Hot Runner Systems in Injection Molding

The use of hot runner systems in the injection molding is rising due to the fact that they provide a more perfect technique of molding plastic parts. The cost saving can be substantial, and part standard is very often much excellent than cold runner.

With the rising sophistication of today’s plastic injection molds, the use of warm runners is becoming an industry standard. Many application just are not possible with old standard sprue and chill runner system, and warm runners provide a best way to maintain uniform wall thickness and get rid of knit lines and flow lines.

What are the benefits of warm runner systems?

  • Capability to decrease gate vestige
  • Uniform wall thickness
  • Lower cycle times
  • Elimination or reduction of knit lines
  • Less waste
  • Best for high cavitation molding
  • Generally the only technique for micro-molding. The center to center distance of the warm runner tips is as little as 17mm.
  • Many big molds rely exclusively on warm runners. Cold runners cannot meet the demands.

What about the maintenance of warm runners?

Warm runners systems need a new level of skill on the part of the mold maker. Anyway, this does not mean that it is overly hard or highly specialized. A well designed system is relatively free from maintenance, once it is rightly installed.

mold maker
mold maker

It can, and does happen, that mold makers become upset with these systems and swear that they are too much issue. This is generally due to the fact that the system is not rightly installed or badly operated in the molding process.

The leading system producers have a well-trained team of experts on hand to help in the right installation and operation of the system. The time spent listening to these experts is time well spent!

Long term advantages

Even though there is a primary investment with hot runner systems. It is simple to justify the long-term advantages. Without rising the complexity of the design of the mold, a hot runner equipped mold can significantly decrease costs. Because the hot runner is designed and produced independently, yet concurrently, the lead times are not affected.

Mold maker should forever advise techniques for his customers to decrease molding costs and rise the output of the mold. Being knowledgeable with different runner system is a best way to demonstrate an active role in supporting the molders bottom line. This in turn makes the likelihood of increased business even bigger for the mold maker.

Injection molders

Lubricant Pellets Cut Scrap & Cycle Times 
    Internal lubricants for a variety of thermoplastics are newly available in a 100%-active pellet form from Axel Plastics Research Laboratories, Woodside, N.Y. MoldWiz pellets come in several resin-specific formulations that contain no binders or fillers. Use levels are as low as 0.25%. 
   Precision Plastic Injection molders can tumble or dry blend these pellets with resin or feed them directly at the throat-an advantage over messy powders. For compounders, they are said to be useful in masterbatches because they improve dispersion of color, fillers, and other additives. MoldWiz internal lubricants reportedly improve resin flow at lower temperatures, helping to shorten cycles and reduce flow marks and knit lines on molded parts. The lubricants also do not leave any residue on molded parts, eliminating the need for cleaning before plating or other secondary processes, Axel says.

More Long-Fiber Pellets For EMI Shielding 
    The Incoshield family of long-fiber nickel concentrates for EMI/RFI shielding has been expanded to include three new masterbatches of ABS, nylon 6, and PBT. Previous grades are based on nylon 12, PC, PEI, PPS, and acrylic. Supplied by Inco SPP, Wyckoff, N.J., Incoshield concentrates contain 60% by weight nickel-coated long carbon fibers. These concentrates are dry blended with resin before being injection molded into housings for computers, electronics, and communications equipment.

FR Agent Doesn’t Get Steamed at a Little Heat 
    A new synthetic, halogen-free flame retardant gives up its water of hydration endothermically at higher temperatures than familiar alumina trihydrate. Basic Aluminum Oxalate (BAO) from Alcoa Industrial Chemicals, Bauxite, Ark., extends the processing range of aluminum-based flame retardants up to 625 F, versus around 392 F for ATH and 540 F for magnesium hydroxide. Price is about $1/lbÑmuch higher than for ATH and competitive with Mg(OH)2. 
    Like ATH, BAO has a white color, high brightness, and low toxicity. But the low soda content of BAO means less impact on electrical properties of wire and cable, Alcoa claims. BAO reportedly can provide UL 94V-0 ratings to a wide range of resins at loadings of 40-63%. Its specific gravity is 2.2. Available mean particle sizes are 0.3 to 2.7 microns.

Plastics Technology

Structural Foam Goes All-Electric

What may be the first all-electric structural- foam molding machine was recently built by Milacron’s Elektron Technologies unit in Batavia, Ohio, in cooperation with structural-foam specialist Uniloy Milacron in Manchester, Mich. This development occurred because a major foam molder wanted a large all-electric machine for the sake of energy savings, oil-free operation, and noise reduction. Uniloy’s Springfield Div. always uses two-stage injection for its structural-foam machines, so Milacron adapted its Sidewinder two-stage electric injection unit to this process. This being the first foam application of a two-stage electric machine, Milacron says, Uniloy developed a new screw design, a barrel-cooling system, and gas- injection metering hardware for the Sidewinder. 

The result was a 550-ton Powerline machine that reportedly provides highly consistent foam melt with both gas injection and chemical blowing agents, as well as a wide range of shot sizes. The separate shooting pot allows use of any shot size from 100% down to 3% of machine capacity. The machine molded an electrical housing (see photo) of GE’s Noryl PPO/PS alloy with nitrogen gas. The part weighs 83 oz and has a 15% weight reduction with a typical foam/skin structure. The Sidewinder unit can be converted to standard high- pressure injection molding with a simple screw change. 

Cooling Screw Cranks Up Foam Output

A new screw design for foam extrusion is believed to be the first to use cross-flight melt channels to increase cooling and foam output. The channels perforating the curved flights scoop hot polymer off the screw root and brings it into contact with the cooled barrel. In the single-screw cooling extruder of a tandem foam line, it reportedly increases output by 25-40%. Developed and patented by Plastic Engineering Associates Inc., Boca Raton, Fla., The Turbo-Cool screw was publicly discussed for the first time at the SPE ANTEC meeting in Dallas in May, though it is already used commercially by several large producers of PS-foam sheet for clamshells and board for construction. 

Integrated Stretch-Blow Machine Is All-Electric

The upcoming K 2001 show in Dusseldorf, Germany, will see the debut of the first all-electric integrated PET injection stretch-blow molder from Automa of Italy (represented here by Automa Machine & Tool Inc., Maple Grove, Minn.). The servo-driven NSB100 system is designed to run at three times the production rate of conventional ISBM machines. For example, it reportedly can mold 16-oz bottles at 5000/hr. NSB100 will have a 5:1 ratio of injection to blowing cavities (up to 20 and four, respectively). 

Automotive TPO Goes Antistatic

Two versions of Sequel 1514, a new mar-resistant TPO from Solvay Engineered Polymers, Auburn Hills, Mich., are being used in the tailgate liner and protective moldings atop the tailgate and side rails surrounding the cargo box on the Ford Explorer Sport Trac vehicle. The liner compound is the first static-dissipative TPO to be used in an automotive role. The parts are molded by Ventra Plastics in Russellville, Ky. 

Although Ford initially specified ionomer for the moldings, Ventra foresaw processing advantages in TPOs that could cut costs. Tests by Ford and Ventra confirmed that durability of Sequel 1514 matched that of ionomer, but the TPO’s improved flow permitted downgauging from 3.5 to 3 mm, and the ionomer required longer cycles to prevent sticking in the plastic mold.

Colorants for Packaging Offer Light Protection

A new line of color concentrates for packaging of light-sensitive retort products has been developed by Ferro Corp.’s Plastics Colorants Div., Stryker, Ohio. The new Light Blocker Concentrates are said to be heat stable and to meet FDA standards for direct food contact at retort temperatures. Five light pastel shades are said to provide both uv and visible-light protection for nutrients in milk-based products. 

These concentrates are intended for use in LDPE, LLDPE, HDPE, PP injection molding, and PS bottles, injection molded containers, and thermoformed sheet. Letdown ratios are 10:1 to 50:1, depending on layer thickness and shelf life. These customizeable concentrates reportedly offer cost- saving opportunities. For example, they can permit downgauging an outer white layer over the light barrier, using a monolayer structure, or eliminating foil.

Custom Plastic Mold

Custom Plastic Mold

If you want to get a good custom plastic mold, many inexperienced customers normally like to find some professional mould manufacturers. But even if you find a good mould maker, you can’t express your needs well or you can’t have a good communication with the company, that’s also can cause bad results. So custom mould is also need some skills.

How to custom mold successfully? What’s problems will appear when custom mould? In custom mold process, which content must be discussed clearly?

We will offer you a chair mould case to explain how to custom a good chair molds successfully, and what’s problems we can avoid on custom mold project.


If you want to custom a good custom plastic mold, firstly, we need to know the product clearly. Such like whether the mould design is reasonable, whether the product on market can bring the profits, etc. How to save cost on the same product, for example, we can make the mould size smaller, use a smaller machine to manufacturing or the mould can use hot runner system to reduce the material cost and shorten the cycle time, etc. For plastic chair, the most important except the style, we also need to consider the chair strength, stacking condition, flash and the design is reasonable or not.


Mould design

Mold design rationality, will bring us great return benefit. Many times, we are wasting money on the mould because of the lack experience.


The below information is the key point that we need to treat very seriously:

  1. Mould structure the simple the better

Because, for the simple plastic mold, there will be less rub during the mould operation, then the mould life will be longer. When take chair mold as an example, some customers think the more interchangeable back inserts the better, and it will be excellent if all the chair back inserts and sit inserts can be interchangeable. However, that will make mould testing very complicated, and you will have a lot of trouble in your future mass production.


  1. High requirements for cooling system

High quality cooling system design can help you a lot on shorten the cycle time that obviously brings directly benefit and effective to the customer. Simpler and better than you hire a wise operating engineer.


  1. The injection gate chooses!

Sometimes it will cause many problems from ignoring the injection forming on design, it is not good if only considered about the surface while not the mould. As we know if the mould with hot runner system, it without the waste material and improve the injection cycle time, but in order to reduce the cost that we will use the recycle material, while it with much impurity is not good for the hot runner. For chair mould, if adopt the famous brand such as YUDO, it’s a waste of the cost. If adopt the common hot runner system, they may not solve the problem, so even if they used the filter, also can not ensure the quality is 100%. In this way, we can choose the cold runner system, if design well for the injection gate location, it is easy to break off the tail and not leave the marks.


Machine selection

To custom mold is not only related to plastic injection molds, actually injection molding machine selection is also a key point of a customized mould.

If you have enough budgets, please consider to choose a greater tonnage machine. A great tonnage machine will have stronger clamping force, it is very easy to solve the flash problem. If you are not able to choose a big machine, definitely you may face a lot of problem during long term manufacturing.

In order to avoid such problems happen, customer have to provide the mould making company detailed machine parameters.

This is our decades experience for clients’ customize mould, if you have more experience and better suggestion please contact us for exchange ideas and mutual-improvement. DONGGUAN SINCERE TECH Co., Ltd one of the molding company and a professional custom plastic mold company. contact us to get your custom plastic molds and plastic molding parts.

Plastic Injection Molds

Plastic Injection Molds

If you demand long-life plastic injection molds, it is insufficient if you only requires good mould from mold supplier; the life of the mold have great relationship with normal operation and maintenance, so a mature molding company usually have plastic mold engineer, who will responsible for mould repairing and maintenance; of course, plastic molds disassembly is a basic work in mold maintenance.

Do you know how to disassemble plastic molds? And what you should pay attention in moulds disassembly? When you disassemble theplastic moulds, you need to pay attention to following matters.

It is necessary to print the mould assembly drawings, clear up each of the parts in the plastic molds and the principle of operation as well as the assembly relationships.

According to the parts list on the assembly drawing, preparing the necessary disassembly tools.

Analysis the plastic injection moulds, learn the injection type, such as normal hot runner, valve gate or cold runner, and check the parting line and ejector system. Make a disassembly order list before do it.

When you disassemble the plastic mold, placing the mould on rubber mat or low hardness plane workbench. Parting surface to be parallel with the table; that means guide pin should perpendicular to the workbench. It can protect the mould parts, such as ejector pin, if the mould is not in correct direction, small pin will be easy to be bend.

Usually, you need to separated the cavity and core, and disassemble plastic injection moulds from back side, it means start disassembling from the ejection and injection systems.

If you don’t know about the mould well, you need to mark all the removed parts, and put in sequential, it will be convenient for installation and it can avoid mistake when you assembling the mould.

Tools to be used correctly make the force balance when you rotating or beating, don’t forcibly disassemble the undetectable parts.

If the tool needs to reach to cavity or core surface, be sure to use less hardness tool than the core cavity, usually, we suggest copper.

If you don’t have any mould engineer in your company, it is not rational to do plastic molds disassembly without any technical support. We suggest you send injection molding molds to local mould workshop, or do the plastic molds disassembly under guidance of mould manufacture.