Proof testing cable clamps

[STRR]

Well, we could just design the hoist with a large safety factor and know we will be safe.

I do NOT recommend fiber core (FC) wire rope as there is a HEAT factor potential. NO plastic when it's hot.
There are several levels of wire rope. IPS -Improved Plow Steel being the least expensive and readily available. IWRC -Independent Wire Rope Core is much safer around heat.
3/8" diameter IWRC IPS has a breaking strength of 13,120lbs. with a Safe Working Load of 2,620 lbs. Reduce this SWL to 80% for the wire rope clips gives you a SWL (with u-bolt clips) of 2,096lbs. This is DOUBLE what Harold wants to load test his rig to.

Keep in mind, most light weight electric winches use 1/4 or 3/8 inch cables. Inexpensive, light, easy to find, easy to work with, and EASY to REPLACE when any wear or damage is found (a person will not be tempted to keep using the cable due to the high cost of replacement).

If the expected load is 700lbs. and a SWL of 2,096lbs that makes a SWL safety factor of 3. OR a Breaking Strength safety factor of 15. Safe Enough?

IF not, a person can purchase EIPS -Extra Improved Plow Steel, EEIPS -Extra Extra Improved Plow Steel, and even EEEIPS If and when you can AFFORD it.

Cheers,
Terry

[Harold_V]

Thanks for the comments and ideas. I've had to make some compromises in the design due to limited space. Cable size is quite small, but according to schedules, adequate for the task (it's only 3/16"). Literature suggests it has a breaking strength of 4,000 pounds. I've tilted the furnace on several occasions thus far and it is obvious that it isn't unreasonable. Size constraints are taken into account so that the cable isn't bent beyond recommended radii---and that's part of what has limited cable size.

While the furnace is tilted, it isn't possible for one to get beneath, nor would one be where they could be. The furnace hinges (by pillow blocks) that are located on the centerline of the discharge spout (launder) so the pouring spout remains in a constant position while the furnace discharges the molten metal.

My concern about the cable pulling out is based on the fact that the cable is not doubled back on itself, as it would be with the typical cable clamp or eye. The clamp is designed to fit the lifting bar on the furnace. Six screws hold the cable captive, plus a cross bar (a hardened 1/8" pin) adds additional compression to the cable at a right angle. The slot is held shallow, so the screws can compress the cable in the slot without the two halves making contact. Tightening displays indentation of the cable in the clamp, so it seems to perform as I hope, but I don't want to take any chances, as I am already borderline with the cable size. Going to a larger cable would just complicate things, as greater radii would be required to keep the cable within acceptable bends. Assuming I stay with the 3/16" cable, which is likely, I can remake the attachment so the cable forms a loop. I can also form a knob end on the cable, to limit its ability to pull out. Considering the fact that the load will be consistent, I suspect that I should be able to come up with a functional design.

H

[STRR]

Harold,

The numbers I have show 3/16" galvanized cable breaking strength of 4200lbs. At a safety factor of 5:1 that gives you a 840lb Working Load Limit. Using cable clips reduces WLL to 80% giving you a SWL of 672lbs. The D/d ratio shows 7 3/8" sheave for 6x7 & 7x7 with a minimum of 5 1/4" with a reduction in cable life. If you are using 6x19 or 7x19 You can reduce that to 4 1/2" with a minimum of 3 3/8" sheaves and a reduced cable life. These figures are intended for a higher usage amount than I believe you are actually chalking up. I believe you may hoist your furnace maybe 3-4 times per day when you're busy and having an average usage of something like 4 hoists per month. Your cable will last a long time at that rate. Keep in mind D/d ratio is extremely important when the cycles number 60 per HOUR which I have repeatedly accomplished. Proper lubrication, use, loading, and D/d ratios allowed me to get 10+ years of life from hoisting cables. If I were to match your hoisting rates, my cable would last a couple of lifetimes.

I would recommend moving up to 1/4" cable using your existing sheaves and plan on replacing the cable more often based on usage. This would increase you safe working load ratings. I also recommend using a loop or eye instead of straight line clamping. While straight line clamping is used, the engineering is way above the accessible documentation and clamping efficiencies are not readily available to the public as the public tends to push the limits and that opens the provider to legal issues.

I hope this helps you out.

Good Luck,
Terry

[David2011]

Harold, another option might be to have the lifting cable made up by a sailboat rigging shop. You have several in the Seattle area. They can swage any number of terminal fittings onto the straight end of wire rope. That would create an attachment that is compact with high strength. The fitting is tested by measuring its O.D. with a gauge after swaging and it could be pull tested as well. It’s been the method of choice for production sailboats and aircraft control systems for over 70 years so the track record is well established.

[Bill Shields]

How much of the full 700# will this cable be supporting?

I am visualizing that the cable is used to tip the bucket that is supported on other bearings

Or am I missing something?

[Harold_V]

Terry,
Thanks for the provided data. It helps tremendously!
As far as usage is concerned, it's highly unlikely that the furnace would be tilted more than a couple dozen times per year, if that. If volume is an issue, the other furnace, which has a greater capacity, has hydraulic cylinders (thanks to rrnut-2 Jim Bronson, and his lovely wife Liz) so this furnace has the potential to see limited service. None of this is intended to be a commercial venture, and is more intended to satisfy my life-long interest in foundry work.

I have observed the reduced minimum sheave size for 7 x 19 rope and understand that it reduces the potential life of the cable. The cable, which is quite short in the scheme of things (about 18' max), can be easily changed. When the furnace is down, the drum will have a full bottom layer of cable, and there's potential room for even two. I assume that the bottom layer provides additional restriction to the ability for the cable to pull from its mount on the drum. The cable exits the side plate and is then clamped (on the side plate) with a similar clamp as I intend to use on the furnace end. I am not as concerned about the cable slipping from the drum, but I intend to test it also, with the same applied weight and a prolonged test period.

My logic in using a straight clamp on the cable was intended to circumvent the reduction of cable strength due to end being distorted by clamping. If you have an opinion, it is welcome.

A loop or eye isn't exactly conducive to this application as it would require that the lifting bar be dismantled from the furnace. The design I have allows it to be removed easily yet should be equally as strong as a loop. The only real question is if the clamping procedure is viable. If it isn't, I can remake the clamp and add about four inches to the amount of cable that is held captive, plus add a full 180° turn to the cable in the process. I would prefer doing that to having to dismantle the lifting bar.

Thanks, Terry. Your input has been invaluable.

H

[Harold_V]

Harold, another option might be to have the lifting cable made up by a sailboat rigging shop. You have several in the Seattle area. They can swage any number of terminal fittings onto the straight end of wire rope.

Thanks for the idea, David. Unfortunately, it is important that I use an attachment that allows the cable to be installed on the lifting bar without dismantling the bar. I addressed that issue in my response to STRR.

I'm also 100 miles distant from Seattle, so any maintenance that I may encounter would be extremely inconvenient. I would prefer, by far, to have something that allows me to do any maintenance with means at my disposal in my shop. I have worked that direction intentionally.

Your comments are appreciated!

H

[Harold_V]

How much of the full 700# will this cable be supporting?

I am visualizing that the cable is used to tip the bucket that is supported on other bearings

Or am I missing something?

Nope! You're not missing a thing! That's exactly how it works.
Not being an engineer, nor understanding the required formula, how much of the weight is the cable bearing? Would it be safe to assume that it carries only half the weight? Both pivot points are on the extreme opposite ends of the furnace (front and back) and approximately the same distance from center. Your thoughts, Bill?

H

[Harold_V]

Harold , I don't understand the part about using the mill ? Is it just have a anchor at one end ?

Correct. My BP weighs about 2,000 lbs. It would make fastening the cable end easy and provide the required anchor.

Did you want to check the entire length of cable ..is that it ?

Nope. I'm not concerned with the cable. I am concerned with the cable not being held securely in the end, which attaches to the furnace. It must not creep. So long as it doesn't move with a 1,000 pound load, I would feel safe in using it. I would not do so without testing by some means.

Keep it simple - example
Take a 8 foot 2 x 4 ( or steel beam) anchor one end with a fulcrum.
Drill a hole 8 inches from that end and mount a link for your cable which is hanging above the 2 x 4 .
Then place a 100 pound weight on the far levered end and you have your 1,000 pound test setup

Rich

Thanks for that idea, Rich. While the concept is familiar to me, it never entered my mind. It would clearly be easy to do and it will be my method of choice barring the use of a scale of some sort. If possible, I'd like to apply a load slowly to see where the clamp fails, if it does. That would be invaluable to me so I could improve the clamp. I guess I could slide the 100 pound bag of sand along the lever to accomplish the same thing. Once at the extreme end, allow it to sit for a few hours.

Good stuff, Rich!

H

[Bill Shields]

Is the 1000# load on the pivot bearings...as in dead weight lift?

Picture with dimensions showing interest dimensions would be nice

[Harold_V]

Bill,
I'll try to post a picture later (tonight) that will show the details. It's not easy, as the camera doesn't communicate with the computer, so I have to upload the images to a thumbdrive on a different computer. Mean time, the load is assumed to be only 700 pounds, not 1,000 pounds, and, as you suggested, it pivots on ball bearing pillow blocks---which I would assume is a simple dead weight lift. Maybe the promised picture will help.

I intend to test to 1,000 pounds.

H

[Bill Shields]

so -> if the bearings are supporting the load...all you are looking to do it 'tip the teapot over', and pour the metal?

what is the maximum weight of the metal that can be put into the empty pot?
what is the vertical distance from the bearings to the anchor point of the cable?
what is the weight of the empty pot?