In the production process of China's pressing plants, unplanned downtime caused by conveying equipment accounts for 60% to 80% of all unplanned downtime. Improving the operational performance of conveying equipment and reducing the failure rate is the focus of attention for all pressing plants, and improving the performance and configuration of conveying equipment is a great concern for the designers of conveying equipment.
Large pressing plant conveying equipment is mainly scraper conveyor, bucket elevator and screw conveyor, the following describes these conveying equipment to meet the full load operating conditions for the improvement of the design of technical points, and a brief introduction to the pipeline conveyor.
1、Horizontal scraper conveyor
1.1 Horizontal scraper conveyor in the production process problems
General supplier in the design of conveying equipment conveying volume is in the contract on the basis of the amount of 5% ~ 10%, when the conveyor in production after the failure of the shutdown it is difficult to restart with material, may appear chain deformation. Scraper with sight glass observation window generally takes one side configuration, it is difficult to see the internal running situation. After the scraper operation is stopped the tail end is prone to residual material, the return of the guide rail is designed as a parallel guide rail, which does not make good uniform contact. In the absence of special requirements, the shell, track, chain material mostly used carbon steel, easy to wear out. The speed reducer and motor are mostly used for general general purpose. According to the national safety management requirements, the original grain silo group area was changed to dust explosion-proof; as the leaching oil plant upgraded the safety precaution level, the design of leaching meal storage were changed to explosion-proof type; the motor was promoted to configure energy-saving type according to the new national specification in 2013.
1.2 Improved design requirements
1.2.1 Shell
The design of the scraper conveyor should have 15% overload starting and continuous running capability under the condition of meeting the rated production. The scraper with sight glass observation windows should be 2 at the head and tail end, symmetrically arranged. The middle section sight glass observation windows are spaced about 10m apart, symmetrically arranged on both sides of the scraper, and the sight glass observation windows are made of toughened glass. 1 hinged observation door at the top of the housing at the head and tail end of the scraper. The horizontal square scraper head is equipped with an overflow door (with limit switch), which opens automatically when needed to discharge the material stored in the scraper. The cleaner is made of flame-retardant polymer polyethylene with a thickness greater than or equal to 25 mm, and the chain is equipped with a guide rail on the return stroke, which is supported by an "eight" shaped upper guide rail, so that the entire bottom edge of the blade is in uniform contact with the guide rail. The material inlet, discharge port and discharge position of the conveyor are customised according to the production process.
The cover and side plates are made of Q235, the liner and bottom plate are made of wear resistant steel NM360 or NM400, the thickness of the side plate liner is greater than or equal to 6mm and the top plate is 4mm carbon steel. Use galvanized U-shaped clips and bolts to fix on the side plate, no need to drill holes in the cover and side plate flange, use M10 galvanized bolts, the middle partition plate is 10mm thick, material NM360, the thickness of the side plate of the head and tail section is greater than or equal to 8mm; the thickness of the bottom plate is greater than or equal to 6mm, the thickness of the liner plate is greater than or equal to 10mm. "In the manufacture of the NM360 plate, it should be tempered twice.
1.2.2 Head and tail wheel section
The head and tail wheel shaft of the scraper conveyor should be machined as a whole, and the transition should be as smooth as possible at the diameter change of the shaft.
Head and tail wheel shaft material 42CrMo, to be heat-treated. Chain wheel to take Martin dissection, take assembly type dissection type or opposite type. Fastened with 10.9 grade anti-corrosion bolts, such as the use of bent plate chain, you can use the split sprocket. The head is equipped with an off-chain sweeping device, which is convenient for the scraper chain to detach and clear the accumulated material in the tooth groove. The head discharge port opens directly to the end, effectively preventing the accumulation of material, and the head is also equipped with an anti-clogging switch to prevent blocking of material. The guard is an oil-impregnated sprocket guard. It adopts split type with seat bearing, vertical installation or horizontal installation according to the situation, also can adopt slider type with seat bearing, adopt packing type seal, packing type seal. The tail wheel takes the split type sprocket, easy to disassemble and install.
The head and tail are designed with a waterproof sealed observation window fixed by quick-open nut or handle on the cover, which is convenient for observing the chain tightness and the wear degree of the head wheel; the observation window is installed on the side plate at 50cm from all inlets to the direction of material running, and the material of the window body is Plexiglas plate with thickness greater than or equal to 10mm.
1.2.3 Reducers, couplings and motors
The maximum surface temperature should not exceed 85°C when the reducer is in a dust hazard area (same below). Explosion-proof gearheads and explosion-proof gearheads are to be insulated according to CE specifications, class F, protection class IP54, IP55. If shaft-mounted gearheads are used, the braking force arm is to be arranged so that it is under tension at all times. All gearboxes are to be lubricated by internal injection or forced lubrication and the lubricant is to reach all running parts such as gears, bearings and seals. Oil seals are to be able to withstand pressure changes within the gearbox due to blocked ventilation or temperature changes.
The coupling should be flexible, rigid coupling is prohibited, the coupling should be easy to disassemble and assemble, the safety factor of the coupling is greater than or equal to 2. A hydraulic coupling should be installed on the shaft when the power of the drive motor is 18kW or more. Shafts with drive motor power equal to or less than 15kW should be fitted with rubber sleeve type or other forms of coupling approved by the owner.
Previously, the motor was designed according to dust-proof design, i.e. dust-proof explosive squirrel-cage motor, according to the provisions of the grain dust explosive hazard area divided into 11 zones. Now YE3 series high efficiency motors are used, YVF2 series frequency conversion special motors are changed to YXVF series high efficiency frequency conversion speed control motors, requirements in the leaching ban area and soybean meal storage should be designed according to explosion-proof motors, explosion-proof motors YB3 type are changed to YBX3 series high efficiency explosion-proof motors, all exposed parts of the motor should be protected by approved and suitable reinforced metal protective nets. All motors should have lifting bolts and the holes for the lifting bolts should not penetrate the motor casing to expose the stator iron chip. The energy efficiency of the motor should not be lower than the national standard. The new level 2 is required to be equipped with oiling nozzles.
1.2.4 Safety protection devices
Protection and explosion-proof grade are required to meet the national standard and IEC standard, including the following: ① stall sensor; ② blockage sensor of the chute at feeding and discharging; ③ limit limit limit switch of tensioning device (on gravity type tensioning device); ④ speed monitoring; scraper conveyor installation material level is resistive and capacitive type; ⑤ temperature measuring system of head wheel bearing.
1.2.5 Chain
Plant raw grain receiving 500t/h scraper conveyor chain speed less than or equal to 0.60m/s, workshop scraper conveyor chain speed in 0.35~0.40m/s.
The scraper chain is made of 40Cr and 45CS quenched, and the quality of the 500mm wide welded bent chain is 30kg per metre and the tensile strength is 600kN. The pin is made of 40Cr and is carburized and high frequency treated. The forged chain has a tensile strength of 1500kN and the chain, sprockets and axles are subjected to quenching, tempering, carburizing, shot peening and tempering. The thickness of the guide rail on the chain is 8~10mm and the guide rail material is wear resistant steel greater than or equal to NM360.
Each section of the chain plate is fitted with UHMWPE wear plates with thickness greater than or equal to 19mm and bent scraper plates greater than or equal to 25mm, UHMWPE wear plates with relative molecular mass greater than or equal to 3.5 million, fixed with 8.8 grade hot-dip galvanized stopper bolts and chain plates.
Install 2~3 cleaning scrapers evenly on the scraper chain, the size of the cleaning scraper is slightly larger than the rubber plate of the scraper, and fix the cleaning scraper on the scraper with screws.
Generally the fixed chain is fixed in a group of 3m each, one end of the pin inside the group is stepped and the other end is hot riveted, the movable pin between the group and the group adopts a D-type pin on one side, the over-measurement fits, and the 6~8mm T-type pin or the threaded pin is used directly to fix it, each whole chain can keep 3~5m of full live section.
2、Curved scraper conveyor
Curved scraper conveyor in the production in addition to the horizontal scraper conveyor problems, in the curved scraper design to consider how to reduce the amount of back material, the amount of back material required to control within 5%. Use in the workshop: ① for conveying high temperature and materials with moisture vapour, such as softened materials, billet sheets, puffed materials and finished meal at 55~65℃, conveying DC out material with temperature over 100℃; ② conveying flammable and explosive materials such as wet meal. Due attention is paid to the following matters in the design.
2.1 Head and tail wheel
Use a standard chain with odd number of teeth at half pitch. The tail bearing uses a split bearing Dodge TAKE-UP integral slider bearing or return tensioning slider bearing. The reducer safety factor of the billet scraper, the scraper conveyor going to the leaching plant, the scraper conveyor coming out of the leaching plant and the wet meal scraper is greater than or equal to 2.0. The head of the conveyor scraper and the DT meal scraper conveyor from the pre-treatment plant to the leaching plant should be provided with an air vent.
2.2 Bending section
The chain is tightly combined, the bending section is selected with the best radius of curvature and natural transition, the lining is made of NM360 or NM400 high strength wear resistant plate. The side plate of the bend structure is 6mm NM360, the height of the lining is greater than the height of the material, the thickness of the guide rail on the chain is at least 10mm, the material of the guide rail is not less than the wear-resistant steel NM360 or Mn65, the interval of the sight glass observation window is about 10m, one pair of sight glass observation window is equipped in the vertical section of the shell immediately adjacent to the bend section. Take welded bent plate chain, scraper form take full face type scraper.
2.3 Seal
Require flange piece flat, head and tail wheel shaft to take double four fluorine packing oil seal, copper sleeve bearing seal, overall seal, before leaving the factory to do assembly seal test.
2.4 Wet meal scraper special requirements
According to 30% containing soluble design processing capacity, DT to DC scraper processing capacity according to the meal containing 16% water design, the line speed is less than or equal to 0.35m / s. Leaching wet meal scraper back to the amount of material as far as possible to adjust within 3%. To reduce stagnant material, reduce friction, using plastic lining, shell material Q235 or SS304, scraper bearing section shell thickness 8mm, bulkhead thickness 10mm, bend section with removable assembly form, with sight glass, bend section chute material Mn65, NM360 or NM400, thickness 10mm, non-bearing material section shell thickness greater than or equal to 6mm, barrel connection flange plane to The thickness of the chain is greater than or equal to 18mm, the chain is made of welded bend plate chain, the liner material is PTFE (capacity 2.1~2.3t/m3), the thickness is greater than or equal to 15mm, the load factor of the chain is greater than or equal to 8 times, the thickness of the head and tail plate is greater than or equal to 10mm, the frequency conversion start or soft start is adopted, and the sealing filler is selected for easy replacement. The straight section of the shell is welded at the top and bottom, and the curved section is bolted (considering the replacement of the middle partition grinding section).
Inlet and outlet position with thickened plate (preferably movable type, easy to replace), scouring resistance; pay attention to the contact surface of the scraper track plate and the chain to be wide; from the leach to DT wet meal scraper, from DT to DC hot meal scraper to be insulated; scraper top to leave the air valve to prevent the shaft seal grease liquefaction, vaporisation. The scraper's bearing seat should be fixed with top wire to prevent the rotating shaft from tampering.
3、Bucket elevator
Bucket elevator conveying volume design to leave a 15% margin (consider starting with a load), control the amount of return material within 3%. The centre line of the belt shall not deviate from the centre line of any pulley by more than 10mm under any conditions between no load and full load. At present, the maximum lifting height of domestic bucket elevators is around 80m.
3.1 Bucket elevator problems in the production process
The strength of the body shell is weak, tilting in the production process, resulting in dustpan friction; positioning errors between the shell flange, resulting in dustpan impact and damage; many bucket elevators appear to return a large amount of material, reducing the actual conveying capacity; belt material and dustpan material is poor, easy to break; stopper using 1 tooth, the strength is not enough; the location of the explosion vent is not right, may be a safety accident; observation window and access door is not the right location. Increase the difficulty of maintenance and repair; feeding method if taken in the direction of the material, reduce the amount of transport; the bottom of the material clearance method is not appropriate, the bottom of the accumulation of more material to reduce the amount of transport or increase the lifting resistance, and in serious cases lead to downtime. If the head shell is integral, it is difficult to open and repair. The line speed is too high or too low, the high speed is easy to damage the equipment, the low speed reduces the conveying capacity of the equipment and may appear slippage. The material and angle of inclination of the inlet and outlet chutes can easily block or increase the load on the receiving equipment below if they are not suitable.
3.2 Improved design requirements
3.2.1 Head
Head shape split shell, parabolic arc, throwing material shell height is relatively small, lined with A8 grade with steel mesh liner plate, steel plate thickness greater than or equal to 8mm, the head seat of the side of the falling material steel plate thickness greater than or equal to 8mm, appropriate with reinforcement bars to increase? The inner surface where the material is impacted should be lined with a polyurethane wear-resistant material (or ceramic sheet material) with a thickness greater than or equal to 10mm, fixed with standard countersunk bolts galvanised. The width of all wheels should be at least 100mm wider than the bandwidth, and the width of the barrel should be at least 50mm wider than the width of the wheel. Runout. Adjustable and removable return baffle (made of polyurethane) and dustpan movable interceptor bar should be installed in the discharge chute. A lifting ring should be provided on the outer cover of the head.
The material used for the wear-resistant plate is UHMW-PE, with a relative molecular mass of 3.7 million. If the relative molecular mass exceeds 1.4 million, the wear resistance increases and exceeds 3.5 million, it is very brittle, and when the hardness is large, the hardness should be reduced and the toughness increased.
Tapered connection shaft is used between wheel and axle to be machined as a whole, at the change of diameter of the shaft, the design should reduce the stress concentration to a minimum. For the axle shoulder, the largest possible chamfer radius should be given according to the actual situation, and the axle and the bearing seat should be connected with a top wire. The head wheel is fitted with an oil resistant, flame retardant, anti-static rubber layer, which can be dismantled and fitted, with a hardness of 60 DURO and a thickness of not less than 20 mm and a convex thickness of not less than 10 mm.
The bucket elevator roller should be a solid wheel, with an adjustable baffle inside the head to eliminate backfeeding. Bucket elevator is equipped with a reversible device to prevent full load or full stop when running in the reverse direction, the reversible device is selected from multi-tooth type, bucket elevator can be in the upstream side of the barrel body of the bucket 100% full load, the base is filled with 1/3 of the conditions of a smooth start, there can be no slipping phenomenon.
3.2.2 Shell
The bucket elevator has its own barrel on the upstream and downstream side. The difference between the internal width of the barrel and the bandwidth is not less than 150mm, and the minimum clearance between the back of the belt and the barrel must not be less than 50mm. the minimum clearance between the largest projection of the dustpan and the barrel must not be less than 75mm. the barrel is made of low carbon steel plate and angle steel and other profiles (or galvanised steel plate), and the sections are connected by bolts with a thickness greater than or equal to 4mm. the height of a single barrel is less than or equal to 3m to ensure that under various load conditions Vertical positioning in each direction under various load conditions with a tolerance of ±3mm. flanges should be fully welded to both ends of the barrel or sealed against corrosion, the barrel should be assembled in such a way as to prevent welding deformation, the sections of the barrel should be flush at the joints and the inner surface of any section should not project more than 2mm beyond the inner surface of the adjacent section. All joints should be sealed with a flexible material such as silicon sealant applied to the flange before screwing on. Sliding joints should be provided inside the barrel to regulate the vertical movement between the head and tail of the bucket elevator. The design should eliminate the touching of the bucket and the joints, and where the bucket elevator is installed in a closed structure, the sliding joints should be sealed to prevent dust from escaping. The barrel adopts pressed and bitten edge structure, fully open observation and maintenance barrel, strengthened scissor support, explosion-proof maintenance section every 2 sections, 3m standard section diagonal error less than or equal to 2mm. barrel adopts standard flange connection, connecting bolt is 5.6 grade chrome-plated bolt.
3.2.3 Dustpan belt, dustpan
According to our industry standard belt speed in 2.8~3.5m/s, in the press shop selected line speed in 2.6~3.0m/s.
Dustpan belt core to polyester, nylon and PVC material composition, oil resistant flame retardant anti-static, tensile strength 600 ~ 800N/mm, dustpan belt surface layer cover rubber thickness of not less than 2mm, dustpan belt 5 ~ 7 layers, the number of layers and thickness should meet the standard of tension and dustpan bolt tensile strength, safety factor 15 ~ 18, dustpan belt in the first use of 12 months after the stretching amount shall not be greater than 1%. The width of the dustpan belt should be at least 75mm wider than the sides of the dustpan fixed to it.
The bucket belt should have a certain thickness of outer edge layer, the bucket belt should be connected by means of a mechanical connection lap, the connection should be connected by at least 6 rows of bucket bolts per side, the bucket bolts should be 8.8 grade hot dip galvanised stopper bolts. The rated maximum permissible working tension of the dustpan belt should exceed the maximum operating tension by at least 15% and the ratio of breaking tension to working tension should be greater than or equal to 9. The protruding part of the dustpan fixed to the dustpan belt connection hitch should not exceed the protruding line of the dustpan fixed to the remaining part of the dustpan belt.
The material of the dustpan is polyethylene, polyurethane and steel 3 kinds, generally use polyethylene (life 1.5 years) and polyurethane (life 3 ~ 4 years), in the material temperature below 70 ℃ choose polyethylene or polyurethane dustpan, higher than 70 ℃ choose steel dustpan. Configure deep buckets and shallow buckets according to the requirements of the material to be conveyed. The buckets can be perforated at the factory or at the site, with belt connectors.
3.2.4 Inlet, outlet and equipment connection chute
The inlet, outlet and connecting chute are made of 6mm NM360 or NM400 steel plate and connected to the body with bolts. Or use polyurethane material with a thickness of not less than 10 mm or wear-resistant ceramic sheet as a wear-resistant liner. It is advisable to install anti-blocking sensors in the inlet and outlet chute.
3.2.5 Access doors and explosion relief doors
Removable access doors and viewing windows should be provided at the head, base and barrel of the bucket elevator. The size of the doors and windows should be sufficient for the removal and replacement of the head, base, guide wheel and dustpan. Access doors and windows should be installed at 12m intervals. The viewing window should be installed in such a way that the internal head wheel operation can be seen.
The surface area to be drained on the bucket elevator should be set at not less than 1m2 of drainage area per 8m of equipment volume. In the appropriate location in the barrel set up the appropriate number of explosion relief ports, explosion relief ports and dust collectors located in the head, middle and tail of the machine, explosion relief film made of approved low inertia lightweight materials, should be at a pressure of no more than 1.5kPa, no more than 1ms time to fully release. Removable for replacement and secured with M8 nylon bolts are required.
3.2.6 Bottom section and base
The bottom section of the bucket elevator is made of steel plate greater than or equal to 6mm thick and is reinforced with solidity. Materials can be fed into the base of the elevator through the front or rear feed chute opening and should be fed in the reverse direction as far as possible. The bottom section should be designed in such a way that the feeding pipe of the cylinder on the upward side should be above the centre line of the tail wheel when it is in the highest position of the stroke, and the feeding pipe of the cylinder on the downward side should be above the centre line of the tail wheel when it is in the lowest position of the stroke. Install the insert plate at the front and rear of the base, or design the base plate in an arc to minimise stagnant material and facilitate the emptying of the base. Both sides of the base should be provided with slotted holes, the length of which should be able to accommodate the full travel of the specified tail wheel shaft.
The front and rear parts of the base section are provided with an inclined insert plate driven by a rack and pinion. Both sides of the bottom section shell are equipped with a "clearing chute" or a hinged cover with a hinged mouth, and the clearing door is of roller or rack and pinion construction. The bottom section can be equipped with a double inlet, self-cleaning roller. A sealing device is fitted between the base housing and the sliding bearing plate so that no material or dust can escape from any position on the bottom wheel during the full tensioning stroke. The tail wheel can be designed as a squirrel-cage tail wheel with a self-cleaning function. The tail wheel is made of a castor strip and the seat is subject to material scouring with a ceramic mat.
3.2.7 Tensioning device
The tensioning device is equipped with a limit switch, using hydraulic tensioning or mechanical tensioning, mechanical tensioning is to take the heavy block box tensioning + filament rod fine adjustment. The tensioning device should be left with sufficient travel, the travel not yet utilised should be not less than 50% of the full length. A sealing mechanism is provided between the bottom section box and the sliding bearing plate, which should slide flexibly and without jamming under the premise of ensuring the sealing effect.
3.2.8 Safety protection device protection and explosion-proof level are required to meet the national standard and IEC standard, with the following contents: ① stall sensor; ② chute blockage sensor at feeding and discharging; ③ tensioning device limit switch; ④ head wheel bearing temperature measuring system; ⑤ speed monitoring, overload sex protection, coupling with shear pin; ⑥ anti-runout device, with mechanical anti-runout device, with the belt contact part as tail wheel roller, or with (5) Speed monitoring, overrunning protection, coupling with shear pin; (6) Anti-running device, with mechanical anti-running device, with the contact part of the belt being the tail pulley roller, or with pressure plate type runout detection device.
4、Screw conveyor (winch)
The screw conveyors used in ports and pressing plants are only used as horizontal conveyors and can convey normal and high temperature materials. According to the process demand, screw conveyor take variable pitch, variable shaft diameter, its intermediate shaft reference GB/T12459, according to Sch80 grade standard. The material thickness is 5mm for the shell, 6mm for the blade and 3mm for the cover.
4.1 Screw conveyor
Conveying distance less than or equal to 30m screw conveyor using high-strength hollow spindle, using hanging bearings, strengthen the triangle type adjustable hanging. If used for distribution screw conveyor to open the lower feed opening according to the position of the receiving equipment below.
4.2 Sealed stranded dragons
In the leaching plant, one end of the sealing strand is the lower material mouth, in front of the lower material mouth design a section of broken leaves, the length of its broken leaves according to the diameter of 1.1 ~ 1.25 times, as the material sealing section. The outer wall at one end of the lower feed opening is replaced by a gravity door, which is hinged to the top of the housing and also acts as a material seal. The material of the sealing strand in the leaching plant is recommended to be SS304 to prevent damage failure due to corrosion or the gravity door falling into the leaching vessel, with a special reminder of the material and strength of the design connecting the gravity door hinges.
In the top of the puffing machine as a feed gantry, the middle of the variable pitch, material sealing section, to the puffing machine stable feed, the puffing machine below the flap cooler outlet, with a gantry to receive the material, connected to the feeding scraper, the role of material sealing, blocking the leaching workshop solvent through the scraper conveyor, etc. into the pretreatment workshop.
5、Conclusion
As the processing scale of the pressing plant now exceeds the actual production needs, there are fewer and fewer new plants and the technical transformation of the pressing plant is highly valued. In the production process, if 1 conveyor equipment fails, it will cause the whole line to stop, and it will take some time to resume production, which not only wastes energy, but also the product quality can only reach the rated product quality index after 2~3h of start-up, and the unqualified semi-finished products have to be added back, causing the processing volume to be reduced for some time. Therefore, the operational stability of the conveying equipment is more demanding than before, which leads to higher requirements for the quality of materials and accessories needed for conveying equipment. In addition, due to the energy saving and safety requirements, the motor was replaced with an energy efficient type, and the reducer and motor were designed as explosion-proof in the meal bank. The design of the bucket elevator takes into account the possible influence of dust and the design of explosion relief and head safety nets.
The media of the curved scraper conveyor used in the workshop of the press plant is different from that of the outdoor infeed curved scraper conveyor, which contains oil and gas, water vapour, solvents, high temperatures and different media densities, as a special reminder.
In addition in the starch, food industry, small particles or powder material long-distance transport, as well as pressing plant degreasing meal and bean skin transport, can use the pipe conveyor, pipe conveyor size in 40 ~ 50t / h. Two pipes can be laid along the wall, bend radius requirements greater than 4D, in the pipe with steel wire rope every 30 ~ 40mm welding a round plate, round plate material selection SS304 or manganese steel The perforation of the circular plate and the welding of the wire rope are key technologies. Compared to wind transport, the pipe conveyor saves electricity and is stable in operation.
