Filtration: It's a Must Have!

We associate cleaning, clarifying, and purification with the process of filtration. Many of us rise each day to enjoy a first cup of fresh brewed coffee that has passed through a filter. Perhaps a filter is running to condition the air we breathe. Start the car engine and efficiently operating oil and gas filters make the trip to work possible. These are a few examples of which there are many more that exemplify how essential filtration is to our daily lives. In fact have you ever wondered why our bodies sustain two operating kidneys to filter our blood and other essential fluids? That is how important these organs are to us. In fact, the kidney is so resilient that only one can do the job of two. Take proper care of your kidneys and they should provide many decades of trouble free service.

Let us consider some general facts regarding the importance of filtration in metal finishing. It should become clear how important proper filtration is to influence optimum performance and quality processing of parts. Water conservation, minimizing drag out losses, closed looping, and easing the burden on waste treatment, all place a critical burden on plating solutions. These are some contributing factors that make filtration so important. It is very common to filter plating solutions. This should also be done correctly and maintained on a fixed schedule. Routine maintenance of the plating bath should include analysis, hull cell, and continuous filtration. Minimizing contaminants in a plating bath greatly affects: meeting or exceeding specifications, salt spray and other wear resistance tests, and realizing anticipated field service life of finished parts. Routine analysis and continuous filtration to maintain sufficient purity, inherently influence the quality of the deposit. Some general considerations with regard to filtering plating solutions are listed. Specifics, focusing on more quantitative information, can be found in many informative publications.

• Carbon. Granular and powdered carbon have been found to be equally effective. Both of these forms of carbon can be used for purposes of continuous filtration. Initially, powdered carbon purifies quicker, due to it’s greater surface to volume ratio. This is why it is preferred for batch purification treatments. Granular carbon is much less dusty, generally cleaner, and much easier to work with. There are some commercially activated carbon grades available that have been chemically treated with special agents that improve adsorption activity and sequester some heavy metals.
  



• Diatomaceous Earth. These are generally forms of clay, which can be used as filtering media. They are commonly referred to as filter aids. In some instances particular organic contaminants may not be as susceptible to adsorption to carbon. Filter aids offer additional binding sites for better removal of these tougher organic contaminants. They also, in combination with carbon, help to remove fine particulates.



• Filter Cartridges. These are normally pleated, having different porosities. It’s beneficial to the plater by the ability to remove particles down to one micron in diameter. In this way, desired clarity is achieved. Deposit roughness and pitting are avoided. The unit may be a simple, single cartridge filter. Or, it could be a multiple chambered system, in which a carbon containing bag or cartridge may be inserted. Pleated or wound sleeves and discs may also be used. Very useful, especially to remove any trace floating floc, that may be flowing in the discharge to sewer pipe. An excellent application for the final polishing of water in waste treatment.
  



• Multiple Disks or Sheets. A very large, effective surface area can be achieved by precoating a series of multiple disks, sheets, or sleeves with alternating layers of filter aid or diatomaceous earth and carbon. The plating solution is continually pumped through the aggregate layers to maximize particle removal and adsorption of organic contaminants. The filter can be precoated with the filter aid of choice at approximately 2 ounces per ft2 of disk or filter surface area. Usually, one half to three ounces of carbon per ft2 of filter is sufficient. Filter disks can be precoated from a slurry tank in the progression of filter aid followed by carbon, with balance of filter aid. Equipment manufacturers will offer specific operating instructions for their specialized filtration units, to obtain maximum operating performance.



• Balancing Activity. Preferred solution turnover is factored with required purification, to obtain the optimum balance and effectiveness. A rule of thumb (general purposes) for nickel and other plating solutions is 1-2 solution turnovers through the carbon packed filter, on a continuous basis. The requirement to replace carbon in the disk chambers or precoat filter may be determined by monitoring the rise in unit pressure versus the decrease in return flow from the filter discharge. Don’t ignore these visual maintenance aids. I have pulled a few solution filter discharge to bath hoses and found a trickle, at best.

Plating deposit defects sometimes signal the urgency to perform a major purification treatment. For example, a nickel deposit may exhibit characteristics, such as: brittleness, pitting, roughness, dull, poorly leveled. The result may be plating rejects, resulting in shutting the nickel bath or an entire line, because of this one solution. How the bath came to this condition is one problem that must be corrected, to eliminate it from happening again. Of immediate priority is the need to purify the contaminated bath, returning it to a satisfactory plating system. The preferred procedure is the batch purification. The heated plating solution is pumped to a previously cleaned treatment tank. Depending on the contamination and magnitude, treatment with powdered carbon and sometimes an oxidizing agent (hydrogen peroxide or potassium permanganate to further breakdown organic contaminants or precipitate iron) is required. The step-by-step procedures are readily available. The addition of carbon may range from 1-5 LB per 100 gallons of the nickel-plating solution. When treatment has been completed, filter aid is added to speed settling of the carbon, iron hydroxide, and any other particles. The conditioned bath is then transferred back to the cleaned & prepared plating tank through a freshly packed carbon filter. Subsequent wet analysis, plating tests, with appropriate additions are made, before trial plating commences.

Once satisfactory production plating resumes, careful review of maintenance or lack thereof usually furnishes corrective action, to prevent repeat or additional problems in the short or long run. In the case of a nickel bath, there are three great maintenance friends the plater can count on: regular solution analysis, continuous carbon filtration, and dummy electrolyzing. Is too much or aggressive carbon filtration bad? My simple answer refers to the best definition of poison: too much. For example, in the case of a nickel bath, the anti pitting agents (wetters), reduce solution surface tension, preventing the formation of stationary hydrogen gas bubbles on parts, that would result in gas pits. These wetters are somewhat carbon sensitive. Overly aggressive carbon filtration will deplete the wetters to low levels, leading to the unwanted gas pits. It is recommended to follow instructions as given for types of carbon and filter aid along with surface area loading commensurate with plating solution volume.

In continuous plating operation, plating baths will always be exposed to some degree of organic contamination. This may for example occur by drag in of cleaners, oils & grease, thermal & electrolytic breakdown of bath additives, and the effects of closed looping. Effective filtration will minimize drag in of organic contaminants and in-tank breakdown products. Bath analysis, hull cell, and dummying will not correct these problems. Only filtration will provide the necessary purification to remove these organic contaminants and particles. I recently spoke with Jack Berg, who reminded me of just how important filtration is. It’s a must have!

Time is Valuable

Of all the measured parameters we deal with, time is perhaps the one that receives the most attention. Have you considered how fragile the success of organized and professional sports would be, without fixed times, to keep the action balanced? How exciting is a football game if the time to snap the ball is unlimited? Would the absence of a shot clock keep basketball exciting? How would unlimited time in soccer affect the penalty kicks, in deciding the game’s outcome? Activities revolve around time, acknowledging it to be a critical parameter to planning, execution, and review. We begin our day, conduct our work and social activities, eat, and sleep, all adhering to some degree of timeliness. If one is not careful, the anticipated schedule can easily be derailed. That is why compensation must always be an integral part of time. In the ‘90’s, time management was a popular phrase, intended to keep us on track. Date planners, electronic messaging, and post it notes, are some of the devices intended to help and remind us. Are these helpful? Certainly, if used properly and within the scope of application. If we do not consider the validity of time, then all efforts will quickly become wasteful.

In the metal finishing industry, the value of time is highlighted in many ways. No matter how inconsequential it may seem, it is surprising just how critical it is. Finishers and suppliers share in the responsibility to focus on the importance of time. It is so important, that the quality of finished coatings and treatments depend heavily on it. Typical processes we deal with include chemical immersion and induced reactions. These revolve around basic scientific principles. No matter how innovative, updated, or new systems are developed, time can be at the centerpiece of success. In another industry aspect, outside considerations from government and regulatory agencies incorporate time as an important factor. Let us consider some of these items, and how they interact with time as a valuable parameter.

Mass Finishing
The process incorporates the action of mechanical energy and chemical reaction to modify the surface of parts, obtaining the desired characteristics. The objective may be cut down, deburring, or burnishing. Any such cycle is dependent on chemical concentration, ratio of media to parts, operating conditions of the equipment (e.g. barrel or vibratory), temperature of solution, and time of the cycle. Solution temperatures do not vary much. It is generally room temperature, rarely warm. Chemistry is normally based on proprietary blends that will accomplish the treatment specified. Time is the allocated driving force to accomplish the end result. Modifying the other listed parameters will normally affect how long or short a period it takes to complete the cycle. This has a bearing on desired production throughput.

Surface Preparation
Cleaning and activation can be included, since there are distinct similarities. In both steps, unwanted surface materials are removed, thereby preparing the base metal for subsequent treatment. Soak cleaning is predominantly an immersion step. Parts are conditioned in an alkaline solution that usually includes surfactants, builders, inhibitors, and alkaline salts. Oily soils and grease are removed in this step. The concentration of this cleaning formulation is based on product development to accomplish the desired effect, in a particular time sequence. It normally meets the range of dwells programmed into automatic process lines. Concentration and temperature will modify the time according to an acceptable target. An old finisher’s measure is very effective: for every 20 degree rise in temperature of the cleaning bath, the required time for cleaning is halved”.

Electro cleaning adds mechanical scrubbing action to further enhance the effect of surface preparation. The applied current density generates a magnitude of gas bubbles (focus is primarily oxygen per anodic condition of the parts), to remove or loosen unwanted surface materials such as scale, oxides, and rust. Voltage requirement is affected by the solution temperature and concentration of the electro cleaning formulation. Desired time is contingent upon concentration and temperature. This electro cleaning surface treatment is usually allocated less than half the time of the previous soak-cleaning step. Time becomes a valuable parameter in cleaning.

Acid activation promotes the surface conditioning to neutralize alkaline films, dissolve oxides, scale, & rust, and activate the surface prior to subsequent finishing. The quality time required is based on the acidic solution concentration and it’s operating temperature. An optimum balance between these two parameters affects the required time for this final surface preparation step. In many instances it may be equal to in duration to the previous electro cleaning step or even half of it.

Electroplating
Every process bath used to deposit a metal or alloy conforms to Faraday’s Law: the quantity of electricity that is transferred per equivalent weight of an element or its ion. The quantitative value is approximately 96,500 coulombs. The desired or required deposit thickness is related to the applied current density and time of application. As the current density increases, the plating time for thickness requirement decreases. There is a balance to the relationship, by which related conditions and parameters are critical. Bath chemistry, permissible temperature and current density ranges, concentrations of chemical additives, and purity of the plating solution, are important to each system. Optimizing these conditions will allow the process to meet the plating requirements in the optimum time relative to it.

Post & Specialty Treatments
There are several types that can be mentioned. They include: chromates, phosphates, black oxides, and rust inhibitors. Optimized temperature and concentration of each specific treatment permits the use of the right time, for the best results. Quality time is valuable. If only occurs if the process is on target.

Our industry also acknowledges time as a valuable parameter in relation to mandates and changes. Regulatory agencies require adherence to specific limitations with regard to effluent discharges and handling of sludges. Any modifications to specific concentrations or materials allow a time period in order to maintain compliance. Manufacturing changes, such as the implementation of RoHS, grant a period of time for finishers and suppliers to conform to new requirements.

Time is a valuable part in any facet of the metal finishing industry. On time: manufacturing, finishing, packaging, and delivery, can only occur if every step in any process is optimized. In so doing, time is a most quality part of the system. There can be lots of time, if used wisely. The clock is ticking. Are you on time?

Safety From an Application Side

Safety is the main subject in this week's blog. I would like to review an area that is very important to any process line. No matter how big or small. No matter how manual or automated. This interest specifically points to selecting the types of chemical process baths and treatments that are available. The user may acknowledge benefits from either or both. In any case, the available selections are tried and true, in their respective applications. For the use of all the materials discussed, adherence to vendor recommendations in their technical literature, drum labels, and MSDS, are a big step in safety.

Surface Preparation

Alkaline Cleaning

Two types of product concentrates are widely used for soak and electrocleaning. These are powdered and liquid cleaners. Both systems contain similar additives such as: alkalinity builders, buffers, surfactants, wetting agents, descalers, water conditioners, and inhibitors. The cleaning dynamics and bath service lives are comparable. Operating costs up front are similar. Although looking at the total picture, liquid cleaners are more economical (much less sludging, easier make up, easier to add, less down time, sometimes easier to waste treat). These benefits, as will be noted, also include enhanced safety.
By comparing actual safety issues, the following practical facts can be readily confirmed for powdered cleaners:

· Usually supplied in fiber drums. Through mishandling or storage problems, the drums can crack open, spilling corrosive contents, resulting in major personal safety issues.

· Aging drums of opened or unopened cleaner tend to harden (moisture absorption). Clumping of product concentrate makes it very difficult to remove the contents when making additions. I have seen shovels and pick axes at work, causing broken off clumps to fly in varying directions. Some innovators have even suspended drums above a tank. Cutting away the drum, resulted in “boulders” of the cleaner tumbling into the process tank.

· Empty drums must be properly disposed on a continual basis to avoid tying up plant floor space.

· Manual additions may give rise to dustiness, with fine powders settling on unprotected skin, causing burns and rashes.

· Additions must be made in gradual steps, to avoid possible splashback, due to localized boiling of added cleaner.

· Good mixing is essential to prevent formation of undissolved clumps that settle to the bottom of the tank. Care must be taken to avoid splashing and spray. The paid for concentrate in this case pays no dividend.

· Cleaner spilled on the catwalk picks up moisture, quickly forming a slippery condition.

· Portions of undissolved cleaner along with sludging, makes for more time consumption to clean out the tank and worker safety issues.

These safety problems are not meant to be an indictment of powdered cleaners. For decades past, the present, and into the future, powdered cleaners comprise the first, critical step in many process cycles. Finishers have successfully used powdered cleaners and will continue to do so, acknowledging these safety issues associated with their usage. OSHA and related government agencies along with insurance carriers put more focus and emphasis on safety. This is good for everyone.

Liquid Cleaners were not only developed to meet the rigorous cleaning applications that powdered blends excel at. In fact concentrated liquid blends have focused on significant advantages offered to the finisher, which do encompass improved safety. These include the following points:

· Supplied in rigorous polyethylene drums and bulk sizes of totes. The drums better withstand handling versus the fiber drums. Totes are placed inside a protective mesh metal cage.

· The concentrated liquid blend cannot harden with time. However protection from freezing temperatures is required.

· Liquids eliminate the problem of dustiness. However spillage is a problem. Burns, rashes, and slippery floors are a concern.

· Additions can be made directly from a drum pump to the process tank, eliminating exposure and handling of the product. The drum or tote can be stored safely away from the cleaner tank and contents automatically added by a pump activated by a conductivity meter.

· Liquid blends are 100% mixed and will not agglomerate or clump on addition to the process tank. Moderate, thorough mixing of additions in the tank is quite simple, minimizing splashing.

· Clean out of the tank after dumping the liquid cleaner bath is simpler and safer, due to much less sludge removal.

· Empty drums may be recycled. Totes are generally returnable, thus making them truly recyclable.

Liquid cleaners have found a niche, operating in many cleaning lines. They also provide an important first step in the surface preparation of parts. Although total safety is never 100% guaranteed, the use of liquid cleaners does provide the finisher overall significant safety advantages when compared to powders.



Acid Treatment

In somewhat of a twist, let us consider the use of liquid acids versus powdered acids. Both are essential to cleaning, descaling, derusting, and overall activation of the surface, before plating or other process. One system employs generic acids while the other provides salts of acids that ionize when dissolved in water. Both processes adequately condition the surface. Each incorporates a degree of safety issues related to their chemical use. Acids are acids and must be handled with the appropriate caution and safety procedures.

Liquid Acids

These would usually refer to hydrochloric and sulfuric. To a lesser degree phosphoric and acetic. Since hydrochloric and sulfuric are most commonly used, these two acids will be referenced. Safety related issues include:

· By nature of the materials, their corrosiveness. Rapid, severe burning of exposed skin. Hydrochloric acid concentrate fumes.

· Additions to tanks must be made gradually to cold water, with good mixing. Acid to water! Sulfuric acid is especially exothermic, rapidly giving off lots of heat, resulting in localized boiling and splashback.

· Pickling and activation of the metal surface results in corrosive fumes that must be properly vented.

· Sometimes mixed acids are required, such as for desmutting aluminum. In this case handling nitric, sulfuric, and hydrofluoric acids, in specific combinations, or together.

· Extreme care is necessary to prevent potentially catastrophic accidents.

· Empty carboys, drums, and totes of acids should be returned for refill promptly. Reducing hazard clutter is important to handling safety.

Liquid acids are used in many finishing and waste treatment applications, on a continual daily basis. The inherent safety related issues are well known. Trained personnel, using proper technique and precautions, handle and use these acids generally without harmful effect. Generic acids will always have a place in metal finishing, because of their importance to specific surface treatments. Safety in understanding the materials and how to handle them will always be very important.

Powdered acids have been available to finishers for many years. This line of products were specifically developed to increase the effect of acid treatments in a safer handling situation. Powdered acids offer several advantages with respect to improved safety. Some of these are:

· Acid salts, that upon dissolution, ionize to provide active acid in the bath. Common among these is Sodium Bisulfate, the acid salt of sulfuric acid. The safety benefit is eliminating the handling of sulfuric acid, and it’s accompanying exothermic heating.

· Acid salts are blended to offer additional acid accelerators in the form of chlorides and fluorides. These agents also ionize in solution, providing hydrochloric and hydrofluoric acids. One concentrate product can eliminate the handling of two or three separate generic acids. This is another safety benefit.

· Unlike liquid acids, the powdered acids may contain surfactants and wetting agents. These allow for improved penetration for surface action. This could result in using less product compared to a higher concentration of liquid for the same application. The less to handle, the safer should the situation become.

· Surfactants and wetters in the powdered acids form a stable, light foam blanket. This may effectively eliminate over 99% of potentially corrosive fumes and mists.

· The powdered acids are supplied in fiber drums. Caking and hardening on aging and storage in humid conditions may occur. Appropriate handling and storage precautions should be followed. However the storage, handling, and shipping of empty liquid acid drums is eliminated.

· Powdered acids may contain special inhibitors, such as to prevent immersion deposits, thereby extending the bath service life. These products are also buffered, to provide longer functioning acid action over time. The benefits include less frequent solution dumps, which means less handling requirements.

Powdered acids offer several safety advantages with respect to handling and use. These benefits along with improved performance have kept these products very popular among finishers. Activation is the next important step after cleaning in the surface preparation sequence. Generic acids and powdered acids can get the job done. Where safety and handling in use are concerned, powders offer an advantage.