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Overheating hydraulic oil of extrusion press

As hydraulic fluid circulates through an extrusion press  hydraulics it both produces heat by doing work and transports that heat away from working components. However, if the heat dissipation is inadequate, or if the hydraulic oil does not have the right heat dissipation properties, then it can be overheating extrusion press hydraulics.

Oil hydraulics of extrusion presses

Typical schematic arrangement of an oil hydraulic system for an extrusion press is shown in Figure 1 [1].

Figure 1 – Schematic arrangement of an oil extrusion press hydraulic system [1]

 The four main functions of hydraulic fluid are [2]:

Causes of overheating hydraulic oil

As hydraulic fluid circulates through an hydraulic system it both produces heat by doing work and transports that heat away from working components. However, if the heat dissipation is inadequate, or if the hydraulic oil does not have the right heat dissipation properties, then it can overheat. Build-up of dirt, debris and clogged hydraulic filters can also affect a system’s ability to dissipate heat and lead to hydraulic fluid becoming too hot, leading to loss of fluid viscosity and reduced lubrication and pump efficiency.

Oil temperature must be maintained below a maximum of 60 ºC. Temperatures above this level lead to deterioration of the oil, loss of lubricating properties, and excessive wear to pumps [4].

The possible reasons for overheating extrusion press hydraulics are following ones [2, 3]:

Incorrect hydraulic oil viscosity

Hydraulic oil not only transmits the power that moves your drives and actuators. It also lubricates internal components and removes heat from the system. Hydraulic fluid is designed to operate at a specific temperature range.

Dirty hydraulic fluid

Fluid that is contaminated with dirt, debris, water and other impurities may cause heat build up in a few ways. Blocked fluid filters, pipes and strainers place undue load on the pump.

Low oil level

Low oil level can result in a condition in which not enough flow is reaching the critical hydraulic components and moving parts. This is known as oil starvation and it will increase metal-on-metal friction and lead to increased heat and wear.


Cavitation is the rapid formation and implosion of air cavities in the hydraulic fluid. When these air cavities collapse under pressure, they generate a lot of heat.  This leads to overheating hydraulics of extrusion press and extremely damages of the hydraulic pump and the system as a whole.

Air in oil

This happens when air makes its way into the system via air leaks at points like pump seals, and pipe fittings.  Air generates heat when compressed, which naturally leads to an increase in temperature. In extreme circumstances compressed air bubbles explode in the same process that powers diesel engines.

Relief value may be set too high

Pressure relief valves are there to ensure pressure does not rise beyond prescribed limits. If the relief valve is set incorrectly, it will not open soon enough and pressure will increase, which generates significant heat.

Faulty oilid cooling system

The design of any hydraulic system must allow oil to dissipate heat in order to operate efficiently. Some systems may do this with an oil reservoir or heat exchanger or combination of both. If the system design does not allow for sufficient heat dissipation, this will result in the oil becoming overheated.

Worn or damaged pumps

As pumps wear, the internal leakage or “slippage” increases. Oil is able to make its way past tight fitting components, which reduces the efficiency of the pump. Oli moves from a high pressure to a low pressure without doing any mechanical work. So potential energy of pressured oil converted into heat [2].

Improper operation of the press

When all the above mentioned reasons have been eliminated, but the oil overheating continues, it’s time to make sure that your press is being operated correctly.

Over working of the press

According to an recognized authority on aluminum extrusion presses, Al Kennedy, the top causes of oil overheating are direct errors by the personnel operating the extrusion press [2].

A common fault of many operators is to give high or full pump volume of oil during the pressure peaking (Figure 4). This causes a large amount of oil to be released through the relief valve. As a result of this oil moving from high pressure to low pressure, it becomes very hot.

Energy conversions during extrusion

The following energy transformations occur in an extrusion press [4]:

High-pressure oil discharged over a relief valve does no usuful work. Instead that energy is released in the form of heat.

Operation of a press without overheating oil

Proper operation of the press will reduce the heating of the oil [2]:

Good operation of a press can be obtained if [2]:

Peak pressure and relief valve

Under no circumstances should a press be held at peak pressure with relief valve blowing for more than thirty seconds at the most.  It is believed that it is much better to cancel the extrusion cycle, reject the billet and stsrt over than to overheat the pomp and oil [2].

One simple solution

Another authority on aluminum extrusion says about the simple solution of the problem [4]:


Oil pressure and extrusion force

The external force given by the extrusion press determines the press capacity. For successful extrusion, the force applied by the press need be more then the force required for

Figure 2 – Schematic of direct extrusion press [5]

The main factor for aluminium extrusion process

The force required for extrusion depends on the following main factors [5]:


Figure 3 – Friction components in direct extrusion [5]

Figure 4 – Variation of pressure and load with ram travel for direct extrusion process [5]


  1. Extrusion //M. Bauser, G. Sauer, K. Siegert – 2009
  2. The Extrusion Press Maintenance Manual // Al Kennedy
  4. Extrusion of Aluminium Alloys /T. Sheppard – 1999
  5. Aluminum extrusion technology /P. Saha 
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