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Writing 6.1: Basic information of plastic

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Writing 6.1: Basic information of plastic

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Plastic play an important role in our life, it is applied to food containers, plastic bags, and rainy coat,... Plastic is a type of synthetic or semi-synthetic material that we use so much nowadays. Plastic has many properties such as being versatile, safe, lightweight, durable, chemically unreactive, and cost-efficient. Modern synthetic plastic was invented one hundred years ago. But it wasn't molded into complex shapes. Now, we can make any shape from plastic. Even it is possible to replace some components in engines. Plastic is easy to mass product, we can save a lot of time and money. However, plastic is hardly degradable. In the future, plastic may be made of plant materials, it is easier to degrade. Plastic has both advantages and disadvantages. The advantages are convenient, cheap, durable, and reusable. But plastic hurt the environment, it is not degradable, and some types of plastic cannot recycle.

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Writing 8.1: Maintenance schedule of a machine tool

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Writing 8.1: Maintenance schedule of a machine tool

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This is the lathe machine I have just bought for DAT workshop. It is used for cutting the workpiece by rotating the workpiece about an axis to perform different operations such as turning, facing, chamfering, and drilling... Now, I need to schedule you on how to maintain this lathe machine. Firstly, we need to check the line pressure gauses, and the air pressure then cleans the chip filters every day. Before using the lathe machine, we should warm up the spindle for five minutes at a low speed. Next, we must inspect all the filters, oil levels, and coolant levels weekly. Then refilling the coolant and oil to ensure engine efficiency. If it is too low, the machine will overheat and maybe malfunction. Finally, if the spindle bearings and the drive belts are worn or slack, the lathe machine won't work at the best efficiency. So we must inspect them at least twice a year and re-tension them or replace them if needed.

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Writing 5: The manufaturing process of a check valve

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Writing 5: The manufaturing process of a check valve

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The check valve is a device is used to prevent backflow in a piping system. It is commonly made of cast iron. There are six step to make a perfect check valve. First, cast iron is melted into liquid of metals using heat. The cast iron is then cooled in a container of its correct shaped. Next, we will drill some hole for bolting. After drilling these hole, the next step is paint this valve with color we need. The paint color can make the valve have a longer using time and more strong. When the paint on the valve is dry, the valve is bolted with the other parts using nuts and bolts. The final step of process is inspection. We make sure that the valve don't have any problems.

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As you can see in the figure, this describes the plastic molding process. there are six steps in this process. First, we move plastic pellets from the hopper to the cylinder. Second, these plastic pellets are moved along the cylinder by a screw and heated into liquid. Molten plastic is continued moved to the nozzle. Third, the molten plastic is pushed out of the nozzle into the mold that can be opened or closed. Next, The molten plastic is inflated and expanded by compressed air from the air hose. After that, molten plastic is cooled by cooling lines and formed into the shape. Finally, the mold is opened and the shaped plastic is ejected. These steps are repeated and become a manufacturing line.

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Manual drafting is a traditional design. CAD (Computer Aided Design) is the new trend in design. with CAD, we can have flexible viewing angles, more intuitive with 3D models. Moreover, accuracy is nearly perfect. We can detect errors quickly and make corrections right on the drawing board. These are all things manual drafting can't do. But CAD also has disadvantages. It takes a lot of money for a CAD project, and the maintenance and upgrade fee is very expensive. And CAD needs some special skills, the training fee is not cheap. Manual drafting is slower, less accurate, and harder to detect errors, but much more cheaper than CAD.

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A gear is a machine component to transmit power. It is the shape of a circle with teeth. Gear teeth mesh together to transmit torque. When two gears engage, they form a gear set. Gears are split into five common types. Firstly, the spur gear is the most common type of gear with teeth projecting towards or away from the center. Secondly is a helical gear, it meshes more smoothly than a spur gear. Some kind of helical gears has continuous teeth, they are called worms. A worm pair with a worm gear which is the third type of gear. The fourth type is rack and pinion, they are used to convert rotational motion to linear motion. Finally, the bevel gear is used to transmit power at angles.

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Couplings are most commonly mechanical devices. They are used for transmitting power from the shafts to the others. There are many kinds of couplings, and I know two main kinds. The first type of coupling is rigid coupling. Rigid couplings can make a perfect alignment of the shafts with each other, and they reduce wear on the machine. They also maximize performance and efficiency, but they will be broken if the shafts are misalignment too much. The most common type of rigid coupling is sleeve-type coupling which consists of a cylindrical sleeve. The flexible coupling is the second coupling that I know. The function of a flexible coupling is the same as rigid coupling. Flexible coupling can help reduce noise and unwanted vibrations. But flexible coupling can't make a perfect alignment. If the shafts are slightly misalignment, the flexible coupling is a good choice. Beam coupling is an example of a flexible coupling. It is cut in a spiral shape. Beam coupling can accommodate several degrees of shaft offset.

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Public speaking is a fear of many people, but presentation skills are very important at work. We need to clearly understand the ways to make an effective presentation. The basic structure of a presentation includes 3 parts: introduction, body and conclusion. In the introduction, you must clearly state the topic and purpose of your presentation so that listeners can easily follow the main ideas. The body of the essay is where you present your ideas, you need to present data, facts and give vivid descriptions. In the conclusion of your presentation, reinforce the main ideas you have conveyed. When you start your presentation, you need to greet everyone to make a good first impression. When presenting, you need to be confident, speak loudly and clearly, use eye contact, body language and smile at the audience. You should wear formal clothes. Don't be shy and don't look and read the newspaper. You can spend about 5 to 10 minutes at the end of the presentation for a question and answer session. That's what you should do to have an effective presentation.

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Writing 8.2: Maintenance schedule of a machine tool

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Writing 8.2: Maintenance schedule of a machine tool

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This is the lathe machine I have just bought for D workshop. It is used for cutting the workpiece by rotating the workpiece about an axis to perform different operations such as turning, facing, chamfering, and drilling... Now, I need to schedule you on how to maintain this lathe machine. Firstly, we need to check the line pressure gauses, and the air pressure then cleans the chip filters every day. Before using the lathe machine, we should warm up the spindle for five minutes at a low speed. Next, we must inspect all the filters, oil levels, and coolant levels weekly. Then refilling the coolant and oil to ensure engine efficiency. If it is too low, the machine will overheat and maybe malfunction. Finally, if the spindle bearings and the drive belts are worn or slack, the lathe machine won't work at the best efficiency. So we must inspect them at least twice a year and re-tension them or replace them if needed.

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Writing 6.2: My understanding of plastic

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Writing 6.2: My understanding of plastic

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Hi. As you know, there are seven types of plastic with different uses and features. They are PET, HDPE, PVC, LDPE, PP, PS, and OTHER PLASTIC. Firstly, PET's code is number one. It is strong and recyclable. We use PET to manufacture food and drinking package. The second one is HDPE. Its code is number two. We use it for chemical bottles and playground equipment because this plastic is strong, thick, hard, and heat resistant. The third type is PVC, its code is number three. It can be rigid for use in the building or flexible to manufacture plumbing, wiring, and flooring. Next, LDPE's code is four. It is a flexible, odorless, transparent, recyclable thermoplastic. Used in plastic bags, food containers, bottles, and wraps. The fifth one is PP, its code is five. It has properties of hardness, sturdy, highly heat resistant, and resistant to fatigue. We use it in car parts and thermo vests. Next, PS has code number six. It is cheap, and highly inflammable but not recyclable. PS is used for disposable products. Finally, OTHER PLASTIC's code is number seven. It is used for strong and tough products, such as lenses, safety goggles, and compact discs. This type of plastic is rarely recycled.

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I know two types of drives. They are belt drives and chain drives. Firstly, belt drives are the most common type nowadays. We can find them in sawmills, water pumps, or rice mill machines. The pulleys were usually made of wood and it was not until recently that the belts were made of anything but leather. These drives use friction to transmit power so tension is very important in these drives. The second is chain drives. Chain drives are most often made of meta. They can slip if they don't have teeth. They are worn down fastly if not properly lubricated. Chains are often narrower than belts, and this can make it easier to shift them to larger or smaller gears. Flat belt drives and chain belts drive have both advantages and disadvantage.

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Writing 7.2: Problems of plastic injection moulding

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Writing 7.2: Problems of plastic injection moulding

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When we work with plastic injection molding, we will see some typical problems, such as void, short shot, or brittleness. Today, I will explain the causes and solutions to these problems. First, voids that are caused by plastic shrinkages or the plastic volume changes when plastic is heated or cooled. Solutions for the void are increasing holding pressure and reducing mold temperature and wall thickness. These solutions will keep the molten plastic cooling faster and its volume is not changed. Next, the short shot happens when there is not enough plastic in the shot. Another cause is plastic pressure loss. To reduce the short shot, we need to check the shot continuously, increasing the filling speed, molding temperature, gate size, and runner. Finally, when the melt temperature is too high or the gate and runner system settings are not appropriate, which will lead to brittleness. We must reduce melt temperature, and adjust the size of the runner and gate to ensure the rigidity of the plastic product.

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Writing 4.2: Describe a specific CAD program

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Writing 4.2: Describe a specific CAD program

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NX is a type of CAD software. It is used for producing detailed engineering designs in 3-D and 2D. NX can create a conceptual design, product layout, strength, and dynamic analysis of assembly and the manufacturing processes themselves, and prepare environmental impact reports. NX has both advantages and disadvantages. Let's begin with advantages, we can rapid development and modify the designs. We can draw objects so quickly that the time needed to bring a new product to market is shortened. another advantage, no extra fee no overhead cost. Next with disadvantages, CAD required Expensive Software and Machines. The maintenance fee is high too. Moreover, the person who used CAD required special skills. And the most limitation is the nature of the material of the object. NX is a program, so we don’t know how it works in reality.

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Speaking 5.1: The manufacturing process of the wheel

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Speaking 5.1: The manufacturing process of the wheel

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Bearing is an important mechanical device. There are two types of main bearing I know. The are journal bearings and rolling contact bearings. They include inner bearings, outer bearings. Rolling contact bearings have rollers but journal bearings do not. The inner ring is used to rotate with the axis, the outer is used to remain stable relative to the shaft and roller is used to support load. There are 4 types of rolling contact bearings, they are ball bearing, straight roller bearing, thrust roller bearing and tapered bearing. The ball bearing use spherical roller to support radial and axial motion.The straight roller bearing use cylindrical roller to support radial motion. The thrust roller bearing use barrel shape roller to support thrust forces and the tapered roller bearing use conical roller to support radial and axial motion.

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Speaking 5.2: The manufacturing process of a gear

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Speaking 5.2: The manufacturing process of a gear

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Speaking 6.1: Basic information of plastic

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Speaking 6.1: Basic information of plastic

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Speaking 6.2: My understanding of plastic

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Speaking 6.2: My understanding of plastic

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Speaking 7.2: Typical problems of plastic injection moulding

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Speaking 7.2: Typical problems of plastic injection moulding