Cleaning & Maintaining Silos

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Silos can last up to 15 to 20 years before they require painting on the exterior. This of course is dependent on the location of the installation. Depending on the condition, they can be spot wired brushed, touched up with primer and/or primed and a finish coat applied to the entire silo. Again, the extent of the project is dependent on the condition of the silo.

It is also possible the condition of the silo requires sandblasting the sheets of the silos before priming and painting. This can be costly.

In some extreme conditions doors, decks or sidewall sheets may need to be replaced. The silo needs to be emptied to make these repairs.

The interior epoxy coating can also be cleaned. The silo needs to be emptied and the slide gate and vacuum take off box removed. The interior is cleaned by wiping down the walls with clean towels or washing down the walls with water. If water is applied, the surface needs to be air or heat dried before refilling. To clean the interior, a workman is lowered into the silo using a boatswain chair.

If you are in need of cleaning and/or restoring your silo, contact us to review the condition of your silos. We can then recommend what needs to be done.

-Ken
The Retired Plastics Guy

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Vacuum Conveying Systems

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A Vacuum Pressure System, also called a Push-Pull System, is a method of pulling material from a rail car to silos, in-plant bins or Gaylords.

The system consists of a vacuum blower to pull resin from a rail car to an inline filter receiver mounted over an airlock. Then a pressure blower pushes the resin to its destination. Some suppliers use one blower to pull and push the resin. I prefer two blowers (one for vacuum and one for pressure) to do the conveying. This allows better control of the vacuum and pressure blowers.
 
The system can be mounted outside, but it is better to install it in a small building or if there is space, inside a silo. There are installations where the power units are inside the silo and the filter receivers are installed outside.
 
To complete the system you need the following:
 
1 – NEMA 4 control panel with the connections for operating the system.
 
2 – Motor starters
 
1 – Rail car adaptor kit with a connection to install a flexible hose.
 
1 – Inlet filter for the opposite side of the rail car
 
1 – 20 ft stainless steel flexible hose to go from the car to a destination which may be direct to the system or to an inlet on a manifold system
 
1 – Manifold system with (4) laterals for each rail car. This can be for (1) railcar or many rail cars depending on the number on a siding.
 
1 – Rail car hatch filter (most cars do not need this since the cars are built with their own filter on the hatch).
 
1 – or more flex hoses on the pressure side to meet the requirement.
 
1 – lot of tubing ,elbows and couplers to match the system.
 
We design the vacuum pressure conveying system to match the capacity required. This is determined by the time frame you want to unload the rail car. This is usually dictated by the amount of time you have before demurrage starts or the amount of time you want to unload the car (i.e. (1) 8 hour shift or longer).
 
Additional requirements that affect the capacity are the length of the vacuum and pressure runs with both horizontal and vertical distances and the number of bends in both the vacuum and pressure sides of the run.
 
The system can be designed for pellet or powder conveying. This information is required to design the system.
 
Contact us at Coast Equipment and Services for an exact quotation to meet your needs.

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Vacuum Conveying

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The cleanest and easiest system for conveying to injection molding, extrusion and blow molding machines is vacuum conveying.

The components needed are:

  • Vacuum blower and motor package (a.k.a. power unit)
  • Floor mounted in line filter
  • Vacuum chamber with sequencing valve for each location of the machine
  • Control panel with the quantity of stations (this is determined by the number of machines to be fed.
  • Tubing and fittings

The size of the power unit is determined by (6) factors:

  1.  Capacity (lbs/hr or kg/hr) for the total number of machines
  2. Horizontal distance
  3. Vertical distance
  4. Number of turns in the line
  5. Is it a single or multiple line system?
  6. Name and/or type of resin

The capacity is the rate that the material is to be conveyed. The horizontal distance is determined by measuring the distance from the point of origin of the resin to the point of discharge. The vertical distance is determined by measuring the distance from the floor to the highest point that the tubing will run. A single line system has one material line to any machine with wyes installed to continue to the next machine.

Its use is to run one material to any vacuum chamber.  It is possible to run more than one line to each station with the ability to change from the machine to any line with the use of flexible hose and quick change couplers.  The use is determined by whether changing lines will affect the contamination of resins.

A multiple line system has one separate line for each vacuum chamber.  This will eliminate the possibility of contaminating the resin with another resin.

The name and/or type of resin being used in the system allows for choosing the type of inline filter need in the system.  It also allows for sizing the of the power unit by using the bulk density of the resin.

Sizing Vacuum Systems

There are several things to consider when you are calculating a vacuum conveying system equivalent feet. The important things to consider is the number of injection, extrusion or blow molding machines, capacity in lbs/hr of each machine, distance from the material origin to the furthest machine, number of turns (elbows) and how the machine will be fed;.

The conveying distance to size the system equals the horizontal distance, the vertical distance x 2 and 20 feet per elbow. If there is flex involved, the calculated distance equals the distance plus 3 ft per foot of flex hose. It is best to keep the conveying distance under 550 ft. The vacuum source should be no more than 50 ft from the last machine.

The vacuum pump is a positive displacement pump. It has an inline filter but an additional stand alone floor mounted filter should be installed ahead of the pump. We size the system after we have the conditions listed above.

Vacuum chambers are manufactured to mount on machine hoppers, blenders or stands. Standard sizes range from 3 HP to 20 HP and include inline sequence valves and an inlet for material and an outlet for vacuum. They are sized with the vacuum pump. Standard tubing sizes range from 1 1/2″ OD to 3″ OD.

Other types of vacuum systems are available for low capacity and shorter distance conveying applications.

This gives you the basic things to look for and what we need to completely design the system. Other accessories may be needed in the final design.

Contact sales@coastequipment.com for sizing and designing your complete vacuum system.

-Ken
The Retired Plastics Guy

Plastic Resin Handling

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A chilly day from the chair of the retired plastics guy…

Today’s topic … The use of resins, regrinds, colors and additives

Many changes have been made over the years in the handling of plastic resins. With the advent of the Maguire Weigh Scale Blender, resins, regrinds, color and additives can be added repeatedly with extreme accuracy. Depending on the requirement, the ingredients can be vacuum conveyed from the source. The resins and regrinds are conveyed in larger quantities and the color and additives are usually conveyed by small compressed air loaders. Sometimes color and additives are hand fed.
 
Pelletized resins are conveyed by standard individual or central loading vacuum systems. The capacity required and the distance to be conveyed determines the line size and power source size. Line sizes range from 1 1/2 ” OD to 4″ OD. Vacuum power units range from 3 H.P. to 25 H.P. Larger sizes are available, but they are not the norm.
 
Regrind material is able to be conveyed by vacuum. The regrind has to be qualified with regards to the screen size of the granulated material and the presence of dust. The type of vacuum receiver is determined by these regrind conditions. In some cases a powder type receiver is used. Standard type vacuum power units are used.
 
In both cases a floor mounted filter is used ahead of the vacuum power unit to protect the blower and motor.
 
As stated above, the standard procedure for color and additives is to convey with a compressed air loader. Depending on the amount of color and/or additives to be conveyed, a central system can be used by adding vacuum chambers.
 
The source of the ingredients can be silos for the virgin pellets, in-plant bins for the virgin pellets or regrinds, Gaylords and/or bags for resins, regrinds, colors and additives. The source is dependent on the process and amount of ingredients being used by the manufacturing facility.
 
This information is based on using Weigh Scale Blenders. Individual volumetric or gravimetric feeders can also be used. The accuracy may be jeopardized by using feeders.

Proportioning units can be used for adding virgin and regrind. This is not as accurate as weigh scale blenders or feeders, but may serve the purpose if the mix is not critical.
 
For more information or to receive a quote, contact Coast Equipment & Services Company or take a peek at our website for details on our comprehensive line of products and services.

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