Powder Compacting Equipment Information
Powder compacting equipment shapes powders as part of a forming process as well as to compress a wide range of materials into compact shapes for transportation and ease of handling. Compaction is done for a variety of reasons, including:
To produce uniform blends or mixtures
To produce a uniform particle size range
To control dust
To adjust flow properties
To control bulk density
To control particle hardness
To improve solution or dispersion rates
Although there are several configurations of powder compactors, listed below, the basic concept is to force fine powders between two counter rotating rollers. As the powder flows through the region of maximum pressure, the material is formed into a solid compact or sheet.
There are seven main configurations of powder compacting equipment (although custom varieties are available). These types are defined either by the shape of the product they produce or the technology used to process materials.
Briquetters turn fine, powdered materials into briquettes or chunk, to improve handling, transportation, scrap disposal, storage, or secondary processing.
Briquetters often consist of a roll compactor with a serrated roll or a smooth roll combined with a granulator/chopper. Briquetters that form discrete cylindrical compacts also exist and can create different briquette shapes such as pillow, almond, and stick form.
Briquetters are most commonly used for the melting process, thermic reactions, landfilling, and to improve storage life. The material used with this type of compactor is often minerals, refractories, charcoal, and metal powder.
|Cold isostatic presses (CIP)||
Cold isostatic presses (CIP), also known as rubber presses, use a chamber to compact the powder or material placed in a sealed tool, bag, or other flexible tooling. Cold isostatic presses use an oil-water mixture pressurized up to 100,000 psi.
This compactor can form complex shapes and it is therefore commonly used for refractory nozzles, blocks, and crucibles. CIPs are also used for sintered filters, artificial bones, and some food processing.
|Hot isostatic presses (HIP)||
Hot isostatic presses (HIP) use an argon atmosphere or other gas mixtures heated up to 3000º F and pressurized up to 100,000 psi. Evacuated steel, metal cans, or a sintered surface are used to contain and maintain a seal during HIPing. The use of this pressurizing system ensures a uniform compaction pressure throughout the powder mass.
HIPs are used for densifying high performance ceramics, compacting of high-speed tool steel, and eliminating voids in aerospace castings or creep damaged blades. They can be used to make shapes of varied complexity.
Pellet mills compress or extrude particles or fibrous materials into a cavity or die to form uniform cylindrical pellets.
Extruding pelletizers generate discrete and uniformly sized particles from a melt or a polymer (reclaimed scrap, post-consumer or virgin plastic), liquid-solid pastes with a binder, or other meltable materials.
The melt or paste is extruded through a die with multiple orifices. The pellet is sheared off or chopped after cooling/ drying. Several types of pelletizers are available such as hot face, air, and cold cutting and underwater.
Roll compactors with smooth rolls compact a powdered material into a sheet with consistent hardness. They are designed to give a low-cost upgrade to undesirable fine by agglomeration of fines into flakes for pyroprocessing, increasing product bulk density, and controlling the product solubility rate.
Roll compactor applications include production of ceramic or metal powder sheet or strip for filter applications or for clad/bimetal production. They are commonly used in pharmaceutical and chemical production.
|Rotary and multi-station tableting||
Rotary and multi-station tableting presses have multiple stations or punches for compacting pharmaceuticals into tablets or metal powders into simple flat or multilevel shaped parts like gears, cams, or fittings.
Rotary types have a series of stations or tool sets (dies and punches) arranged in a ring in a rotary turret. As the turret rotates, a series of cams and press rolls control filling, pressing, and ejection.
Pharmaceutical tablet and high volume metal part production facilities often use high-speed automatic rotary presses.
|Single station presses||
Single station presses are a type of powder compacting equipment that use a single action ram press with a die on both upper and lower punches.
Single station powder compacting presses are available in several basic types such as cam, toggle/knuckle, and eccentric/rank presses with varying capabilities.
This type of compactor is commonly used in the pharmaceutical industry to make tablets since they are high speed machines that can create thousands of tablets in a small period.
When selecting a powder compactor it is important to consider the volume of material that will need to be compacted. The greater the downward force, the larger the volume of material that can be compacted. This efficiency is a function of its feed system and the method by which downward force is generated.
The diameter/width capacity describes the maximum internal diameter of the die cavity that can be used in tableting presses. For isostatic presses, the internal diameter of the chamber determines the diameter or width capacity. For briquetting presses, the roll diameter is stated here, since the cavity can vary dynamically. Depth/fill capacity is the maximum internal length of the die cavity that can be used in the uniaxial or tableting press. For isostatic presses, the internal length of the chamber determines the diameter or width capacity. On briquetting presses, the spacing range of rolls determines the thickness range of compacted sheet.
Other specifications to consider include the maximum operating force, which describes the force required to reach the desired density during part production, and maximum operating pressure, which also describes the force required to reach desired density but varies with material and part geometry.
If the powder compactor will be used in a high-volume production facility the bulk production rate should be noted depending on the number of kilograms per hour that can be processed through the equipment.
Materials compressed by powder compacting equipment include powdered metals, ceramics, carbides, composites, pharmaceuticals, carbon/graphite, ferrites, explosives, chemicals, foods, nuclear fuel, or other materials. Metal or ceramic powder compacts require additional processing such as sintering or forging to provide a finished part.
Materials with a low bulk density tend to hold air entrained internally and thus will resist the precompression that is required in order to pass through the rolls.
Self-diagnostic systems provide continuous monitoring of the progress and functionality of the compaction process. If an error occurs, the operator will receive a warning, the machine will stop at the end of the current cycle, or the machine will be stopped immediately. Errors can be recorded for later investigation.
Communications/remote control allows the powder compaction equipment to be supplied with a networking capability such as Ethernet for monitoring and operation from a remote location or central control station. This feature might include a camera for visual monitoring of the process.
A robotic interface allows the press to be integrated with a robot for automated loading of powder media or extraction of finished parts.
A vacuum can be added to the system when compaction is made difficult by a material with a low bulk density. Vacuums can increase capacity of a powder compactor.
Automation allows for process control and data monitoring.