Cylinder liners for aluminum motor blocks and methods of production

A generally hollow cylindrical piston liner for insertion in an internal combustion engine between a piston and an engine block has a cast aluminum piston liner body with cast iron engine block contact surface structure extending therefrom and securely thermally bonded thereto for exhibiting a roughened outer contact surface adapted to interface with an engine block, and its method of manfacture. The cast iron contact surface member roughened surface is generated by introducing in a first mold step a mold wash substance that generates a substantially uniform bubble pattern within a mold wash matrix layer into which the molten iron is poured to thereby produce a roughened iron interface surface. The aluminum piston liner is then bonded to the iron liner in a second molding step by pouring molten aluminum into a pre-heated mold to bond the cast iron engine block surface structure to the aluminum liner. During the solidification stages, the molds are centrifugally rotated about the piston liner cylinder axis to established the required manufacturing precision required for large diameter piston liners. The piston liners typically form a series of circumferal motor block contact ribs spaced proportionately along the liner length to extend from a cylindrical body for carrying the cast iron contact surface structure.

TECHNICAL FIELD 
This invention relates to iron-aluminum bimetallic liners for combustion 
engines, typically with aluminum motor blocks, and their manufacture, and 
more particularly it relates to bimetallic aluminum-iron cylinder liners 
and for producing the liners by casting methods bonding iron to aluminum. 
BACKGROUND ART 
Cylinder liners are known in the art as typified by U.S. Pat. Nos. 
4,523,554 to H. Ryu, Jun. 18, 1985 and 5,183,025 to J. L. Jorstad, et al. 
Feb. 2, 1993. These liners interface thermal energy transfer between the 
piston and engine block. Cylinder liners are also known having provisions 
for introducing fluid flow paths to control transfer of thermal energy 
from the pistons to the engine block. 
When aluminum cylinder liners are made in part of iron forming a contact 
surface for interfacing the engine block, with the aluminum portion 
interfacing with the piston, there are considerable problems in bonding 
the two metals together well enough to process the considerable forces and 
temperatures encountered in use. Such problems are in part introduced at 
the iron-aluminum interfaces by the large differences in melting 
temperatures of iron and aluminum, and thus make casting of the bimetallic 
cylinder liners difficult. 
Another problem of producing the cylinder liners is the desire to have a 
roughened surface on the iron interface which contacts the aluminum engine 
block as a feature of handling thermal transfer of energy between the 
piston and the engine block. 
Accordingly it has not been feasible heretofore to make inexpensive cast 
aluminum cylinder liners faced with iron liner surfaces, and in particular 
those with iron surfaces having roughened insulation type contact 
surfaces. 
One significant problem in producing thin iron circumferential layers upon 
aluminum liner bodies, is the provision of the precise tolerances 
necessary, particularly for larger diameter pistons. 
Thus, it is the objective of this invention to correct these problems of 
the prior art with a novel bimetallic iron-aluminum cylinder liner and its 
method of manufacture. 
DISCLOSURE OF THE INVENTION 
A generally hollow cylindrical piston liner for insertion in an internal 
combustion engine between a piston and an engine block has a cast aluminum 
piston liner body with a cast iron engine block contact surface member 
extending circumferentially from its outer cylindrical surface. Thus a 
thin iron layer is securely thermally bonded to ribs extending from the 
liner body to exhibit a roughened motor block contact surface. 
The cast iron liner with the roughened surface is generated by introducing 
onto a mold cavity surface a mold wash substance that adheres to and forms 
a layer on the mold cavity surface and in the process of casting generates 
a substantially uniform bubble pattern to thereby produce a roughend iron 
interface surface of appropriate texture before molten iron is poured onto 
the wash layer. 
The aluminum piston liner is then bonded to the iron liner by pouring 
molten aluminum over the iron liner in a pre-heated piston liner mold. 
During the solidification stages, the molds are centrifugally rotated 
about the piston liner cylinder axis to establish the required 
manufacturing precision for large diameter piston liners. The piston 
liners have a series of circumferal ribs spaced proportionately along the 
liner length and these ribs are interfaced with the iron liner surfaces. 
This results in a cast aluminum piston liner for insertion in an internal 
combustion engine between a piston and an engine block comprising a hollow 
cylindrical cast aluminum liner body for receiving the piston having a 
plurality of spaced circumferential aluminum ribs extending from its outer 
surface for supporting a thermal contact iron interface surface between 
the cylindrical liner body and a mating surrounding engine block surface. 
The thermal contact surface is formed as a cast iron engine block contact 
member with a roughened outer surface, wherein the iron member is 
thermally bonded onto the circumferential aluminum ribs extending from the 
cylindrical liner body. 
Thi invention provides a method of molding the cylindrical cast aluminum 
piston liner having externally protruding aluminum ribs covered by a cast 
surface layer of iron roughened at the outer surface for interfacing the 
resident engine block surface. Molds are prepared and preheated, where 
necessary, before pouring the respective molten iron and aluminum metals 
in a sequence of corresponding casting steps. 
For producing a roughened outer surface on the cast iron layer, a layer of 
a mold wash substance is adhered to the mold inner surface to produce, 
before the pouring of molten iron into the mold, a mass of bubbles at the 
outer surface contact interface of the molten iron poured into the mold. 
Placement of such cast iron liners into the aluminum piston cylinder molds 
before pouring molten aluminum then produces the bimetallic iron-aluminum 
piston liner. The piston mold containing iron liners is preheated to 
produce a better bonding at the iron-aluminum merging interface. 
To obtain the very demanding precise cylindrical surfaces that are required 
in particular for larger size pistons and diesel engine pistons, the 
loaded molds are rotated about the cylindrical axis of said piston liner 
during solidification of molten metal. 
Other objects features and advantages of the invention will be found 
throughout the following description, drawings and claims.

THE PREFERRED EMBODIMENTS 
In FIGS. 1 and 2, the typical cylinder liner preferred embodiment 15 is set 
forth. The flange 14 is shown at the top of the liner 15. The size of the 
cylinder varies for different engines and it has been difficult in the 
prior art because of the difference in melting temperatures of iron and 
aluminum to produce any cylinder liner casting with a bonded-on iron 
surface member 16, as displayed on the outer circumference of the three 
symmetrically placed aluminum ribs 17 for establishing thermal surface 
contact interface within a receiving aluminum engine block. In such use, 
strict dimensional tolerances of cylindrical roundness are imposed which 
have been exceedingly difficult to achieve in cast products, particularly 
for larger diameter pistons such as used for Diesel engines, for example. 
The manner of meeting such tolerances by rotating molds about the 
cylindrical axis of the liner is later discussed with respect to the 
precision casting process for manufacture of the cylinder liner afforded 
by this invention. 
The interface bonding of the iron surface member 16 onto the integrally 
extending and thus strongly affixed cast aluminum ribs 17 is critical 
because of the significantly different melting temperatures of iron and 
aluminum. Note that the circumferential alignment of the aluminum ribs 17 
presents the bonded iron surface members 16 perpendicular to the movement 
of the piston in the interior surface 18 of the aluminum liner body 15 to 
thus encounter high stresses at the interface surface between the liner 
body 15 and the aluminum engine block into which it is mounted. Thus, the 
bonding strength between the iron and aluminum components 16, 17, provided 
in the casting process of this invention is a significant improvement in 
the art. 
Consider in more detail the eccentricity problems encountered in producing 
an acceptable product when the ribs 17 extend only about five millimeters 
from the generally cylindrical outer perimeter 19 of the liner body. The 
thinner iron surface contact layers 16 of about one millimeter thickness 
then present significant problems of obtaining precision roundness in 
manufacture. For this reason expensive machining processes and complex 
casting procedures would be required using conventional prior art 
techniques that would unduly increase the production costs of the 
bimetallic iron-aluminum piston liners to which this invention is 
directed. 
FIG. 3 is a flow diagram outlining the process of manufacturing the cast 
cylinder liners 15. The mold washing step 20 is critical in the formation 
of the roughened porous surface characteristic of the iron surface 16. The 
preferred wash constituency is obtained using a mixture of 25 pounds of 
silica flour, 200 mesh, with 0.875 pounds of western bentonite in 12 
pounds of water with 3 ounces of concentrated detergent, typically Orvus 
brand marketed by Proctor & Gamble, is prepared at block 21 and verified 
at block 22. In an intial molding step for processing the iron liner 
member 16, this mixture, after being diluted by water to a viscosity range 
from 20 to 25 seconds, is then at block 20 washed upon the surface of the 
mold, which is then pre-heated to a processing temperature in the range of 
140 to 160 degrees Centigrade in blocks 23, 24. This wash being 
appropriately applied to a thickness of one millimeter on the mold surface 
at block 25 serves to generate a set of substantially uniformly 
distributed bubbles in a solid matrix pattern into which molten iron may 
be poured to produce its roughened, porous surface characteristic. 
The mold wash is applied to the internal mold surface by the use of a 
pressure tank and a spray nozzle. The appropriate bubble characteristics 
are controlled by the choice of air pressure, spray nozzle and the 
movement speed relative to the mold taking into account the mold rotation 
speed at block 26. The air bubbles formed in the dried wash surface 
provide a generally uniformly distributed pattern of pores. By pouring 
molten iron into the bubble formed pattern in the wash layer surface at 
pouring station 27, these pores are filled with iron to accordingly 
roughen the outer contact surface of the iron. 
During the solidification phase, the mold is rotated about the axis of the 
liner cylinder at a desired temperature range as accomplished in block 28. 
After solidification (29) the mold cools to room temperature at block 30. 
After inspection 31, the cooled casting is machined at 32 to establish the 
specified length, internal diameter and outside body diameter. Because of 
the rotation of the molds, the precision tolerances required without 
eccentricity at the thin iron layer outer contact surface are achieved. 
For charging the furnace with either molten iron or molten aluminum, 
starting at block 35, the melting is achieved by an electric induction 
furnace 36 or equivalent electric resistance furnace to provide a charge 
which has a verified chemical constituency and temperature (Block 37). 
Weight is controlled at block 38 for the tapping and ladle inoculation 
step at 39. 
The pouring process for the aluminum cylinder liner block may be done in 
either a stationary sand or metallic mold, which is rotated at 28 during 
the solidification stage, piece shakeout and mold preparation at a 
controlled rotation rate. 
In the general method of this invention for molding a cylindrical cast 
aluminum piston liner block having externally protruding aluminum ribs 
with a cast surface layer of iron the process steps are as follows: 
fabricating, preparing and washing metal or sand molds, 
preheating metal molds for the molding step, 
placement of sand cores into the mold, 
preheating iron liners made in the foregoing way for processing said 
surface layer of iron in a mold, 
pouring the molten aluminum, 
soldifying and shaking out the cast aluminum block. 
For processing the iron rings the method steps comprise: 
producing a roughened outer surface on the cast iron layer by introducing a 
mold wash substance that produces a mass of bubbles in surface contact 
with molten iron poured into the mold, 
placement of the iron liner into a piston mold for producing the aluminum 
piston liner and pouring aluminum after preheating the piton mold and iron 
liner, and 
rotating said loads about the cylindrical axis of said piston liner during 
solidification of molten metal. 
During the processing of the aluminum piston liner block, the pores on the 
outer surface of the iron rings may be filled with molten aluminum to 
strengthen the bond between the iron and aluminum. 
Having therefore introduced improvements to the state of the art, those 
features of novelty relating to the spirit and nature of this invention 
are defined with particularity in the following claims.