Plastic Powder Research Articles

Irreversible deformation of a sintered porous body of a work-hardening plastic metal II. Experimental part

1. An analysis is made of various methods of calculating compressibility curves for porous bodies sintered from plastic metal powders. It is shown that the best approximation to experimental results is given by the method based on the use of rms viscous stresses and strains and on allowance for strain strengthening and macrodefectiveness of structure. 2. Taking into account the nonuniformity of strain due to density variations in compacts enables calculated results to be brought closer to experimental data obtained at low pressures.

正誤表

正誤表

Mixing and homogenizing of granular bulk material in a pneumatic mixer unit

Especially with the plastics that are produced on a large scale in these days, it is important to have constant product qualities such as the melt index, the color values and the number of additives during long production periods. In order to compensate for any fluctuations of those product qualities which can be caused during production, the manufacturers use high capacity mixers of a capacity of 1000 m 3 max. on an increased scale. The fluidized bed mixer units which are often used for plastic powders with particle size of less than 500 (μm) are uneconomical as concerns the mixing of plastic granules because of the high velocity of more than 0.5 m/s necessary for loosening the material. With the new circulation mixer unit, the bulk material is extracted from a silo with a conical bottom into different circular zones and circulated pneumatically by means of a central rising pipe. The mixer works without moving parts and can be operated by a single-stage radial fan because of the low working pressure of about 20 – 120 mbar. An air volume of about 300 m 3 in standard is necessary for the mixing of 1 t of plastic granules. The air flow depends on the necessary mixing time. After the description of the mixer, the experiences already found with the industrial application are published and details concerning the mixing qualities obtained are given.

A method for measuring the thermal conductivity of isotropically compressed powders

This paper proposes a method for measuring the thermal conductivity of compressible powders, in particular of powders which do not permit a calculation of sphere models. The apparatus, which is briefly duscussed, is designed to compress powders hydrostatically up to 600 bars while measuring the thermal conductivity with a hot wire lance. With this range of compression it is possible to determine the thermal conductivity for almost every plastic powder, non-compressed powders as well as quasi-solid materials. Experimental results are given for polytetrafluorethylene (PTFE) and polyethylene (PE) powders. The effect of crystallization on thermodynamic properties of polyethylene under high pressure is discussed.

A Sensitive Detector, System for the Continuous Monitoring of Tritium in the Air

A new design of a flow cell type of scintillation detector system suitable for continuous monitoring of tritium in the ambient air has been developed. The detector records 2500 counts per second with a single photomultiplier tvhbe type EMI 9514S for 1 MPC level of tritium activity release at 50 coutnts per second background and 2.5% coutnting efficiency. Possibility of designing detectors with an efficiency, comparable to that of liquid scintillators, has been discussed. The cell, filled with plastic scintillator powder, does not show any background build up over long periods of operation and has a low gamma response. The performance of the detector has been studied in detail and a complete tritiutm monitoring set up has been described.

Applying ultrasonics to the moulding of plastic powders

Both thermosetting and thermoplastic powders have been experimentally moulded into small cylinders by the application of high-intensity 20 kHz ultrasonic energy and pressure without the use of external heat. Thermoplastic powders have also been fused and extruded through a small orifice by the use of ultrasonic energy and pressure alone.

Plastic powders as metal coatings

Many of you may already be familiar with the term ‘powder coating’. For those of you who are not, I would like to describe the term briefly. Powder coating is a relatively new process by which dry plastic powders are applied to a clean metal surface. After application, the coated object is heated, fusing the powder to form a smooth, tough coating. Available today are many plastic powders offering a wide range of properties and colours. These powders are fully formulated and are free‐flowing ready for application to metal. Previous coatings for such items have been applied from solution. The dry plastic powders are normally higher molecular weight polymers than those used in solution: because of this, the coatings produced have greatly increased durability, toughness and abrasion resistance.

Fusion of Plastic Powders with Macrosonics

Both thermosetting and thermoplastic powders were molded into 12-in. diam cylinders by the application of macrosonics plus a nominal constant pressure without the use of external heat. A series of factorically designed experiments were run using ultrasonic intensity, pressure, and time as the variables. The measured length of the fused cylinder of plastic formed in each experiment was used to evaluate the response. All the variables were found to be relatively important to the fusion process. However, only the interaction of time and pressure was found to be important. This interaction had a negative slope coefficient.

Structuromechanical properties of plastic powder mixtures containing a carboxymethylcellulose plasticizer

1. A study was made of the structuromechanical properties of plastic powder mixtures containing a 30% aqueous solution of CMC. It was established that structuromechanical constants sharply fall with a rise in plasticizer content, from their maximum values at the minimum amount of CMC (lower limiting content) to values corresponding to the constants of the plasticizer (upper limiting content). 2. Structure formation in a plastic powder mixture is the result of adhesion forces acting between the powder particles and the plasticizer and of molecular attraction forces (van der Waals-London forces) acting between the powder particles through a layer of the plasticizer in regions with excess surface energy. 3. Storage alters the structuromechanical properties of a powder mixture containing a 30% aqueous solution of CMC, the most marked increase being shown by the viscosity of the mixture. Remixing restores almost completely the initial properties of the mixture (indicating that the latter exhibits thixotropy).

Structuromechanical properties of plastic powder mixtures

1. It is shown that, with rise in the plasticizer content of the mixture and on passing from a dendritic to a spherical powder particle shape, the elasticity and plasticity of the mixture decrease, while its true relaxation period increases. 2. As the plasticizer content of the mixture is raised from the lower to the upper limiting value, the shape of the curves of the principal rheological characteristics vs specific surface area is reversed. 3. The structuromechanical type of the plastic powder mixture undergoes very little change when powders of different metals are used. 4. It is shown that, in the presence of metal powder, starch paste in the mixture does not decompose on prolonged storage (120 h) and its coagulation structure is reinforced. A treatment consisting of rewetting and remixing restores the original structuromechanical properties of the mixture after storage. This is evidence that the mixture possesses thixotropic properties, which play an important part in production.

Structuromechanical properties of plastic powder mixtures. Part I

1. A study was made of the structuromechanical properties of plastic powder mixtures containing 20% starch paste. It is demonstrated that the powder particles are joined to the plasticizer by adsorption bonds, while bonding between the particles themselves is effected by the van der Waals-London forces through plasticizer layers in areas with a disturbed structure, which possess free surface energy. 2. The effects of the amount of plasticizer and the specific surface area, particle shape, and material of the powder on the structuromechanical properties of plastic powder mixtures have been examined.

Analysis and Design of Plastic Storage Tanks

The author has designed over one hundred major tanks that store plastic powders and pellets. This article gives some practical examples of how to analyze and design plastic storage tanks. Examples were taken from files of completed projects. All tanks are classified as either shallow or deep; an example of each is given. A series of four articles was written to report on a study about vessels made of aluminum or steel, and joined by bolting or welding. The first three articles are “Bolted Aluminum—Alloy Connections,” “Welded Tanks for Dry Bulk Plastic Storage,” and “Bolted Tanks for Storage of Plastics.” The state-of-the-art is presented. Although computer programs have been developed, some equations still used are empirical, and the assumptions are conservative. Not all authorities agree on the proper method of analysis. A research study of the whole tank, rather than its parts, should be made.

Analytic method of calculating the work done in compacting plastic powders

Analytic method of calculating the work done in compacting plastic powders

On the apparent reduction of pressure during vibration compaction of plastic powders

On the apparent reduction of pressure during vibration compaction of plastic powders

Pore Structure of Plastic Powder Compacts

The pore structure of hot-pressed polystyrene and polyvinyl chloride powder compacts prepared at 40-100°Cand 1-8t/cm2 was studied by means of mercury porosimeter. Most polystyrene compacts have two peaks in the open pore size distribution curve, one at 0.01μ and the other at 1-5μ inradius. It has been found that the first peak corresponds to the pore on the surface of starting powder particle and the second to interparticle voids. The latter has been found to shift to smaller radius with increasing compacting pressure and/or temperature. The effects of compacting conditions on open and total pore volumes were studied. And it has been shown that the compacting pressure at which the open pore volume remains unchanged with further increase of pressure decreases as compacting temperature is raised.The increase in the open pore volume was observed on heating the polyvinyl chloride powder compacts prepared at room temperature. This might be explained by irreversible displacement of particles due to the expansion or stretching of particles and other factors. Different features both in the pore structure and its dependence on compacting conditons were observed between the poly-styrene and polyvinyl chloride powder compacts. This would be ascribed to the differences in their softening characteristics and powder parameters.On the basis of the experimental results and discussion, the mechanism of pore volume variation has been presented, and it is suggested that the deformation caused by softening and compression of powder particles is one of the most important factors to be considered in plastic powder compact.

Electrostatic Powder Coatings

SummaryThis paper describes two new electrostatic processes, used for dry painting, plastic coating, talcing, aluminium coating, applying rust inhibitors, applying electrical insulation and vitreous enamelling of sheet steel and castings. These applications are discussed, a wide range of plastic powders being commercially available for use with the processes. In terms of physical chemistry, the main advantages of dry powder spraying are that unfavourable chemical reactions between the liquid vehicle and the solids, or between the liquid and the metal surfaces, can no longer occur, and that the permeability of the final film can be considerably lower, since there are no solvents to boil off during the stoving operation. These factors have recently led to the formulation of interesting materials—particularly some unique epoxide resins. For ideal combination of good anti-corrosion properties, mechanical strength and low cost plastic coatings, there is an optimum thickness of coating. With epoxy coatings, for example, thicknesses of 0.002 to 0.004 in are required. Coatings of this order may be applied automatically by electrostatic powder coating. The process is flexible and coatings of from 0.0005 to 0.04 in can be obtained. For the application of special chemicals, light dustings having a few particlcs/cm2 can be applied.

The duration of photo- and radioluminescence of organic compounds: S.F. Kilin, Optics & Spectrosc., 12 (6), June 1962, 414–416

The duration of the photo- and radioluminescence of plastic scintillators, organic crystals, and powders is measured by a phase method. Measurement of the depth of modulation of the luminescent light output shows that there is a slow component in the quenching of radioluminescence in organic powder luminors. This slow component can produce as much as a third of the total light output. (auth)

Flame Sprayed Plastic Coatings

The history of flame spraying is briefly reviewed. Both guns and powder containers used for applying flame sprayed coatings of plastic powders are described in some detail. Necessary criteria for organic materials both thermoplastic and thermosetting are indicated. Problems involved in producing suitable powders of tough non-friable resins are discussed and indications given of several promising solutions, Properties of flame sprayed Thiokol (a polysulphide synthetic rubber) coatings are reviewed in some detail. Recent work on improvements in flame spraying technique are illustrated by a discussion of the advances in the flame spraying of various polyethylene compounds. This includes comments on current theory, various fuel gas combinations and polyethylene compounding for obtaining specific properties in flame sprayed coatings. Some data is presented on the effect of after-treatments of flame sprayed plastic coatings. Experimental work being done on producing flame sprayed coatings of fluorinated hydro-c...

Short Cuts to the Analysis of Plastics by Infrared Spectroscopy

One of the many applications of infrared spectroscopy of today is the rapid identification of plastics which eliminates time consuming organic analysis and is in many cases more reliable. As for any kind of spectrographic analysis most of the labor is involved in the preparation of the sample. So far three general methods are used: 1. The preparation of mulls which are suspensions of solid plastic powders in a high boiling paraffin oil. This suspension is then spread between rock salt plates and examined as such. The disadvantage of this method is the interference of the oil spectrum with the spectrum of the sample. The preparation of the mulls which includes the grinding of the resin is also time consuming. 2. Thin films of the plastic may be obtained by rolling the material to appropriate thicknesses and then cutting it so that it fits the rock salt window holder instead of the window itself. The disadvantages here are that special equipment is required for the rolling operation and that this operation is limited by size, form and nature of the sample received. 3. The solution technique consists in spreading solutions of the purified resin on mercury glass plates or preferably on rock salt windows. By evaporation of the solvent a solid film of the material is obtained. This method was found to be most suitable and several short cuts could be made so that qualitative analyses of a sample could be accomplished within 1 hour as compared to 1 - 2 days required by the conventional technique. These short cuts consist essentially in the fact that the whole plastic can be examined as compounded without fractionating it.