sheet silicon to make hoses?

Hi Richard

If you're using it under-bonnet than the grade you need will be a Flurosilicone compound, which is resistant to oils and greases, and as it's for a hose you really need quite a high shore hardness grade if you dont want it to collapse. Thats the easy bit answered. However, you would need to buy it as sheet moulding compound (SMC) and then crosslink (cure) it when its the right shape, and thats not so simple. Effective cross-linking needs heat and pressure. Most SMC is compression moulded in heated tools, or shapes like hoses with odd paths are cured in an Autoclave, usually after being wrapped around a former then completely enclosed in a deformable bag which is very tightly 'vacuum wrapped' around the part before it is put in the autoclave.

My knowledge on this is a bit limited though so you could try contacting

or for some advice.

One final word of advice on safety, and this applies to all flouro polymers and flouro rubbers. If this stuff burns and is then extinguished with water don't ever touch it with bare hands. This burning/extinguishing process produces Hydroflouric Acid for which there is no known neutraliser. This stuff can get into your system very easily from a skin burn, and apart from causing systemic poisoning and death, the only way to prevent it spreading is amputation! Unbelievably this stuff is also found in proprietary rust removers, and is also a major hazard from burnt-out cars/bikes. Hope his helps

Peter

Just had a quick peek at your website Richard. I see you're familar with vacuum bagging from the CF work you did, so perhaps this won't be such a problem after all! Sorry for telling you stuff you already knew...

Peter

I bought some silicone hoses for my car and they were d*mn expensive - I can see why now...

Samco brand

I don't know where you got this information Peter but I am afraid it is sheer nonsense. Admittedly hydrofluoric acid is a strong acid and should be treated with caution just the like sulphuric or hydrochloric acids. It also has the unique ability to etch or even dissolve glass, but it can be neutralised in exactly the same way as any other mineral acid. Neutralise it with caustic soda for example and you get water and sodium fluoride, a mineral that is a common ingredient of toothpaste and is added to drinking water by some water companies to prevent tooth decay.

As for rust treatments, maybe you are thinking of phosphorous acid, which is the only acid I know of in such formulations.

Cliff Coggin.

hi I think peter may mean an aluminium cleaner, the first aerosol wheel cleaners had hydraflauric[yes i know i can't spell] acid in them.

The bloke who I saw make hoses worked for silfex or whoever it is that make samco hoses. He didn't vacum the hose he wrapped it with what looked like harness wrapping tape[ no adhesive].

richard

Hello Cliff

says:

"Chemical Information Overview Hydrofluoric acid (HF) differs from other acids because the fluoride ion readily penetrates the skin, causing destruction of deep tissue layers, including bone. Pain associated with exposure to solutions of HF (1-50%) may be delayed for 1-24 hours. If HF is not rapidly neutralized and the fluoride ion bound, tissue destruction may continue for days and result in limb loss or death. HF is similar to other acids in that the initial extent of a burn depends on the concentration, the temperature, and the duration of contact with the acid."

You can NOT neutralise it once it is in your system. This is what I meant I say. Make no mistake this is deadly stuff. Further down the page on the same site it tells this story:

"HYDROFLUORIC ACID FATALITY TO LAB WORKER IN PERTH

Extract from Australian Institute of Occupational Hygienists Newsletter, December 1994:

An accident in Perth highlighted just how hazardous this acid can be and it is worth recounting for the benefit of any lab working or hygienists whose work may involve advising others who use this substance. On November 12, a 37 year old man died in the Intensive Care Unit of Fremantle Hospital after he accidentally splashed about 100 ml of a 70% solution on his right leg on October 28. It was estimated that the extent of the spill covered about 10% of his total body area. The individual was working as a technician in a small paleontology laboratory, which was attached to a private residence. HF is used in the industry to digest silicates in ore samples. The victim immediately attempted to remove the spill from his clothing hosing himself down with a hose attached to a sink in the laboratory. He then ran from the laboratory to the swimming pool in the garden, and he remained in the pool until the ambulance arrived within the hour. At the time he appeared confused, possibly as a result of shock. The following week his right leg was amputated, however despite this, the individual eventually succumbed to the toxic effects of the hydrofluoric acid 2 weeks after the initial spill. There are a number of points that need to be emphasized as a result of this, which are relevant to all users of HF:"

Best to avoid the stuff altogether I think.

Peter

There are special neutralizing jellies to put on to the area after contact with this stuff, but it has to be done immedialty or it won't work (anyone using it would have this to hand before using it). I remember some terrible occurances being reported several years ago before the problems were widely known. Recovery workers and mechanics dealing with burnt vehicles -some seals in vehicles contain this compound- sustained very nast injuries, some resulting in amputation of effected limbs.

This stuff should definately NOT be treated as other acids (and any concentrated acid is pretty nasty!). Personally I wouldn't go anywhere near it.

Regards

Kevin

No, he is not.

If you replace the word "neutraliser" with "antidote" he is actually correct (except I haven't come across it in rust removers either - that's usually orthophosphoric acid).

NaF (sodium fluoride) is okay in tiny doses - but it larger doses it is used as rat poison.

It is extremely toxic to humans too. The acute oral rat LD-50 is 52 mg/kg, and the LD-50 acute human ingestion is thought to be similar - the LD-50 acute human inhalation is considerably lower at an estimated 5-10 mg/kg - inhaling a gram of dust will almost certainly kill you, as will swallowing a teaspoonful.

Those figures are for sodium fluoride, not for hydrofluoric acid, which is even more toxic. Hydrofluoric acid also gets into the human system by absorbtion through the skin.

The real problem with hydrofluoric acid is that it is toxic, not that it is corrosive. Neutralising it doesn't significantly change the toxicity.

Ionic fluoride is equally as toxic as the acid or as the sodium salt - the main, small, difference is that the salt is slightly less easily absorbed through the skin.

The percutaneous (through the skin) action is especially nasty as it numbs the nerves and there is no pain to tell you that you have been exposed - this also makes systemic poisoning more likely as well.

There is no antidote for gross systemic fluoride poisoning, whether it is in the form of hydrofluoric acid or sodium fluoride - both work similarly by depleting the available calcium in the nerves.

Systemic poisoning takes a while to kill, typically 6 to 24 hours, which makes NaF a better rat poison - the rats can't easily tell each other what killed them.

Amputation has occasionally been used in cases where inessential body parts have been exposed, to prevent death by systemic poisoning. It is the only known-successful treatment for large-scale acute percutaneous HF insults (getting too much HF on the skin).

Worse, it only works if you are lucky enough to have only amputatable parts of the body exposed, a tourniquet is immediately applied after the spillage and not ever loosened, and you get treatment in a very short time.

Even worse still, there are only a very few doctors in the world expert enough to be confident and willing to do the amputation - most ordinary doctors and medics will not even start to consider it before the poisoning is irreversible.

will tell you about HF exposure and it's treatment. However the authors, Honeywell, sell more HF than anyone else, and they kinda gloss over some of the nastier aspects.

For instance: the deaths seem not to have happened; accidental or especially chronic occupational exposure apparently does not cause skeletal fluorosis (anything from "scratchy joints" to crippling hunchback arthritis-like symptoms); and cutting arms and legs off is called "primary excision" and is only briefly mentioned (on page 11) with only one reference (49).

Rust remover for toilet fixtures sometimes contain dilute hydrofluoric acid. The concentration is low enough it has the same warnings as any other product containing a strong acid. I've spilt a drop or two on my hands in the past with no negative effects.

Whenever hydrofluoric acid is mentioned in a forum like this there is always someone who has read about its method of interaction with bone after passing through the skin and they give the same hysterical warnings. They don't seem to really understand that the interaction is in the concentration. Seventy percent concentration is very dangerous. One tenth of one percent is at worst an irritant. But then that goes for any strong acid. Note the concentration before opening the bottle. Plan accordingly.

Another example glacial acetic acid can cause severe burns. Dilute acetic acid is nice in salad dressing.

Cheers,

Kelley

dangerous.

bottle.

Kelley,

I've haven't read about it but I'll NEVER forget the scream from the girl on the line where it was used in semiconductor etching at Mullards factory by the Totton roundabout back in the late sixties when she took off her glove and one finger stayed in it. That line was in 'bay 5' iirc and I was in EOD in 'bay 8' - a long way away. They were all supposed to do a pressure test on the gloves before putting them on - the presumption was she didn't and there was a pin prick.

AWEM

Fair point Kelley, and well made. I never meant this to be an hysterical, I-know-more-than-you thing (and hopefully it hasn't been taken that way), just a general warning for anyone who was unaware of the stuff. If in doubt, don't touch it:)

Peter

How do you seal the seam?

Peter and Peter.

Fair enough. I would agree there is no antidote to the effect of HF on human physiology but Peter N's post spoke of neutralise which is a different matter altogether. As a chemist for 26 years who has on occaision handled hydrofluoric acid I am irritated by, and possible over-react to, the misleading sort of response to dangerous chemicals typical of gutter press hysteria. Any such chemical can be handled safely given the right knowledge and suitable precautions, but to demonise it out of hand smacks of tabloid scare mongering.

Cliff Coggin.

Doesn't sounds as dangerous as DHMO...

Hmmm, took sometime for the penny to drop...

Joules

As far as I remember he rolled it and you couldn't even see a seam, I think it was multiple layers of the sheet.

I have several bit's that may be from hoses he made, one of them is like your average samco, cost a bomb, hose but has the reinforcing visible on the outside, the second bit actually looks like it was made from tape found at a slight angle round the former, it is spirally ridged. I know some he made were all shiny and were indistinguishble from Samco hoses.

So you roll it like a swiss roll around the former, then treat it (pressure and/or heat) and it bonds the layers?

Interesting. I'm a bit surprised this works, not because I've particular knowledge of silicon but just I though silicon tended to be pretty inert.

I just had a reply from one of the companies I mailed. They sell it in

50 cm wide rolls either on a polythene backing or on a fabric[reinforcement]. It sounded like making hoses is what it's intended for and a range of reinforcment materials are available, the most popular for intercooler hoses is polyester[the same as coolant hoses]. Probably find it's seriously expensive;-)

richard