Preheating moulds and dies quickly, homogeneously and without damaging materials

Topic of the month

© promeos GmbH

Tool heating © promeos GmbH

Permanent metal moulds enable parts to be produced with a high quality surface finish in large quantities. The quick and controlled cooling behaviour that ensues here can have an impact on the microstructure of the products.

These tools are used in both gravity casting and casting procedures carried out under pressure. This is mainly with regards to moulds in gravity casting, tilt casting, centrifugal casting and low pressure casting processes, as well as die-casting moulds.

Moulds and dies must be preheated before their initial contact with the melt to avoid thermoelectric voltage arising due to large differences in temperature. So as not to reduce the service life of the moulds or damage the coating that has been applied, preheating is mainly carried out using thermal oil which is electrically heated and guided through channels in the mould, or direct fired onto the back of the mould using gas flames. These practices have elaborate mould designs and therefore long preheating times.

Depending on the size of the mould it can take several hours, leading to huge production losses during regular refits and even more so during spontaneous refits. Directly heating moulds with flame burners and controlling the temperature of moulds using thermal casting are both widely used methods today. These methods shorten the service life of the moulds. The waste and therefore the amount of recycled material in the melting furnace rises, which has a negative effect on the product quality. The level of power consumption is also considerably higher compared to the flameless gas burner technology.

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Flameless gas burner technology © promeos GmbH

Simply better process heat

With its flameless gas burner technology, promeos® creates direct heating systems and facilities, which adapt to meet the requirements of the casting process and ensure that moulds are heated quickly and evenly without damaging the material. Overheating caused by exposure to localised fire is completely avoided, meaning that the service life of the mould is not affected.

The burner capacity can be adjusted to any level across a wide range, providing optimum temperature control when preheating.
Shorter heating times equate to gains in production time. In this way, the precisely controlled burners allow for a high level of reproducibility and lead to an improvement in quality.

The intelligently integrated reo®, neo or ceo® burners offer heat in the form of hot air, convection, solid-state radiation and gas radiation from 100°C to 1,400°C. The fields of application for the flameless gas burner from promeos® are extremely varied.

The technology is already being used both for heating moulds in casting machines and in preheating stations. By using various heat transfer mechanisms, different target temperature ranges can be achieved.

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Mobile heating system © promeos GmbH

Short heating times, more productivity

promeos® has developed a new heating system with a flat radiation unit that can, for example, be run between the moulds with a manipulator or pallet truck. The heating system consists of a vertical burner and a flat radiation unit made from highly temperature resistant steel. From the side, the burner dispenses hot combustion gas over the whole length of the radiation unit.

The gas is emitted in the direction of the mould surface via the specially positioned holes on both sides. This brings the whole radiation unit up to the required temperature and heat radiates from it. At the same time, the moulds are blasted with the hot gas that is being emitted.

• Effective surface heating via radiation and convection heat
• Gentle heating without any contact with flames
• Optimum temperature control with variable output regulation
• Robust structure

The radiation unit is interchangeable and can therefore easily be adapted to the geometry of the moulds.

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Robotically controlled flameless burning system for selective preheating © promeos GmbH

Robotically controlled flameless burning system for selective preheating

If an extraction robot with sufficient carrying capacity is available, heating can be carried out using a robotically controlled reo® burner (porous burner). The robot grabs the burner head with a suitably constructed interface and moves across the mould surface according to a preprogrammed model. The unique power density of the flameless burner allows the mould to be heated effectively in a targeted manner, without damaging the material.

Once the temperature has been reached, the compact burner head is then moved back to its resting position. The supply unit with combustion air fans, the control valves and the safety valves are placed in the appropriate position on the casting machine. The mixture is supplied to the burner head via a flexible tube.

• Effective heating via intensive radiation and convection heat
• Overheating of cavities is avoided
• When changing moulds, selecting a different preprogrammed heating process is the only adjustment that is needed.
• The areas of the mould to be heated can be specifically determined.
• 100% reproducible heating.
• No set-up required by the operator - preheating starts at the push of a button.
• Various burner head sizes can be used with different output ranges.
• Compact system
• Suitable for the retrofitting of existing casting machines

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Tool heating for mould halves © promeos GmbH

Heating stations for low pressure die-casts reduce energy costs

For a variety of tasks from preheating to drying coatings or rising pipe constructions, promeos® gas heating is available as solid-state radiation, convection or hot air combined with secondary air. In addition to this, the burner technology can also be used as a heat source for convection ovens. Gentle, even, yet quick heating with low energy consumption is also a significant feature which enables the purchase to be paid off in under two years.

Dies with mounted rising pipe constructions can be heated in their fully mounted state by immersing them in hot gas. For dies with extreme cavities, such as those in wheel rim casting, the die halves are separated from each other and heated individually. Below are two practical applications for such cases.

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Tool heating for closed moulds © promeos GmbH

Separated heating of die halves using convection heat

The specially developed heating system for preheating lower and upper dies in wheel rim casting consists of two individually controlled heating units. These bring the die halves evenly up to a target temperature of 350°C using convection heat. The point at which the temperature is measured is located directly underneath the die surface.

The value is ascertained using a thermocouple and serves as a control variable for the relevant heating unit. A comparison in the heating time and gas consumption between the flameless gas burner from promeos® and a conventional ring burner shows the enormous benefits of this heating solution. The measurement is based on a die for 17” wheel rims. Dies of different sizes can be heated using one station. In relation to ring burners, this station achieves an energy saving of around 75% and shortens the preheating time by around 50%.

Heating assembled dies using hot air

The assembled die is preheated together with the rising pipe construction in this case. To ensure that the refractory lining of the rising pipe construction is properly dried, it is essential to have low temperatures in the range of 100°C and precise temperature control. As the heating process progresses, the die should be brought up to 350°C.

A burner unit with the addition of secondary air encourages the mixture of waste gas and air in an insulated inner chamber. The gas, at its precise temperature, flows through an opening in the lid of the chamber into the rising pipe construction and immerses the die. Temperatures between 100°C and 800°C can be precisely set and adjusted.

With regards to sustainability, process control, energy and material efficiency, and environmentally conscious production, the flameless burner technology from promeos® delivers a crucial contribution to industrial development.