silicon weather sealant around dc motor brushes/commutators
silicon weather sealant around dc motor brushes/commutators
(OP)
I'd like to revisit this topic yet again.
Previous review:
thread237-9155: Excessive brush wear
thread237-178054: Traction Motor Brush Wear Problem
thread237-224692: DC Motor Rapid Brush wear
thread237-32685: 800 HP DC Motor Failure - Severe Brush Wear
http://www.morganamt.com/us/files/Morgan%20Carbon%...
DO NOT USE SILICONE SEALANT TO MAKE THE MOTOR WATERTIGHT
http://www.geindustrial.com/publibrary/checkout/DC...
Silicone, RTV, or Bathtub Seal/Caulking is not recommended for sealing DC motors
QUESTION 1 - Any further good references about this? Our repair shop said they wouldn't hesitate to use silicon sealant on a dc motor cover plate as long as it is not near Hydrogen sulfide like paper mmill. What is standard repair industry practice?
QUESTION 2 - What are alternative weather proof sealants? Something with thick consistency for example to fill a 1 / 16" gap?
I found the following alternatives, but don't know much about them.
http://www.morganamt.com/us/files/Morgan%20Carbon%...
“Urethanes, polyurethanes or elastomeric adhesive sealants are recommended for use around brush type motors.”
http://www.geindustrial.com/publibrary/checkout/DC...
Titeseal
Titeseal is the preferred sealant used on waterproof motors to seal fits and bolts. It is non–hardening,
non–silicone. GE#8064200000.”
Previous review:
thread237-9155: Excessive brush wear
thread237-178054: Traction Motor Brush Wear Problem
thread237-224692: DC Motor Rapid Brush wear
thread237-32685: 800 HP DC Motor Failure - Severe Brush Wear
http://www.morganamt.com/us/files/Morgan%20Carbon%...
DO NOT USE SILICONE SEALANT TO MAKE THE MOTOR WATERTIGHT
http://www.geindustrial.com/publibrary/checkout/DC...
Silicone, RTV, or Bathtub Seal/Caulking is not recommended for sealing DC motors
QUESTION 1 - Any further good references about this? Our repair shop said they wouldn't hesitate to use silicon sealant on a dc motor cover plate as long as it is not near Hydrogen sulfide like paper mmill. What is standard repair industry practice?
QUESTION 2 - What are alternative weather proof sealants? Something with thick consistency for example to fill a 1 / 16" gap?
I found the following alternatives, but don't know much about them.
http://www.morganamt.com/us/files/Morgan%20Carbon%...
“Urethanes, polyurethanes or elastomeric adhesive sealants are recommended for use around brush type motors.”
http://www.geindustrial.com/publibrary/checkout/DC...
Titeseal
Titeseal is the preferred sealant used on waterproof motors to seal fits and bolts. It is non–hardening,
non–silicone. GE#8064200000.”
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RE: silicon weather sealant around dc motor brushes/commutators
I have seen microscope pictures of a commutator surface that looked lika an emeraud paper from some cemical union between copper and silicon. Very abrasive. That commutator consumed brushes in a week.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: silicon weather sealant around dc motor brushes/commutators
A non-hardening building mastic of the type used for expansion joints was fairly effective. I have no idea of the chemical makeup, but it wasn't a silicone based material. A quick Google of building mastic suggests it may be an oil-based material, but it is a good few years ago and the exact brand is long forgotten.
RE: silicon weather sealant around dc motor brushes/commutators
Silicon sealants should never be used on any part of a DC motor nor on any equipment in proximity of a DC motor
RE: silicon weather sealant around dc motor brushes/commutators
RE: silicon weather sealant around dc motor brushes/commutators
As Gunnar pointed out, there seems a widespread practice/belief that silicon simply shouldn't be used anywhere near DC motors. I was surprised to hear comments from our shop that they don't view it that way.. .there are simply some conditions when silicon can get you in trouble and as long as we pay attention to those we're ok (they say).... seems somewhat similar to mikekilroy's comments.
Those are somewhat contradicting views. I will point out that while I've heard it said (on the phone by our shop and on forum by mikekilroy) that silicon can be used safely with proper considerations, I haven't seen it in writing from authoritative source. I'm not questioning anyone's knowledge but in general comments from individual does not hold the same weight as comments from brush manufacturer (National Elec Carbon link above). On the other hand, we know manufacturers sometimes fail conservative with respect to anything to do with their product (SKF recommendation to replace all grease after 3rd relubrication interval comes to mind). On the third (!) and final hand, in face of ambiguity we usually can't go wrong choosing the conservative alternative when practiceable.
It sounds like there are some reasonable sealing alternatives. Good point Scotty about avoiding a sealant that will act like glue... would make brush inspection a headache. Neoprene gasket (as Ray suggested) is what our local shop recommended for customers like paper mills that want to avoid silicon. Here's what they steered us to:
http://www.armacell.com/www/armacell/ACwwwAttach.n...
Are these type gaskets re-usable (removing and reinstalling covers several tiems) as long as inspection shows them good?
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RE: silicon weather sealant around dc motor brushes/commutators
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RE: silicon weather sealant around dc motor brushes/commutators
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RE: silicon weather sealant around dc motor brushes/commutators
This might be a useful read: http://www.dowcorning.com/content/publishedlit/The...
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RE: silicon weather sealant around dc motor brushes/commutators
RE: silicon weather sealant around dc motor brushes/commutators
RE: silicon weather sealant around dc motor brushes/commutators
RE: silicon weather sealant around dc motor brushes/commutators
I am not smart enough to evaluate the data for the rubber sheet that you are considering and to answer your question about whether it is suitable for this application or whether it can be re-used. However, I will say that in a general case that rubber gaskets are reusable if not damaged during assembly or disassembly.
Damage during assembly is primarily caused by overtightening that squeezes the gasket out of the joint and can cause splitting at the bolt holes. In this case, the gasket no longer seals the motor and can cause a problem if not detected early on.
Damage during disassembly can occur if the gasket is stuck and is torn when the cover is removed. In either case, rubber gasket material is relatively cheap and, if replacement is required, would be, at most, a fractional cost increase compared to the total cost of reconditioning or repairing a DC motor.
Next question; In my experience silicone is only a concern only for DC motors. This is because of the arcing caused by commutation. Even if the arcing is not visible, the induction of the coils being commutated, by definition, results in an arc. This arc, even if microscopic, is apparently enough to cause a reaction with the silicone over time. Slip ring motors, whether synchronous or wound rotor, do not have arcing as a 'normal' condition of operation. This being the case, apparently silicone is not a problem for slip rings.
Final question: Do not use silicone...period. I have experience with dock (pier) cranes for ports and shipyards that indicates that a proper rubber gasket is all that is needed to keep liquid water out. However, I will add that in these conditions (high humidity environment) that some heat is recommended when the motor is not running to prevent condensation. Field economy circuits are great since they require no additional equipment but, if this option is not available, then separate heaters are recommended.
I hope this helps.
RE: silicon weather sealant around dc motor brushes/commutators
RE: silicon weather sealant around dc motor brushes/commutators
RE: silicon weather sealant around dc motor brushes/commutators
Looks like a good detailed article from Dow Corning, I will study that.
Good question. From the Dow Corning article:
So it seems there is still a hazard after cure if I'm reading it right.
Revisiting the paper some more - they calculate expected concentration and the threshhold for danger is 10-30ppm. The basis seems to be the vapor pressure shown in Figure 2 which varies as a function of type of silicon and temperature.
The thing I don't quite understand yet - looking at "Case 1" and "Case 2" of the Dow article, they calculate the steady state concentration for a totally enclosed container. The variables of interest seem to include the volume of the sealed container and the area and depth of the silicon. But if it is a simple equilibrium concentration calculation, it should depend only on the vapor pressure, the volume of container and amount of silicon wouldn't matter (they would matter for time to reach equilibrium but not equilibrium). I'll have to study some more to see if I'm missing something (unless anyone can offer an explanation?)
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RE: silicon weather sealant around dc motor brushes/commutators
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RE: silicon weather sealant around dc motor brushes/commutators
RE: silicon weather sealant around dc motor brushes/commutators
Most silicone RTV (Room Temperature Vulcanizing) sealants release acetic acid (vinegar) during cure. This is corrosive, so electrical grades will be designed to release methanol instead, which is non-corrosive. There are also silicones that are platinum catalyzed that do not release anything during cure. These are heat cured and if they are designed to cure at room temperature they will come in two parts that you mix just before use.
It is volatile, low-molecular weight, silane impurities in the silicone polymer that causes problems with commutators in motors. Silanes are the monomers that silicone polymers are made from. These silane molecules in the air will become silica (silcon dioxide, quartz) in an arc. Silica particles are very abrasive. I would also surmise, based on how they are formed and the problem that is caused, that these particles tend to get in-bedded into the commutator or brushes.
The silane vapors could only build to problem levels in a sealed space.
RE: silicon weather sealant around dc motor brushes/commutators
RE: silicon weather sealant around dc motor brushes/commutators