Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Temperature control
Patent
1993-05-17
1995-09-26
Wayner, William E.
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Temperature control
165 30, 236 46F, 236 78D, B28B 1700, B29B 1300
Patent
active
054529999
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a temperature regulating system, method and apparatus, and relates particularly to such system, method and apparatus for cyclic processors. Such processors typically have a pre-set repeating cycle time, and form standard products from a hot melt material which solidifies in a mould.
Although the system is likely to find most application utilising coolant flows to regulate against over-heating, we do not exclude systems utilising heating flows to regulate against over-cooling.
BACKGROUND TO THE INVENTION
Typical cyclic processors are injection moulding machines, blow moulding machines and aluminium die casting machines. For convenience the invention will be described in relation to thermoplastic injection moulding.
In thermoplastic injection moulding machines the hot melt material is introduced, typically injected, into a mould cavity, which cavity is then cooled in order that the material will solidify to form the product to a shape dictated by the mould cavity; the mould is thereafter opened, the formed product ejected, the mould closed to re-make the cavity, and the cycle repeated. For efficient working, the mould operating temperature must be held within an acceptable range defined by specified upper and lower temperature limits, since if the mould temperature is too high the material is slow to solidify, and if the mould temperature is too low some or all of the mould material can solidify in the injection sprue leading to the cavity i.e. premature solidification with a consequent increase in the required injection pump pressure. Furthermore it is considered good practice to maintain the mould within a temperature range which allows the product the minimum shrinkage and distortion during the setting or curing stage, both for product quality and for uniformity amongst the replications of the product being moulded.
The four variables which affect product quality are melt temperature, melt flow rate, melt pressure (each a function of the processor control systems and condition settings) and cooling rate. It is normal practice to seek to maintain product quality by repeated small adjustments of the processor machine controls, usually in response to external changes "outside" the machine controls. A reliable and accurate temperature regulating system is necessary so that the operating temperature, and therefore the cooling rate, can be held within a pre-determined range.
DISCLOSURE OF THE PRIOR ART
In one known mould cooling system a liquid is circulated continuously through channels fashioned in the walls of the mould. One disadvantage of this system is that by using continuously circulating liquid, the thermal mass of the system is large, so that the response time to temperature change is slow; also considerable skill is required on the part of the operator to set the correct external heat input or cooling rate for the liquid to maintain the mould within its working temperature range. The manual adjustment needs to be effected quickly and correctly if reject products are to be avoided.
In an alternative known continuous flow system, fluid is again continuously circulated through the mould, by way of a control system. The liquid temperature is less than that of the mould. If the temperature of the mould increases, the rate of water circulation is increased. This system has the disadvantages of the above known system, including that the mould temperature may vary due to ambient temperature changes, (with an unacceptable level of product rejects until the water circulation rate is manually changed), that the operator needs considerable skill to judge whether the rate needs to be increased or decreased and by how much, and that the mould is being cooled during charge injection, and even prior thereto.
U.S. Pat. No. 1,491,173 teaches that the temperature of a mould should be maintained within a constant range. Fluid preferably liquid, is caused to circulate (intermittently) through the coolant system as rapidly as the position of flow-control valves permi
REFERENCES:
patent: 4354812 (1982-10-01), Wieder et al.
patent: 4902454 (1990-02-01), Steinbichler et al.
Cota Albert O.
Wayner William E.
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