Design and Construction of Automatic Polythene Sealing and Cutting Machine
CHAPTER ONE
AIM AND OBJECTIVES OF THE STUDY
The aim of this project is to design and construct an international standard machine that will automatically and simultaneously seal and cut sheets of polythene bags into a required form. To achieve the stated aim, the following specific objectives were laid out:
- Make the cutting and sealing process fully automated
- Inculcate slicing ability in the machine
- Make the machine safe enough to avoid machine incurred hazards
CHAPTER TWO
REVIEW OF RELATED LITERATURE
CONCEPT OF POLYTHENE
Polythene belongs to the family of plastic called thermoplastic, which has the properties of softening under elevated temperature. This makes it capable of being molded and removed of course. This is the property that makes the material to sealed and cut under a given temperature below it’s melting point thereby supporting the operation of the machine other properties of polythene which makes it useful and suitable for packaging purposes are its flexibility, cleapness, its resistance to corrosion, poor electrical condition etc. The household plastics material called polythene is made from the gas ethylene, a by-product to the petroleum industry. Polythene consists of a long chain of ethylene molecules, which occur during a polymerization process of simple molecules of ethylene called polymer. The long chains of ethylene molecules consist of about 1200 carbon atoms in length the hydrogen atom being attracted to individual carbon atoms.
Polymer can be divided into two groups namely
- thermoplastic
- thermosetting
Thermoplastic materials can be softened, allowed to harden and then resoftened indefinitely by the application of heat provided the temperature is not so high as to cause decompositions. This type of material can be formed into different shapes by the application of heat. Thermosetting materials undergo a chemical change when they are subjected to heat, the change cannot be reversed by the application of further heating. A typical thermosetting material is the bake like polythene is easily stretched and is not rigid because the linear molecular chain are independent of each other and so the material has a relatively low melting point and low energy needed to break bonds between chains. Polythene is a crystalline polymer with melting point of 138oc and glass transition temperature of 120oc is the temperature at which a polymer changes from rigid to a flexible material it from 95% crystallinity.
We have two main types of polythene namely the low density polythene which consist of molecules containing many side braches and is usually about 50% crystalline, they are mainly used for film packaging, examples are polythene bags squeeze bottles, baleen tubing and wire insulation. High density polythene is approximately 90% crystalline because it consist principally of linear molecules that is unbranched molecules. They are used for piping, toys, filaments for fabrics.
DEFINITION OF THE COMPONENTS.
Body Framework:
Plastic fiber is used to fabricate this but analysis shows that this process involved is more difficult than when wood of good quality employed. However, wood is still not satisfactory enough because it cannot often the required rigidity. For a considerate period of time when compared with steel. This is due to the weaker type of joints involved when wood in used. Therefore , mild steel square pipe is to be considered best for the body frame work.
Power Transmission Belt
Although there are a number of other power transmission systems like roller chain, gear wheel etc V-salt is considered most appropriate for the design of this machine. Belt selection involves either choosing a proper belt to transmit a required power or determination of power that may be transmitted by a given belt. In this case, the first case is adopted since the horsepower required is known.
- Pulleys: The machine is made of two power transmission systems, one is responsible for the reciprocating motion of the sealing and cutting unit, the other is responsible for the feeding of the polyphones. Both systems have arrangement of pulleys. For the reciprocating motion, there are two pulleys: the driver and the driver. The former is attached to the spindle of the electric motor. It is made up of cast iron.
- Springs: Two springs are used to suspend the heating unit from the body of the machine. It helps the unit to make smooth return.
CHAPTER THREE
SYSTEM DESIGN
This section shows the full design of the cutting and sealing machine. The machine is made up two general sections; the splicing and the sealing stations. The splicing station puts the bag in desired form then cuts it and passes it to the sealing station. The sealing station seals along the spliced line. The components and integration of the system are analyzed below.
SYSTEM ANALYSIS
Splicing is the process of fixing two ends of film together and cutting away the waste ends. This process is necessary for producing reels of film with the requested size. Reels can be combined to create a larger end product (longer film on a single reel) and bad pieces of plastic or print errors can be removed by cutting away a few meters of film. The joint of the two film ends needs to be at the right location and should be small and neat such that the customer hardly notices that it is there. Therefore, the joint should be an overlap seal instead of a lip seal, see figure 3.1. The lip will always be noticeable in the film, while the overlap seal is hardly visible when the waste ends are trimmed as short as possible. The process of creating an overlap seal is however more complicated, since both waste ends are located on opposite sides of the joined film. Some tests that were done using a manual sealing bar, showed that using the sealing bar as a cutting device (like on the machines in conversion) did not result in proper seals. A strong seal could only be made in the form of a lip seal. When an overlap seal was made, pulling away the waste ends resulted in tearing apart the seal. Therefore, creating an overlap seal requires a separate cutting system for removal of the waste ends.
CHAPTER FOUR
SYSTEM IMPLEMENTATION
This section presents the final design of the machine. Furthermore, some general design considerations of some of the subassemblies are explained in more detail.
Figure 4.1 shows the final design. Comparing this model with machine S1 as shown in figure 3.2, it can be seen that the grey side panels are the part of S1 on which the new machine will be mounted, i.e. the ’splicing location’. A full reel of film (diameter 750mm) is included for comparison. The main dimensions of the splicing station (excluding the mounting frames) are 2200x600x225mm.
Films up to a width of 1790mm (maximum width allowable in S1) can be used in the splicing station. However, since the machine is mainly used for a single customer, the splicing station is designed for film widths up to 1200 mm.
CHAPTER FIVE
CONCLUSIONS AND RECOCMMENDATION
CONCLUSION
The design and fabrication of polythene Automatic cutting and sealing machine have been successfully accomplished. It was observed that the machine performs its required objective of sealing and cutting polythene material automatically.
RECOMMENDATION
Small scale machine like the locally built automatic polythene sealing and cutting machine is necessary to reduce foreign exchange for the procurement of sophisticated machineries. The current foreign exchange problems has made it almost impossible for small scale ushers to imports.
This problem is solved by the use of possible locally available raw materials or accessories to construct a machine that compares favourably well with the so called imported ones in term of durability, efficiency and is affordable. In condemning our locally produced materials. The economy will benefit greatly if this technical revolution is given a change to grow. In improving on this project sufficient fund must be budgeted for operation. Maintenance or the whole purpose of the design will be defeated and a lot of money spent on the project wasted.
REFERENCES
- Theller, H.W., 2017. Heatsealability of Flexible Web Materials in Hot-Bar Sealing Applications. J. Plast. Film Sheeting 5, 66–93. doi:10.1177/875608798900500107
- Selke, S.E.M., Culter, J.D., Hernandez, R.J., 2016. Plastics Packaging: Properties, Processing, Applications, And Regulations, 2nd ed. Hanser Gardner Publications.
- Troughton, M.J., 2018. Handbook of Plastics Joining: A Practical Guide. Cambridge University Press
- Stehling, F.C., Meka, P., 2014. Heat sealing of semicrystalline polymer films. II. Effect of melting distribution on heat-sealing behavior of polyolefins. J. Appl. Polym. Sci. 51, 105– 119.
- F02 Committee, 2018. ASTM F88 Test Method for Seal Strength of Flexible Barrier Materials. ASTM International.
- Coles, R., McDowell, D., Kirwan, M.J., 2016. Food packaging technology. CRC Press
- Hassan, A., 2007. Effect of bar sealing parameter on OPP/MCPP heat seal strength. Express Polym. Lett. 1, 773–779
- Gent, A.N., Kim, E.-G., Ye, P., 2017. Autohesion of crosslinked polyethylene. J. Polym. Sci. Part B Polym. Phys. 35, 615–622. doi:10.1002/(SICI)1099-0488(199703)35:4<615::AIDPOLB9>3.0.CO;2-O
