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  • What is root and cap?

    Im not sure if I missed this back in high school or just wasnt told. My welding instructor was fresh out of college and really didnt know much more than the students.

    So then what is a root pass and caps? Why do you use different types of rods for each?

    Pardon my ignorance. When I need two pieces of steel to become one, I just grab a stick and drag it till theyre stuck. Some welds look good and some like crap but they all hold.
    Who do you call when the lawmakers ignore the law?

    Miller AC/DC Thunderbolt 225
    Miller 180 w/Autoset
    Old cutting torch on LPG

  • #2
    Say you have 2 pieces of 3/8" steel 4" x 6" long.
    1) Put a 30 degree bevel on each of the 6" side. Put them together, leaving a
    5/16" gap in-between.
    2) Put a 2" wide x 7" long 1/4" plate behind those 2 pieces. This is called the
    backing plate.
    3) Tack everything together
    4) Your 1st pass to join those 2 pieces together and the backing plate is
    called the root pass.
    5) Layer your next bead to fill up the void
    6) When you come around 1/16" from the top, You will put the last "layer" of
    beads on the top that will just come over those 3/8" plates. This last
    "layer" is called the cover, or cap.

    Sorry if I made this confusing, a pic would be worth a thousand words,
    but some of the guys would kill me if I went on

    Does anyone have a pic for him or a better/simpler explanation??
    bert
    I'm not late...
    I'm just on Hawaiian Time

    Comment


    • #3
      So in this case youre welding the backing plate to the other two in one weld?

      Any time Ive done something similar I just welded the two pieces with nothing backing them up on either side.

      Why then use different rods for the root and cap?
      Who do you call when the lawmakers ignore the law?

      Miller AC/DC Thunderbolt 225
      Miller 180 w/Autoset
      Old cutting torch on LPG

      Comment


      • #4
        Typically You weld with 6010 to get full penetration in the root but it does not have the ductility for a strong weld in structural applications. So they use 7018 or 7024 for the fill and cap for strength. They do the same thing in pipe welding but you'll have to wait for a pipe guy to chime in I've never welded pipe and don't care to speculate.
        Go get a copy of "The procedure book of arc welding" by Dare I say?? Lincoln It's actually a great book with good information in it and WPS's for practice
        Miller Syncrowave 200 W/Radiator 1A & water cooled torch
        Millermatic 252 on the wish list
        Bridgeport Mill W/ 2 axis CNC control
        South bend lathe 10LX40
        K.O. Lee surface grinder 6X18
        Over 20 years as a Machinist Toolmaker
        A TWO CAR garage full of tools and a fridge full of beer
        Auto shades are for rookies
        www.KLStottlemyer.com

        Comment


        • #5
          The info is correct, root is the first pass and needs to join the two pieces with a gap between them. The gap is for penetration to make sure the weld goes all the way thru, then fill and cap as stated above. I used 6010 for all of it as thats all we had back in the day, 7018 is good but I have problems dealing with all the flux running off it as I never ran enough of it to get the hang of it.........

          mike sr
          mike sr

          Comment


          • #6
            "Welding Dentistry 101"

            Originally posted by Flyingpig View Post
            Im not sure if I missed this back in high school or just wasnt told. My welding instructor was fresh out of college and really didnt know much more than the students.

            So then what is a root pass and caps? Why do you use different types of rods for each?

            Pardon my ignorance. When I need two pieces of steel to become one, I just grab a stick and drag it till theyre stuck. Some welds look good and some like crap but they all hold.
            What college was your instructor "fresh out of?" I can't imagine a CWI not knowing the R-HP-C's of welding.

            Root Pass is the intitial pass (for clarity we'll use pipe as an eg.) when joining 2 sections together. For simplification, 5G will be cited, or a bevel butt joint to be joined with vertical welds. 37 1/2 degree bevels joined to an included angle of 75 degrees with a 3/32" - 1/8" land and 3/32"-1/8" gap or "root opening" A fast freeze/cellulosic rod (6010, 7010, 8010) is literally buried into the root opening to form a "keyhole" and from the 12 o'clock position downhill to the 6 o'clock position, (both sides), subsequent beads are layed. Properly done, this will create "wagon tracks" which must be dressed with a 1/8" grind wheel, and all slag removed. The cellulosic rods produce little slag, and cleans up rather quickly.

            Hot & fill passes are made, built up along the bevels until the last or "cap" pass is layed, then onto the next joint. Depending on type, grade, and transmission of product in said pipe, fill & cap passes can be made "uphill" with 7016, 7018, or other "Lo Hydrogen" rods.

            Recent discoveries and improvements in wire fed consumables has made conventional pipe welding more expeditious through the use of solid, gas shielded, and self shielded wire.

            GTAW is used in root applications, and in the case of high alloy pipe, require "backing gas" or a heavy blanket of inert gas at the bottom of the joint.

            Root passes are not limited to pipe welding, as KC mentioned.

            "Proceedures of Arc Welding," "Principles of Industrial Welding," "Metals, and How to Weld Them," are excellent books available from the Lincoln Library.

            Properly done, root pass pipe welding should sound like a "sea shell," or the sound when you hold one up to your ear. You can literally tell how good the weld is, by the "sound" of it.

            Hope this helps

            Dave
            Last edited by davedarragh; 04-10-2009, 02:05 PM.
            "Bonne journe'e mes amis"

            Comment


            • #7
              The fitters are also starting to use Tig on ammonia lines for the root as well, dont know if they were using purge gas or not.

              mike sr
              mike sr

              Comment


              • #8
                TIG Root

                TIG Roots can be done in any application, mild steel, stainless, low-alloy, etc. It's generally used on smaller diameter pipe, as SMAW and FCAW-G is quicker and less expensive on larger (24" +) diameter pipe.

                "Tents" need to be set up around joints requiring shielding gas in field and cross-country applications.

                If you get a chance, send away for Miller's Pipeworx DVD (it's free) and watch the MIG do it's majic.

                What was once a slow, arduous process, has now evolved to state-of-the-art, computer controlled, space age operation.

                In all of this: "Stick, will never go out of style"

                Dave
                Last edited by davedarragh; 04-10-2009, 02:06 PM.
                "Bonne journe'e mes amis"

                Comment


                • #9
                  Originally posted by Flyingpig View Post
                  Im not sure if I missed this back in high school or just wasnt told. My welding instructor was fresh out of college and really didnt know much more than the students.

                  So then what is a root pass and caps? Why do you use different types of rods for each?

                  Pardon my ignorance. When I need two pieces of steel to become one, I just grab a stick and drag it till theyre stuck. Some welds look good and some like crap but they all hold.
                  Flying pig, I mean no offense, I realize we all have different backgrounds but the one common thread that runs through every wish I could welder's mouth is something very close to "well she don't look so good but she'll hold". This thought process scares the (fill in the blank) out of me. If you went to buy a new truck and heard the sales man say that about some 6 tone multicolored DODGORDOLET (dodge-ford-Chevrolet, all in one. Simillar to a Jonny cat-arctic cat with deere parts) that had different sized tires would you buy it? Me neither so why do I as a welder, CWI, instructor, weld engineer have to keep hearing the same thing from any guy that thinks he can weld? By your own admission you don't know what rod to grab or even what to call it. Please take the time to learn.

                  I will take a lot of heat for this post, and I don't mean to nail you on it personally. My response here is more in general to anyone who reads it and says "yea me to". Please learn what you need to, I understand that sometimes we don't know what it is we don't know but please don't accept that because you took a class and possibly received a certificate from your instructor that you know what it is your doing. My life or my families life might depend on it if you ever build a trailer or other item. I get scared to death thinking about trailers out on the road where some "think I am" ran some wet 7018 downhill and then said" she don't look so good, but...." and then puts a car on top of it and drags it 75 miles per hour down the road. Yep it happens, I have seen them in the ditch.

                  I do applaud you coming out here and asking questions, that is the start. Now please learn the correct principles of welding.

                  OK boys.....let me have it.
                  Last edited by diamondback; 04-10-2009, 04:36 PM.

                  Comment


                  • #10
                    Originally posted by diamondback View Post
                    I will take a lot of heat for this post,
                    OK boys.....let me have it.
                    Naaaaaa, you done good!
                    Caution!
                    These are "my" views based only on “my” experiences in “my” little bitty world.

                    Comment


                    • #11
                      Originally posted by davedarragh View Post
                      What college was your instructor "fresh out of?" I can't imagine a CWI not knowing the R-HP-C's of welding.
                      Remember that conversation awhile back DCEP/DCEN
                      It doesn't take much to get a teaching credential and it sound like his instructor was the same as mine (not to bright)

                      "Proceedures of Arc Welding,"
                      Got it.

                      "Principles of Industrial Welding,"
                      Don't got it

                      "Metals, and How to Weld Them,"
                      got it.
                      Miller Syncrowave 200 W/Radiator 1A & water cooled torch
                      Millermatic 252 on the wish list
                      Bridgeport Mill W/ 2 axis CNC control
                      South bend lathe 10LX40
                      K.O. Lee surface grinder 6X18
                      Over 20 years as a Machinist Toolmaker
                      A TWO CAR garage full of tools and a fridge full of beer
                      Auto shades are for rookies
                      www.KLStottlemyer.com

                      Comment


                      • #12
                        This Explains It All

                        http://books.google.com/books?id=cie..._brr=0#PPA1,M1

                        Comment


                        • #13
                          Originally posted by diamondback View Post
                          Flying pig, I mean no offense, I realize we all have different backgrounds but the one common thread that runs through every wish I could welder's mouth is something very close to "well she don't look so good but she'll hold". This thought process scares the (fill in the blank) out of me. If you went to buy a new truck and heard the sales man say that about some 6 tone multicolored DODGORDOLET (dodge-ford-Chevrolet, all in one. Simillar to a Jonny cat-arctic cat with deere parts) that had different sized tires would you buy it? Me neither so why do I as a welder, CWI, instructor, weld engineer have to keep hearing the same thing from any guy that thinks he can weld? By your own admission you don't know what rod to grab or even what to call it. Please take the time to learn.

                          I will take a lot of heat for this post, and I don't mean to nail you on it personally. My response here is more in general to anyone who reads it and says "yea me to". Please learn what you need to, I understand that sometimes we don't know what it is we don't know but please don't accept that because you took a class and possibly received a certificate from your instructor that you know what it is your doing. My life or my families life might depend on it if you ever build a trailer or other item. I get scared to death thinking about trailers out on the road where some "think I am" ran some wet 7018 downhill and then said" she don't look so good, but...." and then puts a car on top of it and drags it 75 miles per hour down the road. Yep it happens, I have seen them in the ditch.

                          I do applaud you coming out here and asking questions, that is the start. Now please learn the correct principles of welding.

                          OK boys.....let me have it.
                          What you say is true, And I have heard that expression many times.
                          mike sr

                          Comment


                          • #14
                            Poor Students

                            Originally posted by diamondback View Post
                            Flying pig, I mean no offense, I realize we all have different backgrounds but the one common thread that runs through every wish I could welder's mouth is something very close to "well she don't look so good but she'll hold". This thought process scares the (fill in the blank) out of me. If you went to buy a new truck and heard the sales man say that about some 6 tone multicolored DODGORDOLET (dodge-ford-Chevrolet, all in one. Simillar to a Jonny cat-arctic cat with deere parts) that had different sized tires would you buy it? Me neither so why do I as a welder, CWI, instructor, weld engineer have to keep hearing the same thing from any guy that thinks he can weld? By your own admission you don't know what rod to grab or even what to call it. Please take the time to learn.

                            I will take a lot of heat for this post, and I don't mean to nail you on it personally. My response here is more in general to anyone who reads it and says "yea me to". Please learn what you need to, I understand that sometimes we don't know what it is we don't know but please don't accept that because you took a class and possibly received a certificate from your instructor that you know what it is your doing. My life or my families life might depend on it if you ever build a trailer or other item. I get scared to death thinking about trailers out on the road where some "think I am" ran some wet 7018 downhill and then said" she don't look so good, but...." and then puts a car on top of it and drags it 75 miles per hour down the road. Yep it happens, I have seen them in the ditch.

                            I do applaud you coming out here and asking questions, that is the start. Now please learn the correct principles of welding.

                            OK boys.....let me have it.
                            Very well said! Obviously these students have never applied with the Registrar of Contractors and post a Surety Bond to guarantee their work.

                            Dave
                            "Bonne journe'e mes amis"

                            Comment


                            • #15
                              Electrons and Current

                              Originally posted by kcstott View Post
                              Remember that conversation awhile back DCEP/DCEN
                              It doesn't take much to get a teaching credential and it sound like his instructor was the same as mine (not to bright)

                              Got it.

                              Don't got it

                              got it.
                              Yeah, ELECTRONS flow from negative to positive, CURRENT flows from positive to negative. I'll blame Ben Franklin and Thomas Edison for confusion.

                              How's the 12VS treating you?

                              I can run 1/16 (.062) in the 8 VS, but usually just run .045 dual shield and ultra core wire.

                              Dave
                              "Bonne journe'e mes amis"

                              Comment

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