Phil Read Posted November 8, 2020 Report Share Posted November 8, 2020 I have used structural adhesives in the past to fasten alluminium panels on Land Rovers together rather than rivet or spot weld. Has anyone any experience of using structural adhesives on steel, for example to bond the bottom edge of the rear apron to the lower closing panel on a TR3? Quote Link to post Share on other sites
BlueTR3A-5EKT Posted November 8, 2020 Report Share Posted November 8, 2020 No I have never used it on cars. It has wide industry usage though. Peter W 3M sponsored video on metal to metal bonding. https://www.youtube.com/watch?v=Ne8TJWl3RwI 3M sponsored video on corrosion protection https://www.youtube.com/watch?v=qAE5yzYFVPg Quote Link to post Share on other sites
stuart Posted November 8, 2020 Report Share Posted November 8, 2020 New 911`s have the roof bonded on and a lot of modern vehicles have sections bonded on now including most coaches. Its also widely used in aerospace as well. Done correctly and with the right adhesives it does work but prep is everything. Stuart. Quote Link to post Share on other sites
Tim T Posted November 8, 2020 Report Share Posted November 8, 2020 I used them a lot in the sign and exhibition industry. As Stuart says preparation is key, and also choosing the correct spec. VHB tapes are good as well and Adhesive Transfer Tapes. My only concern with adhesives is that you can't really test them without pulling them apart so never really know if they are as strong as they should be! 3M products although expensive always inspire confidence. Good luck Tim PS Also used by GKN in aerospace industry. Quote Link to post Share on other sites
RogerH Posted November 8, 2020 Report Share Posted November 8, 2020 (edited) 13 minutes ago, Tim T said: My only concern with adhesives is that you can't really test them without pulling them apart so never really know if they are as strong as they should be! 3M products although expensive always inspire confidence. Good luck Tim PS Also used by GKN in aerospace industry. Hi Tim, that is exactly what they do in aerospace. Do many test pieces with laid down prep and then pull them apart. If there is an undoubted good join then it is used. Lots and lots of trial and practice. I'm sure they do the same in the auto industry but they are always a couple of steps behind aero Don't use 'BlueTak' Roger Edited November 8, 2020 by RogerH Quote Link to post Share on other sites
Waldi Posted November 8, 2020 Report Share Posted November 8, 2020 The type of load also plays a role; a bond that can be “pealed open” by the force (starting on one side of the bond) is not a good application I feel. Roger will know more precise. Waldi Quote Link to post Share on other sites
RogerH Posted November 8, 2020 Report Share Posted November 8, 2020 11 minutes ago, Waldi said: The type of load also plays a role; a bond that can be “pealed open” by the force (starting on one side of the bond) is not a good application I feel. Roger will know more precise. Waldi Hi Wadli, quite right. That is called peel strength. This is basically the tensile strength of the adhesive. IT is usually lower than its shear strength. Where sheets are pulled apart along their length this is their shear plane and the adhesive works well. Virtually all aerospace adhesive binds are using the adhesive in their shear plane. That is why aircraft fuselages can be so easily 'glued' together just like an Airfix kit. Roger Quote Link to post Share on other sites
Bfg Posted November 8, 2020 Report Share Posted November 8, 2020 (edited) I had understood peel strength was really quite different to tensile strength insomuch as it referred to its ability to adhere to a particular material & surface prep., and at a particular angle, whereas tensile strength is measured free-of / away from the contact surface and the effect that has on its elasticity. For example ; A block of rubber bonded to an inflexible surface ..when placed under a tensile load would neck-in more the further it is away from the contact surface and so elasticity very much comes into it. Whereas at or near the bond face the rubber is being constrained to a fixed surface area and cannot neck-in. Then, under tension, the edges are pulled in shear more than the centre, and so the rubber block peels at those edges. Naturally the shape of the rubber block is very influential.. A rectangular block having corners (edges may peel first) further away from it centre than a cylindrical block would (of the same cross-sectional area). A very common application of structural adhesives used on cars and therefore steel is of course glass-fibre bridging paste. And one of the characteristics of polyester resins used in this paste is shrinkage. This is usually quoted to be around 2 - 3 % but if a 'hot mix' is used - then it can be several times more. Due to this shrinkage the material is trying to peel off as soon as it is curing. And most commonly failure occurs because it peels off / lifts around the edges. Once peeled off - the tensile strength of the detached bridging paste is immensely strong (which may be attributed to the glass fibres within it). Another very common use of bonding structurally to steel (car parts) is in the manufacture of engine mounts, whereby four engine mounts in good order will take the kinetic load of a car, van or boat engine being rolled over. Tyre manufacture likewise use steel bonded into their construction. So, in general I'd have to say that bonding to steel seems work reasonably well.! I guess in the context of the original post this is largely a matter of semantics, but there are lessons to be learnt insomuch as to choose an adhesive with very low shrinkage, choosing one with excellent adhesion to steel (Sikaflex for example have a primer specifically for steel, and another for aluminium, and yet another for glass, others for different plastics, and so forth), and also during application - that sharp corners (either inside or out) peel more easily than round edges. Further to the OP., Three of the great benefits of adhesives are ; the contact face can be spread relatively evenly over a greater surface area. Conversely a rivet or spot weld is a very localised fastening and even a continuous weld is only along an edge. Adhesives can also be used to great effect where the items to be joined are unsuitable for mechanical or weld type fastenings, such as castings and other brittle materials and/or very thin sections, small parts and sheet materials which might easily tear or be distorted where localised attachments are used. Rusted pin-holed steel that has been chemically etched or grit blasted can be a very good surface to adhere to. And then also ; the joined surfaces can be allowed to flex and move without damage. This is particularly useful for dissimilar materials, of different stiffness or even colour ..where differences in stretch might have a less rigid contact-edge or where heat-energy absorption causes thermal expansion of one part more than another. As and aside but as an illustration of where you might come across it ; I had the latter scenario on the coachroof windows of my boat. Those were tinted Lexan and the roof was white fibreglass. For a 2m length of window I needed to allow for 6mm of thermal expansion. I used Sikaflex 4mm deep x 25mm wide for the job (calculated to the ratings for withstanding offshore / ocean waves) ..whereas screwed windows very often leak and localised loads cause the edges of holes to crack. Car's have been using rubberized under-seal and panel seam-sealant for years. The compounds used successfully will give you a very good idea of what mastic sticks very well to steel. Pete. Edited November 8, 2020 by Bfg Quote Link to post Share on other sites
RogerH Posted November 8, 2020 Report Share Posted November 8, 2020 Hi Peter, wow !!! - I couldn't read all you wrote it is too near bedtime. I was trying to keep it simple. Peel strength is where you pull the edges apart - imagine you have two thin plate bonded together. Grab the ends of each plate and pull then apart. Two things may happen - 1, the adhesive will come away from the material 2, the adhesive stays with the material but the adhesive itself breaks down The first could be bad surface prep. The second could be a poor adhesive. This is quiet a severe test and not usually encountered in the real world but could happen. You can then go to the next stage and and try and pull apart say 1 SQ inch in a true tensile pull test. Each test gives some information on the bond. Roger Quote Link to post Share on other sites
Waldi Posted November 9, 2020 Report Share Posted November 9, 2020 Thank you Pete and Roger, As always there are some great resources on this forum! Waldi Quote Link to post Share on other sites
Phil Read Posted November 9, 2020 Author Report Share Posted November 9, 2020 Wow I didnt intend to start a scientific debait, just get an idea of whether it would be a good idea to use a bonding material rather than weld. I dont think there is much of a problem with tensile or shear stresses etc in bonding TR3 body panels together. It may be different if the car had an intergral body, however having had a chat with a body repair specialist over the weekend he pointed out that even vehciles with an intergral body have some bonded panels. I remember back in the 60s/70s Brazing was the prefered method for attaching body panels. I think I will give it a limited go. Quote Link to post Share on other sites
stuart Posted November 9, 2020 Report Share Posted November 9, 2020 2 minutes ago, Phil Read said: I remember back in the 60s/70s Brazing was the prefered method for attaching body panels. I think I will give it a limited go. Triumph used brazing in certain places on the shells (Well Mulliners who actually built the bodies) this was more to tack the shells together on the jig and then they could be spot welded to finish, even back in the 60`s brazing repairs were an MOT failure. Stuart. Quote Link to post Share on other sites
Phil Read Posted November 9, 2020 Author Report Share Posted November 9, 2020 2 minutes ago, stuart said: even back in the 60`s brazing repairs were an MOT failure. I think this was only true on parts that were structural eg chassis. Quote Link to post Share on other sites
stuart Posted November 9, 2020 Report Share Posted November 9, 2020 Just now, Phil Read said: I think this was only true on parts that were structural eg chassis. Nope sill repairs was a favourite. Stuart. Quote Link to post Share on other sites
RogerH Posted November 9, 2020 Report Share Posted November 9, 2020 Hi Phil, Bonded panels are not new but need to be thoroughly investigated and tested. On the TR2 - 6 although there is a chassis the body still twists and bends. The panels do crack etc etc. There are at least shear stresses along the bond line. Most of the hardware stores sell stuff like 'No Nails'. These will indeed bond sheet steel together but!! for how long and how well. The adhesives used in aerospace are not cheap and the prep may not be straight forward. But I would love to have my sills 'glued' in place. The air scoop lid for the heater on my 4A is a home made stainless affair. The hinge on the under side is adhesively bonded t the lid proper. It has stayed together for at least 14 years with no sign of it falling apart. But then it does lead a rather sedentary life. Roger Quote Link to post Share on other sites
Phil Read Posted November 9, 2020 Author Report Share Posted November 9, 2020 I am just going to try it on the lower lip where the lower filler panel meets the bottom of the Apron. If it comes apart in time its an easy area to repair. Quote Link to post Share on other sites
stuart Posted November 9, 2020 Report Share Posted November 9, 2020 1 hour ago, Phil Read said: I am just going to try it on the lower lip where the lower filler panel meets the bottom of the Apron. If it comes apart in time its an easy area to repair. Nice easy place to spot weld Stuart. Quote Link to post Share on other sites
stillp Posted November 9, 2020 Report Share Posted November 9, 2020 From the online MOT tester's manual: 10. Acceptable methods of repair Repairs to structural components must be properly carried out and appear to be as strong as the original structure. This requires the use of suitable materials and any plating or welding extends to a sound part of a load-bearing member. You can only pass spot welded repairs if the original panel was spot welded and the original panel or section has been removed. Stitch or plug welding can be used instead of spot welding. In all other circumstances, patch repairs must be continuously seam welded. Some vehicle manufacturers have recommended repair methods that use MIG brazing, a combination of adhesive bonding and riveting, or amalgamations of these with other joining methods. Such repairs are therefore acceptable unless they are clearly inadequate. 11. Unacceptable methods of repair You cannot accept the following bonding processes for repairs to load-bearing members: gas brazing soldering adhesive bonding fibre reinforcement body filler If you cannot tell which the repair method, you should accept the repair and tell the vehicle presenter. Quote Link to post Share on other sites
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