Plastics Technology Practice - The Hong Kong Polytechnic University

Plastics Technology Practice
• Buffing - Buffing is a polishing operation using a cloth or felt that
contains fine abrasive. The coarseness of the abrasive used depends upon
the original roughness of the part and the degree of luster desired.
Buffing will not ture a surface, but tends to round sharp edges and
produce a lustrous appearance.
4.1.2 Cementing- There are two basic methods of cementing plastics, i.e.
Cohesive and Adhesive-bonding.
• Cohesive Bonding - Cohesive bonding is also known as solvent
cementing, in which the surfaces of the joint are dissolved by a suitable
solvent and then pressed together. However, this method is only suitable
for thermoplastics and the material of the joint must be the same, e.g.
acrylic with acrylic or styrene with styrene.
• Adhesive Bonding - This method is suitable for joining any materials,
similar or dissimilar. It is necessary to find an adhesive which will stick to
the materials involved. Although adhesive-bonding can be used with any
plastics, it is generally not used where solvent bonding is satisfactory. This
means that the most common application of adhesive bonding is with
thermosets or where dissimilar materials are to be joined.
4.1.3 Mechanical Fastening
The use of screws, bolts and nuts for fastening two pieces of plastics is also a
common practice in joining plastics. The decision to use mechanical fasteners is
based on the strength of the plastic
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