How to refill a hole bored on a large casting HELP 1

[sacem1]

This question has also been posted on other groups as I'm really pressed on this one:

We were drilling a 3/8" diameter hole for a lubrication supply line in a cast steel adjustment ring for a conical crusher (around 3 ton weight) the hole is 8 1/2" deep at 8" of depth the drill shattered and stuck inside the body.

We tryed several ways to pull the drill bit out but only the first inch got out so we finally after many trials made a drill bit 1" diameter with a 10 mm cutout in the center and bored around the remains of the drill, half inch at a time then extracted the piece of broken drill also 1/2 inch at a time, the job has been excruciting to everyone involved but finally the full 8" were removed (last piece was only 1/2" long) but it left me with a 1" hole in the casting.

I have to fill the hole and redrill the 3/8" oil passage but the original idea of inserting a bar in the hole in a tight fit and welding the last inch flat with the rest of the casting has been vetoed by the customer as the part has to go thru an ultrasound test and the bar fill up will appear as a casting defect (our customer is the foundry, but they are not the end user wich contracts a third party company to do the ultrasound testing).

Up to now the only solution we have comed up with is filling in the hole by welding with 7024 electrodes but the fear is that some slag can get caught up inside the hole as it is extremly deep with respect to the diameter, MIG/MAG welding would be ideal as it does not leave any slag inside but the hole is to deep and narrow as to allow the welder to move the nozzle inside the hole (we have been trying the welds in scrap pieces with same dimensions)

If we go the electrode way the gases do not allow the welder to see inside the tube and we have fitted a small copper tube to a CO2 supply in order to blow out the gases and allow improved viewing, but still CO2 is not completly clear so we might switch to Argon gas blowing, anyway the Argon or CO2 will provide an inert gas or active gas atmosphere wich should not be harmfull to the weld as it will also protect it.

Question: Is there a better way of doing this?

I have not try it yet but maybe I will have to drill a LARGER hole in order to allow enough space for the welder to see and to direct the electrode but I rather not in order to avoid affecting the strength of the casting even thou it is very solid.

Please HELP

I really have a very short deadline to complete this job.

SACEM1

 

[unclesyd]

Congratulations on completing a tough job.

I know your feedback is appreciated by everyone involved. The only problem is now you become expert.

 

[unclesyd]

sacem1,
If you are still around, here are a couple of sites that might be of future use in your business.
Both companies are the devotees of “flood welding” and have the large electrodes and manipulators to handle them.

http://www.cor-met.com/Default.asp

http://weldmold.com/product.htm

 

[sacem1]

Thanks unclesyd I'll look into them as it is a technique that is worth having around

SACEM1

 

[diamondjim]

Would a large taper pin have been acceptable?
You could have reamed the hole from the od
and spot welded the pin. Then drilled thru the
large taper pin with the 3/8 diameter hole.

 

[sacem1]

No part interruption was admisible as it would show on the Ultrasound.

The piece was completed in said manner and it was approved by the foundry AND the customer inspectors so right now we have peace of mind.

We are starting another piece and the process will be to drill a 5/16" hole for 1/2" depth change drill to the 3/8" final diameter redrill that 1/2", back to the 5/16" and so on until we reach the 8"+ of depth. In that way the steel chips will be free to exith with out rubbing along all the lenght of the hole. BTW this is only done after a normal 3/8" diam x 4" deep hole has been drilled with a standard length drill bit.

Cheers

SACEM1

 

[icrman]

If you have to drill something like that again.
Its better to take some time, rather than fix a mess.
I would peck drill with a full retract to clear chips and use a through spindle, ie coolant through the drill to the cutting edges. And a very moderate rpm and feed rate. Better to spend many hours machining than to scrap or fix something. The only uncontrollable thing that would goof things up is an inclusion of say carbide insert in the path of the drill. Other wise will proper methods that shouldn't have happened. The operator "machinist" needs to watch spindle load meter, and listen.

 

[sacem1]

I agree completly, you don't know really how much.....

It is definitly better to spend 5 more hours drilling than 5 more days trying to extract the shattered drill and refilling and redrilling again.

SACEM1

 

[an0r0v]

Just curious, how/what are you drilling this piece with. I hope you are using a drill press at least. A job like this should never be tackled with a hand drill.

 

[sacem1]

This is drilled in a large Horizontal Boring Mill which allows the piece to be solidly mounted on the rotary table and the holes are located using the rotational indexing capacity of the machine.

A 220 mm deep hole in a steel casting 280/320 BHN would be almost impossible to do with a hand drill evn with several hand drills as they would be burning out one after the other.

Regards

Sacem1

 

[arunmrao]

sacem1
You have become an expert now and one should be very careful while giving you suggestions.

One doubt I had. Did you have access to any portable induction heater ? Reason being that after welding this zone could have been stress relieved. This would perhaps have avoided the second mishap(heart break!!)

 

[sacem1]

Hello Arunmrao:

I agree with you that having an indusction heater could have been used to reduce the hardfacing that the weld produces as being applied to a cooler surface such as the big casting, but I would wonder how much heat should be applied with out risking a heat deflection of the piece.

This casting had allready being turned to a 0.05 mm tolerance on the 1500 mm diameter, and if some heat distorsion was done by the reheating......

I think that the second breakage of the drill was done by a small slag inclusion or cavity left, even thou in ultrasound testing (with the second filling) it showed no such thing.

BTW we finished today a new piece with no problems, either we learned or the other casting was cursed or had a not so even heat treatment.

Cheers

SACEM1