There are five main reasons for the defect of the manhole bolt: 1 With the increase in the purchase price of scrap steel, artificial theft is more serious. 2 There is no blocking cylindrical pin or slot nut at the end of the screw to prevent the loss of the nut, resulting in a large loss of the nut. 3 integrated grease bolts to a certain degree of corrosion. The cause of the rust of the integrated grease-impregnated bolt: On the one hand, the structural design is unreasonable. The length of the cavity nut is shorter than the effective thread length on the screw. After the screw is screwed in the nut, the back cover of the nut (the back cover will be <27). The mm@1 mm round iron plate is spot welded on the back end of the nut. It is often lost by the end of the screw. Chemical materials and rainwater easily enter the nut cavity, causing the hole of the manhole bolt to rust. On the other hand, it is also with the tanker. The chemical properties of the transport medium are related.
Since the liquid alkali transported by the liquid caustic tanker is a highly corrosive medium, when the liquid alkali is filled, the manhole bolt is in a loose state, the screw and the nut often cooperate with the thread exposed and the screw is located above the nut, from the crane tube The liquid alkali splashed out often spills onto the screw thread and enters the nut cavity along the thread gap, causing the manhole bolt thread to be severely chemically corroded and rusted. About 60% of the manhole bolts that cannot be used continuously due to bolt thread rust every year are caused by liquid alkali corrosion. Corrosion of manhole bolts on light tank trucks and tar tankers is mainly due to the loss of the back cover of the cavity nut or the lack of lithium grease in the nut cavity. 4 The loading and unloading personnel repeatedly tighten the manhole bolts repeatedly and tap the bolts with the wrenches, which causes the manhole bolts to be slipped and bent during long-term use so that they cannot be used. The loss of the 5-hole bolt is also serious. The main reason is that after the replacement of the sliding buckle, the screw bending deformation, and the loss of the manhole bolt of the nut, the in-house inspection and maintenance personnel did not timely fix the blocking flat washer sleeved on the connecting pin shaft on the connecting pin shaft. In daily operation, in order to prevent the loss of the screw, the railway vehicle maintenance unit usually welds the connecting pin and the blocking flat washer sleeved on it when the vehicle is regularly inspected. However, this kind of anti-theft measures brings inconvenience to the inspection and maintenance personnel of the enterprise to replace the manhole bolts with the sliding buckle, the bending deformation and the loss of the nut. The inspection and maintenance personnel must use electric welding or knock the down flat washers on the connecting pins or use the saw to disconnect the pins to replace the new bolts. Since the manhole bolt is located at the top of the tank body and is about 4. 3m from the ground level, the operation at the top of the tank body is high-altitude operation. In order to prevent the inspection and maintenance personnel from falling accidents during night work, it is usually in the tank car to be loaded into the car wash. After the stacker or the loading platform, the inspection and maintenance personnel or the loading and unloading personnel shall check and repair the defective parts of the upper part of the tank before washing or loading. Since the car wash stacker and the loading stacker are all first-class flammable and explosive fire-proof areas, if the poorly-used manhole bolts are replaced by electric welding, the railway tankers with liquid medium and tar filling must be pulled out of the stack. For the station, use the electric welding to replace the new screw at the designated hot point; for the light oil tanker with the filling medium of hydrogenated gasoline, benzene and alcohol, it must be in the empty state and after the tank is cleaned. Replace the new bolt with electric welding at the designated hot point.
The use of electric welding to replace the sliding buckle and the curved deformation manhole bolt not only increases the amount of shunting work, but also affects the recognition of the car plan and the timely delivery of the heavy truck. Under normal circumstances, the inspection and maintenance personnel usually replace the manhole bolt by tapping the barrier washer fixed on the connecting pin shaft, but sometimes the sealing washer is partially welded on the connecting pin shaft, and the maintenance personnel are inspected. Or the loader also replaces the manhole bolt by cutting the connecting pin with a hacksaw. It is not only labor-intensive and time-consuming to replace the manhole bolts whether the saw pin is connected to the pin or the flat washer that is tapped on the connecting pin. After the replacement of the new mandrel bolt, the electric welding cannot be used. Welding the blocking flat washer sleeved on the connecting pin shaft and the connecting pin shaft easily leads to the loss of the newly replaced bolt in the future operation, and the above two methods are used in the filling medium in the flammable and explosive area. The replacement of poorly used manhole bolts on a Class I flammable and explosive product tanker does not meet the safety requirements and has great safety hazards.
The poor use state of the manhole bolt not only causes the tank lid to be poorly sealed, but also has the safety hazard of the leakage of the first-class flammable or explosive or toxic and harmful chemical products (or raw materials) and volatile gases, and also increases the daily life of the tanker. Maintenance costs and labor intensity of inspection and maintenance personnel.
The anti-theft integrated grease-impregnated bolt structural nut is still a cavity-type blind hole structure, and has a hexagonal shape. At the entrance of one end of the cavity nut, there is an internal thread of M 20 mm for screwing into the screw; the other end is a closed structure. It is welded and sealed with a round steel plate of <27 mm @ 2 mm. An oil hole is opened in the middle of the cavity nut. The oil filling hole has two functions: one is for adding grease to the nut cavity on the one hand, and the blocking round pin for preventing the loss of the nut at the end of the screw is installed from the oil filling hole after the screw is screwed into the nut cavity.
The screw adopts the basic structure of the integral grease-impregnated screw, and the screw head is a lifting ring pin connecting hole, but a cylindrical end is arranged at the end. A through-hole hole of <6 mm is provided in the radial direction on the cylindrical surface of the end of the screw cylinder for mounting the blocking pin.
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