|sparky mike||29/10/2019 09:01:02|
|196 forum posts|
I am repairing a small crack in a cast iron end plate of a guillotine.
I bought some cast iron electrode rods (supercast) ,veed out the crack but rods did not want to strike, no matter what current welded was set at and keep sticking. Any advise here welcome. The length of the crack is only around 1".
1625 forum posts
I strongly advise drilling a hole either end of the crack, seems to help stop it cracking more when you weld it. You didnt say if your rods had been pre-heated, im guessing not, and therein lies your problem. They need to be hot.
|1335 forum posts|
Some special rods do better at 80 volts. Heating the work might also help, as might peening the weld as it cools.
|Russ B||29/10/2019 10:09:44|
|549 forum posts|
I've never welded cast iron, but I thought preheating the rods and the part, plus peening the weld as it cooled was best practice? Hopefully someone with first hand experience can provide some tips!
Edited By Russ B on 29/10/2019 10:10:51
|Nicholas Farr||29/10/2019 10:32:40|
1997 forum posts
Hi, if you are using these Supercast electrodes, your welder will need an OCV, that is the voltage across your welding holder and the return lead (earth) needs to be at least 45 volts before you start welding. If you are using a DIY buzz box, you may not get that and you will have difficulty striking an arc. The electrodes don't need to be heated but they should be dry, which can be done in an oven at around 100/120 odd degrees for an hour or so. You should not need to preheat the joint to much more than about 150 degrees and you should keep the heat input low by keeping a short arc and not making the runs too long and peening should be done after every run while the weld is still hot. A little post heat can be applied after the weld is finished, but not by an excessive amount and allow it to cool on its own away from the cold and draughts.
Edited By Nicholas Farr on 29/10/2019 10:38:32
|Clive Foster||29/10/2019 10:39:35|
|1886 forum posts|
I've never bothered with proper cast iron welding rods for home shop repairs. There is no doubt that the proper rods in skilled hands produce a stronger job but if you don't have the experience and don't use the correct procedures they can be serious trouble.
My method is to use a 1.5 mm ordinary general purpose rod at the lowest practical current to build up thin layers of weld on the two sides of the crack. Each layer should be peened with the chipping hammer before it cools off. This reduces cooling stresses but means you can only do the weld in short strips. Make sure everything is cool before adding the next layer. Once you have 3 or 4 layers each side do the final fusion in the normal way with a larger rod but don't use too thick a weld. Most stuff I seen needs three or more runs. Peen between runs as before and let everything cool off before the next run.
Yup it takes ages with all the waiting around for cool off but it does work.
Theory is that it sidesteps the two major issues of carbon migration and cooling contraction leading to cause failure if you simply weld cast iron like its steel. Carbon migration produces very hard, brittle joint lines which fail easily under stress. Cooling contraction guarantees plenty of stress. Carbon migration needs high temperatures. The thin layer build up process minimises temperatures and, once the first layer or two is done blocks the weld region from further migration. Peening helps counteract contraction stresses. Being thin layer means less stress anyway. Once you have a few layers of weld on the iron the final joint is weld metal to weld metal so that behaves just like an ordinary joint. Multiple thinner runs peened when hot again keep the cooling stresses down.
This is an official, albeit old fashioned, technique for field expedient repairs. That said I'd be chary about using it on anything liable to take serious tension loads. Frankly I'd be worried about serious tension loads on any home repair.
Lots easier with an inverter welder than buzz box 'cos you can turn the current right down.
|Dave Halford||29/10/2019 11:22:40|
|489 forum posts|
There are many different cast iron rods available from 99% nickel down to various mixtures of nickel and iron. More iron = a harder, as in a non machinable weld.
I have found the rods easier to strike than similar size mild steel ones.
As you don't say what amps nor what size rod it's impossible to be more helpful other than to say 1.5mm rods will work on a 90A welder and have you checked the earth is good.
When it does work or you try to follow Clive's advice, if you hear a small tinkling sound after breaking the arc that's the weld cracking off the casting.
|Alistair Robertson 1||29/10/2019 12:07:21|
|61 forum posts|
Back when I was doing repairs off all types we often got broken castings to repair.
we always discussed the job with the client to make sure that welding was the best (or only!) option.
If a weld repair was all that could be done then we would usually use a high nickel content rod as it was easier to machine after the welding. What we always did is use a welder with a high voltage which made it easier to strike and maintain an arc. A really old Murex/BOC welder was the favorite tool with up to 120 volt AC or DC. Probably illegal now!
A modern inverter welder works really well when set at a high frequency and with the proper rods.
If you do it right it will be as good as the original casting.
|vintage engineer||29/10/2019 12:26:07|
199 forum posts
When ever I weld cast iron, I heat up the weld area to a cherry red with a pepper pot burner, then weld it but use a circular action to pool the rod with the base metal. Then reheat the site to cherry red and pack in dry sand. The alternative is to metal stitch the crack cold.
Edited By vintage engineer on 29/10/2019 12:27:00
2518 forum posts
I've tried welding CI over the years; some were ok others were not, I would recommend you need to preheat the area & weld similar to Vintage Engineer's method. As there seems to be no pressure or liquids involved, & for the size you say I would simply cold stitch it.
|sparky mike||29/10/2019 14:07:21|
|196 forum posts|
The rods are 2.5 I normally keep rods in airing cupboard . I did do a bit of experimenting and after I had managed to lay down a base layer, I tried a normal steel rod, as I at first wondered if the welder/leads were playing up, and found that the normal rod layed down much better.
Now I am wondering if the particular cast iron is different to the good old UK stuff as the machine is Chinese. Maybe more steel content.
If so, perhaps it takes normal rods ok ?
I had thought about metalock principal but where can you get the figure of eight wedges from ? If I could get some I would go that route.
|Harry Wilkes||29/10/2019 14:09:06|
729 forum posts
I needed to do a quick repair many years ago on the oil tank on a Ellison starter as I remebr I vee'd the joint preheated both tank and rods. The weld looked really c*ap but the tank did not leak and although I purchased a replacment tank I never fitted it.
|XD 351||29/10/2019 14:35:57|
1362 forum posts
Its been 30 yrs since i last welded cast iron ! I have used high nickle rods , stainless and buttering runs with GP rods and all work and have their uses .
I would tend to follow what Fizzy has told you .
I would also have a read of the back of the box of electrodes as this will yield some important information like amperage requirements - these are ball park figures but they will get you near to what you need .
Voltage requirements , current type and preferred polarity if AC is not to be used ( some rods can use ac or dc some only like dc .
pre heat , i used to use a big acetylene torch to take the chill out of a part but depending on its physical size you may be pushing the proverbial up hill with a point stick if the part is big and for cooling i used a fireproof blanket or buried the part in a tray of sand if they were small enough to do so .
I also got into the habit of after grinding the V out i would go over it with a carbide burr as it has a cutting action which removes any of the graphite smear you get when grinding cast iron - not really going to cause an issue with a fusion weld but it will with brazing and i just got into the habit of doing everything the same way with cast iron regardless of whether i was welding or brazing it .
|Brian Oldford||30/10/2019 18:50:51|
582 forum posts
Unless you're really on top of your game a better option might be brazing. Even with nickel rods, welding CI often produces brittle carbides at the edges of the weld. Brazing avoids that as the temperature is so much lower.
|XD 351||30/10/2019 18:56:52|
1362 forum posts
May have to Tig braze it as a gas torch might not be able to get enough heat into the part if it is substantial casting .
|Guy Lamb||30/10/2019 22:41:19|
|68 forum posts|
The last time I welded cast iron it was in the form of an ornamental clock face some three feet across, after many cracks appeared in places other than the areas being welded I resorted to a degree of pre and post heat and ultimately covering the whole casting in agricultural lime (slaked) keeping this is hot as I could with a spreader torch for two hours after welding had finished. The shape of the casting, many interconnecting segments, may also have caused uneven stresses to build up in adjacent areas not subject to welding heat. As this casting was more of an ornament than substance my efforts were acceptable I feel.
If pressed again to tackle a similar job I would concentrate more attention on pre and a longer post heat.
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