[kverges]

I am planning to bond the steel roll cage base plates to my track car chassis and am researching methacrylate adhesives (which I suspect is waht was used). Does anyone know exactly what was used and any technical data on its suitability with a steel to aluminum substrate?

Thanks

 

[Mr. Oz]

Mighty putty. Sorry, couldn't resist..

 

[LARRY]

This might help...


Lotus Bonds with Aluminum

By Kermit Whitfield, Senior Associate Editor Kermit's Bio Write Kermit


If aluminum-intensive cars are ever to become more than an occasional curiosity, automakers may have to give up their weld shops. At least that's the conclusion you could draw after talking with the people at Lotus Engineering (Hethel, England). Lotus has been building cars with aluminum chassis for many years, but none of them are welded: they are held together with screws and adhesives. When Lotus first introduced the method on the low-volume Elise in 1996, company leaders were worried about market acceptance for what is essentially a glued-together car, but the technique proved so successful (over 23,000 cars produced with no reported failures) that it has become the basis of a new higher volume venture that may help to bring aluminum-intensive vehicles more into the mainstream. The new project, which uses Lotus' Versatile Vehicle Architecture (see AD&P February 2004, "Lotus' Versatile Venture"), tweaks the lessons learned on the Elise for volume production, but remains true to the fundamental concept: to get the most out of aluminum structures you must design for the material, not treat it like a steel substitute.

Bond, Adhesive Bond. First and foremost, that means not welding it. Why? "The yield strength of aluminum goes down by half once its welded," explains Richard Rackham, vehicle architect at Lotus. So, getting the same strength in a welded aluminum chassis as in a bonded unit requires doubling the amount of material used; since aluminum is usually chosen for its light weight, that dilutes its key benefit. Another big disadvantage of welding aluminum is that stresses are localized along a point or a line, which can lead to material fatigue. Stresses are distributed over a wide part-mating when bonding is used. To gain the full merits of using adhesive, Lotus had to come up with ways to optimize its properties. For example, after determining that the optimum bond gap between parts is 0.2 mm, the question became how to maintain that gap uniformly over the bonded surface. The answer: Lotus designed tiny protrusions, or "pips" on the parts that held them exactly 0.2 mm apart.

Aluminum bonding methods

The shape of things to come? Lotus is bringing the aluminum bonding methods it pioneered with the Elise chassis to higher volume production. The first of the new vehicles are scheduled to be produced at the end of 2005.

To fabricate the main chassis components Lotus chose a process well-suited to aluminum: extrusion. Chassis supplier Norsk Hydro ASA (Oslo, Norway) extrudes the closed-box parts out of 6000 series aluminum and bonds them to folded sheets of recycled 3000 series. Rackham says that one reason extrusions were chosen is because they can be inexpensively produced (he estimates the cost of a die at about $5,000), which helps to offset the higher material costs of aluminum. Another is that they can be formed into complex shapes that serve multiple purposes and help keep parts count down. The proof: the entire Elise chassis consists of only 27 different extrusions.

Higher Volume. The challenge Lotus now faces is translating the aluminum production methods for an essentially hand-made $40,000 sports car to affordable vehicles that can be mass-produced. It's current initiative, which is being conducted for an unnamed automaker, looks to build sub-$30,000 vehicles in the 40,000 to 50,000 annual unit range. To do that, Lotus is making some changes. According to Kerry Osborne, principal engineer, the hand-applied flow drill screws that are currently used to knit the Elise chassis together are being replaced by self-piercing rivets which can be shot more quickly, though they require application tools that generate at least five tons of pressure. But perhaps the biggest change is in the bonding. Realizing that no mass-production operation can afford the Elise's 50-minute curing time (nor would it wish to incur the expense of multiple ovens), Lotus is replacing the heat-cured single part epoxy adhesive used on the sports car, which required temperatures of 180ºC, with one that will cure in the lower heat of the paint oven. (Both adhesives are sourced from Dow Automotive [Auburn Hills, MI].) The savings in process time garnered by these changes could be enough to peak the interest of volume automakers and get them to consider bonded aluminum chassis as a viable alternative for niche vehicle production.

 

[Aedo]

This post in the thread - http://www.lotustalk.com/forums/f23...ed-non-authorized-chassis-repair-ideas-69001/ has a room temperature curing adhesive that is equivalent to the chassis adhesive.

 

[Bane]

Larry, that's very interesting.

I wonder if Lotus is going to go with an automated dispensing process with UV curing for the adhesives in the new VVA chassis.

 

[kestrel74]

Yep, you asked for it...

 

[Goose]

Yep, I think Dow Automotive is the current supplier. I remember the old S1 Elise video in which the original supplier was Ciba Polymers. I'll bet the Dow stuff is cheaper/better...

 

[TimMullen]

The adhesive that Lotus uses doesn't really matter for repairs, etc.

The Elise chassis is bonded then BAKED in an oven where the adhesive heat cures. You can't replicate that process unless you disassemble everything from the chassis and load it back into an oven..

"Room Temperature" curing adhesives is what you are after.

 

[frostylocks]

try red loctite. that air cures.
google it, but it's used in gunsmithing (potentially hi pressure situations).

 

[Flying Scotsman]

Chassis Bonding and Fastening

A key component in chassis rigidity is the Flow Drilling Screws which are made by a company called EJOT in partnership with the company I work for ( Weber Screwdriving Systems ). The fasteners are applied to the two aluminum extrusions with bonding material sandwiched between, and using high rpm and high thrust ( both controlled by computer) and usually fixtured or as an end-effector on a robot. During installation the fastener is applied on the top surface of the materials being joined, it initially heats (locally) then allows the aluminum to "flow" through the mateials in question creating a small threaded hole and boss behind the joint which the FDS fills and is seated to a specific torque. This is 'air and water tight' and contracts & constricts around the fastener as it cools to give a hugely strong and rigid clamping of the materials being bonded. All of this happens in 1.5 seconds. This then allows the extrusions and adhesive to be cured without movement or flex. Lightweight, rigid, and super strong. We also do the Lamborghini Gallardo, Opel / Vauxhall, and the Audi range of vehicles and several other automotive products. Only now are automotive manufacturers looking at this process for US cars.

All the best

Jim
:wave:

 

[xtn]

The adhesive that Lotus uses doesn't really matter for repairs, etc.

The Elise chassis is bonded then BAKED in an oven where the adhesive heat cures. You can't replicate that process unless you disassemble everything from the chassis and load it back into an oven..

"Room Temperature" curing adhesives is what you are after.

It has been mentioned that while Lotus does cure the adhesive with heat, it will cure at room temperature to the same strength. It will just take longer to do so.

xtn

 

[Shine]

I am planning to bond the steel roll cage base plates to my track car chassis and am researching methacrylate adhesives (which I suspect is waht was used). Does anyone know exactly what was used and any technical data on its suitability with a steel to aluminum substrate?

Thanks

You can probably find the info you're looking for in this thread:

http://www.lotustalk.com/forums/f23...ed-non-authorized-chassis-repair-ideas-69001/

 

[DeanG]

I recall reading that they use sikaflex Sika Corporation | United States Important considerations were peel strength and flexibility to handle thermal loads...

To fix a keel leak in our sailboat I let down the 1,100 lead keel cleaned up the surfaces, smeared a couple of tubes of sitkaflex in the gap then lowered the boat back down onto so it rested on the keel. All that remained was to clean up what oozed out of the gap, wait for it to cure and torque up the keel bolts. No leaks.

 

[aschen]

No Idea what lotus uses and I am no expert on the subject matter, but I have had experience using a company called Masterbond for structural epoxies. If you call them up they will hook you up with one of their PHD guys that will talk your ear off about your application. It is company confidential so I cant go into any details, but I have tested some of their adhesives bond strengths in shear and tension with results. Be prepared to spend a couple hundred bucks though. I don't think they are unique to the high end adhesive market but I know there products are trustworthy....

 

[kverges]

Thanks for all the input. I have been researching different adhesives and room temp curing is necessary and all the adhesives I have looked at have exothermic curing reactions that begin at ordinary room temps. The bonding guide from ITW Plexus indicates that epoxies have worse fatigue life than methacrylates, and if so I think I want the latter.

http://www.itwplexus.com/Guide_To_Bonding.pdf

After looking at data sheets for Araldite, Hysol, ITW Plexus, and ASI, it seems the best option may be the Hysol H4800:

Methacrylate Adhesive
Description
Dexter Hysol H4800 is a highly thixotropic, two component, room temperature curing, 10:1 mix ratio methacrylate adhesive system. H4800 is formulated to provide a longer open time for manufacturers seeking between 20-25 minutes to correctly fixture parts. This adhesive forms resilient bonds and maintains its strength over a wide range of temperatures. H4800 is suitable for bonding a variety of substrates with a minimum of surface preparation.

Recommended Substrates: PVC, polycarbonate, acrylic, aluminum, epoxy coated metal, ABS, stainless steel and FRP

Features
Non-sagging gaps filled to 1 inch Superior impact and peel strength
Little or no surface preparation Offers excellent tolerance to off-ratio mixing
Rapid room temperature cure100% reactive Excellent environmental resistance

Typical Cured Properties
Tensile Strength (psi) 3,400 – 3,600 ASTM D 638
Tensile Elongation (%) 25 - 35 ASTM D 638
Peel Strength (pli) 60 ASTM D 3167
Tensile Lap Shear @ 77oF 4,500 – 4,700 ASTM D 1002
Tensile Lap Shear @ 180oF 2,800 – 3,000 ASTM D 1002
Shore D Hardness 75 – 80
Bondline Thickness .005 – 1.00

Typical Uncured Properties
Part A Part B Mixed
Open [email protected] 77oF - - 20 – 25 minutes
Fixture Time @ 180oF - - 45 – 55 minutes
Color Cream Yellow Light Yellow
Viscosity, cps 60,000 – 70,000 50,000 – 60,000 -
Brookfield HBT Spdl 6 @ 10 rpm Spdl 6 @ 10rpm -
Specific Gravity 1.03 .951 .02
Ponds per gallon 8.58 8.83 8.60
Mix Ratio
By Weight 9.71 - -
By Volume 10 1 -

Performance




Handling and Application
Mixing: It is highly recommended that either meter mix equipment or cartridges with static mix nozzles be used to properly ratio and dispense the adhesive. For hand mixing, combine Part A and Part B in the correct ratio and mix thoroughly. Once mixed, H4800 should achieve a uniform color. This is important! Heat buildup during and after mixing is normal. To reduce the likelihood of exothermic reaction or excessive heat buildup, mix less than 100 grams at a time. Mixing smaller amounts will minimize heat buildup.

Applying: Bonding surfaces should be clean, dry, and free of contamination. Extensive surface preparation is not required for H4800, and good bonds can be formed on most substrates after a solvent wipe. To assure maximum bond strength, surfaces must be mated within the adhesive's open time. Use enough material to completely fill the joint when parts are clamped.

Curing: Parts should remain undisturbed during the interval of time between the material's open time and
fixture time. After the fixture time is achieved the material has reached handling strength. Temperature below 55°F will slow the cure; above 85°F will accelerate cure rate.

Clean Up: It is important to clean up excess adhesive from work area and application equipment before it
hardens. Denatured alcohol and many common industrial solvents are suitable for removing uncured adhesive. Hysol H4800 is flammable. Keep containers tightly closed after use. Keep away from heat, sparks, and open flames.

Storage
Hysol adhesives should be stored in a cool, dry place when not used for a long period of time. The shelf life for H4800 is one year from date of manufacture when stored at 40oF and six months when stored at room temperature or 77oF. Exposure above room temperature will reduce shelf life.

Packaging
100 gram clip packs490ml EPS cartridges 5 Gallon Pails 55 Gallon Drums


DISCLAIMER: The information supplied in this document is for guidance only and should not be construed as a warranty. All implied warranties are expressly disclaimed. Including without limitation any warranty of merchantability and fitness for use: All users of the materials are responsible for assuring that it is suitable for their needs, environment and use. All data is subject to change as Dexter deems appropriate.

Users should review the Material Safety Data Sheet (MSDS) and product label for the material to determine possible health hazards, appropriate engineering controls and precautions to be observed in using the material. Copies of the MSDS and label are available upon request

 

[Cthulhu]

According to the service manual, most of the chemicals they use have Dow Chemical numbers. Anodised aluminum (e.g. chassis and components) use Betaseal 1701 (Lotus p/n A082B6281F) or Betamate E2400 (Lotus p/n A082B8415V).

Here be link:

For windshield adhesive:

Betaseal 1701 (300ml Tube) [A082B6281F] - €36.32 : Elise Shop, Performance parts for your Lotus Elise

Umm. Betamate E2400 is the red stuff on the chassis, not sure where you can buy it.

I'll bet that Dow Chemical could sell you a big bucket of it for cheap, although I don't know what the minimum quantity is. Group buy?

BETASEAL
BETAMATE


Oh, and I believe the adhesives are urethanes, not acrylates.

Edit:

You probably want Betamate E2400, it's a two component adhesive w/ high tensile strength, permenantly elastic bonds. It must be clamped withing 5 minutes. They say it requires an airgun to mix it and generate a good bead... but I bet a pointy stick will work just as well...

 

[Kellog]

Hi All,
Just to clarify and provide some corrections - the adhesive used to bond the Elise chassis is a toughened single part epoxy adhesive. It comes in single tubes and at room temp is an extremely viscous semi-solid paste. Normally it needs to be heated to around 60C to reduce the viscosity and enable it to be dispensed. Dispensing can be achieved manually with a simple sealant gun, but during production, it is dispensed using a robot arm. To cure the adhesive it needs to be heated to a minimum of 120C and ideally to 180C where it is cured for 30mins (over 2hrs at 120C). So as was correctly stated above, the whole chassis needs to be put in the oven and cooked - so trying to use this adhesive as a repair aid is not going to be easy though not impossible if you consider using appropriate jigging and some heater blankets.

Originally this adhesive was produced by Ciba Specialty Chemicals (subsequently Vantico and then Huntsman) but in the Ciba days the automotive grade adhesives were sold to Gurit Essex which was part owned by Dow. Latterly Dow took over the adhesives totally and they are now produced by Dow Automotive. The original adhesive was called XB5315 but new versions were sold under the name XD4600 and the adhesive has changed again but without a bit of seaching I cannot remember what it is now called.

With regards to the claim that methacrylate adhesives are superior to epoxies, I would take this with a pinch of salt. Remember ITW are selling these adhesives so of course they will hype them up and it is very dangerous to make sweeping statements about adhesive families. There may well be better or worse epoxies than the methacrylates but it really depends what you are comparing with. Remember Lotus and Hydro Aluminium spent many years developing their chassis system and a lot of adhesives were considered and discarded during that process.

There are probably a lot of adhesives (acrylic, methacrylate and polyurethane based) that will be suitable for your application but please if at all possible remember to get your surface preparation right. Don't just take the manufacturer's claims too literally and not clean at all. The best adhesive in the world will not bond to its best performance on a dirty or ill-prepared surface.

If you want any other assistance I would suggest that you have a look at www.adhesivestoolkit.com

 

[eurosport]

Wow, nice 1st post, Kellog! ^^^ :bow:

Thanks for the detailed info!

 

[perryeyges]

I recall reading that they use sikaflex Sika Corporation | United States Important considerations were peel strength and flexibility to handle thermal loads...

To fix a keel leak in our sailboat I let down the 1,100 lead keel cleaned up the surfaces, smeared a couple of tubes of sitkaflex in the gap then lowered the boat back down onto so it rested on the keel. All that remained was to clean up what oozed out of the gap, wait for it to cure and torque up the keel bolts. No leaks.

I believe that the FRP panels are secured to the Aluminum tub with Sikaflex 1A. I have been "building" my carbon rockers with the suff. It is very workable and takes a few days or so to reach a full cure at ambient temps