Reject chutes for injection molding machines

In the simplest case, fail-safe switches are pneumatically operated. Here, the switching times start at 1.5 seconds. This is sufficient if, for example, only start-up parts and rejects are to be ejected.

Fail-safe diverters used to separate sprues and good parts must switch faster in order to prevent cycle time extensions as far as possible. Depending on the design, switching times of less than 0.7 seconds are possible here – or even less than 0.3 seconds when servo motors are used.

However, it is important to note that the switch alone is not responsible for the cycle time. The quality of the mould and the repeat accuracy of the demoulding are of central importance. It must be ensured that, in the event of delayed ejection of the parts and sprues, the first fraction ejected has already left the diverter flap before the diverter can switch.

Yes. The rotary shaft switch patented by MTF Technik is particularly suitable for working with small parts and flat or pointed components. The special feature of the rotary shaft switches is that there is no relative movement between the switch body and the switch flap; instead, the flap and side guide are a single element in the form of a rotary shaft. This means that there are no gaps in which parts can become jammed.

Abrasion is also prevented here, as the rotary shaft is mounted on ball bearings in an outer body. The diverters are therefore ideal for use in clean room conditions.

Alternatively, conventional flap diverters can be used, in which the switch flap is either made entirely of plastic or a plastic seal is inserted on the side. This also reduces gaps, but there is relative movement between the diverter body and the flap, which leads to abrasion.

Yes. MTF Technik designs and engineers the fail-safe valves individually for each machine and specific application. For the mechanical design, it is first necessary to obtain the essential dimensions of the injection moulding machine. Ideally, 3D data for the machine or the machine frame below the mould halves is available. If such drawings are not available, measurements must be taken on site. The corresponding enquiry form can help here.

In addition, the electrical interface must be clarified. Which signals can be transmitted or processed by the injection moulding machine? Which plugs or connections are available? This is also discussed and planned on an individual basis.

The aim is to ensure that the failover switches planned in this way can be integrated into the customer's system as easily as possible. Ideally, they should only need to be screwed into the machine frame and plugged in.

Yes and no. MTF Technik has already implemented fail-safe switches for many different machine types and applications. If these already implemented types are referred to as "standard", then the answer would be "yes".

However, the reality is often that the machines or the operating conditions are very individual, and so it is rare that the same type of diverter is used. If, for example, the height of containers or peripheral devices located under a diverter outlet changes, the diverter hopper or outlet chutes often have to be redesigned.

Depending on the space available at the customer's site, it may be necessary to install diverters either parallel or perpendicular to the machine axis. Depending on the desired function, the diverters are designed with different drives, seals, cable lengths, plug types, etc. This results in a correspondingly large number of variants for even the same machine type.

Yes. There are special types of switches for this purpose. If sprues are to be ejected separately from the good parts, the production machine or tool must be equipped with a means of ejecting the two fractions at different times. Once the first fraction has been ejected from the mould, fallen down and slipped over the diverter flap, the signal to switch over must be sent to the diverter. This must come from the production machine.

The diverter then switches. In most cases, a query sensor signals that the switching process is complete and the second fraction can now be ejected from the mould. Once this second ejection process has been completed, including the sliding of the parts into the diverter, the diverter must switch back to its starting position.

The drive unit to be used for the switch depends on the customer's specifications. If the cycle time is not important, the simplest type of drive – a pneumatic changeover cylinder – can be used. If the shortest possible changeover times are of paramount importance, a servo drive should be used. The switching times are between a maximum of 1.5 seconds and a minimum of approx. 0.3 seconds.

The mechanical design of the switch body is then determined based on the specifications.

Fail-safe valves are usually mounted under the tools of plastic injection moulding or die-casting machines. The production parts that fall freely downwards fall into the valve body and are directed into a channel according to the set flap position.

They are used to divide the material flow into several channels. This allows, for example, rejects and start-up parts to be separated from good parts and sprues. Alternatively, different containers can be filled one after the other.

Yes. The entire switch design is made of stainless steel as standard. If required, the drop-out switches can be equipped with special drives, bearings, etc. to reduce abrasion even further.

No. The diverter valves can also be mounted on a separate frame or at the outlet of a conveyor belt, for example. They are then used in general to divide a material flow into different outlet channels.