Traditionally, most chrome baths use lead anodes. When we think of lead anodes, we usually just think about the lead part, but in fact the lead anodes that are used are never made of pure lead. Chromic acid in the bath eats away at pure lead, especially when there is no current. Pure lead is also quite soft, does not hold its shape very well and sags under its own weight. This is why lead is alloyed with other metals in order to give it specific properties. Various amounts of antimony, tin and silver are added to the lead depending upon the application.
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Antimony: Provides hardness, rigidity and resistance to curling or sagging and is used whenever strength is required. High antimony contents, however, tend to produce excessive surface scale and a less than optimum trivalent control. Antimony has a density of 0.24 lbs. per cubic inch and a melting temperature of degrees F.
Tin: Provides improved corrosion resistance and conductivity, reduces surface scaling and improves trivalent control. Used primarily in high fluoride baths. Tin has a density of 0.26 lbs. per cubic inch and a melting temperature of 450 degrees F.
Silver: A small amount of silver (0.5 - 1%) greatly extends the corrosion resistance and increases the conductivity. Due to the additional cost, this is used only where an extended anode life is required such as in very high fluoride baths.
C. P. Grade Lead: CP grade lead (99.9 % chemically pure) is the basic material that is used to make the various alloys. CP lead has a density of 0.41 lbs. per cubic inch and a melting temperature of 620 degrees F.
Lead Alloys: The anode materials are purchased from a smelter already alloyed per specification. These materials are available in ingots, cast mats, rolled sheet & bars, extruded pipe and extruded rods or wire in various sizes. Extruded and rolled forms are much denser than cast materials are and will therefore hold up much longer and are better suited for large anodes or ones that need to last for long periods of time.
It is good practice to standardize alloys and use only one type per bath. If several alloys are used then the each type should be marked so they are not accidentally mixed. Lead alloys should never be obtained from a scrap dealer as the quality is unknown. Most lead alloys used for chrome plating have a density of around 0.40 lbs. per cubic inch and a melting point of 580 &#; 600 degrees F.
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Metal finishing operations and managers often overlook the importance of line maintenance. Rapid production demands and ever shifting production schedules lead to conflicts between making repairs and making money. Committing to the required dollars for equipment repair and upgrading is easy to postpone. Plating shops do everything they can to manage their bottom line by controlling short term expenses. Unfortunately, production is often disrupted as a result of avoidable equipment breakdown and failure.
When we talk to industry leaders in plating, they point to the importance of discipline as the key to running their lines at peak efficiency for maximum hours. Specifically, they recommend establishing a checklist that allows them to minimize breakdowns and failures.
Looking at their plating shop from a process viewpoint, operators start with the basics. &#;Walking the line&#; is often a planned daily activity. Checking time, temperature, and chemical concentration are also regular occurrences. Keeping a daily log must be a requirement in order to identify trends. Hull Cell testing can also be added to your checklist to identify problems in the bath and to test potential fixes.
When finishers establish a checklist, it rarely contains new or groundbreaking steps to follow, but is vital to ensuring the quality of the finishing process. These checklists are usually filled with items that every plater know needs to be done, but many platers simply become too busy to complete them. When you look at your shop, ask two major questions:
If you don&#;t answer yes to the first question, you should answer yes to the second. A simple checklist provides discipline in managing your finishing operation. Assigning specific responsibilities with specific completion times will avoid skipping crucial steps due to your teams&#; demanding workload.
Think about your last visit to the doctor. Regardless of the hustle and bustle at their office, before you met the doctor, you were weighed and your temperature and blood pressure were taken. Finally, a nurse asked a few basic questions about your overall well-being. To a doctor who is troubleshooting a patient illness or injury, each of these fundamental steps is essential and saves them time.
The same techniques apply to a finishing operation. Successful operations instill this philosophy in their employees. Managers utilize dashboards to monitor simple checklists and alarms are triggered when key parameters are out of range. Maintaining logs and records holds individuals accountable and increases the odds of finishing good parts.
At Asterion, we&#;re dedicated to helping our clients set up checklists, design measurements and systematically do the &#;little&#; things right.
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