Plastic Industry

Compounding of H.D.P.E. Resins
Injection molders commonly color polyoiefine by blending dry pigments with resin pellets. They also blend linear and high pressure polyethylene pellets to obtain materials intermidiate between the two in flexibility.

Masterbatches may be used in both molding and extrusion to add slip and antiblock to films resins, ultraviolet absorbers to film and monofilament resins, carbon black to pipe resins, to film and monofilament resins, butyl rubber or other elastomers to improve the impact strength of the resin, and glass fibers to improve the strength and heat resistance of mouldings.

Mixing
On-plant mixing of dry colour is usually done in a tumble blender, which may be merely a fiber drum mounted on an axle that may turn end for end or at an angle. Cement mixers are also used or blenders similar to those used at the resin manufacturers plant.

Pigment Dispersants
Dry colouring is faciliated by procating the polymer pellets with mineral oil or other viscous liquids which would stick the pigments to the pellets. This reduces busting, allows the use of higher pigment loadings, which would not segregate from the pellets during handling and shortens the needed mixing cycle.

Masterbatch Blending
Masterbatch is very commonly blended by continuously feeding a stream of masterbatch and a stream of raw resin to the processing equipment.

Extrusion
Approximately 50% of all resins are converted into products by extrusion. The resin is melted in the extruder and then is pumped through a die. The die forms the melt into a shape closely related to that of the final product.

Principles of Plant Layout
Storage Layout:
Storage facilities for raw materials and intermediate and finished products may be located in isolated areas or in adjoining areas.

Equipment Layout
In making a layout, ample space should be assigned to each piece of equipment; accessibility is an important factors for maintenance.It is extremely poor economy to fit the equipment layout too closely into a building.

Safety
A great deal of planning is governed by local and national safety and fire code requirements. Fire protection consisting of reservoirs mains, hydrant, hose houses, fire pumps, reservoirs, sprinklers in building, explosion barriers and directional routing of explosion forces to clear areas and dikes for combustible-product storage tanks must be incorporated to protect costly plant investment and reduce insurance rates.

Plant Expansion
Expansion must always be kept in mind. The question of multiplying the number of units or increasing the size of the prevailing unit merits more study than it can be given here. Suffice it to say that one must exercise engineering judgement; that as a penalty for bad judgement, scrapping of present serviceable equipment constitutes but one phase, for shutdown due to remodelling may involve a greater loss of money than that due to rejected equipment. Nevertheless, the cost of change must sometimes be borne, for the economies of larger units may, in the end, make replacement imperative.

Floor Space
Floor space may or may not be a major factor in the design of a particular plant. The value of land may be a considerable item. The engineers however, follow the rule of practicing economy of floor space, consistent with good housekeeping in the plant land with proper consideration given to line flow of materials, access to equipment, space to permit working on parts of equipment that need frequent servicing and safety and comfort of the operators.

Utilities Servicing
The distribution of gas, air, water, steam, power and electricity is not always a major item, in as much as the flexibility of distribution of these services permits designing to meet almost any condition. But a little pipes should be laid on the floor or between the floor and the 7-ft. level, where the operator must pass or work. Chaotic arrangement of piping invites chaotic operation of the plant. The flexibility of standard pipe fittings regard for the proper placement of each of these services, practicing good design, aids in ease of operation, orderliness and reduction in costs of maintenance. No and power-transmission mechanisms renders this problem one of minor difficulty.

Building
After a complete study of quantitative factors, the selection of the buildings must be considered. A comPETent architect should be consulted to design a building around the process if satisfactory building is not available.

Material-handling Equipment
Consideration of equipment for materials handling is only a minor factor in most cases of arrangement, owing to the multiplicity of available materials-handling devices. But where this operation is paramount in a process, serious thought must be given to it. Again it should be said that engineering judgement must be exercised. Whenever possible, one should take advantage of the topography of the site location, one should take advantage in the process.