The Foundry: Blowing Smoke

In the last post, we saw a fire actually burning in the foundry. The concrete has set, and doesn’t fall apart while being used. After researching other designs, and using some logic, we figured we need to force more air into the system. As we designed previously, there is a large 30mm hole on the side of the forge to allow air into the fire. Unfortunately, this doesn’t seem to provide the amount of air we need to get the desired heat. We have tried a number of ways to force air into the hole, with varying success. First we literally blew into it, like you would a campfire, and it works well, but soon you start to really hyperventilate, and it’s not good. The next idea was to take a chopping board (but any board will do) and flapped it, forcing air towards the hole. This worked much better than simply blowing. Lots of air fuels the fire, and it burns really hot. The big downside is that it wastes most of the air produced, and creates some interesting smoke patterns that seem to be inefficient. Either way, it is a good cheap way to improve the forge performance.

First Tests
The foundry during its first fire, not particularly hot.

The method we eventually used to force air into the system was in the form of a fan. Before I start this section, it comes with a warning, you need to wear goggles if you try this, as will be explained. You have been warned. The initial fan was in the form of an old hairdryer, bought from a charity shop for £3. Putting it right up to the hole forced hot air directly into the hole, with very little waste air escaping. It worked very well, and the fire started to burn much hotter. It also meant we could control the amount of airflow by using the switches on the hairdryer, or simply moving it further away.

Forcing air into the forge
Forcing air into the forge using a hairdryer, the fire is visibly hotter.

Two issues came up while using this method of airflow. The first big problem is the mass of air being forced into the hole needs to go somewhere. The only place it can go is straight up, and as we don’t have a lid it just fires ash into the air. This is dangerous if gloves and goggles aren’t being worn. This ash can be hot and can take some of that fuel and heat away from the forge. A lid will fix this, and that will be covered in the next post. For this test we kept it at a low fan speed, and found a nice point where we weren’t firing ash into the air, but still giving lots of air to the fire. The second problem was that the hairdryer started getting really hot, and the plastic began to melt. Essentially this means it was too close to the fire, but if you move the fan away then the air just misses. To fix this we found a 30mm diameter iron pipe, and attached the hairdryer to it. This allowed the air to be funneled in with the fan unit being further away from the forge.

The fire burning
The fire burning with a steel tin on top to stop the ash flying out.

So what have we learnt from this fire? We need a lid. This will be a topic of further posts, but for now we know we can produce a hot fire, and the air going into the fire can be controlled. Thanks for reading, and hope to come with another update soon.

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