Dross recovery

07 October 2006

While the higher costs of lead-free solder is less of an issue when it is printed, the additional cost for filling a solder bath are considerable. With more dross being created at lead-free's higher process temperatures, it looked like a double-whammy for users of flow solder machines. The losses can, however, be kept to a minimum as EM&T found out.

Wave Soldering has been around for a long time and although it has become more effective and more efficient as a process, one thing hasn't changed much, in that most solder machines generate a high amount of dross. In fact, on average some 75% of the solder in the bath oxidizes over time to become dross which has traditionally been dumped into a bucket and disposed of as scrap.

Reducing the solder dross has not been a high priority for most production engineers. And over the years its low level in the pecking order has resulted in minimum attention paid to the environmental issues of lead oxides from the solder and the financial consequences of large amounts of untreated dross.

With the advent of the more expensive lead-free solders (up to 3 times the cost of tin/lead) and the increasing pressure for companies to be seen to make environmental progress in the quest for ISO 14001.
The task of de-drossing is carried out with varying degrees of thoroughness. Those in a hurry often put as much solder as dross into the scrap bucket. On the other hand, those who have time to spare, may manually squeeze the dross through a perforated ladle, breaking down the crusty oxide coating to release some of the trapped solder back into the bath, before placing the residue into the bucket. However, even this process which extends the wave down time still results in a minimum amount of solder being recovered and takes vital time away from production.

Health and safety regulations however, are continually pushing back the levels of previously acceptable practices to improve working conditions. When dross is being manually squeezed there is a greater chance that these dangerous substances can be released into the workplace and particularly affect the operators squeezing the dross.

First invented in 1995, solder recycling machines evolved through various prototypes. Completely re-engineered by new owners, these machines, the EVS3000 and its larger capacity brother the EVS6000, have since proved to be reliable and profitable in hundreds of installations around the world.

The EVS owes its inspiration to the previously mentioned practice of manually squeezing dross through perforated screens and ladles. The EVS heats and squeezes the dross inside a sealed chamber using a pneumatic piston. It does this very efficiently and recovers, through small slots in the chamber, an average 75% of the weight of dross fed into it as a reusable solder ingot. The ingot, formed in a tray beneath the chamber, is exactly the same alloy as the solder in the wave bath - a claim that has been supported by independent reports from ITRI and Adflex Solutions.

Once loaded, the fully automatic process takes from 6 to 10 minutes, depending on the capacity of the EVS type being used. At the end of the cycle the residual dross is ejected from the chamber through a closed chute into a dross bucket which, when full, can be sent for reprocessing in the normal way.

The EVS is supplied with its own cart and air extraction system, which makes it an entirely self-contained unit capable of being moved safely and quickly between wave solder machines. It requires only a single-phase 220-240v power supply and an airline to operate. One EVS solder recovery system can usually service 2 to 4 wave baths during an average production shift.

Ease and speed of operation is another key factor. Operators simply wheel up the EVS to the wave bath and ladle the dross into the hopper which has its own extraction to eliminate fumes. The EVS will reduce solder bar consumption on average of 50%, speed up your de-drossing time by up to 75%, improve your environmental credentials, and is extremely simple to use. Some people find such performance hard to believe.

The case for solder recycling is best made by those who are already using EVS machines. Chuck Babcock, Schneider Automations' manufacturing Engineering Manager, says, "The EVS Solder Recovery System was installed in our factory in just a couple of hours. The training required was minimal and we started to see the dross reductions and solder consumption shrink instantly. Our experience supports the manufacturer's claims of over 50%

The system is easy to operate with little to no down time. It fits into the standard wave solder dross removal process requiring no additional user time. The system provides a clean, lead-free environment for the users and actually eliminates lead handling with the automated dross into the bucket system that is built in to its optional cart.

The economic case becomes even more pronounced with lead free solder. A major U.S. electronics manufacturer installed 2 EVS machines, one for each of their 2 lead free lines. Savings came in at over $1000 a day, 7 days a week for each of the EVS machines they were using. This level of savings meant that the EVS machines paid for themselves in less than two months.

The EVS is not only suitable for Wave Soldering process but can be used anywhere where volume special soldering takes place, such as for dip pot processes, where the very high cost solders in use make recycling even more attractive.

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