Rock-and-roll machine

There is double-axis rotation, carousel, shutde, clamshell, rock-and-roll machines, and so on. These designs are similar to other molding systems whereby multiple molds can be used to speed up or even simplify production. Double-axis RM uses two platforms to hold molds. The carousel types can have three to six arms for mounting molds. 

Rock and roll machines are commonly used for kayaks and canoes. These machines do not rotate biaxially but will rock back and forth while spinning on... 

For the folloiving products manufactured by rotational molding, indicate whether they would be made with a rock-and-roll or standard rotational molding machine ... 

Figure 14.22. Rock and roll type machine. [Courtesy of Ferry Industries, Inc., USA.]...

The early machines employed a rock and roll movement, in which the mold was only able to rotate 360° on one spindle while the other spindle rocked the mold back and forth. These machines are still in use for production of very big articles because it is difficult to move the mold around two perpendicular axes, as shown in Figure 14.22. 

Fig. 1. A typical rock and roll type moulding machine. 

The rock and roll type of machine is one of the least complicated versions (Fig. 1). Each mould for the machine is built between two parallel hoops. When the mould is loaded on to the machine the hoops rest on a bed consisting of four rollers which, when driven, cause the mould to rotate. During rotation the bed rocks from side-to-side at right angles to the plane of rotation. The mould is heated during this movement by gas jets carefully placed to produce the heat distribution which will give the required material dispersion within the mould. 

Roll action is the process of reducing rock by means of a hard-faced solid wheel traveling over the rock and breaking it by crushing between the wheel and a rigid surface. While it is a form of compression, it is not the same as the direct-compression method and its results are different. Roll action may be accomplished by means of a wheel traveling over a stationary surface or by means of passing the rock between two wheels wherein the reduction is accomplished. This is a feature of many well-known machines. 

In this machine, the breaking is effected by a combination of compression, roll action and beam action. As the crushing surfaces approach each other, compression is brought into play and since the crushing head is always traveling, the friction between the rock and the head causes it to revolve, thereby bringing into play roll action since the head rolls over the rock being broken. 

Crushers are slow-speed machines for coarse reduction of large quantities of solids. The main types are jaw crushers, gyratory crushers, smooth-roll crushers, and toothed-roU crushers. The first three operate by compression and can break large lumps of very hard materials, as in the primary and secondary reduction of rocks and ores. Toothed-roll crushers tear the feed apart as well as crushing it they handle softer feeds like coal, bone, and soft shale. 

General Principles.—There are several mechanical means by which rock is commercially reduced from one size to another. These include compression, roll action, beam action, impact and attrition. Practically all machines use one of these principles or a combination of two or more of them. 

Crusher A machine for crushing rock or other materials—among the various types of crushers are the ball mill, gyratory crusher. Handsel mill, hammer mill, jaw crusher, rod mill, rolls, stamp mill, and tube mill. 

---