On a rotary filling line, bottles change direction many times. They enter the rinser, move to the filler, travel to the capper and exit to the conveyor, all at speed and without falling over. The parts that make this possible are called format parts or change parts: timing screws, star wheels and guides shaped to fit each bottle. When they are well made and correctly set, bottles flow smoothly. When they are not, jams, broken bottles and scuffed labels follow.
The Timing Screw (Feed Screw)
The timing screw sits at the infeed of a rotary machine. Bottles arrive on the conveyor touching each other. The screw, with its gradually increasing pitch, separates them and spaces them to match the pockets of the first star wheel. The shape of each turn must match the bottle profile so that the bottle is controlled throughout.
A poorly designed screw squeezes bottles, causing them to jump or tip. A worn screw lets bottles wobble, creating timing errors at the star wheel.
Star Wheels
Star wheels are discs with pockets that hold bottles as they rotate from one machine to the next. Each pocket must match the bottle diameter at the contact height. Star wheels transfer bottles between conveyors, rinsers, fillers and cappers.
Guides
Fixed guides keep bottles in the star wheel pockets as they rotate. The gap between the guide and the bottle must be small enough to control the bottle but not so tight that it causes friction or label damage.
Materials
Format parts are commonly made from engineering plastics such as UHMW polyethylene or acetal, which are light, wear-resistant and gentle on bottles. Some are made from stainless steel or have steel cores for strength.
Why Format Parts Matter for Changeovers
Every bottle shape needs its own set of format parts unless the machine uses neck handling for bottles with a common neck. Changing a set involves removing and fitting screws, star wheels and guides. Well-designed parts can be changed quickly by hand, with quick-release fasteners and clear markings. Poor designs require tools, shims and trial-and-error adjustment.
Signs Your Format Parts Need Attention
- Bottles falling at transfers
- Scuffing or scratching on bottle bodies or labels
- Uneven spacing at the infeed
- Increased noise at star wheel transfers
- Frequent small stops at a specific point
Making New Bottle Formats Run Smoothly
When introducing a new bottle, provide your machine supplier with accurate bottle drawings and physical samples. Small dimensional differences can matter. A trial with sample parts before full production saves frustration.
Storage and Care
Store spare format parts on labelled racks, away from heat and direct sunlight, which can warp plastics. Clean them before storage and inspect them for wear. Keeping each set together avoids mix-ups during changeovers.
Setting Up After a Changeover
After fitting a new set, run a few bottles slowly through every transfer before increasing speed. Watch each handover point and listen for knocking. Small timing adjustments at this stage prevent jams once the line is at full speed.
Upgrading Older Lines
If an older line struggles with a new bottle, replacing format parts with better designs can transform performance without replacing the machine itself.
Hilden designs and manufactures format parts for rotary rinsers, fillers and cappers, including parts for new bottle shapes on existing lines. Share your bottle drawing and samples to get parts that fit precisely.
