Emgineering Glues

[DSBParticipant @dsb]

When using two part glues such as epoxy resins and single part glues such as Cyanoacrylate (Super Glue) what should the clearence be between the parts? Obviously these clearences are fairly critical if you are to get the best bond possible, and a quick search with Google provided no information. The parts I am working with are typically in the range of 0.125 to 0.750 inches diameter and the metals are mainly steel and aluminium.

 

Assistance would be appreciated. Thanks

[DSBParticipant @dsb]

Questions regarding the use of Engineering Adhesives

[Ian AbbottParticipant @ianabbott31222]

Perhaps the nature of the surface is more important, but epoxies shouldn’t be squeezed tight and the surface roughened as a key.  Super Glue needs perfectly mating surfaces.

Also, Super Glue is anaerobic curing, hence the exclusion of air, epoxy  is a catalytic action, so curing time is governed by the ambient temperature.  Slower curing epoxy is usually stronger.

 

Ian 

[mgjParticipant @mgj]

With respect – I would ring the Tech Services Dept of the makers of your glue.

 

There are all sorts of superglues, some being gap filling (thick non slump)  some being “ordinary” and some being high speed ultra thin types.  -with different peel and bond characteristics. 

 

In the same sense, some glues will out perform others, and others are optimised for all specific applications. The loctite type are one batch of chemicals, (isocyanates?)the cyanoacrylates another which depend on moisture for setting and all sorts. 3M make the 2 pack spray instants. There are shock resistant epoxies, chemical resistant, water resistant (important with epoxies which bond readily to water after setting) and one for every other specialist application.

 

If the application is at all critical, choose a good industruial make, like Devcon or 3M or CIBA Geigy, and talk to the maker before using.Tell him what you want to stick tegether and describe the loads and service conditions, and you’ll get a good answer. 

 

Far better than we can give.

 

 

[MikeDParticipant @miked]

The Loctite website is very good for their range of products – 603 and 222 cover most of my needs. Google “Loctite nnn datasheet”

 

MikeD 

[mgjParticipant @mgj]

If you want to see what just Araldite (CIBA Geigy) makes, just click on the link at the top of the page. Educational!

[DSBParticipant @dsb]

The genesis of this question came from a quote in Harold Hall’s book Model Engineers’ Workshop Projects, where in Chapter 12, Dial Test Indicator Accessories he states on the drawing for the Flexible Joint Clamping Nut, “Use adhesive to fix arm”. This is typical of many of the instructions relating to the use of workshop adhesives in the Workshop Practice Series.

As I was busy building the project, I asked myself, if I am going to use a two part epoxy resin adhesive, which I already had, what were the ideal dimensions for the two components. As I thought about the question, I also thought, what would be the difference if I were to use Super Glue instead?

Thanks to the excellent advice above, I have now summarized the answer to the questions posed with regard to the use of two part epoxy resin adhesives such as Araldite and the Cyanoacrylate (Super Glue and Loctite) type products.

For Model Engineers the idea of KISS (Keep It Simple Stupid) comes to mind so I am going to limit my conclusions to three products from each manufacturer’s range of adhesive.

First the gaps for a good joint turn out to be not as big a difference as first I thought, but there are some differences when you examine the Technical Data Sheets on the Huntsmen and Henkel web sites as these corporations are the manufacturers of Araldite and Loctite respectively. Both sites offer good technical information, some of which was summarized in the posts above but without context. So here is the full information.

Epoxy Resins – Araldite

Various types (formulas) of Araldite exist which can be broken down into broad categories of general purpose, fast setting, gap filling, and special purpose. Here I will discuss only the first three. I have taken three products from the Araldite range. I have concluded that if you have time, want the greatest flexibility, lowest cost, and easiest assembly use general purpose epoxy resin as your first choice. For the Araldite range this is type 2011. This adhesive is a two part adhesive which is usually more economical than Cyanoacrylate. (mileage may vary based on local conditions).

 

For all of  these  two part adhesives, mix equal parts of each of the two components.

The good thing about the two part epoxy resins ,is that they will stick virtually all metals, wood and most plastics and bond metals to wood and plastics, which makes it ideal for model engineering purposes.

The data sheet states “A layer of adhesive 0.05 to 0.10 mm thick (a 0.002 to 0.004″ gap) will normally impart the greatest lap shear strength to the joint.” therefore for cylindrical objects the smaller diameter should be 0.10 to 0.20 mm smaller than the receiving socket. That is 0.004 to 0.008″. This dimension does not change for quick setting epoxy resins such as Araldite 2010-1 , however when using  gap filling Araldite 2015 which is a paste large gaps of several mil could be filled / glued.

For flat surfaces ensure that there is a gap between the parts and do not over clamp and squeeze out the adhesive from between the parts. Small center pop marks on one component will probably raise the surfaces enough to ensure there is a good bond.

For the best results, three other points are worthy of note. The mating components should be rough, not smooth and if they are smooth they should be abraded with rough wet and dry abrasive paper. Secondly, prior to applying the adhesive, the parts should be degreased and cleaned. Finally the parts should be supported if necessary until  the adhesive has set. Curing time for the normal and gap filling adhesives, to the point of handling, is usually a couple of hours at room temperature (20 degrees C) and about 24 hours to full strength, the fast setting adhesive is handle-able in a matter of 5 to 10 minutes and fully cured in about one to two hours under similar conditions.

Cyanoacrylate (Loctite and  SuperGlue)

Various types (formulas) of Cyanoacrylate exist which can be broken down mainly by usage as they all tend to be fairly fast setting.  Again I have taken three products from the Loctite range. The major categories that I looked at were the thread locking, retainer and superglue products often used in the workshop. These were Loctite 222 a low strength thread locking compound, Loctite 603 a cylindrical retaining compound which could be used in the application that was the originally described above, and finally Loctite 406 which is a fast bonding superglue.

Note that all these Loctite products a are designed for use with metal. TThis product performs best in thin bond gaps (0.05 mm).superglue will bond other products as well.

Loctite provide data sheets for each of their products which are generally very good. Since the uses of the thread and cylindrical retainer compounds are task specific, it is very important to read the  data sheets.  Go to Loctite Product Technical Data Sheets and type in the product number.

For Loctite 222, gaps of 0.05 to 0.2 mm are described but at the larger gap size 50% of the retaining strength is lost, although for some applications this may not be  an issue for thread locking.

For the Loctite 603 cylindrical retainer the gap on the data sheet is specified as 0.05 mm to 0.15 mm gap, with no impact on strength. A gap of 0.25 mm (0.010″) can be accommodated with a 40% loss in strength. <

[DSBParticipant @dsb]

Additional post truncated from last post.

Note that aluminium and zinc dichromate do not have as strong a bond as steel.

Loctite 222 and Loctite 603 cure speed can be increased by using an activator compound supplied by Loctite.

For the Loctite 406 the sheet specifically states “This product performs best in thin bond gaps (0.05 mm).” The data sheet states that the setting time for steel is 15 to 30 seconds and for aluminium it is 2 to 10 seconds. It should be noted that this gives precious little time for positioning, so the position must be determined by mechanical devices such as pegs, detent pins or slots.

For the best results, prior to applying the adhesive, the parts should be degreased and cleaned.

 

 

Edited By DSB on 09/09/2009 11:20:45

[mgjParticipant @mgj]

DSB thanks for that.

 

It does just make the point that while all glues stick, it is a huge subject, and while using x or y may not matter in many cases, in others the choice can make a big difference.

[ANDY CAWLEYParticipant @andycawley24921]

There is a good article on the subject in the current issue of Model Engineers Workshop.

[Author]

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