of the equipment.
(2) Determine whether the parts should be replaced according to the impact of the worn parts on the performance of the equipment.
(3) Important stressed parts should be replaced when the strength drops close to the limit.
(4) When the friction condition of worn parts deteriorates, they should be replaced.
- Determine the selection boundary for replacement or repair of worn parts
(1) According to the economy of repair and replacement, decide whether to replace the worn parts with new ones or repair them.
(2) The worn parts selected for repair must be able to maintain or restore the original technical requirements of the parts after repair.
(3) The strength and rigidity of the worn parts selected for repair after repair must meet the requirements of use.
(4) The parts selected for repair should have sufficient life after repair.
(5) Whether to repair worn parts, factors such as the influence of existing repair conditions on the repair cycle should also be considered.
General technical regulations for the repair of worn parts
- The main casting parts of the equipment
(1) If the bed guide rail is bitten and welded, it can be repaired with tin-bismuth low-temperature alloy or epoxy resin. When the wear and deformation of the guide rail surface are within 0.3mm, it can be repaired by scraping. In the range of 0.3-0.6mm, it can be repaired by grinding the guide rail. When it is larger than 0.6mm, it can be repaired by scraping (or grinding) after planing. The original foundation is scraped and grinded, so it should be scraped and repaired as much as possible during the first overhaul. Note: The source is Qianhui.com – machinery and equipment trading website.
(2) The hole where the rolling bearing is installed on the box should be measured after dismantling. The actual size of the holes for installing P4 and P5 bearings should be strictly controlled within the original tolerance range. The actual size of the hole for installing P6 bearings is allowed to exceed 1/2 of the size of the original tolerance zone. The dimensional accuracy of the hole for installing P0-grade bearings can be determined according to the working conditions of the bearing, so as not to cause running vibration and the outer ring of the bearing to rotate in the hole is appropriate. When the size of the bearing hole is seriously out of tolerance, the sleeve method can be used to repair it under the condition that the size of the hole wall allows. If the hole wall is very thin, it should be repaired by coating. Only in special and urgent cases, it is allowed to plate metal layer on the outer ring of the bearing or repair it with epoxy resin adhesive.
There are defects such as damage and oil leakage on the box body, which are allowed to be repaired without affecting the strength and rigidity of the equipment, and can be repaired by repair welding, bonding, buckle and other methods.
- The sliding seat of the workbench and the guide rail on the sliding plate are generally repaired by scraping; If the equipment has been repaired many times, it will often cause the installation dimensional chain to have no adjustment margin. At this time, it should be repaired by bonding nylon plates, polytetrafluoroethylene plates or using wear-resistant coatings to restore the equipment dimensional chain. design requirements, otherwise it should be replaced.
(1) Repairs should be carried out when the spindle bearing journal has the following conditions.
1) The surface roughness is one grade thicker than the original design or the Ra value is greater than 1.6 μm.
2) The roundness error and cylindricity error exceed 50% of the original design tolerance.
3) The radial circular runout error at the front and rear bearing journals exceeds the allowable value. The grinding allowable amount of the main shaft can refer to Table 2-3.
(2) If the thread of the main shaft is damaged, it can generally be repaired with a small outer diameter and the pitch remains unchanged.
(3) The taper hole is worn and can be ground. The value of displacement a of the end face after grinding (as shown in Figure 2-5) shall not exceed the following values, as shown in Table 2-2.
Table 2-2 Allowable displacement of taper hole surface
- When the main shaft has serious scars, bends, cracks or cannot meet the accuracy requirements after repair, it must be replaced with a new one.
- Shaft parts
(1) Generally, the processing workload of small shafts is small, and should be replaced after wear and tear.
(2) Transmission shaft
1) The journal of the sliding bearing should be repaired as a shaft sleeve after grinding the journal. The amount of grinding is shown in Table 2-3.
Table 2-3 Permissible grinding amount of journal of sliding bearing
|Heat treatment||Heat treatment layer thickness c||The purpose of the shaft||Allowable amount of grinding|
|transmission shaft||<10% of diameter size|
|surface hardening||1.5~2mm||Main shaft and drive shaft||<0.5c|
|Carburizing||1.1~1.5mm||Main shaft and drive shaft||<0.4c|
|Nitriding treatment||0.45~0.6mm||Main shaft and drive shaft||<0.4c|
2) Assembling rolling bearings, gears or pulleys are worn, they can be ground and coated after exposure to light.
3) If the keyway on the shaft is damaged, it can be appropriately enlarged according to the wear situation, and the maximum can be increased by one level according to the standard size. When the structure permits, it is allowed to process another keyway at 60° from the original key position.
4) When the curvature of the shaft equipped with gears is greater than the allowable error of the center distance, it cannot be repaired by straightening, and a new shaft must be replaced. The generally slender shaft allows straightening, restoring precision.
(3) The spline shaft can continue to be used if it meets the following conditions, otherwise it should be replaced with a new one.
1) The R value of the surface roughness of the centering journal is greater than 6.3 μm, and the tolerance level of the clearance fit does not exceed the next-level precision.
2) The R value of the surface roughness on the bond side is not greater than 6.3μm. The amount of wear is not more than 2% of the key thickness
3) There are no indentations and scratches that cannot be eliminated on the key side, and the chamfer does not exceed 30% of the height of the side.
(4) If the surface roughness R value of the bearing journal of the crankshaft is greater than 3.2 μm, and the geometric accuracy of the journal exceeds 60% of its tolerance zone, it should be repaired. For the repaired journal size, the maximum allowable reduction is 3% of the nominal size.
(5) The screw can continue to be used when it meets the following conditions:
1) The axial clearance of the screw and nut is not greater than 5% of the original thread thickness.
2) The surface roughness R value of the general transmission screw thread is not greater than 6.3μm, and the surface roughness R value of the precision screw thread is not greater than 3.2μm. Note: The source is Qianhui.com – machinery and equipment trading website.
When repairing the lead screw, it is required that the reduction of the outer diameter of the lead screw shall not exceed 5% of the original outer diameter, and the allowable thread thickness reduction shall not exceed 10%. Generally, the bending of the transmission screw is allowed to be straightened, and the bending of the precision screw must be repaired.
(1) Cylindrical gears and bevel gears
1) If there is severe fatigue pitting on the tooth surface, accounting for about 30% of the tooth length and more than 50% of the height, or when there are serious and obvious dents and scratches on the tooth surface, new parts should be replaced.
2) For chamfering damage, re-chamfering is allowed under the premise of ensuring the strength of the gear.
3) When the contact is skewed and the contact area is lower than the assembly requirements, it should be replaced with a new one.
4) Under the premise of uniform wear of the tooth shape, the wear amount of the chordal tooth thickness is allowed to be 6% for the main transmission gear and 8% for the feed gear. Auxiliary transmission gears allow 10%, and those exceeding it should be replaced.
5) Gears with broken teeth and small and medium modulus should be replaced; if the number of damaged teeth of a gear with a large modulus (m>6) does not exceed two teeth, inserting is allowed; when the repair welding part does not exceed 50% of the tooth length, Repair welding is allowed.
(2) Worm gear, worm
1) When the tooth surface roughness R value is greater than 3.2 μm, it should be repaired.
2) After tooth surface wear is repaired, the tooth thickness reduction cannot exceed 8% of the original tooth thickness.
3) When the contact area of the tooth is lower than the assembly requirement, it should be repaired.
(1) Claw clutch: If there is a crack in the claw or the chamfer of the end face is more than 25% of the tooth height, it should be replaced with a new one. The teeth are allowed to be ground, but the tooth thickness reduction shall not be greater than 5% of the tooth thickness.
(2) Disc clutch: When the parallelism error of the friction plate exceeds 0.2mm or uneven bald spots appear, replace it with a new one. There are scars on the surface. When grinding the plane, the thickness reduction should not exceed 25% of the original thickness, and the number of sheets increased by the thickness reduction should not exceed two.
(3) Cone clutch: When the contact area of the cone is less than 70%, and the radial runout of the cone is greater than 0.05mm, the cone surface should be ground. If it cannot be repaired, one of them can be replaced.
(1) When the sliding bearing of the main shaft has an adjustment margin, it can be repaired and scraped, otherwise it should be replaced.
(2) When the raceway or rolling body of the rolling bearing is scratched, cracked, the cage is damaged, and the rolling body is loose, it should be replaced with a new one.
(3) The shaft sleeve should be replaced when the shaft sleeve is worn and the bearing bush is cracked or peeled off.
- Pulley and flywheel
1) The rim and spokes should be replaced if they are damaged or broken. Repair welding is allowed when the accuracy requirements are not affected.
2) If the working surface is uneven or the surface roughness R value is greater than 3.2μm, it should be repaired.
3) When the radial circular runout and end face runout exceed 0.2mm, it should be repaired.
(2) When the radial circular runout and axial play of the flywheel exceed the standards listed in Table 2-4, it should be repaired. The repaired flywheel must be balanced and meet the design requirements.
Table 2-4 Allowable Error of Flywheel Rotation Accuracy (mm)
|Rim diameter||Allowable radial runout||Allowable axial play|
- Braking device
(1) Brake shoe friction lining should be replaced after the thickness wear reaches 50%.
(2) When the wear of the working surface of the brake wheel exceeds 1.5~2mm and the surface scratch depth exceeds 0.5mm, it should be repaired. The wall thickness of the repaired brake wheel should not be less than 50% of the original thickness.
(3) The shaft wear exceeds 5% of the original diameter, the roundness error exceeds 0.5mm and the tie rod with cracks should be replaced.
(4) If the wear of the round hole exceeds 5% of the nominal size, the hole should be reamed and equipped with a new shaft for repair.
(5) If the spring has cracks or permanent deformation, it should be replaced with a new one.
(1) pulley, roller
1) When there are groove marks on the working face, it should be repaired. The wall thickness after repair should not be less than 80% of the original wall thickness. Otherwise it should be replaced.
2) The wear amount a of the pulley and drum groove surface exceeds 25% of the diameter of the new steel wire rope, and the wear amount of the pulley groove wall thickness b exceeds 15% to 20% of the original wall thickness and should be replaced. Note: The source is Qianhui.com – machinery and equipment trading website.
3) Pulleys and rollers should be replaced when cracks are found.
(2) The hook should be replaced in the following situations:
1) Use a magnifying glass of 10 to 20 times to observe that there are cracks on the surface of the hook.
2) The depth of the wear groove exceeds 10% of the height of the dangerous section of the hook.
3) Residual deformation occurs outside the dangerous section of the hook or at the tail.
4) Cracks and deformation appear on nuts and hook beams; fatigue cracks appear near the undercut or transition rounded corners of the hook tail.
1) The wear of the rim exceeds about 40% of the original thickness, or the part of the rim is cracked and should be replaced.
2) When the diameter difference of the same group of driving wheels is greater than 0.1% of the nominal diameter, it should be repaired.
3) When the rolling surface is uneven, it should be repaired.