Simply put, the roll compaction process, also known as dry granulation, forces fine powders between two rotating rolls in order to remove air and compress material into a compact. The desired properties of the compact can be adjusted based on system configuration settings, and will visually appear based on the roll profile as flat sheets, wavy sheets, or sticks. A critical component to achieve desired results is choosing the correct roll profile, creating a friction between the powder and roll surface. This can be adjusted based on speed of feed screws, roll gap, and roll speed. Once proper force and friction are achieved, lab testing has repeatedly proven that the fixed blade IPA Mill is the most efficient size reduction unit to reduce compact to the desired particle size.
Size reduction does exactly as its name indicates – it is the process of breaking a material down into a smaller, more ideal particle sizes. It can be useful on its own or in conjunction with a roll compaction unit depending on the material and desired outcome. When used with a roller compactor, milling occurs immediately after compaction. Mesh screen sizes should be carefully considered in order to minimize excess fines and maximize useable product. There are various types of mills within the industry, such as an oscillator, low energy, and comminutor mill. However, multiple research studies within the industry undoubtedly conclude the fixed blade (comminutor) mill is the most efficient in producing consistent, repeatable results.
IPA has a strong team with a unique history of employment together; each partner bringing their own experience, expertise, and ideas. We’ve spent years working directly with customers on turnkey roller compaction installations. In creating IPA, we now have the freedom and capability to re-design equipment, improve upon flaws, and manufacture increasingly efficient applications. IPA also differs from competitors based on ability to configure the proper set up of all system parameters, a process that requires balance and a deeper understanding of the equipment. We take into account each piece of the puzzle and observe how one piece must fit with the next in order to form a complete picture.
The heart of all roll compactors perform the same task. Two counter rotating rolls compress the material together in order to form a compact sheet. What makes us different? Our desired Twin Feed Screw Design.
The IPA Roll Compactor’s unique twin feed screw design is exceptionally efficient at processing lower bulk density powders with large amounts of air. It allows for independent capability to adjust feed rate and deaeration of material. Specifically, the HFS controls system throughput while the VFS deaerates the powder. The multiple functions of the VFS allows for pre-compression by removing air between the particles without actually compacting the material. Material then enters the Nip area where it achieves tapped bulk density (TBD). The friction generated between roll surface and material allows it to be ‘pulled’ into the counter rotating rolls to do their primary job – material compaction.
The IPA dry granulation process maintains lower system operating temperatures and higher product yields as compared to a single feed screw design. The IPA Roller Compactor is ideal for processing a wide range of materials.
The best way to process roll compacted material is with a fixed-blade IPA Mill. The IPA Mill is a comminutor mill, and is determined through years of side-by-side research with multiple materials to be the most effective and ideal unit to yield consistent, repeatable results.
IPA’s size reduction process reduces particle size using an “in-air” impact method. Unlike other more aggressive “compression/pinching” methods between the rotor and screen, impact milling shatters material along its natural “fracture point” resulting in the highest first impact yield. This technique is the most efficient as it minimizes the percentage of material requiring a second impact, maintains lower product temperature, and reduces overall fines generation.
The IPA Mill is versatile and can be configured for use with a variety of roll compacted materials. Altering the mill features, such as feed throat, rotor styles, and screen type, this industry “Workhorse” will produce the desired final product.
Over the past decades we have learned from our experiences and honed in on the most efficient process from initial testing through design, manufacturing, and commissioning.
As standard practice, IPA conducts a preliminary analysis on all feed materials for roll compaction projects. Several tests make up our prelim process, including a pressure vs. density curve, moisture analysis, and tapped bulk density (TBD). These results provide necessary information to properly set up the roller compaction equipment for testing.
Applying What We’ve Learned
In order to conduct a successful lab test, it is essential to be properly prepared. IPA takes two main factors into consideration:
- Data from the preliminary analysis
- The customer’s desired objectives
From this information, we determine an optimal roll surface, a roll pressure start point, optimal compact density, mill screen, screener set up, and whether or not vacuum deaeration will be of benefit to the process. After successful testing is achieved, IPA uses all test data to scale a system that meets the customer’s requirements.
Scaling to a Larger System
Testing is conducted for several reasons, with the following being most significant:
- Meeting the customers objectives – particle size, density, dissolution, etc.
- Optimizing system performance once the objective has been met
- Scaling the system’s performance to meet the required production rate
Allow us to give a simple analogy. Operating a roll compaction system at 50 lbs/hr vs. 3000 lbs/hr can be compared to driving a small economical car vs. a semi-truck. Acceleration, braking, turning radius, and changes in speed while driving each vehicle is very different. Similarly, when scaling from a lab test to a larger system producing 3000 lbs/hr of final product at 50% system yield (6000 lbs/hr through the rolls), there is minimum 100 lbs/min traveling through the system. At this rate, if a problem occurs at some point during the process, it will quickly cause a significant overload and back up the system. If a problem occurs in a smaller system, or a smaller vehicle, with 1 – 2 lbs/min traveling throughout, it is much more forgiving.
It is important to acknowledge the high flow rates in large systems and to design & size the equipment accordingly. Specifically, when starting, stopping, and changing flow rates in a system, proper controls play in integral part in maintaining system balance.
Determining the best roll compaction system for a given application has many variables. Common considerations when designing a compactor can include:
Is the building existing or new construction?
How is the feed material entering the system?
How is the final product being removed/transferred away from the system?
What areas of the system require access for routine maintenance?
What are the key operating parameters for this material?
What type of conveyor is best for the application?
Every application is unique with different design requirements, and every application will inevitably have a component that lends itself as a ‘weak link’ in the system. With our team’s experience and knowledge, we proactively size our system’s components to allow for a known ‘weakness,’ which is far better than finding out during production. The design requirements must be well analyzed and thought out in advance to provide a robust system that, if designed properly, can handle minor system upsets with ease.