does anyone have any resources for designing a bulk material handling system for an injection molding outfit? Currently we get material in gaylords and vacuum it to the hopper on each molding machine independently. I would like to start buying pellets by the truckload and stored in a silo to be fed to each machine from a central location. I am unsure of what equipment I would need other than the silo itself to do such a thing. Any leads?

  • Could you put the silo on the roof and have gravity help you? ie what is the building structure? – Solar Mike Jul 14 '17 at 17:24
  • Ideally, id like to put it on the ground outside and, what im assuming, would be some form of vacuum pump system to distribute it to the machines. If I could get plastic from the truck, into the silo, and to the machines without a person handling anything, that would be fantastic. – Corey Jul 14 '17 at 18:11
  • What about an Archimedes screw? – Solar Mike Jul 14 '17 at 18:19
  • I'd have quite a distance to cover with a lot of turns to get to each machine. – Corey Jul 14 '17 at 19:01
  • It seems like pneumatic conveyors may be what im looking for to get my pellets to the machines' hoppers? – Corey Jul 14 '17 at 19:04
up vote 2 down vote accepted

There are several companies out there that can assist with silo/hopper design, which would allow easy offloading of truck to silo,, but that can also offer a solution to use vacuum pneumatic conveying to each machine as you currently have.

Of course there are many technical things to consider throughout the system, therefore it will be best to get a company that has delivered similar system to provide a solution. Each of these components are a science in itself and you can spend lots of money on a system that in the end could be useless if not done correctly.

Some of these include:

Silo design:

  • Material flow out of the Silo: typical you would want a mass flow system rather than a funnel flow system (this will ensure you use the older material first and reduce the risk of buildup in the silo).
  • Do you want level measurement or weight of the silo to know when you are running low and have to order a new truck. You can add load cells in the supports of the silo to its main structure (typical suupliers will be mettler toledo for load cell and Endress Hauser or Vega for level measurement)
  • Also, the silo must be earthed to ensure you don't have static buildup (typical for plastic pellets)
  • A bag filter for when you fill the silo (assuming you will use a supplier with pneumatic pump fitted to the truck) - a typical supplier will be Donaldson
  • an over under valve or bursting disk for the silo to ensure you don't over pressurise it or accidentally get a vacuum generated within the silo that could cause it to implode
  • Depending on the flow ability of the product, the size of the silo you are considering you will have to consider whether you need devices to assist with the material flow out of the silo. This will be as the material will be under its own pressure and dependent on the shape of the plastic pallets. Typical devices that might get added is an inverted cone to break material pressure and air pads to assist the material to flow down the chute of the silo. alternative materials could also be used to assist with the material flow - stainless steel has better flow than mild steel, ultra-high molecular polyethylene (UHMWPE) sheets can be used to line the chute.

Vacuum pump system:

  • What type of system do you want to have - Lean or dense phase (dense phase will be at a slightly higher pressure and slower velocity but will be at lower running cost but with higher upfront costs)
  • You will need a feeder that slowly feeds the material to your vacuum line (this could be a star feed or a rotofeeder, which will gauge the amount of material that gets fed).
  • The vacuum pump sized according to the pressure drop of your system and the material flow rate you want to achieve
  • Air inlet filter with valve at you silo
  • Piping sized based on your route and pump sizing
  • Receiving cyclones/hoppers at your units as what you currently have

Typical global suppliers for these systems will be Flexicon and Schenck Process, but there are smaller companies that can offer similar solutions in every country.

I know of the plastic pellets that you talk about. I would use a aqueduct system to carry them similar how rivers are used to transport logs down stream. Unlike conveyor system since there is much less to break down and can be a closed system using 1 pump to drive the water but I would keep a spare pump tied in. Then at the end of the track use a screened or mesh conveyor belt to catch, dry and preheat the pellets.

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