Conveyor belt games are one of my favourite type of games, I can spend hours on them without noticing. However, what keeps me from doing so with your game is the sound design, I find the voices quite annoying, and the fact that it is almost the only sound in the game is too bad.
I had a hard time figuring out how to play, and what were the cities (at first I thought it was where you could put your factories). When I undertood all of this, I had fun at first, but the voices were too loud and annoying, I wish I could disable them. You put prices in the upgrades and cities, which is nice, but it's too bad you didn't do the same for the extracting factories and assembling factories.
I didn't know what the warehouse were for at first, and I spend quite a lot of money before noticing it was only for your own properties, not somewhere you could put all the thing you extrated to send them later. Also, your resources were difficulte to tell appart, especialy between iron and coal, be careful about that and use different shapes as much as possible to help people (espacially color blind people) to recognise resources. At first I was frustrated that assemblies had on way out that couldn't be moved, but later I thought it was actually an interting challenging feature.
However, I may be a little harsh in my feedbacks, but I think you did quite a good job for 48h by your own, and with a few updates I may play your game a little longer !