Introduction
One of the most common methods of converting plastics from the raw material form

to an article of use is the process of Plastic Injection Mold. This process is most typically used for

thermoplastic materials which may be successively melted, reshaped and cooled.

Injection moulded components are a feature of almost every functional manufactured

article in the modern world, from automotive products through to food packaging. This

versatile process allows us to produce high quality, simple or complex components on

a fully automated basis at high speed with materials that have changed the face of

manufacturing technology over the last 50 years or so.
Historical Background
To understand the engineering and operation of modern day injection moulding

machines, it is useful to first look at the not too distant origins of the process.

The first Automotive Injection Mold machines were based around pressure

die casting technology used for metals processing, with patents registered in the USA

in the 1870's specifically for celluloid processing. Further major industrial

developments did not occur until the 1920's when a series of hand operated

machines were produced in Germany to process thermoplastic materials. A simple lever

arrangement was used to clamp a two piece mould together. Molten plastic was then

injected into the mould to produce the moulded component. Being an inherently low

pressure process, it was limited in use. Pneumatic cylinders were added to the

machine design to close the mould, although little improvement was made. Hydraulic

systems were first applied to injection moulding machinery in the late 1930's as

a wider range of materials became available, although the machine design was still

largely related to die casting technology.
Large-scale development of Plastic Mold Packaging design towards

the machines we know today did not occur until the 1950's in Germany. Earlier

machines were based on a simple plunger arrangement to force the material into the

mould, although these machines soon became inadequate as materials became more

advanced and processing requirements became more complex. The main problem with a

straightforward plunger arrangement was that no melt mixing or homogenisation could

be readily imparted to the thermoplastic material. This was exacerbated by the poor

heat transfer properties of a polymeric material. One of the most important

developments in machine design to overcome this problem, which still applies to

modern processing equipment today, was the introduction to the injection barrel of a

plunging helical screw arrangement. The machine subsequently became known as a

'Reciprocating Screw' injection moulding machine.
The Injection Moulding Cycle
The modern day process has developed and matured significantly to the level where

fully automated, closed loop, microprocessor controlled machines are the

'norm', although in principle injection moulding is still a relatively simple

process. Thermoplastic injection moulding requires the transfer of the polymeric

material in powder or granule form from a feed hopper to a heated barrel. In the

barrel, the thermoplastic is melted and then injected into a mould with some form of

plunger arrangement. The mould is clamped shut under pressure within a platen

arrangement and is held at a temperature well below the thermoplastic melt point. The

molten thermoplastic solidifies quickly within the mould, allowing ejection of the

component after a pre determined period of cooling time. The basic

Plastic Injection

Molding process steps with a reciprocating screw machine are as follows.
Mould Close and Clamping
The mould is closed within the platen arrangement and clamped using necessary

force to hold the mould shut during the plastic injection cycle, thus preventing

plastic leakage over the face of the mould. Present day moulding machines range from

around 15 to 4,000 metric tonnes available clamping force (150 to 4000 kN).
Many systems are available for opening/closing and clamping of mould tools,

although usually they are of two general types. Direct Hydraulic Lock is a system

where the moving machine platen is driven by a hydraulic piston arrangement which

also generates the required force to keep the mould shut during the

Clean Room Injection Molding operation. Alternatively, smaller

auxiliary pistons may be used to carry out the main movement of the platen and a

mechanical blocking arrangement is used to transfer locking pressure from a pressure

intensifier at the rear of the machine, which moves only by a few millimetres,

through to the platen and tool.
The second type of general clamping arrangement is referred to as the Toggle

Lock. In this case a mechanical toggle device, which is connected to the rear of the

moving platen, is actuated by a relatively small hydraulic cylinder, this provides

platen movement and also clamping force when the toggle joint is finally locked over

rather like a knuckle arrangement.
Injection
At this stage in the machine cycle the helical form injection screw (Figure 1) is

in a 'screwed back' position with a charge of molten thermoplastic material

in front of the screw tip roughly equivalent to or slightly larger than that amount

of molten material required to fill the mould cavity.

LSR Injection Molding

screws are generally designed with length to diameter ratios in the region of

15:1 to 20:1, and compression ratios from rear to front of around 2 : 1 to 4 : 1 in

order to allow for the gradual densification of the thermoplastic material as it

melts. A check valve is fitted to the front of the screw such as to let material pass

through in front of the screw tip on metering (material dosing), but not allow

material to flow back over the screw flights on injection. The screw is contained

within a barrel which has a hardened abrasion resistant inner surface.
Deep-well plates are used in a wide variety of applications including compound

storage, fraction collection, sample mixing and preparation. Choosing the correct



Deep Well Plate for your application can mean the difference between

indifferent and great results.
The easy-to-use guide provides selection advice on the use of 24-, 48-, 96- and

384-well deep-well plates that offer individual good volumes from 10ml to 50-

microlitres. The flow charts also enable you to select the optimum deep-well plate

not only by the number of wells but also by well shape, plate height, plate color,

rimmed/unrimmed or the need for sterility.