< Cylinder Block Design >
In the project of three-cylinder locomotive,
I wanted to challenge making 'true' cylinder
block. The prototype's cast cylinder block
is a gather of small caves partitioned by
20-30mm thickness walls. It is impossible
to cut such structure from a cast ingot.
At most, we can only drill steam passages
and leave the casting terribly heavy. So
typical three-cylinder block model is made
from pipes, tubes and plates. But I thought
I can make true cylinder block casting if
I utilize many suitable 'cores' in casting.
Spending several months, I designed the cast cylinder with 3D-CAD. The pattern is halved into front and back parts. I chose gunmetal as material to get away from chill and rust.
Due to S7 lathe capacity, I separated the cylinder block into upper flange and lower main body. Height of the top face from valve chest center is the same as lathe center height from lathe table. Then the valve chest will be easily centered when I finish the top face and reverse the casting on lathe table.
The picture shows the casting in perspective. The colored parts show cores, or caves in the casting. The cores are not only for opening the steam passages but also removing useless metal from the casting. The complete casting will have many caves partitioned by 6mm thickness walls.
It shows cutaway model for the left hand valve chest. Middle part of the chest is steam inlet and the end of the chest is outlet. Between them, there is steam passage to the main cylinder. Necessary internal machining works for the casting are only finishing valve chest bores and cylinder bores. Each bore has 2mm machining allowance in radius.
It is cutaway of the middle valve chest. It has the same connections as the left hand chest, but it shares steam inlet and outlet with the right hand valve chest.
It shows view from the bottom. Useless inside metal of the casting is removed. Estimated weight of the casting is 13.5kg. If I didn't use any cores, it would become over 50kg.
Eight cores are necessary for the casting. Those are 3 cylinders, 3 valve chests, upper steam outlet and bottom metal removal. Cylinder and valve chest cores have conical core prints at both ends.
Gunmetal valve liners will be fitted in the valve chests. The rectangle lines in the valve liner are steam ports to control steam admission to the cylinder. The liner is sealed by O-rings. We need unusual thin O-rings for the purpose. The piston is also sealed by O-ring. Japanese typical locomotive has pierced piston rod that is bushed at both cylinder covers. But I employed standard style, that is, one side bushing.
The picture shows assembled cylinder block. It has a lot of complicated parts including Gresley vale gear. I will prepare the parts from cast gunmetal or cast iron.