Question

Manufacturing Technology

1.
(a) why the injection molding required the reciprocating screw?

(b) why moving forward and backward

2. glass
(a)melting point
(b) process in producing glass

3. Thermoforming
(at least 5) :
(a) material
(b) application
(c) how its work

Answer 1

1.

(a) In a reciprocating screw injection molding machine, material flows under gravity from the hopper onto a turning screw. The mechanical energy supplied by the screw, together with auxiliary heaters, converts the resin into a molten state. At the same time the screw retracts toward the hopper end. When a sufficient amount of resin is melted, the screw moves forward, acting as a ram and forcing the polymer melt through a gate into the cooled mold. Once the plastic has solidified in the mold, the mold is unclamped and opened, and the part is pushed from the mold by automatic ejector pins. The mold is then closed and clamped, and the screw turns and retracts again to repeat the cycle of liquefying a new increment of resin. For small parts, cycles can be as rapid as several injections per minute.Reciprocating screws were developed in the mid-1950s and by 1960 they quickly began to supplant the older systems in Europe and the United States. The great advantage of the reciprocating screw design is that it helped to manage temperature in three critical ways.

2.

(a) melting point of glass:

By its very definition, glass does not have a melting point. A melting point is the temperature at which the atoms in a crystal gain enough thermal energy to break their crystalline bonds. Instead of being fixed in an ordered arrangement, they become free to move about as a liquid.

Glass is not a crystal. When it is cooled from a liquid, the atoms do not line up into that ordered arrangement. Instead, as the temperature is reduced, they move past each other more and more sluggishly. Eventually, a temperature - the glass transition temperature - is reached at which no further movement or rotation of bonds is possible. The atoms are fixed in position, but in their disordered, liquid positions, not an ordered crystal. This sort of frozen-in-place liquid is what we call a glass

When a glass is heated to its glass transition temperature, the atoms gain enough thermal energy to move. Unlike in crystalline melting, there is no breaking of bonds. Instead, bonds become free to rotate. Soda lime glass, used in window panes, undergoes this glass transition at around 800–870 K (530–600 °C).

(b) Process of producing glass:

Glass production involves two main methods – the float glassprocess that produces sheet glass, and glassblowing that produces bottles and other containers.

Broadly, modern glass container factories are three-part operations: the batch house, the hot end, and the cold end. The batch house handles the raw materials; the hot end handles the manufacture proper—the forehearth, annealing ovens, and forming machines; and the cold endhandles the product-inspection and packaging equipment.

Batch processing system (batch house):

Batch processing is one of the initial steps of the glass-making process. The batch house simply houses the raw materials in large silos (fed by truck or railcar) and holds anywhere from 1–5 days of material. Some batch systems include material processing such as raw material screening/sieve, drying, or pre-heating (i.e. cullet). Whether automated or manual, the batch house measures, assembles, mixes, and delivers the glass raw material recipe (batch) via an array of chutes, conveyors, and scales to the furnace. The batch enters the furnace at the 'dog house' or 'batch charger'. Different glass types, colors, desired quality, raw material purity / availability, and furnace design will affect the batch recipe.

Furnace:

The hot end of a glassworks is where the molten glass is formed into glass products, beginning when the batch is fed into the furnace at a slow, controlled rate by the batch processing system (batch house). The furnaces are natural gas- or fuel oil-fired, and operate at temperatures up to 1,575 °C (2,867 °F).^[3] The temperature is limited only by the quality of the furnace’s superstructure material and by the glass composition. Types of furnaces used in container glass making include 'end-port' (end-fired), 'side-port', and 'oxy-fuel'. Typically, furnace "size" is classified by metric tons per day (MTPD) production capability.

Forming process:

There are currently two primary methods of making glass containers: the blow & blowmethod for narrow-neck containers only, and the press & blow method used for jars and tapered narrow-neck containers.

3. Thermoforming:

Plastic Materials for Heavy Gauge Thermoforming

Productive Plastics, a leading thermoformed plastic manufacturer, offers information on plastic materials for heavy gauge thermoforming. Note – The information provided on this page is basic/general – it is only intended to give an overview of some of the plastic material options available and provide preliminary help to identify possible appropriate plastic materials for a project. The content should be used as reference only. Please Contact Productive Plastics for specific assistance with any of these plastic materials in connection with thermoforming contract manufacturing services.

For example, if you wanted to maximize the impact strength property of ABS, the basic formula would be modified to include higher amounts of rubber. This would result in a higher desired impact strength, but would consequently make the material softer and less stiff, making it more susceptible to scratches and abrasions. This is especially true for those plastics categorized as engineered plastics, such as ABS.

(b) Application:

Plastic Material	Advantages	Disadvantages	Industry Examples
Polystyrene	Clear plastic, very moldable, inexpensive, recyclable, high chemical resistance, high electrical resistance, heat distortion ~200°F	Cracks and breaks easily	Disposable cups, disposable applications, decorative applications, electrical applications
HIPS (High Impact Polystyrene)	Very moldable, relatively inexpensive	Marginal crack and break resistance	Picture frames, shower walls, food containers
Polyethylene (PE)	Chemically resistant, high impact resistant, high electrical resistance, fairly economical, can be UV protected with additive	High mold shrinkage – not suited for tight dimensional tolerances, cosmetic deficiencies	Pallets, tanks, truck bed liners, tote bins, tanks, self-lubricating tendency makes it ideal for non-stick/low friction applications
Polypropylene (PP)	High level of stiffness, light weight, high heat deflection, chemical resistance at room temperatures	Difficult to process, high mold shrinkage	Tool cases, applications with a living hinge, food containers, acid tanks
ABS (Acrylonitrile Butadiene Styrene)	Engineered plastic that can be customized to desired levels of stiffness, hardness, heat deflection, and many other characteristics	UV sensitive – requires a UV protective cap layer for extended exposure	Cases of all types, bath tubs, fenders, instrument panels, automotive applications, recreational vehicles, many others
PVC (Polyvinyl Chloride)	Very high chemical resistance, stain resistant, stiffer than ABS, high room temp. impact strength, natural flame retardant qualities	Difficult to process	Shower surrounds, moldings, kick panels, display cases
PVC/ABS (alloy)	Easy to process, very cosmetic, dimensional stability, impressions well off a textured tool, maintains tight dimensional tolerances, retains some of PVC’s natural flame retardant qualities	Not as stiff as pure PVC, heat distortion point lower than ABS	Decorative fascia, equipment covers, mass transportation applications, outdoor applications with UV protective cap, many others
PVC/Acrylic	Easy to process, highly customizable alloy, high impact resistance, very high chemical and stain resistance	Low heat distortion point ~160°F	Aircraft interiors, medical equipment covers, transportation applications, electronic enclosures, outdoor applications with UV protective cap
Polycarbonate	Extremely high impact resistance, high clarity – good for transparent parts, precision molding, good insulator, high heat distortion point ~270°F	Low chemical resistance to certain substances (oil, gasoline, harsh chemicals), can be difficult to process, higher material and processing cost	Visors, plastic guards, transportation components (headlights, taillights, instrument panels), appliance drawers, skylights
Polycarbonate/ABS	When compared to true polycarbonate – less expensive, lower heat distortion ~240°F, much easier to process, higher chemical resistance	When compared to true polycarbonate – reduced clarity, lower heat distortion ~240°F	Computer and machine enclosures, electrical applications, cellular phones, automotive applications
TPO (thermoplastic olefin)	High impact strength (even at cold temperatures), high dimensional stability (low mold shrinkage), stiffness, high chemical resistance	Can be difficult to process due to material sag during heating	Car bumpers and other automotive applications, chemical shields, gear covers
PETG (polyethylene-terephthalate)	Very easy to process, high clarity – good for transparent parts	Not UV stable – unsuitable for extended exposure	Structural automotive parts, hand tools, industrial components

(c) how it works:

Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mold, and trimmed to create a usable product. The sheet, or "film" when referring to thinner gauges and certain material types, is heated in an oven to a high-enough temperature that permits it to be stretched into or onto a mold and cooled to a finished shape. Its simplified version is vacuum forming.

Thermoforming differs from injection molding, blow molding, rotational molding and other forms of processing plastics. Thin-gauge thermoforming is primarily the manufacture of disposable cups, containers, lids, trays, blisters, clamshells, and other products for the food, medical, and general retail industries. Thick-gauge thermoforming includes parts as diverse as vehicle door and dash panels, refrigerator liners, utility vehicle beds, and plastic pallets.