FAQs - DME Hydraulic Locking Core Pull (HLCP) CylinderWhat is the service temperature and limit for this device?
A: This depends if you intend to use the inductive proximity sensors supplied with this device. The service temperature limit of cylinder assembly with supplied inductive proximity sensors used is 176°F (80°C). If external limit switches are used, then the service temperature limit of cylinder assembly alone is 356°F (180°C). But, you must check the service temperature limit of whatever limit switches you choose to use as these may have a lower service temperature limit than the cylinder assembly.
PLEASE NOTE: It is important to always sense when the sliding core is in its full forward and fully retracted positions. If this is not done, there is a risk of opening the mold before the core is fully retracted, or attempting to inject into the mold before the core is fully forward and locked.
What is the service pressure limit for this device?
A: The cylinder service pressure limit is 3625 PSI.
Is hydraulic pressure required at all times?
A: Yes: a minimum of 870 PSI holding pressure or line pressure service is required at all times. If your hydraulic line pressure service varies over time, it is important to ensure that you will not drop below 870 PSI hydraulic service line pressure during normal operation of the mold, the injection press, and any other piece of equipment that is requires hydraulic service while the mold and injection press are operating.
What is the difference between "NPN" and "PNP" sensors?
NPN and PNP sensors function in a similar manner, except the power supply polarities are reversed for each type. NPN inductive sensors are more common in North America, while PNP is more common in Asia and Europe. The HLCP product is delivered with NPN inductive sensors as standard. HLCP cylinders with PNP sensors installed must be ordered as a "Special order" and PNP sensors need to be specifically requested at the time of the order. If PNP is not requested, the cylinders will be delivered with NPN sensors, even for special orders.
Why do the supplied proximity sensors require power?
A: The NPN sensors delivered standard with the HLCP product are "inductive" sensors, which by definition consist internally of an induction wire loop (or coil). Electric current applied to the sensor generates a magnetic field in the wire coil inside the sensor. As a metallic object (in this case, the piston rod inside the cylinder assembly) approaches the sensor, the "inductance" of the sensor's coil changes. In simple terms, the presence of the piston rod in proximity to the sensor changes or influences the magnetic field, which alters the signal across the sensor wires. Without power feed to the sensor, there is no magnetic field in the sensor's coil and no signal change is read.
What if I only have dry contacts at my machine? How do I wire up the sensors?
A: Please refer to the packing slip (installation instruction). Included in the packing slip is a suggested alternate circuit using a DC relay. Please note that the end user is responsible to provide necessary electrical service. If this is not possible, external limit switches may be used in the mold. Again, it is always important to monitor when the cylinder rod is in its full forward and fully retracted positions, for reasons cited above.
How do I determine what size of cylinder is required?
A: It is important first to determine if you require preload. Preload is used when you expect to be shutting all or part of the sliding core face off on an opposing core face in the mold. This is done when you form a "Window" in your molded part and you must prevent flash in front of the sliding core face. Recommended preload is given in the packing slip as well as in the DME catalog for each size of HLCP cylinder. Please note that when preload is used, the net load capacity of the cylinder is reduced.
When determining the required load capacity, it is good practice to consider the entire face of the sliding core, even the portion that will be under preload. This total area should be multiplied by the peak injection pressure expected to be seen inside the molded part cavity. If you are uncertain as to what the peak injection pressure might be, a mold filling analysis can assist you, or, consider the peak injection pressure offered by the injection machine in total. It is good practice to select a cylinder load capacity (a cylinder size) that exceeds by a sufficient margin, the estimated load that expected to be acting on the piston rod.
Can the HLCP be used to provide position alignment the sliding core itself?
Can the HLCP be used to provide rotational alignment of the sliding core?
When I install the HLCP cylinder assembly in my mold, should I account for thermal expansion of my sliding core and mold?
A: Yes. We also supply a spacer or "shim" disk with each HLCP cylinder assembly. This spacer disk is placed between the mounting flange of the cylinder assembly and the installation pocket. The mold maker is expected to grind the spacer disk to achieve the necessary installation of the HLCP cylinder as well as achieve the required preload on the piston rod when the piston rod is in its full forward position.
How do I use heel blocks with the HLCP cylinder?
A: if used properly (including selecting the proper size of cylinder), no heel block is required. The purpose of the cylinder is to lock the piston rod (and sliding core attached to the piston rod) in a forward position. This means the sliding core can be retracted before the mold is opened. This has a benefit when the B-side sliding core is passing through A-side insert while the mold is closed. Note: If the cylinder size is improperly chosen for the intended application, it is possible to have even slight movement on the end of the sliding core, so please take care when selecting an HLCP cylinder size. If you find that the load capacity of the desired cylinder size is very close to the estimated load requirement in the mold, then it is recommended to select a larger HLCP cylinder size. Information on load capacities (with and without preload) is given in the DME catalog as well as in the packing slip.