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RE: [Gauge0] Epoxies

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  • Brian Lewis
    Hi Peter, I have not heard of Timebond - does it string? Regards Brian Lewis Tel: +44 1 275 852 027 Fax: +44 1 275 810 555 ... From: Peter Dobson
    Message 1 of 14 , Oct 1, 2000
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      Hi Peter,

      I have not heard of 'Timebond' - does it string?

      Regards

      Brian Lewis
      Tel: +44 1 275 852 027
      Fax: +44 1 275 810 555


      -----Original Message-----
      From: Peter Dobson [mailto:lner@...]
      Sent: 30 September 2000 00:23
      To: Gauge0@egroups.com
      Subject: Re: [Gauge0] Epoxies

      Hi all

      I do not use epoxy for fixing anything to anything...except when
      making
      split axles.

      Don't you dare ask about split axles.... my current project uses the
      damned
      things 'cos that's what the customer wanted!!!!! but I ended up
      having to
      make a new one else I couldn't get the motor out of the chassis.

      The blasted things ( axles) were an interference fit with the wheels
      so once
      quartered and fixed in position they weren't coming off. Hacksaws are
      useful
      tho'.

      Back to glue or whatever...If I have to ( or choose to) fix items
      like
      smokebox doors, toolboxes, waterfillers/overflow domes then I use
      Evostick
      Timebond which is a thixotropic ( non drip) contact adhesive -
      although I
      usually join the items to be fixed whilst the glue is still wet.

      With carriages that have aluminium roofs and floors then these are
      also
      fixed with the Evostick.

      Peter Dobson


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    • Peter Dobson
      Brian No...at least not anything like the ordinary stuff. Peter
      Message 2 of 14 , Oct 1, 2000
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        Brian

        No...at least not anything like the ordinary stuff.

        Peter
      • Bob Alderman
        Gavin My guess as to what may be happening in these low strength solder joints that the structure of the solder alloy develops massive crystals and the joint
        Message 3 of 14 , Oct 1, 2000
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          Gavin
          My guess as to what may be happening in these low strength solder joints
          that the structure of the solder alloy develops massive crystals and the
          joint fails along these crystal boundaries. I have noticed that there is a
          certain "brittleness" with a low melt solder joint. A sharp knock can undo
          them. Anyone got access to a metallurgical lab and we could check?
          As to the epoxies in aerospace, you should see the surface preparation that
          goes into the joints, degreasing, abrading, pre-treatment and goodness knows
          what else. These joints are also "designed" for their performance and are
          not two ad hoc surfaces and materials being pressed together as we may have.
          Generally a good bonded joint works best in shear, that is the two surfaces
          trying to slide one over the other. The maximum area of the bond is
          employed. If the joint is subjected to tension acting across the bond then
          it will begin to tear apart. One of the tests in an aerospace joint is a
          check on its peel strength. But all this academic as we rarely have dynamic
          joints, simply wanting one part to remain in place on another!
          I will come back to a point I made in an earlier reply that I think that
          often too little of the adhesive and hardener is mixed together to get the
          full properties of the adhesive. The greater the proportions mixed the
          smaller the error in the correct proportions of the mix. It is easier to mix
          when you have a reasonable quantity on the palette.
          Also perhaps insufficient attention is paid to the cleaning of the two
          surfaces to be bonded. Whitemetal castings come with a mould release
          compound on them. In its simplest form this can be talcum powder, or it may
          be a silicone spray. The remains of this have to be removed or the adhesive
          won't be in contact with the base metal otherwise. Fingers can leave enough
          grease on a surface to wreck the bond. Warm soapy water can be an effective
          degreaser in the face of more sophisticated degreasers.
          Roughening the surface with a wire brush or wet & dry helps to key the bond.
          This increases the area to be bonded, all the minute ups and downs. The
          geometry of the roughening helps key the adhesive too.
          This also applies to use of cyano adhesives too.
          There blinded with science!
          Bob

          > -----Original Message-----
          > From: Gavin Eyre [mailto:gavin.Eyre@...]
          > Sent: 30 September 2000 22:22
          > To: Gauge0@egroups.com
          > Subject: [Gauge0] Re: RE:Epoxies
          >
          >
          > ......there is less chance of getting that unholy alloy of 145 and Low
          > Temp Solder that has absolutely no strength at all. (Can anyone
          > explain that too me?)
          >
          > However I remain perplexed as to why can the aerospace and automotive
          > companies make their high tech wonders using epoxies, yet when it
          > comes to brass and whitemetal these joints come undone at the least
          > provocation.
          >
          > Gavin Eyre
          > Gavin.Eyre@...
          >
          >
          >
          > To unsubscribe from this group, send an email to:
          > Gauge0-unsubscribe@egroups.com
          >
          >
          >
          >
        • Brian Lewis
          Now this is interesting and is worthy of debate. I have long held that you cannot keep dabbing away at any soldered joint. In an ideal world, the work will
          Message 4 of 14 , Oct 1, 2000
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            Now this is interesting and is worthy of debate. I have long held
            that you cannot keep 'dabbing away' at any soldered joint. In an
            ideal world, the work will be positioned, heated and soldered once
            only and left to cool.

            I had first hand experience of how repeatedly heated metal causes it
            to go crystalline, when I was involved in construction the MTR Island
            extension in Hong Kong. We were using Delmag D66-22 piling hammers
            hung on 80 tonne NCK Crawler cranes. Anyone involved in piling knows
            how this work knocks cranes about and we suffered repeated cracks
            just below the slew ring on the undercart. We used to weld this up
            and it would last for a few months. We would weld it up again, but
            this time it would last for a much shorter time. Repeated welding and
            the metal was shot and we had to split the crane, i.e. remove
            everything above the slew ring, cut out a section of the underframe
            and weld new metal in.

            (After this hectic work, we used to retire to Diamond Lil's - just of
            the Harcourt Road in Wanchai. But, that's another story......)

            Regards

            Brian Lewis
            Tel: +44 1 275 852 027
            Fax: +44 1 275 810 555

            -----Original Message-----
            From: Bob Alderman [mailto:bob@...-online.co.uk]
            Sent: 01 October 2000 21:08
            To: Gauge0@egroups.com
            Subject: RE: [Gauge0] Re: RE:Epoxies

            Gavin
            My guess as to what may be happening in these low strength solder
            joints
            that the structure of the solder alloy develops massive crystals and
            the
            joint fails along these crystal boundaries. I have noticed that there
            is a
            certain "brittleness" with a low melt solder joint. A sharp knock can
            undo
            them. Anyone got access to a metallurgical lab and we could check?
            As to the epoxies in aerospace, you should see the surface
            preparation that
            goes into the joints, degreasing, abrading, pre-treatment and
            goodness knows
            what else. These joints are also "designed" for their performance and
            are
            not two ad hoc surfaces and materials being pressed together as we
            may have.
            Generally a good bonded joint works best in shear, that is the two
            surfaces
            trying to slide one over the other. The maximum area of the bond is
            employed. If the joint is subjected to tension acting across the bond
            then
            it will begin to tear apart. One of the tests in an aerospace joint
            is a
            check on its peel strength. But all this academic as we rarely have
            dynamic
            joints, simply wanting one part to remain in place on another!
            I will come back to a point I made in an earlier reply that I think
            that
            often too little of the adhesive and hardener is mixed together to
            get the
            full properties of the adhesive. The greater the proportions mixed
            the
            smaller the error in the correct proportions of the mix. It is easier
            to mix
            when you have a reasonable quantity on the palette.
            Also perhaps insufficient attention is paid to the cleaning of the
            two
            surfaces to be bonded. Whitemetal castings come with a mould release
            compound on them. In its simplest form this can be talcum powder, or
            it may
            be a silicone spray. The remains of this have to be removed or the
            adhesive
            won't be in contact with the base metal otherwise. Fingers can leave
            enough
            grease on a surface to wreck the bond. Warm soapy water can be an
            effective
            degreaser in the face of more sophisticated degreasers.
            Roughening the surface with a wire brush or wet & dry helps to key
            the bond.
            This increases the area to be bonded, all the minute ups and downs.
            The
            geometry of the roughening helps key the adhesive too.
            This also applies to use of cyano adhesives too.
            There blinded with science!
            Bob

            > -----Original Message-----
            > From: Gavin Eyre [mailto:gavin.Eyre@...]
            > Sent: 30 September 2000 22:22
            > To: Gauge0@egroups.com
            > Subject: [Gauge0] Re: RE:Epoxies
            >
            >
            > ......there is less chance of getting that unholy alloy of 145 and
            Low
            > Temp Solder that has absolutely no strength at all. (Can anyone
            > explain that too me?)
            >
            > However I remain perplexed as to why can the aerospace and
            automotive
            > companies make their high tech wonders using epoxies, yet when it
            > comes to brass and whitemetal these joints come undone at the least
            > provocation.
            >
            > Gavin Eyre
            > Gavin.Eyre@...
            >
            >
            >
            > To unsubscribe from this group, send an email to:
            > Gauge0-unsubscribe@egroups.com
            >
            >
            >
            >


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