element for heating funnel to constant temp

[westrock]

I need to keep this stainless steel funnel at a constant temp of 150-250 degrees F. The funnel is used to hold and meter out liquid boiled sugar in the making of hard candy. I was wondering what materials, controllers, and circuit I'll need. The circuit should include some type of thermocouple for control because once the correct temp is found I'll need to keep the boiled sugar at a constant temperature. I'm also considering insulating the funnel with some kind of heat resistant material to conserve energy.

 

[dougy83]

You could probably attach some heating elements to the funnel e.g.
**broken link removed** (cartridge)
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with some thermal diffusers to spread the heat.

Then control the whole thing with a PID temperature controller
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You'll need to attach or insert a K-Type thermocouple also
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If your heater element setup is >700W, then you'll also need e.g. an SSR to handle the power
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[ronv]

If it is a fixed installation you might think about some halogen bulbs and a cheapie thermal switch similar to this:

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[westrock]

I can visualize attaching cartridge elements to the side of the funnel and covering with fiberglass insulation, and an outer shell. I'm thinking perhaps copper wire wrapped around next to the stainless steel funnel would act as a thermal diffuser. The thermocouple would stick in through the side of the funnel into the centre of the funnel to monitor boiled sugar temp.

 

[alec_t]

Ordinary ceramic-bodied power resistors would probably be cheaper than cartridge elements.

 

[dougy83]

Ordinary ceramic-bodied power resistors would probably be cheaper than cartridge elements.

Yes, they will probably also be easier to mount and have better contact with the funnel than the cylindrical elements. The multicomp 10W resistor I checked out on element14.com (which is <$0.30) is rated up to 390°F as well, so that should be plenty for the heater. The only issue is that you'll need a heap of them; e.g. 200W will need 20 resistors, which might be getting a bit bulky, although you could run them at a bit more than 10W to reduce the number required I guess.

If the thermocouple is mounted inside the sugar there will be no control of the funnel temperature during start up (so the funnel will get hotter than the sugar and I guess could burn it). If you mount the thermocouple on the funnel, then the funnel will be at the correct temperature and the sugar will be at a lower temperature (you could compensate by increasing the set temperature), but won't burn.

 

[westrock]

Good point about the thermocouple inside the funnel; never thought about that. Flat sided resistors would be easier to mount and the more the better as that might mitigate the need for a thermal diffuser of some kind. How do I wire the resistors, temp controller, and thermocouple all together to create a plug in unit? The funnel is filled with boiled sugar and then moved by hand over the silicone moulds that I make.

 

[alec_t]

Depending on the resistor values and available power source (presumably mains-isolated 'low' voltage) you could probably wire all the resistors in series so would need only two connection wires for those, plus two/three wires for a temp-sensing thermistor or IC (much cheaper than a thermocouple).

Flat sided resistors would be easier to mount

True. Whatever their shape you could embed them in grease/mastic to improve thermal coupling to the funnel.

Edit: BTW, is the funnel sealed at the bottom, or does it have a removable plug?

 

[westrock]

The funnel has a valve at the bottom to control the flow of liquid boiled sugar into the molds

 

[Mr RB]

I would glue a heap of 5W resistors around it in a spiral and solder their legs in series. Then wrap some layers of insulation.

You could use resistance wire in the same way, but it is harder to drive. With X number of resistors you can easily choose the current and dissipated wattage for your existing PSU.

 

[ericgibbs]

The funnel has a valve at the bottom to control the flow of liquid boiled sugar into the molds

hi,
Have you considered a free standing heated block with a cone shaped recess in the top of block, in which the pouring funnel fits into.?

The shaped block could be easily heated and kept at a steady temperature and lagged against heat loss.

E.
Of course the funnel is lifted out of the block when used for pouring.

 

[westrock]

No, I never considered a heating block.....what material would the block be made of in a situation like this, and what does the term "lagged" mean?

 

[alec_t]

Looks as though the handle will also reach 250° if the funnel is kept at that temperature. Will that be a problem? If not, then the funnel could simply be placed in an oven maintained at the required temperature.

 

[ericgibbs]

No, I never considered a heating block.....what material would the block be made of in a situation like this, and what does the term "lagged" mean?

hi,
Lagged is a term used to mean 'thermal insulation', it would reduce the heat loss from the block, so that the block temperature would be more easily controlled and would have a lower heat burden.

I will leave you in the capable hands of 'alec' regarding the block design, an aluminium block would be easy to machine.

E.

 

[alec_t]

Thanks, Eric! It would be a hefty block. That's partly why I was thinking oven rather than block.

 

[ericgibbs]

Thanks, Eric! It would be a hefty block. That's partly why I was thinking oven rather than block.

alec,

As the dispenser is a funnel, where does he 'stand it' when it full of hot candy..

I thought the heater block could also be a holder for the funnel shape, when he wants to let go of it.

E

 

[alec_t]

The block would make a fine holder. A plate (oven shelf) with a hole could act as holder too.

 

[Mr RB]

...
As the dispenser is a funnel, where does he 'stand it' when it full of hot candy..

I thought the heater block could also be a holder for the funnel shape, when he wants to let go of it.
...

I assumed that a large heavy funnel full of very hot sugar would just be mounted in a fixed frame, where new ingredients are added at the top and the bottom (valve etc) dispenses onto a movable tray?

There's no way I would want to be holding that thing up in the air waving it about for hours on end...

 

[ericgibbs]

I assumed that a large heavy funnel full of very hot sugar would just be mounted in a fixed frame, where new ingredients are added at the top and the bottom (valve etc) dispenses onto a movable tray?

There's no way I would want to be holding that thing up in the air waving it about for hours on end...

I did not assume that to be holding that thing up in the air waving it about for hours on end.

This is what the OP said:, there is no mention of using the dispensing funnel as a mixing bowl.???

The funnel is used to hold and meter out liquid boiled sugar in the making of hard candy.

I would say an 'oven' or 'heated block' would be a far more sensible way of heating the funnel, people talk about heating elements and sensors being directly attached to the funnel.!

Just think about the trailing wires or connectors needed to do it that way and the added weight and nuisance in using the funnel if heated that way.

E.

 

[Mr RB]

...
This is what the OP said:, there is no mention of using the dispensing funnel as a mixing bowl.???
...

When I said "ingredients added at the top" that referred to the molten sugar being added at the top, not mixing. My fault, sorry i should have used better description.

I would say an 'oven' or 'heated block' would be a far more sensible way of heating the funnel, people talk about heating elements and sensors being directly attached to the funnel.!

Just think about the trailing wires or connectors needed to do it that way and the added weight and nuisance in using the funnel if heated that way.
...

Exactly why you would not want to be holding it in the hand when dispensing! Wires or not that thing will weigh 4 or so pounds of very hot goo. Not great in the hand.

Also if dispensing for some time the contents will cool, and if heated in a block it reduces throughput as it can't dispense when heating.

The OP hasn't said exactly how the funnel is used, so really it's up to the application. My suggestion for safety, heat and throughput would be to have the funnel fixed in a frame that carries the weight and keeps it permanently hot, and move the target under it.