:: Remoulding Process & Advantages

Broadly the process is classified in to following sub processes.

1. Compounding to produce coloured of Granules
2. Pulverising to convert material in to Resin form
3. Rotational Moulding to produce the final product

» First Process: Compounding by means of Extrusion

The LLDPE raw material with suitable masterbatch is being fed in to the barrel cylinder through storage hopper. The barrel is preheated by heating zones and suitable temperature control system to process the input material. The rotating screw pushes the material towards die end with uniform and homogenized plastics melt. The screw is rotated by suitable AC motor coupled with heavy duty gearbox.The plastics strands extruded from die are fed in to high speed Pelletiser unit after they get cooled and traveled through SS water cooling tank. Pelletiser cuts the strands in to desired size of pellets which can be collected in to storage silo.

» Second Process: Pulverising

The compounded or coloured granules are being fed in to Pulverizing machine as Input material. The granules are fed in to Disc Mill via vibratory feeder which feeds the material as per rate of vibration of the device. The fed material is being crushed in to Mill at very high speed by one Rotating blade and one stationery blade. The crushed material is conveyed in to cyclone hopper at height via efficient suction system.

The Rotory Air lock devise separates the blown air and pulverized resin and allows the powder passes in to Screen Vibro unit. Vibro screen unit screens the powder as per mesh used and discharge the final product in to the storage silo. The course particles are fed again in to the Mill to repulverise the same.

Compounding by means of High speed Mixer
(Incase the Extrusion process is not used to produce thecoloured Granules)

The pulverized resin is being mixed with other ingradients to prepare a ready formulation. This process is also being adopted by many processors instead of producing granules from Extrusion Plant.

In the process the polymers mixed with other ingredients is being loaded in to Mixer vessel. The mixer vessel is made from special double wall construction of SS and MS Plates. In which the material is being mixed by means of specially designed two nos blades running at very high speed. The mixing cycle is decided by the certain set temperature. Normally batch time is 10- 15 minutes depending upon grade, quantity and formulation of material to be mixed. After cycle time is over, the the material is being discharged and collected in to silo. The final material is uniformly and homogenized mixed which is ideal to use as for Rotomoulding process.

» Third Process: Rotational Moulding

In the other Plastics processes like Injection Moulding, Blow Moulding & Extrusion Process ,the plastics material is being melt at certain higher temperature and conveyed forward in to die or mould by special designed Screw. Unlike such processes ,Rotational Moulding is a very simple process. In which it is easy to produce hollow and seamless products of all the sizes and profiles. Since Rotational Moulding is a very simple and economical process alongwith low cost Moulds , it is very popular in India especially to produce the water storage tanks.

It comprises of mainly four steps as per following.

1. Material Loading : The polymer powder is being loaded in to two parts Rotational Mould as per size and shape of product. After loading material manually in to mould , the mould is closed. According to type and shape of Mould , some times the mould are also closed by insulating covers.
   
   
2. Rotational Moulding : The closed Moulds mounted on to Arm are swinged in to closed heating chamber where Hot and forced Air is circulating. The moulds are already rotating in two perpendicular axis at certain low speed as per size of the mould. The moulds are in Rotation in two axis so as to distribute the loaded powder uniformly inside surface of the moulds. The moulds are heated by forced hot air in to chamber up to certain heating time. The material in to moulds fuses after heating and it forms a uniform layer inside the mould.
   
   
3. Cooling : Now the moulds are taken out form heating chamber and swinged to cooling station. The moulds are cooled at cooling station by means of forced air or by spraying water where the moulds are in rotation mode in both axis. After certain cooling period, the raw material gets solidifies in to shape of the mould.
   
   
4. Unloading the finished product : The mould is taken to unloading/ loading part where the mould is opened to get the finished product. After getting the finished product, again fresh polymer powder is being charged in to mould so as to keep ready for next cycle.

Click here to view Rotomoulding Demo

ADVANTAGES OF ROTATIONAL MOULDING

• Economic Tooling Costs
• One-piece construction; virtually stress-free-totally enclose parts or with openings
• Weight reduction - as compared to most metals
• Uniform wall thickness - no thinning in the extremities
• Thickness can be varied if required
• Variety of finishes and color
• The ability to produce multi-wall mouldings
• Design flexibility - from small and intricate to large and complex
• Metal inserts as integral parts
• Economical for short production runs and prototypes as well as volume production
• Minor undercuts are possible - with no draft angles required
• Short lead-time
• Resistance to stress-cracking and corrosion
• Excellent load-bearing properties
• Variety of materials

» Raw material for Rotational Moulding:

LLDPE ( Liner Low density Polyethelene ) is being used with density of 0.930 to 0.936 gms/ Cm cube and Melt Flow Index in the range of 3 to 6 gm per 10 minutes. To produce the good quality water tanks by Rotational Moulding, the material should have following properties.

• Good mechanical strength.
• Good material stability over a wide range of temperature and cycle time.
• Good resistance over warpage.
• Consistency in Shrankage at least 2.5 % or slightly more.
• High ESCR ( Environmental stress crack resistance )
  

» Other Ingradients:

The original LLDPE granules are of natural colour which have to be converted in to either black, white, blue or other colours as per requirement of final product. To produce the coloured granules , basic LLDPE granules have to be mixed with colour concentrate which are called as master batches.

These master batches are readily available in market which are to be added alongwith LLDPE.

The master batch should be of grade which is LD based. The master batch with antioxidants are more preferred. Anti oxidants protects the material from oxidation during the Moulding process which helps to avoid the pin holes on surface of finished product.

Incase of black master batch, carbon contents are very important. Carbon contents act as UV stabilizer. It helps to improve the life of tanks if tanks are exposed to sunlight for longer period and to avoid the crack on tanks.

Some other common additives like flame retardants, anti static agents, foaming agents, are also used as per requirements.

» APPLICATION AREAS

Note: The information of Rotomoulding Demo is property of www.rotomolding.net (Society of Plastics Engineers Rotational Molding Division). We have given just link here to understand Rotomoulding process.