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Re: Skiming Dross From Solder Pot

Horace Johnson

#8612

Skiming Dross From Solder Pot | 9 November, 1999

We have a Ultra 2000 wave solder machine with a Lambda, Omega and Rotary chip waves. We are running three shift and our operators dedross the solder pot every 24 to 32 hours. That is skimming around the nozzles and pumps. Our maintenance does a complete dedrossing every 200 hours that removing the nozzles and pumps then skimming the dross.

The problem we are having is that in a week time there is so must dross build up inside the rotary chip nozzle that the wave will drop. And the only way to correct the problem is to remove and clean the nozzzle and skim the dross. We have another Ultra 2000 machine and it never has this problem. The operators may dedross the machine once or twice between the maintenace dedrossing and they never have a built of dross like the other machine.

So my question is can anyone tell me why we are having that must dross build up in that one machine. PLEAS HELP!!!!!

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#8613

Re: Skiming Dross From Solder Pot | 9 November, 1999

Horace: You weren't real specific about the set-up of the two machines. So what's the diff man?? Big dross generators are:

1 R Woodgate says that pump speed is the biggest driver to dross production 2 Chrys uses low dross cast bar: Alpha HiFlo 3 In reducing excessive dross formation on wave soldering machines, Analog Devices considers: 3a Temperature. High heat facilitates formation of oxide, which is the dross you are seeing (tin oxide/lead oxide). Try a solder temperature lower than 270 deg C. 3b Pump Speed. Faster solder flow rate will increase the contact between your solder and surrounding air, which contains oxygen, which forms oxide.... 3c Solder Contaminants. If 1 and 2 fail, have your solder analyzed. Consult the FF specifications (BS219, ASTM B32-66T). See if your virgin solder bars comply to the specs, too.

Good luck

Dave F

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chartrain

#8614

Re: Skiming Dross From Solder Pot | 9 November, 1999

Could very well be your nitrogen diffusers are blocked. These have to be cleaned on a regular basis as well.Cleaning frequency for the diffusers is flux dependent as well as other factors but could be as little as one month of operation. Once the diffusers are blocked, the chip wave dumps the solder back into a non inerted area and the dross buildup goes from there. To test to see if the wave is inert or not, run a dry hasl or tin lead plated board over the wave. Don't use flux - just the bare board. If the wave is inert, it will solder perfectly.`If the wave is not inert-it won't be a pretty sight. You will see webbing and icicles on the board. This simple test should be performed at least once a month to see the inerting efficiency. Many folks have been running for years with blocked diffusers not realizing their process is no longer inert. Good luck. Ray

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#8615

Re: Skiming Dross From Solder Pot | 10 November, 1999

Hello Horace You're lucky in that you have two of the same machine. You should be able to arrive at the root of the problem by comparison. The problem is likely to occur in one or more of these areas: MACHINE: As said , pump speed and air contact are a contributor. If the pot is too low and you make up for it with pump speed, dross is going to increase. The reason for the increase is turbulance at solder re-entry and air contact. Low solder level also does this. You didn't say if you were inerted (and on both machines) but Ray poses an interesting question. How thick is the dross layer when clogging occurs? If normal, the clog is not likely to be sucked into the pump unless something is severely disturbing the surface. Compare your chip wave settings. This leaves internal generation and the question of proper inerting. As Dave says, check and compare pot temperatures. Most of us like between 475F and 500F. Much more than this and the dross monster will magically appear. BTW check with a calibrated thermometer, check near the business end of the waves and let the waves run for a while before checking. The internal thermocouple may not be accurate and a temperature gradient may exist between the wave and thermocouple location. MATERIALS: Are both machines charged with the same low dross quality of solder? Hi-Flow works well but all the major players have an equal. Low quality, with its inclusions and oxides, makes a difference. OPERATORS: Are they doing the same things? Especially machine settings. If one group tends a specific machine rather than both look for bad (or good) habits to have spread within the group. What about de-drossing technique, aids and tools? APPLICATION: Look for any significant differences between what is being run on one machine to the other. Many small assemblies to a few big ones. Differences between total idle times and total run times. Is the chip wave run less on one machine? Anyway, food for thought. If worse comes to worse, try swapping setup,applications and operators. Good luck. John Thorup

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#8616

Re: Skiming Dross From Solder Pot | 10 November, 1999

All good points to check. But consider that once you have dross in the pump mechanism it�s hard to get it out quick through normal operation. You might empty the pot and clean it sorrowly to get it out of all corners and parts where it sticks. I had to do it years ago.

Good luck Wolfgang

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Andy C.

#8617

Re: Skiming Dross From Solder Pot | 11 November, 1999

Horace ,

We had a similar problem last year on an Ultra 2000 . We cured it by draining the pot , removing the wave forming ducts , pumps and nozzles and cleaning . Refill with fresh solder ( one third solder chips , two thirds solder bars - to get the pot up to temp quicker ) and the problem disappeared . The ducting in the base of the pot was caked with dross which we reckon was being re-circulated around the pot . Note that this is a messy and expensive job .

It also sounds to me like your dedrossing is not being done often enough . We dedross every 4 hours and do a Maintenance strip down and clean every Saturday .

The rotary wave you use - is it the "helix" type design ? . You can order a retrofit rotary wave with a helix design and open top which never clogs up - ask your Electrovert Rep. about this .

Hope this helps .. just my tuppence worth .

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