Introduction to Basic Manufacturing Processes and ... - always yours

160 Introduction to Basic Manufacturing Processes and Workshop Technology
joints and fastening different component of woods. Their size is specified by length and
diameter. These are sold by weight in the market.
Screws
Screws are made from bright drawn wires or thin rods and they are used mainly for
fixing the metallic fittings like hinges and hasps in wooden structure.
Adhesives
Adhesives is defined as the sticking substance such as glue, paste, cement and mucilage
that is capable of holding wooden parts together by surface attachment permanently. It is
commonly used to join together the boards edge-to edge to form a larger surface or face-toface
to increase the thickness. It is applied on large surface areas of material as when laying
veneers and is also used to stick together relatively small surface areas such as wood working
joints. An efficient adhesive or sticking paste or glue is one that maintains good bond between
the wooden elements under the conditions of service that the joint has to withstand. It is
required frequently for joining together the wooden boards edge to edge to form a larger
surface or face to face to increase thickness in joinery work and many other common types
of wood works. It is applied either cold or hot condition. The former is known as liquid or
cold glue and is used when a slow and less strong setting is desired. When applied hot, it is
known as cooked glue that enables a very strong and permanent type of joint between the
adjacent layers of wood pieces. Few commercially available adhesives can be classified as
casein glue, animal glue, vegetable glue, albumen glue, synthetic resins, poly-vinyl-acetate
(PVA), paint and varnishes, rubber cement and plastic cement and few important such adhesives
are briefly discussed as under.
Casein glue
Casein glue is made by adding an alkali to the curd of skimmed milk. It is commercially
available in powdered form in the market. It can be made into a paste, while using, by adding
water. It is thicker than animal glue but squeezes out of the joint quickly when pressed. This
glue requires 15 to 20 minutes to set a wooden joint and therefore thus provides the carpenter
sufficient time to glue and clamp his work. Casein glue is a commonly used adhesive which
is very strong and water resistant. It is used specially in components which are continuously
subjected to high humidity viz. furniture, boat making, veneering, beams and others wooden
components.
Animal glue
This glue is made from hides, hoofs, bones and other waste parts of animals. These
materials are refined and developed in form of sheets, flakes or powder. Before applying, the
glue should be soaked in cold water over night and then heated. It is generally applied hot
and sets very rapidly. It is also available in liquid form commercially which is applied cold i.e.
it does not require any heating before application. An important point is to be noted that this
glue should be applied immediately after heating. Repeated heatings should be avoided as this
weakens the bond of the glue and also its fluidity is lost due to evaporation of water,
rendering it thicker.
Vegetable glue
It is developed from the starch which is obtained from roots, grains and corns of trees
by subjecting them with acid and by grinding to a powered form. It is mainly used in plywood
work and it is not much suitable for general work