This news article was originally written in Spanish. It has been automatically translated for your convenience. Reasonable efforts have been made to provide an accurate translation, however, no automated translation is perfect nor is it intended to replace a human translator. The original article in Spanish can be viewed at Informe general sobre trituración en la industria de inyección de plásticos

General report on grinding in the industry of plastic injection

Agustín Durán Martín. Centrotécnica15/03/2004

The process of grinding of plastics in injection industry; It is to reduce the volume of lava flows (troughs) and surplus generated during the process of molding of the injected parts; as well as the Elimination of occasional defective parts.

For this can use different types of team, whose characteristic will come marked by the following conditionings:

Dimensions of the colada, excess or piece to triturar.
Type of material of the cual is composed.
Capacity of necessary production of the team (Kilos of material by hour)
necessary Size of the material triturado.
Destination of the material triturado.
The dimensions of the colada, excess or piece to triturar, will mark us the necessary dimensions of the camera of trituración of the team; that generally it coincides with the dimensions of the mouth of entrance of the material in the team of trituración.
The type of thermoplastic material to triturar will define us if the team has to incorporate a special treatment antidesgaste (camera of trituración); in the cases to treat of loaded materials (for example PA + FV) that they are highly abrasive.
To the hour to define the team, will have to consider the time production that expect of east; to calculate the size and power of the same.
The size wished of the material triturado, will come marked by the final destination of the same. The equipment can deliver a size or another; but this will affect to his time capacity.
The material triturado, can employ directly in machine, store, be transported to distance, etc. this will mark the accessories that complement to the triturador.

Reduction of volume

One of the main applications of crushing systems in the plastics industry, is the reduction in volume. Both cast, regardless of the size and shape with origin; leftovers as defective, After passing through a system of grinding become material of a uniform size that can easily be transported, stored or dosed. Sometimes this facilitates its elimination through a waste management company; being more profitable transport and/or store shredded material.

Recycling of materials

The vast majority of applications of grinding of plastics; It is aimed at the recycling of this material; will be adding it in a variable percentage to the Virgin material; or as the main material in other parts whose physical characteristics and appearance permit. This is achieved savings in the management of materials that can make the most, render in a short time the investment in such systems.

Different types of computers and applications.

Mills at high rpm

The type of equipment for crushing more widespread in the plastics industry, is the so-called mill at high rpm. It's the type of equipment more simple, economical and easy to use; especially for materials standard and capable of producing. On the other hand is which requires more maintenance, its cleaning is more difficult, increased energy consumption and generates more noise.

The mill at high speed has a mouth of entry; It usually has the same dimensions as the Chamber of grinding of the team; and that it will limit the maximum size of the piece to introduce. This mouth is situated in a hopper of fall of the House of crushing; length responds to security measures that prevent the access of the extremity of the operator to the Chamber of grinding; and avoid to the maximum projection of pieces of plastic to the outside, during grinding.

In the House of crushing we find a central rotor, which can be open or closed; and to incorporate 3 or more blades that revolve solidarity to the rotor; and in the extreme one or more blades fixed; graded so that the passage of the rotating blades, there is an effect of scissors, cutting the material. The rotor is moved by an electric motor, whose power is crucial to the type of piece to grind, shape, material and required hourly production. In these teams, the rotor rotates between 250 and 350 RPM

There is a grid or sieve, with curved shape under the rotor, and surrounding the passage of the rotating blades; and that it will mark the size of the crushed material. Increased size of the holes of the grid, increased size of the crushed and greater time production of the equipment.

Under the grid, there is usually a collection of the crushed box; that you can incorporate a mouth to install a pneumatic system of extraction of the material.

These teams may be small and compact, to work to foot machine, between 2 and 15 Hp of power; or much larger, to work in house party; due to the large generated noise and space required (50 to 100 Hp of power)

Crushers at low rpm

Technology of grinding at low revolutions, is born as a response to the need of the transformer of technical materials; that you reward the quality of the crushed, with the amount of the same. The concepts of inlet and feeding hopper is coincident, but unlike the mills at high revolutions; These crushers only revolve at 25 RPM

There are no blades rotating or fixed; neither nor grid. The rotor has a variable number of blades rough, which precortan into pieces the flows and introduced pieces and a series toothed rollers; that by way of Strawberry are literally biting the material; generating a shredded uniform, free from dust.

This technology uses a lot less power, as it uses a set of electric and reducing engine; that provides a high-torque low-speed. This minimizes energy consumption not only; but also noise and maintenance needs. To be targeted at technical materials usually come covered with anti-corrosion materials; being able to work with abrasive materials without problem. Therefore they tend to assume a greater cost to acquire them; but they will bring benefits in terms of energy consumption, ease of cleaning and minimum maintenance required. The crushers at low revolutions there are from really small models for microinjection; models for machine foot, silent and small size; with large capacity of crushing; and systems of large size for bulky parts, which by its quietness can always work in injection plant. However, no more teams, can produce large amount of Kg/hour.

Heartbreaking

The heartbreaking or rotary cutters, are teams that only allow the reduction in volume of large pieces in more or less large cuts; for a subsequent process of crushing or simply destroy the parts or reduce its size. They are teams, usually quite voluminous, where 2 or more axes, equipped with cutting blades, chop the pieces introduced. They are teams to work in room separate volume; Although the noise generated is not very high.

Combined systems

They are teams that incorporate two different technologies. It's a ripper, which precorta the pieces; and under this is a high speed mill; that generates a usable crushed in machine.

This allows to grind pieces of large volume in a relatively compact team, with a not very high power; getting a high hourly production. They are teams that are often placed in room separate because of its size; though to not be loud, they could work no problem on ground.

Accessories

The systems of trituración can incorporate different accessories that the manufacturer would deliver with the team; such like stravel transportadoras of feeding; extractor systems equipment equipment of the material triturado or others.

The stravel allow to feed of form dosificada the team; allowing to an operario attend to several equipment at the same time or realise other functions. The extractor systems equipment equipment of the triturado; they move the material of pneumatics form until a determinate point to fill a tank, silo, sack, etc. Another option are vacuums tyres, situated on machine; that by means of a valve proporcionadora; disifican the exact percentage of material triturado with the virgin.

Definition of a grinding system

Recovery at the foot of machine

When the work to realise is to recover the material of the coladas, cuts or surplus of each cycle of injection; can situate a small team of trituración beside the machine and, was an operario of manual form or a robot; they can go feeding the team; that to his time can supply directly the triturado to the machine of injection. With this avoid risks of pollution of the material, manipulation, transfers of containers, etc.

Centralized recovery

As his name indicates, treats of equipment, generally of big capacity; that in a determinate point of the plant receive the material to triturar of the different machines. With this system exists greater risk of pollution of materials, mixes and requires of a greater manipulation, space, personal, etc.

Combined systems

Many plants have systems centralized for grinding of large pieces; and equipment to foot machine to retrieve online directly the flows and cuts in each piece. In this way, the teams to foot machine only are sized to the size of the flows, are smaller and economic; and they work automatically.