Removing A Broken Bolt

There are a myriad of methods to remove broken fasteners, but the method you are using works. Messy-I agree. Time consuming-I agree. Are there better methods? Perhaps. The best thing to do is remove the cause of this problem.

The fasteners are heat-treated and tough to drill with an on-hand drill motor. Yet, If there is sufficient room (and the surrounding surfaces are ferrous) then one can employ a magnetic shoe drill press and have the power and slow speed available to drill through these fasteners. If this can be done, sometimes a left-hand twist drill will gain sufficient "bite" to remove the fastener as it is drilling through it.

Typical screw extractors only work if the fastener is not jammed or seized, as they cannot apply much torque. You mention that you are breaking a lot of fasteners, so that tells me that there a combination of stress actions in play here. Are the mating surfaces in excellent contact? If not, this can place an angular stress on the fastener. Are the fasteners being used to transmit motion, i.e., there is no driving key or pin? If they are, that is a poor design for a high-torque application. Ids there an alignment issue? Even a small one will break fasteners.

Without pictures or drawings it is difficult to recommend a course of action. This downtime is costing you much money, so perhaps you should contact the supplier of the milling equipment and ask for a solution. Perhaps it is as simple as a machine alignment, perhaps not.

The method you are using is the last one available when working on a job site, and certainly my least favourite. But, it is often the one that is necessary when the fastener is seized. Think about the soundness of mating surfaces and alignment issues, and also consider whether the screws are being used to transmit driving torque. The thing to do here is to correct the source of the problem, and I realize that may be tough.

Good Luck!

Ing. Robert Forbus

You might try a bolt extractor. The most common is called "Easy Out". They are available in sets or individually for different bolt diameters and are designed to do exactly what you are looking for.

They are tapered with a reverse spiral (either left or right hand) and usually a square head. Drill a pilot hole in the center of the broken bolt, insert the extractor in the pilot and turn in a loosening direction. The extractor digs into the bolt and backs it out. The pilot hole only has to be deep enough to start the extractor. They work well.

You can do a google search on easy out or bolt or screw extractor to find them.

I recall 25 years ago, when I worked as a machinist on new and used wellhead equipment, I'd occasionally have to remove a portion of a stud that had twisted off in a tapped hole. These were usually 7/8" or larger and I could usually get them out with a torch. The trick was to melt the stud and blow out the molten steel without melting/burning the threads. Any remaining flotsam/jetsom could be teased out with a pick or loosened with a tap. When this failed, we'd just fill the hole with new steel with a welder and redrill and retap. I never heard of any blowouts that were traced back to one of my repairs...yet.

Substitution/other thoughts:

• Does the original equipment manufacturer [OEM] specify high-tensile bolts or is this a home-brew modification?
• Has the OEM been contacted with a view to finding a solution?
• What is causing the bolts to break? Is there any adjustment that can be made elsewhere in the equipment that will give these bolts longer life?
• Why is the item bolted and not secured some other way, like engineering adhesive, Huck fasteners, hot rivetting or welding?
• Why are there only 12 bolts? Could the number be increased without loss of strength in the part they are screwed into?
• Can the design of the part be modified so that more stresses are taken elsewhere, and therefore less by these particular bolts?

I have to agree.

I have seen a number of situations where a high tensile bolt will, but a lower strength bolt is fine.

This is due to the higher strength resulting in a more brittle bolt, so when a shock load is put on it, it will snap. A lower strength bolt will yield a minute amount under the same condition, but will not break. Usually, the deformation is not enough to cause problems removing the bolt.

Good luck!

Hi Mr. Guest,

I used to manage a feed mill a few years ago, and I'm familiar with your problem. You are talking specifically about a pellet mill. You have not mentioned what size of pellet mill you have, but regardless of size, the die speed you mentioned may just be too fast. At 500 RPM you are running this at almost double the normal speed of most pellet mills. The range of speeds is just between 100 to 260 RPM. Depends on the pellet size and the configuration or the number of rolls you have, could be 2 or 3 rolls. Bigger diameter dies are run normally slower, since the die tract speed becomes faster.

At the higher speed that you are running your mill, there is most like to have a choking effect on the die holes with the product not having enough time to exit the die. With a clogged die there is going to an unbalanced pressure on the lead roll, and this could break your mounting bolts.

I would suggest that you also check your drive motor speed. Most of the pellet mills I have come across are fitted with a 1200 RPM motors, whether it is 15 or 500HP.

The broken bolt problem is just the result of a clogged die. If you resolved the clogging of your die, there is really no tendency to break any bolt in the machine.

presently we are using welding method to remove the broken bolt. In his case this is the only option.

At 500 RPM you are running this at almost double the normal speed of most pellet mills

Fully agreeing with you and this is disbalancing & breaking the bolts.

Question please? where does the 500rpm come from?

I think the original poster states 300rpm.

Sorry, 300 RPM is correct! mistype the number, but still this is too fast.

Clearly the freq of bolt shear is too high. However changing bolt material/composition could certainly create a greater problem.

Is it a through hole or blind? If a through hole, can a slightly longer bolt be used so that it might be extracted from the other side without interfering with operation; at least until root cause is determined and resolved.

cr3

Various reasons?

Safety shut offs, overloads, over torqued - what?

It is always easier to prevent problems than to repair them! Perhaps the bolts are too hard (high tinsel strinch),? Overtorque? Under-torqued?

However that does not answer your question - removal - drill and use an easy-out, if the surface contour will permit or if by grinding you can achieve a flat surface, using a center punch to guide your drill you might be able to remove the stub left when the bolt broke.

Install the easy-out apply torque, then heat the base material as fast as you can, using either gas or electric heat, keeping the maximum torque, twist three times to the left three times to the right, pray, and maybe you can remove the bolt!

Other wise, call a machine company that has the right equipment, Team Industrial, Watts, CBI, or WSI, and many other 'in-setu', companies, and they will make short work of bolt removal!

Are you using American made bolts?

Or third world junk?