P84 moulding powder for high-performance parts

Hot compression moulding is the sintering of the material at temperatures above the glass transition temperature under a pressure of 35 MPa (5,000 psi). Moulding temperature is 350 °C (662 °F). The necessary equipment is a press which is able to maintain 100 metric tons over a 15 hour cycle, and a top and bottom heated mould with heater-band.

Example: the production of a 20 cm (8 in) diameter 5 cm (2 in) high billet.

A suitable release agent is recommended. Before filling the mould, the powder must be dried to eliminate the equilibrium moisture. Drying can be done at 100 °C (219 °F) over 2 hours for a 1.8 kg (4 lb.) loading. At the filling step, the mould should be preheated to 250 °C (480 °F) and the powder should be transferred directly out of the oven into the mould. The first compression up to 17 MPa (2,500 psi) should remove the air from the loading. After this step the heating starts with a ramp up to 300 °C (572 °F). At this temperature the first dwell time with 1 hour is necessary. Then the full pressure of 35 MPa (5,000 psi) is applied and the ramp up to 340 °C (647 °F) starts.

Moulding cycle hot compression moulding of TECAPOWDER P84

Reaching this temperature, a dwell time of 4 hours is needed to get uniform heat penetration. At the end of this program a slow cooling ramp starts to reduce temperature within 4 hours down to 250 °C (480 °F) under the full pressure. After reaching this temperature the part should be released.

Fillers/Reinforcement materials:

Graphite

Ensinger tested most available graphite types to choose the best material for TECAPOWDER P84. The following properties are significant for use:

• For a homogeneously machined surface fine particle size is needed.
• For high wear resistance, a good incorporation of the graphite in the matrix is needed, the surface morphology is important.
• For improving the mechanical properties, the particle size of filler should be roughly the same as of matrix-resin, the matrix material must be coating the filler-surface after blending.
• For blending: the function of blending time and filler-coating is very important. Premixes are necessary.

PTFE

To get a uniform matrix and best friction and wear properties the use of very fine PTFE particles is necessary. Also, the melting point of the additive material should be at the same level as the matrix materials Tg.

MoS₂

The lubrication of MoS₂ is based on surface-smoothing through material transfer. In this respect it is very important to have very fine particles as a filler and the right percentage in composition. For being able to process MoS₂ at approximately 345 °C (650 °F) Ensinger offers a special grade of TECAPOWDER P84.

This process is used to make smaller stock shapes of TECAPOWDER P84 resins. The diameters are limited by the handling possibilities of the moulds. Common mould sizes have outside diameters of 20-25 cm (8-10 in). The moulds have to be able to maintain pressures up to 69 MPa (10.000 psi) at 400 °C (752 °F). This indicates the use of high wall thicknesses and hot working steels to be used for the tools. Sintering can be done in a simple air circulation furnace which can maintain temperatures up to 400 °C (572 °F).

The following steps will describe how to mould and sinter during this process.

1. The predried powder over several hours is filled into the mould and compacted for 5 minutes for degassing.
2. The closed mould is placed in a preheated oven (350 °C (662 °F)) and kept for several hours, depending on the size. After each full hour it has to be taken out and compacted again with 35 MPa (5000 psi) for 5 minutes. Then placed again in the oven.
3. When the calculated end of the dwell time is reached, the mould is placed in the press, loaded with 55 MPa (8000 psi) and cooled to 250 °C (480 °F). At this temperature the part can be released.

The calculation for the sintering time (dwell time) should be approximately 1.5 hours/2.5 cm (1 in) wall thickness.

This method for moulding finished parts is possible if metal-moulding equipment is available. Changes in mould and feeder are necessary. The mould needs heater cartridges (see drawing) to be able to maintain temperatures up to 250 °C (480 °F). The feeder needs to be heated by oil or electrical heating to maintain temperatures above 200 °C (400 °F). Moulding pressure is approximately 345 MPa (50,000 psi). Dwell times have to be calculated to 30 g/s. The addition of 0,5 to 1 % PTFE (lubricant type) as a release agent is necessary. Ensinger is offering finished blends ready for moulding. Sintering must be done in an oven with nitrogen or inert-gas flow following the temperature curve shown underneath. The sintering causes dimension changes on the moulded parts. In the mould direction they are approximately +10 %, in the cross-mould direction -5 %. The obtained density is approximately 95 % of the hot compression moulded shapes. The mechanical properties obtained are 80% of compression molded values.
Blended formulations containing graphite, graphite/PTFE, glass/PTFE and molybdenum disulfide are available.

Sinter cycle for direct moulded parts

Hot compression moulded or ram extruded P84 can easily be machined to narrow tolerances by using standard metal working equipment. It is recommended to use carbide tooling if a long tool life is particularly important. High-speed steel can also be used for short runs on multiple-point tools.

When machining TECAPOWDER P84 the following rules should be adhered to:

• Use the maximum positive rake angle possible and sharp cutting edges.
• Avoid high cutting pressures and subsequent overheating.
• Use low feed rates.
• Plastics have a higher thermal expansion than metals. Allow the workpiece to cool before finishing.
• Avoid deflection caused by the clamping pressure. It is recommended to use O.D. or 1.D. collets. If a chuck is to be used, provide for soft jaws. A higher number of jaws helps distributing the holding force. Reduce the clamping pressure.
• Cool the workpiece with air, water or coolant.

The cutting depth has no influence on the surface quality. In order to achieve very close tolerances, it is recommended to rough turn the part and allow it to cool before finish turning. In case of threading, the depth of feed should be lower than 0,0127 cm (0,005 inch) to prevent the threads from chipping. To avoid chattering deflection of long workpieces with small diameters, it is recommended to support them by means of moving collar.

Turning

P84 parts machine easily using standard turning equipment. It is recommended to use carbide-tipped tools. For rough and finish turning operations use a cutting geometry similar to that used for aluminum, for turning on a numerically controlled lathe. The nose radius of the cutting tip should be between 0,1 and 0,2 mm (0,004 and 0,008 in) to guarantee a good surface finish. It is important the cutting tip be level to the center of the piece to be turned. Sharp cutting edges allow high cutting speeds use low feed rates. 

Lathe tool

Milling

TECAPOWDER P84 parts can be machined with all standard HSS or carbide-tipped milling equipment. Multiple-point milling cutters are preferably used. To avoid edge chipping, we recommend the milling be performed from the outside of the block towards the center and use small exit angles. Cutting speed should be between 6,35 and 10 cm/min (2,5 and 4 in/min) and feed rates lower than 0,7-0,15 mm (0,03-0,006 in). The lower the feed rate, the better the surface finish. Lubricating or cooling is not required.

Conventional milling

Drilling

SS drills (point angle 90 °C) or carbide drills (point angle 90-120 °C) can be used to drill holes into P84 parts. If the drill diameter is more than 2 cm (0.8 in), reduce the web thickness. Work at drilling speeds of 2,3-2,8 m/s (450-550 ft/min) and feed rates lower than (0.004 in). To avoid local heating in the workpiece, provide for good chip removal.

Parting

TECAPOWDER P84 materials can be cut with circular or band saws. If you use hard metal tipped blades, tool life will be longer. Saw speed for circular saws should be 2-3 m (80-120 in), for band saws 0,3-0,4 m (12-16 in). If plates are to be cut with circular saws, adjust the blade height in such a way that the blade breakthrough is within 2-3 mm (0,08-0,12 in) to the surface to avoid edge chipping.

Grinding

P84 parts can be ground to close tolerances with surface grinders used for metal working. Round bars and tubes are ground on centerless grinders. Use double-coated tape to fix the material to the table and cool with water. Table surface speed should be about 0,3 m/s (60 ft/min) for rough grinding and 0,18 m/s (35 ft/min) for finish grinding.

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