What is the best material to install in a motor bonnet to fill the void? The 30 HP motor is mounted on a reaction drive mineral separator and is subject to some rather high g-forces and vibration. We have tried numerous materials, from high-temp silicone foam to Duct-seal. Any suggestions would be greatly appreciated.
Motor bonnet vibration dampening
- Thread starter Calamar
- Start date
- Status
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I'm thinking maybe it's a less controversial term for a peckerhead? If you are unfamiliar with THAT term too, it's the motor connection / termination box.
If so, generally I never "pack" it with anything; too much of a mess to deal with later. I use tried and true connection techniques involving multiple steps (depending on the size of motor involved) that reduce the likelihood of failure. I did a lot of rock crusher and vibrating screen motors for a while, for those without fixed mount terminals, I would use split bolts, covered with a layer of varnished cambric tape, followed by 2-3 layers of rubber splicing tape, followed by black electrician's tape. More recently I've used what are called "Polaris blocks", then covered them with rubber splicing tape and then electrician's tape. The rubber splicing tape is because when the electrician's tape gets rubbed through as it vibrates against the side walls, the rubber tends to last a lot longer. The electrician's tape is to just hold the rubber tape in place until it fuses, the varnished cambric is so the rubber doesn't stick to the connectors (not needed for the Polaris connector).
If so, generally I never "pack" it with anything; too much of a mess to deal with later. I use tried and true connection techniques involving multiple steps (depending on the size of motor involved) that reduce the likelihood of failure. I did a lot of rock crusher and vibrating screen motors for a while, for those without fixed mount terminals, I would use split bolts, covered with a layer of varnished cambric tape, followed by 2-3 layers of rubber splicing tape, followed by black electrician's tape. More recently I've used what are called "Polaris blocks", then covered them with rubber splicing tape and then electrician's tape. The rubber splicing tape is because when the electrician's tape gets rubbed through as it vibrates against the side walls, the rubber tends to last a lot longer. The electrician's tape is to just hold the rubber tape in place until it fuses, the varnished cambric is so the rubber doesn't stick to the connectors (not needed for the Polaris connector).
Last edited:
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
I was a fan of T&B motor stub boots. Very thick walls. if vibration was a issue could wrap with some Skotch 70 tape
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
Stone wool thermal insulation.
It won't provide much vibration damping, if any, but it will fill the box, hold the wires & terminations more-or-less in place, and prevent them from knocking against each other or against the walls. It'll never become sticky or messy and will be easy to remove & replace whenever service is required.
www.rockwool.com
It won't provide much vibration damping, if any, but it will fill the box, hold the wires & terminations more-or-less in place, and prevent them from knocking against each other or against the walls. It'll never become sticky or messy and will be easy to remove & replace whenever service is required.
Why stone wool | ROCKWOOL
At ROCKWOOL, we use the inherent properties of stone to create a wide range of stone wool products that can improve your quality of life and help keep you safe, healthy, comfortable and much more.
www.rockwool.com
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Used fiberglass wool insulation in motor termination box that we kept having troubles with on a shaker type of machine and that helped. Same issues you mentioned, terminations wearing through from knocking against the walls.Stone wool thermal insulation.
It won't provide much vibration damping, if any, but it will fill the box, hold the wires & terminations more-or-less in place, and prevent them from knocking against each other or against the walls. It'll never become sticky or messy and will be easy to remove & replace whenever service is required.
Why stone wool | ROCKWOOL
At ROCKWOOL, we use the inherent properties of stone to create a wide range of stone wool products that can improve your quality of life and help keep you safe, healthy, comfortable and much more.
True vibrator motors use two blocks of foam rubber with cavities cut for the splices. Two bearing vibrators are the worst. Four bearing designs are much better. An easy option is order the motor with an IEC terminal block. It’s an option with most vendors. Then use crimped on lugs with proper strain reliefs and you are done.
With North American style...
First other than the 3M boots use crimp on bolted lugs. File down every sharp edge. No burs. Second use varnished cambric or back wrapped Scotch 88 (sticky side out) at least two layers half overlapped (4 layers total) minimum. Everything metal must be covered. Maximum stretch (cambric doesn’t stretch). At least 30-50%. We want it tight. This protects the next layer from cutting plus serves to prevent rubber tape from becoming a sticky mess that is very hard to cut off. Next fill deep voids with Scotchfil. Use scissors to cut strips. Pack like putty. Next rubber splicing tape 130C. Again two layers half wrapped minimum but wrap more layers to get it even. Finally at least two layers 88. First layer tight because 130C will partly melt in service. Outer layer smooth it all out and minimal stretch to prevent flagging (end of tape loosens like a flag).
Now take more Scotchfil. Cover every sharp edge in the enclosure itself or use pieces of rubber sheeting or glastic. Be careful with steel cords in used conveyor belts...don’t defeat yourself. Even wood can work. In home made boxes (regular junction boxes mounted in place of factory peckerheads) on large motors frequent practice is to cut 1 or 2 1x4s or 1x2s enclosure width and push them between the cover and door to protect against the ends of screws or secured with sheet metal screws. Remember the screw heads when you put the cover on. That’s what the wood is for. Make sure the screws aren’t too long. Or use blocks or something in the corners. Tape or tie wrap all the leads and splices tightly together in as solid of a mass as you can and look for any place where cables can or do touch. If they do secure them. Secure it all in such a way that it cannot touch the walls. If it rattles around that’s not good. Practice in most electrical applications is to keep everything open and isolated in “free air”. In a peckerhead it will rub. This sounds physically impossible but do a little at a time and keep poking and pulling and looking for free cables. Leave nothing to get loose later. I keep an assortment of cable ties both the more typical small ones and “monster” ones for this. Clip all tie wraps short and try to avoid the sharp edge. Tape if you have to. I’ve seen some guys do creative things with tying the cable to the fittings or to itself. Even using an extra nut can sometimes help but in practice just getting it all tightly tied together makes the big difference and rarely is securing the “mass” productive.
A few things I’ve tried that don’t work. Since I worked in mining for 25 years and I work for a motor shop now I’ve seen every kind of bad idea tried. Rubber coated terminal blocks such as Insultaps and giant tape balls are two. There is one idiot on my crew that insists on using 6 full rolls of tape on every motor job. His mess looks like it should be hanging from the back end of a large male farm animal and doesn’t do any better than a proper splicing job. It looks very effective and it is until the rubber wears through. What the extra mass does is add inertia so the cables bounce around more. So now the farm animal visual makes even more sense. Most solutions for “filling” rely on this idea except treating the box instead of the cable. It just delays how long it takes to chew through it. Unless you secure the wiring this is not a long term solution and it makes it harder to secure everything.
Mechanical terminations in general (mechanical lugs, wire nuts) in particular have high failure rates. My current employer banned them on motors. Lugs need to be fine strand rated for motor lead wire. Second is silicone F1 tape aka Scotch 70. Silicone tape is great in high voltage situations but it easily splits and years where vinyl doesn’t and rubber tape practically self heals. Again in non-high stress applications it’s harmless. There are a couple plants around here that insist on it so we put a little under the final 88 layer so they feel like they have something but it’s just too fragile. There is an upgraded non-3M version with Kevlar reinforcing mesh in it that works pretty good but it’s a pain to apply since it doesn’t stretch. Biggest advantage with both is that unlike rubber tape it splits and falls right off when you touch it with a knife. Hence it’s probably not the best choice around motors. Anything that isn’t “rubber” that bounces back like spray foams and duct seal just smears out of the way because of impacts so I haven’t found that it really does anything. I’ve also tried filling with packing peanuts stuffed in a peckerhead. Even the non-cornstarch types shrink and don’t do much for very long.
With North American style...
First other than the 3M boots use crimp on bolted lugs. File down every sharp edge. No burs. Second use varnished cambric or back wrapped Scotch 88 (sticky side out) at least two layers half overlapped (4 layers total) minimum. Everything metal must be covered. Maximum stretch (cambric doesn’t stretch). At least 30-50%. We want it tight. This protects the next layer from cutting plus serves to prevent rubber tape from becoming a sticky mess that is very hard to cut off. Next fill deep voids with Scotchfil. Use scissors to cut strips. Pack like putty. Next rubber splicing tape 130C. Again two layers half wrapped minimum but wrap more layers to get it even. Finally at least two layers 88. First layer tight because 130C will partly melt in service. Outer layer smooth it all out and minimal stretch to prevent flagging (end of tape loosens like a flag).
Now take more Scotchfil. Cover every sharp edge in the enclosure itself or use pieces of rubber sheeting or glastic. Be careful with steel cords in used conveyor belts...don’t defeat yourself. Even wood can work. In home made boxes (regular junction boxes mounted in place of factory peckerheads) on large motors frequent practice is to cut 1 or 2 1x4s or 1x2s enclosure width and push them between the cover and door to protect against the ends of screws or secured with sheet metal screws. Remember the screw heads when you put the cover on. That’s what the wood is for. Make sure the screws aren’t too long. Or use blocks or something in the corners. Tape or tie wrap all the leads and splices tightly together in as solid of a mass as you can and look for any place where cables can or do touch. If they do secure them. Secure it all in such a way that it cannot touch the walls. If it rattles around that’s not good. Practice in most electrical applications is to keep everything open and isolated in “free air”. In a peckerhead it will rub. This sounds physically impossible but do a little at a time and keep poking and pulling and looking for free cables. Leave nothing to get loose later. I keep an assortment of cable ties both the more typical small ones and “monster” ones for this. Clip all tie wraps short and try to avoid the sharp edge. Tape if you have to. I’ve seen some guys do creative things with tying the cable to the fittings or to itself. Even using an extra nut can sometimes help but in practice just getting it all tightly tied together makes the big difference and rarely is securing the “mass” productive.
A few things I’ve tried that don’t work. Since I worked in mining for 25 years and I work for a motor shop now I’ve seen every kind of bad idea tried. Rubber coated terminal blocks such as Insultaps and giant tape balls are two. There is one idiot on my crew that insists on using 6 full rolls of tape on every motor job. His mess looks like it should be hanging from the back end of a large male farm animal and doesn’t do any better than a proper splicing job. It looks very effective and it is until the rubber wears through. What the extra mass does is add inertia so the cables bounce around more. So now the farm animal visual makes even more sense. Most solutions for “filling” rely on this idea except treating the box instead of the cable. It just delays how long it takes to chew through it. Unless you secure the wiring this is not a long term solution and it makes it harder to secure everything.
Mechanical terminations in general (mechanical lugs, wire nuts) in particular have high failure rates. My current employer banned them on motors. Lugs need to be fine strand rated for motor lead wire. Second is silicone F1 tape aka Scotch 70. Silicone tape is great in high voltage situations but it easily splits and years where vinyl doesn’t and rubber tape practically self heals. Again in non-high stress applications it’s harmless. There are a couple plants around here that insist on it so we put a little under the final 88 layer so they feel like they have something but it’s just too fragile. There is an upgraded non-3M version with Kevlar reinforcing mesh in it that works pretty good but it’s a pain to apply since it doesn’t stretch. Biggest advantage with both is that unlike rubber tape it splits and falls right off when you touch it with a knife. Hence it’s probably not the best choice around motors. Anything that isn’t “rubber” that bounces back like spray foams and duct seal just smears out of the way because of impacts so I haven’t found that it really does anything. I’ve also tried filling with packing peanuts stuffed in a peckerhead. Even the non-cornstarch types shrink and don’t do much for very long.
- Location
- Illinois
- Occupation
- retired electrician
I have never had an issue with filling the motor junction box with duct seal for applications like that. As long as you get it packed 100% full, the leads do not vibrate and where through the insulation of the conductors.
The use of duct seal was in the manufacturer's instructions for some rotary sand sreeners that I hooked up a long time ago, and after that, where I had similar installation with the motor being mounted to the vibrating part of the machine, I would use duct seal.
In my experience no matter how you made the connections up, the vibration would soon cause a failure. It was not typically at the point of connection, as that ended up being much thicker than the actual conductor insulation. If a few cases, it was not insulation damage from the vibration causing wear through, but metal fatigue resulting in a broken conductor.
The use of duct seal was in the manufacturer's instructions for some rotary sand sreeners that I hooked up a long time ago, and after that, where I had similar installation with the motor being mounted to the vibrating part of the machine, I would use duct seal.
In my experience no matter how you made the connections up, the vibration would soon cause a failure. It was not typically at the point of connection, as that ended up being much thicker than the actual conductor insulation. If a few cases, it was not insulation damage from the vibration causing wear through, but metal fatigue resulting in a broken conductor.
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