Injection Molding products China manufacturer

Polymer Processing: Historical Survey
The beginning of plastics prcessing and extrusion prcessing is associated with the introduction of guta-percha into England during the 1840s and its commercial development as insulation for electrical wire. One of the eary pioneers of the new industry was Thomas Hancock’s younger brother, Charles Hancock, one of the founders of the Guta Perch a Cmpany. In his patents of 1846 ~1847, Chares Hancock described fabrication of guta-pfcha using a processing technology similar to that developed in the rubber industry largely by his brother. He used a “pickle” -type masticator for compounding guta-percha with additives incuding sulur and softeners. He also sheeted with rollers and vulanized the products wtih sulfur.
The first foamed plastics and rubber products were developed in 1846 in separate patents by the Hnacock brothers. Chares Hancock (English Patent No. 11032) foamed guta-percha using ammonium carbonate and similar compounds. Wilam Brockedon and Thomas Hancock (English patent No. 11455) produced foamed products using sulur chloride dissolved in a rubber or guta-percha solution.
The first ram extrusion devices were described in the patents of 1845 by Richard. A Broom  an (English Patent No. 10582) and Henry Bewley (English Patent No. 10825), which dis  cussed the manufacture of guta-percha thread, tubes and hose. Brooman’ s patent uses a five  hole die that produces five simulaneous continuous filaments which are extruded into a bath and taken up on a rll Bewley’s patent extruded tubes and hose. Chares Hancock, who was a part  ner of Bewley in the Guta Percha Company, is said to have developed insulation coating for wire using Bewley’s extrusion methods. Methods of coating wires are described in patents by Barow and Forster (Englsh Patent No. 12136) and by Siemens (English Patent No. 13062) in 1848′ 1850. The first great successes of guta-percha were its application to electrical insula  tion of the Dover-Calasi and trans-Atantic cables.
The development of continuous extrusion of plastics using screw extruders began with guta-percha and natural rubber and dates from the 1870s. The concept of screw pumping seems to be atributable to Archimedes. The earier use of screw pumps in the soap industry is described in the patent literature. The frst patent for screw extrusion is that of Mathew Gray of London in 1879 ( English Patent No.5056). Interestingly, the reason for the invention as cited by Gray is the existence of defects in coatings placed on wires. The extruder was fed from a two-roll mill or calendering device. There seems to have been independent developments of the screw extruder in Germany and the USA about the same time, but Gray’s patent is the first clear statement.

The  next stage in the development of cellulose nitrate as a plastics. The first moves in this direction during the 1860s by Alexander Parkes and Daniels Spill in England met with only limited success. Cellulose nitrate could not be melted and they used a range of volatile solvents that evaporated from their products. There left high levels of residual stresses which caused shrinking and cracking. Parkes and Spill had rubber-processing backgrounds and apparently used rubber-processing machinery. In the USA, John Wesley Hyat and his brother Isaiah Smith Hyat found that compounds or solutions of celulose nitrate in nonvolatile camphor produced more desirable products. This was caled Celuloid. The Celuloid Manufacturing Company was formed in the 1870s in Newark, New Jersey, to exploit this product and proved to be a great success. The Hyats and their associates developed many important industrial process  ing operations to exploit Celuloid.
An 1872 patent by the Hyat brothers (US Patent No. 133229) contains both the reinvention of the ram extruder and the first ram injection molding machine. They caled this a stufing machine. John Wesley Hyat later described the use of complex muliple-cavity molds to be used in conjunction with the stufing machine. This would either mold objects or coat cores of objects in the mold.
In an 1878 patent, John Wesley Hyat (US Patent No. 204228) described the extrusion of Celuloid from the stufing machine over a mandrel coated with a lubricant. This mandrel could be programmable and expand to produce complex holow shapes. This led to the development of blow molding in 1881 by the Hyate’ coleague, Wiliam B Carpenter (US Patent No. 237168). Here, a preformed extruded tube is placed in a mold and is then expanded to fil the moldby pumping a heated fuid into the tube. These inventions were largely employed to produce a range of products incuding components of dolls and liners for pipes.
The 1880s saw the development of the synthetic fiber industry. Brooman’ s 1845 patent for the formation of guta-percha thread sets out clear procedures for producing fibers from the melt. The synthetic fibers sold commercialy in this period were produced from cellulose nitrate which could not be melted. A method of producing fibers by extruding acetic acid so  lutions of celulose nitrate into a water or alcohol coagulation bath was described by Joseph Wilson Swan (English Patent No. 5978) in 1883. Swan’s patent described the later carboni  zation of the fibers with heat and thus represents the beginning of the carbon-fiber industry. Swan’s application was filaments for incandescent lights. Shorty thereafter in France, the Count de Chardonnet (US Patent No. 394559) described a prcess for forming fibers from either alcohol solutions into a water coagulation bath. De Chardonnet produced much finer fibers than Swan, he formed a company and commercialized them as an artificial silk. Later, de Chardonnet (US Patent NO. 531158) described a dry spinning prcess in which the filaments were extruded into the air where the solvent was evaporated. Also, during the 1890s, using the system of and colaborating with Cross, Bevan and Beadle, Stearn invented a reactive spinning method in whch celulose is dissolved in a mixture of sodium hydrxide and carbon disulfide to form cellulose xanthate, which is extruded into an acd coagulating bath that regenerates the cellulose. This material became known a rayon.
The first truly synthetic plastics, phenol formaldehyde resins, were developed commercialy by Leo Hendrik Baekeland, a Blgian immigrant to the USA, just before 1910. These were poured as low or intermediate molecular weight liquids into molds where they were polymerized into three dimensional networks. Bakelte prducts were compression molded.

Hot Runner Systems
Hot runners are cassifed according to the ways they are heated: insulated-runner sys tems ( It is not described in this artice) and genuine hot-runner systems.
The later can be further sub-cassified according to the types of heating: internal heating and external heating.
Heating is basicaly perormed electricaly by cartridge heaters, heating rods, band heaters, heating pipes and coils， etc. To ensure uniform fow and distribution of the melt, usualy a relatively eaborate control system comprising several heating circuits and an appropriate number of sensors is needed. The operating voltage is usualy 220 V to 240 V, but smal nozzles fequently have a low volage of 5 V, and also 15 V and 24 V operating voltage.
Runner systems in conventional molds have the same temperature leve as the rest of the mold because they are in the same mold block. If, however, the runner system is located in a special manifold that is heated to the temperature of the melt, al the advantages listed below accrue. Runner manifolds heated to mel temperature have the task of distributing the mel as far as the gates without damage. They are used for al injection molded thermoplastics as wel as for crosslnking plastics, such as elastomers and thermosets.
In the case of thermoplastics, these manifolds are usualy refered to as the hot-runner system, the hot manifold, or simply as hot runners. For crosslinking plastics, they are known as cold runners.

A. Hot-Runner Systems
Hot-runner systems have more or less become established for highly-automated production of molded plastic parts that are produced in large numbers. The decision to use them is almost always based on economics, i. e. production size. Quality considerations, which played a major role in the past, are very rare now because thermoplastics employed to  day are almost al so stable that they can be processed without dificulty with hot-runner sys tems that have been adapted accordingly.
Hot-runner systems are available as standard units and it is hardly worthwhile having them made. The relevant suppliers ofer not only proven parts but also complete systems tailored to specifc needs. The choice of individual parts is large.
B. Economi Advantages and Disadvantages of Hot-Runner Systems
1 Economic Advantages
Savings in materials and costs for regrind.
Shorter cycles; coolng time no longer determined by the slowly solidifying runners; no nozzle retraction required.
Machines can be smaler because the shot volume - around the runners一is reduced, and the camping forces are smaler because the runners do not generate reactive forces since the blocks and the manifold block are cosed.

2. Economic Disadvantages
Much more complicated and considerably more expensive.
More work involved in running the mold for the first time.
More susceptible to breakdowns, higher maintenance costs (leakage, failure of heating elements, and wear caused by filed materials) .
3. Technological Advantages
Process can be automated (demolding) because runners do not need to be demolded. Gates at the best position; thanks to uniform, precisely controled coolng of the gate system, long flow paths are possible.
Pressure losses minimized， since the diameter of the runners is not restricted.
Artificial balancing of the gate system; balancing can be perormed during running production by means of temperature control or special mechanical system (e. g. adjustment of the gap in a ring-shaped die or use of plates in fow channel Natural balancing is beter). Selective infuencing of mold filing; needle valve nozzles and selective actuation of them pave the way for new technology (cascade gate system: avoidance of fow lines, in-mold dec- oration) .
Shorter opening strke needed compared with competing, conventional threeplaten molds. Longer holding pressure, which leads to less shrinkage.
4. Technological Disadvantages
Risk of thermal damage to sensitive materials because of long fow paths and dwel times, especialy on long cyces.
Elaborate temperature control required because non-uniform temperature control would cause diferent melt temperatures and thus non-uniform filling.
C. Design of a Hot-Runner System and is Components
Hot-runner molds are ambitious systems in a technological sense that involve high tech  nical and fnancial outay for meeting their main function of conveying melt to the gate with  out damage to the material Such a design is demonstrated.
D. Externaly /Internaly Heated Systems
The major advantages and disadvantages of the two types are immediatey apparent from reaserches.
E. Externaly Heated System
1 Advantage
Large fow channels cause low fow rate and uniform temperature distribution.
2. Disadvantage
The temperatures required for external heating have to be very much higher. For PA 66， for example， the mold temperature is approximately 100°C and the manifold temperature is at least 270 °C ; this means there is a temperature diference of approximately 170°C from the mold block, which means:
Special measures required for fxing the hot - runner nozzles to the gates because of the considerable thermal expansions.

The mold is at the core of a plastic manufacturing process because its cavity gives a part its shape. This makes the mold at least as critical-and many cases more so-for the quality of the end product as, for example, the plasticating unit or other components of the processing equipment.

Molds used in injection molding consist of two halves; one stationary and one mova ble. The stationary half is fastened directy to the stationary plate and is in direct contact with the nozzle of the injection unit during operation. The movable half of the mold is secured to the movable platen and usualy contains the ejector mechanism. There are many possible mold designs, incuding multiple piece molds for complicated parts. On production injection molding equipment many artices may be shot at the same time by the use of multiple cavity mol ds. The use of a balanced runner system caries the plastic from the sprue to each individual cavity. At this point the material passes through a gate into the cavity. The gate is a restriction, smaler than the runner,to provide for even filing of the mold cavity and to alow the products to be easily removed fom the runner system. With most injection molding systems, the artices can be snapped away from the runner or sprue without additional trim mingo Products that have been injection molded can usualy be identified by finding where the gate was broken of. The gate wil usualy be located at the edge or parting line of an object or in the center of cylindrical product.

Molds are expensive, as are the machines. Yet, once the product has been designed, molds made, and production started, artices can be produced in quantity at low cost. Virtualy al thermoplastics can be injection molded through variations in mold and ma chine design.
Mold (and die) parts that are mass-produced and standardized in shape and dimension are referred to as “standards” (or, “standard parts”). Specialized operators of miling ma  chines, lathes, electronic discharge machining (EDM) equipment and grinders produce mold components, independenty of each other, folowing detailed mold part drawings. Finaly, al these items come together with the standard mold base and hardware and are assembled by the mold maker. Today, standard components for the moldmaking industry are marketed by a number of companies.

Glory plastics company limited in China dedicated in producing high quality plastic molds and injection molded plastic parts from China to customers around the world.

Happly New Year of 2009 to all ~!

Molds used in injection molding consist of two halves; one stationary and one movable. The stationary half is fasterned directly to the stationary plate and is in direct contract with the nozzle of the injection unit during operation. The movable half of the mold is secured to the movable platen and usually containers the ejector mechanism. There are many possible mold designs, including multiple piece molds for complicated parts. On production injection molding equipment many articles may be shot at the same time by the use of multiple cavity molds.

The introduction of molds.

The mold is at the core a plastic manufacturing process because its cavity gives a part its shape. This makes the mold at least as critical-and many cases more so-for the quality of the end product as,  for example, the plasticating unit or other components of the processing equipment.

1. The hopper

Thermoplastic material is supplied to molders in the form of samll pellets. The hopper on the injection molding machine holds these pellets. The pellets are gravity-fed from the hopper throat into the barrel and screw assembly.

2. The barrel

The barrel of the injection molding machine supports the reciprocating plasticizing screw. It is heated by the electric heater bands.

3. The reciprocating screw

The recipprocating screw is used to compress, melt, and convey the material. The reciprocating screw consists of three zones: the feeding zone; the compressing zone; the melting zone.

While the outside diameter of the screw remains contrast, the depth of the flights on the reciprocating screw decreases from the feed zone to the begainning of the meleting zone. These flights compress the material against the inside diameter of the barrel, which creates viscous heat. This shear heat is mainly responsible for meleting the material. The heat bands outside the barrel help maintain the material in the molten state. Typically, a molding machine can be have three or more heater bands or zones with different temperature settings.

For thermoplastics, the injection molding machine converts granular or pelleted raw plastic into final molded parts via a melt, injection, pack, and cool cycle. Atypical injection molding machine consists of the following major components:

 A. The Injection System

The injection system consists of a hopper, a reciprocating screw and barrel assembly, and an injection nozzle. This system confines and transports the plastic as it progresses through the feeding, compressing, degassing, melting, injection, and packing stage.

Injection Molding Machines and Selection Resin

Injection molding machines are manufactured in many sizes. There are rated according to size by the amount of material which can be injection in one cycle, ranging from a fration of an ounce in the samll laboratory models to many pounds in large production equipement. Laboratory models are used in the rearch and development of new polymers and  molding techniques.

There are two basic unit of an injection molding machine; one for injecting the heated plastic and other for opening and closing the plastic mold. The first unit includes a feed hopper, heated injection cylinder, and an injection plunger or screw system. The second unit comprises a hydraulic operated moving platen and a stationary platen on which the halves of the mold are mounted. Injection molding machineare also available in vertical models.

There are many variations in injection molding machine design, however, the basic machines are of either the screw-ram, of plunger type. The main differences between these types is the method in which the plastic material is delivered from the hopper to the nozzle of the machine. Machine of the reciprocating-screw type are used more because of faster cycles, lower melting temperaturers, and better mixing of the material.

The injection molding machine has a variety of instrumentation used for the clamping unit, mold, and injection mollding machine shows the most important possibilities of the instrumentation. In fact, there is no known direct method for in-line checking of the condition of the mold.

It’s time to discuss some plastic terminology.  I am not an organic chemist of plastics engineer.  I’m gathering this information from other sources and I may not be explaining it as accurately as I need to.  Be warned. 

Polyolefin – is a polymer produced from a simple olefin, or alkene as a monomer.  For example, polyethylene is a polyolefin produced by “polymerizing” the olefin “ethylene”.  Another common polyolefin is polypropylene.  I consider polyolefin a general term for a family of plastics.  (http://en.wikipedia.org/wiki/polyolefin)

Polyethylene – is a semi-crystalline plastic with excellent chemical resistance, good fatigue, and wear resistance.  They can have a wide range of properties which are determined by the length and degree of branching of their polymer chain.  In general, polyethylenes have good resistance to organic solvents, high impact strength, are light weight, resistant to staining, and have a low moisture absorption rate.  They are easy to distinguish from other plastics because they float in water.              (http://en.wikipedia.org/wiki/polyethylene)

HDPE (High Density Polyethylene) – HDPE is the most common polyethylene used in industry.  It offers excellent impact resistance and high tensile strength.  Technically speaking, it has a low degree of branching and thus a stronger intermolecular forces.  HDPE is non-toxic and meets FDA and USDA certifications for food processing.  It is commonly used for the manufacturing of milk jugs, margarine tubs, detergent containers and trash cans.  It is also an excellent material for use in trench drain and storm sewer pipe. 

Polypropylene  is an economical material that offers a combination of outstanding physical, chemical, mechanical, thermal and electrical properties not found in any other thermoplastic.  It has a lower impact strength that does HDPE, but it also has better tensile strength and superior heat resistance. 

Structural Foam – is a structure imparted to an olefin during processing that gives the plastic addition strength and resilience.  More on this later. 

PVC (Polyvinyl Chloride) – Is a widely used thermoplastic polymer.  Over 50% of the PVC products manufactured are used in construction as a building material.  PVC offers excellent corrosion and weather resistance and has a high strength-to-weight ratio.  PVC is inexpensive, easy to clean, and a popular replacement for wood and concrete building materials.  It is used in house sidings, drainage pipe, window profiles and plumbing fixtures (such as some trench drain).  Despite appearing to be an ideal building material, concerns have been raised about the costs of PVC to the natural environment and human health.    (http://en.wikipedia.org/wiki/polyvinyl_chloride)

Fiberglass Reinforced Polyester – Polyester is a category of condensation polymers which contain the ester functional group in their main chain.  This group also includes polycarbonates.  Polyesters are popular for being used as a woven fabric.  When fiberglass is added to polyester, the resultant material is more durable and resistant to impact. 

UV Inhibitors – These are chemical additives that are added to plastic which help to retard the damaging effects of ultraviolet light to the plastic.

Injection Molding – This is a forming method by which intricate trench drain products (or other plastic shapes) can be shaped.  In this process, a heated and liquid thermoplastic is injected into a plastic mold that contains a cavity that has the shape which is desired.  Once injected with plastic, the mold and part is cooled.  The resulting plastic shape is removed from the mold and trimmed of flashing (excess plastic).  This method is needed to form pre-sloped trench channels.  Though mold costs are expensive, one mold is required for each size of pre-sloped channel.

Extrusion – Another method of making trench channel is extrusion.  In this process, a heated batch of thermoplastic is continuously injected through a water-cooled die.  The shape of the die will determine the cross-section of the extruded part.  This method can be used to make simple, non-complex parts such as pipe, tubes and u-shaped channels.  The most inexpensive channel drain products are made using this forming method