Mani'Facti'rk (»!• Ckmknt Pll'I': 



79 



start the machine, whereupon the packer descends to the table and 

 then begins to rise again. Mortar is discharged automatically into 

 the jacket, and the packer-head, beginning at the bottom, revolving 

 and gradually rising, forms the mortaf^nto a tile. In case a perfect 

 tile is not formed, as happens occasionally, then it is "stripped" im- 

 mediately and the mortar is shovelled back into the hopper again. 

 Experience in handling the machine is of much importance ; the 

 selection and screening of the sand and the degree of wetness of 

 the mortar are of even greater importance. 



Fig. 6 shows the largest size sewer pipe machine, in which the 

 table is turned, and a special bell packer at the bottom is operated 

 automatically. The bell and spigot joint is shown in Fig. 7. In 

 California and the Southwest, however, the bell and spigot joint is 

 not much used, the tongue and groove joint being preferred. This 



joint is illustrated in the cover cut. 



The groove is made at the bottom by 



means of a small iron ring or pallet 



placed in the form, and the tongue 



at the top by an equivalent ring on the 



under side of the guide hopper. A great 



advantage of the tongue and groove 



joint is that the pipe can be laid in the 



trench much faster than bell-ended 



pipe. Also, there is less breakage in 



handling the tongue and groove pipe 



There is no valid reason why this joint 



should not be used for sewer pipe as 



well as for irrigation pipe ; indeed, it 



should be preferred in the interest of 



economy. 



Since the forms are corrugated, the outer surface of the pipe is 



corrugated. This probably adds to the strength somewhat, but the 



more immediate purpose of the corrugations is to prevent the tile 



from slipping from the mold while being carried to the curing floor. 



Corrugations on the inside, however, would be very objectionable, 



since they w^ould reduce the capacity of a pipe line greatly. 



The bottom pallets must be left under the pipe until the mortar 



is set sufficiently to permit turning the pipe over. If the pipe are 



cured in the open air, this requires from 24 to 48 hours, depending 



upon the season of the year. The pallets are released by a gentle 



tap of the hammer. Many pipe manufacturers in the Middle West 



Fig. 7. — McCracken sewer pipe 

 with bell and spigot joint. 



