Compression molding.

Molding

Molding is a technique generally use for thermoplastic and thermosetting materials.

This technique is used to produce sheet like, hollow and solid materials, from very small to very large materials. The various molding process are

Injection molding.

Extrusion molding.

Blow molding.

Compression molding

This technique is widely used in automotive (vehicle motors) industries to produce parts that are large, thin,strong,stiff. This process is also used in household goods and electrical industries.

The polymers processed from compression molding are epoxies (EP), phenolics(PF), melamine formaldehyde (MF) and urea formaldehyde (UF).

Compression molding occurs by the following steps:

Compression molding.

A pre-weighed polymer with additives and fillers (called charge) is placed in the lower half of the mold.
The charge may be powder, pellets,putty like masses.
The charge are heated before placing on the lower half of the mold as the heated polymers are soft which reduces the molding cycle time.
The upper half of the mold moves downwards which forces the charge to fill in the gap of mold (called mold cavity) of the lower half.
The mold is opened the molded part is seperated by means of ejector pin.
If polymer is thermosetting, the mold can be open when hot because the cured thermosetting retain its shape and dimension when hot.
If polymer is thermoplastic, the mold and molded part is allowed to cool and then open.

Comments

Determination of molecular weight of polymers by viscosity method.

Determination of molecular weight of polymers by viscosity method. It is a simple method for determining the molecular weight of polymers. Addition of polymers in the solvent increases the viscosity of the solvent, due to introduction of inhomogeneities by the polymers. If η₀ is the viscosity of the solvent and η is the viscosity of the solution at the same temperature, then the relative viscosity is given by Relative viscosity. Specific viscosity: It is defined as the relative increase in viscosity and is given as Specific viscosity. Reduced viscosity: It is defined as the relative increase in viscosity per unit concentration (C) of polymer and is given as Reduced viscosity. Intrinsic viscosity: The reduced viscosity is dependent on concentration (C). If a graph is plotted between reduced viscosity vs concentration then the extraplotation value when C=0 is called intrinsic viscosity. Intrinsic viscosity. Graph of reduced viscosity vs concentr

Determination of molecular weight by Light scattering method.

Determination of molecular weight by Light scattering method. Due to big size macromolecules in solution, turbidity is produced. The light rays get scattered, when pass through macromolecule solution due to turbidity. The turbidity T is given by Where I₀ is the intensity of incident light. Iₜ is the intensity of transmitted light after passing through a solution of length l. In case of proteins or higher polymers the turbidity is small and is determine from the intensity of light scattered at 90° to the beam. This can be done by using a simple photometer as shown in figure below. Turbidity increase with increase in concentration as well as molecular weight. The Turbidity is related to molecular weight by the equation given by Debye. Hc/T=1/M+2Bc Where B is second virial coefficient and H is a constant. If we plot a graph between Hc/T vs c we get a straight line with intercept 1/M. Thus This curve was plotted by Zimm, so is called Zimm's Curve. Thus the c

Polypropylene (PP)

Polypropylene (PP). Polypropylene (PP) is also known as polypropene. Polypropylene is made from the polymerisation of propylene gas in the presence of Zeiglar Natta catalyst or metallocene catalyst. Polypropylene. Thus propene (or propylene) is the monomer of polypropylene. Polypropylene is a highly flammable material. It is sensitive to microbial attacks, such as bacteria and mold. It exhibits excellent resistance to diluted and concentrated acids, alcohols and bases. Polypropylene is used to make lunch boxes, margarine containers, yogurt pots, syrup bottles etc. Disposable syringes is the most common medical application of polypropylene. Polypropylene rope and twine are very strong and moisture resistant very suitable for marine applications. Polypropylene, highly colorfast, is widely used in manufacturing carpets, rugs and mats. Uses of Polypropylene. Questions on polypropylene; Q1) What is polypropylene? Ans) Polypropylene is a polymer of propylen

Polymers

Search This Blog