PEEK screws for high temperature to 400F & corrosion resistance

Q: I’m designing laboratory equipment that will be utilized at 325-400F and I need screws that have immunity to organics and low concentrations of acids, as well be FDA approved. Would that be a ceramic?

A: You probably don’t want a ceramic screw. Though they are corrosion resistant and offer high purity, they are typically reserved for extreme temperatures. In addition, ceramics typically aren’t FDA approved. For your situation, you might want to consider PEEK screws. They offer an economic solution to temperatures up to 500F. In addition PEEK screws are an FDA approved. PEEK screws also offer excellent corrosion resistance to organics, salts, oils, and moderate concentration acids and bases. Depending on the strength you need, PEEK may be an excellent choice and are also available in reinforced glass and carbon if extra strength is needed.

Ceramic fastener compatibility with metal

Q : I am looking to purchase a ceramic threaded rod, but I was curious as to its compatibility with metal. The mount I intend to use made of stainless steel; would this mate well with a ceramic rod?

A: While you might be able to thread the ceramic rod into a female thread, the biggest problem you may encounter if there are elevated temperatures is the mismatch in thermal expansion. Because the ceramic is brittle, the steel’s expansion may crack the ceramic. Typically ceramics are used because of their high temperature and corrosive resistance, as well as electrical insulation properties. For example, Alumina is offers usability to 3000°F, where as stainless cannot handle such extreme temperatures.

If you are not using the ceramic at elevated temperatures the the parts should thread as they are made to ANSI standards.

Are ceramic fasteners fragile

Q: Are ceramics fragile? Do I have to worry about them breaking compared to metals?

A: Compared to metals ceramic fasteners are indeed fragile. Unlike a metal, there is very little yield before it fractures. Additionally ceramic fasteners and susceptible to thermal shock.

Bolts for high temperature vacuum furnace: Metal vs. Ceramic

Q: I’m using a high temperature vacuum furnace at 2500F. What type of material do you suggest using and is there any advantage of using a metal over a ceramic?

A: Under vacuum conditions with little to no oxygen present, there are some metallic options for fasteners which include molybdenum and tantalum. These metals are considered referactory metals and could be used up 2900F and 3600F for molybdenum and tantalum fasteners respectively. In addition to metals, alumina and zirconia ceramics could be used as well.

The advantages of each come from what is most important and the conditions of your application. For example, if quenching is involved, you might not want to use ceramic fasteners due to the thermal shock which will cause failure. However if having low thermal conductivity through the fastener is important, then ceramics are a good choice. If the fasteners are to hold higher loads, the molybdenum and tantalum metals might be more robust.