Grivory® HTV - 4X1 BK 9205

Grivory HTV-4X1 Black 9205 is delivered dry and ready for processing in sealed, air tight packaging. Predrying is not necessary.

Storage

Sealed, undamaged bags can be kept over a long period of time in storage facilities which are dry, protected from the influence of weather and where the bags can be protected from damage.

Drying

During its manufacturing process Grivory HTV-4X1 Black 9205 is dried and packed with a moisture content of £ 0.10 %. Should the packaging become damaged or the material is left open too long, then the material must be dried. A too high moisture content can be shown by a foaming melt and silver streaks on the moulded part

Drying time

If there is only little evidence of foaming of the melt or just slight silver streaks on the part, then the above mentioned minimal drying time will be sufficient. Material, which is stored open over days, which shows strong foaming, unusually easy flowing, streaks and rough surface on the moulding part, then the maximal drying time is required.

Warning : Silver streaks can also be caused by overheating of the material (over 350°C) or by too long melt residence time in the barrel

Drying temperature

Polyamides are subjected to the affects of oxidation at temperatures above 80°C in the presence of oxygen. Visible yellowing of the material is an indication of oxidation. Hence temperatures above 80°C for desiccant dryers and temperatures above 100°C for vacuum ovens should be avoided. In order to detect oxidation it is advised to keep a small amount of granulate (light colour only !) as a comparison sample.
At longer residence times (over 1 hour) hopper heating or a hopper dryer (80°C) is useful.

Use of regrind

Grivory HTV-4X1 Black 9205 is a thermoplastic material. Hence, incomplete mouldings as well as sprues and runners can be reprocessed. The following points should be observed:

• Moisture absorption
• Grinding: Dust particles and particle size distribution
• Contamination through foreign material, dust, oil, etc.
• Quantity addition to original material
• Colour variation
• Reduction of mechanical properties

When adding regrind, special care has to be taken by the moulder.

Grivory HTV-4X1 Black 9205 can be processed economically and problem-free on all machines suitable for polyamides.

Screw

Wear protected, universal screws (3 zones) with non-return valves are recommended

Shot volume

The metering stroke must be longer than the length of the back flow valve (without decompression distance)

Selecting the injection unit : Shot volume = 0.6 - 0.9 x (max. shot volume)

Heating

At least three separately controllable heating zones, able of reaching cylinder temperatures up to 350°C. A separate nozzle heating is necessary. The cylinder flange temperature must be controllable (cooling).

Nozzle

Open nozzles are simple, allow an easy melt flow and are long lasting. There is however the danger that during retraction of the screws following injection of the melt, air maybe drawn into the barrel (decompression). For this reason, needle shut-off nozzles are often used.

Clamping force

As a rule of thumb the clamping force can be estimated using the following formula:
Clamping force : 7.5 kN (in cavity pressure of 750 bar) x projected area (cm2)

The design of the mould tool should follow the general rules for glass fibre reinforced thermoplastics. For the mould cavities common mould tool steel quality (e.g. hardened steel) which has been hardened to level of 56 - 65 HRC is necessary. We recommend additional wear protection in areas of high flow rates in the tool (e.g. pin point gates, hot runner nozzles)

Demoulding / Draft angle

Parts moulded from Grivory HT-PPA solidify very quickly showing excellent dimensional stability. Asymmetric demoulding and undercuts are to be avoided. It is favourable to foresee high numbers of large ejector pins or a stripper plate. Demoulding draft angles between 1 to 5° are acceptable. Following values can be considered:

Gate and runner

To achieve an optimal mould-fill and to avoid sink marks, a central gate at the thickest section of the moulding is recommended. Pin point gate (direct) or tunnel gates are more economical and more common with technical moulding. To avoid premature solidification of the melt and difficult mould filing, the following points should be considered:

Gate diameter : 0.8 x thickest wall section of the injection moulding part
Runner diameter : 1.4 x thickest wall section of the injection moulding part (but minimum 4 mm)

In order to prevent burning marks and improve weldline strength, proper venting of the mould cavity should be provided (venting channels on the parting surface dimensions: Depth 0.02 mm, width 2 - 5 mm).

Mould filling, post pressure and dosing

The best surface finish and a high weld line strength is achieved with a high injection speed and when a sufficiently long post pressure is employed. The injection speed should be regulated so as to reduce towards the end of the filling cycle in order to avoid burning. For dosing at low screw revolutions and pressure the cooling time should be fully utilised.

Basic machine settings

The required tool surface temperature depends on the geometry and the wall-thickness of the part. As a rough roule can be said, the thinner the wall-tickness, the higher the tool surface temperature. Tool surface temperatures up to 190°C are usual for small wall-thickness.

Start up and purging

Foreign materials in the cylinder should be removed with suitable purging materials. Hot-runner systems should be purged likewise. Glass fibre reinforced polyamide 66 is a suitable “bridging material”.
Cylinder heating should start with a clean, productfree screw, starting from the temperature level of the “bridging material” of 300°C up to the required temperature level of 340°C (see processing data). After at least three full dosings (free-shot) the start up procedure can be implemented. After completion of production with Grivory HT-PPA the screw, cylinder and melt distribution system should be cleaned out thoroughly

Conditioning

The dimensions and the mechanical properties of Grivory HT-PPA products are only marginally influenced by moisture absorption. For testing purposes, parts can be stored in a climatic chamber until an increase in weight of 1 % has been achieved. In order to avoid stress through swelling conditioning in hot water is to be avoided.