CLTE of Nylon vs Aluminium

So why do you want to use something with a higher CLTE?

RHABE has given great advice as uysual.

milo

Dear RHABE,

Good advice received but the Acrylic(Plexiglas) is not suitable for this application though it has the better dimensional stability and less water absorbsion because the application of this component is in spectroscopy where it need the fully opaque, black and non reflective, non glossy surface. The service temperature of the part is almost more then 200 deg C. so i prefer to select the nylon 66 as its HDT is 275 deg C. The water absorbsion does not effect much because of the service temp is very high. continues drying is going on during utilisation of the component.

Dear Paras Desai, I would never think of using Nylon 66 at near 200°C! There is the transition temperature with drastic changes in mechanical data: elastic modulus, CTE, anything else. You are right that at continuous high temperature the moisture problem is not as big as near room temperature. But another obstacle will be the brittleness of this amterial at low water conten. And: there is nothing like a "fully opaque, black and non reflective, non glossy surface". Depending on the wavelengths you intend to use the blackening will be very difficult. Plastics - also if black for our eye - are transparent in the near IR. Optical black is suitable if coated above aluminum, brass, bronze and other metals. If on plastics I have seen only limited temperature range up to 110°C. If you want to stay with plastic then widen your scope of possible candidates to PI, PAI and PEEK. And search for the very best optical black. RHABE

Dear RHABE,

Staying with plastic has the reason that it has the low cost as well as low wastage and getting finished component by only one process, rather then doing machining on aluminium and then powder coating will increase the lead time and decrease the productivity as well as it also increase the cost and also the secondary process of black powder coating.

As you suggested for PEEK or PI(High performance Plastics), i have selected PPA (HTN- Du pont make) after subsequent discussion with Material Manufacturer but because of the commercial availability i has to go with nylon66 which has slightly inferior functional property then HTN.

I has made one prototype of the component from the Rod of Nylon66 (unfilled) and tested for its functional requirement it works well but under high temperature, when we tried to dismantle the component from its mounting position we found that it is very tight and difficult to remove. During assembly it was easily assembled but during removal it found tight because it expands under high temperature.

If i found some solution for the CTE, then it is good otherwise we have to add some clearance for thermal expansion in assembly if it is possible. If addition of clearance is not possible then i have only choice to search the solution for reducing CTE.

Dear RHABE,

Staying with plastic has the reason that it has the low cost as well as low wastage and getting finished component by only one process, rather then doing machining on aluminium and then powder coating will increase the lead time and decrease the productivity as well as it also increase the cost and also the secondary process of black powder coating.

As you suggested for PEEK or PI(High performance Plastics), i have selected PPA (HTN- Du pont make) after subsequent discussion with Material Manufacturer but because of the commercial availability i has to go with nylon66 which has slightly inferior functional property then HTN.

I has made one prototype of the component from the Rod of Nylon66 (unfilled) and tested for its functional requirement it works well but under high temperature, when we tried to dismantle the component from its mounting position we found that it is very tight and difficult to remove. During assembly it was easily assembled but during removal it found tight because it expands under high temperature.

If i found some solution for the CTE, then it is good otherwise we have to add some clearance for thermal expansion in assembly if it is possible. If addition of clearance is not possible then i have only choice to search the solution for reducing CTE.

Dear RHABE,

As you previously told that calculation of the CTE by composition will not give the realistic result because the part geometry and distribution of the filler / fiberglass will also effect the CTE.

You are absolutely true but do you have some idea about any thumb rule by which we can determine approximate value of percentage of the filler so that the CTE will be approximately near to Al's CTE. we don't want the exact CTE of Al in Nylon. If it will be near to Al's CTE then it will be fine for our application.

Dear Milo,

As you asked, why i want to use some thing with higher CLTE. then listen, i don't want to use something with higher CLTE, Higher CLTE is the obstacle for using something which is better cost effective, easy to fabricate with minimum wastage and that is why i am searching some solution that will reduce the CLTE of Nylon.

Sticking with the existing one, just only for some obstacles, is not the engineers' attitude. we have to solve the problem for some betterment, to get the better quality, better product, cost effective product. Continues change is the fact of the life. If our forefathers did not accept this philosophy, then we all might be still living in stone age only.

If you don't have the solution, then please don't post anything just to increase your number of posts. I don't like the persons with negative attitude, like who are not ready to accept the change. Perhaps you might be the best in posting the answer like 'Black hole in wifes wardrobe? '. but all the engineering problem is not like the 'Black hole in wifes wardrobe..........'.

Dear Paris, not a negative attitude at all. honest attempt to clarify the question.

I was puzzled by your words "The CLTE(Co-efficient of Liniar Thermal Expansion) of Nylon is much higher then the Aluminium, I need to use Nylon as a replacement of Aluminium in spectroscopic application."

That did not make sense to me. Sounded backwards from the logic and my personal experience. Especially as the Baird and ARL optical emission spectrometers in my chem lab used machined aluminum to mount the optical components.

Your further posts about trying to reduce cost of components from machined powder coated aluminum by going with Nylon make it clear what you are trying to do. But the stability of Nylon over the long run, and at the 200 degrees that you mention remains a concern. If the application is short lived, Nylon which is cheaper in the short run, may be the best economic solution. But if the instrument is to be long lived, warranty costs for replacing nylon in the long run will need to be considered vs the savings in the short run. I wouldn't think that "Reputation" would be a factor in the engineering determination, but it certainly ought to be in the business decision. MAking things "Better" needs to be better, and not just "cheaper."

Not all "negativity" is "against change;" sometimes one tries to help people understand that taking actions they propose may not be in their best interest. "Protect the customer is the first priority." Sometimes The clarity of the posted problem statement is insufficient to be clearly understood. Hence the suitability of follow up questions to try to better elucidate the issue.

We thank you for your counsel about posts nevertheless. Some posts are about having fun with appreciative colleagues. Some are about helping people so that they can become appreciative colleagues. Some posts try to protect people from doing harm to themselves or others . And some posts just teach.

peace.

milo

Dear Milo,

Sorry for using some harsh words, i should understand that your dought might be because of some incomplete information provided by me in my question.

Dear Milo,

As you told that for the long run it is not good to convert the Aluminium to Nylon because it effect the reputation.

You are true but here the case is different because the component is assembled with the lamp and it is an embedded part so to replace the lamp, customer has to replace this part also. we are providing this part as a spare with our machine and then also frequently customer is asking for the same part regularly.

During all the replacement we or customer is wasting the aluminium as the aluminium part is absolutely perfect so it is also the requirement of the part to match the service life with its assembly component.

Thanks and sorry for my previous communication. it was my mistake that i could not understand your kind affort.

Makes perfect sense to match life of both components, if both have to be replaced at the same time. I am thinking that you have not been able to redesign so that only the lamp needs to be changed,; probably because the alignment is so crucial or assembly so difficult that the simultaneous unitize approach is the best solution. Thats a difficult tradeoff.

No harm, no foul on the comments; It is pretty easy to interpret almost anything as a "punk question" without context. I look forward to seeing your contributions on this forum in the future.

milo

Hi Paras Desai,

nobody (?) is making good electrical, mechanical lampholders or similar from Nylon.

That is not really sound.

Have a look at either the well non plastics used for multi-pin electrical connectors or for Torlon. This little bit of extra cost will give you a big benefit!

RHABE

Dear RHABE,

Thanks for suggesting me the good material. (Torlon). I searched the website of the manufacturer of the Torlon i.e. SOLVAY ADVANCE POLYMERS. and also study its data sheets of different grades. It's CTE is also very near to Aluminium's CTE. Aluminium has 23 ppm/C and Torlon has 31 ppm/C. Instead of using Nylon with 120 ppm/C, Torlon is better choice as it also fulfill my other requirements like HDT needs more then 250 deg C.

Thanks for giving good idea and suggestion.

Hi,

I would try the same percentage as is used in glass reinforced epoxi that is used as printed cirvuit boards.

RHABE