Mould Theory

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(5) - Explain the different type of material - Use of the different material. - Identify the different material. - Explain the necessity of mould - Explain the working principle - Explain the functional requirement of each parts. . . .

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(9) ~ Plastics is a unique class of materials, came into existence by the virtue of their superior properties and cost performance balance over to conventional materials like wood, ceramics and metals. ~ Plastic materials based on their characteristic performance were classified as ( ( and ( ((

(10) materials. ~ It is well known that the former class of materials distinguished from the latter by their processing behavior and characteristic properties. ~ Example for thermoplastic includes PS, PP, PVC, PET, PA,POM ~ Examples of thermo-sets include PF, UF, and MF etc. ( ( ~ Commodity plastics ~ Engineering plastics ~ Specialty plastics.

(11) These are low performance, high volume resins, characterized by: HDT 100°c and tensile strength, œ<50MPa. Two of them, PE and PP are semi crystalline, thus their properties depends on nucleation and annealing. The glossy resins (PS, PVC, and PMMA) are available as either rigid or impact modified varieties, viz. GPPS, PVC-R, and PMM or HIPS, PVC-F, and HI-PMMA. All these polymers can be formulated as filled and reinforced grades excellent for film blowing or blow molding. Five types of resins belongs to this category polyamides (PA), polyesters (PEST), polycarbonates (PC), poly-oxy-methylene (POM) and modified poly-phenyleneether (PPE). By definition, the resins are characterized by HDT À 100°c and tensile strength œ>40MPa. They can be formed to precise and stable dimensions. Their consumption is about 12% of total plastic. There is a great diversity of performance within each of this type, especially considering the great chemical verity within the PA, PEST & PC type as well as profusion of blends, filled, and reinforced systems comprising engineering resins. To this category belong low volume, high performance, high temperature, and high cost polymers. Their consumption amount to less than 0.1% of total plastics. By definition, the resins are characterized by high modulus, tensile and impact strength. They can be formed to precise and stable dimensions. Their continuous use temperature is CUT À 150°c. Most of specially polymers are available as GF or CF filled grades. . .

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(14) 0hy we use plastic material in the first place instead of traditional and familiar material such as metal. In general plastic offers impressive advantages over metals. Some of it is listed below ~ ~ ~ ~ ~ ~ ~ ~. They are not subjected to corrosion They are light in ;weight with good strength to weight ratio Very cost effective The speed with which they can be produced. They give design freedom They provide with good electrical insulation property They are available in wide range of colures Reduced assembly time. In addition to it each plastic material offers some special property which serves a particular application or can be made to do so by the incorporation of suitable additives with the plastic materials.. Thesuccessful use of plastics usually derives from a combination of cost savings and improvement in performance or appearance, but often the cost saving alone is sufficient to justify the choice of a plastics material. Plastics can offer the following technical advantages. All plastics have low densities, generally in the range 830 to 2500Kg/m3.These figures can be extended upwards or downwards. For example, foamed materials can have densities as low as 10 Kg/m3, and filled plastics as high as 3500Kg/m3. In comparison the density of aluminum is about 2700 Kg/m3 and that of188 stainless steel about 7900 Kg/m3.There are two consequences of the low densities of plastics. Large volume of material for unit weight that can be obtained with metal. Some plastics are extremely tough, and objects made from them are difficult to destroy by mechanical treatment. Other plastics are less tough, and still other is fragile. Plastics show some of the behavior associated with rubbers in accommodating relatively large strains without fracture and in recovering their original shape and dimensions when the stress is removed.

(15) The quietness in use of plastics gear trains and bottle crates depends on the inherently high degradation of mechanical energy to heat.. .

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(18) Some plastics appear to perform remarkably satisfactorily in situations involving dynamic stresses or strains. Plastics / plastics and plastics metals combinations have low coefficients of friction and can often perform un-lubricated without fear off seizing. Plastics are good insulators, their thermals conductivities being many orders of magnitude lower than those of metals. This low conductivity may be exploited in handles for utensils and in the design of pipes for carrying hot fluids, where a lagging effect may be built in. In general, plastics are complementary to metals in their chemical resistance, in that they are resistant to weak acids, weak bases and aqueous salt solutions, although strong oxidizing acids may cause some attack, leading to discoloration and possible embitterment. On the other hand, organic solvents to which metals are generally inert, may cause swelling, deterioration of properties and eventual dissolution. The plastics material of the environment and on the temperature. Some plastics are transparent, some are translucent and a few are opaque. Acrylics, polystyrenes, methyl pentene polymers, polycarbonates and certain grades of PVC can be very transparent indeed to visible light. All plastics can be colored by incorporating a wide range of dyes or pigment s, thus avoiding the need for painting. However, subsequently painting or plating is possible with some, if required

(19) A variety of automatic and semi-automatic techniques allows easy, economical and reproducible fabrication of articles and components. Although often unnecessary, further finishing operations are easy to carry out on most plastics.

(20) ~ To know the material. Used in any product ~ For processing of scrap material. ~ For product indigenization. .

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(24) ~ Appearance ~ Method of fabrication ~ Penetration to hot rod and cutting with knife ~ Floatation Test ~ Scratch resistance ~ Colour ~ Odour ~ Tear ~ Solubility ~ Burning characteristics ~ Melting Point ~ Melting Point ~ Confirmation test ~ Transparent - PS, SAN, PMMA, PC, PVC, PET ~ Translucent - PE, PP ~ Glossy - ABS, PC, POM ~ Milky 0hite- PTFE ~ Dark colors- Phenolics ~ Yellowish - Epoxy Resins and unsaturated polyesters

(25) ~ Injection Moulding - Thermoplastics and injection mould able thermo-sets (Gate marks, Flash Marks) ~ 0ithout any mark - Nylons (Polyamides), HDPE, PTFE. ~ Films - PE, PP, PVC, PET, CELLULOSICS

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(27) ~ If a shaving can be pared of with a knife it is probably thermoplastics. ~ If the material s rigid and difficult to pare off it is probably thermo-set ~ PMMA and polystyrene are difficult to pare off ~ 0hen a hot electric soldering iron is kept on the material. ~ Thermoplastics melt and sink but thermo-set do not melt but degrade ~ ~ Drop a piece of sample in water, if it sinks then it is PC, PS, SAN, CA, PVC, NYLON, PTFE, PMMA, Poly-acetals ~ If it floats then it is PE or PP but mineral filled grades sink in water ~ Low gloss easily scratch able - LDPE, LLDPE ~ High gloss can be scratched - HDPE ~ High gloss can not be scratched - PP . .

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(31) ~ Take the sample and drop on the hard surface ~ Metallic Sound ± PC, PS, SAN, PPS ~ Dull sound ± CA, PVC, NYLON, PTFE, PMMA, POLYECETAL

(32) ~ Camphor smell ± Cellulose Nitrate ~ Plasticizer - Plasticized PVC smell ~ ~ ~ ~ ~. Tough, stretches before tearing - Polyethylene Tough stretches a lot before tearing - Polypropelene Tears Straight - Polystyrene Stretches then tears raggedly - PVC Tear easily and straight - Cellulose Acetate.

(33) ~ Bends and tends to remain unbend - PE, PP ~ Cracks but retain unbend - Polystyrene ~ Bends and tend to remain - ABS ~ Bends easily and spring back ± PVC(Rigid) ~ Cracks and splinters difficult to bend - PMMA ~ Spring Back - Nylon ~ Thermoplastics - solvents ~ Cellulose Esters - Ketones, Esters ~ PVC - Cyclohexane one dimethyl formamide ~ Polyacrilic Acid Esters - Aromatic Hydrocarbons, Acetone ~ Polymethyl Acid Esters - Chloroform, Dioxin, Aromatic hydrocarbon ~ Polyesters - Ketones ~ PET - Cresol, Conc. H2SO4 ~ PC - Chlorinated Hydrocarbons, Dioxan ~ PE - At elevated temp. Dichloroethelene, Tetralene, Decalene ~ PS -Toluene, other aromatic hydrocarbons, Ethyl Methyl Ketone, ~ Polyvinyl Acetate - Acetone, Methanol, Aromatic Chlorinated Hydrocarbons.. .

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(36) ( ( ( ( . PE. . Blue base yellow tip burns Continuously. ( . . No smoke. Drips. 0axy smell. PP. Blue base and yellow tip. No smoke. Drips. Lubricating oil smell. PS. Orange yellow flame, fast and continuously burns. Black soot. No dripping. Merry Gold Smell. HIPS. -do-. -do-. -do. Burning Rubber smell. ABS. -do-. -do-. -do-. -do-. SAN. -do-. -do-. -do-. Merry Gold Smell. . . ABS and HIPS can be differentiated by detection of nitrogen by elements analysis : SAN and PS can be differentiated by detection of presence of extra elements . . .

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(42) . ( Thermo-sets undergo a chemical Thermoplastics are softened by heat, and become change during moulding, becoming solid on cooling. This process can be repeated solid, and therefore, they Cannot many times. be melted. Overall chemical resistance of thermo-sets in Unequalled by any thermoplastic. Dimensional stability is excellent.. Chemical resistance of thermoplastics is limited to fewer compounds than is the case with thermo-sets.. Creep over a prolonged time period is well below even glassreinforced engineering thermoPlastics. This means better dimensional stability and better resistance to property deterioration.. Creep is one of the major problems with the thermoplastics 0hen subjected to long term loads. This means sizable Dimensional changes and Strength degradation. Creep Resistance is improved by filler s and reinforcements.. Moulded-in stresses with compression moulded parts are parts are lower than in other moulded parts , and where minimal distortion is a factor, it can be a deciding consideration. Toughness is a property that can be found in Thermo-sets at a considerable cost; by using reinforcing materials such as fabrics and/or Fiberglass mat.. Since thermoplastic respond more readily to the influence of heat, they also tend to fluctuate in dimensions. Some polymers vary more than others, but as a group they would Rank second to thermo-sets.. Injection moulded thermoplastics have moulded in Stresses in varying degrees that are caused by part design, Processing parameters and mould design.. Most thermoplastics are inherently tough materials and for this reason one used whenever this requirement is needed. They provide good toughness at low cost.. Colors in thermosetting compounds Thermoplastic materials can be coloured to any are limited in variety and their desired shade of appearance and normally maintain stability is not Satisfactory. The the colour throughout the life of a product. resins tend to discolour over Prolonged periods of time. Very few thermo-sets are available in clear, see Through materials.. The selection of clear material in thermoplastics is quite large.. . .

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(45) 1. Plastics are generally --------material. 2. As per their characteristic performance plastic materials are classified as -----------and -------------material. 3. Give some examples of thermoset and thermoplastic material? 4. 0hat do you mean by commodity plastic? 5. 0hat do you mean by engineering plastic? 6. 0hat is specialty plastic or modern plastics? 7. 0hat are the benefits or characteristics of plastic? 8. 0hat are the technical advantages of plastic? 9. How plastic materials can be identified? 10. -------, -------, ------- are transparent materials. 11. ------, ------are glossy material. 12. 0hat is floating test in water of plastics? 13. ------flames appear in case of PP. 14. 0hat is the behavior of plastics in flame? 15. Differentiate thermoset and thermoplastic material. 16. ------ materials can be reused and ------materials cannot. 17. 0hat is the full form of ABS, PP, PE, LDPE, HIPS & PVC? 18. Plastic materials based on their characteristics performance were classified as ««.. & «««. Material. 19. Based on applications plastics are classified in «.. , ««.. & «« plastics. 20. 0rite two identification techniques to identify the plastic material. 21. ««« & «« are used to produce transparent components. 22. 0hich plastic undergoes chemical change during demoulding ? 23. ««.. gives metallic sound on hitting. (PC, SAN, PS) 24. Cellulose nitrate produces««. Smell. 25. ------plastics can not be reused. 26. A mould is an assembly of ««« & «««. 27. ««gives external shape of components. 28. ««. gives internal shape of component. . .

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(49) It is an assembly consists of an Impression, which is a recess or gap similar to the Component formed by the two Mould members termed as µCORE¶ and µCAVITY¶ , into which the molten Plastic Material is Injected under Pressure an is allowed to be cooled either by water or air till the component gets hard.. It is female part of the mould, which gives the external shape of the Component. Pockets, Slots, holes are considered as Cavities. These are highly polished to a mirror finish, requires better finishing appearance on the outer surface of the component.. It is male part of the mould, which gives the internal shape of the Component. All Projections are considered as Cores. These are not required high polish as the Component is to be sticks on to core. .

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(53) ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~. Top Clamping Plate / Top plate: Location Ring or Retainer Ring: Cavity Plate : Core Plate : Core back plate : Bottom Clamping Plate / Bottom plate: Spacer/ Riser : Ejector Plate: Ejector back plate : Feed Buttons: Guide pillars / Leader pins: sprue Bush : Sprue Puller : Return Pins / Push back pins: Guide bush : Cavity: Core: Parting Surface:. .

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(57) ( Holds the stationary part of the mould to the stationary platen of the injection machine. (

(58) Fits into a counter bore in the top clamping plate and is used to locate the mould on the platen of the press so the nozzle and sprue bushing are aligned. (( ( Part of the stationary section of the mould into which the leader or guide pins are mounted. Also used to hold core, cavity blocks, and sprue bushings. ( ( Top plate of the movable section of the mould. Forms the parting line of the mould with cavity retainer plate. Used to hold the leader pin bushing as well as core and cavity blocks. ( Mounted behind the core retainer plate to keep this plate from bending under the high pressure used in injection molding: ((

(59) ( Holds the moving portion of the mould to the movable platen of the injection machine. Mounted on the bottom clamping plate under the support plate to form a space which allows the ejection bar to move when the piece parts are ejected. . .

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(62) (( ( Counter bored for the heads o0f ejector pins, ejector return pins, and spur puller pin. ( ( Bolted together with the ejector retainer plate to form a unit. Acts as a back up plate for the pins in the ejector retainer plate. (( Pressed into the bottom clamping plate, they are lands for the ejector plate. Round bars placed between the support plate and bottom clamping plate . The same height as the parallels. Bolted to the bottom clamping plate, they are used as additional support for the core retainer plate.

(63) Butted up against the nozzle of the injection machine. Has a conical-shaped hole through which the material is forced into the mould runner. Pin located directly under the opening of the spur. Used to pull the moulded spur out of the bushing after shot has been made. Located in the ejector retainer plate. Force the ejector plate and ejector retainer plate, and therefore the ejector pins, to the bottom position as the mould closes. Hardened and ground steel pins pressed into one of the plated. Align the two halves of the mould base. Hardened and ground steel bushings which are pressed into one of the plates. Serve as bearing surfaces for the leader pins. Some injection mould bases are manufactured with the parallels welded to the bottom clamp plate. The unit thus formed is called the Ejector housing. ( The female portion of a mould which gives to the moulding its external form. The male portion of a mould which forms the internal shape of the moulding. (

(64) That part of the mould plate, adjust to the impression, which butt together to form a seal and prevent loss of plastic material from the impression.. .

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(73) - Distinguish the different moulding processes - Explain the individual process. - Distinguish different types of mould - Explain the application of different types of mould & its limitation, advantages & disadvantages.. .

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(77) COMPRESSION MOULD. TRANSFER MOULD. INJECTION MOULD. BLO0 MOULD. EXTRUCTION MOULD. THRRMOFORING MOULD. ROTO MOULD. . COMPRESSION HAND. FLASH. POSITIVE. ! ( . .

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(80) . TRANSFER MOULD. POT TYPE. PLUNGER TYPE . INJECTION MOULD.

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(86) . BLO0 MOULD. EXTRUCTION. INJECTION. STRETCH . .

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(90) Plastics are shaped by a Varity of methods such as molding, calendaring, extruding, blow molding, vacuum forming, etc. For thermo-setting materials hot compression molding, Transfer±molding, laminating and castings are the most common methods.

(91) ~ The hot compression molding method is the most commonly used method of shaping a thermo-setting plastic to some desired form. The basic principle in molding is that plastic material softened by heat and pressure takes the shape of cavity due to pressure acting on it and it gets hardened by the heat and pressure causing a chemical change and the desired shape is obtained ~ In general, compression and transfer moulds are made of High Carbon and High chromium of hot die steel. The core and cavity should be heat treated to the required hardness for maintaining the dimensional accuracy of product and also the life of mould. There are different types of compression moulds in use. . .

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(95) Thermo plastic materials are used in injection moulding. The thermo plastics soften and become plasticized in state by the application of heat and harden when cooled. There is no chemical reaction taking place during the process of heating and cooling. These materials have linear molecular chains that flow over each other when heated and solidify into a new shape when cooled without significant chain breakage.

(96) ~ Basically, blow molding is intended for use in manufacturing hollow plastic products: a principal advantage is its ability to produce hole ±low shapes without having to join two or more separately molded parts. Although there is considerable difference in the available processes, as described below, all have in common production of a parison (precursor). Enclosing of the parison in a closed female mold, and inflation with air to expand the molten plastic against the surface of the mould, where it sets up into the finished product. ~ Differences exist in the way that the parison is made (i.e., by extrusion or by injection molding); in whether it is to be used hot as it comes from the extruder or injection molding machine (as in conventional blow molding), or stored cold and then reheated (as in cold perform molding); and in the manner in which the parison is transferred to the blow mold or the blow mold is moved to the parison. ( ( 1. Melt the material. 2. Form the molten resin into a tube or parison. 3. Enclose the parison in the blow mould. 4. Inflate the parision inside the mould. 5. Cool the blow moulded part. 6. Remove the part from the mould. 7. Trim flash, as needed. ~. In many cases, all theses steps can be carried out automatically, with the finished products conveyed to downstream stations for secondary operations and packaging.. ~. Although there are many variations, the two basic processes are extrusion processes injection blow molding. Extrusion processes are by far the more widely used, but injection blow molding and injection stretch blow molding have captured significant market segments. 0hile reviewing these methods, the reader is urged to refer to Chapters 4 and 5 additional background material. .

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(100) ~ In rotational molding, the product is formed from liquid or powdered thermoplastic resin inside a closed mold or cavity while the mold is rotating biaxial in a heating chamber. To obtain this mold rotation in two planes perpendicular to each other, the spindle is turned on a primary axis, while the molds are rotated on a secondary axis ~ Rotational molding (also popularly know as roto-molding) is best suited for large, hollow products requiring stress-free strength, complicated curves, a good finish, a variety of colors, a comparatively short (or very long) production run, and uniform wall thickness. It has been used for products such as fuel tanks, furniture, tilt trucks, industrial containers, storage tanks, portable outhouses, modular bathrooms, telephone booths, boat hulls, garbage cans, light globes, ice buckets, appliance housings, and toys .The technique is applicable to most thermoplastics but is most widely used with polyethylene.. ((

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(102) 1. Virtually unlimited design possibilities (parts as small as a golf ball to a 22,500- gallon agricultural tank). 2. Relatively low machinery cost. 3. Low tooling costs. 4. Economical prototyping. 5. Strong outside corners in virtually stress-free parts. 6. Part finish from matte to high gloss. 7. Simultaneous processing of multiple colors. 8. Simultaneous processing of different parts. 9. Quick mold changes. 10. Possibility of moulding in metal inserts. 11. Molded-in multicolor graphics. 12. Multilayer moulding for chemical resistance or strength. 13. Double-walled parts molding for additional rigidity. 14. Possibility of minor undercuts. 15. Virtual 100% usage of material (no scrap).. .

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(105) ( ~ There are essentially four basic steps in rotational molding: loading, molding or curing, cooling, and unloading. In the loading stage, either liquid or powdered plastic is charged into a hollow mold. The Mold halves then are clamped shut and moved into an oven where the loaded mold spins biaxial. Rotation speeds should be infinitely variable at the heating station, ranging up to 40 rpm on the minor axes and 12 rpm on the major axes. 4:1 rotation ratio generally is used for symmetrically shaped objects, but a wide variety of ratios are necessary for molding unusual configurations. ~. In the oven, the heat penetrates the mold. Causing the plastic, If it is in powder form, to become tacky and stick to the mold surface, or if it in liquid form, to start to get. On most units, the heating is done either by air (as in a units, gas fired hot-air oven) or by a liquid of high specific heat, such as molten salt; where jacketed molds are used (see below), heating is cone with a hot liquid medium, such as oil.

(106) ~ Thermoforming is the process of heating a plastic material in sheet form to its particular processing temperature and forming the hot and flexible material against the contours of a mold by mechanical means (e.g., differentials in air pressure created by pulling a vacuum or using the pressures of compressed air). 0hen held to the shape of the mold and allowed to cool, the plastic retains the shape and detail of the mold. Because softening be heat and curing by the removal of heat are involved, the technique is applicable only to thermoplastic materials and not to thermo-sets. ~. Examples of thermoformed products are plastic or foam dinnerware, cups, meat and produce trays, egg cartons, refrigerator liners, computer housings, interior and exterior automotive parts, blisters for packaging, and countless others. These common and often taken-for-granted products are not usually thought of as the result of detailed tooling design, precise controlled heating and forming, expert material technology, and trimming/ finishing operations. Clearly, the thermoforming process is an important link in the plastics industry.. ~. Advantages of thermoforming over most other methods of processing plastics include lower tooling and machinery costs, high output rates, the ability to use pre decorated plastic sheet, and good- quality physical properties in finished parts.. ~. Its disadvantages include the need to begin with sheet or film rather than less costly basic resins, trimming material used to clamp sheet for forming, and the problem of trim scrap reclamation.. . .

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(110) ~ Hand moulds ~ Semi-automatic moulds ~ Automatic moulds Hand Moulds are usually small in size and do not weight more than about 10kg for ease of handling. The material is put into the cavities and the two halves of the mould are assembled and placed between the platens of the press. After the press has been closed and parts molded, the mould is removed from the press closed and the parts molded, the mould is removed from the press and the parts ejected from the mould on a conveniently located bench. The process is then repeated. Hand moulds are used for making sample parts, or when a limited number of small parts are to be produced. Hand moulds, being removed from the press, facilitate the loading of inserts. (( Vary greatly in size. These moulds are mounted on to the platens of the press by clamps. The mould is loaded with material and the two halves close. After the pieces have been molded some sort of ejection mechanism pushes the parts out of the cavity or off the plunger. The press operator then places the molded parts in a suitable container or on a bench for flash removal etc. The operator cleans the mould of the excess material and the process is repeated.. .

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(113) (( ~ Are similar to semi-automatic moulds but do not need and operator once the mould has been set up for production run. The automatic moulds, through the use of combinations of loading devices, timing devices positive ejector systems, sweeps, micro-switches, safety devices and cleaning apparatus, lend themselves well for molding many articles. There is a purpose for each type of mould, and many factors such as the size of the piece part and the production requirements, determine which of the three is used.. .

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(116) Æ ««««. &«««««. are two main members of a mould. PÆ ««««. is a female part of mould, which gives the external shape of the component. 3Æ «««. is a male part of mould which gives the internal shape of the component. îÆ «««« is used to located the mould into the moulding machine platen during loading a mould {Æ «««. Act as a channel through which molten material flows from the machine nozzle to the cavity. ëÆ ««..forces the ejector assembly to its original position. ¦Æ Bottles are manufactured by «« moulding process. xÆ Food packaging products are manufactured by ««« moulding. ½Æ Pipes are manufactured by------ moulding process. Æ Big size plastic products like water tank are manufactured by ------process. Æ ««««.. is the most commonly used method for thermoset plastic materials. PÆ «««.. is a semi solid form of plastic material enclosed in blow moulding process. 3Æ ««. Materials are used in injection moulding. îÆ Incase of bottles having thicker cap area or having variation in thickness at cap portion are manufactured by «.. blow moulding process {Æ ......, «.., «.. & «.. are four basic steps in rotational moulding. ëÆ Thermoforming moulding method is applicable only for «.. «.. material. ¦Æ ««. are usually smaller in size and operated manually. xÆ «««. & «««. are two methods of thermoforming moulding process. ½Æ ««.. pins are used to pull the moulded sprue out of the bushing after processing. PÆ ««« & «««.. are used to align the two halves of the mould base. PÆ ««. & ««.. are two methods of blow moulding process. PPÆ The taper angle of sprue bush generally varies from «« to ««««V P3Æ «« gives a proper landing to the ejector assembly and provides provision for easy assembly of mould ejector. PîÆ Generally the component shrinks on to the ««. after opening.. .

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(124) - Explain the types of compression moulds - Distinguish different types of compression moulds. . " . .

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(129) ~ Compression and Transfer Molding Processes are mainly used for the manufacture of thermosetting plastic products such as Electrical Switches, Cooker Handles, Miniature Circuit breakers, Ceiling roses, Switch gears, Switch boxes and also various consumer oriented products. To some extent this process is also used for thermoplastics components which are otherwise not possible to produce by other conventional processing methods due to processing limitations. Example includes PTFE liners, Gears and 0ashers, UHMHDPE products etc. Several technological advancements have taken place in these areas which are mainly aimed at improving the quality of the product and enhancing the production rate Robotics and process automation with microprocessor based on control systems have revolutionaries, the entire compression and transfer molding line and specially designed thermo set injection molding process. ~. The quality of products largely depends upon the machine and the mould. In this context, the requirement of precision mould can not be less emphasized. (( (

(130) . Three important factors that must be controlled in compression molding are: ~ ~ ~. Temperature Pressure Cure Time. ( Thermo-setting materials which are used in compression molding are cured by heat and pressure. Heating is and important phase in the molding operation. Heat softens the material sufficiently to allow it to flow under the influence of the press pressure into any openings in the mould to the desired shape. Heat causes a chemical change or polymerizes the material into its hard infusible finished state. Temperatures for molding thermo-setting materials vary from 270°F to 350°F. Temperatures for molding the various materials can be determined by experimentation or by getting the information from the manufacturer of some particular material. Temperatures the finishe4d article. Temperatures which are too low do not allow the material to flow properly and result in incompletely filled cavities and insufficiently cured piece parts of poor consistency. Mould temperatures must be maintained within 5°F. For best results molding temperatures not only vary with the material used, but with the geometry of the molded article, the type of mould, and whether loose powder or pre-heated performs are used. . .

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(134) : The two methods most commonly used in heating press platens and moulds using thermo-setting materials are steam and electricity. Steam is favored by many molders because of its economy and heating qualities. Electric heating of moulds is replacing steam in many instances because of its cleanliness and lower maintenance costs. Pressure as well as temperature must be regulated in order to produce satisfactory parts economically. Pressure needed to mould a particular article depends on the flow characteristics of the material, the cavity depth, and the projected are of the piece part. Generally, It is recommended that minimum molding pressure of 225kg/cm² of projected area be used. However, in practice, about 375kg per Cm² of projected area is used to compensate for any variables that may be encountered. ( Varies with the materials use. The size and shape of the molded article, and the method of molding. In compression and transfer molding, cure time is the time elapsed when the movement of the press stops until the pressure on the molded part is released. For smaller and thin wall pieces, cure time may be only a minute or two. On larger pieces, and pieces with thick sections, the cure time may be as high as 15 minutes. ( During the process of compression molding, gases are formed as the chemical reaction takes place in the material. Some provisions must be made to get rid of the gases otherwise poor quality piece parts will be the result. Gas pockets can cause incomplete shots or blistered piece parts. One method of getting rid of the gases is to allow the mould to breathe that is the mould is ( ( closed and then opened again for about 3mm to get rid of the gases and then closed again. Other methods used are in small flats ground on the periphery of the plunger that telescopes ground on the periphery of the plunger those telescopes into the cavity. Small grooves 0.050 to 0.25 mm deep and about 3mm wide ground into the top portion of the cavity wall. This type is used on large cavities. ( ( . .

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(139) To prevent the wastage of material for efficient molding, it is important to load the proper amount of material into the mould. This is done by one of the following three ways: (

(140) ( " ( ~ The volumetric method is most efficient when used with ferrous materials. A containner of predatermined volume is filled with material and the contents poured into the cavity. ~ The weight method is used with materials in which the amount of material cannot be controlled rea-dily by volume. A predetermined amount of material is weigh-ed on a balance and then placed into the mould. ~ The third method used is a predetermined amount of material which has been compressed into pre-form of desired shape size and weight. The use of performs is a very efficient method of loading moulds. ~ Smaller in size and weight not more than 12kg for Easy Handling. ~ Production is limited to small parts, short runs or Prototype 0ork. ~ Overall height of the molding is controlled by land areas on mating surfaces of the top force and cavity Maximum Density of the molding may be maintained by clearance between the side wall of the top force and the cavity. Used as a single cavity mould on a Rotary. .

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(143) Press and molding pressure is controlled at each station. Flash must be removed in the land area otherwise it will result in damage or breakage of the lands. It is advisable to provide additional pressure pads outside the cavity. ( #

(144) ($ ~ The POSITIVE type of compression mould. The plunger telescopes within the cavity compressing the material and molding the piece as shown. There is very little clearance between the plunger and the cavity wall. In the positive mould, almost all the pressure is exerted on the material and very little material is allowed to escape, the clearance between the plunger and cavity varies between 0.036mm to 0.130mm per side, depending on the size of the mould and the material to be molded. The amount of material that escapes through the clearance between the plunger and cavity is called flash. The flash is formed vertically on the type of mould shown. The disadvantage of the positive type of mould is that after frequent operation the cavity walls become scored and ejection of piece parts is difficult. Flash is formed on every piece part molded by the compression method. The thickness and position of this flash depends on the design of the mould, type of material being molded, and accuracy of the mould. Flash is removed by filling, sanding, and tumbling. The positive mould is used primarily with material containing coarse fillers. The amount of material placed into the mould cavity must be measured accurately as there is very limited means for the excess material to escape.. ~ ~ ~ ~ ~. Used for high bulk materials and large deep draw parts when maximum density is required. It is single cavity mould and uses and accurately weighed charge of material. All the applied pressure is exerted on the material. Flash between the top & bottom force can be produced in the direction of pressure. Flash thickness varies according to the clearance between the loading chamber and top force.. . .

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(147) ( : The principle of the semi ± positive type of mould. As the two halves of the mould begin to close, the mould acts much like a flash mould as the excess material is allowed to escape. As the plunger telescopes into the cavity, full pressure is exerted on the material and produces piece parts of maximum density. The mould becomes a positive mould for the distance X as shown on the illustrations. The distance X varies with the size of the mould and material used. There is very little clearance between the plunger and side walls of the cavity, which results in a very thin vertical flash being formed. This type of mould takes the advantages of the free flow of material in a flash mould and the quality of producing dense parts of the positive mould. ( ( ( ~. It controls maximum density and critical dimensions as related to cavity and top force.. ~. Easy removal of flash on large parts and leaves no flash line scar on the side of the parts. ( ( ( ~. It is less costly and more popular.. ~. It is recommended for close tolerance parts and assures minimum flash finish.. . .

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(150) # ~ The FLASH type of mould. The cavity is filled with material and the excess is squeezed out over the lands which are about 3mm. 0ide. External landing bars are provided so the plunger does not crush the top of the cavity when the mould is completely closed. Clearance between 0.050mm and 0.125 m is provided so excess material can escape and the cavity is not damaged. Fig. shows the flow of the material and illustrates the thin horizontal flash formed with this type of mould. The flash type mould is not generally used with coarse-filled materials or for pieces which require a high density. The flash type mould lends itself well to shallow-depth articles such as dinner-ware plates and saucers. (

(151) Another type of mould construction is the split wedge or split cavity mould. This mould is used primarily for articles that have undercuts, such as spool shaped pieces. These projections or under cuts prevent the piece part from being removed from a conventional mould cavity. In order to overcome this difficulty, the cavity is constructed in to two or more sections. 0hen these sections are together, the C ± plunger inside surface has A & B - Conical Cups E ± upper heating plate required shape, and D ± lower heating plate F mould casing L ± heating bandage the exterior of these G ± location dowel & CAM combination sections has a wedge like shape,

(152) K ± knock out pin. .

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(155) illustrates one type of split wedge mould in. closed position.

(156) illustrates the semi-automatic type of construction with the mould mounted on the platens of the press,

(157) shows the two sections of the cavity split, the projections on the piece part released from cavity, and the piece part ready for removal from the mould. As the mould is closed, the spring loaded pins ± heads of which are in T-slots in the wedges ± pull the wedges up the wear plates on the angle shown and the two halves of the cavity close. By proper timing of the knock out system which controls the action of the pins, the cavity is closed before the plunger enters the cavity. In the type of mould shown in

(158) per forms are generally used and are placed on the top of the plunger. After the piece part has been molded, the plunger is withdrawn and the pins are activated to push the wedges down the wear plates, opening the two halves of the cavity. The wedges are held along the wear plates by T-slots and keys. Landing buttons or bars are provided for the wedges to make certain that there is no gap between the two halves of the cavity at the parting line when the mould is closed. This type of mould, some times called a basket mould, is mounted on the press as shown because of the ease of removal of molded pieces and ease of cleaning the mould. Moulds of this type can be of single as well as multiple cavity variety :. .

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(161) . : : 1. Compression and transfer moulding is used for ------materials. 2. ------ are used for articles having undercuts. 3. ------plates are used on the headed block or split to resist wear and can be removed. 4. ------, ------ & ------are three main factors that affect the compression moulding process. 5. Temperatures for moulding thermosetting material vary from ------ to ------VF. 6. ------ Or ------are generally used raw materials for compression moulding. 7. The overall area of the component top view is known as ------. 8. The time taken to get the thermoset material permanently asset is known as ------. 9. As the thickness of the moulding increases the area time of the process------. 10. ------ are given in the mould to escape out the air from the cavity on the moulding. 11. Generally the width and depth of the vents are ------ & ------ respectively. 12 as the projected area increases the pressure ------.. 13. 0hat is positive type compression mould? 14. 0hat is semi positive type compression mould? 15. 0hat is the difference between semi positive vertical flash type and horizontal flash type mould? 16. 0hat is the use of knockout plate in compression moulding.. . .

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(168) . - Explain the functional feature of compression mould & transfer mould. - Explain the application & limitation of compression mould & transfer mould. - Select the mould & moulding process for a particular given component. . % . .

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(172) Transfer moulds are of the semi automatic type and are made in single and multiple cavities, There are two basic types of transfer mould according to construction; ~ (( ~

(173) ( ( : The pot transfer is used in the conventional compression moulding press.

(174) illustrate the pot type transfer mould and the functioning of this type of mould.

(175) Shows the mould in the position in which the pre-form is loaded into the pot or loading chamber. The pre-form is shown in place. The arrow to the right indicates the movement of the mould in the press. The material is heated by the hot mould and combined with the pressure 0f the pot plunger, the material becomes fluid and is forced into the sprue, runners, gates, and into the cavity to form the piece part. This is illustrated in

(176) Pressure is kept on the material until the piece parts are cured. Excess material forms a cull at the bottom of the pot and also forms a dovetail shape in the plunger called the cull pickup. After the parts have been cured, the mould opens as shown in

(177) . As the plunger comes out

(178) of the pot, the sprue is broken at the small diameter of the taper. The cull pickup on the plunger carries the cull out of the pot and the spure out of the spure bushing. As the press continues to open the down ward movement of the plunger plate is halted, while the rest of the mould below the parting line continues to move. The mould is constructed as that the molded pieces remain in the cavities. Continuous movement of the press activates the knockout bar and the molded parts are ejected from the cavities. The mould in the completely open position is shown in

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(182) To protect the edges of plunger, a soft headed mallet is used to drive off the cull pickup and cull from the plunger. The piece parts are removed from the mould and the runner are scrap and cannot be re-used. The piece parts are set aside for further finishing if necessary. All excess material is removed from the cavities pot and plunger. The mould is closed until the parting line is mated and the mould is again in loading position. (See

(183) .) The pot is then loaded and sequence is repeated.

(184) illustrates another version of the pot transfer type of mould. In this design, the material flows directly from the sprue into the cavity; no runner or gates are used. If the material is forced directly into the cavity as shown in

(185) the small diameter of the sprue should be constructed as shown in

(186) . A break point is furnished so the sprue does not pull material from the surface of the piece part. The operation of the mould follows the same sequence as described for the previous transfer mould. Another variation has two sprues feeding the material into a single cavity.. .

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(190) ~ The plunger type of transfer mould in the closed position with the pre-forms in the target area and the plunger on its down ward stroke. The combination of the heat of the mould and the pressure of the plunger on the pre-forms causes the material to become fluid and to flow through the runners and gates into the cavities. The plunger transfer differs from the pot transfer in that the plunger is part of the molding press and not a part of the mould itself. By the use of this plunger, the sprue is eliminated and very thin cull of small are is formed above the target are, thus reducing the loss of material. The top clamp plate is fastened to the stationary platen of the press. The arrow at the right indicates the movement of the mould base at the parting line. This type of mould is loaded in one of two ways. ~. The pre-heated pre-forms are placed or stacked in the target are. As the mould is closed, the pre-forms are lifted into the transfer sleeve. After the mould is completely closed, the plunger is activated for its downward stroke.. .

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(193) ~ The mould is closed, and the pre-forms are loaded into the closed mould through the opening at the top of the transfer sleeve. The plunger is then activated, forcing the material throughout the mould.. ~ Fig. Illustrated two other methods used in feeding the material into the runners in a plunger type transfer mould. The view at the left shows the construction when the round type of runner is used. In order to maintain a constant volume flowing into the runner system, the runners are machined at an angle in the runner plate. See sections A-A and B-B. On the right is shown the construction used for trapezoidal runner. See section C-C Distance X should be two or three times the width of the runner. The type of loading depends on the height and size of the press used. ~ It is recommended that a clamping pressure 700 to 800 Kg per square Cm be used to keep the mould together at the parting line. Pressure on the transfer plunger is generally about 550 kg per cm². All transfer moulds must be vented to allow air to escape from the cavities. . .

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(198) ~ Both the pot and plunger are made from a good grade of wear resistant tool steel which is heat treated and ground. Pots and plungers are made square, rectangular or round in shape. The shape is determined by the shape of the piece part, number of cavities, and available space in the mould base. Round pots and plungers are preferred because less machining difficulties are encountered. A clearance of 0.025 to 0.075 mm per side is provided between the pot and plunger. ~ The area of the pot should be 20% to 30% greater than the area of all the cavities and runners. The dimensions of the pot, if it is round or square, can be calculated once the area is known. ~ To determine the volume of the pot, the total volume of all the piece part, the runner and the sprue, plus a small amount for a 0.375 to 0.75 mm thick cull, is approximately calculated. At least twice this volume is to be used for the pot volume. Knowing the area and the volume, one can easily arrive at the depth of the pot by dividing the volume by the area. The additional volume in the pot is provided to compensate for the bulk factor of the pre-forms used and to allow the plunger to enter the pot a short distance before exerting pressure on the material. High bulk factor materials are generally not used in transfer moulding. The bulk factor of the pre-forms used in transfer molding is approximately 1 to 2.Figs. illustrate some of the construction details of the pot and plunger. ~ For sufficient strength, horizontal distance ³Y´ should be equal to the depth of the pot ³Y´, - A1.5 to 3mm radius is provided at the top edge of the pot. A1.5 mm radius is machined at the bottom of the pot to facilitate the flow of the material and to simplify the machining of the corner. A 2.5 to 3mm radius is machined at the bottom of the plunger. The difference in the radii on the plunger and the bottom of the pot results in a clearance so that the plunger will not wedge in the pot but will land on the flat surface of the pot. In assembly there is a small clearance between the plunger and the transfer pot. ~ In practice it was very difficult to maintain the clearance for long time. Fitting the plunger to the cold pot size ± the plunger staying relatively cold during operation but the pot having to heated ± the clearance widened between them allowing material outflow. ~ Adjusting the plunger to the chamber when expanded by heat prevented its entrance in the cold state was difficult. So it frequently occurred that the plunger was forced into the pot strongly on clamping the mould and there was seizing the cracking and other damage occurred. ~ This problem is solved by adjusting the plunger to the cold pot with running fit, but permitting material flow around the plunger so as to form ~ a collar when solidified according to the hot pot size, thus preventing material flow out, during molding. A sealing groove approximately 2.5 mm wide and 0.8 mm deep is cut into the perimeter or periphery of the plunger. ~ During the operation of the mould this groove fills with the molding material and acts as a natural sea, allowing very little material to escape past the bearing surface of the plunger. Flats or grooves are ground on the bearing surface of the plunger for venting purposes. A clearance of 0.75 mm per side is machined above the bearing surface of the plunger. This clearance keeps the bearing surface narrow to prevent galling, and allows flash and excess material to. .

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(201) escape. The sprue and the interior or the pot is polished so the material can flow easily. The sprue has a taper of 2 to 3 per side. The large diameter of the sprue varies in size from 9 to 12 mm with a 1.5 to 3 mm radius at the entrance of the sprue. The small diameter (at the runner or piece part) varies from 3 to 6 mm depending on the size of the piece part. 0edge-shaped slots called cull pickup are machined in to the plunger. The thick or heavy section of the cull pickup is located directly above the sprue as shown in fig. The length of the cull pickup varies from the width is generally 2 to 3 times the diameter of the sprue..

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(203) ~ The clamping pressure provide by the chamber is an important consideration, ~ If the total cavity area is greater than the total pot area , the hydraulic pressure exerted by the plastic compound would tend to open the mould at the parting line. ~ So insure perfect mould locking, the area (Ap) should be 25% to 30% greater than the combined area of the molding surface and the area of all runners and sprues. ( If it is round or square can be calculated, once the area is known. (( Ap = total projected area of cavities, runners and sprues + 25% to 30% of total projected area.. .

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(206) ( = total volumes of all the piece parts, runners and sprues + Approximate volume of a small amount of .5 to 1mm Thick cull multiplied by bulk factor of the compound.

(207) ( ( = Vp/Ap. . .

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(210) . : : 1. 0hat is the use of transfer mould? 2. How many types of transfer moulds are there? 3. 0hat do you mean by cull and what is its purpose? 4. 0hat is plunger transfer moulding? 5. 0hat is the use of transfer sleeve in plunger transfer mould? 6. The area of the pot should be ------greater than the area of component and runner. 7. How the volume of the pot can be calculated. 8. 0hat is bulk factor? 9. 0hy a clearance is provided in the bearing surface of the plunger. 10. ------to ------taper angle given in the sprue. 11. Depth of the pot is calculated by ------. 12. 0hat is champing pressure? . . .

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(215) After end of the lesson/session trainees should be able to - know the injection mould - know the injection moulding process - know the injection moulding machines - know the injection mould parts materials Flow chart for designing injection mould - Different. steps for designing injection mould. - Know the calculations point of view - Know the different parts of moulding machine - Explain the mechanism & functional feature of moulding machine. - Specify the moulding machine according to production requirement. - Explain the safety precautions to be taken during operation Æ. . & . .

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(222) ~ Injection moulding is one of the most versatile processing methods by means for manufacturing small clips to large industrial crates. Technological advancement was taken place over the last two decades. Sophisticated Micro processed Control of injection moulding; Structural From Molding,

(223) , Gas Assisted injection Moulding etc., are gaining more and more popularity in developing countries. Precision moulds are essential to meet the stringent quality requirements of the end product. 0ith this point in view the necessary in put data required for the mould manufacture in the area of design and fabrication of moulds has been provided in this chapter. ~ It is not for being true to say that there are probably as many design for injection mould as there are different plastics products, each product to be molded has its own peculiar problems which most be considered when designing the moulds. ~ From a practical point of view, a classification of injection moulds should be based on the main design features and manner of operation. ~ The type of gating and means of de-gating ~ The type of ejection ~ The presents or absence of external & internal under-cuts on the products ~ The manner in which the product is released form the moulds (( ( ~ Standard moulds (two or three plate moulds) ~ Split cavity moulds ~ Stripper plate moulds ~ Stack moulds ~ Hot runner moulds ~ Insulation runner mould (

(224) ~ The process of injection moulding essentially consists of plasticize the raw material in a cylinder by the application of heat and then injecting it under pressure through a nozzle by means of a ram into a closed mould, where it is allowed to cool, and then opening the mould and removing the moulded component. ~ There are two methods employed to inject the plastic material into the mould:

(225) and ( which transports the materials during which time it is plasticized and then it is injected. ~ Shows a simple injection mould in the closed position after a shot has been made shot is a term used to describe the total amount of material that has been injected into the mould in one cycle, including piece parts, runners, gates, and sprues.The material is placed in a hopper, in the form of a granules or pallet; the. .

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(228) hopper is located at the end of and electrically heated cylinder. To distribute the heat evenly throughout the material ~ The spreader causes the material to flow against the wall of the heating cylinder. The material heated in this cylinder softens and the plunger forces the molten material (when has the consistency of thick syrup) through a nozzle into a sprue and fills any opening in the closed mould. The material cools in the relatively cold mould and hardens to a solid state. ~ The injection plunger is retracted, the mould is opened at the parting line, and the piece parts are ejected from the mould. As the mould opens, the sprue puller pulls the sprue out of the bushing. The sprue is separated from the molten material at the small diameter at the nozzle as shown in Fig. ~ The piece parts, runners, gates, and sprue are ejected from the mould as a unit. The place piece parts are then removed from the sprue and runners at the narrow gates. 0ith the mould in the open position and the injection plunger retracted, material is fed into the heating cylinder, the mould closed and the sequence repeated. Illustrate the simple gravity type of feeder arrangement. Other more practical and efficient methods of feeding material into the heating cylinder include volumetric, weighs type, and pre-plasticizers. ( (

(229) (( SL.NO PARTS NAME MATL. HRC 1 2. Top plate Cavity plate. 3. Core plate. 4 5. Core back plate Spacer or Riser block Ejector plate Ejector back plate Cavity back plate Core Cavity Locating ring Sprue bush Pillar Bush Spure puller Ejector pin Pushback pin Or Return pin Rest button. 6 7 8 9 10 11 12 13 14 15 16 17 18. REMARKS. MS MS, Tool steel (P20, EN8-31-24) MS, Tool steel (P20, EN8-31-24) Ms/ EN8 Ms/ EN8 Ms/ EN8 Ms/ EN8 Ms/ EN8 P20,H11,H13,EN24 P20,H11,H13,EN24 Ms P20,OHNS,H11,H13 EN36,31,24 EN36,31,24 Carbon steel, D2 Carbon steel, D2 Carbon steel, D2. 50-52 50-52 45-50 48-50 48-50 48-50 48-50 48-50. STD STD STD. Carbonsteel,D2,En31 48-50. . .

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(258) ~ STUDY OF PLASTIC COMPONENT ~ STUDY OF MOULDING M/C TO BE USED ~ METHOD OF CONSTRUCTION OF MOULD ~ DETERMINATION OF NO. OF CAVITY ~ SELECTION OF PARTING SURFACE ~ TYPES OF LAYOUT OF CAVITYS ~ SELECTION OF RUNNER ~ SELECTION OF GATE ~ SELECATION OF TYPE OF MOULD ~ COLLING SYSTEM ~ TYPES OF EJECTER GRID ~ EJECTION SYSTEM ~ MOULD VENTING . .

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