After filling the steel drum, a closure device must be installed on the top of the drum to isolate the contents from the external environment, preventing leakage or reactions with the surroundings.
For closed-end steel drums, common closure accessories include bungs, gaskets, and safety caps. For open-end steel drums, typical closure accessories include drum hoops, gaskets, wrenches (levers), or bolt and nut assemblies. The type of closure accessories varies with different drum mouth designs. Figure 1 shows common installation components for metal drum closures.
Installation of Closure Device for Closed-End Steel Drums
The main component for installing closure devices on closed-end steel drums is the bung. There are three standard specifications commonly used: ventilated G3/4 bung, injection G2 bung, and injection G4½ bung.
Bung Installation Tools
The installation of drum bungs generally requires the use of specialized bung wrenches. Bung wrenches can be custom-made, and common G2 bung wrenches are shown in Figure 2, while G3/4 bung wrenches are shown in Figure 3.
Bung wrenches can be manual, pneumatic, hydraulic, or electric. Figure 4 shows common manual wrenches for various closure specifications, and Figure 5 shows common automatic wrenches.
Before installing the bung, the closure gasket must be pre-fitted on the threaded root of the bung. The gasket should be made of a material compatible with the contents.
Torque for Bung Installation
The torque for bung installation should be appropriate. Excessive torque may damage the gasket, resulting in a loss of sealing effect, while insufficient torque may lead to leakage from the drum mouth.
The drum manufacturing facility installs the bung on the steel drum when it leaves the factory, but the torque is slightly lower than the post-filling torque requirements. Therefore, even if some bungs are not removed during filling, all bungs must be reinstalled after filling.
Installation of Cover (Safety Cap)
After installing the bungs, it is common to add a cover (safety cap) on the drum cover. The cover is typically made of thin tinplate and is stamped, with holes and pull rings on both sides. Along the pull rings, there are two grooves on the cover. The cover is secured using a cover installer. Once locked, the edges of the cover are necked down and secured at the narrow part of the drum mouth. When it is necessary to open the drum cover, tools such as pliers are used to pull up the pull ring on the cover, tearing the cover along the grooves. Once torn, the cover is destroyed and cannot be restored, hence it is also called a safety cap or waterproof cap. In summary, the cover serves both as an anti-theft device and to prevent rainwater from entering the drum mouth. Figure 6 shows common cover installers and the actual cover.
For open-end conical steel drums (convenient drums), the drum cover itself acts as a closure. The drum cover has a circular "skirt" around its perimeter, similar to a pull ring. When sealing, a cover installer is used to secure the cover. After sealing, the "skirt" part is necked down and wedged into the drum mouth's curled edge. When it is necessary to open, tools can be used to pull the "skirt" pull ring towards the periphery. Figure 7 shows a photo of the seal of the steel drum cover before sealing, with the "skirt" of the drum cover not yet necked down. Figure 8 shows the working diagram of the cover installer for steel drums.
Installation of Closure Devices for Open-End Steel Drums
Common closure devices for open-end steel drums include bolt fastening types and lever types. Figure 9 shows the external shape of the bolt-type closure device, and Figure 10 shows the external shape of the lever-type closure device.
The installation of closure devices for open-end steel drums is straightforward. During installation, the hoop is loosened, the drum cover with gaskets added is placed on the drum mouth, and then the drum hoop is placed over the edge of the drum cover. The next step is to tighten.
For bolt-type closure devices, a socket wrench or regular wrench can be used for tightening. Lever-type closure devices generally do not require tools for tightening, and hand latches are sufficient.
It should be noted that, to prevent closure devices from loosening during storage and transportation due to vibration, open-end steel drum closure devices need to have anti-loosening structures. For bolt-type closure devices, a small hole can be drilled at the end of the bolt. After the nut is tightened onto the bolt, a wire is threaded through a hole behind the nut to create a locking ring, preventing the nut from loosening. Alternatively, a locking pin can be used to prevent loosening. For lever-type closure devices, there is usually a self-locking pin. After the lever is tightened, simply insert the self-locking pin into the pinhole to prevent the lever from loosening.
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