recognizing and eliminating flux concentrator failures presentation

8/10/2019 Recognizing and Eliminating Flux Concentrator Failures Presentation

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Confidential Property of Fluxtrol Inc.

Mr. Robert Ruffini

President

Recognizing and

Eliminating FluxConcentrator Failures

1




Overview

• What are the failure modes of a fluxconcentrator?

• How do we improve the design to

prevent the failure in the future?• Examples of coil lifetime

improvement by proper use of flux

concentrators

2




Common Flux Concentrator FailureModes

• There are three commonthings that can lead to fluxconcentrator failure:

– Mechanical Damage – Excessive Temperature

– Electrical Break

• The failure modes may bedifferent depending upon fluxconcentrator type

3

Rusted laminations beginning toseparate at the ends of the stackon a crankshaft coil




Mechanical Damage

• Inductors oftentimes operate underrelatively harsh conditions in heat treatingapplications

• Mechanical flux concentrator failure isgenerally caused by one of the following: – Coil/concentrator impact with the part or a part

of the machine

– Coil is dropped/damaged outside of the machine – Coil movement due to electrodynamic forces

– Coil movement due to thermal expansion of thecopper

4




Mechanical Damage Due to Impact withPart

• Clamshell side-shieldimpacted by

counterweight ofcrankshaft

5




Concentrator Breakage Due to ThermalExpansion of Copper Tube

• Common Failure Mode in applicationswhere inductor profile has a smallnose for concentration of power in aradius

• Copper has very high current density,leading to high power density, whichheats copper

• Concentrator has a thin profile,which is not strong and breaks on

expansion• Due to concentrator breakage,

current concentration is not as strongin nose and pattern is compromised

6

Concentrator often looksdarkened, but source oftemperature is coil copper,not radiation!




Coil Movement Due to ThermalExpansion of the Copper

7

Insufficient water cooling of the copper caused copper toexpand vertically, breaking off sections of the flux concentrator




Excessive Temperature

• Inductors oftentimes operate under relativelyharsh conditions in heat treating applications

• Thermal flux concentrator failure is generallycaused by one of the following: – Too high coil copper temperature causes oxidation of

concentrator – Large gaps between concentrator and copper – Low thermal conductivity of adhesive – Poor application of adhesive

– Exposure to 3-D fields (especially for laminations)• Thermal failure in heat treating applications isvery, very rarely caused by radiation from thepart

8




Proper Design & Glue Adhesion

PROPER AIR GAP DESIGN AND GLUINGALLOWANCES

GOOD GLUINGTECHNIQUE

POOR GLUING TECHNIQUE Black on rest of the concentrator oil

from the part heating

9




Glue layer too thick, which caused formationof air pockets and local overheating

10

Thermal conductivity of epoxies much lower than for Fluxtrol materials andmuch, much lower than for copper. Air pockets, have almost no thermalconductivity, which cause local buildup of heat where they are present.This area of big air bubbles caused the concentrator to overheat, crack andseparate from the glue. Other sections of the inductor had no issues.




Non-Water Cooled Inductor for HighTemperature Melting Application

Temperature ofsusceptor

around 1000 Cfor 1 hour, butconcentratorcool to touch

11

Radiation in Heat Treating isnot the cause ofconcentrator overheating!




Electrical Break

• Flux concentrators are not true dielectrics.When exposed directly to high electricpotential, a break could occur

• The areas of concern are as follows:

– Turn to turn breakdown on multi-turn coils – Breakdown in the leads area

– Coil to cooling plate or structural component

– Conductive dust, debris or scale is present

• Electrical breaks are a greater concern forhigh frequency and large diameter, multi-turncoils

12




Arced Laminations

• Turn to turn arc onlaminations on theleads side caused by

overheating due to 3-D fields andsubsequent oxidationof lams leading to a

bridge between turns.

13




Improving the Design

• Different Failure Modes Require DifferentSolutions to Resolve

• Some Good Design Practices will BeProvided to Prevent Failures fromOccurring

• Case Stories of Implemented Solutions will

be Provided

14




Preventing Mechanical Damage fromImpact

• Part Guides/Concentrator Protectors – Non-Magnetic Stainless Steel/Brass

– Fiber Reinforced Plastic (G-11 or similar)

– Ceramic or Carbide (shoes on crankshaft coils)

– Potting in plastic or casting in ceramic

15




Resolving Issues Associated with CoilMovement from Electrodynamic Forces

• Electrodynamic forces causecyclic vibrations of theinductors during the process

• The main solution is to

segment the concentratorinto shorter segments

• Also, retainer rings are usedto limit coil deflection andhold concentrator in place

• This can extendconcentrator lifetime by anorder of magnitude

16

Crankshaft coil with segmentedconcentrator to allow the coil toflex during the process




Case Story of Solving Thermal Problem

• Customer had coillifetime problems withheating of a stem of aCVJ

• After a certain numberof parts, the nose of theconcentrator wouldbreak off and patternwould be lost

• Customer blamed theconcentrator for thefailure.

17

Copper nose starting to melt. Thecopper clearly is growing andconcentrator machined down to knifeedge. This knife edge is breaking.




Head Design Improvement to ReduceCopper Temperature

• Excessive coppertemperature was thecause of the failures

• By redesigning the

copper nose and coolingpocket, coppertemperature wasreduced 25%

• This increased the coillifetime from 25,000 to100,000 pieces withoutchanging the pattern

ORIGINAL COIL DESIGN

OPTIMIZED COIL DESIGN

Small radius Large and Small Ball Nose Endmills

18




Case Story of Overheating ofLaminations Due to 3-D Fields

• Application at 3 kHz for heatingof off-highway component

• Laminations overheating due to3-D field and actually pushingcopper keepers over until they

arced with the part or patternlost in fillets

• Coil lifetime around 13,000 parts• Replaced laminations with

Fluxtrol LRM without keepers.

• Result was lifetime of around50,000 pieces and improved heattreat pattern

19




Case story for Electric Breaks on ColdCrucible Melting Coil

20

• Two types of arcs wereoccurring – Turn to turn arcs from the

stud, through theconcentrator, to the stud

– Stud to stud arcs from thestud, through theconcentrator, through thefaraday ring, through theconcentrator, through the

stud• Application was for making

powder metal, so largeamounts of conductivepowder present




Solutions to Arcing Problem

Use of stud insulators andconcentrator split

Elimination of studs onconcentrators

21




Conclusions

• Magnetic Flux Controllers are a very importantcomponent of the induction heat treating coildesign

• Magnetic Flux Controllers have a beneficialeffect on many types of inductors

• Flux Concentrator failures are often resolvedby very minor design changes, which can havea drastic effect on the coil lifetime

• If you run into an issue with insufficient coillifetime, do not hesitate to contact yourFluxtrol representative

22




Thank you!

23

More Information

More information about magnetic

flux control, controllers and

application technique may be foundon www.fluxtrol.com

http://www.fluxtrol.com/

recognizing and eliminating flux concentrator failures presentation

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