CA2178762A1 - Electrically Heated Metal Melt Cell - Google Patents

Abstract

Process and Apparatus for a fully automated magnesium melt system. Raw magnesium ingots are moved through a preheater chamber heated by radiant heat panels where they are thoroughly dried by being controllably heated to a temperature range of about 150°C to 250°C preferably 200°C to 225°C before they are introduced into a melt cell also referred to as a furnace. The ingots, are monitored for temperature by an infra red temperature sensor or a direct contact type thermocouple and this determines whether the ingot is ready to be charged into the furnace. A furnace metal level probe monitors the metal level and a control unit causes ingot charging as determined by a process level set point or temperature overshoot. The melt cell, or furnace uses a closed loop P.I.D. (Proportional Integral Derivative) equation that is enhanced in a PLC (Programmable logic controller) program by introducing variables that are interactive with an ingot being charged to the furnace metal bath, the die cast machine being started and placed into automatic cycle or semi-auto, and also by which furnace control mode the operator has selected via the operator computer interface. The two furnace control modes are run mode (production) and idle mode (non-production, weekend). There are two zones of heat in the furnace with each zone supplied by its own 3 phase zero cross fired silicon controlled rectifier firing boards which are gated by A 4-20mA gating signal. This controls how much the SCR's are allowed to conduct. The amount of error between the metal bath set point and the actual metal bath temperature automatically determines how much of the 4-20mA gating signal is required to maintain the predetermined metal bath temperature. Liquid magnesium is transferred from the furnace to the die cast machine shot sleeve pour hole by a siphon transfer tube which has two sets of electrical heating elements. The melt cell upon receiving a request from the die cast machine for material will, as long as all conditions are met in the melt cell PLC program, allow the transfer tube to lower to the die cast machine pour hole. The transfer tube valve then opens for the length of time set by the operator via the operator computer interface. Providing all safety conditions are met and sensor activated for signal to PLC. Upon completion the valve closes and the transfer tube raises to its home position to be ready for the next cycle. The signal to the die cast machine that the pour is complete is given as soon as the valve closes and the tube begins to raise. Interactive communication between the die cast machine computer, a control computer and other monitoring or remotely located computers provide complete process control and information.
This provides total control of the temperature of the magnesium at all times, for safe operational quality and cost effective casting.