Making Foam Seats - UPDATE

[oldbutnotslow]

I have for several years used foam seats in my car and have found them to be excellent for providing 'real' support whilst on track. However I have had varying success with the seats and over a period of time the foam always starts to shrink thus requiring them to be either made aftesh or 'toped up'

 

I have spoken to several people in the past who were supposed to know about the best method to use and the ratio of the two parts ie 1:1 by weight or by volume and have been told by some that it was by weight and others by voilume and not much else.

 

However as I have learned there is actually a bit more to it than just this if you want to get the thing right.

 

Ive recently poured a new seat for YBNS with a very poor result. It started off OK but within 2 days it had shrunk considerably resulting in the Duct Tape cover resembling the skin of a 3 week old apple

 

Whilst the chemicals are not that expensive they are not cheap either!

 

So, faced with a useless base I managed to speak to a technical man at the foam manufacturers who opened my eyes to a number of things that I was doing wrong.

 

I got him to send me some information on common problems which I now detail below:-

 

COMMON PROBLEMS ASSOCIATED WITH HAND OR BATCH MIXING TWO PART POLYURETHANE FOAM

 

 

The following is a collection of several of the most common problems arising from the mixing of two part Polyurethane systems. Whilst it is not always possible to achieve absolutely perfect foaming conditions, a repeatable satisfactory result can be arrived at by bearing the following points in mind.

 

INCORRECT TEMPERATURES

 

Polyurethane chemicals are temperature sensitive in that the viscosities of the two components vary significantly in the range 5-30°C and the reaction rate is dramatically affected. Chemicals below 15°C will be significantly more viscous than above, and this will translate into a much greater difficulty in mixing the components sufficiently well. Temperatures much above 22°C will speed up the reaction enough to make foaming difficult, the recommended temperature range will be given in the technical information, hut will probably be l8 to 22C.

 

INCORRECT RATIO

 

Two component Polyurethane systems require that the materials are mixed in the correct ratio, usually expressed in the terms of weight, and given in the technical information. An excess of the polyol component will give a soft feeling foam, often light and fine celled in appearance, which will probably shrink in time, an excess of Isocyanate will give a hard feeling foam often dark and coarse celled, which will be more brittle and less resilient than foam made at the correct ratio. Weighing is much easier to do accurately than measuring by volume, but it is vitally important that what is actually mixed together is the correct ratio, rather than what is initially measured out. This means that where one component is poured into another, allowance must be made for the amount left m the container, which it was poured from, it is much better to weigh one component directly into the other on the scales.

 

CONTAMINATION

 

Both components are affected by atmospheric moisture. The Isocyanate component reacts slowly to give a hard plastic product and Carbon Dioxide gas. the hard product is the “skin” which forms on Isocvanate left open to atmosphere. The Polyol component absorbs water vapour very quickly, hut shows no visible difference, however, when the two components are mixed the water reacts with the Isocyanate component to give Carbon Dioxide gas and a plastic called urea. The Carbon Dioxide gas blows the foam to give a lower density than specified for the system, and the Isocyanate which has reacted with the water is not available for reaction with the Polyol Component, resulting in a foam which is under density and short of Isocyanate. both of which will give unstable foam.

 

Various other contaminants will give difficulties, for example, oils or excessive wax type release agents will cause cellular collapse, and foam which is reacted against insufficiently cured fibreglass will have a weak ‘furry” layer caused by the free styrene in the surface of the fibreglass.

 

CORRECT DENSITY

 

Most Polyurethane systems are not designed to be allowed to react totally “free rise”, ie. Usually they should be subject to a certain amount of restraint to give the required density throughout the foam and particularly to avoid the “stretching” of the foam cells which can occur in free rise foams. The required density will vary from system to system. and for any given system a relatively small thin , moulding with a lot of surface area will require a much higher density than a large compact moulding. Generally once the required amount for a particular moulding has been decided upon, U should be adhered to, with only slight variations to accommodate extremes of ambient temperature.

 

EFFICIENT MIXING

 

Generally the more efficient and forceful the mixing the better the quality of foam. A guideline to the time available will be given in the technical data, the cream time is the time from the start of mixing to the point at which the foam starts to react and rise. This time will vary depending on temperatures, efficiency of mixing and the total amount mixed, but it is best to have mixed the foam and poured it into the cavity to be filled before it is rising significantly. It is best to mix air into the Polyol component before mixing the two components together, and as a guideline if the mixing method in use can significantly aerate the Polyol component in the mixing time to be used to mix the two components, then it is sufficient, anything less will riot give the best results. A propeller type agitator in a high speed air or electric drill is usually suitable for quantities up to 20kg.

 

POURING METHOD

 

As soon as the foam is sufficiently well mixed it should be poured into the cavity to be tilled. obviously this must be done as quickly as possible. ensuring that all foam is poured before any significant amount of rise. It is also vitally important that the foam is placed in the correct position in the cavity, the ideal scenario is for the liquid foam to start rising from the bottom of the cavity, pushing the displaced air in front of it towards a breather point at the highest point in the cavity. Whilst it is not often possible to realise this ideal completely it is important to ensure that the foam can push all of the air out of’ the cavity through~ suitably sited breathers.

---

 

So to recap

1. Its temperature sensitive so you need to have an ambient temperature of around 20 degrees which my garage certainly was not!

2. Both parts of the mix need to be at room temperature for a couple of hours before you start to mix.

3. The CORRECT ratio is 1:1.13 by weight or 1:1 by volume. Even a small variation will cause problems (pouring one part into another will leave some chemical behind and thu will affecting the ratio!

4. Part A (the light coloured part) should be mixed on its own for a couple of minutes in order to get air into the mix BEFORE pouring it into part B for mixing.

5. The two parts need to me mixed 'mechanically' at 2000 rpm for 10 to 15 seconds and not just whisked around with a stick as I have been doing!

6. You have about 25 to 30 seconds from the start of mixing Parts A & B ( known as cream time ) after which the reaction will start.

7. You will therefore have about 15 seconds after the initial mix to pour the stuff into the bag and about another 1 1/2 minutes max to get the person sat in place.

8. Don’t try to pour too large a quantity at one time. It is possible to pour the whole seat (back and the base in one go) if you are experienced but I find it easier to do them as two parts.

9. Once the tins are open they have a shelf life of only 4 months so buy only a size of tin that you need as it wont keep.

10. The two chemicals need to be stored in a reasonably warm place ie between 10 and 30 degrees.

 

Happy seat making

 

 

Grant Taylor

OBNS Motorsport

www.obns.co.uk

 

😬 183 BHP of Black and 'Stone Chip' excitement. 😬

 

 

 

Edited by - oldbutnotslow on 8 Feb 2007 12:49:36

 

Edited by - oldbutnotslow on 16 Feb 2007 21:41:02

[GregP]

Slight hi-jack (sorry OBNS) but does anybody know how to remove set seat foam from aluminium? The previous owner of my car 'missed' when pouring his seat and there is a significant quantity of the stuff set rock hard behind the passenger seat which I'd really like to remove.

 

Thanks

 

Greg

[MartinWoodham]

busy at work then Grant?!!

 

good writeup - wish I'd known that a couple of years ago....

 

Greg, a sharp knife is all I can recommend, it might be worth tapping Grant's contact to find out what a good solvent would be

 

Martin

Aero'd Roadsports B with a garage slowly filling up with upgrade parts

[Dickie Normuss]

Cue the story of an engineer, a canoe and some stairs 😬

 

VX HPC - Loud and proud here

Seek forgiveness, not permission.

Rules are for the interpretation of wise men and the obedience of fools.

[swifta]

Thanks Grant ,

I was just about to try and make my seat but will wait for warmer weather.This info was just what I needed.

[Graham Perry]

Thanks for this as it reminds me that I need to make a couple of minor repairs to mine and to give it a fresh coat of black GRP resin before the summer.

[ECR]

Whilst the ratios given are undoubtedly correct for the foam system used, different raw material suppliers may well use slightly different ratios. Check the paperwork supplied with the cans.

[Jason Plato]

Weighing is much easier to do accurately than measuring by volume, but it is vitally important that what is actually mixed together is the correct ratio, rather than what is initially measured out. This means that where one component is poured into another, allowance must be made for the amount left m the container, which it was poured from, it is much better to weigh one component directly into the other on the scales.

---

 

exactly what I do .

 

I weigh out about 250g of each part directly into a cut down platic 2L milk carton, this results in about 3 (@500g) pours for the typical seat base.

[jonhill]

Cue the story of an engineer, a canoe and some stairs 😬

 

That'll be this then...

 

----------------------------------------------------------

 

A friend of mine once built a canoe. He spent a long time on it and it was a work of art.

 

Almost the final phase was to fill both ends with polyureathane expanding foam.

 

He duly ordered the bits from Mr Glasplies (an excellent purveyor of all things fibreglass) and it arrived in two packs covered with appropriately dire warnings about expansion ratios and some very good notes on how to use it.

 

Unfortunately he had a degree, worse still two of them. One was in Chemistry, so the instructions got thrown away and the other in something mathematical because in a few minutes he was merrily calculating the volume of his craft to many decimal places and the guidelines got binned as well.

 

He propped the canoe up on one end, got a huge tin, carefully measured the calculated amounts of glop, mixed them and quickly poured the mixture in the end of the canoe (The two pack expands very rapidly).

 

I arrived as he was completing this and I looked in to see the end chamber over half full of something Cawdors Witches would have been proud of. Two thing occurred to me, one was the label which said in big letters "Caution - expansion ratio 50:1" (or something similar) and the other that the now empty tins said "approximately enough for 20 small craft."

 

Any comment was drowned out by a sea of yellow brown foam suddenly pouring out of the middle of the canoe and the end of the canoe bursting open. My friend screamed and leapt at his pride and joy which was knocked to the ground as he started trying to bale handfuls of this stuff out with his hands.

 

Knocking the craft over allowed the still liquid and not yet fully expanded foam to flow to the other end of the canoe where it expanded and shattered that end as well.

 

A few seconds later and we had a canoe with two exploded ends, a mountain of solid foam about 4ft high growing out of the middle, and a chemist firmly embedded up to his armpits in it.

 

At this stage he discovered the reaction was exothermic and his hands and arms were getting very hot indeed. Running about in small circles in a confined space while glued to the remains of a fairly large canoe proved ineffective so he resorted to screaming a bit instead.

 

Fortunately a Kukri was to hand so I attacked the foam around his hands with some enthusiasm. The process was hindered by the noise he was making and the fact he was trying to escape while still attached to the canoe.

 

Eventually I managed to hack out a lump of foam still including most of his arms and hands. Unfortunately my tears of laughter were not helping as they accelerated the foam setting.

 

Seeking medical help was obviously out of the question, the embarrassment of having to explain his occupation (Chief Research Chemist at a major petrochemical organisation) would simply never have been lived down. Several hours and much acrimony later we had removed sufficient foam (and much hair) to allow him to move again.

 

However he still looked something like a failed audition for Quasimodo with red burns on his arms and expanded blobs of foam sticking everywhere. My comment that the scalding simple made the hairs the foam was sticking to come out easier was not met with the enthusiasm I felt it deserved.

 

I forgot to add that in retrospect rather unwisely he had set out to do this deed in the hallway of his house (the only place he later explained with sufficient headroom for the canoe - achieved by poking it up the stairwell.

 

Having extricated him we now were faced with the problem of a canoe construction kit embedded in a still gurgling block of foam which was now irrevocably bonded to the hall and stairs carpet as well as several banister rails and quite a lot of wallpaper.

 

At this point his wife and her mother came back from shopping......

 

Oh yes - and he had been wearing the pullover Mum in law had knitted him for his birthday the week before.

 

----------------------------------------------------

 

[oldbutnotslow]

Well we managed not to fill the garage as post!!! 😬 😬 😬

 

YBNS and I have just made a base and back using the correct method.

 

What a difference ❗

 

Very solid with good structure. The foam density is much better than all previous efforts. Very strong.

 

We got the garage up to 22 degrees and followed the instructions to a tee.

 

The foam previously got hot but nothing like this pour. This time it got up to 41 degrees. well that was about the colour of his nether regions so he said. Not quite but nearly smokin

 

Very satisfied.

 

 

Grant Taylor

OBNS Motorsport

www.obns.co.uk

 

😬 183 BHP of Black and 'Stone Chip' excitement. 😬

[Graham Perry]

OBNS, don't forget you can fill any holes (there are usually a few) by mixing small amounts of mixture and dripping it into them. Its very satisfting watching the hole slowly fill up. You can then use a surform or aggressive rasp to get to the required shape

 

Edited by - Graham Perry on 17 Feb 2007 08:18:35

[Jason Plato]

😬

[millsn]

Doing this industrially, the foam can reach in excess of 65 degs C (up to 100) when poured in bulk say 2ft square box of it. So do take care. I would also recommend that if you attempt to restrict the foam you should wear goggles as eye protection.

 

NB: If you're ever pouring large (25kg) amounts in one hit:

If you restict the foam expansion and then it finds a small way out, the result can be quite dramatic. People where I work have failed to take these precautions and wound up in hospital. I would avoid resticting its expansion path if at all possible. We use breather hoses of 32mm OD which do the trick if you need a guide.

 

For a seat, two small pours is safer than one big one.

[TopQ1967]

I read this topic with great interest.

 

What kind of sacks are you using as mould to sit in?

How do you get the vents in without leakage?

 

 

Cheers,

 

Quirin

 

[Graham Perry]

I used an large garden refuse sack which was a bit bigger and stronger than the normal refuge sacks

[susser]

Grant

"We got the garage up to 22 degrees "

What a delight it must be to walk into a garage at room temperature, pick up room temperature spanners, work on a room temperature car ,,,,,,,,,,,,etc etc.

I bet you even go in the garage in slippers an all.

Susser

( garage at slightly below ambient temperature)

[Roger Ford]

Grant: Did you get your materials from CFS? I assume the ration 1:1.13 is for A:B? That is, more (by weight) of part B than part A? Can you confirm - I'll be making (yet another) one on Friday and intend to weight the quantities this time.

[Neil A]

I used a survival bag from millets to make mine.

 

Always remember to take a leak before you start. All the heat around the boys make you want to go 😬

 

Fellas, smoke me a kipper, I'll be blatting for breakfast.

[oldbutnotslow]

Hi Roger Sorry I did not get back earlier. I had to do some work.

Yep CFS

yes A1:1.113 B

I cut the end from 2 refuse sacks as this opens out the gusset I then cut one bag in half and place this over the full bag open end and stick down using Tessa Tape just to be 'safe'.

A single bag is just too short to be 'safe' for a seat base of a seat back.

The open end of the bag acts as the vent. Don’t be tempted to put any holes anywhere else because as Millsan says it will bust out and it will stick to whatever it touches including you FOR EVER!

As you were going to do this on Friday I assume that you have made them now. How did you go on?

 

 

Grant Taylor

OBNS Motorsport

www.obns.co.uk

 

😬 183 BHP of Black and 'Stone Chip' excitement. 😬

[Roger Ford]

Yup, done mine now. The mechanical mixing certainly seems to have given a more stable and even-textured foam. Also heated the garage up to 20-22 degrees C, though the car was still at 16.5, even sitting in the garage all night.

 

I use wheelie bin liners, which are long, but do taper towards the bottom which is a bit of a pain.

 

We'll have to see if this one lasts any better than previous attempts without shrinking.

[oldbutnotslow]

Good Man Roger

 

Grant Taylor

OBNS Motorsport

www.obns.co.uk

 

😬 183 BHP of Black and 'Stone Chip' excitement. 😬

[Martin S.]

This info is just what I need and will be making a seat when the warmer wheather arrives. Given that the CFS supplis website says that 1Kg will make 1 Cu ft I presume the 2Kg pack will be enough for a seat base and back?

 

Class 4 Zetec ....and suffering withdrawal symptons

[MartinWoodham]

Martin, I've made a couple of these now and the 2kg pack is enough. It's well worth making in 2 parts - base and back, plus they're easier to handle afterwards especially if you swap the seat in and out.

 

Martin

supersported ex-Roadsports B

[Martin S.]

Thanks Martin

[Z3MCJez]

Well, I'm going to finally have a go at this this weekend (assuming that it's warm enough for me to actually be able to heat the garage to a reasonable temperature). I have bought survival bags for pouring the mixture into, and have hopefully read everything I can on the matter. So, before I go ahead and pour, any last words of advice?

 

Jez

 

Build Photos

 

Edited by - Z3MCJez on 31 Mar 2009 18:08:50