Sheet metal forming processes are those in which force is applied to a piece of sheet metal to modify its geometry rather than remove any material. The applied force stresses the metal beyond its yield strength, causing the material to plastically deform, but not to fail. By doing so, the sheet can be bent or stretched into a variety of complex shapes. Sheet metal forming processes include the following:
l Bending
l Roll forming
l Deep Drawing
l Stretch forming
Bending
Bending is a metal forming process in which a force is applied to a piece of sheet metal, causing it to bend at an angle and form the desired shape. A bending operation causes deformation along one axis, but a sequence of several different operations can be performed to create a complex part. Bent parts can be quite small, such as a bracket, such as a large enclosure or chassis.
V bending and Wipe bending
Roll forming
Roll forming, is a metal forming process in which sheet metal is progressively shaped through a series of bending operations. The process is performed on a roll forming line. Each station has a roller, referred to as a roller die, positioned on both sides of the sheet. The shape and size of the roller die may be unique to that station, or several identical roller dies may be used in different positions. The roller dies may be above and below the sheet, along the sides, at an angle, etc. the roller dies are lubricated to reduce friction between the die and the sheet, thus reducing the tool wear. Also, lubricant can allow for a higher production rate, which will also depend on the material thickness, number of roll stations, and radius of each bend. The roll forming line can also include other Sheet Metal Fabrication operations before or after the roll forming, such as punching or shearing.
Deep drawing
Deep drawing is a metal forming process in which sheet metal is stretched into the desired part shape. A tool pushes downward on the sheet metal, forcing it into a die cavity in the shape of the desired part. The tensile forces applied to the sheet cause it to plastically deform into a cup-shaped part. Deep drawn parts are characterized by a depth equal to more than half of the diameter of the part. These parts can have a variety of cross sections with straight, tapered, or even curved walls, but cylindrical or rectangular parts are most common. Deep drawing is most effective with ductile metals, such as aluminum, brass, copper, and mild steel. Examples of parts formed with deep drawing include automotive bodies and fuel tanks, cans, cups, kitchen sinks, and pots and pans
Stretch Forming
Stretch forming is a metal forming process in which a piece of sheet metal is stretched and bent simultaneously over a die in order to form large contoured parts. Stretch forming is performed on a stretch press, in which a piece of sheet metal is securely gripped along its edges by gripping jaws. The gripping jaws are each attached to a carriage that is pulled by pneumatic or hydraulic force to stretch the sheet. The tooling used in this process is a stretch form block, called a form die, which is a solid contoured piece against which the sheet metal will be pressed. The most common stretch presses are oriented vertically, in which the form die rests on a press table that can be raised into the sheet by a hydraulic ram. As the form die is driven into the sheet, which is gripped tightly at its edges, the tensile forces increase and the sheet plastically deforms into a new shape. Horizontal stretch presses mount the form die sideways on a stationary press table, while the gripping jaws pull the sheet horizontally around the form die
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The internal environment fan gearbox is a closed gear system that communicates with the outside through the vent. The lubricating oil used is L-CKC150 industrial closed gear oil, each with a fuel quantity of 110 liters, a lubricating oil viscosity of 143 mm 2 / s, a mechanical impurity of not more than 0.0067, and a flash point of not less than 250. The lubrication in the tank is combined with the oil pool dip bath and the simmer oil flow lubrication, and the tank maintains a certain amount of oil storage. During summer operation, the oil temperature in the tank is generally between 4055.
The external environment cooling tower is a mixture of high temperature and humidity. The temperature is constantly changing due to the temperature of the return water and the outside air temperature. The general return water temperature is between 3438. In the summer high temperature season, the temperature in the tower can be close to 40, and the circulating water evaporation It is 632t/h, the drift is 1.5t/h, and the relative humidity in the tower is 80å缪乖 test? 40Pa.
Actual operation effect In order to further explain the impact of the wind turbine operation on the gears in the winter, the gear failures occurred in the winter operation of the wind turbines were counted in recent years.
Fan gear failure statistics table No. Model No. No. Fault phenomenon 1 Follow the L92DFN-001 small helical gear with 6 teeth surface lower 10mm peeling 2 one TVF-LITEFN-002 small helical gear with 5 tooth surfaces 2mm2 Peeling off 3 TVF-LITEFN-006 small helical gear has 1 tooth surface with peeling phenomenon 4 follows TVF-LITEFN-007 small helical gear tooth surface has peeling phenomenon 5 follows TVF-LITEFN-008 small helical gear tooth surface a bit Eclipse phenomenon 6 LF85FN-013 small helical gear tooth surface a little eclipse phenomenon 7 one LF85FN-014 small helical gear 1 tooth lower fracture 8 two LF92FN-004 small helical gear has 2 teeth lower 10mm broken 9 second LF92FN-006 small helical gear has 1 tooth broken 2/310 2 LF92FN-007 small helical gear 1 tooth lower 2mm2 peeling 11 second LF92FN-012 small helical gear all tooth surface peeling can be seen through winter After the operation, the faults of the first and second circulators have reached 11 faults. The fault forms are pitting, spalling and broken teeth. The fault parts are all small helical gear faults. Among them, 6 wind turbines are overhauled and 4 gearboxes are replaced.
Fault cause analysis The fan is a large-scale rotary equipment. The reverse running time spans 5 months throughout the winter. According to statistics, the cumulative running time of each wind turbine in winter is only about 300h, which is 1 than the monthly full-load running time of a single wind turbine in summer. /2 is still small, although the running time is short, but it is destructive. If it is not handled properly, it will directly affect the peak operation of the summer wind turbine. There are many reasons for the formation of wind turbine gear failures in winter. Reversal is only one of the main factors, and some minor factors also have different degrees of influence in winter operations.
Restricted by the process conditions, the fan reversal is not simply a change in the direction of rotation, but mainly affects the fan gear. First of all, a significant feature of the winter fan reversal is the short running time and high starting frequency. The number of fan operation depends on the icing condition. Generally, each fan runs 6 times a day, and the whole winter starts about 180 times. Each running time is within 30 minutes. Frequent starting will not only cause fatigue pitting and tooth surface peeling on the gear. Moreover, the impact on the fan gear is large at each start and stop.
Affected by the lubrication environment, the minimum temperature in winter can reach -30. At this time, the oil temperature in the fuel tank also drops significantly. Although the fan sometimes has a low speed rotation, it is not enough to fully agitate the oil to warm it. The low temperature causes the lubricating oil to be viscous and the flow is not smooth, and it cannot climb to the surface of the gear quickly at each start-up to form sufficient lubrication, causing dry start and making the gear wear faster. In addition, the steam in the tower will penetrate into the gearbox from the various sealing interfaces and mechanical seals such as the gearbox oil window, and will condense into water to make the oil contain water. In this case, the lubricating oil is easily emulsified and deteriorated, which will lead to several results. (1) The viscosity of the lubricating oil is lowered, so that an oil film of a certain thickness cannot be formed on the surface of the gear, so that the bearing capacity of the lubricating oil is lowered, and when the gear is overloaded, the gear is easily damaged; (2) the good lubricity is broken, and the gear surface is made The friction increases, which will accelerate the wear; (3) due to the increase of friction, the heat is increased, and the cooling effect is reduced, thereby breaking the thermal equilibrium state, causing the temperature to rise continuously to damage the gear; (4) destroying the lubricating oil. The vibration damping effect further increases the impact on the gear.
Restriction and prevention of gears in cooling tower operation