Page 301 - Injection Molding Advanced Troubleshooting Guide

294 30 Flash

tonnage is being applied? These are questions that could impact the ability of a
machine to hold a mold closed. If the clamp unit of the machine is not providing
uniformly distributed tonnage to a mold the risk of flash will increase in areas that
are not receiving the correct clamp force. Review the machine manual for recom-
mended procedure and schedule for clamp verification.
Tie bar stretch can be determined following the recommended machine specific
guidelines. In simple terms conducting a clamp single point adjustment requires
the following steps:
1. Verify machine level with a machinist’s level. See machine service manual for
locations and procedure.
2. Check tie bar nuts to ensure they are tight.
3. Mount single-point frame to machine base.

4. Install four dial indicators on the single-point frame. Each indicator should con-
tact the flat end of one of the tie bars. Adjust all indicators to zero with the
clamp open.
5. Close and lock up the clamp on a mold or test block.
6. Check the dial indicators to determine the tie bar stretch for each tie bar. Varia-
tion between the tie bars will vary based on tonnage but variation greater than
0.002–0.003 in will call for adjustment.

7. If tie bar stretch is uneven adjust the tie bar nuts to equalize strain on each of
the four tie bars. Make sure to follow the machine manufacturer’s recommended
methods and techniques; this is a simplified reference.
8. Recheck strain and adjust accordingly.
Also general preventative maintenance on platens should account for keeping the
platens clean and smooth. Use a large surface area polishing stone to remove any
burrs on the platen surface. Wiping platen and mold surface with a cleaner or lu-
bricant such as WD-40 will help to keep surfaces clean.

30.3.3.3„ Machine: Core Pressure
To adequately resist plastic pressure against a mold action such as a core the
hydraulic pressure of the core circuit must be set properly. If core pressure is set
too low the hydraulic cylinder will not be able to maintain a forward position and
as a result there will be flash.
Verify that the pressure has been set correctly on the machine controller. It is also
important to determine if the machine is actually producing the desired pressure.
A hydraulic gauge can be installed in the core circuit to determine the actual
amount of hydraulic pressure acting on the core cylinder. Sometimes the pressure
relief valve has been set to restrict the core hydraulic pressure regardless of what
the set point is on the machine.