Foundry Continuous Sand Mixers
Bad Fish says….not all sand mixers are alike. There are many brands of continuous sand mixers on the market, and to the novice they all look the same. I used to be a novice. I remember my first two weeks at KO Steel using technology that was outdated, high maintenance labor and cost, and frankly no fun to be around. I had the opportunity to work in three foundries before I started building and selling foundry equipment. Each of those foundries were unique and all three had older brands of continuous sand mixers.
At the time, my job was to keep them making molds, which I did. If they broke, fix them fast. If they were out of calibration, figure out why and get them running again. And, oh, by the way, hurry up.
Then I got to make sand mixers. I remember the first time I built personally a continuous sand mixer. It was my first week or two of work at major equipment OEM, and an introduction of the complexities of building it 100% perfect (100% perfect is not a common term in the middle of a foundry especially when your mixer is broke down). When you work in a foundry your job is to keep the equipment running, no matter what. A lot of duct tape, bypassed safety circuits, wrong parts, etc litter many machines that were formerly 100% factory, smooth running machines.
So what? Aren’t all sand mixers about the same? If you look at them from 100 feet away, yes. They are all very similar. An example…I went to China 7 times in order to build and promote U.S. designed sand mixers within the Chinese market. Well, a brand of machine that had been common there in the past was Dependable Fordath. I saw a lot of them - both U.S. built and Chinese copies. In one communist rail foundry, they had one of each. They looked exactly the same from the outside, however, the U.S. version used 1% binder and the Chinese version used about 1.3% binder. Hmmmm. Maybe something on the inside of the machine matters?
There are things that matter on a sand mixer. It is my opinion that they are:
- A brutally well made machine that features heavy steel will last longer, period. If you compare the mixers we supply to any brand X, you will clearly see that ours are robust. Not just the shell, but check the mixing shaft out also. If you buy a cheaper, lighter weight machine, your will invariably get vibration in the mixer shaft over time. We have heard this complaint from many foundries that own others' machines. Our mixers are very heavy, the shafts are machined to very tight tolerances, and the shafts are large diameter ensuring stiffness and rigidity. This is important.
- Robust resin delivery system. Delivering resin to a sand mixer is simple. It really is. However, some folks out there feel the need to glue a bunch of fancy controls, bells whistles, lights and assorted other B.S. to their control systems. KISS (Keep It Simple Stupid). Use a DC motor with high torque, use the correct size pump for the job, use STABLE and ROBUST DC controls, use the right size resin delivery hoses and pipes, and presto chango mucho magic………your resin delivery will be consistent. Isn't that what you want? Quit buying in to fancy dancy control systems that are only trying to cover the flaws in the base resin delivery package. Buy a robust resin delivery system, calibrate it from time to time (using good statistical process control methods), and concentrate on making good molds.
- Spare parts. Buy a machine from a vendor that does not scratch off part numbers. How frustrating is it to try to get a part for your machine, but the vendor made a "customized" part that you do not have access to. Buy from a manufacturer that uses off the shelf parts so that you can maintain the machine locally…
- Sand flow. Super tricky subject. Sand is the least likely material in a sand mixer to behave yet it is by far the highest percentage in the mix. Resins are actually pretty easy compared to sand. In general, reduce the variables. If you have an "adjustable" slide gate, you just introduced a major variable. Sand mixers vibrate and "adjustable" sand gates change their opening size when confronting vibration. Operators also tend to adjust adjustable sand gates. Operators are huge variables. It has been my experience that fixed orifice sand gate assemblies at least have a chance to supply consistent amounts of sand. Also, if you have a mixer and don't calibrate sand flow, this is a big mistake. Sand flow will change long before resin levels will change simply due to the nature of sand, its flowability characteristics, mixer blade wear, etc. So, calibrate your sand to make sure all is well.
- Service. Call references. Call your competitors that you know run a particular brand of mixer. Find out who stands behind their machines. I have heard too many stories where we lost an order to a cheaper competitor, later to find out that the customer has had nothing but troubles followed by poor service and excuses. Buy from reputable machine manufacturers that stand behind their equipment.
Bad Fish says buy good stuff, not cheap stuff. Bad Fish also believes in the adage, pay now or pay later…