A stamped outer panel is a difficult conveyor load: 18 kg, thin, oily and visible on both sides. A scratch on the Class A surface is a reject, and a dent is a scrap. The conveyor had to move the part 14 metres without either.
The process
The press produced a part every 9 seconds. The part was picked by a robot and placed on a conveyor that carried it to a deburring cell, then to inspection and packing. The original conveyor was a roller conveyor with steel rollers, and the reject rate from scratches was 3.2%.
The oil on the part made it slide on the rollers, and the part sometimes rotated and hit the guide rail. The rollers also left marks on the Class A surface.
The conveyor change
We replaced the roller conveyor with a chain plate conveyor using stainless slats with a protective coating. The slats were 3 mm thick and had a low-friction, non-marking surface. The chain was a heavy roller chain with a 1-inch pitch, sized for the load and the 9-second index.
The part was located on the slats by a set of low-profile pins that engaged the forming holes. This prevented rotation and kept the part away from the guide rails. The pins were replaceable and were made from a soft material to avoid marking.
| Parameter | Before | After |
|---|---|---|
| Conveyor type | Steel roller | Coated chain plate |
| Part location | None | Pins in forming holes |
| Scratch rejects | 3.2% | 0.3% |
| Part rotation | Frequent | None |
| Noise | 82 dB | 74 dB |
Oil and drainage
The slats were spaced with a 4 mm gap, which let the oil drain away instead of pooling under the part. A drip tray was added below the conveyor and connected to the existing oil collection system. The gap was small enough that the part could not catch.
The chain was lubricated with a high-viscosity oil that would not wash off with the stamping lubricant. We also added a chain guard to keep the oil off the floor.
What we learned
The pins were the key. Without them, the part would still have rotated and hit the guide rail, even on the new slats. The pins had to be soft enough not to mark the hole and hard enough to survive 20,000 cycles; we used a hardened polymer.
The second lesson was the slat coating. The first coating we tried was too soft and wore through in three months. The second coating was a ceramic-filled polymer that lasted more than a year.
Maintenance
The chain is inspected monthly for tension and wear, and the pins are checked every week. The slats are cleaned at the end of each shift to remove metal dust. The drip tray is emptied daily.
The conveyor has run for two years with one chain replacement and two sets of pins. The customer considers it a low-maintenance asset compared with the roller conveyor it replaced.
Frequently asked questions
Why not use a belt conveyor with a protective belt?
A belt would have absorbed the oil and become slippery, and the part would still have moved. The chain plate with pins gave positive location.
Can the conveyor handle different part sizes?
Yes, the pins are mounted in slots and can be repositioned for a different part. The change takes about 15 minutes.
How was the noise reduced?
The coated slats and the chain guard reduced metal-to-metal contact. The chain tension was also set correctly, which removed the chain slap.
If you are moving heavy, visible stampings, send the part drawing and the oil type to our engineers through the contact page.
