Homemade electric melting crucible furnace

So, furnace for melting of metal. I didn`t discovered anything, trying to produce a device from available parts and trying not to fail in production process.
 Melting oven with transformer. Upper part of oven is called “melting device”, the bottom one is control unit. Don`t be afraid of white box on right side – it is just transformer.
 Main parameters of oven:
- Capacity: 1000 WA;
- Volume of boil: 62 cm3;
- Max.temperature: 1200ºC

Melting device

As I had task not to spend time for trials with corundum-phosphat combinations, but to really spare time by using of ready components, I used the ready heater of company YASAM and his coupling device – ceramic muffle.

        

Heater: fechrale, wire`s diameter 1,5mm, there are studs (d= 3mm) welded to output ends. Resistance is 5 Ohm. Muffle is not necessary because inside of heater – the wires are without coating. Dimensions of heater: D=60/50x124mm. dimensions of muffle: D=54,5/34x130mm. You should make a hole in muffle`s bottom for studs` lifting.
 Make housing of melting device from common stainless steel pipe D=220/200, turned until required thickness of walls is achieved. I didn`t taken the height value randomly. As we will have grog brick as felting, height includes 3x thickness value of brick. It`s correct time to show you the mounting drawing. In order not to overload current homepage, I will provide you refers instead of drawings: Part1,  Part2.
Boil is positioned on disk made of grog brick. This grog brick is not clearly evident on the first drawing. Height of this disc depends on type of boil. There is a hole for core bar in the middle of disc. Core bar is sharpened and in upper position it doesn`t touch the boil.
 As above mentioned, felting of oven si made of grog brick of type SHL0,4 or SHL 0,6 of size #5. Brick dimensions are: 230x115x65mm. Muffle is processed with saws and sand papers. I guess you will have to change saw very often :)

Processing of grog brick. On the right side – there is brick on beginning of work Straight sipes are to be made by saw for wooden, for curved sipes – I used self-made saw from saw plate with large teeth, with reduced (abrased) plate`s width.
While manufacturing of felting you have to keep the following rules:
- Don`t use any mortar for fixing of parts. Everything should be dry. Anyway it will destroy it
- Please avoid contact of the parts of felting to any other parts, ther should be gaps and no tension
- Large parts of felting (if you will make it from other materials) – it`s better to divide it on small parts, anyway it will be cracked. That`s why it`s better if you will do it by yourself.

  

  

Please make hole for thermocouple in third ply, making gap in first and second ply between heater and felting. Gap should be so minimal that thermocouple will hardly slide in hole, located as near as possible to heater. You can buy thermocouple on YASAM-market, but I prefer the self made one. Not because I`m greedy (although they are of high price there), but specially leave uncovered soldering area for better heat contact. But in this case you have risk to burn incoming circuits of controller.

Control unit

Cover and bottom of control unit contain meshes for cooling of heater`s outcomes. Diamater of outcomes should be 3mm. There is also heat emission through bottom of melting device. Cooling of controller is not needed – because there is capacity of 10Wt only. You should cool the cold ends of thermocouple also.
 Control unit with temperature control Thermodat-10K2. On upper right corner – power switcher is located. Upper left – lever of boil`s lift with core bar of lift (electrode for stainless steel d=3mm).

Why did I select Thermodat as a controller. I had experience with Oven, but once after keeping device in non-heated room during winter, fixing sewing was lost. Thermodat survived several winter seasons and kept not only its sewing, but the settings also. And – this device has strong metal housing – it is very reliable. (Manufacturers of this device owe me certain amount of money for my advert, certainly :)
You can use power element of this set, also. Control unit of simistor BUS1-V01. This unit is accommodated to work with Thermodat devices specially. Hereby please operation manual for Thermodat-10K2.
Circuit plan. High-amperage circuits are marked with bold line. You should use wire of section 6mm2, at least.

I`ll inform you about transformer later. Now – few words about control unit. It will be switched by toggle switch T1, is protected by fuse of 0,25A. There is a surge filter built-in into transformer`s housing and is aimed to provide power to controller. You should use simistor TS142-80 (1420V, 80A, I`ve signed out it in CHIP and DIP). I located the simistor on the radiator, but as my experience showed, it doesn`t get heat too much. Please don`t forget to make an insulation simistor against of housing. You should use mica or ceramic. You should isolate either simistor separately, or - simistor assembled with radiator.

         

On pict.12 you can see that behind of Thermodat there is fan`s control unit located. I added this control unit to fan later, and the fan itself I put on lower mesh. Construction of control unit is very simple: transformer, bridge and condenser. Output is 12V. The fan (cooler) I dismantled from computer.
 Output of heater. Output will occur through mesh, isolated in ceramic pipes. I used across drilled screw to connect it to the terminal.

                                    

Input of thermocouple in control unit. If you don`t have such ceramic pipe, then you have to pay this money in YASAM-market. Please notice: mounting is done by using of common mounting wire, high amperage circuits are done by using of cables with section not less than 6 mm2. Ends of cables from thermocouple have been put direct in terminal box. BUS in its in-plant-manufactured appearance doesn`t pass in its place, therefore I had to dismantle cover (it doesn`t make life easier, but I don`t care :). Other items are well shown on picture.

Transformer

Despite of its fearsome appearance, this device is common transformer for 1 kWt. It has such appearance because it was several times as different device in the past in use (graphit melting device, welding device etc.). This device obtained a housing, automatic switching, power consumption indicator and other pretty things as well).

       

You don`t have to make such device like I did – a simple transformer for 1kWt is quite enough. Base is transformer from iron Ш-shaped. Depends on need, I make re-winding without disassembly and I don`t change the initial first coil. Why should we use a transformer?
 In order to let the heater work for certain time, diameter of wire should be as thick as possible.
After review of this chart, we can make a disappointing conclusion – the wire should be as thick as possible. And for sure it will be not 220V.

Therefore you will not find in serious devices the heaters made for 220V. If you will connect this device to power net, the need of consumption will be 9kWt – it means you will switch off power in whole house and heater itself will get a serious hit – the last hit. That`s why there are the schemes in use which limit the voltage. I mean the most suitable approach is to use transformer.
 Well, first coil:
- 1,1 V / each wind cycle;
- no-load current: 450 mA.
The second coil:
- for load 5 ohm and capacity 1,000 Wt, resistance will be 70V;
- Current of second coil: 14A, cable`s section 6 mm2, length of cable 28m. This heater doesn`t have nine lives, certainly. But I can easy change it, after i`ll find the appropriate wire and after re-winding of second coil.  If have read the operation manual for Thermodat, you`ve recognized that limiting of maximal capacity is possible. But this is not convenient for me because we mean the middle-ranged capacity of heater. Being in mode of distributed pulses, like we have, we will have pulses for 9 kWt and we will have dance party. There will be enough power for neighbors also, because the automats in houses`s power net are calculated to be for middle-ranged capacity.
For those who doesn`t like to read operation manuals I provide the memo-sheet containing data about coefficients and alignments for individual oven. After having settings on Thermodat done, you just have to switch transformer on and you are ready to work.

Indicator of incoming current – due to inertia effect – will show the middle-sized capacity as well. Until the heater is cold, we will have current close to 5A, then a little bit lower – after warming up phase (due to increasing of resistance of heater). The closer to the prescribed value, it will decrease almost till 0 (work of heater`s PID).

Work

Boil with metal. The cover inside has felting done by lightweight grog with mortar intended for firestones and ovens.
 Special for curious readers (as I am, actually): There is a show window made in cover, this window has been covered by mico ply.

                         

Temperature is above +1,000ºC, but the melting oven`surface hasn`t been any significant warm. This signs the quality of felting. Content of boil was melted in 30-40 min.
 After melting completion, you should press lever of lift, then you can catch the boil by using of grab. On the picture, there is a groove in upper part of boil shown, in order to assure more reliable grabbing.

P.S. As for boils.YASAM company provides its ovens with graphit crucible, working with these heaters. If you work with gold or silver, there is a sense to purchase this set. But I`m against this lavish items. It means, stainless steel pipe D=32/28 matches to diameter of graphit boil. I let you make the conclusions ;)