Infeed starwheel (container change part)

01

Match the pocket pitch to the timing screw and turret

Frain Industries' whitepaper on timing screws describes metering containers into a starwheel on a capper or other machine as one of their applications. In its example the screw synchronises bottles entering the infeed starwheel of a rotary filler at a 1:8 ratio: for every one-eighth revolution of the starwheel the screw makes one revolution and releases one bottle into each pocket, so if the starwheel's pockets are 6 in apart the screw's discharge pitch must also be 6 in. The same holds for a screw carrying bottles from one machine's discharge starwheel to the next machine's infeed starwheel. [1]

The whitepaper defines a timing screw's outside diameter, root diameter, pocket (cut to the shape of the container) and pitch, notes that pitch need not be uniform along the screw and is critical only at points such as the discharge, and says that more pockets between infeed and discharge give gentler acceleration and less tipping, and can matter for line synchronisation when buying replacements. [1]

Editorial calculation: in the 1:8 example the starwheel has eight pockets, so a 6 in pocket pitch puts them on a pitch circle of about 8 × 6 / π ≈ 15.3 in (388 mm) diameter. [1]

Give the supplier the machine make, model and turret pitch circle, the starwheel's position (infeed, transfer, discharge), number of pockets, the container drawing or samples for every size, timing screw data, hub and shaft fixing, guide parts needed, material and food-contact requirements, and changeover method.

02

Choose the material and have parts made to drawing

Plastic Products Inc. supplies replacement parts for packers, uncasers, fillers and cappers — starwheels, profiles, cams and sprockets — made from customer drawings or samples, in USDA/FDA-approved materials including nylon, acetal, TFE, polypropylene, PVC, UHMW-PE and PEEK. [2]

Ask for the material's food-contact declaration for your market, the machining tolerance on pocket profile and pitch, and how the starwheel locates on the machine so that pockets stay in time with the screw and turret after a changeover. [2] [1]

03

Plan how the change parts are swapped

US patent 5,689,932 (FCI Inc., priority 1996) describes neck-handling star wheels on fillers and cappers, in which bottles hang by the neck ring in pockets of neck support assemblies around the star wheel, held in by a rear guide between entry and exit. In the prior art it describes, a large star wheel assembly carried nineteen neck support sections, each bolted on at four or five places with a torque wrench, or the whole hub and star wheel was exchanged for a pre-assembled one for each bottle size, followed by adjustment and retiming. [3]

The patent locates each neck support on threaded studs that can use the existing bolt holes and on a hub clamp pin with a groove engaged by a spring piston, so that the support is aligned to receive bottles as soon as it snaps in. Compare this with made-to-drawing plastic starwheels and the timing screw that sets the pitch the pockets must match. [3] [2] [1]

Editorial calculation: replacing 19 bolted sections at 4–5 bolts each means removing and refitting 76–95 bolts per wheel at each size change.

State how many container sizes the line runs and how often it changes, and ask whether starwheels and guides are supplied as complete wheels or as tool-free segments, and the change-over time per machine.

04

Check what an FDA-compliant acetal claim covers

Starwheels and guides on fillers and cappers are offered in materials described as FDA-approved, acetal among them. [2] For acetal copolymer, the US rule is 21 CFR 177.2470, which lets polyoxymethylene copolymer (trioxane with ethylene oxide, or with at most 5% by weight butanediol formal) be used in food-contact articles under stated conditions: a minimum number-average molecular weight of 15,000; stabilisers totalling no more than 2.0% and no single stabiliser above 1.0% of polymer weight; net chloroform-soluble extractives from the finished article of no more than 0.5 mg per square inch of food-contact surface; and, for ground resin, total extractives of no more than 0.20% in 6 h refluxing distilled water and 0.15% in 6 h refluxing n-heptane. The conditions of use are articles intended for repeated use, a use temperature not exceeding 250 °F, and thorough cleansing of finished articles before their first use in contact with food. [4]

Editorial calculation: 250 °F is 121 °C, so an acetal starwheel in a line that is washed down or sterilised above that temperature falls outside the rule's conditions of use, and another listed material may be needed. Editorial note: the regulation addresses the resin and the finished article, so ask the supplier for a declaration naming the resin grade and 21 CFR 177.2470 (or the applicable section for UHMW-PE, nylon or PEEK), not only the words FDA-approved. [4] [2]

05

What a change-part machinist needs before quoting a starwheel

Ask any supplier for the drawings they work from, pocket count and pitch, pitch circle diameter, pocket profile for your container, material and food-contact certificates, hub and quick-change fixing, matching guides and timing screws, tolerances, and lead time per change-part set.

06

Wheel, screw, guides and hub: the parts that keep a container in its pocket

The pocket pitch only works if the timing screw delivers containers at the same spacing, so the wheel and screw rows belong in the same order. [1]

07

Pocket count, pitch circle and resin grade on a starwheel enquiry

The machine and container drawing fix the hub, thickness and tolerance rows; the reviewed sources supply the pitch and pocket count of one worked example and the food-contact limits for acetal. [1] [4]

08

Send the machine, container and timing data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Machine: [make; model; turret PCD]
Position: [infeed; transfer; discharge]
Pockets: [count; pitch]
Containers: [drawings; samples; sizes]
Timing screw: [ratio; discharge pitch]
Material: [UHMW; acetal; food contact]
Fixing: [hub; quick change]
Quantity: [sets]

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