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I realize what you say is true, but for what we are doing and for the length of time it will be in service, it will work. It is mostly for software development so the logic and algorithms can be proven and demonstrated on a little test engine. Big engines already have big expensive valves. After it homes, softly, on each startup it will know where it is and not go to the ends of travel during operation. Pushing the plastic nut in and out of the natural gas fuel stream will load nothing. It is more of an obstruction than a. Does the stainless lead material drill nicely?
Linear space is limited, but I could use a larger shaft. How does this sound? We use your plastic nuts for the plugs, mill them flat on the sides and maybe all four sides. Put a piece of 3/8 lead screw in a lathe collet, drill and ream it to the size of the stepper shaft. Glue or set screw it solid. There would be threads almost all the way to the stepper body. It is not important that the attachment is perfectly coaxial. It can wobble around in the hole a bit and still do the job. How much torque will it take to turn the shaft in the nut?
I had a look at the actual production volumes for the mill in question. They moved about 4000 truckloads of pipe last year. That works out to about 22,000 layers of pipe. (22,000cycles). At 200 inches of total travel per cycle that’s 4.4million inches of linear travel per year. I’ll assume the screws can run at 7,000lbs thrust load at 130rpm for the fast and empty return cycle. What formula or curve would I follow to determine loaded speeds with thrust loads from 7,000lbs to 57,000lbs. So that they only have to replace the parts once per year? Based on 2.2 million inches of travel per year with pipe?
I would use: 7kip thrust @ 100rpm (or faster if possible) / 37kip thrust @ 50rpm / 57kip thrust @ 30rpm
The forks will weigh approx. 2000lbs per fork so that results in an extra 6700lbs of thrust load on the screws either loaded with pipe or empty.
OK, the fastest cycle time is at a lower load so in that instance we could limit the load to 9,000lbs per fork (30kip thrust) and reduce the speed to say 65rpm. That would equate to 32.5in/minute or 3 minutes to deliver pipe fully loaded. Could it then return empty at 100rpm? That would be 2 minutes to return. So on our fastest cycle if we have 6 minutes to go out and come back that leaves 1 minute to roll pipe onto the forks. Or do anything else. Under full load (15,000lbs pipe load per fork) we have about a 10 minute cycle. So at 50kip thrust we could reduce the speed to. Say 30rpm. That’s 15 inches/minute or 6.7 minutes to travel 100inches to deliver a row of pipe. We could then come back. At 100rpm empty. That’s 8.7 minutes of travel time. Our total allowable cycle time is 6 minutes to 20 minutes depending on pipe size. We are going to run this with a PLC and we will have the weight of each pipe so in theory the machine could run under a PV operating curve whereby it travels only fast enough to keep up with production. It would be ideal if we basically planned to be able to run under a PV operating curve for a whole year between shutdowns. We are quoting four machines to a group who want to do a pilot project at one plant. They have a couple of dozen plants worldwide. I am hoping that we could get some budgetary numbers together this week?
The machine handles a row of pipes that can weigh up to 30,000lbs. The pipes are supported by two fork assemblies, hence 15,000lbs load per fork. The load c.of.g. is 60inches from the acme nuts so that’s a 900,000in-lb moment. Each fork assembly has two screws 18” apart. So to resist the momentThe screws each see a 50,000lb thrust load. The screws would see minimal radial loading as the cam followers should handle the actual vertical weight. Slight radial loading would occur when the forks tip putting some vertical loading into the acme nuts through the trunnions. This is because the trunnion slots only isolate the nuts from vertical loads when the slots are purely vertical.
Regarding duty cycle:
The machine would go out loaded and come back empty each cycle.
Load varies from 4,400lbs to 15,000lbs (per carriage assembly), load varies based on casing size.
Total travel per cycle is 200 inches.
Number of cycles per hour : 3-10 (depends on production rate of casing)
Max distance travelled in a year: 9.3million inches
There is one shutdown per year for maintenance.
It’s an outdoor environment with temps of -40C thru 40C with rain, snow, hail, icing, dust, etc.
