Custom precision hot plate from scratch - heating element?

[julianf]

For some time I've been wanting to make myself a precision hotplate.

My plan is to have a billet of alloy, about 20inches long by about 8inches deep, and have some sort of element attatched to it, set in it, etc. and then have a thermo couple attatched to a PID, driving a solid state relay, for quick PWM of the power to the element.

I'm fine with all the control, it's just the attatching / setting into the block of the element that I have little idea about.

Max temp will be about 150c, so not really that hot at all, but I need it accurate, hence all the messing about.

Any ideas / suggestions for the element?

Thank you.

 

[PhillipM]

Silicone pad heater bonded to the plate (or some are self adhesive).

 

[piman]

Hello Julian,

consider making your block as a sandwich of two sections, mill out the sections to take tubular resistance elemenst sufficient in number to make up the desired power, in other words the elemenst being the filling in the sandwich. Elements are available in different lengths and can also be bent if desired.

Alec

 

[slim_boy_fat]

My plan is to have a billet of alloy, about 20inches long by about 8inches deep, and have some sort of element attatched to it, set in it, etc. and then have a thermo couple attatched to a PID, driving a solid state relay, for quick PWM of the power to the element.

How about an element from an air fryer?

 

[Kayos]

Cartridge heater(s) into machined holes would be my preference, lots of data on tolerances and heat transfer

 

[Bullet2012]

Glow plugs ?

 

[hotponyshoes]

Silicone heater mat on the underside,
The self adhesive type will work fine, use some high-temp silicone sealant around the edges to protect it unless you are milling a recess for it to sit in.

Get a pad with an overtemp sensor/switch built in. You can then mount the temp probe nearer the top/user surface. You will want a pid controller and may need to give it a couple of dry runs in learning more for a block that large.
Ps, you can run several pads at once which might work out cheaper than buying one large one

 

[slim_boy_fat]

Silicone heater mat on the underside,

Will one of those [or more] have enough 'ooomph' to heat through 8"? [assuming it's going to be on/close to the underside and not recessed into a deep milled cut-out]

 

[hotponyshoes]

I would have thought so,
I have got a 1500w one that boils a bath of 20 odd litres with no problem.

Test tube heaters are blocks of alloy about 8" and they work fine off a single mat of about 50w

 

[PhillipM]

I'd think so, you should be able to get at least 1.5kW out of a 20" heat mat.

 

[hotponyshoes]

What are you using this hotplate for?

I fancied making a teppanyaki plate, either from some heavy anodized aluminium or some stainless steel.
Most of the affordable heater mats seem to be about 150degC continuous rated though and I'm not sure if that's hot enough?

 

[daleyd]

How about a plate heater set into a machined slot under the block - I’d think the mass of the block would be enough to distribute the heat around. Either that or a silicone mat type.

If doing it on the cheap would an old element off a cooker hob work, sat in a machined recess??

 

[PhillipM]

What are you using this hotplate for?

I fancied making a teppanyaki plate, either from some heavy anodized aluminium or some stainless steel.
Most of the affordable heater mats seem to be about 150degC continuous rated though and I'm not sure if that's hot enough?

I used to machine the cutouts for heater elements for huge ones of those on the mill - about 6ft x 2ft with a 12mm bar heater sandwiched between two 2" plates - IIRC they did about 300c in hot zone and ~100c at the edges.

 

[julianf]

What am i using it for -

Curing of ink on printed parts. Its fairly fussy on temp, and, whilst i have an overhead dryer, its not as even as i would like, and ive ended up over baking things in the past. Its meant for tshirts really.

As the print is onto alloy, i figure a big lump of alloy, at the right temp - if i drop a thin plate onto the top, its going to get to the same temp as the block pretty much instantly, and then i can just start the timer.

 

[julianf]

I dont care if this thing takes 10 mins to heat up or anything like that really - so its not like i need a million watts for instant heating.

I really have little idea about the losses etc at present though!

 

[Kayos]

https://www.omega.co.uk/prodinfo/cartridge-heaters.html#