Serkan Orhan, 030070165, 7th Week Part2

4)The Firing Process (seramics) [Group: Manufacture Method]

[Old]
After the shaping but before firing, the ceramic piece is said to be green (the same term as in powder metallurgy), meaning not fully processed or treated. The green piece lacks hardness and strength: it must be fired to fix the part shape and achieve hardness and strength in the finished ware. Firing is the heat treatment process that sinters the ceramic material; it is performed in a furnace called a kiln. In sintering, bonds are developed between the ceramic grains, and this is accompanied by densification and reduction of porosity. Therefore, shrinkage occurs in the polycrystalline materialin addition to the shrinkage that has already occured in drying. Sintering in ceramics is basically the same mechanism as in powder metallurgy. In the firing of traditional ceramics, certain chemical reactions between the components in the mixture may also take place, and a glassy phase alsoforms among the crystals that acts as a binder. Both of these phenomena depend on the chemical composition of the ceramic composition of the ceramic material and the firing temperatures used.

(Fundamentals of modern manufacturing: Materials,Processes, and Systems, Yazar: Mikell Groover, Page 375-376)

[New][Better]

The firing process can be defined as the process where ceramic powders and/or clay, which have been compacted, are heated to a temperature where useful properties will be developed. The firing process encompases chemical and physical changes in the ceramic body accompanied by a loss of porosity and a subsequent increase of density. The compacted powder body becomes bonded together in a rigid matrix by vitrification which involves glass formation or by sintering where little or no liquid is present. The major ceramic product groups and their primary bonding systems are shown in the following chart.

(Firing Ceramics,  G. Bickley Remmey,1994,p. 3)

5)Cone Clutches  [Group:machine element]

[Old]

The clutch is a component that connects a driving and driven part in a mechanism. When the clutch is engaged, the power produced by the engine is transmitted through the clutch to the transmission. When the clutch is disengaged, the power flow stops at the flywheel. The clutch is generally made up of the clutch housing, the flywheel, the clutch disc (or discs), the pressure plate, the release assembly, and the controls. The clutch forces plate surfaces together under pressure. A cone clutch consists of inner and outer conical surfaces. The outer cone is keyed to the driving shaft, while the inner cone is free to slide axially on the driven shaft due to splines. The axial force required to engage the clutch is provided by means of helical compression spring. In engaged position, power is transmitted from the driving shaft to the outer cone by means of the key. Power is then transmitted from the outer cone to the inner cone by means of friction. Finally, power is transmitted from the inner cone to the driven shaft by means of splines. In order to disengage the clutch, a fork is inserted in the shifting collar to shift it axiallt towards right side. This releases pressure between inner and outer cones and no torque can be transmitted.

(V.B. Bhandiri, Design of Machine Elements, p.461)

[New][Better]

In a cone clutch, as shown in Figure 14.16, the contact surfaces are in the form of cones. In the engaged position, the friction surfaces of two cones A and B are in complete contact due to external spring pressure which keeps one cone pressed against the other all the time. 

When a clutch is engaged, torque is transmitted from the driving shaft to the driven shaft through the flywheel and friction cones. For disengaging the clutch, the cone B is pulled back through an actuating lever mechanism against the spring force. In cone clutches, the normal force on the contact surfaces is larger than that on the disc clutches, therefore, for the same axial thrust, the cone clutches can transmit more torque. However, a cone clutch exposed to dust and dirt may create some difficulty in disengagement. Further, score marks on the friction lining surface may impede sliding.

(Design of Machine Elements, C. S. Sharma,Kamlesh Purohit,2005, p.536)