Questions about parts for home made oven

General Composites Discussions Equipment Talk
#1

Apologies in advance for the length of the thread!
As with my vacuum bagging thread, the purpose of this is to help me sort out pricing.

The plan for my oven is to construct it out of the rigid, foil back insulation foam using either 50mm or 60mm thickness. Internal size wise - would guess around about 1m x 1m x 1m. May make it bigger once the foam sheets get bought (they’re 2400mm x 1200mm in size). Thinking of getting the temps up to 100-130 deg C.

Seeing as the foam is rigid, the idea was to make it self supporting - i.e not making an external wood or metal frame.

As for the individual parts;

There are several heating elements I found, but don’t have a clue which would be best?

http://uk.rs-online.com/web/p/cabinet-enclosure-heaters/7166100/
http://uk.rs-online.com/web/p/cabinet-enclosure-heaters/0603328/
http://uk.rs-online.com/web/p/ceramic-heating-elements/3762688/
http://uk.rs-online.com/web/p/ceramic-heating-elements/7241772/
http://uk.rs-online.com/web/p/air-heaters/3742319/
http://uk.rs-online.com/web/p/air-heaters/6151637/

Temp controller;

Is a PID controller the only one to get - as opposed to an on/off version?

http://www.cdautomation.co.uk/temperature-controllers/setpoint-profilers/atr620/
http://uk.rs-online.com/web/p/pid-temperature-controllers/0461212/

Fan;

Is a fan necessary? If so, what sort do I need that’ll survive up to 130 deg C temps?

Solid state relay;

REALLY clueless regarding which one I’d need.

Is that everything I’d need? I really appreciate people taking the time to read my thread :slight_smile:

Thanks.

#2

Cay your foam handle 100 to 130*C?

Most extruded polystyrene products are only stable to 75*C. Your foam might be just fine though. Just double checking. :slight_smile:

You should most certainly have a fan of some sort to circulate the air. Otherwise, you will end up with hot and cool spots in your box.

Can you get a Ranco Controller in your area? These simple units have a build in relay and don’t require the need to step down the voltage for the controller. With the Ranco unit you simply run the power in and the power out to the heating element.

Here is thread to how I built one of my lower temp ovens (60*C). I’ve swapped out the thermostat for a Ranco unit and put in a larger fan that can handle the heat without throwing the bearings (Rated for 70*C). I know that you need a higher temp oven so I just throw this out for ideas.

#3

This will be one of my next projects as well (planned for summer). My plan will be using metal shelving as walls and Rockwool (good to 1200°C) for insulation. I’ve pulled heating elements and a fan from an old oven. I will also start with the thermostat from the oven but change to digital when it all works.

I thought about using just foam insulation but it seemed too fragile. I also need to mount my parts in a frame, which would be too much weight for the foam.

If you are going to put parts in a vacuum bag inside you will need access for the hose and some type of mesh to keep the bag away from the heating element.

#4

Wyowindworks, the only reason for me wanting to work between temps of 100 - 130 deg C was because the date sheet of the resin I’d like to use say that post cure temps of the ones I’ve mentioned mean less time spent in the oven. Therefore it’ll mean I can get more done in the day if I’m not having to wait as long for cure cycles to finish.

I can get one of those Ranco units, yes. Found a website that sells them.

Datas - I think I may end up building a breeze block ‘oven’ and line it with rockwool. It may be cheaper than using the solid foam insulation. That way I can include sturdy shelves like you will do. Is it necessary to have a hose attachment inside the oven? My plan was to put the vacuum bagged part inside without any further vacuum pressure.

#5

no, you can have the hose go through a hole in the side. It is easier to seal off the hose thermally with an attachment inside the oven but it shouldn’t be too much different just making the hose fit tightly in the hole.

I have a regulated vacuum pump and don’t leave bags unattached. I always keep parts under full vacuum until cured.

#6

fan, you can mount the motor outside, and shaft going through the oven wall. metal blades obviously.
PID can be any, there are a few that are specificity for a heater control. The relay is for routing the heater though. You can NOT power a few 100w heater from the PID. The PID will control the relay on and off, and the heater is routed through the relay. The relay has to have a power rating above the heater power. simple ohm’s law to figure that out, if the relay is rated in V/I and the heater is W/V

I have an Overkill9000 coffee mug heater with an Omega PID and Solid State Relay. The PID gets feedback from the thermocouple, and sends a small electrical signal to the relay to turn on and off, just like a switch. The heater is wired to the relay, and the relay inturn, to the wall power. So there is no connection from the heater to the PID. But if I want to go from 50w heater, to a 500w heater, all I have to do is plug in a new heating element.

heating element: anything that is in a good power range, and easy to mount. Depending on your size, and temp needs, 1000w should be fine.

#7

Thanks for the responses everyone. :slight_smile:

#8

Here are some suggestions, based on a few ovens I’ve made:

Outside a welded steel or bolted aluminum frame to hold the stuff.
Foam: used on the outside of the oven wall polyisocynurate sheets sandwiched between 500microns of aluminum.
Main insulation: 70-100mm of rockwool.
Inside face: galvanized steel sheet.

Make a double walled inside where the divider is for plenum and the fan. Run a hightemp ball bearing supported though the walls with a metal fan at the end.

You can make your own PID controller from an Arduino based board and control the fan and heater independently, or you can use a commercial PID temp controller. Remember, a huge difference in power to the fan (inductive load) and heater (resistance load). The solid state switches which switch at the zero-voltage sine curve are best, and for the trouble you’re going through are also not too expensive. You can get the Crydom SSR on RSwww site where you’re getting the resistance. Oversize your SSR always and heat sink them well.

Crydom SSR’s have a light based isolation from the control and power sides, the light based uses a LED. Currently this is the safest way to drive your loads without frying equipment. So any PID signal that can drive a LED will work for your appl.

Now, be careful with high power, all this info is without any guarantees and what you do is your responsibility.

#9

Thanks for the replies everyone :slight_smile:

#10

I just bought a fuji pxr controller
http://www.instrumart.com/products/4714/fuji-pxr-temperature-controller
and a 40A Solid State Relay
http://www.instrumart.com/products/4533/carlo-gavazzi-rs1a-series
from a company called instrumart. they were nice enough to talk me thru what i needed to get the thing working and even found some heat elements that would fit around a tube for me.
you would be looking at about $200 to get it to you…