Alternatives to welding

[Arthur Marshall]

When my boat was replated last year, they gritblasted all the old gunk off the sides and in the process blew a hole about four inches wide just below he waterline. This, it appeared, had been patched at some time with a car fibreglass repair kit.  As it certainly hasn't been done since I had the boat, it's been there for at least thirty years.  After some discussion at the yard, we decided not to replace it with more fibreglass...

[nb Innisfree]

4 hours ago, bizzard said:

 

Cellulose paint on top of oil based enamel would have reacted instantly and all pickled up, Around the other way, ok.

Yes I realised that a bit later when I went back into the garage. Never to be repeated, lesson learned. 

[MtB]

2 hours ago, roland elsdon said:

Could you weld the rivets in place?

 

No that would never work...

[Dr Bob]

There are two pack room temperature cured epoxies that will 'glue' a steel plate on a hull. They have been around for 20 years. Just as strong a welding as long as you grit blast first. Ford were gluing cars together in the 80's. Boatyards however are tuned to welding and so it continues. On problem with adhesives is that the bit glued on may not be electrically bonded to the main hull which could have corrosion implications.

[Chewbacka]

1 hour ago, Dr Bob said:

There are two pack room temperature cured epoxies that will 'glue' a steel plate on a hull. They have been around for 20 years. Just as strong a welding as long as you grit blast first. Ford were gluing cars together in the 80's. Boatyards however are tuned to welding and so it continues. On problem with adhesives is that the bit glued on may not be electrically bonded to the main hull which could have corrosion implications.

The big problem with adhesives and this is especially true when bonding glass is that when the joint is made it is fine and all the test parts will pass strength tests etc, but give it say 10 years and the bond can loose most of it's strength and come apart.  So it is essential that the whole bonding process is in a well controlled environment etc.  Not sure how many boat yards could guarantee that.

 

[Dr Bob]

7 hours ago, Chewbacka said:

The big problem with adhesives and this is especially true when bonding glass is that when the joint is made it is fine and all the test parts will pass strength tests etc, but give it say 10 years and the bond can loose most of it's strength and come apart.  So it is essential that the whole bonding process is in a well controlled environment etc.  Not sure how many boat yards could guarantee that.

 

Glass is not the easiest of substrates for adhesives. Steel however is easier and has chemical groups on the surface that epoxy sticks to. The adhesive bond is therefore far more durable. The glass to matrix bond is a weak point and this is how GRP laminates can fail, the water wicking up the interface. Steel is afar bettter bet. That said, you do need to control the conditions so a good surface by grit blasting to a standard ( not difficult), temp of 20-25C (only seasonal then unless a good paint shed) and dew point low enough (humidity).

[Jen-in-Wellies]

11 hours ago, roland elsdon said:

Could you weld the rivets in place?

Modern rivets are welded on. On old boats the rivets were glued on with glue made from superannuated towing horses. The change from horse towing to diesel engines meant that boat builders had to find a new way of fixing on rivets once the stock of dobbin glue had been exhausted.

Jen

Edited December 23, 2017 by Jen-in-Wellies

[Chas78]

Weetabix or any other serial for that matter left in a bowl overnight becomes a very good bond with the said bowl its almost as if they are one 

[Dr Bob]

2 hours ago, Dr Bob said:

Glass is not the easiest of substrates for adhesives. Steel however is easier and has chemical groups on the surface that epoxy sticks to. The adhesive bond is therefore far more durable. The glass to matrix bond is a weak point and this is how GRP laminates can fail, the water wicking up the interface. Steel is a far bettter bet. That said, you do need to control the conditions so a good surface by grit blasting to a standard ( not difficult), temp of 20-25C (only seasonal then unless a good paint shed) and dew point low enough (humidity).

Now that didnt work. I was trying to edit a typo in the quoted post. DUH!

Edited December 23, 2017 by Dr Bob

[jenevers]

12 hours ago, Arthur Marshall said:

When my boat was replated last year, they gritblasted all the old gunk off the sides and in the process blew a hole about four inches wide just below he waterline. This, it appeared, had been patched at some time with a car fibreglass repair kit.  As it certainly hasn't been done since I had the boat, it's been there for at least thirty years.  After some discussion at the yard, we decided not to replace it with more fibreglass...

Well there you go. Technology from 1987, good for 30 years. That’s why I raised the subject. Don’t suppose riveters thought that much about welding being a good idea. Don’t suppose welders think glueing is a good idea.

Edited December 23, 2017 by jenevers

[Chewbacka]

4 minutes ago, jenevers said:

Well there you go. Technology from 1987, good for 30 years. That’s why I raised the subject. Don’t suppose riveters thought that much about welding being a good idea. Don’t suppose welders think glueing is a good idea.

When adhesive works it's very good, but when it doesn't it can catastrophically fail without much warning.  The main reason for the difference is the prep and control of the bonding materials and process.  Not sure how many little boatyards have the discipline to get that right EVERY time.

[MtB]

25 minutes ago, Dr Bob said:

Now that didnt work. I was trying to edit a typo in the quoted post. DUH!

 

Lol we've all done that from time to time Dr Bob!

As we cannot delete our posts, the only way to save face is to actually edit the whole text of the offending duplicate post to say something like "changed my mind" or "posted in error". Whn doing this you can delete the text quoted of your previous post too. 

Then, only people who have done the same themselves will figure out what a numpty one is! And in reverse, you'll start seeing the odd post of mine like this

[Dr Bob]

12 minutes ago, jenevers said:

Well there you go. Technology from 1987, good for 30 years. That’s why I raised the subject. Don’t suppose riveters thought that much about welding being a good idea. Don’t suppose welders think glueing is a good idea.

I dont think the technology has changed much since 1987. The epoxies & polyesters were as good then as they are now. There have been a few attempts at making them more applicable over damp or oily surfaces but nothing seems better than it was then. The reverse has actually happened where the 'good' stuff in various adhesives and sealant has been banned so they can no longer be used. I would be very happy using the 1987 technology. It works. Maybe silicones are an area where progress has been made.

One area that has been significantly affected by restrictions in materials is the coatings industry where from the end of the 1980's, companies were forced to go looking for alternative solvents to get 'volatile organic content' (VOC) down - so replaced all the good organic solvents with ones that could be mixed with water. Lots of the formulations with high VOC that you could get in the 80's are thus replaced by inferior coatings that are more difficult to apply or just dont work as well. Progress? I guess so for the painters but for the rest of us....?

[MtB]

3 minutes ago, Dr Bob said:

I dont think the technology has changed much since 1987. The epoxies & polyesters were as good then as they are now. There have been a few attempts at making them more applicable over damp or oily surfaces but nothing seems better than it was then. The reverse has actually happened where the 'good' stuff in various adhesives and sealant has been banned so they can no longer be used. I would be very happy using the 1987 technology. It works. Maybe silicones are an area where progress has been made.

One area that has been significantly affected by restrictions in materials is the coatings industry where from the end of the 1980's, companies were forced to go looking for alternative solvents to get 'volatile organic content' (VOC) down - so replaced all the good organic solvents with ones that could be mixed with water. Lots of the formulations with high VOC that you could get in the 80's are thus replaced by inferior coatings that are more difficult to apply or just dont work as well. Progress? I guess so for the painters but for the rest of us....?

 

Looking at the bigger picture, why are VOCs in paints such a Bad THing? Are they one of the causes of the greenhouse effect or is it something else?

[Dr Bob]

20 minutes ago, Mike the Boilerman said:

 

Looking at the bigger picture, why are VOCs in paints such a Bad THing? Are they one of the causes of the greenhouse effect or is it something else?

I am actually not sure. I was tech manager of a coatings, adhesives and sealants team in the 80's but cant quite remember the details. At the time, refrigerants were being banned because of green house gas, but a lot of solvents were also banned because of toxicity. The drive was towards water based rather than solvent based coatings so likely a bit of both green house gas and safety.

[bizzard]

Very sticky with a good grip is ''Bondabean''. Bondabean can be used for sticking many things, from sticking stamps into albums, tiles to walls, busted false teeth, to even sticking motorbikes, aeroplanes and space craft together. Made by the likes of Heinz, C&B, HP ect and comes in large and small  tins.

[dmr]

2 hours ago, Dr Bob said:

I dont think the technology has changed much since 1987. The epoxies & polyesters were as good then as they are now. There have been a few attempts at making them more applicable over damp or oily surfaces but nothing seems better than it was then. The reverse has actually happened where the 'good' stuff in various adhesives and sealant has been banned so they can no longer be used. I would be very happy using the 1987 technology. It works. Maybe silicones are an area where progress has been made.

One area that has been significantly affected by restrictions in materials is the coatings industry where from the end of the 1980's, companies were forced to go looking for alternative solvents to get 'volatile organic content' (VOC) down - so replaced all the good organic solvents with ones that could be mixed with water. Lots of the formulations with high VOC that you could get in the 80's are thus replaced by inferior coatings that are more difficult to apply or just dont work as well. Progress? I guess so for the painters but for the rest of us....?

Can you explain a bit more, I am genuinely curious. I know that conventional paints use a solvent that evaporates as the paint dries, but you are inferring that epoxies also contain a solvent. I thought that epoxies consisted of two components which, if mixed in the correct ratio, underwent a chemical reaction to set as the two different molecules combined, so I don't see why any solvent is required, is it just to aid brushing? What happens if some of the solvent does not evaporate before the chemical bonding is complete????

...............Dave

[Dr Bob]

2 minutes ago, dmr said:

Can you explain a bit more, I am genuinely curious. I know that conventional paints use a solvent that evaporates as the paint dries, but you are inferring that epoxies also contain a solvent. I thought that epoxies consisted of two components which, if mixed in the correct ratio, underwent a chemical reaction to set as the two different molecules combined, so I don't see why any solvent is required, is it just to aid brushing? What happens if some of the solvent does not evaporate before the chemical bonding is complete????

...............Dave

Almost all paints use 'solvent' to assist in application (brushing, spraying etc) to get the right viscosity and to allow flow and bubble release once applied. Yes, all expoxy paints use a solvent. The epoxy base and hardener are just too viscous to spray or brush. From memory, we used circa 30% solvents in the modified epoxy paints we were making (specifically formulated to go on oily steel). At the start of our work we were using a blend of organic solvents but as the VOC regulations came, we had to switch to solvents that were miscible with water. For spraying it is standard practise to add more solvent if the grade used is not designed for spraying. So the answer is yes, solvent is added to aid in application.

It is vital to allow the solvent to evaporate otherwise it stays in the coating and stops the full properties develop in a twin pack system. For that reason, it is important to follow the manufacturers advice on coating thickness (too thick and solvent cant get out as easy) or temperature (too low and the solvent cant evaporate - and the chemical reaction of the 2 pack goes too slowly and doesnt get to full completion). Further - and relevant to us on narrowboats - is the immersion time, ie the time you have to leave it before putting it back in the water. This is to make sure the solvent gets out as is the overcoat time which again is all about solvent evaporation and the interaction between  the new solvent laden coat over the previous coat where you want most of the solvent out. All of this makes it important to ensure the temperature is high enough as solvent just wont come out at low temps. Personally I would never attempt painting unless it was over 15°C as almost no coatings are developed to be applied at temps below that.

The above is all relevant to paints which are applied as a thin film hence letting the solvent out. For sealants and adhesives, you cant use normal solvents as they would never evaporate. Epoxies are a good viscosity for adhesives so dont need to be any 'runnier'. Often they are thickened with fillers or thixatropes. Epoxy adhesives therefore tend to be just the two reactive parts. There is such a thing as reactive solvents - and polyester resin - used to make GRP (or fiberglass to the uninitiated)- is a good example. Here you dissolve an unsaturated polyester (which is a solid at room temp) in Styrene which is then a solvent. That is what you get when you buy 'resin'. When you bung in some peroxide (and cobalt accelerator) then this sets off a reaction combining the styrene with the unsaturated groups on the polyester - and hence cross linking to form the solid matrix we get in GRP. The styrene is both a reactant and a solvent - but you dont need to get rid of it as it reacts. If you see a 'high build' coating, ie where you are applying coats over one mm thick, then they may well be using reactive solvents in the blend (maybe as well as normal solvents) so solvent evaporation is not so critical.

Looking at the Material Safety data sheet (MSDS) usually tells you what is in the paint or sealant.

Hope that gives you some info.

[jenevers]

4 hours ago, Dr Bob said:

I dont think the technology has changed much since 1987. The epoxies & polyesters were as good then as they are now. There have been a few attempts at making them more applicable over damp or oily surfaces but nothing seems better than it was then. The reverse has actually happened where the 'good' stuff in various adhesives and sealant has been banned 

I bow to your superior knowledge but must say that I’m amazed that adhesive technology hasn’t changed much in 30 years! When you think of the almost logarithmic growth of technology in other fields (mobile phones, internet etc), its hard to believe.

[WotEver]

4 hours ago, Mike the Boilerman said:

 

Looking at the bigger picture, why are VOCs in paints such a Bad THing? Are they one of the causes of the greenhouse effect or is it something else?

Something else

VOCs really love ozone and happily combine with it to create O2. Very nice for all living things to breathe but not so good for the UV protection that the ozone layer provides. 

You recall all the talks about ‘holes in the ozone layer’?  That was put down to VOCs in paints, aerosol propellants (so now they use butane!), refrigerants, etc etc. 

[Dr Bob]

27 minutes ago, jenevers said:

I bow to your superior knowledge but must say that I’m amazed that adhesive technology hasn’t changed much in 30 years! When you think of the almost logarithmic growth of technology in other fields (mobile phones, internet etc), its hard to believe.

Yes, it is surprising. Chemistry which is the basis of coatings etc hasnt really advanced much. We know so much about how it works, there is no real progress. Look at industrial chemistry - Petrochems plants, Refineries - the only real progress is the plants can be built bigger so when 200Kte/a (200,000tes/year) was 'world scale' 40 years ago it is now 2Mte/a (10 times bigger). Bigger furnaces, Biggger compressors, bigger distillation columns - all due to engineering advancing. The basic chemistry in use is the same. Maybe the odd catalyst is now better for Polyethylene/Polypropylene or say Methanol, but I cant think of one new process in the last 20 years. We still cant find an adhesive to stick polyethylene together properly despite people looking for 50 years.

Advances have been made in the nano area - with the much smaller stuff allowing us to do things we couldnt do before viz electronic chips etc. Nano sized materials have changed things. Biochemical/Pharma applications have moved on a great pace with some wonderful inventions for medicine but not general chemistry - unless you can think of something we didnt have in the late 80's?

I am struggling to think of where we have different things today. We had the technology to stick cars and aeroplanes together in the 80s. We had the coatings. We had all the stuff that is used in construction. Also, it is not for the want of trying. There are many people over the last 30 years doing chemistry and industrial chemistry research.

[dmr]

1 hour ago, jenevers said:

I bow to your superior knowledge but must say that I’m amazed that adhesive technology hasn’t changed much in 30 years! When you think of the almost logarithmic growth of technology in other fields (mobile phones, internet etc), its hard to believe.

Not even sure that core technology has really moved on that much. Mobile phones are all about packing a lot more electronics into a much smaller space with a lot more software, but the actual semiconductors and software concepts have not really changed much in the last 40 years. We have got some new battery chemistry and some new "electro-chemistry" in the displays. The www was a sort of breakthrough, as was the concept of the mobile phone "cell". Internal combustion engines are much the same, everything is about optimising what we already have and squeezing every last bit of efficiency out of it.

Everything is smaller, lighter, faster, but not that much is really fundamentally new?

..............Dave

[WotEver]

2 hours ago, dmr said:

Everything is smaller, lighter, faster, but not that much is really fundamentally new?

Even radiotherapy cancer treatments remain fundamentally the same. The machines are now far more advanced and can shape the waves and focus them far better than in the 80’s with much improved outcomes. Developments currently in the pipeline will (I’m told) vastly improve the treatment over the next 20 years but the fundamental technology hasn’t really changed at all. 

[cereal tiller]

8 minutes ago, WotEver said:

Even radiotherapy cancer treatments remain fundamentally the same. The machines are now far more advanced and can shape the waves and focus them far better than in the 80’s with much improved outcomes. Developments currently in the pipeline will (I’m told) vastly improve the treatment over the next 20 years but the fundamental technology hasn’t really changed at all. 

Had Radio Therapy in 2005, All Computed Actuated then .Face Mask on and Lay back and think of England.The Staff just Clamp you Down and Scuttle off the Control Room and Press one Button.no "Egor " Stuff at all !

[Dr Bob]

3 hours ago, dmr said:

 

Everything is smaller, lighter, faster, but not that much is really fundamentally new?

..............Dave

Ecofans?