vacuum-furnace-wsTungsten is used in vacuum furnaces when there is a need for structural integrity at elevated temperature and/or in situations where other materials may degrade, such as when lower melting point eutectics are a concern. One example of its use in is roller rail assemblies in which graphite wheels are positioned between molybdenum rails using tungsten axles.

Tungsten (chemical symbol W) is a member of the family of refractory metal (Mo, Nb, Re, Ta, W) and has the highest melting point and vapor pressure of this group. Due to this unique property, it is commonly used as a material of construction in specific areas of vacuum furnace hot zones operating above 1315ºC (2400ºF). Tungsten can also be used for heating elements given that it has the highest duty temperature, typically 2800°C (5075°F). In practice, this rating is often downgraded as it is for all heating element material choices. Tungsten will become brittle, however, if exposed to oxygen or water vapor and is sensitive to changes in emissivity. In general, tungsten is resistant to corrosion below 60% relative humidity. By Dan Herring 

moly-hot-zone wsVacuum furnace hot zones are manufactured using materials that can withstand temperatures in the range of 1315ºC (2400ºF) and higher. Of the various types of refractory metals in use, none is more common than molybdenum.

The popularity and widespread use of molybdenum in vacuum furnaces is due to the wide range of properties that it exhibits, namely: high melting point, 2620ºC (4748ºF), low vapor pressure, high strength at elevated temperature, low thermal expansion, high thermal conductivity, high elastic modulus, high corrosion resistance, and elevated recrystallization temperature, between 800º - 1200ºC (1470º - 2190ºF). Mechanical properties of molybdenum are influenced by purity, type and composition of any alloying elements and by microstructure. Properties such as strength, ductility, creep resistance and machinability are enhanced by additions of alloys such as titanium, zirconium, hafnium, carbon and potassium along with rare earth element (La, Y, Ce) oxides. By Dan Herring 

Figure-1 wsLubricants in vacuum applications include wet and dry lubricant types (Table 1), greases and oils. So-called “wet” lubricants tend to stay wet on the surface to which they are applied, while dry lubricants go on wet but dry as they are applied. In general solid particulates do not stick to dry lubricants but they do not tend to last as long as wet lubricants and as such need to be reapplied. By contrast, greases adhere better than oils and tend to last longer. Oil is preferred where the lubricant needs to be circulated.

The major disadvantage of conventional liquid lubricants is that they have relatively high vapor pressures (= 1.3 x 10-4 Pa at room temperature) and surface diffusion coefficients (= 1 x 10-8 cm2/s) with low surface tensions (in the order of 18 – 30 dyne/cm) and can volatilize or creep away from areas of mechanical contact resulting in high friction, wear or mechanical seizure. In addition, their volatility can cause issue with achieving proper vacuum levels and/or depositing on component part surfaces. The presence of other gaseous species in a vacuum environment (e.g., water vapor, oxygen, carbonaceous gases) can cause the force of adhesion between metal surfaces joined by liquid lubricants to be so strong that the joined areas can only be separated by fracture. By Dan Herring 

Installation-wsWe continue our discussion on the factors that must go into the decision making process during the acquisition phase of a vacuum furnace. Part One focused on how one goes about choosing the right furnace for the job and talked about the various choices for hot zones (e.g. insulation, heating elements, etc.). Part Two discussed pumping systems, controls and ancillary support items (e.g., grids/baskets/fixtures, water systems, features & options). It is now time to understand how your supplier partner will handle the project once an order is received, including project management, codes & standards, approvals, installation, commissioning and long-term support.

Order Processing; Okay, you have selected a vendor partner to supply your vacuum furnace, so what type of support should you now expect? To begin with, it is important to understand how your order will be handled internally by the company you have selected. The first task they face is to transfer the order from their sales team to their engineering team and, ultimately, to the manufacturing and service/support teams. After receipt of an order, your supplier partner will typically schedule an engineering “kickoff” meeting where the project is given to engineering and a project manager (or project engineer) is assigned. Out of that meeting will be generated the final equipment specification and this should be provided to the purchaser shortly (e.g., 1 – 2 weeks) after receipt of the purchase order for approval. By Dan Herring

Tips for Selecting Vacuum Furnace Equipment – Part One

Tips for Selecting Vacuum Furnace Equipment – Part Two

 

Figure-1 wsWe continue our discussion on the many factors that must go into the decision making process during the acquisition phase of a vacuum furnace. Part One focused on how one goes about choosing the right furnace for the job and talked about the various choices for hot zones (e.g. insulation, heating elements, etc.).

 We now continue this discussion by looking at other common vacuum furnace features and options. Recall that the four common elements of any vacuum furnace are; Hot zone (c.f. Part One), Heating elements (c.f. Part One), Pumps and Controls. Once decisions have been made in these areas, other ancillary items (e.g. partial pressure control, loaders, etc.) must also be considered and will be talked about here as well. By Dan Herring

Tips for Selecting Vacuum Furnace Equipment – Part One

Tips for Selecting Vacuum Furnace Equipment – Part Three

 

h-vacuum-furnace wsAcquisition of a vacuum furnace represents a major capital equipment investment and one that creates a long-term relationship with your supplier partner. Thus the choice of what to buy and who to purchase it from requires careful planning and considerable up-front research.

You need to know when and how to apply vacuum technology, if it will be the most cost effective solution for what you need to do, what questions to ask and what information to provide. The process begins by understanding your specific needs and asking all the right questions. Is it more prudent to upgrade an older piece of equipment, purchase new or purchase used? Is it better to have one large furnace or two smaller ones? Is a batch solution best or is a continuous approach better? By Dan Herring

Tips for Selecting Vacuum Furnace Equipment – Part Two

Tips for Selecting Vacuum Furnace Equipment – Part Three

vac-aero-vacuum-furnace-wsFastener applications are demanding. Whether fasteners are being used in the petrochemical industry, in medical or mining applications, for assembly of marine or nuclear components or in the aerospace, automotive or construction world, vacuum processing allows us to repeatedly achieve the highest quality and metallurgy.

Most fastener materials, including stainless steels and superalloy grades, benefit from or actually require vacuum processing for heat treatment instead of being run under protective atmospheres. In general, there are three main sets of applications that where vacuum heat treatment is used: processes that can be done in no other way than in vacuum; processes that can be done better in vacuum from a metallurgical standpoint or processes that can be done better in vacuum from an economic standpoint. By Dan Herring

 
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