This guide will provide an overview of bulk weighing and batching systems, including the types of products handled, the equipment used, and the criteria for selecting equipment and integrators. Covering all the regulations applicable to each area and product is much too involved for any one document, but a good system designer or integrator should be knowledgeable enough in your product to bridge the gap.
Common Product Classes and Their Requirements
The type of product being handled in a bulk weighing and batching system is the leading factor in equipment selection and will determine material flow.
Food Products
Food products for both humans and pets face an increasing level of scrutiny for contamination, and this is reflected in the regulatory environment. Contact surfaces can be carbon steel prior to “Kill Steps” like boiling or pasteurization. In post-processing, a maximum of a 32 RA* finish is allowed on stainless steel, which is required for its corrosion resistance and preferred for its ease of cleaning. While 32 RA is considered the minimum, better finishes will make cleaning easier and more effective.
Pharmaceuticals
Pharmaceutical products face an even stricter regulatory environment than food and beverage products. Because smaller quantities are being handled and ratios are much more important, pharmaceutical manufacturers will always require smaller-scale, more accurate equipment, at least accurate to a decimal place past your maximum allowed variance. To manage cross-contamination risk, a maximum RA of 20, and sometimes down to 15 is required. But often these values are exceeded by a mirror finish, which is 6-12 RA, so looking for “mirror” or “electropolish”** finish is a common way to indicate equipment meets this spec.
Chemicals
There is a tremendous amount of diversity in the chemical category. Corrosiveness, flammability, toxicity and other health and safety considerations are the primary drivers of equipment and material selection.
Construction Materials
Construction materials like cement, sand, and aggregates produce a high volume of dust which can cause abrasion. Carbon steel is usually acceptable, but special precautions must be taken to minimize the risk of friction damage. Bolt-on paddles and arms are used in mixers and tumblers so they can be swapped as they wear. Belt conveyors are the preferred method of transport, and product is preferably weighed during conveyance.
Equipment Used in Bulk Weighing and Batching Systems
Storage Silos
Silos are one of the most commonly-used methods for storing dry, preprocessed raw materials and can be made from a variety of materials including polymer and stainless steel. Assembly methods are most commonly either smooth-wall (pre-welded) or bolt-together. Smooth-walls carbon steel silos are powder-coated on the outside to protect it from the elements. The bolt-together construction method is dramatically cheaper, but much more difficult to assemble. Further, they are not suitable for many products due to increased risk for rust. They also tend to have shorter lifespans, especially when being filled by a truck. In these cases, the pneumatic silo lines cause regular expanding and retracting, creating excessive wear. Silos capacity commonly ranges from 8,000-lb. (of grain), up to about 80,000 lbs. with 20,000-lb. as the industry average. Increasing silo capacity is often a strategic way to lower costs and gain greater economies of scale.
Bulk Bag Unloaders
An intermediate step between 50-lb. bags and silos, bulk bag unloaders let you buy product in bulk bags/super sacks, (2,000 lbs. of grain). Standard configurations require a forklift to lift bags onto the frames. Hoist-and-trolley units can be used for greater labor savings, although this typically requires substantially more investment than traditional forklifts.
Hoppers and Bins
Hoppers and bins are commonly made-to-order storage solutions tailored to the user’s preferred dimensions . They can be useful mix in, provide a staging area between batch and continuous equipment, or to add product into an otherwise closed conveying line. They are available in plastic and metal, and for dry materials they can either be connected to an external dust collection system by ports or have one on the unit. Auto-pulse bag dumps will start to draw air in when the lid is lifted, and reverse-pulse the filters when the lid is closed to return the product to the process. Conveyors
Conveyors are another highly varied type of equipment that should be selected based on the specific application. Some of the more common types include screw, auger, vibratory, tubular drag, roller, magnetic, bucket, and flat, tube, corrugated, and cleated belt conveyors. A good process engineer will evaluate flow rate, material, distance, power, slope, cleaning requirements, along with other factors to determine the most effective solution for a given application. Conveyor systems are the tie together the various unit operations of any production process so common standards can dramatically simplify maintenance and operations.
Mixers and Blenders
The line between mixers and blenders is fine and depends on how high the shear effect of the equipment is on the product. Different products will be more resilient than others, so sometimes you will see the same piece of equipment being called a mixer in one situation, and a blender in another. There are many solutions out there, but these are the most common.
Mixers are available with several features to improve efficiency including vacuum, microwaves, and various agitators for different products. Paddle mixers are the most gentle, low-shear option and work well with powders but are not good with products that are extremely runny, sticky, or thick. Ribbon mixers are the oldest method and are extremely efficient, even with the runniest products, but do not function well with sticky product and create too much shear for others. For this reason, they are often called ribbon blenders. Hybrid mixers combine both methods and carry some of the same mixing patters. Most hybrid mixers are ribbon/paddle, but these are still not good for sticky products. For sticky products, ribbon/fluidizer hybrids are usually best. Other less common but still prevalent methods are tumble, conical, and vertical mixers.
Another popular mixing technology is the V-blender which is shaped like a v and spun slowly. They are very gentle compared to other techniques and for this reason they are the most popular method for pharmaceuticals.
If you are unsure what type of mixing technology to use for your product, many manufacturers of mixing equipment will work with you to test samples and ensure that you are selecting the right machine for your specific needs.
Scales and Load Cells
Scales are generally classified into lab, bench (tabletop), floor, and hanging categories and are typically produced with stainless steel contact surfaces. NTEP certifications are not required for batching and internal use, but are required when the product is being sold based on weight. Regardless of whether or not your application is regulated by NTEP, it is important to have your scale regularly serviced and calibrated to ensure accuracy. It’s worth noting that obtaining the NTEP certification is expensive and is often skipped—not because the scale isn’t able to pass it, but because the certification won’t help the OEM sell more.
Load cells will differ in material and configuration depending on whether the cell is being compressed or pulled and can even be integrated into the base of equipment to provide minute-by-minute monitoring (dynamic weighing). This is a great way to verify supplier shipments, monitor internal loss, and know your inventory levels precisely. It can also be used to automate a batching system but is not the best method for this.
Weighing Systems & Automation
The most obvious way to automate a batching system is to put all your tanks on load cells but if automation is your goal, you are better served by a central weighing solution/scale package. This involves putting only one hopper/tank on load cells and feeding product into it to be weighed before going to its destination. Filler feedback† is sent from the central weighing system to the other equipment to manage the system as a whole. This method is superior because first, it’s dramatically cheaper. Second, it’s more precise. Not only can load cells have much higher resolution when they’re weighing pounds instead of tons, but it can auto-correct each batch. For example if load cells under a silo are told to send 700 lbs. of product, it will be off by 0-3%. If a central weighing system pulls 200 lbs. of product at a time, it will pull the first three batches to reach 600 lbs., notice that it only got 580, then pull 120 in the last batch to make up the difference.
Control Systems
Each piece of equipment will have a standard PLC†† configuration, but for batching and weighing systems you will want to have multiple pieces of equipment chained into one, which is controlled on the floor by an HMI‡‡. These methods of operation won’t be going away anytime soon, but some of the functions HMIs have been responsible for are now also being handled by site-wide control software that is accessible from managers’ desktops. More powerful software is not only able to use plant-wide data to generate helpful reports for decision-making, it can also combine functions of other software, like ERPs to enact equipment control. For example, if you’re low on a product, a system can shut off or use a substitute. There are number of packages available ranging from DSO Sentinel for small operations to FactoryTalk for large ones.
Dust Collection Systems
Dust collection is helpful for most processes involving powders to keep air and floors clean and deter pests. When milling is involved, any slightly flammable materials will become explosive because as the surface area increases exponentially, so does its explosivity. In such applications they are required by the codes of a municipality. There has been a recent surge in demand for these systems because of tightened NFPA 68 Standards, so if you are unsure, it will be worth it to find out if it’s required for your product.
Cartridge dust collectors use those pleated filters you’re used to seeing in your car or home. They filter to small particles, consume little space, and are easy to maintain, but will fill quickly in high-volume applications because there is little room for fabrics of descending micron size.
Baghouses use a series of bags and therefore have plenty of space to filter materials progressively, but they require a large footprint and bag changes are more cumbersome.
Cyclone dust collectors use centrifugal force rather than fabrics to pull materials out of the air and therefore can accommodate huge volumes with low maintenance demands, but they’re large and let small particles through.
How to Select Equipment Make/Model
The difference between selecting the right machine and the wrong one can be thousands to millions of dollars of waste and lost productivity. A qualified systems integrator can help ensure that you are selecting equipment and vendors that maximize your long-term odds of success.
Choose an Integrator
This step is best done first—or at least early—because systems integrators like ABM Equipment will reduce the time-suck and risk inherent in the rest of the steps. Integrators will have subject matter expertise and bring the experience of working with different products, equipment types, and vendors. They can also manage your sub-contractors. They will guide you through the process of selecting the appropriate units of equipment for your application and facility and ensure that those units all can work seamlessly together. As part of your integrator selection process, find out what they do in-house and what they outsource. A lot goes into a system, and it’s ideal to find someone who designs the system, builds the transitions, modifies equipment, installs it, and services it all under one roof. Reps differ from integrators in that they don’t engineer and fabricate. They will typically be very well-versed in the working of a machine, but not how to achieve predefined effects on products or how to make a system out of them.
Define Requirements
First, you must understand the physical and chemical properties of the materials to be handled. The most important metrics you will need for equipment quotes are the product type, bulk density, volume, abrasiveness, any hazards associated with the material, and its tendency to bridge, clump, or stick. You will also need to know certain metrics about your product such as the moisture content you want it before and after various stages.
Evaluate Technology and OEMs
Once you know what kind of equipment you need, you need to select the manufacturer(s). It is important to keep in mind that this machinery will be likely be on your production floor for many years and should be thought of as the long-term investment that it is. With that in mind, it is important to consider not just the upfront price, but the viability of the OEM to provide training, parts, and service for the entire life of the machine. Yearly maintenance will seem like a lot, and monthly will feel like daily. How difficult are these parts to access? How much do they cost?
Any savings on purchase price can quickly be offset by a machine with a higher-than-anticipated downtime rates. There are no hard-and-fast rules with respect to OEM selection, but as a general guideline, equipment from low-cost manufacturing regions like China and Vietnam tend to pose greater support challenges and are not typically advised unless you have a strong maintenance team that feels capable to solving problems with your supplier.
Regulatory Compliance
Ensure all equipment and processes comply with relevant industry regulations and standards, such as USDA, OSHA, FDA or local municipalities.
Safety
Implement safety measures to protect workers and prevent accidents. This includes proper guarding of equipment, emergency stop functions, and regular safety training.
Lead Time
Most manufacturers build equipment to order, especially if it requires any kind of application specific customization. If you are trying to coordinate multiple vendors and project timelines the lead time on various options will certainly become a deciding factor from time to time.
Energy/Utility Requirements
Energy cost will be a significant factor in your operating expenses, and energy availability can easily restrict your choices of location. Factor energy use into the cost of your equipment, and make sure you will have enough draw for your anticipated growth. A utility drawing should be part of any good design and include requirements for electrical (110v vs 220v vs 440v), compressed air, and steam if needed.
Scalability and Flexibility
If you plan to grow within your current space, select equipment that can be easily scaled or adapted to future production increases or changes. For example, more tubing can be added to a pneumatic conveyor to extend it (to an extent), and an extra belt conveyor can be added to existing ones, but a screw conveyor would need to be cut. Modular systems are also available for many types of equipment so you can add functionality as you can afford it.
Cost and Value
This is the most obvious and most difficult consideration because everything depends on what you need. With engineering-related projects there is a temptation to let “the perfect become the enemy of the good”. All systems will have strengths and weaknesses and every day of inaction you are losing out on the upside of improved capacity and efficiency new equipment could bring.
Conclusion
Designing and implementing a bulk weighing and batching system requires careful consideration of the products, equipment, and integrator(s). By understanding the specific requirements of your materials, selecting suitable equipment, and partnering with experienced professionals, you can ensure a system that is efficient, accurate, and reliable. Investing time and resources into planning and selecting the right components will yield long-term benefits in terms of product quality, operational efficiency, and overall profitability.
*RA stands for Roughness Average, or how rough a surface is, so a maximum value is the minimum amount a surface—particularly the product contact area—should be polished. (RA is not an actual unit of measure. Microinches are the standard unit unless otherwise specified in the US, and micrometers are usually the default elsewhere.)
**Electropolishing is a method of polishing rather than a specification. Generally, it is only used when necessary, and can be trusted as an indicator. But technically extremely rough steel could be electropolished and not come remotely close to the RA requirement.
***Best-practice for such extreme applications is to forget stainless scales altogether and simply put a lipped stainless plate over the platform. This will protect the load cells and cost much less to replace when it corrodes.
†Filler feedback is when a filler is told to stop or start based on feedback, ie. stop filling because a hopper or mixer has reached a certain weight.
††Programmable logic controllers (PLCs) send the electrical signals to the machines triggering a drive to start, stop, etc. They can be controlled by preset triggers or human interaction, but if it’s the latter, it will be by a simple switch or button.
†††Human-Machine-Interaction controllers are visual representations of PLCs, showing the operator which equipment they’re effecting and how they’re effecting it. These are usually touch-pads.
‡‡Enterprise Resource Planning software combines companies’ purchasing data into an interface so that purchasers can more effectively coordinate ingredient purchases. This helps ensure they don’t run out and that they are able to buy in bulk as much as possible.
‡Original Equipment Manufacturers build novel pieces of equipment for a category of goods. Independent fabricators will then modify the equipment for the specific use-case if needed.
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