Hot Isostatic Press Features
While we offer many sizes, pressures and types, these are the most common units purchased by universities and laboratories.
AIP systems offer the best price versus performance of any brand on the market, are simple to operate, and feature the most advanced controls and furnaces available.
Our HIP systems come standard with ASME coded and National Board registered pressure vessels, which are accepted worldwide.
The AIP HIP unit is controlled by an Allen-Bradley programmable controller and supervised by a Pentium computer using the latest graphical control software for extremely easy use and accurate logging.
Control can be local or remote, including over the internet. The system performs completely automatic cycles from start to finish.
The HIP unit features a Hydro-Pac, Inc. electro-hydraulic compressor to allow pumping to 30,000 psi reliably. Each system is supplied with one furnace of choice.
The choices are; either a 2200 C Carbon furnace,
1450 C Molybdenum furnace,
or 1200 C Kanthal.
All furnaces are easily plugged into the vessel and fully interchangeable.
Therefore you can purchase additional furnaces for use in the system either initially or later.
Hot zones vary slightly with temperature. Many customers purchase different furnaces for various applications.
Carbon furnaces are used for high temperature ceramics work, and also when Nitrogen use is of interest.
Carbon furnaces can also be used under vacuum to 1700 C allowing sintering (binder less only) and low pressure work to be done.
The vacuum level achievable is typically around 100 to 200 microns.
Molybdenum furnaces are very clean and used for ceramics such as Alumina and Zirconia, as well as most metals.
Molybdenum furnaces can only be used in Argon.
Kanthal furnaces are rugged and can be used for metals and castings.
They can also be operated in up to 20 percent Oxygen therefore allowing use with superconductors and oxide ceramics that are prone to breakdown.
We also offer units in 45,000 psi (300 Mpa) and 60,000 psi (400 Mpa) versions which can be advantageous for ceramic and nano-powder work when you need to lower the temperatures to reduce grain growth.
GENERAL HIP AND CIP BACKGROUND
Isostatic presses are used for many applications ranging from casting repair to ceramic ball bearings. The process can use cold, warm or hot temperatures to accomplish the desired task. Cold isostatic presses are used mainly for pre-forming of powders prior to a further densification by sintering or hot isostatic pressing. Cold Isostatic Presses come in two types; wet bag, and dry bag. In a wet bag press the pressure vessel is full of water and the rubber bag (mold) is removed each cycle and refilled. This type of press is common when large, complex, or many different parts are required. Dry bag presses have the bag as an integral part to the vessel and are used when lots of the same style parts are made. Dry bag presses are limited to smaller sizes, and simple shapes that can be removed easily. Dry bag presses are typically automated from the powder filling to the part removal stage. The main benefit of isostatic pressing is uniform density, which results in predictable and repeatable shrinkage upon sintering. In small parts a uniaxial die press can produce acceptable parts, but in long tubes or large complex parts, die friction causes non-uniformity. This is where isostatic presses come into use. Most cold pressing is done with some form of binder to help hold the part shape. This binder is typically burnt out of the part in a furnace or during the sintering process.
Sintering is a process to consolidate a performed part. It can be done in vacuum or gas pressure. The gas type may be any of a wide variety to accomplish the desired reaction with the part material. Sintering is done at a temperature close to the melting point of the part and densification will occur as the powder particles diffuse together. Sintering has many variables and can produce parts of very high densities, typically 94 to 99 percent dense. For many applications this is all the part needs and further processing is not required.
Hot isostatic pressing is the application of heat and pressure simultaneously to a part causing it to shrink and densify uniformly. It can be used directly to consolidate a powder or supplementary to further densify a cold pressed, sintered, or cast part. The pressure medium is typically a gas (argon or nitrogen) but can be a liquid (glass) or molten metal. Heating is most always with an electric furnace. To densify a powder directly requires a can to transmit the pressure to the powder. This can (mold) can be mild steel, stainless, an exotic metal, or a glass capsule. This method is used when a simple shape is required. When a complex shape (such as a turbocharger blade) is required, it is common to cold press first because a rubber mold is much easier to make than a stainless steel mold. The cold pressed part (called a green body) can then be sintered to a high enough density to close any interconnecting porosity. This part can then be hot isostatically pressed without a can (mold) as the part itself will transmit the force to any internal porosity. This method is also used extensively on castings. It is hard to cast 100% dense castings, especially all the time, therefore hot isostatic pressing is used to fully densify castings after they are made. Many titanium castings are HIPped to ensure no internal porosity exists. HIPping can be used on just about any material from plastics to metals, to ceramics, to metal matrix composites. HIPping results in a very uniform grain structure and exceptional properties. Fatigue life is often better than achieved by any other processing method. HIPping can also be used to consolidate unusual powder combinations such as superconductors, ferrite’s, nuclear wastes, etc. It also is used to diffusion bond same and dissimilar materials that cannot be bonded otherwise. Many applications such as transparent ceramics cannot be manufactured any other way than HIPping.
There is much literature regarding both hot and cold pressing. Some sources include American Powder Metallurgy Institute, American Ceramics Society, APM, and Gorham Advanced Materials Research Institute. There are articles regularly in Ceramic Industry, Ceramic Bulletin, Industrial Heating, and Advanced Materials and Processes magazines. There is also information starting to appear on the Internet, including www.mpif.org. Many universities now have isostatic presses, and some specialize in isostatic pressing. Penn State and Michigan Technological University are leaders in powder metals, while Alfred and North Carolina are leaders in ceramics.
The major drawback to HIP has always been the high cost of the equipment and the process. This has started to change as higher material properties and parts value have increased to allow HIP to be considered. Many HIP units are custom designed to meet special requirements. These include Oxygen HIP units, Triaxial isostatic presses, Ultra fast HIPs, and Low Pressure Sintering HIP’s for silicon nitrides.
VARIOUS HIP USES
Aluminum castings: For void closure to improve properties and to meet x-ray NDT requirements.
Typically the voids must be under vacuum to allow closure.
Titanium castings: For void and crack closure to increase fatigue ratings and allow predictable life
Super Alloys: Parts are produced directly from powder. The benefits are reduced machining,
improved properties, complex shape capability, and material cleanliness.
Noble Metals: Gold and Platinum can be HIPped to eliminate voids, increase properties, and to
create compounds and alloys only possible with powder metallurgy.
Refractory Metals: Tungsten, Molybdenum, Niobium, and others all can be made to near theoretical densities from powders. HIPping also allows bonding of similar or dis-similar materials.
Powders: Chrome, Beryllium and others are materials that can be of much higher purity when
HIPped from powders.
Oxides: Alumina, Zirconia, and others are routinely HIPped. The density improvement adds
considerable benefits in toughness and cracking resistance.
Nitrides: Silicon Nitride is among the most promising material for HIPing. Fatigue and creep
properties are increased. HIPping is one of few methods capable of SiN4 production.
Carbides: Tungsten Carbide and Silicon Carbide are widely HIPped to increase fracture resistance.
There are numerous composites with both ceramic and metal matrixes that are being HIPped. The capability to densify and bond dis-similar materials of widely varying melting temperatures is a unique feature only offered by high pressure HIPping.
SOME OF THE PARTS BEING PRODUCED:
Zirconia knife blades
Zirconia biomedical implants including knee, hip, teeth, and ear parts.
Zirconia pump plungers and seals
Zirconia can sealers for the beverage industry
Alumina substrates for microchips
Alumina valve parts
Alumina for translucent dental braces
Alumina for microchip track laying pipets
Silicon Nitride ball bearings
Silicon Nitride valves
Silicon Nitride turbocharger blades
Silicon Nitride thrust washers for jet engines
Silicon Nitride disk brake pad inserts
Silicon Nitride missile nose cones
Silicon Nitride cutting tool inserts
Silicon Carbide for armor
Silicon Carbide for cutting tools
Silicon Carbide for nozzles
PZT ultrasonic transducer parts (Oxygen HIPing widely used)
Barium Titanate for numerous magnetic parts
Ferrites for magnetic and video recording heads
Chromium sputtering targets
Tungsten rocket nozzles
Tungsten sputtering targets
Tungsten Carbide for oil well drilling bits
Tungsten Carbide for water jet cutting nozzles
Tungsten Carbide for wear parts
Tungsten for golf club heads
Super alloy for rolling machines
Super alloys for train wheels
Super alloys for power generating turbines
Super alloys, bonding for orthopedic hip implants
Titanium castings for valve bodies
Titanium castings for jet engine parts
Beryllium mirrors for telescopes
Beryllium structures for gyroscopes and guidance systems
Rare earth magnets
Ultra High Molecular Plastics for orthopedic implants
Spinels for transparent window applications
Compounds (Zeolite) for nuclear waste disposal including ceramics, concretes, and metal containers.
Bonding of nuclear fuel and dis-similar metals
Silicon Oxy Nitrides for nose cones
Graphite densification and impregnation for improved properties
Aluminum castings for turbochargers
Aluminum castings for explosion proof housings
Aluminum castings for diesel motor pistons
Aluminum castings for numerous small machine parts, latches, levers, etc.
Carbon Carbon pitch impregnation for clutch plates, brake pads, nose cones
Steel to make dense parts from powders including car alternator housings
Steel to make porous foam materials
Indium Tin Oxide to make sputtering targets for flat panel displays
Molybdenum powder nuts and bolts
Inconel castings and powder made parts for deep sea apparatus
Gold and Platinum for sputtering targets
Gold and Platinum for jewelry
Superconducting materials from ceramic compounds (Oxygen HIPping used)
Fluorides for laser applications
ADVANCED CERAMICS PROCESSING
There are many methods to process ceramics. These can vary depending on the desired properties of the final part.
Three of the normal methods for processing include:
Raw Powder - need to spec properly
Milling of Powder - to blend binders or sintering aids
Preform -Die press uniaxially, cold isostatically, slip cast, or injection mold
De-binder (dewax) - if required, via vacuum or flow through gas
Sinter- under vacuum or partial pressure (2 to 50 psi) (Zirconia usually air fired)
These steps may achieve the desired product.
Hot Isostatically Press - this additional step might be needed to improve properties. The actual pressure and temperature could vary depending on desired product. Alumina and Zirconia are typically HIPped at 1500 C, 15,000 psi for 2 hours. Silicon Nitride is being pressed at 1500 psi, but some are using higher pressures to 45,000 psi. Higher pressures typically produce better properties, but often the minimal gain is not cost effective. By Sintering to above 92 percent you would typically achieve a non porous part that will not require any HIPping membrane (container).
Milling - if required
De-binder - if required
Glass encapsulation - to provide a barrier membrane
Hot Isostatically Press
Milling - if required for sintering aids. Binders not typically required as part goes from powder to product. Binders are usually added to facilitate handling of a pre-form.
Hot Uniaxial Press - in vacuum, or partial pressure.
This method will produce reasonably good parts that may satisfy part requirements. Parts may have minimal density variations, and will probably require more machining than an isostatically pressed component.
For some ceramic materials, binders can be burned off in low cost ovens at atmospheric pressure either in air or in a non-oxidizing atmosphere. After binder removal the work is then transferred to a sinter furnace.