Overhead conveyors accumulate differently from floor lines. The chain keeps moving, the trolleys stop, and the hanger hangs from the trolley. If the stop acts on the chain instead of the trolley, the chain wears and the hanger swings. If the hanger is not designed for the stop, the part moves even when the trolley does not.
Key takeaways
- Stop the trolley, never the chain.
- Hanger sway is controlled by geometry and by the stop's deceleration, not by adding weight.
- Hanger pitch and stop spacing must match the process and the oven length.
- Accumulation should be placed where people work, not in the middle of a process section.
Three stop types and where they belong
Mechanical stops are simple and robust. A lever or a paddle blocks the trolley. They are suitable for manual load and unload stations and for buffer sections where the stop is set by the operator. They do not release automatically, so they need a return spring or a manual reset.
Pneumatic stops release automatically and can be controlled by a PLC or a sensor. They are used where the line must index or where a station needs a precise stop position. They cost more and need an air supply, but they are the right choice for automated lines.
Gravity or spring stops are used on inclines and on accumulating sections where the trolley pushes past a light resistance. They are simple but less precise, and they are not suitable for heavy hangers.
Hanger design: load path and sway
The hanger should hang from the trolley at a point that is directly above the centre of gravity of the part and fixture. If the centre of gravity is offset, the hanger will tilt and the part will swing when the trolley stops. Offset hangers are sometimes necessary for spraying, but they need a stabiliser or a lower stop speed.
The hanger should be stiff in the direction of travel. A hanger made from thin rod will flex at every stop and fatigue at the weld. Use a gusset or a thicker section at the hook. For parts above 20 kg, use a two-point hanger or a cradle rather than a single hook.
Pitch, stop spacing and buffer size
The hanger pitch is the distance between trolleys. It must be large enough to clear the largest part and the oven opening, and small enough to give the required output. If the pitch is 800 mm and the line runs at 4 m/min, the output is 300 hangers per hour.
Stop spacing in an accumulation zone should be a multiple of the pitch, so that each trolley has its own stop position. If the stops are closer than the pitch, only every second or third trolley can stop, and the buffer capacity is lower than the physical length suggests.
| Hanger load | Recommended stop | Hanger type | Pitch |
|---|---|---|---|
| Up to 10 kg | Mechanical paddle | Single hook | 500–700 mm |
| 10–25 kg | Pneumatic with damper | Two-point or cradle | 700–900 mm |
| 25–60 kg | Pneumatic, double stop | Cradle with locating pins | 900–1,200 mm |
| Above 60 kg | Powered stop with brake | Custom fixture | 1,200 mm+ |
Where to put accumulation
Accumulation belongs at the load station, the unload station and any manual operation where the operator's pace varies. It does not belong inside an oven or a spray booth, where the process time is fixed. A buffer before the oven can help, but it must not change the residence time once the part enters.
A common mistake is to add accumulation in the middle of a long straight section because there is space. That buffer is difficult to reach and does not help the operators who need it. Put the buffer where people are.
Controls and safety
Pneumatic stops need a sensor to confirm the trolley is present and a signal to release. The control logic should prevent a stop from releasing while the next trolley is too close. A simple PLC with a photo-eye at each stop is enough for most lines.
Overhead conveyors are often above walkways, so the hanger and part must be restrained against falling. Use a secondary retention pin or a safety hook. Inspect welds and hooks monthly, and replace any hanger that shows cracking or deformation.
Frequently asked questions
Can I add accumulation to an existing overhead line?
Yes, if there is straight track and enough space. You will need to add stops, sensors and a control sequence, and possibly reinforce the track at the stop points.
Why do hangers swing at the stop?
The stop is decelerating the trolley faster than the hanger can settle. Use a damped stop, reduce the approach speed, or add a stabiliser rail. Increasing hanger weight usually makes the problem worse.
How often should hangers be inspected?
Monthly for visual cracks and deformation, and every six months for weld inspection on hangers above 25 kg. Replace rather than repair a cracked hanger.
Send the part weight, hanger drawing and line layout to our engineers via the contact page; we will check the stop and hanger design before the line is built.
