Rotary Indexing Table

Consider going with a conveyor belt that runs continuously through the blast area. You load the items on the belt as it travels and remove it at the end of it's travel path. You wouldn't even have to remove the item manually. It would just drop off the end of the belt. Rotary devices have to be well protected from abrasive grit. I can envision a cabinet where the blasting would take place, followed by another cabinet which would sweep everything clean of abrasive dust with plain compressed air before exiting at the end of the belt.

Thanks, my first thought was actually a conveyor and is actually the most likely I will go with as cabinets can be had for under 2000 dollars the conveyor would be simple to install. My thinking however was a single person might find it easier to stand in front and load, then have the part come back around. The problem is that the part has plastic on it as well and I have to design a way to hold it to protect the plastic while cleaning the exposed metal, so to have them drop off the end I would have to configure a way to remove them from the holder, which is not difficult but was thinking a simple rotating table with holders might be less space taking and simpler for the individual. I am awaiting discussion with my client to see which he prefers and his actual space requirements and have found several suitable cabinets as well.

The types of tables you are interested in are usually OEM built. they are costly.

But it sounds like accuracy is not that big an issue. but they still have to be OEM built, if you can't build them yourself.

Check out "Empire Basket Blasters" it may be what you are looking for.

Does it (the rotation) need to be automated? What level of production are you anticipating -- a dozen parts per day, a few hundred, thousands? 

The simplest method could be to simply use a "lazy susan". (A platter sitting on a large diameter bearing.) The operator manually rotates the platter as required.

That was actually one of my thoughts, but I wanted a little more automation either where the part would be placed on and it would turn automatically or push a button, but manual is also an option and I may go that route, I have found a rotary table for blasting which rotates continuously, and it may work fine but if a cheaper indexing system were available it would be better.

Buy a gearbox that you can orient the output shaft vertically. Mount your table on the output shaft. You will want a gearbox that is robust enough to handle the load on the output shaft. The load is from the table weight, and any tooling that pushes on the table etc. If the output shaft is designed to handle a belt or chain drive it already has a lot of side-load ability designed into it. Drive the gearbox with a standard motor.

To have the multiple stop positions, put one stationary limit switch below and facing the bottom of the table. Put features on the bottom of table that activates the switch. Little ramps if the switch is a mechanical limit switch and just bumps if the switch is a proximity type. Six bumps make six stop positions with simple start circuit. Every time the human operator finishes a load/unload sequence they push double palm buttons to index. Two buttons ensure both hands are clear.

For automatic interface to tooling use an SLC or similar controller.

After the motor is turned off the table will overshoot a little. This is not a problem if it is repeatable overshoot. Just adjust the switch accordingly. A high reduction ratio would probably be good so use a worm type gearbox. Most can not be back-driven. If the stop is not accurate enough use a motor with a built in brake that is automatically applied when power is cut. Check with the manufacturer that the brake can operate the needed cycles per day week year.

There are more sophisticated drives that will do this more accurately, such as servo. The approach I described is very robust and simple and uses some simple relay logic that many electricians can handle themselves. The one limit switch approach can be applied to various types of drive arrangements to get multiple stop positions.

You can also use this one limit switch method along with a pre-made rotary table. You just add multiple operators (bumps, ramps, see above) to the pre-made table.

Thank you, I have thought of limit switches we used to have in the plant i worked but the control circuitry was fairly complex as it was tied into the entire line. A simple circuit would handle this and might be the route I take. I also thought of a servo motor using a direct drive as well, since the load is relatively minimal, likely less than ten pounds total depending on the size of the table, but 18-24 inches would likely be the size I end up with.

"each part would spin around as it gets to the nozzle to clean the entire surface."

Damn the details! What would make the part spin? Impingement? If you have a stationary nozzle, how can it clean the entire surface? Will the part spin in multiple axes? _{Or will it rotate about those axes?}

Seriously, if you've ever glass beaded things, you know that you have to turn them different ways so that all surfaces are treated.

I'm liking a home brewed knock-off of that batch blaster. But, we don't know how big your parts are.

Actually, if the parts are mounted on a holder and the holder is in a bearing or bushing and on the bottom a gear which, when the part goes around to the nozzle a small gear with a motor catches it then it would revolve while being blasted.

Actually, you did not reveal anything even close to this level of complexity, so far. How do you propose to keep all these bearings, gears and motors isolated from the abrasive medium. Maybe you can do it, hope so.

Good luck.

Well I have not gone that far yet, however it has been in my consideration as I know the abrasives will wear on the bearings, however if the table is mounted in such a way as to have a seal between the table and the underside then the bearings underneath will be reasonably protected. certainly this is a major consideration. But the simple fact is I was looking for a simple, low cost rotating table with perhaps some indexing capability.

Good luck,

I hope you find the table.

My two cents: I work with automation. Compact Automation makes a vane style rotary index unit with built-in unidirectional clutch for indexing using pneumatics called a Turndex.

I am going to suggest a totally different methodology.

There are a number of firms that make "blast" cleaning equipment using crushed dry ice- the ice penetrates under the dirt/paint/grease and then vaporizes, removing the material and dropping it to the ground.

Consider using such a system with a relatively high velocity upblast and "dumping" the materials to be cleaned into the top of the "blast cleaning" chamber. The materials being cleaned would be slowed down and "tumbled" by the high velocity upblast and the dry ice particles and would automatically "fall" slowly onto a moving open chain mesh conveyor located below the upblast CO2 nozzles. The blower discharge would be below the product conveyor. The removed materials could fall down the sides of the chamber to another tight mesh conveyor below the product conveyor and blower.

The cleaned parts would come out into or onto some form of container or conveyor and the scrap would go to some automated trash receptacles for disposal or recycling.

I would suggest a conveyer belt where the actual belt is manufactured of wire mesh inplace of the normal belting. The abrasive jets could be placed withijn a booth and positioned both above and below the belt and thus clean both sides of the part as it passes by without having to turn the part during the cleaning process. If the parts are very small and there is a chance that the force from the abrasive jets will displace the parts and cause them to move around on the belt, then I would suggest providing a clip on the wire mesh belt that the part could attach to and thus the part be hold securely during its travel through the cleaning process. You mention there are some plastic bits on the parts that need protecting during the cleaning process, You don't say much about the parts but could you manufacture steel "cups" or hoods that are designed specifically to clip onto that particular part and protect only the vulnerable bits from the blast. Once the rest of the part has been cleaned and passed through the booth on the conveyer, the operator can simply unclip the protecting steel hood for re-use. the single operator could fit the protecting hood onto the part and place it on the conveyer, once the part has been cleaned by the abrasive jets and then rinsed, they fall onto an inclined chute that makes a 90 degree bend and brings (slides) the parts back to the operator at a lower level for unclipping of the protecting hood and immediately reclipping the hood to the next incomming part for cleaning, thus reducing the handling of the part and the protecting hood. I expect the average engineering shop could knock something up. Im not sure if the application is correct as I have assumed to a certain degree.

Would a Geneva mechanism do the job?

Actually, thank you all very good suggestions and I have thought about dry ice as a possibility. the part is metal and has plastic on one end so only one end needs cleaned. I have thought about the geneva mechanism, but am still awaiting more details from my client to gain a little better understanding of things, and have even looked at pneumatic actuation but it is a little more complex than is needed, but still worth looking at. Right now I am just looking for ideas and the lowest cost which will still accomplish what we need. I have even thought of a cog system where thepart rotates through to several nozzles at each nozzle it hits a rack which turns a gear, or even just a strip of rubber to turn it, thus eliminating the abrasive-gear-bearing issue for that part of it.

Hello,

May I propose a different angle all together. We have a blasting cabinet which uses a hanging platform and is continually rotated by a drive system outside and above the cabinet. The roof of the cabinet is slotted and the shaft the platform is mounted to penetrates the ceiling of the cabinet where all the turning equipment is located. This virtually eliminates the worry about protecting any of the delicate equipment. As I stated our cabinet continually rotates the product however I am sure you could use a stepper motor if you thought you needed to turn and stop in a position. Good luck.

Actually I have decided the geneva mechanism might be the best solution and would eliminate all of the electronic controls and would only require a motor with perhaps variable speed control. I have and am considering a top mount system if a suitable method for holding the parts can be obtained, however I am still waiting to speak to my client to discuss specific details. the method shown below I think would provide the best means for this. Thank you all for your input as it helped me to make some good decisions.

Does the small gear turn and engage/disengage the big gear.

If the two gears hit point to point this will just lock up. You may be able to detent the big gear to prevent this.

Another issue may be if significant table acceleration is involved, the first tooth on the little gear and the start position teeth on the big gear will wear quickly.

I have thought of this and also the fact that a locking mechanism would be needed to prevent the large gear from moving when the teeth on the small gear are not engaged. The solution I am thinking is one, a smaller gear on the same shaft as the larger and a cam on the shaft of the smaller gear with a spring loaded plunger so as the gear teeth are not engaged the cam pushes a pin into the other gear to hold it stationary. As far as preventing tooth wear and lash I have thought of a system such as is being used on some rack systems where rather than gear teeth on the smaller gear, it would utilize round rods. Since precision is not critical there can actually be quite a bit of free play so wear should be relatively minimal, and if the metal rods (similar to the roller pinion systems through nexen group at www.nexengroup.com) Also, this system the rpm for the drive gear would likely be less than one rpm, so the parts should mesh nicely.

you might also contact a shot peen shop in your area. they may have excess capacity and be willing to take the off-load or they might have excess machine inventory they would sell. these cabinets have the type of material handling systems you'll need already installed.

You may want to check out Starion,

http://starioncomponents.com/

Cheers

I'll throw out another method that can be done with just a few pneumatic logic components.

Drive the table with an air cylinder. The cylinder moves the table the to the next stop position then retracts. The pawl on the cylinder tip catches when extending the cylinder, then the spring loaded pawl moves out of the way when retracting the cylinder. The table has detents to keep it there until the next cycle.

Obviously this method requires a small amount of mechanical design, but if it is not asked to do extra functions it is likely inexpensive.

Actually, after a long discussion with my client he has opted to use a conveyor system with wire wheels instead of abrasive blasting. I am puting out requests for quotes for a simple timed conveyor to which we can mount a system with wire wheels, polishing wheels, and a few other attachments he is looking for. Thank you all very much very good suggestions though.