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Water bath for acid
This article presents a DIY to heat acid in a water bath.

Why such a device?

The need : To etch stainless steel damascus or stainless steel suminagashi, they must be soaked in hot chlorhydric acid!

Risk management : Handling acid is not without risks. I've often seen jars of acid lying in a pan of water. The pan is placed on a hot plate. The whole thing is installed on a more or less stable table in the workshop...
In short, not so good for the safety aspect!!

Obviously, acid handling must respect the usual precautions (PPE, ventilation, stability of equipment) under the responsibility of the person handling it.

The following device allows to :
> To respect the maximum safety.
> Ensure the stability of all elements.
> Minimise the quantity of acid to be handled.
> To be able to perfectly control the temperature.
> Have a reasonable cost price.

First of all, this is what it looks like when finished:

Hardware
First of all, the shopping list:
> A wood board from scrap that will serve as a base and support for the whole.
> A tall and narrow glass jar that will be the container for the acid. The most practical format is for canned asparagus (like 17cm high and 6cm in diameter).
> What to tinker a support for this jar (metal sheet, metal wire).
> A domestic old kettle (or a basic model).
> A box to install all the electrical junk.

For the temperature control, I have chosen a REX C100 kit ordered on the internet (ebay) for a small amount sum (12€).
The kit includes :
> Temperature controller module REX C100, think to check the supply voltage (220VAC) and the type of output (SSR).
> Solid State Relay (SSR) 40A with its heatsink (which will not be used here).
> Thermocouple K.

As the K thermocouple is not waterproof, I bought a PT100 waterproof (IP68) temperature sensor from Gotronic.

To ensure proper operation, the same kind of verification can be done as for the tempering oven.

A measurement of the resistance between the two wires of the PT100 should give a little more than 100 ohms at room temperature (about 108 ohms at 20°C).
Assembly
The assembly is rather simple.

(1) The support is built by a metal sheet and metal rods welded together underneath. The dimensions must be adapted to the jar. Leave at least 1cm between the base of the support and the bottom of the kettle. The top of the pot should be a little higher than the top edge of the kettle.


(2) Attaching the kettle support to the basis. I put some wooden shims and neoprene glue, but screws can be used if the shape of the support allows it...

(3) Make a hanging system for the temperature sensor. A hook and some collars will do the job.

(4) It's time to get out the the soldering iron! Here is the schematic diagram.

And the implementation.

NB : Do not forget to connect the earth of the kettle to the earth of the mains plug.

Getting Started
The first thing to do is to configure the C100 for the PT100 sensor. Enter the binary value "1000" for parameter SL1.

Then:
> Position the acid jar in its support.
> Fill the jar with acid (pay attention to safety).
> Fill the kettle with water. As the water does not boil, it is possible to exceed the maximum level indicated in the kettle.
> Position the PT100 sensor so that it is well immersed.

> Switch on the kettle.
> Set the desired temperature (SV of C100).

Let's go!

The acid is at the right temperature in about a quarter of an hour.