Experiment 5

CDB 4423 Polymer Process Engineering Engineering

May 2017

LAB REPORT

EXPERIMENT 4

: INJECTION MOULDING MACHINE

GROUP

: 3

GROUP MEMBERS

: KOI ZI KANG

18868

 NORANISAH BINTI JAMIAN

19339

SADADINE MAHAMAT YOUSSOUF

17839

LECTURER

: DR WAN ZAIREEN NISA YAHYA

DATE OF EXPERIMENT

: 10th JULY 2017

Table of Contents

Chapter 1: Introduction 1.1 Abstract .................................................................................................................... 1 1.2 Objectives ................................................................................................................ 1

Chapter 2: Literature Review 2.1 Molecular Weight Distribution and Material Processing ........................................ 2 2.2 Molding Processes ................................................................................................... 3 Chapter 3: Methodology ............................................................................................................ 4

Chapter 4: Results and Discussions 4.1 Results...................................................................................................................... 5 4.2 Discussions ...........................................................................................................5-6

Chapter 5: Conclusion ............................................................................................................... 6

References .................................................................................................................................. 7

CHAPTER 1: INTRODUCTION 1.1 Abstract

Injection molding is the most commonly used process for the manufacturing of plastic material. A wide variety of products are manufactured using injection molding such as containers, toothbrush and plastic toys. The products vary greatly in terms of their sizes, complexity and application. Basically, injection molding process requires the use of an injection molding machine, raw plastic material and a mold. The raw material is melted in the injection molding machine and then injected into the mold, where it cools and solidifies. Common raw materials used for injection molding include polyethylene, polypropylene, polycarbonate, acrylonitrile  butadiene styrene and acrylics. This experiment was designed to improve understanding on working principles of injection molding machine.

1.2 Objectives

The objective of this experiment is improve understanding on working principles of injection molding machine which is one of the most common methods used to shape plastic resi ns.

1

CHAPTER 2: LITERATURE REVIEW 2.1 Molecular Weight Distribution and Material Processing

Molecular weight is a major parameter that influences polymer s’ flow behavior at temperatures above glass transition temperature or melting point (TA Instruments, n.d.). Normally, polymers are composed of polymer chains with various chain lengths or different molecular weights after  polymerization which result in a continuous molecular weight distribution (McCrum, Buckley, & Bucknall, 1988). There are two types of molecular weight distributions which are single modal and bimodal as shown in Figure 2.1.

Figure 2.1: Single Modal and Bimodal Molecular Weight Distribution

For single modal molecular weight distribution, the curve could be either a broad curve or a narrow curve as shown in Figure 2.2 (McCrum, Buckley, & Bucknall, 1988). Polymers with  bimodal or broad molecular weight distribution are suitable for extrusion process as the shorter  polymer chains will melt quickly and contribute to the flow while the longer polymer chains will hold the materials together. Polymers with narrow molecular weight distribution are suitable for injection molding process that requires the feed to melt at the same temperature.

Figure 2.2: Narrow and Broad Molecular Weight Distribution 2

2.2 Molding Processes

There are several existing commercial polymer molding processes in which the selection of any process is depending on one’s budget, expertise and resources. Although injection molding  process is the most commonly used manufacturing process, other processes including blow molding, compression molding, rotational molding, thermoforming and extrusion are also widely used for production of different types of products. Few examples o f molding processes and their common uses are listed in Table 2.1 (Fibertech Plastics, 2015). Table 2.1 Molding Processes and Their Common Uses No.

Molding Process

1

Injection Molding

2

3

Blow Molding

Common Uses •

Produce high volume custom plastic parts

•

Large injection molding machines can produce car parts

•

Production of bottles, plastic drums and fuel tanks

•

Commonly used for production of small parts in very high volume

Compression Molding •

Heavily used in automotive industry as final product is very strong and durable

4

5

Extrusion Molding

Thermoforming

•

Production of PVC piping, straws and hoses

•

Manufacturing of disposable cups, containers, lids, trays, blisters, clamshells and other products for food and general retail industries

3

CHAPTER 3: METHODOLOGY

The experimental procedure of this experiment is as follows: 1. All the safety devices were ensured to be operational and the  EMERGENCY STOP button was under awareness. 2. The chiller unit was switched on. The cooling unit and the water pump indicator were being confirmed to be in ON position. 3. The RESET button was released and menu screen was switched on. 4. The required temperature was set and the heater key was turned on. 5. The menu screen was being monitored until the temperature was raised to the required temperature set earlier. 6. Then, the raw material polymer, polypropylene (PP) was filled into the hopper. 7. The safety gate was then closed. 8. The MOULD CLOSE key was pressed until the mould was locked up. 9.  Next, the NOZZLE ADVANCE key was pressed until the nozzle was pressed tightly against the mould. The sensing ring was then moved until it was sensed by the nozzle forward proximity switch. 10. To fill the polymer in the screw position, the CHARGE key was pressed. Then, the INJECT key was pressed to fill the mould cavity and the cooling process was let to happen. 11. The MOULD OPEN key was pressed and the EJECTOR ADVANCE key was pressed twice to eject the moulding product. 12. The product was examined and the pressure, temperature, stroke and time were adjusted as needed. The procedure was repeated until satisf ying product was obtained. 13. The raw material was then changed to high density polyethylene (HDPE) and steps 1 to 12 were repeated. 14. The RESET button was pressed to shut down the system. 15. The isolator was switch off and the cleaning process was carried out.

4

CHAPTER 4: RESULTS AND DISCUSSIONS 4.1 Results

Figure 4.1: Dog-Bone-Shaped PP and HDPE Produced via Injection Molding

4.2 Discussions 1. Explain the principle of injection moulding machine.

The type of injection moulding machine used in this experiment is a single-screw injection moulding machine as shown in Figure 4.2 (McCrum, Buckley, & Bucknall, 1988). First, the raw material of polymer in pellet form is fed into the charging barrel by using a hopper and is pushed forward by the rotating screw through a heating element that melts the solid  polymer feed (Scarlet, 2011). The homogeneous melting process is also contributed by the heat produced from intense friction between the polymer feed and the barrel while the feed is being pushed. Then, during moulding process, the screw stops rotating and is rammed forward to inject the fused polymer into mold cavity through a nozzle after the mold is closed (McCrum, Buckley, & Bucknall, 1988). The scheduled pressure during molding  process is well maintained until injected material cools (McCrum, Buckley, & Bucknall, 1988; Scarlet, 2011). After the molded polymer completely solidifies, the solid polymer is ejected from the mold while screw moves backward and the mold opens (Scarlet, 2011).

5

Figure 4.2: An Illustration of a Single-Screw Injection Molding Machine

2. Can we mix polymer A and polymer B to produce a polymer blend AB? Explain your answer.

Yes, we can. The polymers used for this experiment are HDPE and PP in which both have the same melt flow index (8 gm/10 min) ,

are

miscible and exist as a single phase (Salih,

Hamood & Alsalam, 2013). Therefore, they can be mixed t o form a polymer blend and used in injection molding machine. Nevertheless, it is important to note that only polymer with narrow molecular weight distribution is suitable for injection molding because the process requires the feed polymer to be melted at the same temperature so that no obstruction could happen when the feed is pushed forward through the charging barrel or when it is being injected through the nozzle. Also, polymer with broad or bimodal molecular weight distribution product is not suitable for injection molding because the components in the  polymer with different chain lengths will cool down and solidify at different rates which could result in production of irregular-shaped product.

CHAPTER 5: CONCLUSION

From this experiment, we were exposed to the working principles of injection molding machine through practical experience. Adjustment of parameters such as temperature, pressure, stroke and time are important to make sure that satisfactory product that has regular shape is obtained. Two dog-bone-shaped PP and HDPE materials were produced from this experiment and will  be used in the next experiment for tensile stress testing. The possibility of mixing the two  polymers used in this experiment was discussed.

6

REFERENCES

Fibertech Plastics. (2015). A Simple Guide To Plastic Molding Is Rotational Molding Right For You? Retrived July 16, 2017 from http://fibertechinc.net/custom-rotational-

molding/a-simple-guide-to-plastic-molding/ McCrum, N. G., Buckley, C. P., & Bucknall, C. B. (1988). Principles of Polymer  Engineering: Oxford University Press.

Salih, Hamood & Alsalam. (2013). Comparison of the Characteristics of LDPE : PP and HDPE : PP Polymer Blends. Modern Applied Science, 7(3), 33-42. doi: 10.5539/mas.v7n3p33 Scarlet, Q. Y. (2011). Basic Principles of Injection Molding Machine. Retrieved July 16, 2017 from https://hongchaomould.wordpress.com/2011/04/01/basic-principles-ofinjection-molding-machine/ TA Instruments. (n.d.). Understanding Rheology of Thermoplastic Polymers. Retrieved July 16, 2017 from http://www.tainstruments.com/pdf/literature/AAN013_V_1_U_Thermoplast.pdf 

7