Dosing Furnace, Melting Furnace or Holding Furnace? Which Furnace Fits the Die Casting Process?

The Right Furnace Depends on Its Function in the Metal Flow

Furnace selection should not begin with temperature or furnace capacity alone. The first question is what the furnace has to do within the production process.

A foundry may need to melt solid metal, buffer molten metal between production steps, maintain stable temperatures, provide a defined shot quantity or combine several of these tasks.

This is why the terms melting furnace, holding furnace and dosing furnace describe primarily the function of the equipment. Depending on the furnace design, a single unit may cover more than one function.

Melting, Holding and Dosing at a Glance

From Solid Charge Material to Molten Metal

A melting furnace is designed primarily to provide the thermal energy required to transform solid metal into molten metal. Depending on foundry requirements, different furnace technologies and heating principles can be used.

In aluminium processing, the furnace may receive ingots as well as suitable return material from the casting process. Furnace design, charging method, metal throughput and production concept determine how the melting stage is organized.

Once the required molten metal is available, it can be transferred to a holding furnace, transport ladle, dosing system or another downstream part of the metal supply system.

FISS offers used melting furnaces for foundry and die casting applications.

Keeping Molten Metal Available for the Casting Process

Once the metal has been melted, the next challenge is keeping it available under suitable thermal conditions until it is required by the casting process.

A holding furnace therefore focuses less on melting large quantities of cold charge and more on maintaining the molten metal within a defined process window.

Depending on the production concept, a holding furnace can act as a buffer between a central melting furnace and one or more casting machines. It may also be used to stabilize the metal temperature before further transport or dosing.

Supplying a Defined Quantity of Molten Metal

A dosing furnace combines molten-metal holding with controlled metal delivery. Its task is to provide the casting machine with the required quantity of molten metal for the next cycle.

In aluminium casting systems, dosing can be carried out using pressure-controlled furnace concepts in which molten metal rises through a delivery system and a defined amount is discharged. Control of the dosing process is important for achieving repeatable metal quantities from cycle to cycle.

In cold chamber die casting, a consistent amount of molten metal supports repeatable filling conditions in the shot chamber. The dosing furnace therefore becomes an important part of the automation concept of the complete cell.

Current equipment can be found under used dosing furnaces .

Melting Furnace vs. Holding Furnace vs. Dosing Furnace

How the Furnaces Can Work Together in Cold Chamber Die Casting

Not every foundry uses all three furnace functions as separate machines. Nevertheless, the following process sequence illustrates how the tasks can be divided in a larger aluminium die casting system.

Why Temperature Stability Matters

The furnace is not simply a container for hot metal. Metal temperature influences the conditions under which the melt is transported, dosed and cast.

Excessive temperature fluctuations can change the thermal conditions of the casting process from cycle to cycle. At the same time, unnecessarily high holding temperatures can increase energy demand and place additional thermal load on the furnace system and the molten metal.

Furnace capacity, heating system, insulation, control strategy and metal throughput should therefore be matched to the actual production demand rather than selected independently.

Why Dosing Accuracy Is Important in Cold Chamber Die Casting

In cold chamber die casting, the molten metal required for each shot must be transferred into the shot chamber before injection. Variations in this quantity can change the conditions inside the shot chamber and influence the subsequent casting cycle.

A reproducible dosing system therefore contributes to a stable starting condition for each shot. The correct quantity depends on component, runner system, overflow volume, shot chamber and casting process.

Which Furnace Is Right for the Production Process?

Furnace selection begins with the production requirement. The furnace must fit the alloy, required metal quantity, casting process and integration concept.

• required alloy or range of alloys
• melting capacity per hour
• required holding capacity
• shot weight and required dosing quantity
• production volume and cycle time
• cold chamber, hot chamber, gravity or low pressure casting process
• required temperature stability
• dosing accuracy and repeatability
• heating technology and available energy supply
• insulation and thermal losses
• automation level and control interfaces
• available installation space
• metal transfer between furnace and casting machine
• maintenance access and cleaning requirements
• safety and environmental requirements

What Should Be Checked When Buying a Used Furnace?

With a used furnace, the nameplate and nominal capacity are only the beginning of the assessment. The thermal system, refractory lining, controls and — in the case of a dosing furnace — the dosing technology must also be evaluated.

• furnace type and actual function in the previous process
• manufacturer, model and year of manufacture
• nominal capacity and usable metal capacity
• condition of refractory lining and insulation
• condition of burners or electrical heating elements
• temperature sensors and temperature control
• furnace pressure system where applicable
• dosing mechanism and delivery system
• metal-level measurement and sensors
• control system and machine interfaces
• gas, electrical and compressed-air requirements
• maintenance and repair history
• available manuals and electrical drawings
• availability of spare and wear parts
• transport dimensions and installation requirements
• required refurbishment before recommissioning

FISS offers different used furnaces for foundry applications , including melting furnaces and dosing furnaces .

A Used Furnace Must Fit the Existing Die Casting Cell

A furnace can be technically functional and still be unsuitable for a specific production line.

For example, the available heating capacity may not match the required metal throughput, a dosing furnace may not provide the required shot quantity or the existing control system may not communicate with the die casting machine.

The evaluation should therefore include not only the furnace itself but also its integration into metal supply, automation and the complete casting process.

Furnace Technology Is Part of the Complete Casting Process

In cold chamber die casting, metal supply directly precedes the actual shot sequence. The furnace system and dosing technology therefore form part of the process chain that also includes shot control, die temperature, spraying, extraction and downstream automation.

If you want to understand how the complete production cell works, see our Knowledge article on automation in the die casting cell .

For the basic distinction between die casting machine concepts, see cold chamber and hot chamber die casting .

First Define the Furnace Function, Then Select the Machine

Melting furnaces, holding furnaces and dosing furnaces fulfil different tasks in the metal supply system. The melting furnace produces molten metal, the holding furnace keeps it available under controlled thermal conditions and the dosing furnace supplies a defined quantity to the casting process.

Depending on the furnace design and production concept, these functions can overlap. The correct selection therefore cannot be made from the furnace name alone.

Alloy, metal throughput, storage capacity, dosing requirements, energy supply, control technology and integration into the complete casting cell should always be considered together.

Questions About Melting, Holding and Dosing Furnaces