5 Reasons Why Your Business Needs Wet Process Equipment Manufacturer？

5 Tips for Selecting and Optimizing

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Wet Processing Equipment

Subtle modifications to standard wet processing equipment can make it more flexible, efficient and productive.

Microfabrication operations such as metal lift-off, stripping, etching, plating/coating, cleaning, and de-bonding are typically wet processing procedures. Yet, selecting the equipment to perform those procedures most efficiently and cost-effectively is often not a simple matter. In most cases, the users of wet processing equipment &#; whether for semiconductor, MEMS, biotech or other applications &#; can benefit substantially from having industry design experts review and evaluate the entire process and then recommend specific equipment solutions.

Even among research and educational applications where off-the-shelf, manual wet benches may be presumed as standard solutions, such applications can gain valuable flexibility, quality or safety though relatively inexpensive customization of the apparatus design by the equipment manufacturer.

Here are five tips that can help users to select wet processing systems that can optimize their processes by making them more flexible, efficient and productive.

Don&#;t reinvent the wheel

&#;So many wet processing equipment designs/fabrications have been standard for some time and are usually a variation of one of these standards.&#; says Louise Bertagnolli, president of JST Manufacturing (Boise, ID). &#;The l design process is a matter of choosing the most appropriate solution and then tailoring it to meet the customer&#;s specific application requirements.&#;

A nationwide manufacturer of manual and automated wet processing equipment, JST&#;s mechanical, electrical, and chemical engineers have many years of experience in industries including semiconductors, both silicon and compound , MEMS, photovoltaics, LEDs, Flat Panel Displays , and sensors.

Bertagnolli says that to optimize quality and throughput for a wet processing solution, it is advisable to consider the process involved so that a qualified, objective recommendation &#; including the tools and accessories &#; will be proposed. The equipment manufacturer should have the research and development engineers, facilities and experience to propose appropriate manual or automated process equipment plus necessary auxiliary equipment such as chemical handling, automation and product fixturing.

Take a close look at fixturing

In addition to determining how a customer&#;s process will be finalized, one of the most important elements to consider is the customer&#;s fixturing &#; the devices that will hold or position the products being processed,&#; says Bertagnolli.

She adds that most customers are mostly concerned about the temperatures and concentrations of chemicals &#; things that are going to materially affect their processes &#; and how they are going to control those.

&#;But at the design stage, there are also more fundamental decisions to be made, such as how the product in process should be transported to and from the wet processing tools and fixturing most efficiently in the process baths,&#; Bertagnolli explains. &#;In some cases the products may be too heavy for workers to handle, so appropriate manual or automated transporting equipment must be selected. Additionally, the wet processing chemistry must be determined: How does the chemistry arrive at the tool, and how is the chemistry extracted safely?&#;

Fine-tune processes in the &#;application lab&#;

Before finalizing a wet processing solution, visit an equipment manufacturer that has a well-equipped laboratory so that the process can be fine-tuned and tested on-site. This can ensure that the best solution is proven, and that equipment overkill is avoided.

&#;Advanced application labs should be equipped with metrology [advanced measurement] equipment offering real-time testing results that provide the data and technologies needed to optimize the process,&#; explains Bertagnolli.

The applications lab also enables users to control the optimization of multiple processes, and can minimize the amount of chemicals required and/or determine the tool features they need for their applications. This can save the customer money by eliminating features they do not need.

Bertagnolli suggests that by utilizing 3_D modeling software such as SOLIDWORKS facilitates making modifications to best suit an application in a timely and cost effective manner. . For automated wet processing, the equipment manufacturer&#;s control software should be able to interface with a customer&#;s host system when required in order to be able to remotely operate the tool.

&#;Also, many customers forget to determine how they are going to accommodate the new equipment in their clean room; how it will enter the facility, how much space it will occupy, how much power, water, chemicals and gases it will require, and so forth,&#; explains Bertagnolli. &#;So, the equipment design engineers will need to plan for all those factors.&#;

Consider evolving application requirements

Like other manufacturing processes, wet processes such as cleaning and etching often evolve over time. The upgrading or expansion of equipment to meet future requirements can be unnecessarily expensive and time-consuming unless the requirements are integrated into the original equipment design.

&#;If tools are designed to be modular, there is not usually any problem in reconfiguring or expanding them,&#; Bertagnolli advises. &#;But the engineers that design the tool need to be aware of the customers&#; future plans to upgrade their operations for reasons such as added throughput. All sorts of process expansions are possible, but it is very important for the design engineers to be aware of future plans at the initial design phase.&#;

In some cases the customer&#;s initial wet processing equipment is semi-automated because production volume does not mandate a fully automated system. But over time the volume may increase to the point when a fully automated system is warranted in order to optimize production.

&#;It is not unusual for a customer to come to us with a requirement, new process, new technology or something they have been doing manually and now their volume requirements have increased to the point where they need to automate because of a higher throughput requirement,&#; says Bertagnolli.

Ensure that safety is built into the solution

Although production throughput and product quality may be the highest priorities of many users of wet processing equipment, operator safety of both manual and automated equipment should also be a paramount concern, particularly when processes involve the use of dangerous chemicals.

The potential for fires from electrical problems is a great concern within processing laboratory environments. For that reason, explosion-proof motors and a variety of safety mechanisms are required when wet processing chemicals warrant such measures.

With most designers and fabricators, both manual and automated systems must meet the safety standards set forth by organizations such as NFPA (National Fire Protection Association), SEMI (Semiconductor Equipment and Materials International) and NEC (National Electric Code).

In some cases a low-throughput research facility will automate wet processing simply for safety purposes because they don&#;t want employees to be exposed to potential hazards. In other instances, design engineers may advise customers against choosing a certain process or configuration, recommending a safer way to perform the operation.

In Bertagnolli&#;s opinion safety comes first. &#;As far as JST is concerned: If there is a hazard, we strive to eliminate it,&#; she says.

For information contact: JST Manufacturing Inc., 219 E. 50th S., Boise, ID  ; : 800-872-, 208-377-; Fax: 208-377-; : ; or visit the web site jstmfg.com

There are many equipment choices and system designs to consider when wet processing fine materials to produce sand that meets construction grade specifications for

Additionally, several factors pertaining to speciality sands for the glass, industrial and frac sand markets, including the quality of the sand itself, need careful review before developing the design of a processing system.

The process design of the system and the equipment to be used should be based upon the following application factors:

1.

Particle size distribution of material, either from the deposit or from the crushing, screening and other processing upstream of the processing plant.

2.

Product specification(s) required for the market area.

3.

Extraction method of the material to be processed.

4.

Required plant mobility ? portable or fixed.

5.

Planning constraints such as height or water use restrictions.

Previously discarded dust fractions (typically -5mm or 6mm) from hard and soft rock quarries can often be washed, classified and dewatered to produce specification construction sands, thus maximising use of the deposit. These finished products are often referred to as ?manufactured sand?.

SAND PROCESSING OPTIONS

The simplest form of wet sand processing is the removal of fines from a typical -5mm natural/alluvial or manufactured (crushed) sand fraction, followed by the dewatering of the washed product for stockpiling and transport purposes (fines permissible in construction sands commonly ranging from zero to 15 per cent passing 63 microns). 

Sand washing and dewatering equipment includes hydrocyclones, siphon (vacuum) assisted hydrocyclones or separators, dewatering screens, spiral screw classifier washers and bucket wheel dewaterers. The equipment that is most suitable for your process is dependent upon the previously stated application factors.

Spiral screw washers are self-contained, low profile units that sit directly on the ground and require minimum power. They may be slurry or dry fed (with a water addition) by gravity from an elevated sizing screen above and can be used in either portable or fixed plants. 

Limitations include limited water capacity, which often leads to an excessive loss of useful fines when incorrectly configured and product final moisture content in the range of 25 per cent by weight.

The bucket wheel is also a simple, self-contained device. These units are typically slurry fed from a wash screen but also have limited water volume capacities, increasing the risk of fine sand loss. More modern 

units incorporate pump fed hydrocyclones for fines recovery where necessary. 

Increased product fineness and/or marginally cold operating weather, which causes icing of the slots or holes in the dewatering buckets, can lead to excessive moisture in product sand. 

Hydrocyclone and separator-based washing plants can handle high capacities and slurry volumes and, if properly sized, are more deliberate in the control of the retention or removal of fines. Typically, these units are elevated on towers or situated within compact structures to allow direct stockpiling or further processing from the discharge. 

Hydrocyclones and separators contain no moving parts yet a correctly configured vacuum-assisted separator will provide a consistently dewatered product at the underflow, with as little as 18 per cent moisture by weight, irrespective of the feed solids content.

Hydrocyclones, however, must be correctly pressurised at their inlet and fed close to their design feed rate to produce dense underflows.

Utilising tangentially produced centrifugal force, hydrocyclones produce a high G-force on solids, which, in combination with greater attrition due to the scrubbing action and higher velocities experienced in the pumped feed arrangement, ensures a very clean product.

The removal of adhered silts and clays from the surface of each particle leads to increased mechanical strength in the final construction sand product and the ability to handle dirty feed materials more effectively.

All the above technologies have limitations in respect of dewatering the final product. The most proven method for this area is the dewatering screen. 

A dewatering screen uses fine mesh screening media that provides a mechanical acceleration to particles to break the surface tension and aid in the gravity drainage of the sand. 

Dewatering screens are limited in their ability to accommodate large volumes of water but are able to handle direct sand slurry feeds with solids contents above 35 per cent by weight. For more dilute feeds, hydrocyclones may be utilised to achieve pre-concentration when necessary. 

Despite low power consumption, the dewatered sand moisture content is typically half that of most other equipment options, typically 12 to 15 per cent by weight, which produces a drip-free sand product. 

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All dewatering screens lose fines along with the water through the screen mesh. These fugitive fines may be recovered by recirculation back to the feed source or by recovery with a small hydrocyclone returning the recovered fines to the discharge point of the dewatering screen.

Further removal of moisture can only be achieved by technologies such as stockpile dewatering or a thermal drying system. 

SAND CLASSIFICATION EQUIPMENT

Due to inconsistent particle size distribution or grading deficiencies, many sands need to be classified to meet specifications for final use. Some deposits are suitable for the production of multiple products. 

It is important to consider the nature of the sand product(s) required and the available market. The possibilities include single, unchanging specification sand or a diversity of specified sands, first separated by sizes into discrete fractions, then either blended in-line or delivered to a storage hopper for blending by recipe according to specification. 

Recipe plants allow far greater versatility for varying market conditions and more efficient use of a feed whose particle size distribution varies. Such plants, though, with their inherent complexity and sophistication, are often more capital intensive.

Typically, sand classification equipment will be considered when one or more of the following conditions exist:

1.

Two or more specification products are to be made.

2.

Excess intermediate sand grains in the -2mm to +150 micron size range exist.

3.

Accurate grading or specifications are demanded.

Types of classifiers include:

1.

Multi-station sand classifying tanks (trajectory classifiers).

2.

Hydrosizers or flat bottom classifiers (density separator).

3.

Up-current classifiers (elutriators).

Any of these devices are at their most efficient when the slurry feed is consistent in terms of solids concentration and flow rates and is within the limits specified by the manufacturer.

Multi-station sand classifying tanks perform best when the feed contains no more than 10 or 15 per cent passing 63 microns. Pre-conditioning the feed to meet this criterion may be achieved most simply by a hydrocyclone. 

Hydrosizers and flat bottom classifiers perform best when the feed is concentrated to approximately 50 per cent solids content by weight. In both cases, pre-conditioning the feed to meet this criterion may usually be achieved by use of a hydrocyclone.

Multi-station sand classifying tanks, while widely used in North America for classifying sands into construction grades, have seen limited use in the global marketplace. 

Automation via computer controlled systems allows this equipment to optimise construction sand grades used for typical concrete or asphalt grade specifications. For optimal classifying performance it is important that the incoming slurry remains at a consistent solids feed rate. 

Single units are suited for processing up to 350 tonnes per hour. In high capacity needs, multiple sand classifying tanks are installed side by side above dewatering equipment.

Hydrosizers and flat bottom classifiers are capable of making sharp single cuts in the size range of 800 to 100 microns. Equipment selection is dependent upon the average feed particle size distribution and the sand products required by the market. These classifiers are often the principle size separation equipment used within an in-line blending or fractionated sand plant. 

Two or more units may be employed, in parallel or in series, to create differing or successive cuts, whether for the production of construction sand, frac sand, glass sand or in support of another mineral processing operation.

IS CONTAMINATION PRESENT?

As new high quality deposits are becoming scarcer, previously uneconomic materials with poor particle size distribution and/or contamination in the form of peat, root, wood and lignite (coal) are now required to be processed. 

Flat bottom classifiers, sometimes known as density separators or sortifiers, are used in the removal of low specific gravity contaminants such as lignite. 

Any coarse?sized, low specific gravity contaminant fractions are first removed by sizing screens, or ?throughs?, comprising all the sand, and the fine contaminants are directed to the flat bottom classifier for purification. 

Within the classifier, a gentle up-current maintains a heavy, non-turbulent but fluidised sand bed and creates conditions in which low density particles float. A PLC resident control algorithm closely controls the underflow discharge valves so all the fine contaminant, but very little (if any) fine sand, reports by way of the classifier?s overflow to waste.

Hydrosizer type classification units, commonly used for wet processing of frac sands (sands for hydraulic fracturing of oil bearing rock), are now widely in demand in natural gas and oil extraction. 

These sands, if meeting the stringent requirements of strength and sphericity, must be sharply classified to specific sizes and then dewatered for further processing to meet final requirements.

FINE SILT AND CLAY DEWATERING

After the sand has been washed, classified, dewatered and stockpiled, the resultant remaining waste stream, containing primarily -63 micron solids, is commonly sent to large settling ponds consuming many hectares of land. This method of handling fine, slow settling solids, either for disposal or to enable reuse of the water, can incur considerable operational costs and management time. 

Even if planning constraints allow such practice, silt lagoons may present an ongoing environmental hazard. Local authorities now commonly restrict access to fresh water sources. This restriction provides an incentive to quickly recover the water and to remove the solids waste in a safe portable form.

Ever greater numbers of wet processing facilities utilise thickening/clarification equipment to dewater their waste streams that contain fine solids, producing a dewatered fines ?cake? and clear water suitable for rapid reintroduction to the process. Such incoming slurries are commonly dilute (in the five per cent range solids) and require a two-stage treatment process, the first stage being a thickener. 

Carefully controlled flocculent dosing encourages the fine suspended solids to coagulate and then to settle to the bottom of the thickener tank, where a slow turning rake or deep cone gently directs the resultant paste concentrate towards the underflow discharge point located bottom centre within the tank. 

Meanwhile, crystal clear water (as much as 90 per cent of that entering the thickener) is permitted to overflow the unit?s weir before being electro-statically neutralised and once more ready for recycling to the plant.

The ?thickened? solids underflow is generally in the order of 35 to 50 per cent solids by weight. These ?volume reduced? fines can be pumped to smaller, permanent storage/disposal areas or further dewatered by a variety of press equipment. Today recessed plate and membrane filter presses offer a simple, efficient solution with low operating costs.

Recessed and membrane plate filter presses use little or no further chemicals, utilising high pressure for dewatering thickened solids and discharging a resultant cake comprising up to 80 per cent solids by weight. Lacking any free water, the silt/clay cake solids can be belt conveyed or transported by truck immediately. 

MORE ART THAN SCIENCE

As with many material handling problems, developing an efficient system for sand processing can be more art than science. While many operators have tended repeatedly to utilise the same methods over the years, refinement and development by equipment manufacturers continues to provide ever more efficient and innovative solutions, making possible both the rapid recovery of effluent water for reuse within the plant and the recovery of previously rejected ?waste? for value-added use within the product stream. ?

With thanks to Craig Dewsnap, Charles Grocott and Dave Schellberg of McLanahan Corporation for input to this article. This article originally appeared in the September issue of Quarry Management (UK) and is reprinted with kind permission.

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