Hydraulics and Injection Molding
“For controlling the enormous pressures created by relatively small energy inputs, hydraulic systems have been unparalleled,” states Deirdra Barr of Ethyl Petroleum Additives Ltd. in her informative article for Machinery Lubrication, titled “Injection Molding Hydraulics – The Pressure is Rising”.
While rudimentary hydraulic systems have been evolving since the earliest days of civilization, the thermoplastics industry is a relatively recent development, gathering steam throughout the 20th Century. Thermoplastics first debuted in the industrial world around 1900 with the invention of celluloid by John Wesley Hyatt. These revolutionary materials were the modern marvels of their time. Thermoplastic materials quickly demonstrated their extreme versatility. Though we tend to think of modern thermoplastic materials as “space age technology”, many were actually developed by the 1930s.
The new wonder plastics could be molded to any conceivable form with the proper application of heat and pressure, and then retain that precisely determined shape when they cooled. The possible applications for manufacturing and industry were endless. Thermoplastic production technology was accelerated by two world wars and the rapidly advancing aviation and automotive industries. These were the catalysts that resulted in the myriad of plastic products which today are common household names including PVC, Teflon, and polyethylene.
Hydraulics and the Injection Molding Machine (IMM)
Thermoplastics were the perfect match for 20th Century trends in industrial process automation and the first IMMs, plastic injection molding machines, were developed. Hydraulic systems were used right from the start on the earliest IMMs to apply high clamping pressure to the two mold halves while liquified plastic substrate (melted pellets) was injected under pressure by a screw device. Hydraulic clamp tonnage available in the early IMM hydraulic systems was very low and IMMs were limited to producing small parts from simple molds which weighed no more than a few ounces.
Pumping Up the Hydraulic Muscle in Modern Injection Molding Machines
Today, huge parts of up to 50 pounds are produced by modern IMMs and clamping pressures can exceed 8,000 tons. The automotive industry uses IMMs to crank out complete bumper assemblies, to name just one of many examples. But small plastic part manufacturing today doesn’t necessarily correlate to low operating pressures either.
Even micro-molding processes for intricate medical and electronic components operate in the 10-30 ton clamping pressure range, though the precisely manufactured finished products may weigh just fractions of an ounce. The fastest growing clamping range in the IMM market today is between 200-500 tons.
While electric and hybrid IMMs (electric/hydraulic) are available, the market is still dominated by all-hydraulic machines chiefly for their competitive manufacturing advantages (in the 100 billion dollar US plastics industry) when dealing with production demands for:
- Greater clamp forces
- High linear speeds
- High plastic nozzle pressures
- Longer holding times
IMM Hydraulics and Reliability
All hydraulic systems at the basic level contain a motor-driven hydraulic pump, control valves, pistons and a network of interconnecting pipes, fittings, and hoses. When hydraulic systems are used on a high-production, high-pressure continuously running machine like the modern IMM the importance of preventative maintenance rises proportionally.
Hydraulic Leaks and the IMM
Hydraulic fluid leakage is a universal challenge for lube engineers with any system, but unpredictable pressure drops in an IMM can disrupt production by impeding cycle speed and increasing rejects and material waste. With the clamping tonnages we’ve discussed above it’s obvious that the hydraulic system on any IMM requires the highest quality hoses and high-pressure industrial fittings to prevent downtime.
In worst case scenarios leaks can cause expensive mold damage and even put the entire 1/2 million dollar capital investment for a large IMM at risk. When pressures fluctuate unpredictably due to intermittent failures in hoses, valves, or fittings sophisticated precision controls can be rendered useless. Heavy investments in new OEM pump and sophisticated valve technology allowing leak-free operations up to 10 million cycles for state-of-the-art IMMs can all be wiped out if substandard hoses and fittings fail elsewhere in the IMM.
Modern hydraulic IMMs use integrated systems for pull in, clamp, and ejection operations, and many rely on variable volume pumps with proportional hydraulics for optimized energy efficiency. Fluid leaks are the monkey wrench which can disrupt any or all of these high-speed production processes.
IMM Hydraulic Fluid Quality and Condition Monitoring
Hydraulic fluids in IMMs need to resist oxidation and protect mechanical parts from high pressure and heat in the demanding thermoplastics manufacturing environment. Antiwear additives are required in the fluid used in IMMs to protect hard mold surfaces which come together under immense pressure. Thermal control systems are required to keep fluid temperatures between 110 and 120 degrees under operating conditions to prevent accelerated fluid breakdown.
80% of hydraulic IMM problems are caused by fluid contamination. While fluid cleanliness is fundamental to all hydraulic operations, filterability for IMM hydraulic fluid is held to an even higher standard. Only fluids passing AFNOR NFE 48-691 under wet conditions are suitable.
For all of the reasons mentioned above, rigorous analysis and monitoring of the hydraulic fluid condition should be performed regularly while the IMM is in operation to predict the useful remaining working life of the fluids and schedule necessary maintenance periods to minimize production downtime.
Preventative Maintenance For Industrial Machines at Custom Hose Tech
Lube engineers and plant operators can optimize scheduled machine downtime with our preventative maintenance programs which prevent costly machine problems before they occur or worsen. At Custom Hose Tech we offer the flexibility to meet your company’s production needs and we’re willing to work with you to coordinate maintenance schedules. Special labor rates, product discounts, and free service calls are some of the benefits of our preventative maintenance program.
Of course, our mobile teams are strategically located throughout the Twin Cities region, and emergency field service is usually available within 1 hour. Our expert hydraulic technicians are at your service 24 hours per day and 7 days per week to keep your industrial operations optimized and producing. We can provide onsite custom fitting and fabrication and we carry an enormous stock of hydraulic and pneumatic hoses, fittings, valves, controls and more. To keep your IMM or any other industrial hydraulic system up and running at its most profitable peak condition don’t hesitate to contact us.