wire and cable troubleshooting guide.pdf

8/10/2019 Wire and Cable Troubleshooting Guide.pdf

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COMMON PROBLEMS ENCOUNTERED IN THE EXTRUSION OF PVC AND THEIR SOLUTIONCOMMON PROBLEMS ENCOUNTERED IN THE EXTRUSION OF PVC AND THEIR SOLUTION

A. Voids occurring generallythroughout the entire wallof jacket or insulation.

B. Voids occurring normallyjust beneath outer surfaceof jacket or insulation,sometimes giving a roughor grainy surfacedepending on severity ofproblem.

Entrapped air in extrudedsection.

Moisture in material.

Heavy-wall jackets andprimary insulations.

Any construction.

Melt zone too far forward inbarrel to force entrapped airback through hopper.

Inadequate screw design forlow back-pressureextrusions.

Too-large construction forextruder capacity.

Humid weather andprolonged storage of feedstock in damp locations.

Increase screen pack more or finer screens.

Decrease space betweenwire guider and die.

Use long land dies.

Adjust screw cooling.

Raise temperature ofcontrolling barrel heat zones.

Preheat feed stock to aconstant temperature prior toextrusion.

Dry material in hopper dryerinstalled on extruder.

Prevent moisture pickup by:

1) Minimizing inventory during humid seasons.

2) Locating storage areas in warm dry locations.

3) Storing materials in tightly closed containers.

Move water bath closer todie line.

Decrease line speed.

Switch heavy-wall construc-tions to larger machines.

Dry material in oven.

Reextrusion of wet stockafter regrinding to obtainnonporous construction.

Extend barrel length.

Replace screw withshallower flight depthmetering section screw.

Installation of hopper dryers.

Investigation of other means ofremoving volatiles duringextrusion such as ventedextruders, etc.

II. POROSITY

Symptom Basic DefectConstructions Normally

Exhibiting Defect Cause of Problem

Immediate Corrective Action

Preferred AlternativeMajor Improvements

Needed

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C. Voids occurring

sporadically in wall ofjacket or insulation,usually accompanied bychunky surface rough-ness.

Volatiles from degraded

stock in extruded section,e.g., HCI gas fromdegradation of PVC.

Any construction, but

especially a multiple-conductor constructionrequiring a complete diedesign.

Excessive stock temperature.

Extended runs withoutcleanouts or screenchanges.

Poor streamlining or flow inapproach and crosshead.

Dirty or pitted dies, guiders,and breaker plates.

Improper startup and

shutdown procedures.

Lower temperature ofcontrolling barrel heat zonesand crosshead. Decreasescreen pack fewer orcoarser screens. 1-40 and 1-60 minimum screen packrecommended. Adjust screwcooling. Increase spacebetween wire guider and die.

For extended runs withoutadequate shutdowns forcleanouts, maintain stocktemperature under 380F.Provide for screen change at

least every eight hours.Decrease crossheadtemperature.

Maintain dies, guiders,breaker plates, and approachso they are clean, highlypolished, and free from rust,pits, burs, and any buildup.

Standardize startup,

shutdown, and cleanoutprocedures to provide:

1) Adequate bleeding beforebeginning new run.2) Continuous bleeding atlow RPM with screw coolingturned off and barrel heatsdecreased during temporaryshutdowns.3) Sufficient flushing ofbarrel with head open beforeshutting down for extendedperiods.4) Proper cleanup of tools

while still warm. Tools anddies should never be burnedout to clean.

Possible need for more-

effective temperaturecontrols.

Possible need for replacingscrew with one of properdesign.

Redesign dies, guiders,breaker plates, and approacheswith smooth angles and goodstreamlining.

Decrease speed.





Needed

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A. Fine pimples similar tograins of sand sprinkledover surface.

B. Coarse grainy surfaceaccompanied by porosityjust under the surface.

C. Fine grainy surfaceoccurring over entiresurface or portions of it atregular intervals.

Uncolloided resin particlesdue to inadequate shearingby the screw or inherenthard gels.

Moisture in material.

1) Material sticking to dies as it leaves crosshead.

2) Strains due to elastic turbulence at high rates of flow.

Any construction; inparticular, those with heavywalls.

See IIB.

Any construction.

Peculiar to high-speedextrusion.

Inadequate screw design forlow back-pressureextrusions.

See IIB.

Cold, pitted, or dirty dies.

Poor streamlining andabrupt angles in approach todie.

Increase screen pack moreor finer screens.

Decrease space betweenwire guider and die.

Use long land dies.

Adjust screw cooling.

Raise temperature ofcontrolling barrel heat zones.

See IIB.

Thoroughly clean die. Polishuntil all depressions areremoved.

Raise stock temperature by:1) Adjusting screw cooling.2) Raising temperature of barrel and crosshead.3) Increasing screen pack.



Replace screw withshallower flight depthmetering section screw.

Extend barrel length.

See IIB.

Replace die and improveprocedure for care andcleaning of dies and tools.

Lengthen approach to die.Eliminate abrupt angles andstreamline die and approach.Increase land length of die.

D. Large blisters or bubbles

in insulation.

Volatiles carried into the

crosshead by marker threador conductor which aretrapped by the extruded PVCand expand upon leavingthe die to give blisters.

Construction using stranded

conductors and/or markerthreads.

Moist or oily conductor.

Conductor with a loosestrand.

Wet marker thread.

Clean, wipe, and preheat the

conductor. See IA.

Check stranding of wire tobe sure it is tight anduniform.

Preheat marker thread inoven or dry by passing itover heat lamp whilerunning.

Improve and clean upstranding operation.

III. SURFACE DEFECTS





Needed

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D. Sporadic lumps of large

size, usually accompaniedby porosity. In severecases, whole sectionsbreak down, leavingcraters in the surface.

E. Sporadic lumps andgeneral bumpy surface(orange peel).

F. Sporadic lumps contain-ing different colored or

textured materials. Highincidence of sparkerfailures.

G. Raised lines on surface.

H. Grooves in surface.

I. Dimples in surface.

J. Holes or splits in jacket.

Degraded stock which has a

consistency stiffer (highermelt viscosity) than normalPVC at extrusion tempera-tures.

Uneven stock viscositycaused by hot and coldstock or, in extreme cases,fused and partially fusedmaterial.

Foreign contamination instock.

Uneven die surface.

Degradation buildup oninside of die lumps ofdegradation stock too stiff to

flow through the die.

Uneven distribution of stockflow around complex shape.

Drawdown of materialexceeding elastic limit ofextruded stock.

See IIC.

Any construction.

Any construction.

Any large constructions,particularly heavy-walljackets.

See IIC.

See IIC.

Small thin-walled tubed-onjackets.

See IIC.

Nonhomogeneous meltdelivered to die.

Break in screen pack. Noguards on hopper. Careless

handling of feed stock or ofmaterial containers.

Damage to die due toimproper handling and care.

See IIC.

See IIIC2. Also guider anglemay not correspond to angleof die.

Die opening too large outof proportion for construc-tion requiring excessivedrawdown.

See IIC.

See IIIA.

Flush out extruder barreland thoroughly clean head.

Avoid storing feed stock inopen containers. Take carewhen emptying bags to keeppaper out of hoppers.

Thoroughly clean die. Polishuntil all depressions areremoved.

See IIC.

See IIIC2.

Raise crosshead and dietemperatures. Cut RPM.




Decrease takeoff speed andextruder RPM.

Extrude insulation directlyon small conductor ratherthan on tubing.

See IIC.

See IIIA.

Install guards aroundhopper.

Place hardware cloth overhopper opening to theextruder to prevent largeobjects from entering feedsections of extruder.

Replace die and improveprocedure for care andcleaning of dies and tools.

See IIC.

See IIIC2. Gradually changeshape of guider and die tofinal geometry of construc-tion from round shape ofapproach.

Replace with die havingsmaller opening properlyproportioned to desiredconstruction dimension.





Needed

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wire and cable troubleshooting guide.pdf

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