Putting the lid on 4 common cap sorting problems: proper cap sorting set-up leads to a faster, more efficient packaging line - Cap Sorters

Food & Drug Packaging, Dec, 2003 by John Henry

Cap sorters--sometimes called feeders or orienters--are often taken for granted. Yet they can cause packaging line slowdowns or shutdowns. This article will look at some common types of sorters, typical problems and how to solve them.

Sorters used on cappers can be divided into three basic types: vibratory, centrifugal and vertical wheel.

* Vibratory sorters consist of a stainless or aluminum bowl mounted on springs. Generally they are driven with electromagnets but can also be driven pneumatically for use in hazardous environments.

* Centrifugal sorters are similar to vibratory sorters because they are round and horizontal but that's where the similarity ends. The centrifugal sorter's bowl is rotated by a motor and has a rim several inches above the bottom of the bowl.

* Vertical wheel sorters consist of a vertical rotating disk with a hopper mounted on a slight angle from the vertical.

Here are four typical problems that can occur with cap sorters and how they can be solved.

1. Vibratory challenges

A vibratory sorter depends on friction between the cap and the track. When the track gets slick, the cap will slip and feed rates will slow. Many plastic cap manufacturers will use a silicone mold release in their molding process to improve efficiency. Over a period of time, usually months or years, this mold release will build up in the feeder. It may not be visible but the track will feel smooth and slick to the touch. The release gets into the surface of the track and is tough to remove with any kind of solvent or cleaner.

The best way to restore performance is to use a 150 to 200 grit emery cloth to abrade the surface of the track and roughen it slightly. The sanding action should be across the track rather than along it's length to help assure the best grip. Another cause of slickness is that the caps themselves, especially if made of metal or hard plastic, will polish the track over time. Again, the solution is the use of emery cloth to break the glaze on the running surface.

Some other problems include:

* Broken springs. Springs are hardened steel and can fatigue or crack over time. Several springs are usually mated together which can make it difficult to see problems. Remove all springs and carefully inspect them, replacing any that are damaged. Hint: After removing the spring, cracks may still be hard to see. Rapping them with a hammer and listening for a dull sound indicating a crack can help.

* Loose components. In the event that any components of a vibratory feeder system are not completely tight, vibratory forces will be lost. Check all bolts and tighten as necessary. Generally speaking, it is difficult to over tighten but be sure to use high tensile strength bolts if any need replacements. Check also all tracks and welded components in the feeder to assure that cracking has not occurred.

* Faulty magnets. Electromagnets are just a coil of wire and generally highly reliable, but they do fail from time to time. To check them, hold a screwdriver or other steel object near the magnet. If no magnetism is felt with the power on, the magnet may be faulty.

* Magnet gap. If the gap between the magnet and spring is too great, power will be lost. If too small, they will hit very noisily. Generally the gap will be between 0.15 and 0.35 inches depending on manufacturer and feeder size. Use a feeler gauge to verify that the gap is uniform and in accordance with the manufacturer's specifications. Be sure to remove any rust or dirt from the mating surfaces of the magnet and spring. Even a small amount of rust can cause excess noise and lost performance.

* Frequency. Vibratory sorters are tuned to be driven at a specific vibration frequency, generally 120--but sometimes 60--pulses per second (achieved by rectifying normal current) in the U.S. In most sorters speed is controlled by voltage with frequency dependent upon incoming power. In recent years, frequency controllers with accelerometers have become more common. These allow the frequency to be varied while holding the voltage constant.

2. Sorting out centrifugal issues

An advantage of centrifugal sorters is that the cap is exposed and it is easy to check for incorrectly oriented caps in the bowl instead of in the track where they can cause jams. A simple photoelectric sensor can identify caps that are incorrectly oriented. These can then be blown back into the bowl without slowing or stopping the system.

Control of the level of caps in any sorter is important. But it is critical in a centrifugal sorter. Centrifugals depend on the ability to transfer caps up the ramp and onto the bowl rim for orientation. If there are too few caps, they may not be able to push themselves up. If there are too many, they will interfere with each other, causing loss of feed rate and jams. The rule of thumb is that the bottom of the bowl should be covered with a single layer of caps. A pre-feeder or hopper is used to meter caps to the bowl and control the level. It is essential that the paddle switch or other control be correctly adjusted to maintain the level. Speed of the pre-feeder should be set so that it feeds caps slightly faster than they exit the sorter rather than dumping relatively large amounts of caps from time to time.