Industrial Hydraulics in Plastics Retrofits/Rebuilds Key Challenges Extent investment in existing equipment Increase productivity Increase reliability Increase ease of use Benefit from applying the latest electrohydraulic controls to proven mechanical molding equipment Increase competitiveness without major capital investments Key Rexroth Solutions VT-HACD controllers offer an unequaled combination of accuracy, repeatability, and load compensation. They give you more capabilities and flexibility in open- and closed-loop control, including the ability to nest loops. The controllers are available in application-specific configurations for clamping, injection, and transport. SY-DFEE pumps save space and simplify design with a built-in open- and closed-loop proportional amplifier for precise control of flow and pressure. HNC 100 controller is a programmable, bus-capable NC control for electrohydraulic drives using open- and closed-loop control algorithms specifically tailored to the special characteristics of hydraulics. Proven Improvements Through Retrofitting A typical example of a rebuild project was a mid-1980s 700-ton injection molding machine. This machine was rebuilt with the following components: PLC using a DeviceNet™ network VT-HACD-DPQ and VT-HACD-DPC to control all major machine functions. A high-performance proportional valve for the injection cylinder. Existing clamp cylinder and ejector cylinder control valves were retained; both were determined to be adequate for closed-loop control. A clamp safety valve was added to meet new ANSI safety standards for plastic machinery, An additional fixed displacement pump was added to increase the injection and clamp speed. The goal for the project’s success was to meet "World Class Standards" for injection machine performance as defined by a third-party manufacturer of test and measurement equipment for the injection molding process. Before the rebuild, only Ejector Repeatability could pass the world class test; after the rebuild all measured criteria exceeded world-class standards. In addition, the rebuilt machine is running at 0.3% scrap rate, while the plant's average scrap rate is 3%. The calculated cycle time for the molded part is 40 seconds but this machine is producing the same part at a cycle time of 38 seconds. The reduced scrap and faster cycle time translates into additional annual plant savings of approximately $38,000!         Criteria   Before Rebuild   World-Class Machine Criteria   After Rebuild   Hydraulic Injection Pressure Response (s)  Failed  0.20  0.145  Injection Speed Linearity (%)  28.28  10.00  8.41  Injection Load Compensation (% kpsi)  88.10  <3  0.610  Clamp Repeatability (mm)  7.188  2.540  1.676  3-Stage Capability (Velocity Pack, Cavity Pressure, Transfer)  No  Yes  Yes  Ejector Repeatability (mm)  1.78  2.54  0.251  Decompression Repeatability(cc)  Not repeatable  <25  9.940  Injection Speed (cc/s)  700  N/A  900  More on Plastics Processing Productivity Learn the full story on Bosch Rexroth’s advanced hydraulics solutions for plastics manufacturing. For more information or to order brochures and catalogs, contact your nearest distributor.