GB2080166A - Improvements in water cooled permanent mold casting machines - Google Patents

Abstract

A cooling system for a water cooled permanent mold casting machine having a plurality of indexable molds (12) which includes a flow path for water from a central supply (26) through each mold half (16) and a plurality of normally closed thermostatic valves (36) in the water outlets (31-34) of each mold half which are of the wax power element type set to open quickly at a predetermined temperature reached after pouring to allow a large volume of cooling water to flow through the mold to cool the mold quickly back to an optimum pouring temperature. <IMAGE>

Description

SPECIFICATION Improvements in water cooled permanent mold casting machines This invention relates to permanent mold casting machines and concerns an improved system for controlling the temperature in water cooled permanent mold casting machines.

Permanent mold casting machines, both of the air cooled type and of the water cooled type are well known in the art. The basic objectives in cooling the molds in a permanent mold casting machine are to provide an ideal mold temperature when the casting metal is poured, and to be able to cycle the mold at the fastest rate possible, in order to obtain maximum yield and maximum mold life, with a minimum scrap rate.

Prior art water cooling systems have provided a constant flow of water which has been treated in a closed cycle system. Such systems have not been entirely satisfactory for several reasons, including the fact that the system was not capable of uniformly cooling molds of differing sizes and consequential differing cooling requirements, and the system did not respond to varying pouring temperatures and varying soot deposits. Also, the water treatment system itself was extremely complex, required a large volume of cooling water for the heat exchanger employed, required auxiliary heating to bring the system to operating temperature, and also required a great deal of floor space.

In the operation of a permanent mold casting machine, it is desirable to obtain an optimum mold temperature when the metal is poured. In practice, when working with grey iron, it has been determined that a mold temperature of 350'F (1 77 C) will yield the least casting scrap and the longest mold life.

To operate a mold in this manner at the fastest cycle obtainable requires the mold to be cooled rapidly over a precise time period after the castings have been removed.

In a typical permanent mold casting machine, the molds are arranged in a circle, and progress through six steps or stations which define a complete casting cycle. These stations are 1. core setting, 2. pour, 3. solidification, 4. mold opening, 5. casting removal and 6. soot application. Since there is always a mold at each station, the duration of each step must be equal. Experience has shown that the most critical time period is the half of the cycle between pouring and casting removal, during which time the castings solidify. If cooling is too great during this time period, the casting can be damaged. If cooling is too slow, a maximum production rate cannot be obtained.Once the time for this half of the cycle is established, the last half of the cycle, during which the mold is cooled to the optimum pour temperature, must occupy the same time period, since the next pour is then going through the critical portion of the cycle. In operating the prior art constant flow cooling system, it was found to be impossible to obtain the optimum mold temperature during the opening through core setting portion of the cycle in the same time as the pour through removal portion; therefore, it was necessary to extend the duration of the cycle, resulting in a low production rate.

The present invention provides a permanent mold casting machine including a plurality of mold members arranged in a circular pattern for indexing through a plurality of casting steps, and a system for cooling said mold members by introducing a liquid coolant into passages formed in said mold members, said system for cooling said mold members comprising inlet conduit means for conducting coolant from a central source to each of said mold members, an inlet port formed in said mold member and connected to said inlet conduit means, an inlet passage formed in said mold member and connected to said inlet port, a plurality of cooling passages formed in said mold member and intersecting said inlet passage, an outlet passage formed in said mold member and intersecting said cooling passages, a plurality of outlet ports formed in said mold member and connected to said outlet passage, a plurality of outlet conduits connected to said outlet ports to conduct coolant from said mold member to a drain conduit, and a normally closed thermostatic valve disposed in each of said plurality of outlet conduits, said thermostatic valves being operable to open when coolant in said outlet conduits reaches a predetermined temperature.

The thermostats employed may be of the wax power element type used in marine engine applications, and which characteristically pop open quickly once their set temperature is reached. When the thermostats open, a comparatively large volume of cooling water flows through the mold member to quickly cool the mold back down to its optimum pouring temperature.

A specific embodiment of the present invention will now be described by way of example and not by way of limitation with reference to the accompanying drawings, in which: Figure 1 is a schematic plan view of a permanent mold casting machine in which the invention is incorporated; Figure 2 is a schematic diagram of a typical prior art water cooling and treatment system for a permanent mold casting machine; Figure 3 is a schematic diagram of the water cooling system of the invention; Figure 4 is a schematic plan view of a typical mold half; Figure 5 is a side elevation view of the mold half of Fig. 4; and Figure 6 is a graph of mold temperature vs time for molds of a machine incorporating a prior art water cooling system and the water cooling system of the invention.

Referring to the accompanying drawings and first to Fig. 1, there is illustrated a permanent mold casting machine, designated generally by the numeral 10, comprising a plurality of mold units 1 2 which are movable around a central axis 0. Permanent mold casting machines per se are well known in the art and will not be described in detail.

Each mold unit 12 comprises a frame 14, and mold halves 1 6 which are movable between an open position and a closed position.

The mold units are attached to a central carousel frame (not shown) which is driven clockwise to index the molds about the axis 0 for the various steps or stations in the casting cycle. In the illustrative embodiment, the machine 10 includes 1 2 mold units which operate in pairs, such that there are six stations in a cycle. In station A of the cycle the mold halves 1 6 are in the open position, and any cores which must be positioned in the mold cavities being poured are set in place at this point. When the carousel is indexed to position the molds at station B, the mold halves are closed, and molten metal is poured into the mold. At station C the mold halves remain inthe closed position as the mold heats due to the addition of the molten metal, and the castings therein solidify.At station D the mold halves are moved to their open position and the castings are removed. At station E the mold halves remain open while the mold cools, and at station F the mold halves are subjected to a soot application operation which is carried out within an enclosure 1 8.

At this point, the molds are ready to be indexed to station A for the start of a new casting cycle.

In order to provide a full appreciation of the advantages of the inventive cooling system, the prior art system which it replaces is illustrated schematically in Fig. 2. In the prior art system a constant flow of treated water was supplied to the mold halves 1 6 by a system which includes a water inlet line a from a city water supply to initially fill the system and thereafter supply make-up water, a heat exchanger b, a scale control unit c, a water tank d, a 130KW heater e inside the tank, a pump fand the associated valves and controls necessary to support a closed system.

Referring to Fig. 3, the present temperature control system comprises an inlet line 20 from a city or other central water supply, an inlet valve 21, a pressure regulator 22, a flow meter 24, a rotary coupling 26 to allow for the rotation of the casting machine about the axis 0, a line 27 from the rotary coupling to the mold, a cutoff valve 28 in the line 27, mold inlet lines 29 and 30 directing cooling water into the mold halves 16, mold outlet lines 31, 32, 33, 34 directing water out of the mold halves and into a drain line 35, thermostatic valves 36 in outlet lines 31-34, a check valve 37 in the drain line 34, and a drain line 38 connecting the rotary coupling to a drain 39. The rotary coupling 26 is installed at the center of the carousel and provides central, stationary water supply and drain connections and a rotating manifold which conducts water to and from the twelve molds.This type of rotary coupling or manifold is well known in the art and readily available commercially, and will not be described herein in detail.

Fig. 4 is a somewhat schematic view of a mold half 1 6, the view shown being of the outer surface 5 of a mold half 1 6 installed in the machine 10, as shown in Fig. 1. Each mold half is a solid piece of metal having a plurality of cavities 40 formed in one surface.

It can be appreciated that in actual practice the cavities 40 would define somewhat complex shapes; however, the cavities form no part of the present invention and are illustrated herein simply as rectangular shapes.

The cavities are interconnected (not shown) such that when the mold halves are closed, metal poured into a common opening will flow into all the cavities.

Cooling of the mold halves is provided by a plurality of first parallel passages 42 formed in the interior of the mold which are intersected by an inlet passageway 44 and an outlet passageway 46. The passageways 42, 44, 46 are formed by boring into the sides of the mold half and then closing the ends by means of plugs 48. An inlet port 50 for connection to the inlet line 29 or 30 is formed by boring into the face of the mold opposite the cavities to intersect the inlet passageway 44, and outlet ports 51 and 52 for connection to the outlet lines 31 and 32 or 33 and 34 are similarly formed by boring into the mold half to intersect the outlet passageway 46.

Referring to Fig. 5, each mold half 1 6 has two normally closed thermostatic valve units 36 received in the outlet lines 31, 32 and 33, 34. In the illustrative embodiment, the thermostatic valve employed is a valve of the Vernet or wax power element type commonly used for marine engine applications, which is set to open at 143"F (62"C), and is installed in a modified pipe union 54, which is shown partially cut away to show the locafion of one of the two thermostats associated with each mold half.

Referring to Figs. 3, 4 and 5, in operation, water is supplied at approximately 55"F (13"C) to each mold half 16 via inlet line 20, and pressure regulator 22 which insures a flow of water at constant pressure to the rotary coupling. From the rotary coupling water is supplied via line 27 to each of the twenty four mold halves in the system illustrated. Water enters the mold at inlet port 50, flows through inlet passage 44 to the connecting passages 42 where it picks up heat from the mold, and then flows into the outlet passage 46 to the two outlet ports 51 and 52 to the outlet lines 31 and 32 or 33 and 34 and the thermostatic valves 36.Once the water temperature reaches 143OF (62"C) the thermostatic valves 36 will open, and water will flow through lines 31-34, line 35 to the rotary coupling 26 and from the rotary coupling to drain via line 38.

Fig. 6 represents actual operational experience with the prior art system and with the present system. In both systems the mold temperature will be at 350 (177"C) when the metal is poured. As metal is poured into the mold the mold heats up to about 450"F (232"C) during the time period T1, at which time the castings have solidified and are removed. During time T2 period it is necessary to cool the mold down to 350"F (177"C) quickly for another pour.As shown by the dashed line, the prior art system operating at constant flow cannot react quickly enough to get the mold back down to 350"F (177"C) in the same time that it takes for casting solidification, which means that T2 must be extended. Since the carousel indexes at regular intervals, the entire cycle time must be extended to allow extra time for mold cooling. It has been found that T2 cannot be shortened by lowering the temperature of the input cooling water since excessive cooling during solidification (T1) damages the castings.

In the present system, the dual outlets and the characteristic quick opening of the Vernet type thermostats enable the system to react quickly to the temperature rise during solidification, allowing the mold to cool quickly for the next pour, as shown by the fact the T2 = T, for the inventive system. Another advantage afforded by the use of quick opening thermostats is that any scale which tends to collect in the molds is flushed out by the sudden flow of cooling water when the thermostat opens.

Claims (6)

1. A permanent mold casting machine including a plurality of mold members arranged in a circular pattern for indexing through a plurality of casting steps, and a system for cooling said mold members by introducing a liquid coolant into passages formed in said mold members, said system for cooling said mold members comprising inlet conduit means for conducting coolant from a central source to each of said mold members, an inlet port formed in said mold member and connected to said inlet conduit means, an inlet passage formed in said mold member and connected to said inlet port, a plurality of cooling passages formed in said mold member and intersecting said inlet passage, an outlet passage formed in said mold member and intersecting said cooling passages, a plurality of outlet ports formed in said mold member and connected to said outlet passage, a plurality of outlet conduits connected to said outlet ports to conduct coolant from said mold member to a drain conduit, and a normally closed thermostatic valve disposed in each of said plurality of outlet conduits, said thermostatic valves being operable to open when coolant in said outlet conduits reaches a predetermined temperature.

2. A machine as claimed in claim 1, in which each of said mold members comprises a metal block having a plurality of cavities formed therein, said inlet and outlet passages and said cooling passages comprising elongated passages disposed adjacent said cavities.

3. A machine as claimed in claim 1 or 2, in which said thermostatic valves include a thermostatic element of the wax power element type.

4. A machine as claimed in any preceding claim, including a pipe union in each of said outlet conduits, said thermostatic valves being disposed within said pipe unions.

5. A machine as claimed in any preceding claim including a plurality of mold units, each unit comprising first and second mold members movable toward and away from each other, each of said mold members having two outlet conduits and a thermostatic valve in each outlet conduit.

6. A permanent mold casting machine substantially as hereinbefore described with reference to, and as shown in, Figs. 1, 3, 4 and 5 of the accompanying drawings.