SZ Stranding Parameters: What Must Buyers Verify?

A production manager comparing SZ stranding proposals needs to know more than the fastest displayed line speed. The useful decision is whether the offered equipment can form the specified loose-tube cable core, retain its agreed geometry and provide evidence tied to the actual production setup.

Approve SZ stranding parameters as a product-specific recipe and evidence record, not a list of independent machine maxima. Define the lay measurement, reversal pattern, incoming elements, binding arrangement and sample checks together before accepting a running speed.

This article concerns loose tubes and fillers assembled around a central member. It does not describe optical-fiber drawing, copper-conductor stranding or every cable design that happens to contain optical fiber. It provides a framework for a technical review, not a universal starting recipe or instructions for tuning an operating machine.

Separate Helical Lay From the Reversal Pattern

Use separate names for a one-turn helical lay, a reversal-to-reversal interval and an average lay calculated over that interval. The drawings identify their endpoints; they are geometric explanations, not a machine recipe or measured trial result.

For a regular helical section, follow one identified tube through a full 360-degree turn. Mark A and B at the same angular position, one complete turn apart, and measure their separation along the cable axis. Do not measure the curved length of the tube. Draka’s Bundled fiber optic cables publication defines helical pitch as this longitudinal distance for a complete wrap.¹

Principle schematic, not to scale: A–B identifies a complete helical turn within one direction. Solid and dashed parts distinguish the near and far sides of the same illustrated path; they are not different tubes.

For a reversal interval, identify adjacent winding-direction changes R1 and R2 and measure their axial separation D. A reversal has a transition region, so the inspection method should state which reference position within each transition is used. The unwrapped view separates angular motion from axial distance; it is not a side photograph of a cable.

Principle schematic, with no angular or production scale: D is the axial interval between the agreed reversal references. Record the turns N separately, including a partial turn where applicable.

The Pirelli publication Method of determining lay length of S-Z stranded buffer tubes describes average lay as D divided by N. It explicitly accounts for fractional turns of the tracked tube. This is a different measurement basis from selecting one complete turn in a helical section.²

Corning’s Variable lay stranding also distinguishes helical portions and reversal-related geometry and describes arrangements with changing local lay.³ Do not assume a local one-turn measurement equals an interval-average value. These publications support the distinctions, not a HONGKAI machine limit or an acceptance tolerance.

In the HONGKAI checking approach described for this guide, compare the produced pattern with the corresponding screen setting. This guide does not assert which geometry a particular controller label represents. Match the HMI field name and unit to an agreed annotated sample before using that comparison for acceptance.

Do not accept the word “pitch” without identifying the element concerned. A binder setting, a tube-lay measurement and a distance between reversals answer different questions. Nor should a motor-speed readout be treated as a core-geometry measurement without an explained relationship.

Note: A controller’s label is not a definition. Keep one-turn lay, reversal interval, transition length, turn count and binder pitch distinct in the technical schedule; using the same unit does not make them interchangeable.

Match the Recipe to the Incoming Elements

A parameter sheet is incomplete without the cable construction to which it applies. Begin with the approved drawing and the actual incoming loose tubes, fillers and central member. Identify each element position rather than relying on the finished fiber count alone.

Functional review map, not a fixed equipment bill: qualify the incoming elements and required binding arrangement before comparing a recipe.

For HONGKAI’s initial SZ configuration review, also specify the required stranding lay and element count. Confirm whether the cable specification calls for a double-head binder, a single-head binder or both. A reference configuration containing both is not evidence that every cable needs both arrangements.

The following worksheet is a review tool, not an assumed equipment bill.

A completed tube is not the same material as an individual coated fiber. Do not transfer a fiber-pay-off tension value to a tube or to the assembled core without an approved engineering basis. Likewise, a full cable-factory route does not establish the input condition of a particular SZ trial.

A HONGKAI HK-800/12 configuration reference lists separate tube pay-offs, a central-member feed, an SZ unit, binding and water-blocking functions, traction and take-up. Those are relevant functions to review, not a universal promise that every order includes the same arrangement.

HONGKAI’s Micro Cable production reference places SZ core formation between loose-tube production and final sheathing. Its video boundary explicitly leaves the final element arrangement, lay settings, speed and supplied scope to the project. Use the reference to locate the process; use the approved proposal and sample to establish the actual order.

Compare Controlled Trials, Not Peak-Speed Screenshots

Two runs are useful for comparison only when their differences are recorded. If one trial uses another tube diameter, binder, central member or reel condition, keep that change beside the result. Do not quietly label the higher observed speed as performance for the customer’s original construction.

Start with a documented baseline that meets the agreed sample checks. Any subsequent trial should state its purpose and the authorized changes. The equipment supplier must determine how changes are implemented within the machine’s permitted operating procedures; the buyer’s record should make the comparison understandable.

Blank comparison framework, not a completed test report: keep the common basis visible and record each intentional difference.

This is a blank comparison structure, not a test result. No speed, duration, pass rate or improvement is implied by the table.

Keep the operating state with the observation. A sample taken during established running does not automatically demonstrate behavior during acceleration, deceleration or another agreed event. Conversely, an isolated transient should be investigated in its actual context rather than used to invent a permanent production limit.

The commercial comparison should specify the product, accepted quality, operating condition and evidence. Machine maximum speed, an observed trial speed and an agreed production commitment are separate statements.

HONGKAI’s experience provided for this guide makes the usable running speed conditional on the cable construction and required lay. Ask the supplier to distinguish a machine’s structural limit from its actual operating condition, and to distinguish rotational speed from linear cable speed. A figure stated in revolutions per minute must not be substituted for a value expressed as cable length per minute.

Locate the Defect Before Choosing an Adjustment

A photograph of a loose reversal or an uneven core can identify a symptom, but it does not establish the cause. In HONGKAI’s described review, start by checking variation in the incoming loose-tube outside diameter. That tube-quality verification belongs to the preceding loose-tube production stage and should be completed before the material enters SZ stranding.

Once the incoming tube condition is established, check the produced stranding against the agreed setting and inspect the binding process separately. HONGKAI identifies binding-tension consistency and binding concentricity as relevant checks; the sample method and acceptance limits still need to be agreed for the actual construction. These are different checks from measuring an extruded insulation wall.

Inspection-boundary diagram, not a one-cause diagnosis: identify where an observation first appears before assigning it to an SZ adjustment.

Use the following table to keep the production boundaries visible. It is an inspection framework, not a conclusion that one symptom always has one cause or an instruction to change control settings.

Inspection should follow the factory’s safe procedures. Never reach into an operating strander, defeat an enclosure or bypass protection to obtain a closer view. Sampling, access and parameter changes belong to authorized personnel and the equipment supplier’s instructions.

Keep input-quality checks separate from SZ-stage checks and finished-cable release. A later sheathing or handling problem should not be assigned to the SZ machine merely because the cable passed through it earlier. Equally, a good-looking bound core is not a substitute for the required optical and finished-product evidence.

Release a Recipe With a Retrievable Evidence Record

The buyer needs a result that can be traced back to a known setup. An operator should be able to identify the drawing, inputs, recipe, running record and retained sample that supported the decision.

For the SZ acceptance review described by HONGKAI, agree the core outside-diameter criteria, achieved stranding lay, before-and-after optical attenuation comparison and the relevant binder/SZ fault-alarm checks. Include the agreed acceleration and deceleration observations rather than recording steady running alone. Use the customer’s actual manufacturing and acceptance requirements where provided, and put the agreed test methods and limits into the contract. A generic dimensional value or alarm list should not silently replace those product-specific requirements.

Evidence to request: A trial identifier connecting the cable drawing, actual material and reel inputs, recipe revision, agreed parameter definitions, sample locations, measurements, operating video and open-item disposition. Specify which records are supplied and retained before the trial, rather than assuming every controller logs every channel.

Evidence relationship diagram: the common identifier connects the records; the illustration does not imply a passed trial or resolved open item.

For the wider acceptance process, the cable production line FAT and SAT checklist explains how samples, configuration comparisons and open items fit into the agreed test scope. An SZ-specific record still needs its own lay and reversal evidence; a generic FAT form alone is not enough.

• ☐ The offered and tested core construction is identified.
• ☐ Lay, reversal and binding terms have agreed definitions.
• ☐ Actual inputs and any departures from the ordered trial are recorded.
• ☐ Sample observations and measurements link to the running condition.
• ☐ Numerical limits and the basis for acceptance are stated in the approved test plan.
• ☐ Open items have an owner and a defined verification step.

Release only the scope supported by that record. Untested constructions and unresolved settings remain open; a selected demonstration does not qualify the entire future product range. The next repeat run should reference the accepted setup and record any change that requires renewed review.