PVFD

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Polyvinylidene fluoride is a semi-crystalline polymer that I don't believe is suitable for HF (whatever the F really is) nor high pressure (whatever that pressure might be) and I won't even bother trying to define temperature for you.

Being a polymer, high frequency energy and temperature will age the film rapidly causing the chemical bonds and/or chains to break down prematurely.

Without any specific information about the environment, I think your best off contacting the machine supplier and asking them.

Have some real values at hand before making the call.

PVFD can have piezoelectric properties if processed correctly.

Thank you Lyn,

My problem that I have inherited this machine from previous engineer who did not know much about PVFD. Actually another firm who was overseeing the process of putting the factory together

The outside firm submitted specs to the manufacturer call for 350 F at 100 PSI and they insisted to use PVFD as a liner. One thing to mention that the HF (Hydrofluoric acid) is used after it is heated to 280 F, originally the concentrations of HF used was 70%, we later dropped that to 40%. The liner peeled off when they were running at 70%.

Then refer it back to the equipment manufacturer and get them involved in finding the solution. One hopes it is still under warranty.

"...The outside firm submitted specs to the manufacturer call for 350 F at 100 PSI and they insisted to use PVFD ....."

.

PVDF has a melting point of 350° F, and since it is a thermoplastic and not a thermoset, whenever it reaches that point it will melt again. That is an odd thing for the outside firm to insist upon.

If you only know. Many issues coming up every day

What's "HF"--high frequency, or hydrofluoric acid?

Hydrogen fluoride.

Well, it could have been hot fudge.

Alphabet soup!!!!!!! I hate it!!!!!!!

PVDF is completely resistant to alphabet soup, as its pH is near neutral.

PVDF...as in Kynar, I actually transpose the letters are PVFD sometimes too, not sure why....anyway, Kynar is one of the preferred materials as far as compatibility with Hydrofluoric acid. It is well suited to high pressures and even very rapid changes in pressure, as PVDF transducers are used to measure pressure in explosive reactions.

.

If the high temperature you mention exceeds around 175° C, that will most likely be the culprit. By 180° C Kynar is completely molten.

There are several materials compatibility websites on the internet. Try this:

http://www.coleparmer.com/Chemical-Resistance

<...high pressure and temperature...>

Some numbers on those descriptors would be essential! Please state whether or not the temperature and pressure of the HF were stated to the machine vendor prior to accepting the quotation for its supply and delivery?

With PVFD aka Kynar, be careful with your application. If the temperature is too high and the Kynar starts to ignite and burn, a noxious gas is formed and thus can kill/maim if inhaled.

Is that after the HF has done its stuff or before it?

Before

Then it is time to stop using it. About the only things HF won't eat are Kynar and some types of glass.

We just switch to rubber, and it is fine now.

I put this question on to find out more about PVFD (Kynar). We have it everywhere in the factory and I wanted to make sure that we run within the kynar conditions. This machine failed and when I came on we dropped the % of HF and changed the liner.

Bye-bye warranty!

<unsubscribes>

Warranty

It was long gone; this machine was setting idle for over three years because of other issues at the other end of the building.