Why Choose Magnetostrictive Sensing for Hydraulic Cylinder Position Control? From Injection Molding to Metallurgical Presses

Hydraulic cylinders are one of the largest application areas for magnetostrictive displacement sensors. Why has cylinder position control become almost a "home ground" for magnetostriction? Because it hits exactly the operating conditions that hydraulic cylinders find hardest: long stroke, oil contamination, high temperature, and years of non-stop running. This article starts from those conditions.

Why cylinder position is hard to measure

The working environment of a hydraulic cylinder is extremely unfriendly to sensors: the piston rod's reciprocating motion brings continuous friction and vibration; hydraulic oil temperature can reach eighty to ninety degrees; the site is full of metal swarf and oil sludge; strokes range from a few hundred millimetres to two or three metres. Traditional contacting displacement transducers (potentiometers, resistive scales) wear quickly here and have a short life, often drifting within a few months.

In-cylinder vs externally mounted: how the series map

By mounting method, magnetostrictive sensors fall into two broad groups:

• In-cylinder (inside the cylinder): the sensor is fitted directly into the cylinder cavity, the rod is coaxial with the piston rod, and the position magnet is fixed to the piston. Representative products include the Series 17 hydraulic-cylinder integrated type and the Series 13 mobile hydraulic type (in-cylinder integration, IP68–IP69K, 25 g vibration / 100 g shock). The construction is compact and well protected, making it the first choice for injection molding machines and presses; Series 13 also suits construction-machinery cylinders.
• Externally mounted (outside the cylinder): the sensor is mounted on the cylinder body, with the magnet on the piston rod or on an added carriage. Representative products include the Series 18 externally mounted type (follower-rod and sliding-carriage). Choose this when retrofitting older machines or when the cylinder cannot be opened.

Typical applications: from injection molding machines to metallurgical presses

• Injection molding clamp / injection: an in-cylinder sensor feeds back screw and platen position in real time for closed-loop control of clamp force and shot size;
• Metallurgical / servo hydraulic presses: long stroke and high pressure, requiring profile or integrated types rated 300–600 bar;
• Water-conservancy gates / hoist machinery: outdoor, wet, long stroke, relying on high protection and maintenance-free operation on neglected sites.

The maintenance dividend of non-contact measurement

The position magnet and waveguide do not touch, which means there is no wearing mechanical friction part. Fitted once inside a cylinder, it will often run with the machine for years without attention. For a production line, avoiding one shutdown to change a sensor saves far more than the cost of the sensor itself.