Injection Molding Press Tie Bar Repair

One of my 1996 Battenfeld molding presses just broke a tie bar... again. This has happened before, and was sent out for repair, which was expen$$ive. This time I'd like to try to get the repair done locally, but I'm wondering if anyone here has ever been involved with this.

The bars always break in the threaded section... the originals because Battenfeld used a strange tapered washer that collapsed and gripped the thread so hard that it spalled chips off the thread, which then led to cracks propitiating from the chips. The repaired ends welded an extension on, then machined a new thread, and provided new cylindrical spanner nuts. The one that just broke did so at the weld, and there is a slag inclusion in the break... sh*t happens.

Since I already have an account with a tool welding shop that does all sorts of mold and die repair, and also an account with a heat treater, I figure I can get stub welded on the broken end, send it out to have it stress relieved, and find a local shop to turn the weld smooth, cut the thread, and and make a matching nut, rather than try to match Battenfeld's metric threads. The total size of the bar is 50mm (2") x 60" long. The last repair threads were 1.75 X 6 TPI.

My question mostly concerns the welding, since the Battenfeld documentation does not specify a steel for the bars, and I'm sure an inquirey is going to get "just order zee replacement from us..." for a response. My guess is something like 4140 would be suitable, but does anybody know? Just how much trouble will mis-matched steels cause the welder? Heat treat should be a simple anneal cycle... Judging from the upsets the nut lock set screws left on the ends of the bars, they are not hardened at all.

Anyone ever do this sort of work? what am I missing?

Dennis (out of his league, but trying to stay in the ball park)

Is that one of the BF's that uses the tiebars as rods for hydraulic cylinders. too. We once had some 55 tonners that worked that way, instead of having one central clamp cylinder.

Year ago, I made a few tiebars for small Arburgs. The main company in Mich would send the steel to me. 99% sure it was LaSalle Stressproof.

I figure it is difficult to get a good weld that will hold the load a tiebar has to hold. Be careful, broken tiebars can become projectiles.

I worked in that business for almost 20 years and saw more than a few break on a variety of brands - and never anywhere else besides somewhere within the threads or at the thread termination. Unfortunately, they are almost impossible to repair satisfactorily. Might be cheapest to buy a dead machine and salvage all four.

If you must go forward with the exercise, I'd turn down the bar, sleeve it with the stub, bore a big hole perpendicular thru stub and shaft, then weld it and redress. They probably are 4140 and unhardened - a good weldor would pre and post heat treat. The big pin might help it stay together.

I visited Van Dorn once and watched a machinist working on a huge lathe to make a tie bar for a 700 ton hydraulic press. The tour guide said it took them four full work days to turn, thread and polish one bar - small wonder they cost a fortune...

I've never seen a tie bar out of a press. Are the threads simply cut in a full diameter bar?

gbent said:

I've never seen a tie bar out of a press. Are the threads simply cut in a full diameter bar?

Click to expand...

Yes - single point turned.

gbent said:

I've never seen a tie bar out of a press. Are the threads simply cut in a full diameter bar?

Click to expand...

As a rule, the end that goes into the front (stationary) platen has a step, or a groove for a split ring, so the nut can be tightened snug. There is often a large undercut radius to minimize stresses where the threads stop.

On a ram-type press, a similar arrangement is usually found on the rear stationary platen also.

On a toggle press, the threaded portion is longer, so the shut height can be adjusted. Often, the tie-bar nuts are turned by a a hydraulic motor via a ring gear or chain.

No, this is a 66 tonner, CDC600 IIRC, with a central clamp cylinder and four conventional tiebars. The tiebar nuts have steel plates fastened over them with four 10mm bolts, which keeps the opening platen from pushing a broken bar out of the machine, and also hold a pair of set screws that lock both the bar and nut from rotating.

I don't doubt that tiebars always break in the threads; that's where all the stress risers are, and it's been my experience that the fixed platens can "jiggle" a bit as they try to cope with less than perfect molds. The platens can also try to wrap around the mold, which I am told was a big problem with the Battenfelds that used the hydraulic cylinder rods as tiebars. In either case it puts a bending forces on the bar where it enters the platten, and again where it exits into the nut. Battenfeld tried to compensate by providing a reduced section U groove where the bar went through the platten, and also a nut with a tapered section that bears in a tapered washer. The problem is the taper was so steep that it locked the nut tightly on the threads, then chipped the threads. We replaced the nuts with flat ended cylindrical nuts that bear directly on the platen, like what is common on most American presses on the ends we had repaired, with good results.

Over the years, I've had several tiebar ends repaired by welding, a couple on this press, and a couple on the 70 ton Kawaguchi it replaced. All of them gave good service, until this one broke at the weld, and as I said, there is definately an inclusion at the break. Well, sh*t happens, but for what I paid for the last repair, they could have X rayed the damned thing. I figure maybe $100 for the welding, fifty bucks for heat treat, and maybe four hours of machine time to clean up the repair, thread it, and make the nut. That's a long way from the $900 or $1000 I paid for the last repair. I need to see if I can do better.

Thanks for the comments. Anyone else?

Dennis

Dennis- I know a guy not all that far from you that was making and repairing tie bars for customers from all over the country last time I saw him 6-7 years ago. He would be worth talking to. It's Dave Sacquitine at Kirkeby Welding and Machine in Decorah, Iowa. His number is: 563-735-5770. Last time I was there he was telling me about a molder from Detroit that would fly big tie bars in to the Decorah airport on their company plane, and then wait until he remade or repaired them. I even remember those as being from Battenfeld presses, but could be wrong.

Dennis just my 2 cents worth we replace tie bars on die cast presses some up to 1200 ton 12 - 14 inch diameter we replace these as they break engineer for the company we do the replacement for used 4140 annealed for awhile with some luck we finally went to 4340 heat treated and have not had a failure on a replacement rod some have been running for 4 years i'd consider having one made from 4340 but just my opinion

I do part time at a small shop in Rockford that could make new tie bars for you. Thread mill or lathe turned. Interested? pm me on here. John

Thanx to all who replied. I effected a temporary repair Friday (don't ask) and got the press running again, so I have some time to pursue a permanent fix.

While several people have made suggestions for material for new bars, no one said the magic words, "Battenfeld tiebars are made out of DIN 12345, and that's the same stuff as 4340..." So, I don't really know what steel the parent material is, or what the heat treat for the repaired bar should be. I suppose that's why the shops that repair them get the big bucks... they've done enough of them to know what works. Or so they say.

Barry, I'll give your guy a call later in the week. If he's done Battenfeld bars before, maybe he has the welding and heat treat down pat.

John, I'll keep your offer in mind, but the thought of precision grinding the diameter on five feet of 2" stock sounds spendy. Anyone have a handy source for 50mm percision ground round stock?

Dennis

Centerless ground should be pretty cheap. Forte grinding in Franklin Park, Il should be able to do that in short order.
We can mill the threads or lathe turn them

Hello,
Have you contacted the mfgr's. rep about the issue? Have there been any
recent improvements in these parts?
1045 TGP, is used to mfg. most hyd. cylinder rods. Have you had one of the
broken ends, checked for hardness before torching/welding?
Trying to make a tiebar, that will match the other three, for tensile strength,
may end up being more expensive in the long run, than writing a check up front, for the correct part. Do you have enough machines that use this part,
to justify a spare?
Are the platten bushings, in good condition, and properly lubed? Proper torque on the tiebar nuts?
Best wishes,
Bob

Thanks Bob. Battenfeld and I don't talk to each other anymore. Not since I had it out with them over a persistent hydraulic leak years ago that turned out to be due to porosity in the filter housing casting, and they refused to honor the warranty until I got the Chief Executive of Battenfeld of America involved. They also don't support their power supply, or control, both of which they outsource... "Send it to us in Germany and we'll send it back to the manufacturer, and they will eventually send you a nice big bill..." They are not even Battenfeld of America anymore; they split the injection press line from the blow molders and now they handle service direct from Germany, or Austria, or Lower Slobovia... Good riddance to that pack of scoundrels.

More to your question, I don't want original replacements, because the original design is flawed. I've had more broken bars on this machine that the other three combined. I kind of figured I'd get all eight ends repaired (I was half way there) and then live happily ever after, until this repaired end broke again.

I can't torque the tie-bar nuts, becase they don't pull up aganst anything solid; they are not under tension until the press is closed and under pressure. I've set the bars using a tie-bar strain gauge (two magnetic V blocks connected by a precision indicator) of the type that was commonly used to set the bars and qualify the clamp tonnage on a toggle press, but never got very responsive readings. The first time I had to pull one of the bars, I found out why; the 50mm (nominal 2") bars are relieved to about 1.28" where they pass through the platens, so most of the stretch is happening right there. After that, I made a comparative measuring fixture; a piece of pipe cross drilled for two dowel pins that I can hook on the machined faces of the platens and measure with Jo blocks when the press is under tonnage.

The tie-bar bushings and skates on the movable platen are grease lubed, and kept well greased. This press is a bit odd in that only two tie-bars run through the movable platen; the platen is cut out around the top two bars, and therein lies the secret of my emergency repair. The press is currently running with two lengths of 1.75-5 B7 threaded rod in the top positions, covered with lengths of 2" tubing so any hoses that should drag on them don't get eaten by the threads. But, I do need to come up with a more permanent solution, because when a bottom bar breaks (and it will break) I'm screwed.

That leads me to the 1045 TGP suggestion. It looks like the stuff, and I found a source of 50mm ( I still need to determine the tolerance range on the originals). I see it's rated as 110,000 PSI in tensile... the B7 is rated something like 125,000 psi.. maybe that's why it doesn't break? It does look like a possibility to just get four new bars made.

Now to find a source of 1.75" nuts with better finish than the grade eight nuts I'm using on the threaded rod.

Dennis