The frame is composed of longitudinal beams and cross beams etc, welded together. The longitudinal beams are made of web and lower wing welded together and are used for bearing loading and mounting the important components such as traction pins, suspension and supports.
2. Traction pin
Traction pins are used for connecting the tractor truck to the semitrailer and are bonded with the saddle of the tractor truck, so that the semitrailer can be hauled to move. Traction pins come in two sizes: No. 90 and No. 50.
The semitrailer uses mechanical support which can bear the load from the fore part of the semitrailer when the tractor truck is disconnected from the semitrailer. The support comes in two types: single-acting support and interlocking support. It comprises the reduction gearbox, internal/external pipes, screw drive mechanism, base plate, control handle, etc.
The support can raise or lower quickly if the handle is pushed in and rotated and slowly if the handle is pulled out and rotated. Whatever the case may be, if the supporting disk touches the ground, the support can only raise or lower slowly, so as to protect the drive mechanism from damage.
1. Front bracket 2. Non-adjustable drag link 3. Drag link bearing 4. U-bolt 5. Leaf spring 6. Middle bracket 7. Drag link pin 8. Balance arm 9. Balance arm shaft 10. Adjustable drag link 11. Rear bracket
The suspension is the whole assembly that bonds the frame of the semitrailer to the axle shaft. It is used to transmit the loads and forces acting between the wheels and the frame and to mitigate and eliminate the impact load and vibration transferred from uneven road surfaces via the axle shaft to the frame, therefore enabling the emitrailer to travel smoothly. The steel plate springs are fixed by U bolts to the shaft of the wheel axle assembly; two or three sets of steel plate springs are connected in a string via the movable support; the balance arm can swing freely in certain range; the loads of two or three axles can be balanced in certain range.
The axle of a semitrailer can be optionally installed based on the needs of the user. The axle comprises of wheels, wheel hub, brake, axle shaft, etc. Its structure is described in the Operating Instruction of the axle. The axle assembly provides the functions such as travelling and braking.
6. Pneumatic braking assembly
The semitrailer uses a double-pipe air inflation braking system. This system comprises air circuit joint, air inflation line, control line, emergency relay valve, air cylinder and braking air chamber etc and provides the functions such as safe startup, travel braking, emergency braking and parking braking.
Safe startup: after the pipe of the semitrailer is connected to that of the tractor truck, the air inflation pipe inflates the air cylinder via the emergency relay valve. If the air pressure is less than 400 KPa, part of the compressed air is passed via the emergency relay valve into the braking air chamber, the brake is engaged and the truck is able to move; if the air pressure in the system is greater than 400 KPa, the compressed air in the braking air chamber is discharged via the emergency relay valve into the atmosphere, the brake is disengaged and the truck able to move.
Travel braking: if the driver treads, the compressed air is fed via the control line to the emergency relay valve for air inflation and the compressed air enters each braking air chamber via the emergency relay valve,the brake is engaged to achieve proper travel braking.
Emergency braking: if the air inflation leaks or bursts or the tractor truck is suddenly disconnected from the semitrailer during travel, which results in disconnection of the pipes, the compressed air enters each braking air chamber via the emergency relay valve and semitrailer can brake independently.
Parking braking: when the truck stops travelling, the semitrailer starts braking using the air in the air cylinder. If the air pressure is insufficient, parking braking will be achieved by the diaphragm spring braking air chamber of the double rear axles. If the brake is to be disengaged without air source, the transmission screw of the diaphragm spring braking air chamber needs to be tightened to disengage the brake.
7. Electrical system
The electrical system of the semitrailer consists of coupler, seven-core cable, external illuminating devices and external signal device and it is very important for improving the efficiency and safety of transportation. The illuminating devices mainly include tail lights and license plate lamps; the signal devices mainly are outline marker lamps, brake lamps, turn signal lamps and triangular reflector. Their operating voltage is 24 V.
8. Safety guard
Any of our oil trucks has safety railing on both sides and such railing is removable. The rear part of any truck has rear bumper to protect the truck from collision by a following vehicle.