Compression moulding plate

The investigations were done on isotactic polypropylene (iPP), grade HD 120 MO from Borealis. Both injection and compression moulded plates were used. The melt tempjerature in injection moulding was 245 °C, the mould temperature was 40 °C. The mould has a film gate with a width of the half of plates thickness. 

Ultra-thin sections approximately 35 nm thick were cut from compression-moulded plates with a diamond knife (35° cut angle, DIATOME, Switzerland) at —140 °C on a cryo-microtome and used for transmission electron microscopy (TEM) analysis. The slices were collected on a copper grid with a carbon-hole-foil. The specimens were investigated on a Zeiss Libra 200MC (Zeiss, field emission cathode, point resolution 0.2 nm) with an accelerating voltage of 200 kV. 

Example 4.10 A circular plate with a diameter of 0.3 m is to be compression moulded from phenol formaldehyde. If the preform is cylindrical with a diameter of 50 mm and a depth of 36 mm estimate the platen force needed to produce the plate in 10 seconds. The viscosity of the phenol may be taken as 10 Ns/m. ... 

The injection-compression process is an important variation in which rubber is injected into a partly closed mould under low pressure used for moulding-on of rubber soles to footwear uppers. Rubber is injected into a gap between the shoe upper and the sole plate, which is held 3-4 mm wider than it would be in its final position. After injection at the first mould station of a multistation machine the sole plate is closed in the manner of compression moulding at the second mould station and rubber is pressed along the sole and over the toe cap. The importance of the process is that it becomes possible to mould without using normal high injection pressures which tear and distort canvas, leather or synthetic uppers. 

Towflex (Hexcel Composites) is based on carbon, glass or aramid fibres impregnated with polypropylene, polyamide, PPS, polyetherimide, PEEK. Product forms include flexible Towpreg, woven fabric, braided sleeving, UD tape, chopped compression moulding compound, moulded plates, thermoformable laminates. 

In rubber testing, the surface finish of metals is of importance, for example on mould surfaces and compression set plates. There are a number of standards in the ISO Geometric Product Specification series but the most relevant is ISO 428729 which covers terms, definitions and surface texture parameters relating to the profile method of measuring surface finish. There are apparently over 1000 different parameters to characterize surface finish30 but only a few are generally encountered. The most commonly found is Ra (previously called CLA) which is the mean deviation of the surface profile above and below the center line, followed by Rz, a measure of the peak to valley height. For example, the arithmetic mean deviation (Ra) of the compression plates for compression set tests must be better than 0.2 m. 

Composites containing 0-50 vol% glass were prepared by milling at 170°C for 15 min on an open two-roll mill and compression moulding at 190°C into 3 mm thick plates. The cooling rate was approximately 40°C/min. The samples were stored at room temperature for several years before the measurements. 

In the Paudal mixer-granulators24), the moistened compound is transferred, compressed and forced through a moulding plate. 

The testing geometry is shown in Fig. 2. Specimens were prepared from compression-moulded rectangular plates of 170 x 200 mm, which were sawn into 80 x 25 mm samples, about 10 mm thick. 

The rods were first cut and kiln dried at 80°C for 90h in the case of polyamide 6.6, and 16h in the case of polyoxymethylene. Then, they were accurately laid down, side by side, in a rectangular mould cavity (170x200mm). Rods of polyamide 6.6 were compression moulded at 290°C for 20min, rods of polyoxymethylene at 200°C for 15min. Plates of different thicknesses, in the range 5-12mm, were prepared for the present study. 

A rolled sheet of each specimen was made from granulate. This rolled sheet was then compression moulded to form a plate. The surface resistance of the pressed plate was measured with a ring electrode (DIN 53 482). The measured values represent the resistance... 

According to Bragg s law the positions of WAXS reflexes refer to the distance between crystalline planes within the crystallites. In the compression moulded as well as in the injection moulded plates a couple of crystalline reflexes could be identified. The reflexes with the highest intensity within the relevant angular region are summarised in table 1. 

Polyimide materials can be used as unfilled base polymers or have graphite, PTFE and molybdenum disulphide added to further enhance the low frictional properties and can be used to replace metal and ceramic parts. Material is available as moulded stock shapes, e.g. rod, rings and plate, which can be machined to the final dimensionally accurate product. Some grades can be processed by compression moulding while other grades can be processed to produce a finished product by direct forming. 

In a laboratory kneading chamber polycarbonate (PC) of medium viscosity (e.g. Makrolon 2600, Bayer) is mixed with different amounts of highly structured carbon black (CB, e.g. Printex XE2 (Evonik), up to 10 wt% in steps of 1-2 wt%) at ca. 280°C with a suitable defined mixing rate tiU a homogeneous mixture is obtained (typically 5-15 min). The melt will be taken out of the mixing unit, cooled down, and flat plates of the composites are prepared by compression moulding at ca. 280°C between two planar steel plates by means of a heatable hydraulic press. To hinder sticking of the composite at the metal plates, the plates may be covered with a release film and a frame can be used as distance holder to control the sample thickness. 

Heated steel molds, preferably hard chrome plated, are used, which may be of multicavity design. Tooling costs are higher than for compression moulding since appropriate gates and runners must be included in the mould. 

Ticona has co-operated with SGL Carbon to produce a graphite-filled liquid crystal polymer, also for fuel cell plates. There are likely to be 200 bipolar plates for each cell, and two cells per vehicle. The filled polymer is meant to be injection moulded, but this requires much higher throughputs than compression moulding to be economic. 

Several other carbon products are now becoming established in the plastics industry. Weidmann Plastics Technology is manufacturing the bipolar plates for fuel cells by injection-compression moulding of thermoplastics filled with over 80% of graphite. A single fuel cell requires about a thousand bipolar plates. 

Fig. 2.32 The FM21 SP Electrolyser. (a) The overall construction, (b) A single electrode, which has a nominal projected area of 0.21 on each face. The photograph shows the electrolyte ports and the current feeder busbar. A symmetrical lantern blade electrode is shown complete with its compression-moulded gasket, (c) An assembled, multi-electrode reactor, showing the electrolyte manifolds and the end plate. The electrolyser unit is capable of taking up to 60 electrode pairs, which would provide a projected cathode or anode area of up to 25 m. A double-pack version utilizes a central plate extending, the capacity to a maximum of 120 electrodes (50 m ). The construction of FM21 electrolysers for chloralkali production is considered in Chapter 3. (Photographs supplied by ICI Chemicals and Polymers Ltd.)...

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