Ultrasonic Sealing

[Bikeguy]

We have been debating this question and looking for guidance on classifying Ultrasonic sealing with no luck. I am hoping someone might provide guidance. For those who don't know how ultrasonic sealing works I'll provide the dumby's guide.

In our application of bag sealing, an ultrasonic transducer converts elec energy into sonic mechanical movement. This is tranmitted through a mechanical amplifier (specially shaped metal) into a horn (another piece of metal) The horn then compresses two layers of a poly bag between itself and the anvil and delivers the sonic energy into the plastic causing the molocules of the plastic to vibrate, heat up, and fuse. There is no actual heat delivered from the horn or anvil. Any heat realized is conducted into the horn and anvil as a result of fusion

The debate has been if the horn and sealing surface fall within the jurisdiction of the code (NEC/IEC) for the purpose of classifying a component for Cl II Div 1. The transducer, the actual electrical device does not necessarily get hot.

If the transducer can be ratedhermetically sealed and intrinsically safe and all other electrical wiring and connections are per code for this class, then does the jurisdiction stop at the transducer and the temperature of the sealing surface is not part of the classification consideration but should be taken up as a separate safety consideration for the area.
I am arguing that the temperature at the sealing surface should not be a factor in considering a piece of equipment for this purpose.

Have there been an interpretations or writings on the topic?

I hope someone has some experience with this.

 

[rbalex]

You may need to dumb this down even further for me. The process you described doesn't seem to require Class II classification in the first place. "Dusts" don't seem to be a process consideration.

Assuming the classification is nevertheless correct, hermetic sealing would not seem to be an appropriate protection technique [Section 500.8] since an enclosure's surface temperature is the primary concern. Intrinsic safety is also questionable if enough heat can be generated to fuse the plastic.

 

[Bikeguy]

Good question and part of why this has been such a difficult question to answer.
Dust is an issue because it is a combustible dust. kst 3. So we must consider electrical equipment surface temp in these applications to address the dust layer question in NFPA 499.
But when people have looked at this from a high level they look a the entire machine. They say that the sealing surface could exceed the temperature for the dust and therefore it does not meet the compliance for Cl II Div 1. The transducer doesn't get hot. Just the sealing surface. Remember my question is around where does the jurisdiction of the NEC start and End.
To use an analogy, you have a motor and a pump, pumping a very hot liquid and located in a Cl 1 Div 1 area. The motor must be listed for the area it is being installed and include a T rating in line for the conditions. But the pump that is coupled to the motor might exceed the safe temperature. It does not have any requirement for labeling or qualification according to the jurisdiction of the NEC. It does need to be addressed separatly according to OSHA 1910, for safety reasons but you stop considering the device at the motor output.
In my case I challenge that the transducer needs to comply with the NEC but the sealing surface which is a mechanical (friction) energy, does not fall under NEC jurisdiction and should be evaluated separatly.
If each electrical component including the wiring method from the power input to the transducer meet the requirements of the NEC, then we should be compliant with the overall installation. Again the heat at the sealing surface should be addressed separately for the rated area, much like a Hot pipe that might run through an area.

I hope this helps. It is a somewhat complex concept to understand and explain.

 

[rbalex]

I don't know what "kst 3" is and a google search didn't help. Perhaps you could post an appropriate MSDS.

Again, assuming the location is properly classified, it would seem your transducer is fine for Class II, Division 2, hermetically sealed, intrinsically safe, nonincendive or not. In fact, if the mechanical sealing surface could ignite the material, see NFPA 499, Section 6.5, particularly 6.5.3.

Electrical area classification is for selecting electrical equipment. See Section 500.1 and NFPA 499, 6.1.1

 

[Bikeguy]

I do apologize. K_ST is one of many factors used to measure the explosibility of a dust. A K_st of 3 is the worst case, and one we have to deal with in our business.

I think your information has been very helpful. I know this is something that people don't want to definitively say one way or the other.

But I think if we can make our own assessment as to where the electric ends and the mechanical begins we can clear out one factor of the argument against using this technology.

I hope others might also weigh in. Especially those directly connected with the NEC interpretations. Or those that may have had some experiences with similar evaluations. How would an inspector interpret this if they came across this installation. If all the components met the area class but the heating surface it self were > T number allowed. Hard to say without seeing it, but this is a discussion.

Thanks

 

[GoldDigger]

In that limited context, I would have to say that the electrical portion of the equipment ends at the transducer, but only in the same way that electrical portion of a tubular element heater ends at the outside of the tubular element.

The outside surface of the transducer does not get hot, so you have a strong argument that the electrical classification ends there too.
In the case if microwave energy rather than acoustic energy, the demarcation would, IMHO, not be as clear cut.

Tapatalk!

 

[rbalex]

I do apologize. K_ST is one of many factors used to measure the explosibility of a dust. A K_st of 3 is the worst case, and one we have to deal with in our business.

I think your information has been very helpful. I know this is something that people don't want to definitively say one way or the other.

But I think if we can make our own assessment as to where the electric ends and the mechanical begins we can clear out one factor of the argument against using this technology.

I hope others might also weigh in. Especially those directly connected with the NEC interpretations. Or those that may have had some experiences with similar evaluations. How would an inspector interpret this if they came across this installation. If all the components met the area class but the heating surface it self were > T number allowed. Hard to say without seeing it, but this is a discussion.

Thanks

I finally found a reference to K_ST. It appears to be an IEC concept. It isn't relevant to the NEC/NFPA; i.e., the violence of a dust explosion isn't relevant, only that the electrical system isn't the source of ignition. The Group [E, F or G] and Layer or Cloud Ignition Temp are also relevant.

As far as, "... those directly connected with the NEC interpretations", you may want to review my profile.