I seek a more durable plastic material 2

[marfotd]

We have a cooking machine that cooks al kind of food, like
sauce, rice, scrambled eggs etc. To keep the inner stainless steel wall free of the burned food residu, we use ptfe(eriflon) scrapers (l=162mm,b=50mm,d=20) The scrapers
are pressed against the wall with a spring construction.
The problem is that the scrapers have to be replaced once
a month, because the material is wornout. There are 9 scrapers in the machine and is a expensive part of maintenance. We use steam as heatsource(2.5bar=180degreesC)
and can also cool the food to 10degr.C(icewater 3'C) So there is a great variation in temperature.
The material must not be harmfull for consumption and resistant against moisture.
The plastic cant be to hard, because it is undesirable that
the steel wall wears(in case off metal parts in the food)
I hope someone has a suggestion for my problem, because no one ive contacted has(including plastic engineers)
Thanks

 

[insideman]

Not sure, but worth a try is ultra high molecular weight polyethylene. Fantastic wear resistance.

 

[wmv]

Your application poses a few problems, you need a high temperature material with superior wear resistance, yet not to hard and above all else FDA approved for food contact.

You have only a few options, Teflon (PTFE) with a 10% polimide filler, this would be twice the cost of your unfilled material but may increase life by 3 or 4 times. The second would be a Ryton with heavy Teflon filler (30-40%) for softness you require. This would be the ideal material, however I'm not 100% sure it's FDA approved. Check<

http://www.resinnet.com>

Phillips Chem and confirm.

This is an excellent bearing material it may be soft enough and will increase life several times. Good Luck

 

[rhc]

Polyimide is great but deteriorates quickly (cracking)in very hot water.
Forget UHMWPE at 180 deg C
We have experience with scraper blades that are required to work for years at and above 200 deg.C, but are unfamiliar with USA FDA regulations.
I hope by now you have solved your problem but if not maybe we can help.

 

[GFSeals]

There are other fills for PTFE that can enhance its steam resistance. Willastonite and some other minerals do not alter its FDA aproval or increase its abrasion to mating materials but can greatly affect its gemoetric stability.

 

[Soupcat]

Are there cost restrictions?, if not you should consider Ticona's Fortron (PPS). Unreinforced PPS possesses a comparably medium heat resistance. Adding glass fibres and glass fibre/mineral mixtures allow the heat distortion temperature and the strength of Fortron to be attained. The following properties give Fortron its high performance polymer characteristics:- operating temperatures up to 240°C, temporarily up to 270°C inherently flame retardant (UL 94:V-0, partly 5 VA), very good chemical and oxidation resistance,high hardness and rigidity, very low water absorption and good creep resistance even at high temperatures. Another option could be a filled grade of Acetal

 

[nbucska]

I suggest using wood -- I would prefer some fibers in my
food to all of the different plastics -- and design it
so it is easy to change.





<nbucska@pcperipherals.com>

 

[rhc]

Hi nbucska I agree with your sentiment but it woodn't do because you wood end up with a lot more fibre than you wood bargain! Try hitting wood with high pressure steam at 180 deg. C.
As an engineering excercise my choice would be to use a fully cross-linked high molecular (novalac) phenolic resin binder because it is one of the lowest water soluble substances known and retains excellent mechanical & wear properties well above above 200 deg. C.
Choice of re-enforcement would be treated carbon fibre to compliment the phenolic resin and provide unrivalled wear while acting as an efficient scraper without chewing into the inner s/s wall.
marfotd would only have to change his scrapers every 2 or 3 years instead of every month even if he used them 24/7 at 200 deg. C. Is it FDA approved? probably not. How much % material would wear into the product. go figure.

 

[patprimmer]

Soupcat
From my reading of the initial question, the only problem with PTFE is the cost of replacement vs life value, for money

UHMWPE is definately out due to the 180 deg C

Acetal is definitely out at 180 deg C (thats about its ideal processing temp),and especially in water as it is quite sensitive to hydrolysis and has a limited life in water at 80 deg C

Ryton is fairly rigid and might not scrape clean, depending on the design of the scraper and the cooker. Also, I don't think it is food approved, but I could be wrong on that

Fortron will perform quite similarly to Rytron as a scraper, but I think it is food approved, but once again, not really sure.


Nylon 4.6 (Stanyl) might be worth a try as it has really good bearing properties to nearly 300 deg C, but there are question marks re hydrolysis at 180 deg c and food aproval.

Aromatic nylons such as Trogamid or those offered by Emserwerk, Hulls or DuPont(I forget their trade names)might also be considered.

I expect that after much research, you will find PTFE is best. Fillers might help, but might not. Friction and wear is a funny beast and laboratory tests results do not often represent the situation in the field.

LNP and DSM have some very good data on wear and friction in plastics
Regards
pat

 

[nbucska]

Cooking sauce ( with unspecified ingredients) etc. at 180 C
may be acceptable
BUT
I think the company intending to use the process have the burden of proof that it won't generate dangerous byproductsa.

I think, using this kind of unprooven processes should
be a crime !
<nbucska@pcperipherals.com>

 

[patprimmer]

Inhaleing the smoke from burnt tobacco is still not a crime despite the proven potentially deadly results. Work that one out.
I am not sure of the surface temperatures on a hot BBQ or on a grill, so I cannot say that cooking at 180 deg C is unproven.
The question did not relate to the issue of cooking at 180 deg C, but to the value for money re fear rate vs cost of a scraper at up to 180 deg C in the presence of water, with the specification that it must be safe for consumption.
As far as I can see the only material to meet all criteria is PTFE, despite it's cost and short life. It is also not clear if the 180 deg C refers to cooking or cleaning temperatures Regards
pat

 

[rhc]

Look at marfotd's original spec:&quot;To keep the inner stainless steel wall free of the burned food residu, we use ptfe(eriflon) scrapers (l=162mm,b=50mm,d=20) The scrapers
are pressed against the wall with a spring construction.&quot;
The key word here is burned. PTFE is great stuff but in this application it is used as a scraper ie hard up against the cooking face. the 180 deg. C is only a rough average and you must expect various parts of the cooking surface will well and truly exceed 180 deg. C by a significant amount. (that word burned!) When PTFE gets hot enough it will decompose into nasties. Once a month they replace with a new set of scrapers so all that PTFE burned or not burned goes downstream into the process!

 

[rhc]

As I recall Phenolics decompose around 300 deg C. Regardless of their excellent mechanical properties at elevated temperatures, when burnt, they give off a characteristic &quot;Bakelite odour&quot;. The barest trace (I believe parts per billion)is easily detectable by smell or taste and that characteristic alone automatically precludes that group of plastics from selection.

 

[patprimmer]

I agree that PTFE gives off nasties in the form of fluorine gas at about 400 deg C, but it appears to me the heat source for cooking is steam at 180 deg C. I can't explain the statement burned food at that temp. I presumed he meant overcooked not carbonised.
I can't see how the food can get hotter than the heat source without being subjected to ridulous levels of shear.
At 180 deg C PTFE is safe. It has been used as a non stick coating for cookware since the 1960's, with no apparent detrimental effects.
It is soft and therefore a poor scraper of hard contaminants, but despite my recomendations of possible alternatives, I still cannot think of an alternative material that will be pliable, food safe and will withstand steam at 180 deg C, if that is what is really required Regards
pat

 

[Soupcat]

Patprimmer,
A glass filled acetal has a vicat softening temperature of around 160 deg C and is pliable'ish', I had thought the 180 deg C at source would have meant that the plastic would have been subjected to a lesser temp. Agree with you on the hydrolysis sensitivity though. If material rigidy is going to be a problem then PTFE is probably the only option.

Kieran

http://www.moulddesigner.com

 

[nbucska]

Phenolic, fluorine, fiberglass... what a hard choice... <nbucska@pcperipherals.com>

 

[buut]

ptfe filled with polyimide or ekonol do have Food approvals and they can do the job better than virgin PTFE.
Another option is to use a special material like Zedex 100 from Wolf in germany.
See

http://www.plasticbearings.com

best regards,
Ernst
ernst.Buter@home.nl

 

[NicSacco]

What you need is rulon 123, 1000 times the wear resistance of teflon, fda approved and not overly expensive. Try searching Saint-Gobain on google and you will be set

 

[nbucska]

I don't know what YOU need, but what WE need is a law,
which criminalizes the processing of food by untried, unproven means, just to increase the profit margin.

<nbucska@pcperipherals.com>

 

[koen]

Dear Marfotd,

I don' t now the exact construction u are having,
But there is a new kind of PTFE that is called TFM.
This material has some properties which are simulair like pTFE glassfilled. If you could send me more details i could find out if this will solve your problem.