Moulds that work, part 7: The outsert technique

Editor's note: This issue's featured mould is a 12-cavityhot runner mould for microhousings in polyphthalamide (PPA). Mould design,mould construction, and production were carried out by Reiter Präzisions-Spritzgussund Formenbau GmbH in Hilpoltstein, Germany. The hot runner system is fromGünther Heisskanaltechnik GmbH.


A metal strip has 12 microhousings per cycle injected onto it by theoutsert technique using an externally heated, all hot runner mould, withsix open double nozzles, on a vertical injection moulding machine. Thehot runner block, which has not undergone rheological balancing, ensuresgentle treatment of the sensitive polyphthalamide, with a calculated residencetime of only 30 seconds.

Specific requirements of the microhousings are economic production andminimal thermal damage to the polyphthalamide (PPA) through a short residencetime in the manifold system. These may seem to be conflicting requirementsto some extent, but they are both fulfilled through the use of a hot runnermould with double nozzles that provide direct gating to the moulded parts.Günther Heisskanaltechnik, Frankenberg, Germany, manufactures thedouble nozzle.

The thermoplastic injection moulding compound to be processed is a semicrystallinepolyphthalamide with 33 percent glass fiber (PPA-GF33) which is injectedonto a punched mesh strip (1) in tin-plated bronze (outsert technique).The strip is mechanically unwound from the roll and positioned over theindex pins (9) in the mould. The moulding compound is then injected aroundit, and once demoulding has been completed, an external stepping motormoves the strip a distance equivalent to 12 times the interval betweenthe cavities. Following this, the strip, which has had the moulding compoundinjected around it, is wound up again, together with the finished microhousings,and sent for further processing.

The weight of the moulded part without the metal insert is approximately.28g; the wall thicknesses are between .15 and 2.7 mm, and the mouldedpart dimensions are approximately 8 mm wide by 11 mm deep by 6 mm high.

The Mould

The mould is a 12-cavity, all hot runner mould with external heatingfor both the hot runner block (2) (230V) and the six open hot runner nozzles(24V), all of which are equipped with control systems.

The gate diameter is .75 mm. The neck on the moulded part into whichthe melt is injected has a diameter of .8 mm. The inside dimension of thecavities is 12 mm, which means that a total of 12 moulded parts can beproduced at the same time with six double nozzles, which have a center-to-centerspacing of 24 mm (see Figure 5).

The six double nozzles, which are positioned directly against the hot runnerblock in a heated and pretensioned state, are all accommodated in a jointhousing (4) that is 160 mm by 40 mm by 43 mm in size. Air pockets ensurethat the loss through heat conduction is kept to a minimum. The heatingcapacity for each of the nozzles is 200W, with two at 650W for the hotrunner block.

Given the low moulded part weight of .28g (3.36g for 12 parts, withoutthe metal insert), it was decided to dispense with rheological balancingof the hot runner block, and this did not result in any quality impairment.The calculated melt residence time in the hot runner system is approximately30 seconds. The nozzle and hot runner block temperatures are 340 C, andthe mould wall temperatures are between 80 and 160 C. The mould has fourseparate temperature circuits.

The process calls for an injection moulding machine with a vertical injectionand clamping unit. The melt is injected into the mould at a pressure ofapproximately 1,100 bars. The injection unit is not retracted after injection.Screw decompression is necessary in order to prevent any dripping fromthe open nozzles. The height of the residual sprue measures less than .3mm.

Contact Information:
Günther Heisskanaltechnik
Mr. Herbert Günther
Sachsenberger Str. 3
D-35066 Frankenberg
Germany
Tel: +49 (6451) 5008-0
Fax: +49 (6451) 5008-50