Burcu Atay, 140060029, 11th week

Truck-Mounted Mills

Installers of construction products occasionally find it necessary and often more economical to form the products at the job site.

For example, to reroof an existing building, the architect may specify over 100-ft (33-m) long sheets. Because transporting and handling these sheets from the plant to the job site is not practical, it is easier to move the complete line to the job site.

Most special, trailer-mounted lines have their own diesel generator, hydraulic or other drive, cutoff press, and an uncoiler that can be loaded from ground level (Figure 2.29).

Figure 2-29 Trailer-mounted roll forming line

These self-contained units are also used in less developed countries or at any place where, owing to the lack of proper infrastructure, it is easier to transport the equipment in one truck and the coils in another one than to ship many truckloads of finished products.Several types of truck-mounted units are used by contractors for job site manufacturing of eavestrough, sidings, soffits, and similar products. These units usually have a “plug-in” electrical motor drive. Small items such as eavestrough are often manufactured in a “stop-and-go” operation, and the products are cut by a manual shear mounted at the end of the mill.

(Halmos,G.T, Roll Forming Handbook,Taylor & Francis,2-17,18)

Vulcanization

Vulcanization is a process generally applied to rubbery or elastomeric materials. These materials forcibly retract to their approximately original shape after a rather large mechanically imposed deformation. Vulcanization can be defined as a process which increases the retractile forces and reduces the amount of permanent deformation remaining after removal of the deforming force. Thus vulcanization increases elasticity while it decreases plasticity. It is generally accomplished by the formation of a crosslinked molecular network ( fig.1.)

According to the theory of rubber elasticity, the retractile force to resist a deformation is proportional to the number of network supporting polymer chains per unit volume of elastomer. A supporting polymer chain is a linear polymer molecular segment between network junctures. An increase in the number of junctures or crosslinks gives an increase in the number of supporting chains. In an unvulcanized linear high polymer (above its melting point), only molecular chain entanglements constitute junctures.

Vulcanization, thus, is a process of chemically producing network junctures by the insertion of crosslinks between polymer chains. A crosslink may be a group sulfur atoms in a short chain, a single sulfur atom, a carbon to carbon bond, a polyvalent organic radical, an ionic cluster, or a polyvalent metal ion. The process is usually carried out by heating the rubber, mixed with vulcanizing agents, in a mold under pressure.

(Mark, J., Erman, B., Eirich, F.R., Science and technology of rubber, 3^rd Edition, pg.322)

Hubbing

Hubbing is a deformation process in which a hardened steel form is pressed into a soft steel (or other soft metal) block. The process is often used to make mold cavities for plastic molding and die casting. The hardened steel form, called the hub, is machined to the geometry of the part to be molded. Substantial pressures are required to force the hub into the soft block, and this is usually accomplished by a hydraulic press. Complete formation of the die cavity in the block often requires several steps- hubbing followed by annealing to recover the work metal from strain hardening. When significant amounts of material are deformed in the block, as shown in our figure, the excess must be machined away. The advantage of hubbing in this application is that it is generally easier to machine the positive form than the mating negative cavity. This advantage is multiplied in cases where more than one cavity are made in the die block.

(Groover, M.P, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, 4th Edition, pg.419)

Flowability

It is that property of the metal powder by virtue if which it flows readily, uniformly and rapidly into the die or mould cavity. It governs the time required to fill a die or mould and the rate of production. The shapes of the particle, size and its distribution, coefficient of inter-particle friction and the absorbed moisture are the factors affecting flowability. Coarse and spherical particle possess good and maximum flowability whereas fine and irregular particles have poor as well as reduced flowability respectively.