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Rotomoulding

About Rotomoulding

Rotational moulding process is a very simple process for manufacturing hollow, seamless products of all sizes and shapes. Due to its simple operation and relatively low cost moulds, this process has become very popular for manufacturing hollow items like water storage tanks.

Rotational moulding is a Four- Stage process.

Stage 1
Polymer powder is loaded in the mould manually and mould is closed.

Stage 2
The mould is then shifted to the heating oven. Here the mould is heated by forced hot air circulation. While the mould is heated it is also rotate about two perpendicular axes simultaneously. The polymer melts and forms a homogenous layer inside the mould.

Stage 3
The mould is shifted to a cooling station where forced air cools the mould.

Stage 4
The mould is open and finished part is taken out. Unlike injection and blow moulding, rotational moulding does not involve high pressures, hence the products are stress free and have uniform wall thickness. Accurate control of process is very important for producing quality products in rotational moulding.

What is Rotational Moulding ?

Rotational moulding process is a very simple process for manufacturing hollow, seamless products of all sizes and shapes. Due to its simple operation and relatively low cost moulds, this process has become very popular for manufacturing hollow items like water storage tanks.

Rotational moulding is a Four- Stage process.

Stage 1
Polymer powder is loaded in the mould manually and mould is closed.

Stage 2
The mould is then shifted to the heating oven. Here the mould is heated by forced hot air circulation. While the mould is heated it is also rotate about two perpendicular axes simultaneously. The polymer melts and forms a homogenous layer inside the mould.

Stage 3
The mould is shifted to a cooling station where forced air cools the mould.

Stage 4
The mould is open and finished part is taken out. Unlike injection and blow moulding, rotational moulding does not involve high pressures, hence the products are stress free and have uniform wall thickness. Accurate control of process is very important for producing quality products in rotational moulding.

Rotomoulding

Rotomoulding Process Flowchart

  • Step 1: Natural LLDPE granules (from suppliers like Reliance, IOCL,OPAL, Haldia, etc.) mixed with masterbatch as required.
  • Step 2: This mix of Natural LLDPE granules and masterbatch is fed into the extruder.
  • Step 3: Extruder out the polymer in thread form
  • Step 4: The polymer in thread form is fed into the cuts the polymer threads to form colored granules.
  • Step 5: These colored granules are fed into the Pulveriser to get LLDPE powdered form as output.
  • Step 6: The LLDPE powder is charged into the mould for the four stage Rotomoulding process (charge, heat, cool, demould) to begin.
  • Step 7: Rotomoulded Product is ready for finishing and packaging operations to be performed.

Raw Materials

Rotomoulding
Rotomoulding

To obtain the desired end product, the choice of a quality powdered resin is essential in rotational molding. LLDPE (Li near Low Density Polyethylene) in its powdered form is most widely used raw material in Rotational moulding.

LLDPE Powder is generally recommended for:

  • Overhead water tanks
  • Storage bins
  • Toys and traffic barriers
  • Sanitation & Agriculture products
  • Rotomoulding applications requiring outdoor exposure

In- house storage care:Bags should be stored in dry / closed conditions at temperatures below 5oo C and   protected from UV or  direct sunlight.Bags must be kept away from the furnace or any other imflamable objects.

Foaming in Rotational Moulding. PE foam increases rigidity and stiffness of rotational moulded parts while minimising weight. Insulating properties of foam may also have useful applications. Rotational Moulding with PE foam is very simple if machine is equipped with proper process controls. “Vinodrai” machines are highly suitable for making foam products and insulated water tanks.

Advantages of LLDPE Foam Tank.

  • Keeps Water Temperature Normal.
  • Higher Thickness and Rigid Tank.
  • Value added product, better customer preference.
  • Higher realization & better profits.

For other resources such as Powder Suppliers, Plastic Lid Suppliers, Books on Rotomoulding, Rotomoulding  Websites.

Machine Selection

Selection of a rotational moulding machine is based on the following considerations
• Capacity of tank which have max share in market.
• Monthly expected production in terms of ltr.
• Range of tanks required in market (Loft, Roof, House hold, Horizontal ).
• Running cost of production.

The machine must be selected from the point of view that it should produce the capacity of tank most economically which have max. share in market.

Machine must be able to produce required volume of tanks which are salable in market.

And finally running cost that matters and not capital cost. In the competitive world, running cost of production is the key to survival of a company. The running cost depends upon the selection of the machine. If you selected the machine which is unable to control the fuel, electricity consumption. Employing heavy maintenance and need skilled labour then such machines though are cheap but finely take away the entrepreneur towards the loss.

Therefore machine must be :-

  • Fuel saver.
  • Less power consumable.
  • Must not be labor oriented.
  • Maintenance free and hence interruption free.
  • Essay to operate.
  • Productive and efficient.
Vinodrai

Applications

Rotational moulding is exceptionally versatile process that can produce a huge range of plastic products. Rotomoulded products are used in many key sectors like:

  • Household: Water storage tanks, septic tanks, garden planters, ice boxes and washing stations.
  • Industry: Chemical storage tanks, containers, crates, pallets and insulated fish and cooler boxes.
  • Agriculture: Composters, spray tanks, fertilizer tank, and Tractor attachments.
  • Healthcare: Stretchers, Instrument casings, vaccine boxes, organ storage boxes and cabinets.
  • Military: incendiary bomb casings, missile containers and drop boxes.
  • Environmental: Garbage bins, road cones, road barriers and road signs.
  • Marine: Kayaks, canoes, boats, floats, buoys and pontoons.
  • Automotive: Truck mudguards, ducting, diesel fuel tanks, toolboxes and tractor dashboards.
  • Furniture: Table, Chairs, Luxury LED furniture, study desks, lighting and decorative products.
  • Toys and playground equipment.: Slides, Outdoor gym equipment, amusement and water park equipment.

Process Comparison

Sr No.FactorsRotational MouldingBlow Moulding
1Typical product volume range1,00,000 litres1,000 litres
2Raw material used• Linear Low Density Polyethylene (LLDPE)
• Medium Density Polyethylene (MDPE)
• High Density Polyethylene (HDPE)
• Cross linking Polyethylene (XLPE)
• Polyvinyl Chloride (PVC)
• Polycarbonate
• Nylon
• Polypropylene (PP)
• Several others
• Low Density Polyethylene (LDPE)
• High Density Polyethylene (HDPE)
• Polyethylene Terephthalate (PET)
• Polypropylene (PP)
• Polyvinyl Chloride (PVC)
3Raw material formPowder or LiquidPellets
4Mould materialSteel/AluminiumSteel/Aluminium
5Mold pressureSteel/AluminiumSteel/Aluminium
6Mould costLowHigh
7In-mould graphicsYesYes
8Labour IntensiveMoreLess
9Cycle timeSlowFast
10Wall thicknessUniformity possibleTends to be non-uniform
11Insert feasibilityYesYes
12Residual stressLowHigh

Resources

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