Lauda Heat Exchanger Failure Analysis

Lauda Heat Exchangers installed in SEZ Spin Etch equipment present a number of faults that significantly impact tool down-time.

The faults can be categorized as follows:-

·         Mechanical

·         Electrical

·         External Corrosion

Mechanical
Failure analysis of Lauda Heat Exchangers in the field has identified that bearing failure is the sole cause of mechanical faults. The main factor in this has been determined to be ingress of condensate into the bearing caused by the failure of the lower shaft seal and aggravated by the high running temperature of the motor.

The probable failure mechanism is as follows:-

• The lower shaft seal moves down the shaft and becomes ineffective.
• The bearings dry up due to motor heat and contamination by condensate.
• Corrosion and subsequent wear causes the bearing to seize.
• The bearings may rotate in their aluminium housing or the motor stalls which generates extreme heat. This can result in deformation and failure of the plastic fan or associated electronic components. It should also be noted that any aluminium housing wear can make the unit noisier in operation due to the increased bearing clearance.

Electrical
Electrical faults with Lauda Heat Exchangers fall under two distinct categories:-

·         Faults caused by corrosion at or near the heater coil.
·         Electronic Failure

Faults caused by corrosion at or near the heater coil are generally ground faults. The coil short circuits to earth due to the ingress of moisture through cracks and pits caused by acidic water. Shorting can also occur at the heater coil-case interface. The electrical connections to the element passes through the case surface through an insulation gland. Unfortunately the electrical connection at this point is only loosely shrouded and therefore effectively open to the elements and if corrosive condensate is present this can lead to corrosion building up around the conductor that grows until it makes contact with the case. Once the current through this material reaches a certain level (usually 60 mA) the unit fails or trips out the tool’s Ground Fault Contactor (GFC).

Also shown to be of concern is the paper ribbon cable connecting the display and control pc boards. Extreme care should be addressed here, most notably with the older "S" units. The solid ribbon leads can be fragile and are often affected by heat and age of the unit, not to mention any subsequent handling performed during initial trouble-shooting. Symptoms include erratic heating and controlling of the heating element as well as the absence of an alarm status light when the unit is in an alarmed state.

Electronic failure at the component level has been known to occur but this is rare.

Corrosion
Corrosion, pitting of metal surfaces and the build up of "crud" occurs simply because the quality of the city water being used is poor or the flow rate is too low or unstable. HF is particularly mobile across the thin-wall tubing in the heat exchanger casing. If the city water flow is too low the pH will build up to corrosive levels and attack the heating coil and thermocouple.

Corrosion causes problems which eventually lead to electrical or mechanical damage as described above. The float switch may stick in the down position even though water is present at the correct level and therefore the unit will not operate. Alternatively it may stick in the up position when the water level is low giving the possibility of burning out the element.

Solutions

Prevention
Ensure that you have clean, relatively neutral water with a constant trickle flow. Around 60cc per minute should be adequate. You will have to adjust carefully to optimise this so that the heater efficiency is not compromised AssureTech Ltd. recommends a daily check of the flow to insure proper unit operation. Mark your setting on the city water manifold so that you can easily tell if the flow has changed.

Regularly inspect the units for corrosion damage and the city water manifold for correct flow rates. Carry out an earth leakage test on the tool with only the heat exchangers turned on. Leakage currents in excess of 15milli-amperes should give cause for concern.

Cure
AssureTech will refurbish your Lauda Heat Exchanger unit to a functionally as-new condition. This includes upgrading the bearings with integral moisture seals which prevent the ingress of condensate and dramatically increase the lifespan of the unit.

To have your Lauda Heat Exchanger refurbished please complete the Heat Exchanger Refurb Tracking Form  and return it to us along with your damaged unit. We will contact you with a quotation before carrying out any repairs. Refurbishments are normally returned to you within 7 days. Please call us if you want us to arrange collection from your plant.